Gold lodes and placers of the Willow Creek District. Mineral resources of the upper Matanuska and Nelchina valleys. Preliminary report on the Broad Pass region. Mining in the Valdez Creek placer district
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GOLD LODES AND PLACERS OF TBE WILLOW CREEK DISTRICT. By S. R. CAPPS. . INTRODUCTION. The term Willow Creek district is commonly used to designate a rather indefinite area. in the southwestern portion of the Talkeetne. Mountains. The name ha8 gradually come to be applied not only to the basin of Willow Creek, which drains most of the western por tion of the area, but also to all the mountainous portion of the basin of Little Susitna. River, and it is in this more general sense that the term is used int.his report. The area considered lies between. latitude 61° 40' a.nd 61° 52' and longitude 149° 7' and 149° 30'. Both topo graphic and geologic maps of the region have a.heady been pub lished, but these are on a relatively small scale. The base map used for the present investigation will be published on a scale of 1 to 62,500, or approximately 1 mile to l inch. This map and a geologic map of the same area are now in preparation and will be published later with a more complete report on the ge0logy and mineral resources of the district. In 1898 G. H. Eldridge and Robert Muldrow,1 of the United States Geological Survey, ascended Susitna River and crossed the divide to the head of Nenaua River. In 1905 G. C. Martin 3 spent three weeks in a study of the lower Matanuska. Valley coal field. His geologic map included a portion of the Little Susitna basin. During the same year W. C. Mendenhall,8 while attached to a War Department expedition in charge of Ca.pt. F. W. Glenn, had ascended Matanuska. River to its head and crossed the broad basin to thenorth east as far as Delta. River. The next geologic expedition to the TalkeetnaMountains was undertaken in 1906, when T. G. Gerdine 8Jld R.H. Sargent carried a reconnaissance survey a.round this mountain 'Eldridge, G. R., A reoonnalssanoo in lhe Sushitru. basin llJld adJacent territory, Alaskll, In 1898: U. s. 0901. Survey T'!nmt:letb Ano. JUpt., pt.. 7, pp. 1- 29, 1900. Martin, G.' c., A reconnaissance or the Yataouska coal Jlcld, Alaska, In 100/l: U. a. Goo!. Survey Boll. 289, 1906. li!endenluill, W. C., A reconnaissance rrom 11.eswTectlon Bay to I.he 'hanna·River, Ala.,lln: U. S. Oeol. Sarvey Twentieth AJUL Rept., pt.. 7, pp. 20/i-.340, 1900.
MINERAL RESOURCES OP ALASKA, 1913. mass, and Sidney Paige and Adolph Knopf 1 mapped thegeology of the area surveyed. Their geologic map covered the Willow Creek district, but the small scale of the map OJld the hasty manner in which t.hefield work was necessarily done imposed sharp limitations upon the &mount of detail which could be presented. Paige spent only a. few days in the Willow Creek district, but in that time he succeeded in dividing the rocks into the three main groups, which a.re still recognized. In 1910 F. J. Katz &nd Theodore Chapin, &fter having spent the summer in the Matanuska coal field, made a four days' trip into the Willow Creek district. In Katz's reports on the geology and mineral ra'louroes of the area he described the economic development which had ta.ken place up to that time 8Jld made some corrections to the geologic map of Paige Md Knopf. GEOGRAPHY. S'Ult.ll'AOE FEATURES. The Willow Creek district includes the southwest corner of the Talkeetna Mountains. It is bordered on the south by the rolling, lake-dotted lowland which lies between Knik Arm and the moun tains, and on the east by the broad Susitna. Valley. The aooom pa.nying map (PL X ) does not extend fa.r enough westward to embrace all the area. commonly included in the district, but it shows that portion in which valuable discoveries of minerJl.1.s have been made. The district is limited on the east and north by the basins of Little Susitna. River and Willow Creek and their bendward tributaries. The mountains rise to heights of about 4,000 feet at the western edge of the area mapped, but increase in elevation to the ea.st and north, the highest peaks in the district, near the head of Little Susitna River, reaching elevations of almost 61000 feet. West of a north south line through the mouth of Craigie Creek the mountain tops a.re smooth and rounded. East of that line they are generally ragged and contain many narrow ridges and sharp peaks. The valleys in genera.1 a.re widely U-shaped a.nd bead in cirques. Except for the south front of the mountains, Willow Creek drains the western half of the district, :flowing nearly due west to empty into Susitna River. Little Susitna River is much the largest stream in the area. Its bed is filled with large bowlders; a.nd although its course in the mountains is only 15 miles long, it drains several smalJ glaciers a.nd before emerging from the mountains has so greatly increased in volume that during the summer season it can be forded with diffi.oulty and only at a. few places. In the winter alJ tbe strea.ms freeze over and their :How is greatly reduced. 1 P1llge, SidDey, and Kllopf, Adolph, Oeoloelo TeClOl1Dalssanc in the llatanuslta and Talkeetna basins, Aluka: u. s. OeoL Survey Dull. 327, Kata, P.1., Anoonnfpt0 oeoftbe Willow Creek cold ncJon: U. 8. GeoL Sarvey Bull. 480,pp. t-W, lOlL
Pla te X
GOLD LODES AND PLACERS OF WILLOW CREEK DISTRlCT. GLACIATION. The present surface forms of this district are in large measure due to the erosive action of the great glaciers which once occupied all the ·valleys. Four glaciers stili exist in the district (see Pl. X), but these are ell small and are only the disappearing remnants of vastly greater ice tongues. At a time geologically not long ago all the larger valleys in the Talkeetna Mountains were occupied by ice tongues which pushed down from tbe valley heads and extended beyond the moun tain borders. The Susitna Valley was then occupied by a great ice :field, extending at least as far south as the Forelands, and the Mata nuska Valley contributed a great ice stream to this glacier. ROUTES OF TB.AVEL. The village of Knik, on the northwest shore of Knik Ann, is the center of supplies for the Willow Creek district. Knik is above the head of navigation for ocean-going vessels and can be reached by launch only at high tide. At low tide the tidal flats off the town a.re bare. The upper part of Cook Inlet is closed to navigation during half of the year on account of the formation of ice. During the open season of 1913 one stearoship, plying from Seattle through south eastern Alaska to ports on the Gulf of Alaska and Cook Inlet, made trips at intervals of three weeks to Knik Anchorage, at the mouth of Ship Creek, a.bout 18 miles below Knik. From the anchorage all freight is lightered in scows to Knik, and passengers are transferred by launch. Steamships of another line call weekly at Seldovia, in lower Cook Inlet, and some freight and passengers are brought to Knik from that point in small steamers or launches. In the winter the mail is brought by dog sled overland from Seward to Turn.again .Arm, and thence across the divide at the bead of Crow Creek and around the head of Knik Arm to Knik, but this service is slow and iITegula.r. From Knik to the mines of the Willow Creek district two summer trails were formerly in general use. One headed north from Cotton wood, crossed the Bald Mountain ridge to Wet Gulch, and thence followed up Willow Creek to the camps. This trail is still used occasionally. The other route was the old Carle wagon road from Knik, leading in a northeast direction to Little Susitna River below the canyon and thence up that stream and Fishhook Creek. In tlie spring of 1913 a new wagon road, following in a general way the route of the Carle road, was completed by the Alaska Road Commission to upper Fishhook Creek. This road is well graded, is furnished with good bridges, and is now used for practically all the summer travel to the mines and also for winter travel to the Fishhook and Little Susitna basins. The winter road for sledding to upper Willow Creek heads north from Knik, skirts the west end of Bald Mountain Ridge, and proceeds up Willow Creek.
MINERAL RESOURCES OF ALASKA, 1913. The summer freight rates by wagon to upper Fishhook Creek are 4 to 5 cents a pound. To Willow Creek supplies must be transported by pack horse from Fishhook Creek, a.ta considerable additional ex pense. In winter freight may be sledded to the camps by ei$er the new wagon road or the Willow Creek winter road at about half the cost of summer haulage. VEGE'J1ATION .All the mines and nearly a.U the prospects in this district a.re located above timber line, and the problem of obtaining for lumber and for fuel is a. serious one. The prospector for bis ce.mp purposes usee alder almost exclusively, as it may be obtained at much greater elevations than the more desirable spruce,, but even the alder must in many places be brought for a distance of 2 or 3 miles. In Little Susi.tna Valley soµie good spruce formerly grew as far north as the mouth of fuhhook Creek, but the demand for this timber has already ca.used the cutting of practically all the good trees above the canyon, and it is now necessary to haul logs a distance of about 7 miles to the mines on Fishhook Creek. Timber for the mi.ne on Cra.igie Creek i'l obtained at a distance of about 4 miles, the upper limit of spruce being at about the mouth of Craigie Creek. Spruce trees 2 feet in die.meter at the base are not uncommon and furnish a. very fair grade of lumber for mining uses. Spruce is also generally preferred for firewood. Some cottonwood grows in the valleys, and birch is com mon in the lowlands and grows locally up to elevati~ns of about 11500 feet. Alder3 grow profusely in the timber and just above timber line, and patches of them may be found up to elevations of 2,500 feet. Small willow bushes extend even farther up the valleys. Forage for stock is everywhere abundant from the middle of .May until early inSeptember, when thefirst heavy freeze of autumn usually occurs. The commonest grass is the redtop, which grows in great luxuriance, both in the timber and above it to elevations of a.bout 21500 feet. After frost comes this grass withers and loses its nutri tive value and stock must be fed on grain and hay. GEOLOGY. . The general distribution of the rock types represented in this dis trict is shown on Plato X. This map differs in some details from the previously published geologic maps of th.e area, but the main subdivis:ionc;i shown are the same as those made oµt by Paige and by Katz. No determinable fossils were found during the present inves tigations, and the age of one of the rock gr<>ups is not known, while that of two other groups can be inferred only by comparison with rocks in adjacent areas in which more definite evidence could be obtained.
GOLD LODES AND PLACERS OF WILLOW OBEBK DISTRICT. The oldest rocks of the district lie for the most pa.rt between the crest of Ba.Id Mountain Ridge and Willow Creek. These are highly fissile, thoroughly foliat.ed mica schists and a.re very uniform in ap pearance throughout their extent. On the north they are cut off by the intrusive quartz diorite; on the south they are in part overlain by gneisses and in part by the Tertiary sediments. The schibts a.re described by Paige and Knopf 1 as garnetif erous mica schists and cblorite-albit.o schists. They have been intruded by some dikes, which have themselves suffered metamorphic;;m a.long with the schists. As wiU bo shown later, the schists are probably the source of some of the placer gold of the district, but although they a.re cut by numer ous quartz veins, including some of considerable size, no encouraging gold-lode prospects have been found in the schist area.. The rocks next younger than the schists are the granitic rooks and assooiated gneisses. A l&rge pa.rt of the Ta.lkeetna Mounts.ins is formed by a. great intrusive body of granitic texture, which is often spoken of as granite, but most of which is more properly termed quartz diorite. This rock cuts the older schist and is thus younger. Near the southern edge of the quartz diorite mass, espooia.lly near Fishhook Creek and eastward to the border of this district, the rock shows a decidedly banded gneissic structure and includes considerable masses of basic crystalline rocks and some large bodies of nearly pure horn blende. In many pla.ces the unaltered diorite seems to merge grad ually into the gneiss, but east and southeast of Government Peak the gneissic character is particularly well developed; the banding is very pronoun.nood, and it appears likely that some meta.J'.!lorphosed sedi ments are included in the gneiss. From a. study of this looality a suspicion a.rises that the gneisses are older than the unaltered granitic rocks, but in the present investigation it was not found to be pra.cti ca.ble to separate the gneisses from the unaltered quartz diorites, and theyhave been mapped as a unit. The granitic rocks of the Talkeetna. Mountains we.re assigned by Paige and KnopP to the Middle Jurassic. The youngest indurated rocks of the district constitute a. thick series composed of arkoses, shales, sandstones, and conglomerates. These were deposited upon an old erosion surface and lie upon both the gneisses and the schist. They cover the south slope of Bald Mountain Ridge and form the southeast rim. of the portion of the Little Susitna. basin included in this investigation. The beds contain abundant fragment.a of leaves and plants, but none were found that were sufficiently well preserved to be identifiable. In the eastward continuation of this formation, however, Paige and Knopf and Martin and Katz found plant remains which have shown the beds to be oi Eooone age. rage, and Knop!, Adolph, op. cit., pp.10-ll. .Paige, Sld.o.ey, and Knopf, Adolph, op. ell., pp. 14-lb. ltCartin, o. 0 ., and Kat&, F.1., Geolcgy and co&! &Ida of Ule lower Matanuaka Valley, Alaa):a; u. B. OeoJ, Burvty Bull. 600, 1912.
MINERAL RESOURCES OF ALASKA, 1913. The deposits left by glaciers and streams a.re largely confined to the valleys. The glacial deposits consist for the most part of clayey materials in which bowlders, gravels, e.nd angular pieces of rock are embedded. InLittle Susitna Va.Hey, at the mouth of Fishhook Creek, the valley sides are covered by this ma.teria.1 for over 1,000 feet above the river, and bedrock crops out in the valley bottom a.t only a few places between the canyon e.nd the cirques in which the river and its tributaries head. Lower Willow Creek ba.s also extensive deposits of glacial materials. The present stream gravels are of remarkably small development in this district. The larger streams for most of their length occupy valleys trenched into the glacial material .APJ a result the streams have been employed since the retreat of the glaciers in deepening rather than widening their valleys, e.nd the stream beds are consequently narrow and a.re filled with large bowlders. In the area. shown on Plate X, Little Susitna. River and its tributaries have developed no considera.ble flood plains, and the gravels occupy too small a.n area. to be shown on a. map of this scale. Willow Creek below the mouth of Grubstake Gulch ba.s a gravel fiatwhich in places reaches a width of several hundred feet. MINERAL RESOURCES. GENERAL P'EATURES. The mineral resources of the Willow Creek district that have been sufficient to encourage mining and prospecting a.re the gold-quartz lodes and gold placers. The gold placers as developed in 1906 ha.ve been described by Paige e.nd Knopf .1 By 1909 reports of the discovery of gold lodes in the district had begun to attract attention, and Brooks 2 published a brief ac.count based on reports of prospectors and others. F. J . Katz e.nd Theodore Chapin were thefirst members of the United States Geological Survey to study the gold lodes, and the results of their four days' visit to the district were published in 1911.1 Short accounts of the de~elopments in this mining district in 1911 and 1912 were given by Brooks, who visited the ea.stern part of the district in 1912. GOLD PLACERS. GRUBSTAKE GULCH. Practically all the placer gold tha.t ha.s been recovered from this district has been mined on Grubstake Gulch and on Willow Creek near the mouth of Grubstake. According to 0. G. Heming, the :first 1 Paige, Sidney, and Kn.op!, Adolph, Recvmnelsannt In UM Matallmkamd Talkeetna basins, witb notes, region: U. 8. Oeol. Survey Bull.814, pp. U&-118, lDO?; Geologlcrecmntssnce In the Mat&nusb and Tallteetna bMIDI, Alaska.: U. 8. Oeol. Survey Bull. 327, pp. ~7, lll07. Brooks, A. .IL, T be m.lnlng lnduatry In 1000: U. 8. O.ol. Baney Bull. 442, pp. 3$-30, 1910. 1 Katz, F. 1.1 A recon°fence or tbe Willow Creek Sold ncloD: U. 8. o.ol. Survey Bull. 480, pp. 162, 1911. Broob,A. R., TbemlDJng lndunry tn 1911: U. 8. O.al. Survey Bull. QO,pp. 28-20, 1911; Tbemlnlne industry in 1912: u. s. Oeol. Survey Bull. 6'2, p . 39, 1912..
GOLD LODES AND PLACEBS OF WILLOW CREEK DISTRICT. 251 two claims were staked in 1897 by M. J . Morris e.nd L. H. Herndon on Willow Creek at the mouth of Grubstake. In 1899 A. Gilbert staked two claims on lower Grubstake Gulch. In 1900 the Klondike & Boston Co. bought up the claims on Grubstake Gulch and a number on Willow Qreek and attempted to operate them for several yea.rs. Over 6,000 feet of steel pipe, ranging from 9 to 24 inches in diameter, was placed on the ground, and hydraulic methods were used. The most productive years for this comp~y were 1904 and 1905. The company later became involved in financial difficulties and failed, and in 1908 its ground was relocated by 0. G. Heming, who now holds 33 claims on Grubstake and Willow creeks. Grubstake Gulch, which enters WiUow Creek from the southeast, is a hanging valley, glacial erosion having lowered the Willow Creek valley below the level of this tributary. A lateral morain~ of the Willow Crook glacier was built across the mouth of Grubstake Gulch, and the stream has now cut through this material and developed a steep, naITow canyon in bedrock beneath it. Fi·om the forks of the stream to the canyon, a distance of about half a mile, the stream falls about 200 feet. Through the canyon it drops about 150 feet in a short distance. Below the canyon an alluvial fan has been built out upon the WiUow Creek flat, and the stream is now somewhat into this fan. The placer ground that has been worked includes part of the bars of Willow Creek below the mouth of Grubstake Gulch, a portion of the Grubstake alluvial fan, the bed o( the canyon, and the bars of Grub stake Gulch for some distance above the canyon. The bedrock is mica schist, and the schistosity strikes across the creek and dips at moderately steep angles, thus affording a rough bedrock surface admirably adapted to retain placer gold. The schist is cut in all directions by tiny stringers of quartz, and quartz veins reaching a width of 3 or 4 feet were seen at several places within the schist area. The :first placer production was made in 1898, the gold being recovered from the claims on Willow Creek at the mouth of Grubstake Gulch. It is reported that about $4,000 was taken out. In 1899 about $3,000 was recovered above the canyon on Grubstake Gulch and a small production· was made from Willow Creek. During the next-four yea.rs little active mining was done, but in 1904 and 1905, when the hydraulic plant had been installed, the production reached its maximum. Fm; the last few years mining has been carried on in a desultory fashion and the.production has been small. From what could be learned at the time of visit, the largest area of ground mined lies immediately above the canyon, where throughout the length of. one claim ground averaging -about 200 feet wide has been worked out. The gravels averaged from 2! to 9 feet in depth, and on the lower half of the claim the gold was recovered from the surf ace of a bed of clay about I foot above bedrock, whil~ on the upper half
.RESOURCES OP ALASKA, 1913. of the Claim the gold lay on the steeply dipping schist bedrock. About 1,200 feet of sluice boxes, 27 inches wide and 30 inches deep, built on 1 and ll inch lumber, with 3-inch square fra.mes, were set on a grade of 6 inches to the box length, the average grade of the bedrock. Water for hydraulic sluicing is brought from a dam at the forks of the creek through a. ditch a.nd steel pipe. The pipe is 24 inches in diameter at the intake but is reduced to 9 inches ·at the giant, and 3 and 4 inch nozzles are used. The head of water decreased as mining progressed upstream but was 180 feet at a distance of three.fourths of a mile below the dam. It is reported that the creek bed has been worked as far upstream as the dam. The gold is fairly coarse and the largest nugget had a value of $14; a number of $5 nuggets were found and pieces worth 50 cents to S1 were numerous. The gold is said to assay a.bout $16.60 an ounce. At the time of visit, late in August, 1913, assessment work on these claims had just begun. A giant was set about 1,300 feet above the canyon, a.nd a cut was started to prospect the thick deposit of gravels on the east side of the creek. The gravels were there from 8 to 15 feet deep, thickening to the east, as the bedrock surface seems to dip in that direction. Fewlarge bowlders were encountered, and scarcely a.ny rocks were uncovered which two men could· not handle. Tbe rocks were for the most part .flat, so~ewhat rounded slabs. of schist which did not move freely before the giant, and it was frequently necessary to remove them by hand, the larger ones being first broken with a hammer. Boxes 20 inches wide were in use, a.nd two men were mining. It is reported that a good pay streak was .discovered east of the present channel of the creek. The total placer production from Grubstake and Willow creeks is said to have been about $25,000. · The task of determining the bedrock source from which the Grub stake Creek placers have been derived presents some difficulties. Veins rich in free gold cut the quartz diorite on Craigie and upper Willow creeks, and at once suggest themselves as an adequate source for the placer gold a.long Willow Creek . . Upper Grubstake Gulch, however, lioo entirely within an area of mica scl?.ist, a.nd the richest placers are localized in this basin. It is therefore apparent that the placer gold above the Grubstake Canyon must have come from the schist.a, probably from the veins and veinlets of quartz which are known to carry some gold. Below the mouth of Grubstake Gulch some gold from this gulch is unquestionably included in the gravels of Willow Creek. Placer prospects have been found on WiUow Creek above Grubstake Gulch, and their gold was probably derived in part from veins both in the quartz diorite and in the schist. Tp.e absence of placers immediately below the outcroppings of the rich gold-quartz veins in the quartz diorite is to be explained by the severe erosion of
GOLD LODES AND PLACERS OF WILLOW CREEK DISTRICT. glacial ice, which removed any accumulation of gra.vel a.nd the in cluded gold and incorporated it in the gla.cial materials deposited farther downstream. The present placers a.re the result of postgla.cial concentration of gold from the glacial deposits and from the post glacial erosion of bedrock. WILLOW CREEK. Prospecting has been carried on at various pla.ces a.long Willow Creek since the first placer discoveries in 1897, but so fa.r the only ground mined on this stream has been that just below the mouth of Grubstake Gulch, already mentioned. The Alaska. Hoosier Co. holds 32 claims on Willow Creek below the moo th of Wet Gulch, extending 2 miles downstream, but only assessment work has been done on them. Some yea.rs a.go a. ditch was built from Wet Gulch down the south side of Willow Creek valley for the purpose of hydraulicking some t.erra.ce gravels, but no considerable a.mount of mining was done. The ground has been prospected by pits and by means of a. spring-pole drill. Holes have been sunk to a depth of 22 feet, but in the valley floor none have reached bedrock. FISHHOOK CREEK. In 1906 some prospecting for placer ground was done on lower Fishhook Creek. Encouraging prospects could be found in many places, and the creek was diverted into Little Susitna River. A 12 foot pit sunk into the channel showed fair values but no ground suffi ciently rich to pay. The best prospects were found in the creek bed and the values decreased with depth. Bedrock was not reached. A 12-cent nugget was the largest found, and all the gold was fairly coarse, but large bowlders were so abundant that mining costs would be prohibitive. The pla.cer gold along Fishhook Creek and Little Susitna River is doubtless a postglacia.l concentration of gold scat tered through the mora.inal deposits, but the large number of great bowlders along these streams make it improbable that placer mining on them would pay. GOLD LODES. GENERAL CONDmONS OF OCOURRENOE. The principal gold-lode minor and prospects of this district a.re described in the following pages, but a. statement of the general con ditions under which the lodes occur seems desirable. All the pro ducing mines and the more promising prospects lie in the area of quartz diorite bordered on the south by Willow Creek, the east-west portion of Fishhook Creek, and upper Little Susitna River. Most of them are included man area 6 miles long from east to west and 5 miles wide from north to south. Within the narrow limits of this produc
MJNEBAL RESOURCES OF ALASKA, 1913. t.ive area the quartz diorite is for tho most part lll88Si.ve and unaltered, though a few prospects along the southem edge lie within a. somewha.t gneissib phase of the granitic intrusive. Without exception the gold-bearing lodes a.re quartz veins cutting the qua.rtz diorite. In many places they are banded, and most of them contain some clayey gouge along one or both walls, showing that the period of vein filling was accompanied by movement n1ong the fractures. Although the banding shows tha.t tho vein filling was continued througho"Qt a con siderable period ol time, evidence of only one general period of vein filling ha.s so far been obtained. The veins, while showing consider able variation in strike and dip, for the most pa.rt belong to a set which strike in. a general northwesterly direction and dip from a few degrees to 45° SW. In places two or t~e veins in the same mountain a.re found to be parallel to one another and 'also parallel to a prominent set of joints. Almost every well-defined vein that was studied is par alleled by a strong set or joints. It a.ppears, therefore, that the gold quartz veins a.re fillings of joint cracks. The fact that certs.in joints of a set have a quartz filling while other equally prominent join.ts of the same set conta.in no vein material indicates that only a part of the joints had been formed by the end of the period of vein deposition and that after the circulation of the mineralized quartz-bearing solutions had ceased other joints pe.rallel to the eBrlier ones. were formed. The veins of the district are practically all fillings of :fractures parallel to the jointing, with well-defined, generally regular walls. The quartz usually breaks free from the walls, from which it is com monly found to be separated by clayey gouge. Some veins show brecciated wall rock cemented by quartz, and horses of country rock surrounded by quartz a.re not uncommon. The surf ace croppings of one vein indicate that it is contJnuous horizontally for about 1,500 feet, and other veID.s, while not so well exposed, will probably be proved to be at least equally continuous. '£!nderground workings a.re not yet extensive, but one adit tunnel 886 feet long 'a.nd another 240 feet long have been driven on fairly cont.inuous veins. The veins vary in thickness from place to place and are characterized by pinches and swells. The quartz is white to bluish gray in color and in many places is banded. Near the surface it is usually oxidized, and the visible minerals accompanying it consist chiefly of native gold and limonite. The oxidized ore is commonly full of cavities formed by the leaching out of sulphides. A short distance below the crop pings the ore is unoxidized, and sulphides, particularly pyrite, are comm.on. The gold occurs for the most pa.rt as free gold in the quartz, but some gold is entangled in the pyrite. Reports of tellurides have been comm.on, a.nd chemical tests of a number of these ores were made. The particles of tellurides in the ore examined were too small to enable the identification of the mineral. Besides free gold, the following
GOLD LODES AND PLAOEBS OF WILLOW OREEK DISTlUOT. metallic minerals were identified in the district: Pyrite, arsenopyrite, stibnite, cha.lcopyrite,- bornite, cha.lcocite 0), malachite, galena., molybdenite, cinnabar, and an unidentified teUu.ride. Details of the several veins are given in the following descriptions of the mines and prospects. MINE OF .ALASKA FREE GOLD MINING CO. The property of the Alaska. Free Gold Mining Co. comprises a. group of 13 claims lying on the bold mountain ridge which forms the west wall of the Fishhook Creek valley, north of Hatcher Creek. The claims, covering practically all of the east slope of this ridge and including a. part <?f the west slope, near the summit, have been sur veyed for patent, os has also a. mill site on Fishhook Creek. The company is organized as a stock company but is now operated under an eight-year lease, beginning in 1912. It was on this property that the fust discovery of gold quartz in this district was made, the first claim being staked on September 16, 1906. Since that time develop ment work and mining have been carried on ea.ch summer. The improvements at the mine consisted at·the time of visit of a. mill and blacksmith shop on Fishhook Creek, and adjoining bunk and mess tent.ato accommodate about 30 men; two main tramways and branch tram connecting the mill with the ore bodies; two inclined tunnels 50 and 85 feet long on tJ:ie lower vein, connected by drifts and stopes; a. 95-foot adit tunnel on the ma.in upper vein, and numerous short tunnels, open cuts, 8.)ld pita on the vein croppings on the several claims. The mill, operated by a. Pelton wheel working under a 35-foot head of water, is a Lane slow-speed Chilean mill, designed to turn about 7 revolutions a minute, and to crush to 40 to 60 mesh. It was first put into service about August 1, 1912. Its maximum capacity is a.bout 25 tons in 24 hours, the ore bemg passed through a. rock crusher before entering the mill. The water supply is adequate to operate the mill only during a portion of the open season, and a 16-horse power gasoline engine has been installed to furnish p >wer during periods of low water. From the mill the crushed ore passes to two sets of amalgamating tables e.nd thence is fed to two Bartlett con centrating tables, operated by a small overshot water wheel. From 1 to 2 per cent of the ore crushed is saved as concentrates. From 70 to 75 per cent of the gold saved is said to be amalgamated in the mill, and the remamder is caught on the plates. At present the con centrates and tailings are not treat.ad but are being stored until a. cyanide plants installed. Two principal ore bodies have been opened on tbis property, although there are openings at a number of places on veins which may or may not be continuations of these two ma.in veins. The lower
MINERAL RESOURCES OF A.LASKA, 1913. of the two bas been opened at the head of the south tramway, at an elevation of about 4,300 feet, 900 feet above the mill. It will here be called the Homestake vein, as the principal workings a.re near the boundary between the claims known as the South Homestake and North Homestake. This vein crops out at about the same elevation a.nd hos the same genera.I strike and dip as the Granite Mounta1n vein of the Alaska Gold Quartz Mining.Co., 1,500 feet to the north, and it appears likely that the vein is more or less continuous between these two properties, although it has not yet been directly traced through out the intervening distance. At the head of the tramway the vein is opened by two inclined tunnels 50 feet apart, one 85 and the other 50 fe~t long, connected at 50 feet from the surface by a. drift. The ore was brought to the surf ace ina.car tram operatedbya windlass. Most of the ground between these tunnels isstJped out for 25 feet below the outcrop. The average strike of the vein is here a.bout N. 13° W.1 and the dip varies from 30° at the surface to 42° at the tunnel face. The vein filling, lying between quartz diorite wa.lls, was from 6 to 24 inches thick and was associated with some gouge and clayey matter. The vein cropping has been exposedfor severalhundred feet a.long the sur face. To the north it has been traced as far as the north tramway, and to thesouth it was followed to the edge of a. large taJusslide. It is said that to the southit pinches out to a thin edge. A large part of the ore milled at this minein 1912is so.id toha.vabeen taken from this vein . . The upper main vein on this property, known a.s the Skysorap8t' vein, is opened by a tunnel ·at an elevation of a.bout 4,600 feet on the north slope of Skyscraper ;Mountain, near its top. These work ings are at thehead of a.n 850-foot branch aerial tram, which runs in a. northeast direction and discharges a.t the head of the ma.in north tram, 2,500 feet from the mill. At the time of visit the adit tunnel, which is equipped with a oar tram, was 95 feet long, and work was in progress in the breast. At 40 feet from the portal a raise reaches the surface 36 feet above. As opened by this tunnel, the vein ranges in thickness from 18 inches to 8 feet of soJid quartz, associated with some gouge. The vein matter is generally free from the wa.lls1 and there is evidence that considerable movement has taken place a.lo~ the walls. The vein pinches a.nd swells, but the strike and dip are fairly uniform. The average strike is a.bout N. 15° W. and the dip 40°-45° w. A short distance southeast of the tunnel and above it, on the out crop of the sa.m.e vein, is a large open cut which supplioo about two thirds of the ore milled in 1913. In this cut the vein is split into two parts by a large horse of diorite measuring 15 feet in greatest thickness. Above the horse there is said to be a.bout 5 feet of milling ore, and below it from 4 to 10 feet of ore. At a point 380 feet south
GOLD LODES AND PLACEBS OF WILLOW CREEK DISTRICT. ea.st of the tunnel mouth is another open cut on the sa.me vein, showing about 9 inches of quartz. The tunnel is being driven for this point. The quartz of the Skyscraper vein is in general massive, though locally showing a banded structure. In the open cuts it is rusty from iron oxido and full of cavities formed by the leaclring out of the sulphides. A short distance from the surfa-0e, however, oxidation of tho sulphides has taken place only along cracks in the vein, and the massive quartz has a light to dark blue-gray colm·. It contains, besides native gold, rather abundant pale pyrite and some chalc<> pyrite. A little galena. is reported. The native gold occurs both as particles in the quartz not immediately associat.ed with pyrit.e and as intergrowths in the pyrite, as can be seen from the delicate crystals projecting into the cubical cavities from which the pyrite has been leached. The production in 1913 was diminished by the scant supply of water, as the mill was operated to capacity for only a part of the short open season. A. third vein of proved economic importance crops out on the Eldorado claim, about 3,000 feet south of Skyscraper Mountain. This vein has been developed by several large open cuts and by a 30-foot inclined tunnel, at an elevation of about 4,270 feet. The country rock is a. ~uch-decayed quartz diorite. The vein ranges in thickness from 1 inch to 18 inches of solid quartz, associated with some clayey gouge. It strikes N. 24° W. and dips about 36° W. and is therefore nearly parallel with the other veins on Skyscraper and Granite mountains to the north. The quartz is oxidized and rusty, as is also the country rock, even at a distance of 30 feet from the surface. It is reported that in 1912 about 100 tons of ore from this voin was dragged down a trail to a point from which it could be trammed to the mill. A number of other open cuts and short tunnels on this property expose quartz veins of varying size and gold content, but none of them has yielded ore in commercial quantity. In 1911 a few tons of ore from this property was milled in the mill of tho Alaska Gold Quartz lvfining Co., and this was tho first gold produced from this mine. lq the spring of 1912 the Chilean mill was installed, and a.bout 525 tons of oro was milled that summer. In 1913 the mill was nm to as great capacity as the water supply per mitted and a.bout 25 men were employed continuously during the ~orking season. MINE OF ALASKA GOLD QUARTZ M'ININO 00. The property of the Alaska Gold Quartz Mining Co. lies for ,the most pa.rt in the upper portion of the valley of Fishhook Creek, on the east slope of Granite Mountain. It comprises a group of five 60553°- Bull. 592-14-17
MINERAL RESOUBOES OP ALASKA, 1913. claims and a mill site, all of which ha.ve been surveyed for patent. The claims form an irregular tier extending from Fishhook Creek up the mounts.in to the west and include a portion of the divide .between Fishhook Creek and Willow Creek. The claims were located in 1907, and development work and mining have been carried on each year since. The improvements consist of a 4-stamp mill, located on Fish hook Creek, two aerial tramways extending from the ore bodies to the mill, a group of tents in the valley, a blacksmith shop and car tram at the main tunnel, several hundred feet of adit tunnels and stopes, and a number of open cuts on the croppings of the ore bodies. The mill is operated by a smell Pelton wheel, which works under a 120-foot head and develops about 15 horsepower. The mill equip ment .fu"St in.stalled consisted of a prospecting mill of three 600-pound stamps, manufactured by the Min~ & Smelter Supply Co. Later a 1,250-pound Neis.sen stamp was added. The capacity of the four ata.mps was a.bouts; tons in 24 hours, with the small stamps dropping 98 times a minute and the large stamp 90 times. The ore is crushed to 40 mesh and passes from the stamps over amalgamating plates and thence over a Wil.fl.ey concentrating table. The concentrates are said to bear a proportion of about 1.80 in the more or less oxidized portions of the vein and of about 1.40 in the unoxidized ore about 400 feet from the surface. The concentrates and tailings have been saved for future treatment, but up to the present time all the values recovered have been in free gold by amalgamation in the morta.rs and on the plates. When the mill is running to capacity the plates are cleaned every 24 hours and the mortars once a week. Two 2-bucket aerial trams equipped with I-inch cable lead from the ore bodies to the mill. The lower of the two, heading a t the mouth of the ma.in tunnel, is about 1,700 feet long and is supported by one tower near the mill. The other tram is 2,460 feet long in a single span and has a vertical distance of about 1,100 feet between the ends. Two principal ore bodies crop out on this property. The ma.in tunnel on the lower or Granite Mountain vein, which has furnished most of the production, and which crops out on the walls of a. small cirque, i:S at an elevation of 4,150 feet, or 500 feet above the mill. The upper or Independent vein lies high on the mountain, 620 feet ver tically above the Granite Mountain vein, and has so far been pros pected only by shallow opening. The country rock is everywhere the quartz diorite which forms all the northern part of this district. The Granite Mountain vein is developed by a. main adit tunnel 386 feet long, another adit tunnel 80 feet long, several short tunnels and open cuts, and several stopes, some of which connect the two larger tunnels with each other and with the surface. In general the vain strikes N. 14°-20° W., thestrike varying somewhat indifferentpart..s of therein. The dip also is ra.the1·irregular, varying from 10° to 42° SW.,
GOLD LODES AND PLACERS OF WILLOW CREEK DISTRICT. but averages about20° SW. At the portal of the main. tunnel the vein cropping shows only 1 or 2 inches of quartz, but in the tunnel the qua.rtz vein matter varies in thickness from 2 inches to 4 feet, rarely pinching to less than 8 inches and averaging about 22 inches. The vein pinches and swells abruptly and contains some horses of coun try rock but is continuous throughout the tunnel. In one place a dip fault has displaced the vein about 4 feet. The vein walls are distinct and smooth, are generally slickensided, and are in most places separated from tho vein by a layer of gouge matter of varying thickness. The quartz is characteristically massive, though it is banded in places. It is of a light-gray to dark blue gray color and where unoxidized shows, besides native gold, rather abundant pa.le pyrite, some chalcopyrite, and specks of some uniden tified dark sulphide. The vein matter has been somewhat shattered and slickensided. Very near the surface the ore is rusty and most of the sulphides have been removed by oxidation. Fartherunderground iron oxide occurs along certain cracks in the ore, but most of the sulphides are unaltered a sho1·t distance f{'.om the surface. The better ore from this vein occurs in chutes, four of which were en countered in a distance of 386 feet along the strike of the vein. The upper vein on this property is known as the Independence vein and is connected with the mill by an aerial tram at an elevation of 4,770 feet, 1,120 feet above the mill. The vein strikes N. 12° W., or approximately parallel to the Granite Mountain vein, and its average dip is a.bout 42° W. Although it.q southward continuation has not been directly proved, it is without much doubt on the same plane as the main upper vein on the property of the Alaska Free Gold Mining Co., and future developments a.re likely to show that the vein is continuous between these two properties. The developments at the time of visit consisted of an open cut about 100 feet long and a 15-foot tunnel at the head of the tramway, and other open cuts on the vein both to the north and to the south. The vein, as seen at the several openings, is fr.om 2 inches to 2 feet in thickness, averaging about 12 inches, and is accompanied by considerable sheared matter and gouge. The walls consist of blue-gray diorite, eomewhat sheared near the vein. The vein near the tramway is forked, a portion of it cropping out a.bout 30 foot below the tunnel. The vein quartz is less ma'>Sive than that of the Granite Mountain vein, is generally banded, e.nd consists of interlocking crystals of quartz containing free gold, a little pyrite, and small quantities of some other sulphides. Only a small quantity of ore from this vein had been mined up to the fall of 1913, but it was planned to build a cabin near the outcrop and run a tunnel on the vein that fall. It WM reported that on September 3, 1913, this tunnel had been driven 34 feet on the vein, and that approximately 4 feet of good ore showed in the tunnel face.
MINERAL RESOURCES OF ALA.SRA, 1913. In 1913 difilcu lies were encountered in keeping the mill in operation, numerous causing a. serious curtailment in the output, although enough ore we.a a.va.ilable to supply the mill, and the water supply was sufficient to furnish power throughout most of Pla.ns were being ma.de to install a. new mill that winter. MtNE OF GOLD BULLION MINING 00. The Gold Bullion .Mining Oo.'s property is situated on the southeast wall of the Cra.igie Cree'k valley, about 4 miles above the mouth of the creek. The first claims were staked in 1907 by William Bartholf, and the group now includes five full claims and a fractional claim, which have been surveyed for pa.tent. The improvements consist of a group of buildings and a 7-etamp mill located in the valley, two branch aerial trams supplying a main aerial tram to the mill, a. short aerial tram and a car tram at the upper workings, which a.re provided with a stone house, blacksmith shop, and bunk tenta, several hundred feet of tunnels and stopes, and numerous open cuta and strippings. The main working$ a.re connected with one another and with the mill by trails. Power for the mill is provided by a. 12-inch Peltonwheel operated under a 28-foothead, about 25 horsepower being developed. Some power is needed to run the main tramway. Two 1,000-pound Hendy stamps were installed in 1909, and in 1911 five 1,000-pound Halla.die stamp were a.dded. The ore is :first passed through a. coarse crusher and then fed to the stamps, which are regulated to drop from 100 to 103 times a minute, to 40 mesh, and discharge over two sets of amalgamating plates and thence over a. Wilfiey concentrator. The capacity of the stamps is a.bout 21 tons of ore in three shifts of eight hours each, and the ore con centrat~ in about the ratio of 1 to 200. In 1909 the two stamps then installed were supplied with ore brought to the mill on pack horses, but the next year o. cable tram was insta.Ued. The me.in tramway which now supplies the mill is a 2-bucket aerial tram, equipped with i-inch cable, and is 3,253 feet long, with a rise of 850 feet. It is sup ported on a number of towers. The buckets ba.ve a. ca.pa.city of 400 pounds, and the tram is of sufficient capacity to keep the mill well supplied with ore. At the head of the main tram there a.re ore bun.kem supplied by two trams, one about 1,600 feet long from tunnel No. 5, and one 1,450 foot long from tunnel No. 2, ea.ch equipped with l-inch co.hie e.nd two buckets. These trRJllS both consist of single spans unsupported by towers. From tbe mouth of tunnel No. 2 a. ca.r tram 945 feet long follows the mountain slope to the northeast and is fed by an aerial tram 635 feet long, which heads at Discovery, on the Gold Dust claim. The vein croppings on the Gold Bullion property occur near the summit of the ridge which separates the upper valleys of Craigie and
GOLD LODES ~ND PLAOEBS OF W1LLOW CBEEK DISTRICT. 261 Willow creeks. The workings are at elevations of 4,400 to 4,600 foot, and the mill in the valley bottom is a.t 3,050 feet, or about 1,500 feet below the ore bodies. The discovery of the veins on this property in the high, craggy ridge top is no doubt due to the good exposures of bedrock which occur there. Below the workings most of the bedrock is so concealed beneath a covering of talus a.nd of glacial deposits that prospecting is difficult. The ore milled in 1909, which yielded the first gold recovered from this property, is so.id to have been obtained from the talus and from open cuts on the Gold Dust claim, the place of the original discovery. During the years from 1910 to 1912 the ore milled was taken from tunnels Nos. 3, 4, and 5, No. 5 furnishing most of tho production. In 1913 the production was obtained largely from open cuts and from tunnel No. 1 on the Gold Dust claim, from the same locality that was first mined . . At the time of visit access could be had to the many open cuts on the property, and to ad.it tunnels Nos. 1, 2, and 4. Tunnels Nos. 3 and 5 had caved in at the portals and we1·e inaccessible. Active mining was being carried on in open cuts near tunnel No. 1 and in that tunnel it.sell, which was 30 feet long, and a prospecting tunnel, No. 2, was being driven along the vein and had peneLrated several hundred feet into the mountain. Between these two tunnels numerous open cuts and strippings have exposed the vein, and although the exposures a.re not continuous, it is most likely that both tunnels, and No. 3 as well, a.re all on the samo vein. Tunnels Nos. 4 and 5, while somewha.t higher on the mountain tha.n the projected dip of the vein from No. 2 would indicate, are in ground that has been somewhat faulted and disturbed, and it is not improbable tha.t the veins on which they were driven are parts of the same ore body exposed in the other workings. The vein may, however, be somewhat displaced by faulting, or it may even prove to be a. distinct oro body. At tunnel No. 1 the vein strikes about N. 28° E. and dips 15° W. Open cuts show its continuation on the opposite side of the ridgo t.o the south. At the time of visit the tunnel was 30 feet long, but it is reported that by October 15, 1913, it had been driven t.o a. length of 184 feet. As exposed in the tunnel the vein is from 3 to 7 feet thick and is composed largely of white or bluish quartz, rusty along the fractures. Shea.red matter and gouge occur both a.hove and below the vein, which cuts the quartz diorite. Visible particles of free gold could be seen in many pieces of the ore, as woll as small a.mounts of pyrite and chalcopyrite. Particles of some other finely disseminated sulphides are also present, and copper carbonate stains are common. Although both the country rock and tho vein a.re much fractured, IllfillY of the fra.ctures being filled with ice, the ore a.t even so short a distance as 30 feet from the portal of the tunnel is not greatly oxidized,
MINEB.A.L RESOURCES OF ALASKA, 1913. except along fractures, and many of the sulphides are unaltered. The open cuts at this place have disclosed a large amount of oxidized a.nd broken vein quartz mixed with the surface detritus, and this loose surf ace material supplied a coilsiderable proportion of the ore milled in 1913. The surface portion of the veins seems to yield somewha~ higher returns than the fresher material from tbe underground workings, probably as a result of the freeing of some gold by the oxidation of the sulphides. At present the only gold recovered is free gold, obtained by amalgamation. Adit tunn.el No. 2 h88 yielded a little milling ore, but most of it has been driven in thehope of open ing an ore body. The tunnel.is on the Golden Wonder claim, and the vein,. which ranges in thickness from 5 feet to the vanishing point and averages about 2 feet, strikes approximately N. 30° E. and dips about 14° W. In the breast of the tunnel the vein had thinned out to a small stringer. It is reported that on October 15, 1913, the tunnel had been driven to a length of 240 feet and the vein had widened out, giving a width of 3! feet of paying ore. Tunnel No. 3, about 400 foot west of No. 2 and presumably on tha same vein, is now caved in but is reported to have yielded consider able good ore. Adit tunnel No. 4 is said to be 300 feet long, and the vein ranges from 2 feet in thickness down to a small stringer. No work was being done on this tunnel in 1913. Tunnel No. 5, which is now caved in and abandoned, furnished most of the ore milled in 1912. The ve.in is said to have had a maxi mum thickness of 14 feet, though averaging much less than that. In 1913 a small quantity of ore was recovered from the outcroppings of the vein near the site of the old tunnel entrance. In the mill practice at this mine the only metal which has been recovered so far has been the free gold caught by amalgamation in the stamp mortar boxes and on the plates. In 1913, during the time when the mill was running 24 hours a day, the plates were cleaned up at the end of each 8-hour shit and the mortars were cleaned every 48 hours. The concentrates from the Wililey table have been stored separately and all the tailings have been impounded. About 4,000 tons of tailings are now stored ready for treatment, and plans are being made to install a 30-ton cyanide plant in 1914. In 1913 the mill was run three 8-hour shifts a day, and two shifts were worked in the mines. About 30 men were employed continu ously during the summer. In the fall the number of stamps in operation was reduced as the water supply diminished. The 5-stamp mill ran during the season for a total of 59 days, and the 2-stamp mill for 72 days. It was planned to continue underground mining all winter.
GOLD LODES A.ND PLACEBS OF WILLOW CREEK DISTRICT. HABEL MINE. The Mabel mine is situated on the west wall of the Little Susitna Valley, 3 miles above the mouth of Fishhook Creek. The workings, at an elevation of 3,700 feet, are in a small gulch tributary to Little Susitna. River, and the camp is near the same gulch, about 800 feet below the workings. The property (10mprises a block of 12 claims staked to cover the known outcroppings of the veins. The claims were staked in the fall of 1911, and a. moderate amount of develop ment work has been done since that time. In 1912 an open cut was made on the vein and an inclined tunnel driven down the vein for some distance, but water in this tunnel became bothersome and it was decided to drive an adit tunnel below to crosscut the vein. At the time of visit the open cut and inclined tunnel were badly caved and little could be seen, but in places a slip zone, said to be on the vein and containing about 8 inches of gouge and a little quartz, was observed to cut through the quartz diorite country rock. This zone strikes in a general northerly direction and dips about 45° W. The vein, as opened in the inclined tunnel, is said to range from 2 to 18 inches in thickness. Ore taken from it showed a decided banding of white quartz With visible intel~ck:in'g crystals and dark blue-gray fine-grained quartz. Several tons of quartz were obtained from the workings in 1912, and 6 tons was shipped to Tacoma for smelting. · In 1913 an a.dit tunnel was started 20 feet below the earlier work ings and when visited had been driven 51 feet under cover. It was expected that the vein would be struck within a short distance. ~ear the mouth of this adit tunnel is another quartz vein cutting quartz diorite. This vein strikes N. 52° W. and dips 55° SW. It is from 6 to 8 inches thick and consists of massive rusty and oxidized quartz which breaks free from the walls and contains some horses of country rock. The sulphides have for the most part been removed by oxidation in this surficial portion of the vein, though some pyrite remains. It is probable that the amount of sulphides will be found to increase at no great distance from the surface. Visible free gold could be seen in many specimens of the quartz, and small pieces mortared and panned gave many colors of free gold. A good horse trail has been built from the wagon road to the ca.mp and also to the tunnel mouth. Plans were under consideration to construct an aerial tram from the tunnel to a mill site on Little Susitna River in 1914. ARCH PROSPEOT. The Arch prospects situated on the south side of Archangel Creek, about 1t miles above the mouth of that stream, at an elevation of 3,200 feet, 550 feet above the valley bottom. This property, which
MINERAL RESOURCES OF ALASKA, 19la. consists of a group of four claims called the Arch group, has been genera.Uy known as the Fern, Taulman & Goodall prospect but changed hands in the summer of 1913. At the time of visit there was no one on the ground, and the main tunnel was caved and partly filled with water, so that little could be seen. A good stone ho'llse and blacksmith shop have been built near the prospect, and a good trail extends from the ca.bin to the main trail in Little Susitna Valley. The vein, which cuts quartz diorite, bas been developed by a num , ber of open cuts and by an inclined tunnel said to be 80 feet long. The tumiel follows down the vein, which in the somewhat disturbed ground through which the outer portion of the tunnel is driven strikes N. 33° E. and dips 21° NW. In the accessible portion of the tunnel the vein was from 10 to 40 inches wide and the filling was mostly -a clayey gouge, with little quartz.. It is said that farther in 1J?.e tunnel a maximum of 12 inches of quartz was obtained. The quartz, as seen on the dump, is banded and consists of interlocking quartz crystals surrounding pieces of altered country rock. Sul phides are present only in small amounts. Under the new management a new adit tunnel to crosscut the vein 180 feet below the old incline was started in the fall of 1913, and two other drifts are reported to have cut the vein, showing from 12 to 20 inches of gold-bearing quartz. It is planned tO install two small Lane mills on Archangel Creek in the summer of 1914, water for. power being obtained from the tributary which joins the creek from the south near the mill site. BARTHOLF-ISAACS PROSPECT. The four claims of the Bartholf-Isaacs prospect are located in the upper basin of Archangel Creek, about a quarter of a mile above its mouth. They were staked in June, 1912, ·and only assessment work has been done on them. No one was working on these claims at the time the area was surveyed, and they were not visited by the writer. It is reported that five open cuts have been made which show the vein at its greatest size to cut quartz diorite and to contain 2 feet of quartz and 5 feet of gangue. PROSPECT OF BROOKLYN DEv:ELQPMEN't CO. The Brooklyn Development Co.'s property consists of five mining claims and a mill site in the basin at the head of Willow Creek. The claims are said to have been located in 1909, and have been surveyed for patent. The developments consist of two buildings in the valley bottom, a large number of open cuts and trenches, and two adit tunnels, 40 and 180 feet long. The upper adit tunnel, at an eleva ti.on of 41400 feet, is driven through quartz diorite. Itwasstarted on
GOLD LODES AND P LACEBS OF WILLOW OBEEK DISTRICT. a. quartz vein 6 to 8 inches thick, striking approximately east and dipping 15° S. A short distance from the entrance the vein was cut off by a fault, and the remaining portion of the adit shows no con tinuous vein, although the diorite is seamed and fractured and a little clayey material appears along some of the fractures. The quartz from the vein near the entrance is rusty and much fractured and shows some banding. The vein is now for the most part concealed, but the few bits of quartz obtainable showed little mineralization. Nothing was learned of the gold content of this vein. The main a.dit, about 60 feet below the shorter one, is a somewhat crooked tunnel 180 feet long, and there are three 10-foot crosscuts extending from it to the south. On the surface there is said to have been a vein cropping of about 7 inches of quartz, but the tunnel fol lows a seam in the quartz diorite, containing some clayey material but almost no quartz. In the breast of the tunnel there are a few small quartz stringers, and one crosscut shows 2 inches of clayey gouge with a little quartz. No ore body has been developed in this tunnel. The numerous open cuts and trenches on the property a.re caved in, and little could be seen in them. A stamp mill for this property was purchased several years a.go and freighted in to a point on Willow Creek 7 miles below the cabins but never delivered at the site upon which it was to be installed. GRIMES PROSPEC'r . The Grimes prospect comprises a group of eight claims, known as the Dolores group, situated on the north side of the ridge which divides the Fishhook Creek drainage basin from that of Archangel Creek. The ground was staked in 1912. The developments consist of a number of open cuts distributed throughout a vertical range of 300 feet and supposed to be on the same vein. The line of cuts strikes a little east of north, but little could be seen of the vein in place, as the sides of the cut.<3 have caved in. The lowest cut, at a.n elevation of about 3,600 feet, shows on the dump pieces of quartz from a vein at least 10 inches thick. The quartz shows some banding and contains bits of altered country rock but is for the most pa.rt rather massive white quartz, somewhat oxidized. The country rock is quartz diorite, cut by a prominent set of joints striking N. 15° W. and dipping .43° SW., and the vein is probably a filling of a joint of this set. Another cut, at an elevation of about 3,200 feet, has on the dump considerable rusty banded quartz stained with malachite. The vein is evidently at least 6 inches thick. Another open cut above the two already described is said to expose 14 inches of quartz which carries sulphides and free gold.
MINERAL BESOUROES OF ALASKA, 1913. BATCHER PR-OSPEOT. The Hatcher prospect comprises three claims known as the Little Gem group, in the upper basin of Archangel Creek, about a mile above the mouth. The claims were staked in August, 1913, .and were not visited by the Survey party, as no development work had been done a.t the time that portion of the area was mapped. It was reported in September that an ad.it tunnel 15 feet long had been driven on this property, disclosing a quartz vein from 1 to 10 inches thick, cutting the quartz diorite country rock. This vein is said to be traceable for 1,500 feet along the surface and to carry considerable gold. A large specimen from this vein showed abundant free gold in co&rse specks. It is planned to install a.n aerial tramway a.nd a 3-ste.mp prospecting mill on this property in 1914. M.cOOY PROSPEOT. The McCoy prospect includes a group of 19 claims on the ea.st slope of the mountain which lies west of the lower Reed Creek valley. The claims were located on June 28., 1913, and prospecting during the year was confined to digging open cuts to uncover the vein croppings. At the time the property was visited no one was working on the claims. About 20 open cuts were examined. None of these are large, and only a part of them reached undisturbed bedrock. Several of the cuts had a small amount of quartz on the dumps, and one showed 4 inches of clayey gouge in place, containing a little quartz. The country rock on this mountain is all coa.rse quartz diorite, with some inclusions or segregations of a gray sugary porphyritic rock. It is repor~ that the best showing of quartz on the property is north of the cuts visited. There are said to be three veins, the largest reach ing a. maximum known thickness of 7 feet. The veins a.re reported to strike in a. northwest direction and to dip to the southwest. MAMMOTH PROSPECT. A group of four claims, known as the Mammoth group, ~located in the Willow Creek valley on the mountain. which lies north of the pass between Fishhook and Willow creeks. The main workings lie at an elevation of 3,800 feet, or 450 feet above Willow Creek. Active development work was carried on during the winter of 1912-13, a 200-foot ad.it tunnel, with 73 feet of crosscuts and a 12-foot raise, being driven. The vein at the tunnel entrance shows a large body of quartz 28 to 30 feet wide, striking approximately east and dipping 68° N. About 30 feet from the tunnel entrance a fault has cut oft the vein abruptly, and the remaining 170 feet of tunnel on this level was driven on a slip zone full of clayey gouge, but the vein was not again encountered. The country rock is a somewhat gneissic quartz diorite which has been broken by slips in several directions. The
GOLD LODES A.ND PLACERS OF WILLOW CREEK DISTRICT. walls of the slip zone on which the tunnel was driven are well defined, and although they show some rolls, the direction of the zone is fairly consta.nt. 'l'he walls are smooth and in many places show slicken sides, and the rock has been much altered. In the breast there is a.bout 3 feet of clayey gouge a.nd shes.red, altered diorite, with good wa.Ils of solid rock on either side. A 35-foot crosscut to the north leaves the main adit 100 feet from the portal, a.nd one or two other short crosscuts ha.vo been made, inn.one of which was the vein encoun tered. About 70 feet from the portal a 15-foot raise on a. slip zone entered a body of quartz, but a. 28-foot crosscut from the raise out through the quartz body, which proved to be an irregular portion of the vein sUITOunded on all sides by faults. The faulted-off portion of the ma.in vein has not been found in the underground workings. The quartz is for the most pa.rt massive white vitreous quartz, mottled with patches of a. bluish-gray colo.r. It shows scattered specks of pyrite a.nd chalcopyrite with stains of copper carbonates. The assays that have been made show the vein to be ore which is of low grade for this district. The vein is, however, the largest seen in the region, and if its underground continuation is established and the tenor holds, there is here the possibility of a mine from which much gold might be recovered·. MINE OF MATANUSKA GOLD MINING 00. The property of the Matanuska Gold Mining Co. is situated on the north side of a cirque in which Fairangel Creek has its head. At the time of visit there was no one on this ground, on which only assess ment work has been done for the last two years, as the property is now involved in litigation. The fou.r claims of this group were staked in 1909, a.nd considerable development work was done in 1910 and 1911. A good trail was built from the Little Susitna Valley to the workings, many open cuts were made, and adi t tunnels aggre gating over 200 feet in length were driven. The ca.mp, consisting of several tents, is near the ·creek at a.n elevation of about 3,500 feet. The country rock in this vicinity is a coarse gray quartz diorite with many inclusions of a gray sugary porphyritic rock. The diorite is cut, nea.r the vein croppings, by small aplite dikes, locally called "quartzite." The dikes are older than the vein fillings, for in places the quartz veins cut the dikes, and cracks in the dikes are quartz filled. The working nearest camp, at a.n elevation of 3,680 feet, is a 20-foot tunnel in diorite. No veins show in this tunnel, which was evidently driven to crosscut a. vein that crops out on the slope 50 feet a.hove. At the cropping a. 22-foot adit shows two quartz veins in the breast, one from 1 to 3 inches thick striking N. 22° W. and dipping 42° NE. and the other from 3 to 8 inches thick striking N. 47° E. and dipping
MINERAL RESOURCES OF ALASKA, 1913. 71° NW. Above the tunnel the smaller vein has been exposed by stripping for a vertical dista~ce of about 50 feet. At a point about 75 feet west of this exposure an adit tunnel, which is said to be 85 feet long, has been driven to intersect the larger of these veins." A cave..in has closed this tunnel about 60 feet from the portal, but it is reported that the position of the vein is believed to be a.bout 10 feet beyond the breast of the tunnel. The tunnel is driven on a. slip zone, from 12 to 18 inches wide, which contains much gouge and o. little quartz and which strikes N. 44° W. and dips 72° NW., or approxi mately parallel to the vein in the tunnel. The vein matter, as seen in the tunnels and on the dumps, is from 3 to 12 inches thick and consists of banded whlte and blue-gray quartz. The quartz contains some visible particles of free gold and considerable sulphides, mostly pyrite. Near the surface it is somewhat rusty and shows small cubical cavities containing iron oxide, the result of the leaching of the pyrite.
At an elevation of a.bout 3,930 feet, or approximately 250 feet above the vein just described, is another quartz vein closely associated with an aplite dike. The vein is younger than the dike, the quartz cutting across the dike and filling fractures in it. An ad.it tunnel has been driven for 84 feet along the vein, which strikes N. 33° E . a.nd dips 45° W. The vein is distinct on the hanging wall, there being in places 12 to 15 inches of solid quartz. Below this hanging-wall quartz there is a stockwork of reticulated quartz veins inclosing frag ments of diorite and containing some gouge. At many places the walls and the ore show slickensides. The same vein is exposed a short distance a.hove the tunnel by strippings and by an open cut. Here the dike and the vein come together. The dike, which along its ~mtcrop varies in thickness from 1 to 6 feet, is at the cut about 6 feet thick and has qu1ntz lying parallel to it b_oth above and below. The vein pinches and swells but in places showed 30 inches of vein matter, mostly quartz, with small inclusions of altered diorite. Some caving has taken place in this cut, and the relations have thereby been partly obscured. The vein walls, the quartz filling, and the diorite fragments inclosed in the quartz a.II show .£ne specks of sul phides, mostly pyrite. Another 24-foot adit tunnel on this property was driven on an aplite dike. The dike rock shows disseminated pyrite. Mll..LER PROSPECT. The Miller prospect is on the east side of Little Susitna River, 1 mile below the mouth of Fishhook Creek and a.bout 60 feet above the river. The developments consist of two cabins on the west side of the river, a footbridge across the river, and a 30-foot adit tunnel driven from the bottom of a. steep, narrow gulch. The tunnel follows
GOLD LODES AND PLACERS OP WILLOW CREEK DISTRICT. a thick ba.nd of siliceous rock which has been locally called a vein but which proves from study in this section to be an altered igneous rock. The "ore" is white to greenish gray in color and in places contains considerable quantities of sulphides. The so-called "vein" is ill defined in outline and but little of it is exposed. The associated rook is coarsely crystalline and belongs to the gneiss series. Only assessment work has lately been done on this property. Nothing definite wo.s learned of the value of the ore, ag assays are said to have given conflicting returns. MOGUL PROSPECT. The Mogul prospect comprises two claims situated on a. high rock bench in the upper Reed Creek valley, 2; miles above the mouth of that stream, at an elevation of about 4,000 feet. The claims were staked in September, 19121 a.od have been developed by three open cuts about 15 feet from one another along the croppings of a. quartz vein that outs quartz diorite. The southernmost cut, a.bout 10 feet long on the bottom, shows about 6 inches of clayey gouge with 2 inches of quartz. The middle cut shows 18 inches of clayey vein matter with 1 to 4 inches of quartz. The north cut shows 4 inches of quartz and gouge above, separated by 18 inches of altered diorite f.rom a lower 12-inch vein of quartz. The vein quartz is very rosy, and small, slender quartz prisms project into the cavities. Much iron oxide is present, and some sulphides. The vein is reported to have given high assays in gold. RAE PROSPECT. The Rae prospect consists of four claims called the J endings group, situated on the divide between Fishhook Creek and Little Susitna River, 1 mile north of the ea.strwest portion of Fishhook Creek. The claims lie in an. area. of more or less gneissic quartz diorite, which is cut by a considerable fault or shear zone. Two open cuts on the Fishhook Creek side of this property were examined. The larger of these cuts was dug from the bottom of a steep gulch, at an elevation of about 4,000 feet, or 1,100 feet above the valley floor, and extended 15 feet into the mountain side. The country rock is deeply oxidized and decayed gneissic diorite, and the cut was driven on a layer of sticky yellowish clay orgouge from 8 to 18 inches in thickness, striking in a general northeast direction and dipping 43° NW. Some quartz occurs in the clayey material and contains free gold, chalcopyrite, pyrite, galena., and copper carbonates. A second open cut, 20 feet above the first, shows the same altered country rock, with thin rusty seams. 'rhe slight a.mount of work done on these claims is insufficient to either prove or disprove the presence there of ore bodies of ooonomic importance.
MINERAL RESOURCES OP ALASKA, 1913. ROSENTHAL PROBPEOT. The Rosenthal prospect comprises the Sun, :Moon, Morning Star, and Evening Star claims, all located on the high ridge which borders the Fishhook Creek basin on the northeast. The claims were located in 1907 and have since that time been owned by several different persons. The developments consist of a fair trail from the valley of Fishhook Creek, a crude blacksmith shop, and two arlit tunnels. The larger tunnel is on the west side of the ridge, is about 95 feet long, and is driven along a vein which cuts the quartz diorite country rock. The vein consists of white, somewhat banded quartz, strikes N. 40° W., and dips 10° SW. It ranges from 1 to 3 feet in thiclmess and carries some visible specks of free gold and finely disseminated pyrite. This fiat-lying vein is close to the mountain top, and the a.mount of ore in it, even if it is continuous in all directions, is necessarily small, as the projected plane of the vein comes to the surface everywhere within a few hundred feet of the main tunnel. On the ea.st side of the mountain a 30-f oot tunnel, driven on the same vein, is not now accessible. The ore is reported to be "spotted/ 1 rich ore being closely succeeded by almost barren quartz. No work was being done on this property at the time of visit. SAN JUAN PROSPECT. The San Juan group of two claims is an the crest of the high mountain ridge whidh forms the west valley wall of Little Susitna River just north of Fishhook Creek. The open cuts on these claims were not seen by; the writer, but it is reported that a gold-bearing quartz vein 9 feet wide has been exposed. Pieces of ore said to have been taken from the property appear to be pegmatitic in character, with large quartz and feldspar crystals. If this rock proves to be workable ore it is of different character from the other proved ore bodies of the district. SHOUGH PROBP'EOT. The Shough prospect is located on the Oregon group of .claims, on the west side of the Little S~itna. Va.Uoy 2 miles north of Fishhook Creek. The ca.mp and workings are at an elevation of 31550 feet, or 1,800 feet above Little Susitna. River. Development work on these claims was begun in the spring of 1913, and the improvements con sist of tents, a blacksmith shop, a horse trail built from the ma.in valley trail to the workings, an ad.it tunnel which a.t the time of visit was 35 feet long, a shallow shai'.t, and several open cuts. The shaft was sunk on "vein No. l,ll a quartz vein which strikes N. 13° E. a.nd dips 62° W. It is reported that the vein, which cuts a pinkish decayed diorite country rock, reached a maxi.mum thickness
GOL.D LODES AND PLACERS OF WILLOW OBEEK DISTRICT. of 15 inches. On the mowitain slope below the shaft a.n. adit tunnel was driven for the purpose of intersecting the No. 1 vein. In this adit another quartz vein with a. greatest thickness of 12 inches was encountered and followed. The vein strikes in general a.bout N. 36° W. and dips 45° E., but both strike and dip vary greatly within short distances. The country rock near the tunnel breast is a. dark blue gray diorite, a.nd the quartz is considerably shattered a.nd much stained with copper carbonate. A third vein, imperfectly exposed in open cuts, is said to reach a. width of 3 feet. Its general strike is east and its dip 68° N. Notwithstanding the high assays reported from these veins, the vein matter shows little or no free gold and yields uosa.tisfactory returns when mortared and panned. The principal visible metallic minerals present a.re azurite, what appears to be chalcocite, iron oxide, and some galena. In the shallow depths reached, however, the quartz is more or less oxidized, and the iron oxide probably rep resents original pyrite. Insufficient work had been done at the time the property was visited to determine the permanency of the veins or to learn the average gold content in any considerable quantity of ore. The Shough prospects lie just east of the line of a fault zone cut ting the diorite. This fault has been traced for a. distance of over 2 miles in a northeast direction, a.nd several prospects have been lo cated near it. The relation of this fault to the veins near it ha.s not yet been determined, as only a small amount of development 'vork has been done along it and the surf a-0e exposures a.re unsatisfactory. It may be, however, that the fault has offered a. passage through which mineralizing solutions have circulated, and that the veins near it have a close genetic relation to the fault. SUMMARY. Lode mining began in tho Willow Creek district in 1908, and since then some $300,000 worth of gold has been recovered. The actual recovery from the ore that has been milled is $42 a ton in gold with some silver. This does not include the values contained in the con centrates or in several thousand tons of tailings which have been stored for future treatment. It is probable that the actual gold con tent of the ore crushed averages at least $50 a. ton. These figures are borne out by the assay returns kindly furnished by various operators. The veins already shown are in general parallel to pronounced systems of jointing. Though not yet mined to any great depth, in dividual veins have been traced to considerable distances on the sur face. There is no reason to believe that the veins will not be per sistent at increased depth. Below the zone of oxidation, which does not exceed a few feet in thickness, they should show no greater vari ation in value than within the present limit of mining.
MINERAL RESOURCES OP ALASKA1 191.3. The occurrence of this zone of mineralization along the contact of intrusive gra.nodiorite is similar to that of some of the gold deposits of southeastern Alaska and elsewhere in tho Territory. The geo logic evidence at hand is all in favor of the presence of commercial ore bodies in this district. The present operating costs are high, owing to the fact.s th&t trans portation from Kruk is effected by wagon and that this port can be reached by ocean freight only from May to November. It is estimated that thus far the freight charges to the mines have varied from $50 to $85 or more a ton. Operations have also been hll!Jlpered by the lack of water at the altitudes at which mills have been installed and by the great cost of fuel. Many of these conditions will be over come if the Willow Creek district is made tributary to one of the proposed railroads into the Yukon or Kuskokwim basin.
MINER.AL RESOURCES OF THE UPPER MATANUSK.A .AND NELCHINA· VALLEYS. By G. c! MARTIN and J. B. MERTIE, Jr. INTRODUCTION. The district described in this report comprises the uppe,r half of the Matanuska Valley and a contiguous area on the h eadwaters of Nel china. River, which is tributary to the Copper through the Tazlina. It includes parts of the ea.stem Ta1keetna and northern Chugach mou~tains, which are separated by the valley of Mata.nuska River. The district ~onsists of moderately rugged mountains 5,000 to 7,000 feet high, which gra..de eastward i,nto the rou.nded hills, about 4,000 feet high, lying on the western margin of the Copper River Plateau. The Ma.t&.nuska Valley can be reached either from Koik, which is the head of navigation on Cook Inlet and to which vessels of shallow draft can go athigh tide, or from Cordova or·Valdez by way of Chitin a and Tazlina road house. Near the lower end of Knik A.rm there is a good anchorage, which ocean-going vessels can reach at any stage of the tide except during the winter, when the upper part of Cook Inlet is frozen or filled with floating ice. At present freight can not be taken in by way of Cook Inlet during the Winter, as the inlet is usually blocked with ice from November 1 to May 1. Passengers can reach the region during the winter by goingin from Seward with sleds, but the Seward routes not available for heavy freight. The best winter route to the upper Matanuska and Nelchina.district is by way of Chitins. or Valdez. The distances from Chi.tin.a and Valdez to the headwaters of the Matanuska by way of Ta.lina road house a.re 125 and 170 miles, respectively. A good wagon road has been built from Knik to Little Susit;na River. From mile 25 on this road a trail hf¥! been cut for a distance of about 8 mile.s, to the mouth of Moose Creek, where it joins the old Matanuslra trail from Cottonwood. The trail from Moose Creek up the valley reaches Chicks.loon. River about 24 miles from Moose Creek. From the Chickaloon ford the trail ascends on a good grade until it reaches the forks near the south end of Boulder Creek flats, a distance of about 7! miles. From this point the Nelchina district may be reached by either of three routes by the old Ma.ta.nuska. trail a.round Sheep Mountam, by the Hicks Creek trail, or by way of Boulder Creek.
MINEBAL BESOUBCES OJI' ALASKA.1 1913. The o1d M.a.tanuska. trail extends east a.long the southern base of Anthracite Ridge to the forks of the Hicks Creek tra.il at Index Lakes, a distance of 11 miles. The trail turns east at Index Lakes e.nd crosses Hicks Creek at a distance of a mile 8Jld a half.. From Hicks Creek to Caribou Creek, about 10 miles, the trail lies parallel to the river. After crossing Caribou Creek it follows the southern slope of Sheep Mountain. About 13 miles east of Caribou Creek it passes through a saddle at the east end of the mountain, descends to Squaw Creek, and goes up the Squaw Creek valley for about 5 miles, whence it turns northward along the western margin of the Tazlina. Valley. The headwaters of Crooked Creek ma.y be reached by turning up the hill at the lake a.bout 4 milei:i above .the Squaw Creek crossing. By the route thus described the junction ·ot Albert and Crooked creeks is about 55 miles from Chicke.loon ford, or about 110 miles from Knik. The Hicks Creek ~rail leaves the Matanuska trail described above at Index Lakes, going up the valley of Hicks Creek to its head, a dis tance of about 1oi miles; down Divide Creek to Caribou Creek, about 3 miles; down Caribou Creek about 3 miles, to a point half a mile above the mouth of Allred Creek, where it turns east to a.void the canyon half o. mile up Allred Creek; then up Alfred Creek for a.bout 10 miles to the point where the main creek comes from the northwest; thence northeast for 3 miles. From .Albert and Crooked creeks itis about 48 miles to the Chfoke.loon ford and 103 miles to Knik by this route. The Boulder Creek trail turns up Boulder Creek fiats at a. point H miles east of Chickaloon ford and follows the open gravel bars of Boulder Creek for about 13 miles. It then climbs sharply a.nd reaches the summit of a pass a.bout 3 miles distant, at an elevation of 4,800 feet. From this summit it descends into Caribou Creek. For about 3 miles, or nearly to timber line, the trail follows the creek cloaely, then climbs up the western bank, which it follows to the mouth of Chitna. Creek. Thence it follows the gravel bars for about 3 miles to the mouth of Divide Creek, where it joins the Ricks Creek trail. By this route it is about 51 miles from Albert a.nd Crooked creeks to Chickaloon ford, or about 106 miles to Knik. Timber line in this district is at a general elevation of 2,500 to 3,500 feet, above which there is the customary growth of small bushes, moss, and grass. The trees include spruce, birch, and several kinds of cottonwood. The growth is in general not dense. Most of the spruce trees are under 12 inches in die.meter, and the largest one which the writers noted had a. circumference of 5 feet. The timber is moderate in amount and of only fair quality, but, e:x:cept in the higher valleys, it is probe.bly sufficient for local demands, provided that forest fires, which the dry clime.ta favors, are kept under control. The local supply of timber will probably prove in&de
UPPER MATANUSlli AND NELCRINa VALLEYS. quate as soon as extensive mining is undertaken. There is no timber suitable for export. The more open birch forests, as well as the areas which have lately been burned, are covered with a dense growth of grass, chiefly redt<>p. There are also large areas of bunch grass above timber line at some localities, especially in the eastern part of the district. These natural meadows are large enough to furnish feed for whatever stock is likely to be locally needed. GEOLOGY. West of Chickaloon River the Talkeetna Mountains are probably composed chiefly of granite, although metamorphic rocks and small bodies of sedimentary rocks are known to be present. East of the Chickaloon the Talkeetna Mountains a,re made up of stratified rocks of Jurassic and Cretaceous age, including both sedimentary and volcanic beds, overlain in parts of the area. by Tertiary conglomerate and lava and tuff. The rocks immediately south of the Matanuska include Tertiary and Upper Cretaceous sediments, volcanic rocks of probable Lower Jurassic age, schists, and granitic intrusives. The geology of that part of the Chugach Mountains which lies south of a belt bordering the river is practically unknown, but the rocks are probably in themain crystalline and largely metamorphic. The general stratigraphic sequence is given· in the following table: Stratigraphic sequence in tM Matanuska Valky. Age. Llthologic cilaracter. Thick· ness (feet). Q.uateroarY. Alluvium. Glaolal and high-level terrace gravels. Pliocene ( 1) J3asalt lc breccias, and tulfs. 1,ooo+ Tertiary. MloceDe (7) Eocene. Eskaconglomerate. Chlckaloon formation; coal-bearing shale o.nd sandstone with the flora of the Kenai formation. Arkose, conglomerat;o, and shale.<> 2,500 2,000:!: 2,000:!: Upper Cretaceous. Shale and Sandstone. 4,SOO:l: Lowel' Cretaceous. LlnKlstoDe. 800:!: Upper .Jurassic. Shale, sandstone, llild conglomerate. 1,000: lllddJe Jura.sslo. Shale and sandstone carrying tbo fauna of the Chtnltna shale or Cook Inlet. Sandstone with the fauna or the ruxednl sandstone of Cook Inlet. 2,000: 1,000: Lower Ju~!c. Andesitlc greenstone, tu1!s, agglomera~, and bl'OOCias; rhyo lites, dacites, and tufts. · 3,000: Early Mesozoic or older. (?) Paleozoic. Mica scbists and other scltistose and gnelssio rooks. (?) a Thestratigraphic position or these rocks Is not definitely establl.sbed. They may Include beds equiva lent topart orthe Eslc&conglomerateand Cbickaloon formation, &9 well as beds older than the Chlclc.9.loon. (See pp. 286-286.)
MINERAL RESOURCES OP ALASKA, 1913. MINERAL RESOURCES. KBTALLIP'B:SOUB DEPOSITS. GENERAL CONDITIONS. The geologic formations of this district which seem most likely to carry valuable metallilerous deposits a.re the schists and the J,,ower Jurassic volcanic rocks. The schists south of the Matanuska are in general similar to the gold-bearing schIBts of Wtllow Creek, but, unlike those rocks, they have not yet been found to contain gold-bearing veins or to be the source of gold placers. Their area. is not easily accessible and has probably not yet been thoroughly prospected. The Lower Jurassic volcanic rocks have been in general considerably altered. They are extensively fractured. and at many places contain multitudes of calcite veins or are impregnated with much fine disseminated pyrite. The copper deposits described on pages 281-282 occur in these rocks, which have not el.sewhel'& been proved to contain valuable deposits. Paige and Knopf 1 said of these rocks: Though placers have not been foWld within the areaa of older volcanic rocks, miner alization has occurred. West of Hicks Creek a la?ge cropping of goiiean about100 feet wide was found. This red capping is due to the oxidation of finely divided pyrite diBBemi.nated through a quartz porphyry. A 11UDple selected for aimy showed a tmce oi gold and no silver. The Middle and Upper Jurassic, Cretaceous, and Tertiary beds and the intrusive rocks which cut them are not known to contain metal liferous deposits1 although there is a. possibility (seep. 280) that some of the placer gold is derived from the small veins in tbeMiddle Jurassio shale and sandstone or in the dikes which. cut those beds, or from the Tertiary conglomerate. The extensive Quo.ternary gravels at the head of Matanuska River may contain srna.11 amounts of :finely disseminated placer gold, ·but are not likely t-0 be either of direct economic importance or even the indirect source of reconoontrated placers. Their glacial origin is unfavorable to the occurrence of extensive placer deposits, as their rapid mode of accumulation precluded the sorting and concentration which is necessary for the formation of workable placers. The present stream gravels are largely derived from the reworking of these older gravel sheets. Even with this partial reconcentration the gold content, at least in most places, he.a not boon increased sufficiently to .PS.Y for working. Productive placers are more likely to be found on such streams as are directly engaged in erodlng o. gold bearing bedrock, especially rock containing mineralized quartz stringers. 1 'Paige, Sldney, and Knopf, Adolph, Oeologlc recount.i.ana. ln the Matanllllka and 'l'&lkeetna bulna, Aluk&: U.S. Geo!. Survey BuU. SZ7, p. 66, 1907.
UPPll M.t.TA.NUSKA AND NELOHINA VALLEYS. PLACER GOLD. IllTJlODVOTIO . The stream gravels of the upper Ma.tanuska. and N elchina district had been prospected for many years prior to 1913 without marked success. Promising indications of workable placer ground have been reported many times from various places, but owing either to the difficulty and cost of traDSporting supplies, or to lack of diligence in prosecuting the work, or to the lack of the gold itself, no producing mines have developed. Interest in this district was renewed in 1913 by the discovery of workable placers on Albert Creek, a small tributary of Crooked Creek, which :flows into t.he Nelchina. About 65 ounces of gold was obtained in a few weeks irom the Discovery claim. Probably only about 20 men were in the district during the working season, and most of these accomplished little or nothing except tho requisite amount of assess ment work. At tho close of the season 100 or more prospectors went in from Knik, Vnldoz, nnd other places and a. large amount of ground was staked. It is to bo hoped that sufficient machinery and supplies were sledded in during the winter to test tho district adequately during the coming summer. £1.BJ:llT AlO> OllOODD OB.l!!EJCS. Albert Creek is a. small stream which enters Crooked Creek from the west about 9 miles above its mouth, at nn altitude of a.bout 3,500 feet. Albert Creek has two named tributaries-Dick Creek, entering it from the southwest about 2,200 or 2,300 feet above Discovery, and P orphyry Gulch, entering it from the north at about the center of claim 11No. 2 u.bove. Crooked Creek, to which Albert Creek is tributary, flows into Nelchlna River, which in turn is tribu tary to the Copper through Tazlina. River. Crooked Creek, so named from its meandering course, flows at a low gradient over swampy bottom lands where the depth to bedrock is not known and may be considerable. The country surrounding Albert Creek consists of low, rounded hills which, like the valley of that creek itself and of the other tributaries of Crooked Creek, a.re entirely devoid of timber. Small cottonwoods and willows grow along the creek, but even these a.re few. The nearest timber is about 31- miles east of the mouth of Albert Creek, on the edge of t.he Copper River flats.' There is also timber about 8 miles to the northeast, near the mouth of Crooked Creek, and a.bout 9 miles to the southwest, on Alfred Creek. At none of these places is the timber abundant or of good quality, but at any of them enough can be obtained to supply a small ca.mp with houses, sluice boxes, and fuel. There is abundant bunch grass along the upper slopes of Albert Creek and probably at numerous other locali ties in the vicinity.
MINERAL RESOURCES 011' ALAS!il, 1913. The rocks exposed along Albert Creek a.re mostly sandstones and shales, probably of Middle Jura.ssio age. They dip at moderately steep angles and are cut by dikes which are mostly small. The hill south of the lower course of the creek consists of altered igneous rocks which were regarded by Paige and Knopf 1 as "lower Middle Juras sic" (subsequently called Lower Jurassic) greenstones. There is a. possibility that these rocks are altered intrusives. Albert Creek heads at the east end of a ridge capped by late Tertiary lavas. These ma.y be underlain by Tertiary conglomerate, as they are at other localities farther west. If this conglomerate is here present it is a probable source of the placer gold. Bench gravels probably occur in the valley of Albert Creek, but they were not noted by the writer, there being snow on the ground when he was there. They were observed, however, in the valley of Crooked Creek 2 miles southeast of Albert Creek, up to an elevation of at lea.st 3,800 feet. Placer gold was discovered on Albert Creek by Fred Getchell, Duncan McCormick, and 0. D. Olsen in 1912. The fust ground was staked in March a.nd April, 1913. In August, 1913, claims had been staked from "No. 4 below," which lies at the mouth of Albert Creek, crossing over Crooked Creek, to "No. 7 above," and also on Dick Creek and Porphyry Gulch, two of the tributaries. Sluicing began on the Discovery claim on July 12, 1913, a.nd at the close of the sea.son, a.bout September 1, it was reported that 65 ounces of gold had been obtained. The gold is bright and clean and well rounded, of very uniform size, a large proportion being worth from 1 to 3 cents and the largest nugget found being 11- pennyweights. From 3-i to 4t feet of gravel was shoveled in. This was said to run as high aa $.14.50 to the ya.rd and to average a.bout 36. The gold-bearing portion is said to extend throughout a width of 30 feet, with only one side found. It lies on a shale bedrock, and has about 9 feet of overburden. Only prospecting and assessment work was done on other ola.ims tha.n Discovery. Claims were staked and gold reported to be found on Crooked Creek and on several of its other tributaries, including North Creek and South Creek, which enter Crooked Creek from the west half a. mile north a.nd 1 mile south, respectively, of Albert Creek, and on Sleigh Creek, which enters it from the east near the mouth of North Creek. · ALJ'll.ll:D omx. Alfred Creek is a. large stream tributary to Caribou Creek from the east about 13 miles above its mouth. The upper pa.rt of the valley is open and lies among rounded hills, but the lower part is deeply incised, the creek passing through.several canyons, of which the low Pt.lge, Sidney, and Knopf, Adolph, Geologic reoonna.Jssance In the and Talkeetna besln8. Alaaka: U. B. Geo!. Survey Bull.327, Pl. ll, UI07.
' UPPEB MATANUSKA AND NELOHINA VALLEYS. est one, which is about half o. mile long, tenn.ino.t-Os a.bout half or thref\ qua.rters of a mile above the mouth of the oroek in o. broad flat. The trail follows the creek except o.t this lower canyon, which it a.voids by passing over the bench to tho north. A moderately dense growth of small spruce extends a.long the lower half of the stream. In the upper pa.rt of the valley there is no vegetation larger than willows and small cottonwoods a.long the stream course. The1·e are numerous patches of good grass on the hillsides. The rocks exposed alo:ng the upper half of .Alfred Creek consist of Jurassic sandstones and shales cut by small dikes. Along the lower half of the creek the only rocks exposed o.ro Upper Cretaceous shales, except a.t tho lower end of the lowest canyon, whore there is a. large dike of coarse dio.ba.se. The rocks exposed on the tributaries a.re prob ably in large part the same as those on the ma.in creek, except that the high ridge north of the creek is known to be capped by Tertiary volcanic rocks. These may be here, as they are at so many pla.ces in this district, underlain by Tertiary conglomerate. If so, this con glomerate is a likely source of the placer gold. Alfred Creek has a.ppe.rently been stoked throughout the greater pa.rt of its length, but on only a. few claims bas more than technical assessment work been done. The discovery was made in 1911. A total of a.bout $1,500 of gold is said to have been recovered from this creek. Ma.zuma. Creek is tributary to Caribou Creek from the northeast at an altitude of about 3,300 feet. The lower part of its course is in an inaccessible canyon, but the upper open pa.rt of its valley may be reached by a trail lea.ding across the hills from the mouth of the stream entering Caribou Creek next below Ma.zuma Creek. The entire valley is a.hove timber line and coots.ins no vegetation larger than nl.Oderate-sized willows and small cottonwoods. The nearest timber is on Caribou Creek about 2 miles below Ma.zuma. Creek, where there is a spa.rse growth of small spruce. Grass is abundant a.long the trail leading into the upper Mazuma Valley. The rocks on Ma.zuma Creek a.re basaltic lavas and tuffs, underlain along the upper pa.rt of the creek by coa.rse conglomerate. An exposure at an a.altitude of about 4,600feetsbows coarse, poorly consol idated conglomerate overlain by angular blocks of lava. which were probably transported from the hillsides above. The conglomerate swell consolidated near creek level, but looser above. This difference may be either the result of local cementation, looa.l lea.ching, orrework ing. It is probably due to reworking, for tho looser pa.rt is decidedly than the well-consolidated conglomerate the creek level. The well--00nsolida.ted conglomerate consists of bowlders, in general not over 6 inches in diameter, and contains lenses of shale and sand
MINERAL BESOUROES 011' ALASKA, 1913. stone, while the looser conglomerate has numerous bowlders from 1 to 2 feet long. Tho bowlders a.re chiefly gra.optic and fine-grained igneous rocks with some sandstone, shale, a.nd porphyry. The con glomerate, both above and below the contact of the better and the less consolidated pa.rt, is thoroughly induta.ted along vertical fissures which stand out like dikes. The creek gravels, so far as noted, con tain only material which might be derived from the conglomerate or the overlying volcanic rocks and include numerous large bowlders. Claims ha.vo been staked from 3 to 5 miles above the mouth of the creek. The discovery was made in 1906. Nuggets up to 16 or 18 cents in value a.re said to havo been found. It is reported that a large number of them havo "cement" sticking to them. There has appar ently been little or no production from this creek. The improvements consist of a wing da.m, several prospect holes, and a ditch which will deliver water from a tributary stream under moderate head. Whatever gold occurs in the gravels of Mazuma. Creek was prob ably derived by reconcentra.tion from a more disseminated deposit in the conglomerate. If there is, as there appears to be, a loose reworked conglomerate lying upon and derived from an older and more thoroughly indura.ted co~glomerate, the contact of the two is possibly gold bearing. DLOHI1'4 Jt.IVU. Nelchina. River itself was not visited by the writers, and no le.ter information is at hand than that published by Paige and Knopf ,l as follows: · Two prospect.ore from Copper Center, who were met in the headwater country of the Nelchina and Tyonek rivers, reported that gold waa preeent iJl all the stream gravels, but in very small quantities. The gold obtained on the Tyonek .iB almoet exclusively in the form of em.all round plat.ea, worth about a Ci?Dt. apiece. Occasion.al small ehotty nuggets occur, not exceeding 5 or 10 cents in value. It ia reported that the hard conglomerate intemtrati.fied with Iuzal!IPc eha.lee and 88.ndstonee, when p&DDed, failed to yield col0?8. Yet in view of the unaltered and unmlnecallied character of the prevailing sandstones and ahalee, and in view of t.be compan.tive coarseness of the gold. it ia neverthel988 probable that t.be meager gold content of the preeent stream chan.nela baa been derived by a concentration of the ancient conglomerates. aovacm or TJD GOLD. The source of the placer gold in this district is not known. There seem to be at least three possiblo sources-(1) concentration from small veins in the bedrock, (2) reconcentration from disseminated gold in the glacial gravels, and (3) reconcentra.tion from disseminated gold in the Tertiary conglomerate. It may be tha.t there is either e. general source, which w111 account for all the placer gold, or that the various occurrences have sources of different kinds. If the latter 1 Pat&e, Sidney, and ll:Dopf, Adolph, Oeoloclc reooonlasnoe l.n tbe Matanum and Talkeetna bulua, Alub: U.S. Geo!. Surrey Bull. 327, p. 57, 1807.
UPPER KAT.A.NUSJU AND NELOBilU VALLEYS. poss~ility is admitted, then nono of the t.hree sources suggested above can be denied, and t.be problem must be disn:Us.sed until further local evidence is obtained. If one general explanation is insisted -upon, then it may be con cluded that the source can not be assigned to local mineralization of the bedrock, unless it is assumed that the rocks of Alfred and Crooked creeks and those of Mazuma Creek have been mineralized. The former include Jurassic and Cretaceous sandstones and shales cut by small dikes; the latter include Tertiary lavas, tufts, and con glomerates. In none of them are veins conspicuous. This explana tion, as a. goneral one, accordingly seems improbable. Reooncentration from glacial gravels will not answer as a ganeral source, for such gravels are not present on Mazuma Creek. Thia explanation would perhaps serve for the deposits on Crooked a.od .Alfred creeks if it were assumed that these streams lio lo the course of an ancient spillway from the Copper River basin. Such is e.ppar ently not tho case, however, for the valleys of Squaw Creek a.nd of the ma.in headwaters of the Mat.anuska would naturally serve as such a spillway rather than the higher divide between Crooked and Alfred creeks. Reconcentration from disseminated gold in the Tertiary con glomerate will not expla.in all these occurrences unless it is assumed that the Tertiary lavas on the headwaters of Allred and .Albert creeks a.re underlain by such a conglomerate. It is not known positively that the conglomerate is present there, but probably it is. However, this conglomoro.to has not yet been shown t-0 be gold bearing, although si.tn.µar conglomoru.tes in other places probably carry gold.1 COPPER. There is an interesting occurrence of copper ore on Sheep Moun tain, near the headwaters of the Matanuska.2 Sheep Mountain is an isolated rugged mountain mass lying north of the Matanuska, east of Caribou Creek, south of Squaw Creek, and west of Tahneta. Pass. The rocks composing the mountain consist of andesitio tufts, breccias, and lavas of Lower Jurassic age, with some interbedded shale, sand stone, and chert. They have been intruded by at least one mass of granite. The volcanic rocks are greatly shattered, and a.re traversed by a network of small veins which consist mostly of calcite. Consid erable alteration has taken place. These rocks were described by Paige and Knopf as follows: For eeveral milee the whole 110uthem flank of Sheep Mountain, at the head of Mata. nuska River, ie colored a strong red from the oxidation of pyrite in the At t Prl:nllle, L. ll., A geolog!o reconna.lssalJce of t.he Clrcte quadranglo, AJulca: U. S. 811"'9Y B un. 538, p. 67I 19J8. t Broota, A. JI., The mining Industry ID 1912: U.S. OeoL Survey Bull 642, p. 39, 1913. P&l&:e, Sidney, and Knopf, Adolph, reconnal!a&noein lb Matauuaka and Talkeetna be.sins, Alaab: U.S. Oeol 8urvey Bull. 3Z7, p. 68, 1007.
MINERAL RESOURCES OP A.LASKA, 1913. aome points the sulphuric acid formed du.ring the oxidation of the pyrite hae bleached the greenstones to a pure-white color. The rugged range, thus tinted in vividly con trasting colors, preeenta a marked scenic eifect. C&tain streams emerging from the range are eo highlyclwged with iron ealt.B ae to color their gravel red with oxide. The "Pyriti.z&tion of the greenstones, which are here roughly echistoee, he.a affected a great thickne88 of rocb butisof a dlffll8ed character. .Anassay of a sample selected as show ing the maximum mineraJizatlon yielded only a trace of gold and no silver. The copper prospects are on East End Creek, which heads just.west of the easternmost high peaking Sheep Mountain, and is the third creek west of the eastern extremity of the mountain. It enters the Mata nuska. about 7 miles above Caribou Creek, or 2 miles above the forks of the Matanuska.. The copper ore apparently occurs as irregular lenticular masses in the more porous and shattered parts of the rock. The abundance and wide distribution of small fragments of copper ore on the ta.lus elopes indicate that the mineralization is general rather than localized and apparently promise the discovery of many small, lenticular ore bodies rather than a few large, persistent ones. A mineralized zone was observed by the writeM on the west bank of the creek at an altitude of about 4,200 feet, nea.r the upper forks. It trends N. 40° E. and stands about vertical, being approximately pa.ro.Jlel to the bedding. Disseminated sulphides (mostly chalcopy rite) occur in small masses throughout a width of about 5 feet, and the zone is thoroughly stained with malachite and a little azurite. Specimens (No. 252) taken at this locality were found to contain chalcopyrite, malachite, a little pal&-blue carbonate, quartz, and cal cite. Veins containing quartz, calcite, cha.lcopyrite, etc., occur in a shattered basic igneous rock. The chalcopyrite is weathering to cop per carbonates. Specimens (No. 252-a.) obtained in the creek bed and on talus slopes near by.contain bornite and cha.lcopyrite. The gangue appears to be quartz, epidote, and calcite. The copper sul phides are weathering to malachite. A specimen (No. 251) obtained at the camp site at the mouth of the gulch of East End Creek, which i3 believed to have been obtained on thi~ creek, appears to represent a sulphide replacement of basic igneous rock. The copper sulphides, which appear to be bornite and oha.lcocite, are altering to malachite. Epidote occurs in the gangue. CO.AL. AREAL DISTRIBUTION. The coal of the Ma.tanuska Valley occurs in several detached fields, pa.rt of which lie within the area here described and pa.rt of which a.re in the lower Matanuska Valley, a description of which has already been published. Martin, G.C., and Kala. F . Geoloc7 and ooe.l lltlcb ol th lowllf Malanusb Vallay, Alaata: u. s. Geo!. Survey Bull. 600. 1912.
UPPER l!UTANUSKA AND NELCHINA VALLEYS. The coal of the upper Mata.nuska. Valley is found in two separa.te fields which are distinct not only a.really but in the geologic occur rence and probably in the character of the coal. One of these two fields (neither of which may be strictly a. unit) lies in the Ma.tanuska. Valley proper below Hicks Creek, including the .Anthracite Ridge area. and an area south of the Matanuska1 and is the eastern extension of the Chickaloon1 Kings River 1 and Coal Creek area. of the lower Ma.tanuska Valley. The other is the upper Boulder Creek and Caribou Creek field. The areal extent of the assemblage of rocks which carry the coal is indicated on Plate XI. The areas indicated as coal-bearing are those which may carry coal, as distinguished from the areas shown in blank on the map, which a.re believed not to carry coal. The areas represented as probably coal bearing, or as containing the so-called "coal-bearing rocks," can not be assumed to be underlain wholly by beds of coal of workable character and thickness. More over, parts of these areas probably have no coal under them. The lack of knowledge as to the exact stratigraphic position of the coal beds, the uncertainty as to what stratigraphic part of the "coal bearing rocks 11 is represented by each of the observed surf ace out crops, and the concealment of the rocks by gravels over broad areas make the precise areal distribution of the coal a problem which can be solved only by drilling or other underground exploration. The tables given below indicate the probable and possible areas of supposed "coal-bearing rocks 11 in the lower Matanuska Valley as previously published 1 and with subsequent revision. The Chicks. loon and Kings River area and the a.rea south of the Matanuska1 as given in the :first of these tables, include lands as far east as longi tude 148° 20', as is shown on Plate VIII of Bulletin 480. These are la.rger tracts than were described in detail in Bulletin 500 and include land lying in the area described in the present paper. The first of these tables shows the areas of probable c<;>al or the areas known to be occupied by the so-called "coal-bearing rocks,11 a.s de fined above, and by the conglomerates and other beds which overlie them. The second table shows the areas of possible coal or the areas which may also be underlain by these rocks, but in which, because of concealment by gravels or of other lack of definite information, there is a possibility that other formations may be present. These esti mates when first published were described a.s "provisional and sub ject to modification, perhaps· considerable, when the region is more thoroughly prospected." It should be noted that they have already been modified by the later geologic work, which has shown that part of the area, east of Chickaloon River and both north and south of the t M'.art1n, 'G. C., Preliminary reportona. survey of part ol the .Matanuska coal fti!lds: U. S. Geo!. Sarvey Bull. SO, p. 134, 1911. Martin, G. C., a.nd Katz, F. :r., Geology and COlllfti!lds of the lower .Mat& nuska Va.lley, Awn: U.S. Geo!. Survey Bull. ooo. p. 76, 1912.
Original Revbed estimate. estimate. Lower parts or valleys or Kings River and Granite Creek Valleys or MOO!Ml and Eska croon MINERAL RESOURCES OF ALASKA, 1013. Ma.tanuska, included in the 44 square mile and 8 square mile items, is not occupied by the coal-bearing Chicka.loon formation, but by the non coal-bearing marine Upper Cretaceous, while another part of the 44 square mile area is occupied by a conglomerate of uncertain horizon which contains no coal outcrops and may not be underlain by coal. Areaa ofmpposed coal-bearing rod:a in the lower Matanuska Valley. (Square miles.] Odglnal osttmate. Revlsod estlmato. Valleys of Chlclmloon and KIDgs rivers . . Soutli of M.atanuska River in vicinity of Kings MoWltaln and Coal Creek.
Areas of possible ~™of the B1tppo1ed coal-bearing rock.t in the lower Matanuaka Vall.ey. [Square miles.] The followi.J'.!g tables contain similar estimates of the areas which probably or possibly contain some' coal in the11pper Matanuska Valley proper, below Hicks Creek: Areas of probable coal-bearing rock.t in the upper Jlatanu.d:a Valley. [Square mllee. t Anthracite Ridge and low country south of its eastern half 22. 7 South of the Matanuska near O'Brien Creek. S. 0 Areas of poasible ooal-1>£aring rock.t in tht upper Jlatanwka Valley. [Square miles.) Conglomerate and trap ridge district south of west half of Anthra cite Ridge and of lower Boulder Creek. . . . . . . . . . . . . . . . . . . . . . . 2L 1 Alluvial flats of the Matanueka near O'Bri~n and Gravel creeks. .. S. 2 Conglomerate area. west of Gravel Creek 2. S These area.a added to the revised estimates for the lower Matanuska Valley, as giv.en above, show that the entire Matanuska Valley proper below Hicks Creek has an a..rea of 96 square miles that probably
UPFB:S lliliTANUSKA AND NELOHINA VALLEYS. contains some coal and an additional. area of 51t square miles that possibly contains some coal. The area of coal on upper Boulder Creek and Caribou Creek can not, for reasons which will be discussed below, be estimated with even approximate certainty. The total area. within which some traits of coal may occur--na.mely, that of the conglomerate and of the over lying lavas (which may not everywhere be underlain by conglom orate)- is possibly 200 or 300 square miles, but it is reasonably certain that oply a small fraction of this area is actually coal bee.ring. STUATIGRAI'IDO OOOURRENOE. The coal· beds the part of the Mata.nuska Valley proper which is here under discussion·, like those of the lower Matanuska Valley, are all known to be of Tertiary age and to agree approximately in general stratigraphic position with the cool of the Kenai formation on Cook Inlet. They all, except those at the Gravel Creek locality described as section No. 24 (p. 293), occurin.theChicka.loon formation, which is the middle local division of the Tertiary rocks as described in the report on the geology of tho lower Mn.tanuskn. Vnlloy. Their exact position within this formation bas not been determined, but they seem to be in general distributed throughout the greater part of its thickness. Nothing definite is known as to tho persistence of individual beds or of gro~ps of beds. The coal on Billy Creek and elsewhere in the Caribou Creek and Nelcb,ina. valleys has hitherto been assigned to the Jurassic, a.nd has been described 1 n.s follows: The coal-bearing rocka o( this [the northeastern] field include an area. of aboui 500 square miles. Coa.J is found at various localities, but never in thick beds, the best discovered having a. thickness o( 3 feet. The rocks are of Jurassic age and from fossil evidence are divided into a Middle and an Upper JUI'8ll!lic ljeries. The character of the coal appears ina general way to bein accordance with this separation-thatis, the older rocks cany bituminous coal, and the younger, coal of o. lignitic character. The Middle Iu.raasic rocks generally are severely shatt6ed and crushed, or sheared and slickeDSided, a.nd a.s a. rule present a. decidedly unflworable appearance for tlle presence of workable seams of coal. Locally the strata are closely folded, as on Billy Creek,where thecoalha.developed a strong cleavage andha.s asaum.ed a semianthracitic character. That the high-grade coal is restricted to such belts of sharp defomis.tion is rendered probable by the fact that the rocks in the less disturbed areas are found to contain only fragments of carbonized wood and small stringers of lignite. The Upper Jurassic strata lie in comparatively und:i.eturbed attitudes, with prevail ing low dips. Minor dislocations of the beds are of widespread occurrence. extensive faulting is occasionally met with, a.son Billy Creek, where faults or several hundred feet throw are revealed with diagrammatic cleameai. Coe.I was seen at only two localities, on the head of Billy Creek and on the south fork of the Tyonek. At these localities the outcrops were obscured by mud and Blide material, but the amount 'Paige, Sidney, aud Knopf, Adolph, Oeologic reoounaissance ln the M.atannska and Tall:eetnA b&ruis, Alaalr:a: u. s. GilOl. Survey .Bull. 327, pp. 66-07, 1907.
MINERAL RESOUBOES OF 'ALASKA, 1913. of coal represented was probably small. The coal found is a black lignite which checks on drying. Mendenhall reports thin beds of coal interstratified with theshales a.n.d sandstones a.long the south fork of the Nelchina. · The writers believe that at least the greater part of the coal in this district, and probably as much of it as occurs in distinct beds (that is, otherwise than as coalified sticks and small stringers), is not Jurassic. but Tertiary. The evidence for this belief is as follows: The coal-bearing rocks at the locality on Billy Creek described above contain. abundant, well-preserved, and distinctive Tertiary plants. The lithologic character of the beds· in which the fossils occur is similar to that of the recognized Tertiary rocks of the Ma.tanuska Valley and entirely unlike that of the undoubted Jurassic rocks. The "greens tone amygdaloids" of the section on Billy Creek resemble some of the Tertiary igneous rocks at least as closely as they do the Lower Jurassic volcanic rocks, and conse quently they m.e.y be regarded as either an infaulted block of late Tertiary basaltic lava or as an intrusive mass injected under light load. A bed of coal exposed near the headwaters of Boulder Creek lies beneath the Tertiary lavas and above a massive conglomerate which rests upon Upper Cretaceous rocks. These coal-bearing beds carry fossil plants, which are either Upper Cretaceous or Tertiary. Coal float was seen by the writer on several of the other tributaries of Billy and Caribou creeks, and in ea.ch place it was .on a stream that heads in the conglomerate underlying the Tertiary lavas. No coal was seen by the writers in place in the Jurassic rocks, and no coal float was seen on streams other than those that head in areas · of Tertiary rocks. According to Knopfrs notes coal was not seen in the undoubted Jurassic rocks except as "stringers" and was found as float only on those creeks (except for Tyonek Creek) which head in known or probable Tertiary areas. There is consequently little doubt that the coal beds of this district a.re Tertiary. They evidently can not be assigned to the Chickaloon formation. The conglomerate with which they are associated may either hold the position of the Eska conglomerate or be the equiva lent of beds lower down in the Tertiary sequence. It is believed that the beds at this horizon are only locally coal bearing. COAL BEDS. ' The following pages contain measured sections of all the coal ~eds that were accessible. These measurements were all made at natural exposures, there being no prospect openings or tunnels. No attempt has been made to correlate the beds:, as the complex structure and
UPPER !LATANUSKA AND NELCfilNA VALLEYS. the fa.ct that none of the beds can be traced from point to point make correlation impossible. The sections in the Me.tanuska. Valley proper a.re arranged in order from northwest to southeast. l. Creek flowing northwest. ioto Boulder Creek from oear tho west eod or ADthnv cite Ridge, altitude S,700 reet. Coal blOll!!Om (bed concealed) oear outcrop of dark shale. Strike N. 68° W., dip 63° SW. 2. South face or ADthracite Ridge, 2 miles east. or it.a west end, altitude S,900 feet. Ci06l bloeaom. No exposure obtAinnble. s. Creek bed 1.2 miles s. 52° w. from 6,280-root. peak at hea.d or PurintDD Creek, altitude S,300 to 3,500 reet. Ft. In. Crumpled shale . . . . . 85± Cot.I l Shale . Shale .. 25 O Coal 1 Shale 25 o Sandstone . 18 Shale . 18 Shale : S Shale 12 Sandet.ono 24 Strike N. 62° W., dip 45° S. 4. West Fork of Purinton Crook, altitude 4,200 feet. Intrusiw rock (diabaee). Sha.le roof. Ft. In. Dlabase sill. . Shale . s Coal with much shale . . . . . . . . . . . . . . . . . . . . . . . 1 Shale . . . Very carbonaceous shale and coal Shale. Strike N. 88° E., dip 43° S. 5. West Fork of Purinton Crook, altitude 4,100 feet. Apparently two bode of coal, each 5i 01 6 feet thick, 2 or 3 leet apart, but more probably one bed repeated by sur face slipping. Strike N. 65° W. 1 dip 30° SW. 6. West Fork of Purint.on Creek, altitude S,900 feet. Co11l, 40±foot. Neither roof no~ Boor of this coal bed could be found. The coal is apparently cut off o.t eo.ch end of the exposure across what appeo.rs to be tbe beddl.Dg. This is tho exposure whicll hae previously been deecribed 1 aa a 38-foot bed ot anthracite o.nd of·which au auo.lyaie is given on p. 295. It showd probably be regarded as a swollen pockot lying in o. closely folded overturned syncline and probably cut by o. fault. An exposure of bale in the creek 15 or 20 feet below the coal gave thte() readings on tho bedding aa follows: Strike N. 72° E ., dip 11° NW.; strike N. 76° W., dip 12° NE.; etrilce N. 73° E ., dip 21° NW. Martto, O. c., A. recon08'ssa0 c.oClbo Kat&nuakn- lleld,Ataska, lll 1UOS: U. 8. Oeol. Survey & , p. 18, UIO&.
MINERAL RESOURCES OF ALASKA, 1913. 7. Weet Fork of Purinton Creek, altitude 3,880 feet. Shale roof. Ft. I) , Shale (some coal) ... . Coal. . . .. . . . 3 Coal . . . .. .. . . Shale with some coal . . . . .. .. .. . . .. . Shale . . 2 Shale with some coal.. . . . ... . . ... . Coal . .. . . 1 Black shale.. . . 1 Gray shale .. . 12± Shale with eome coal .. . ... .. . . Black shale. . . ... . . . . . . 1 Coal. . . . .. ·· . l Shale .. . . ... . Coal with a little shale . .. . ... . ... . . 1 Gray fissile shale ftoor. Strike N. 87° W., dip 556 S. 8. East bank of East Fork ot Purinton Creek, about 570 feet upstream from eection 9 Shale and 8&Ddstone, much folded. Peet. Coal with eome shale. .. . ... . 7± Covered ... ... . ... .. Coal with some shale 4± Sha.le and sandstone, much folded. 9. East Fork of Purinton Creek, altitude 3,480 t.o 3,560 feet. Diabase. Fi. In. Shale, with coal blossolDll. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 7 Shale ftoor. Strike N. 80° W., dip 55° S. The section given below WM measured by Martin 1 in 1905 on the east fork of Purint.on Crook or 011 the next creek east of it, on the south slope of Anthracite Ridge. Flaggy sandtiton.e. Feet. Coal ang shale . . .. . . ... . Coal . .. . . . Coal .. ... Coal.. .. . Shale . . . Strike N. 89° E., dip 65° SE. 1 Martin. G. C A reoonnalssanoo of tho Mato.nuska COii.i field, Alaska, In™: U. 8. Geol. Survey Ball. 2811, p. 19, 1906.
UPPll MATANUSKA AND NELOIDNA VALLEYS. 10. Creek bed 1.3 mllee S. U 0 E . from 6,280-foot peak at head ol Purinton Creek, altitude 3,850 to 3,950 feet. · Ft.. m. () Shale 4 O Coal. . l Panly ehale, partly co~d 21 Coal. Shale 16 Shale with th.in eill.e . 23 O Coal : ·· 2
Shale (partly covered) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 'l:1 Strike N. 86° E., dip~ 0 N. 11. Creek bed 2.9 milee S. 55° E. Crom 6,280·foot peak at head of Purinton Creek, altitude 3,880 to S,891S feet. · :rt. In. Shale with coal bloeeolll8 ... 50 Coal 3 5 Shale. . 24 Coal.. 2 Shale . 21 O Strike N. 82° W., dip 20° N . 12. Creek bed 2.9 miles 8. 64° E. from 6,280-foot peak at head of Purinton Creek, altitude 3,830 to 31850 feet. Shale roof. ft. to. Coal .. .. . ... l Shale . S Coal . ... . . Shale . . 2 Coal ... 3 Shale 1 Coal .. Shale floor. Strike N. 82° W ., dip 20° N. The two following sections deecrtbed by Paige and Knopf were measured by Knopf on either thls creek orthe next one ea.st olit: Stdion of coal on Anthradte Ridge, alti.tude S,100f~t. Fl. In. Sand.st.one and shale... .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lO:t Coal and shale .. 6 O Coal ... . Shale Coal Shale 2 Strike N. 70° W. (magnetic), dip 40° S. 'Paige, Sidney, &114 OeoielCJO recon,,_,ce l!l lbt Matuuata aiid Tallteeaia AIMta: U. 8. Oedl.. Barny Dall. m,-pp. a-44, 1907. 60553°-Bull. 592-1419
MINERAL BP:SOUROES OF ALASKA, 1913. Section ofcoal ""!' .AntltraciU Ridge, altitude4 3,600/~t. Sand.st.one. Ft. 111.. Coal 2 Coal and ahale Coal Coal and fenugiDou.e clay Coal Sh.ale Coal Shale 12 O Coal.. 1 Shale . .. 5 O Sandstone .'.. 1 O Shale I Clay ironstone nodule8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shale 1 Clayironstone nodulea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Highly carbo~u.s ehale . . . . . . . . . . . . . . . . . . . . . . O Coal .. 1 Shale : 9 O Sh.ale 15 O Coal Sh.ale .. 4o Coal 2 Shale 4 o Coal Shale 2 Coal and eh.ale.. Sh.ale footwall. Strike N. 80° E. (magnitude), dip 34° S. 13. Muddy Creek, altitude S,700 feet. Weet bank of creek. Ft. tn. Band.et.one 20 Carbonaceouuhale, locally coal.. . . Coal 1 Shale ... 3 Coal 1 Carbon.aceoua ehale . Shale, with dt.turned ironstone nodulee 3 Coal l Shale . Ferrugino11.1111&11d8tone 1 Oarbonaceoua ehale, locally coal Coal Carbonaceoua ahale, locally coal Sh.ale floor. Strike N. S2° W., dip 45° W . I See Ula!71Ja No. 22 In \able of &nal7eea, m.
UPPER MATAN'OSKA AND NELCBINA VALLEYS. 14. EaBt bank of Muddy Clteok, altitude 3,690 feet. Sh.ale roof. Pt. tn. Ooal .. . . . 1 Shale 6 Sandstone . . . . 4 Shale .. . . . Coal 1 Shale parting. .. . . Ooal 1 10 BhJl.le ... 8 Shale 3 Coal ... ... 1 Shale 6 Coal 1 Covered. Strike N. 65° E., dip 45° S. 15. Bed of Muddy Creek, altitude 3,340 to S,415 feet. .Feet. Oubonaceous sha1es co11taining 6 to 12 coal eeama ranging in thick neee from 1illchto18 illchee. Badly crushed and sheared 22 Sandstone, thin bedded, and abale . . . . . . . . . . . . . . . . . . . . . . . 28 Strike N. 8° E., dip 25° W. 16. Crest. of spur between Muddy Creek and Pac.k:Baddle Gulch, altitude 4,400 feet. Covered. .Feet. Ooal. ll+ Covered. Strike approximately east, dip 90°±. 17. North bank of Matanuska River, half a mile above Gravel Creek. Fillli.le gray shale. Ft. to. Coal, clean . . . . l Coal, somewhat shaly.. . . . . . . . . . . . . . . . . . . . . . . . . . Fiel'lile gray shale. Strike N. 49° E., dip 30° NW. The entire exposure at this poillt cousist.8 of about 200 feet of bale and et.ndstone, with aeveral carbonaceous zonea 10 to 40 feet thick, io !!Omo of which there are coal beds several inches thick. The coal bed deecribed above ia near the base of the section and extends along the face of the bluH for a considerable distance, ill which it shows no indication of lenticularity. 18. Gulch 0.3 mile weat of O'Brien Creek, altitude 1,800 feet. Black abale with some coal. Fl.. tn. Gray sandy shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Gray nodular llhale. S S Coal 2 Gray abale, much stained by iron
MINERAL RESOURCES OF ALASKA, 1913. Coal : Shale with a little coal . . . . . . . . . . . . . . . . . . . . . . . . Ironstone band . . . . . Coal . .. Coal ... ... .. Sha.le Concealed. Strike N. 78° E., dip 40° S. 19. O'Brien Creek, altitude 1,500 feet. Gray shale under clay. Coal Shale . . . Coal .. .. ... Shale with some coal . Coal ... Coa1y shale Coal Shale withiroll!tone concretions . . . . . . . . . . . . . . . (loa.1 Sha.le Sbille Coal :. Coal Shale . Coal : . . . . . Coo.land shale (squeezed) .. Coal Shale .. .. .. .. Gray shale with ironat.one concretions .. . . . . . . . . . . . Ft. In. O l!'t . In. IO 2 lt
11 t l! s o Gray shale withironstone concretioll8.. . . . . . . . . . . . . . . . . . . . . . . . . . 3 Sandstone with some interbedded shale . . . . . . . . . . . . . . . . . . . 14 10 Shale, eomewhat sandy... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Strike N. 70° W., dip 87° SW. 20. O'Brien Creekabout100y&rds farther upstream. Coalwith many thin partings, 25feet. Thisbedis apparentlybelow the one described above. · · 21. Near top of west bank of O'Brien Creek.a short distance above No. 20. Large coal outcrop which apparent~y consists of the bed represented in section 20 folded back upon itself in an overturned syncline.
UPPER :MATANUSKA AND NELOHINA VALLEYS. 22. Gulch one-third mile east of O'Brien Creek, altitude 1,800 feet. Shale roof. Ft. In. Coal .. 3 Concealed. Rocb dipping gently northeast. 23. Gulch one-third mile east o( O'Brien Creek, altitude 1,900 feet. Sandy gray ehale roof. Ft. In. Coal. .: Sandy shale. Concealed. Roe.ks dipping about 20° NE. 24. About i; miles up the creek which enters Gravel Creek from the west 21 mile1 a.bove its mouth, altitude 2,100 feet. · Covered. Ft. lo. Coal, impure, sheared 1 Shale , Coal, impure, sheared 1 Covered. Dip 75° s. The rocksat this localitycannot withcertainty beaeeigned to the Chickaloon forma tion, whichincludesall the other known coal bedsin the main valley of the Matanueka. Thecoal at this locality mayrepresenteithera local coal-bearing bed in the pre-Ohicka loon strata, or a small blockof the Chickaloon formation folded or faulted into the maee of rocks which are otherwise barren of coal. Information concerning the coal of the upper Boulder and Caribou valleys is much loos abundant than that already presented concern ing the coal of the Matanuska Vo.Hey itself. This is due pJl.l'tly to the fact that the examination of this field was less detailed than that of the other, but chiefly to the fact that the field contains far less coal The following is a. typical section: Section 1UaT waUl"fall on 11ort.hwe1t ride ofBQ1.l.Ukr C'ruJ; t6; milu nort.htaat ofit. mouth. White sandst.one and shale with carbonaceous beds. Ft. In. Coal and shale . 1 Ooal' ... . l Sb.ale . 1 Coal . White 811.!ldstone and shale. Strike N. 11° W., dip 20° NE. The exposure of coal-bearing rocks on the small tributary to Billy ·Creek from the east 2t miles above its mouth contains numerous car bonaceous beds and coaly streaks a.nd several th.in beds of coal. The largest observed bed attains a maximum thickness of 3 feet, a large portion of which is shale and bone. The greatest observed thickness of pure coal at this locality is not over 12 inches. 1 Included in mmple No. 19346, p. 2115.
¥JNERAL RESOUROES OF ALASKA, 1913. Small fragments of coal were also observed in the beds of several of the other tributaries of Billy Creek, notably the one entering it from the east 6 miles above its mouth, on some of the creeks tributary to Caribou above Billy Creeli, and on Hicks and Tyonek creeks. CHARACTER OF THE COAL. PHYSICAL PROPERTIES. The coal of the Mata.nuska Valley is of three kinds-anthracite, high-grade bituminous, and low-grade bituminous. All of these have boon found within the area here described. The last two occur also fa.rther 'West in the lower Matanuska Valley and have been described in a.n. earlier report.1 The anthracite is known only in a small area near Purinton Creek on the south face of Anthracite Ridge. The high-grade bituminous coal occw'S on the south side of the Matanuska and probably on Anthracite Ridge. The low-grade bituminous coal occurs at the east end of .Anthracite Ridge and on upper Boulder a.nd Caribou cree~. The investigations that have thus fa.r been made a.re not sufficient to permit an attempt to outline precisely or to estimate the areas of the several kinds of coal. The anthracite has the ordinary physical characteristics of most coal of this ki.nd. It is heavy, firm, ha.rd, a.n.d not much fractured for surface coal a.n.d has a high luster. Pyrite was not observed in it. The high-grade bituminous coal is fragile and soft, like all coal of this variety, and the beds show the effects of having been severely crushed and at many places are without any well-defined bedding planes or places of fracture. The friability of the coal is so great tha.t it will probably not stand shipment without being badly crushed. This is not so great a detriment a.s might a.t fi.r.:Jt seem, because many of the beds contain so many impurities tha.t the coa.1 from them ought to be cMJShed and washed. It is, moreover, highly probable that some of this coal can be used in. the manufacture of coke, a. pwpose for which lump coal is not desired. Coal which possesses coking properties, as much or all of this coal does, can, by proper handling, be burned as slack a.bout as well as in lumps, for the slack coal when thrown into the furnace will fuse and cake, thus preventing loss of coal through the grates. · The low-grade bituminous coal is on the border line between bitu minous coal and black lignite. It is harder than the higher-grade bituminous coal. Many of these beds too have been crushed, and a large proportion of lump coal can not probably be obtained from them. This coal probably possesses no coking properties and is likely to be used only under stationary or locomotive boilers. It is not so good 1lartln, O. c., and Kati, F. 1., Geology and 0081 fields or the lower ll.atanuaka Valley, .Alaska: U. 8. <nol. Survey BnlL 600, 1912.
UPPER :MATANUSKA AND NELOHINA VALLEYS. for thls purpose as t.he higher-grade coal, but the latter, being better suited for the manufacture of coke and for use as smithing and naval · coal, will command a higher price and may thus leave a lower-price market for the poorer coal Some of the low-grade coal can probably be mined more cheaply than the high-grade coal. The two kinds of coal will, to a. certain extent, be noncompetitive, each having it.sown special markets. The following table includes a few analyses of characteristic samples of coal from various pa.rts of the area. Sample No. 19346 was taken during the investigations here described. The analyses of samples 1 and 22, which were collected in 1905 and 19061 have been published in Bulletins 289 and 327. The other analyses represent samples col lected in 1911 by Dr. Joseph A. Holmes, Director of the Bureau of Mines. All the samples were obtained from surface prospects or from outcrops, and were consequently somewhat weathered. The reason that more samples were not obtained is that the absence of openings made it impossible to obtain other than samples of weathered coal, which a.re of comparatively little value . .AnalyBtB and ttata of .Matanml:a River coala. Proximateanalyab. Ultimate analyala. v ue. r .g
J z a
fll j
..; ""
o8:D 1 ! !
!1 z J Ers.
'- - Q) (b) as.o 6.26 116.U 5.99 0.57 3.07 7,588 13,655 .43
(6) 2.18 30. 60 S0.06 9.1& 71.'3 1.ao 7,303 13, 146 Theaeanal~ were made by F. V.Btanton on tbesamuampleeas tboae with oorreepondlngnumbert on pp. eo, 81 or Bllllettn 377. The dlt!erences In proximate ana1,_ are due to the fact that the samples dNd 111mewhat In the months wbiclt elapsed betw_. analyses Md &hat 111mewbat dlllorent metboda ofanalysis were llMd. (Bee U.S. Geol. Sa rvey Boll. :lllO, pp. 29-30, lllO&.) t Not det.ermJned. 1. West fork of Purinton Creek, <ltude 3,900 feet. (See MCI.Ion 8, p. 287.) 21 Booth faoeof Ant.braclta Rldge. (Seep. 290.) 1113C8. Near wata1&11 on nort!west sideof Boalder Creelc l&i mllee abon lta mouth. (Beep. 293.) COJCJrO P:t.OPS&TD.I. Comparatively little is known of the coking properties of the coal of this part of the Mat&nuska Valley. A rough coking test 1 made on some of the coal from Chickaloon River indicated that by proper treatment a coke of satisfactory grade can probably be produced. No further test.a have been made by members of the Geological Survey. The analyses indicate, however, that the high-grade bitum.i:nous coal of tho upper Mata.nuska Valley, like that on Chick& 1lartln, G. C., and Kats, F . 1., Oeology and coal fields of the lower Kat&nualca Valley,AWka: U.8. Oeol. Burvey Bult aoo, 92, 1912.
MINERAL RESOU1lCES OF ALASKA, 1913. loon and rivers and on Coal Creek, is proba.biy coking coal at least in part, and that such of the low-.gra.de bituminous coal as is similar in composition to the coal on Moose, Eska, and Young creep, in the west end of the lower Mata.nuska. Valley, is probably non coking. MINING CONDITIONS. The possibility of minin,g the Ma.te..n.uska coal a.t a profit depends on a variety of !actors, some of which are geologic and will be <lis cussed below, while others, such as the cost of labor a.nd supplies, purchase or leasing charges, transportation, and markets, are eco nomic and do not belong strictly within the province of this report. The geologic factors that affect the possibility of mining include the character of the coal, such as it.s composition, heating power, firmness, smoking and clinkering qualities, and coking or other special properties; the character of the coal beds, such as their thick ness, persistence, freedom from partings and binders, and the nature of the roof a.nd floor; tho attitude of the coal beds, including their depth below the surface, steepness, and structural regularity; and the presence of extraneous detriments, such as intrusive roclm, water, gas, and dust. A large number of these factors a.re variable within the field, either regionally or from bed to bed. These must be considered in detail, both locally and by beds, in connection with each proposed mining project, and they ca.n not be the subject of a general discussion here. Others of these factors have a.lre&dy been considered in the preceding pages, so far as the available inform.ation permitted. There remain, however, several factors concerning which it is possible and desirable to present brief general discussions. EFFECT OF FOLDING AND FAULTING. The steep dips and complex structure of large parts of the coal areas introduce serious problems in coal mining and .call for careful investigation of the structural conditions of each individual tract before the development of mines is attempted. It is believed that in some areas in the Matanuska Va.11ey the structure is so complex that coal mining will be practically impossible. Such areas probably include at least part of Anthracite Ridge and part of the coal area south of the .Ma.tanuska. The exposures on the north bank of the Matanuska from a point 1 mile above to a point 4 miles below the mouth of Gravel Creek show gently dipping and regular beds. H the coal exist.s beneath these beds there should be no difficulty in mining it. The distribu tion of the coal outcrops, which occur in two belts,· one of them along the south fMle of Anthracite Ridge and the other south of the Mata.nuska, indicates that the broader structure of this part of the
UPPER Mil'ANUSKA AND NELOHINA VALLEYS. valley is synclina.l and that the coa.1 beds occur low in tho stro.ti gra.phic sequence. In this case the center of the va.11.ey should be underlain by coa.1, but there is no evidence as to the depth at which the beds may lie. 'l'be hill north of Boulder Crook and immediately east of Chick aloon River is composed of gently dipping Eska conglomerate. H the coal beds persist beneath tho conglomerate, and if the coal bearing rocks were not folded before tho conglomerate was la.id down, mining should not be difficult, a.t least so far as structural conditions are concerned. It should be remombored, however, that the vertical distance from the Eska conglomoro.to to the workable coal is not " known a.nd that the coal may at this point be at a prohibitive depth or under a prohibitive load. Throughout the greater part of tho ma.in Matanuska Valley the structural details a.re not known, but there are indications that complex strocturo is the general condition. It is probable that there a.re areas in which the structure will permit tho mining of the coal, but also that there a.re larger a.reas in which the structural conditions will make the mining of the coe.l difficult and expensive, if not im possible. It will probably be found that where the structure is ~imple the coal is of low grade. The character of the structure must be regarded. as a problem to bo solved by underground exploration before the feasibility of mining at a profit the coal of any particular tract can bc demonstrated. The coal areas on upper Boulder and Caribou creeks in general possess simple structure, &!though intense folding was notod on Billy Creek. (See p. 285.) In this district sharp folding is restricted to narrow zones between which the rocks aro nearly dat. The coal of this district is, however, of small amount and low grade a.nd is not easily accessible .. EFFEOT OF INTRUSJVE ROOKS. Intrusive rocks a.re abundant throughout the area. of coal outcrops in the upper Matanuska Valley. They are both large a.nd numerous along the '3outh front of Anthracite Ridge in the area. of both the anthracite and the low-grade bituminous coa.l. The a.real distribution of the larger of these intrusive ma.as~ is indicated on the map (Pl. XI, p. 292). Small dikes and not repre'3ented on the ma.p, are al.so present throughout practicaUy a.11 the coal a.reM. Whero the intru sive rocks cut the coal bedc:1 the coal is rendered worth~ for a distance of a few inches from the contact. Tho small dikM and sills, on account of the short distances to which tboir effect extends, do not affect the coal seriou~ly, oxcopt that the E-ills show a. habit of seeking coal beds for thoir planes of intrusion. It is clear that if a sill is intruded into a coa.l bod for a long distanco a large amount of w9rthl0Sc:1 coal wiU result, but if it is intruded between rock strata,
RESOURCES OF ALASKA1 1913. even il only a few feet away from a coal bed, or il it cut':! across the coal bed in the form. of a dike, its effect on the coal will be slight. The larger intrusive masses are of much more seriom1 importance than the small dikes and sills, :first, because their size is of itself suffi cient to reduce the coal areas considerably, and second, because each of them is likely to have sent off many apopbyses in the form. of sills in or a.long the surfaces 9f coal beds. The dimension~ of these masses are, moreover, probably grea~r underground than at the surf ace. There may also be many intrusive masses which do not outcrop but which are near enough to the surface to be encountered in mining. In conclusion, it must oo stated that tho presence of intrusive rocks in the coal fi.old introduce':! fe.ctoM that make an undetermined per centage of tho coal areas of very doubtful value. The r:ize and dis tribution of these intrusive masses beneath the surface, as well as at the surface in the areas of scanty outcrops, can not be determined without underground exploration. The effect of the smaller intrusive masses on the coal depends on the extent to which these mas~e':I have been intruded into or along the surfaces of coal beds. Where the intru':live mSSP is in contact with the co&l the coal ia worthless, bot where it is a few feet away the quality of the coal is probably unim paired or may even be improved. UNDERGROUND WATER AND GAS. In any large mines which are opened in this region it will be neces eary from almost the beginning of mining to pump or hoist mine water. It is not believed that it will be possible to open any large mines having natural drainage. The amount of underground water whlcb will be encountered will probably not be great, unless the minee. a.re opened on the outcrop. Precipitation in this region iE so slight that large amounts of water can get into the mines only from the If ordinary precautions a.re ta.ken to prevent streams from breaking into the mine openings the mines ought to be fairly dry. The heavy cover of gravel which exists at the lower altitudes throughout most of the Matanuska. Valley will cause certain dangers in mining. Un1EYis the depth of the gravel at difierent points and the shape of the underlying rock floor a.re determined by drilling there will be danger of the mine workings breaJ?ng through the surfa.co of the rock into the gravels. The gravels probably carry large amounts of waoor in tiome places and accidents might thus result. Gas will probably be a. serious problem in local mining from the very start. The experience of the tunnel;i on Chicks.loon River indicates that these coal bedo will yield large amount'l of dangerous gases. Some provision ought to be ma.de in advance of mining for the enforcement of suitable regulations insuring the protection of the minel"3 and the mines against ga;~ explosions.
UPPER MATA.HUSKA A.ND NELOHINA VALLEYS. CONCLUSION. The outlook for profitable coal mining on a. large scale in the upper Ma.ta.nuska Valley is not promising. The doubt concerning the workability of the coal of the lower Matanuska Valley 1 applies with greater force here, where the coal is apparently of lesser a.mount and of lower grade, is folded and intruded tl. at lea.st the same degree, and is less accessible than it is in the lower part of the valley. H mining is attempted in the upper Mata.nuska. Valley the proposed mine sites should be selected only af tcr' a careful study of local con ditions, which should be accompanied by drilling. The selection of a site should be governed by the accessibility to the railroad and by the structure of the rocks. The structure should be determined in detail for each property by careful drilling or otherwise, in order that the mine ma.y be opened at such o. point that the underground haulage of the coal and the disposal of tho mine wators may be accomplished at a. minimum expense . .Although many of tho coal beds outcrop at the surface, they dip for the most part at steep angles. No localities have yet been found in this district at which it would be possible to mine any considerable a.mount of coal above the level of the outcrop of the coal bed. The a.mount of coal above the general drainage level is not great, and it will be necessary from the very beginning of mining to sink shafts or slopes to considerable depths. If any large mines a.re opened it wili probably be found desirable to sink shafts to the coal beds at con siderable distances from their outcrops. The local region will furnish none of the supplies needed in coal mining, except timber, and even this is not abundant and is of poor quality. Everything else in tho line of mine equipment.t and tools will ha.ve to be shipped from points outside of Alaska, which would add greatly to the expense of mining. The development of the .M:ata.nusko. coal fields on a. large scale is dependent on the construction of a railroad to tidewater, and on the existence of an. outside market for the high-grade coals. Under ex isting conditions of the mineral-fuel market on the Pacific coast it is only such coal as is suitable for coking, smithing, or for the Na.vy that will probably find such a. market. The local conditions under which coal of this chara.cter has been observed indicate that its mining and preparation for market may be so expensive that it can not compete with high-grade coal from other regions. The possibility of mining the low-grade coal at a. profit is dependent either on the construction and operation of a railroad for other pur poses than the shipping of such coal alone, or on the development of a. local market. Tho latter may follow from the possible extensive development of gold mines. 1 Martin, 0. c., and Kalt, F . J., Ooology and coal needs of tbo lower .Mat.a.nmta Valley, Alaska; u . s. Oeol. Barny Bull. 600, p. 94, 191 2.
PRELIMINARY REPORT ON THE BROAD PASS REGION.1 By FRE.D H. MOFFIT. INTRODUCTION. The Broad Pass region includes the upper parts of Chulitna and Nenana rivers. As here used, the name Broad Pass designates ·an area of indefinite boundaries; extending westward from Susitna River and for the most pa.rt lying south of the main a.xis of the Alaska Range. The headwaters of Chulitna River and the vicinity of Broad Pass were first visited by Government exploring parties in 1898. In that year G. H. Eldridge 3 and Robert Muldrow, ·of the United States Geological Survey, ascended Susitna River from Cook Inlet to the mouth of Indian Creek, whence they ma.de their way northeastward through the Indian Creek valley and a valley parallel to the upper Chulitna, which succeeds the Indian Creek valley, to Jack River. They then descended Jack River and the Nenana to the mouth of Yanert Fork, where the failure of their supplies obliged them to turn back. The same year Sergt. Yanert,5 of the Fourteenth Infantry, United States Army, with one companion and an Indian guide, ascended Ohulitna River from a point near the mouth of Indian Creek to Broad Pass and Nenana River, but he, like the Eldridge party which preceded him a few days, was compelled by lack of food to return to Susitna River without seeing the Tanana. Many prospectors and hunters have visited the region since that time. In 1903 a private reconnaissance railroad survey, crossing Broad Psss, was run from Cook Inlet to the Tanana, yet neither topographic nor geologic mapping was 9one in this region until 1913, although the adjacent Bonni.field and Valdez Creek districts were surveyed in 1910 and the exploratory expedition under Brooks 6 more extended accotmt o! the Broad Pass region Will bo published In a forthcoming bolletin. Mr. 1. E. Pogue has rendered etficlont asslstanoo In both the 1!old and office work, of which this report ls the result. t Eldridge, G. H., A reoonnaissen~ In the Sushitna Basin and ad,Jacent territory, Alaska, In 1898: U.S. GeoL Survey Twentieth Ann. Rept., pt. 7, llP· l-29, 1900. Yanert, Wflllam, A trip to the Tanana River: Explorations In Alaska, pp. Wash.ington, 1900. 'Ho:tllt, F. H., HOBdwater regions of Oul.kana and Susitna rivers, .A.llW:a, with accounts of tho Valdes Creek and Ch1atochlna piece dJstriets: U . S. Geol. Survey Bo.II. 491<, 1912. Brooks, A.H., The lfcKJnley region, Alaska, with d.escrlptlons of theJaneous rooks and of the Bonnideld and KanUshna districts, by L. M. Prindle: U.S. Oeol. Sorvey Prof. Paper 70, 1911.
MINERAL RESOURCES OF ALASKA, 1913. crossed the Nenana. just above Yanert Fork in 1902. Plans were formulated for making such surveys in l912, but could not be carrie.d out on account of delay in the appropriation, although supplies had boon sent to Valdez Creek in the early part of that year. The work was therefore not undorte.ken till 1913, wh!)n two parties were sent into the field. The season included less than 55 working days, and the working time was reduced still further by frequent rains and by a heavy fall of snow on August 27. The Broa.d Pass. country ma.y be ente1'{)d from the south by the SusitDA River, Indian Creek, and Chulitno. River valleys; from the north by the Nenana Vall~y; and from the east by any of the trails lea,Qlng westward from the military road through the Valdez Creek district. There a.re no established trails lee.ding into it, and each of the general routes mentioned presents difficulties of on.e kind or another. Nenana. River is unfortunately too swift and has too many rapids in its course to afford a summer route from the Tanana for small boats. The Susitna-Chulitna route is long and difficult. The route from the east is perhaps the best for summer travel. Any one of the three may be used in winter, but the Nenana. route is of course available only for those who are already in the interior of Alaska. R.ilLW.A.Y ROUTES. Broa.d Pass offers one of the most favorable railway routes from the Pacific seaboard to the Te.nana e.nd Yukon basins. The Chulitna, flowing into the Susitna. on the south, and Jack River, flowing into the Nenana, a. tributary of the Tanana, on the north, both head: in Broad P ass, which therefore marks the watershed between tho Cook Inlet e.nd Yukon drainage basins. Tho waters of the Nenana. in the past ran through Broad Pass into the Chulitna but were diverted by the glacier that formerly occupied the region. Since the disappe~ a.nee of the ice the drainage has not reverted to its preglacial coume. The approach 1 to Broad Pass from the south along the headwaters of the Chulitnais so far as known a gradual ascent, and a ro.ilway route of comparatively lmv grade could probably be found along it. The pass itself is a fiat a.bout 4 miles in width a.lfording no engineering difficulties. It stands about 2,500 feet above sea level. North of the pass the railway route would .be down the valley of Jack River to the Nenana, and here, too, a good grade could probably be found. The main Alaska Ra.age would be traversed by the valley of the Nenana River, which for a.bout 10 miles :flows through a steep-walled ce.nyon. While.Broad Pass probably affords tho most feasible ro.ilway route, because it is most direct, there are other low divides leading from the Susitna into the Nenana basin. A gravel-floored flat connects the 1 Railway routes In AlaP;a (report of Alaab Rallt-1 ()ommbelon): B . Doc. No. 1346, &:M Cong., ad -.. p. 83, llll3.
BROAD PASS REGION. upper Susitna Valley near Va.ldez Creek with N ena.na River. .Another low pass lies between the headwaters of Deadma.n. Creek, flowing into the Susitna. on the south, and Brushkana Creek, flowing into the Nenana. on the north. VEGETATION AND GAME. Most of the mapped area is above timber line; that is, more tha.n 2,500 feet a.hove sea level. V egeta.tion is therefore not so dense as at lower altitudes. .A sparse growth of spruce is seen a.long sU.sitna River as far north as the glaciers at the heads of ita two main forks. A similar growth of spruce covers the broad, flat divide between Susitna River and the Nenana. Spruce of much better quality grows on Butte Creek and near the mouth of Jack River, but the timber on the head of Chulitna River is similar to that on the upper N ena.na and the Susitna.. The better timber, like that on Butte Creek, is suitable for local mining need'l and has been used on Valdez Creek for all purposes since the supply close at hand was exhausted. In most of the region travelers are dependent on willows or alders for camp uso. Good willows can nearly always be found on the smaller streams at elevations between 2,500 and 3,000 or 3,200 feet above sea level. The large willows are :rarely found higher than 3,500 feet above the sea. The elevation of about 3,000 feet also affords the best traveling, for brush as well as timber is absent and grass for horse feed is most abunda.nt. Ga.me is fairly plentiful in most of the region, but would doubtless disappear, as it has in the vicinity of V a.ldez Creek, if mining or other enterprises should bring in a considerable number of white men. The India.n.s, of whom there are a.bout 30 at Valdez Creek, live almost entirely on game during a large part of the year and find their best hunting grounds on Jack Riv or and Y alert Fork of Nenana River. Ptarmigan, caribou, moose, and sheep are the principal game ani mals. Ptarmigan are abundant in most of the willow thickets above timber line. Caribou may be seen at certain seasons in nearly all part.8 of the area mapped. :Moose appear to be most numerous on the head of Chulitna River and in that vicinity. Sheep are found chiefly in the.Alaska Range, particularly on the north side, and are especially plentiful in the mountains about Yanert Fork. Bear also are numer ous in this vicinity. Y alert Fork, on the whole, is much the best hunting ground of the region. Grayling and kout a.re taken from many of the lakes and clear-water streams. Some of the lake trout grow to very large size. GEOLOGY. In most of the area mapped on Plate XII unconsolidated morainal deposit.8 and granular igneous rocks such as granite and diorite pre- dominate, yet slate, graywacke, conglomerate, and limestone are widespread.
MINERAL BESOUROES OJI' ALASKA, 1913. The consolidated sedimentary formations range in age from Devo nian to Tertiary. AU are folded and metamorphosed but in places allow these alterations in little or only moderate degree. In general, the more argilla.ceous and siliceous rocks range from slate, gra.ywa.cke, and dense hard conglomerate to crystalline schist. Some of the more highly altered limestone beds are so silicified as to retain little of their original character. The granular igneous rocks may for field use be designated as granites. They include granite, quartz, diorite, and related rock types and present no unusual features. They are associated in a.t least one locality with rhyolitic lava. flows. More basic igneous rocks, of which the moet widespread a.re basaltic and andesitic lavas, are present in the southeastern part of the region, but are subordinate in a.mount to the granite and quartz diorite. The general distribution of consolidated sedimentary and igneous formations in the region (see Pl. XII) is described in the following paragraphs: Granite and quartz diorite predominate in the mountains south of Nenana River. The basalt mountains south of Butte Creek, the TriMsic slate belt north of it, and the Jurassic( t) slate, gra.ywacke, and conglomerate mountains about upper Jack River ma.ke up the rest of this area except that occupied by unconsolida.ted deposits. Granite and diorite occupy a large pa.rt of the mountain area between Nena.no. River and Y o.nert Fork, but are associated with a. variety of sedimentary formations that differ greatly in age and include slate, shale, grn.ywacke, limestone, conglomerate, and schist. Devonian fossils were collected from limestone in a succession of limestone, slate, and conglomerate beds on lower Jack River. At this place the bells form a narrow east-west belt between younger sedimentary formations on the north and south. This narrow belt of Devonian beds comprises all the Paleozoic rocks known in the district. The Devonian formations are succeeded on the east by a. group of sedi mentary beds, including slate, limestone, graywacke, and schist, that form the mountain mass about the heads of Nenana River and the West Fork of Susitna River. The age of the rocks included in this group is ·not known but is considered provisionally to be Mesozoic. The higher ridges of the Alaska Range, north of the belt of Devonian and Mesozoic ( ¥) formations is made up of conglomerate, sandsto.ne, shale, slate, gra.ywacke, e.nd schistose equivalents of the same rocks, all belonging to the Cantwell formation (Tertiary). The Cantwell formation was formerly provisionally assigned to the Oa.rbonif erous, butwas found in the Broad Pass region to carry Eocene plants. This formation is an important structural member of this part of the Alaska Ra.nge, having a maximum width of at lee.st 18 miles and ex tending westward from Cathedral Mountain to Muldrow Glacier.
U. S. QE.OLOGICAL SURVEY BUU.EYIN &9~ PLATE XII Plate XII s s '10 zoMileS -- Fault GEOLOGIC SKETCH MAP OF BROAD PASS REGION. )( Gold plar~r
BBOAD PASS REGION. One peculiarity of the Cantwell formation is the progres.give increase in·closeness of folding and intensity of meta.morphism from wost to east in the area between Nenana River a.nd Cathedral Mountain, where the openly folded, little-altered conglomerate, shale, and sand stone pass into closely folded beds of slate a.nd schist. All this region has been profoundly glaciated and shows on overy side the usua.l evidences of mountain glaciation, including modified topographic forms, moraines, and glacial lakes. MINERAL RESOURCES. The association of intrusive granite and diorite with the slate an<.l limestone formations suggests the possibility of mineralization and the presence of metalliferous deposits, but so far as hasty observa tion shows the mineralization in the region visited is less than would be expected from a knowledge of the geology. Some of the slate formations, however, are gold bearing. Placer gold in small amount has been found on Butte, Wickersham, and other creeks near by a.nd also on the bee.cl of the West Fork of Sueitna River. Some copper is present in thelava flows south of Butte Creek, but is not known to be of commercial importance. Coal of commercial value is not known in the district, although it is present in thin beds on the head'of Jack River and has been found in thicker beds on Coal Creek, a tributary of Susitna River south of Butte Creek. Prospecting in the Broad Pass region is difficult on account of tho distance from sources of supply and the lack of transportation. The region has not been thoroughly prospected, but it ma.y be said that such work as has been done has not yielded very encouraging results. 60553°- Dull. 692-14-20
MINING IN THE VALDEZ CREEK PLACER DISTRICT. By F:rum H. MoFFIT. Valdez Creek is a headwater tributary of Susitna River. It lies about 65 miles west of the V alden-Fairba.nks road and is one of the three kno'\'Vn placer-gold districts on the south slopes of the Alaska. Range. Gold was discovered on Valdez Creek_in the fall ofJ9.03. The first gold produced was ta.ken from gravel deposits along the stream, but gold was found later in a.n old buried channel of Valdez Creek that joins the present channel on claim No. 2 above Discovery. The claims a.long this gravel-filled canyon proved to be some of the most valuable property in the district, although other claims on Valdez Creek and some of its tributaries, notably Lucky Gulch, have been gold producers. The district was visited by United States Geological Survey parties in 1910, and the progress made in exploiting its gold deposits at that time was described in a paper published the following year.1 During the three years since 1910 mining has been carried on in the old chan nel gravel deposits, on-one or two of the creek claims near by, and on Lucky Gulch. In addition, assessment work has been performed on many other claims that have not been important gold producers. Since 1910 the Monahan tllll.Jlel in the old canyon gravels has been ext.ended a.bout 500 feet, or from 700 to 11200 feet, thereby proving that the gold-bearing gravels continue that dists.n.ce but yielding no evidence to indicate where the east end of the canyon is situated. Bad air made work in the tunnel slow and difficult, yet mining was conducted profitably so long as the work was carried on. The tunnel is now aba.ndoned, the need for it having been ended by the introduc tion of hydraulic mining. Since 1910 nearly all claims on the lower part of Valdez Creek, including the bench claims north of the creek through which the old channel runs, have come under the control of the Valdez Creek Placer Mines Co. This company in 1913 inst~ed a small hydraulic plant lld:otAt, F. ll., Theupper Suaitn&tllld Cbis100hln&districts: U.S. Geol Survoy Bull. '80, pp. llf-12§, 19ll. Seeabo Molllt, F. B., Heldwaterrepmsof Oolkaua1111d Susitnarlvers, .Alaska: u. S. Geol. SUJ'\·oy Bull. a, pp. 63-66, 1011
MINEBAL RESOURCES OF ALASKA, 1913. and began mining at the lower or west end of the old channel, where the Monahan tunnel beg.ins. Nearly a mile and a quarter of ditch was constructed and a line of pipe was laid to the giant at the working face. With this plant enough of the gravel filling in the old canyon was removed between the first of .August and the e,nd of the season to lay b&re a small area of bedrock. This work was preliminary to the installation of a larger plant in 1914. It is planned to replace the small pipe now used by a.bout 4,800 feet of pipe ranging in size from 36 inches at the penstock to 18 inches at the pit and to substitute 6-inch giants for the small ones. This equipment will make available an abundant supply of water under a head of nearly 300 feet. About 100 feet of head is lost under the present arrangement, for the pipe at hand was too short to reach from the giants to the ditch, and the water had to be turned into a depression ao.d picked up again at a lower level. A sawmill will be built and also an elect'ic plant, operated by water from Timberline Creek, to furnish light and power. The old channel of Valdez Creek is favorably situated for hydraulic mining, there being a good supply of water and an excellent dump for tailin,gs. Itis probable, however, that the large number of granite bowlders in the upper part of the gravel deposit will cause consid erable trouble. The well-established winter trail on the ice of Oulkana, Maclaren, and Susi.tna rivers is still used for carrying freight to Valdez Creek, but the summer trail leavi.a,g theVe.ldez-Fairbanks road at BearCreek below Oulkana is now practi.cally abandoned in favor of the shorter trail from Pa.xson. The gold production of the Valdez Creek district in 1913 was small, coming in large pa.rt from Lucky Gulch, for, as has been shown, most of the season was given up on the main stream to wh&t may be called dead work. Probably not over 26 men were engaged in mining in the district at any one time during the summer, but it is expected that this number will be nee.rly doubled in 1914.