Economic Geology and the Bulletin of the Society of Economic Geologists 1922-05: Vol 17 Iss 3

1922 · Historical

Economic Geology and the Bulletin of the Society of Economic Geologists 1922-05: Volume 17 , Issue 3. Digitized from IA1518511-02 . Previous issue:…

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

VoL. XVII. MAY, 1922. No. 3

The Economic Geology Of The Mount Bischoff Tin Deposits, Tasmania.

J. G. Weston—Duny.1

CONTENTS. Introduction General descriptions Physiography Rock formations Sedimentary Porphyries Faulting Irregular tin deposits Individual faces (open cuts)

Replacement and ore genesis The porphyries Mechanics of intrusion Pneumatolysis Topazization Tourmalinization Cassiteritization Hydrothermal replacement Sericite, gilbertite, damourite, Quartz, tin, (?) chlorite Prosopite, pyrrhotite, calcite, (?) fluorite. 0.- Arsenopyrite, (?)-marcasite, (?) pyrite, chalcopyrite. Galena, sphalerite, fluorite, dolomite, siderite. Weathering and denudation Other replacements Slate and sandstone Basic igneous rocks Conclusion Acknowledgments

1Frecheville Fellow (1921), Royal School of Mines.

154 J. G. Weston-Dunn.

Introduction.

The tin deposits of Mount Bischoff offer an unusual oppor- tunity for geological study, particularly with respect to the origin of the valuable deposits and to the character of the metasomatic changes in the rocks, preceding and accompanying the tin min- eralization. The wealth of exposures disclosed in the numerous large open cuts (locally termed “ faces ”) permits a detailed study of the structural features which influenced metallization, and also gives evidence tending to clarify the disputed point as to the lode, or alluvial character of these tin deposits.

The study of the Mount Bischoff tin deposits was undertaken at the suggestion of the Frecheville Research Fellowship Commit- tee. Originally it was intended to form part of a more general investigation of “ the relation between country rock and enclosed deposits,” but the paucity of geological and petrological descrip- tion made it rather more advisable to deal with the area sep- arately.

Previous Literature.—At the present day the main tin-bearing material at Mount Bischoff is a loose, often incoherent pyritic (marcasitic) deposit. Until quite recently only the oxidized zone of this was exposed, and the true nature of the occurrence was not understood. This oxidized zone was represented in places by an extensive highly ferruginous gossan (as in the early Brown Face), and in other places by a loose sandy disintegrated mate- rial (typical of the North Alluvial Face and the White Face). These deposits were referred to first by Johnston,? Wintle,® and Gould,* and later by Kayser,® Montgomery,’ Twelvetrees and

2 R. M. Johnston, “Geology of Tasmania,” 1888.

3S. H. Wintle, “Stanniferous Deposits of Tasmania, Mount Bischoff,” Trans. Roy. Soc. N. S. W., 1875, p. 87.

4C. Gould, Quart. J. G. S., vol. XXXI., 1875, p. 109.

5H. W. F. Kayser, “Geology of Mount Bischoff,” Aust. Assoc. Ad. Sc., Hobart, 1892, vol. IV., p. 352; and Proc. Inst. Civil Eng., vol. CXXIIL., pt. I, p. 377.

6 A. Montgomery, “The Mineral Resources of Tasmania,’ Dept. Mines, Tas, 1804.

Pre Reid

The Mount Bischoff Tin Deposits. 15

oi

Petterd,’ and Millen* as of detrital or residual origin. Herman,’ however, was the first to show that this view was untenable, and to point out “that the detrital stanniferous material of Mount Bischoff is now, and probably has been throughout its existence, of quite minor importance, and that the great bulk of what apparently is and has been held, by the majority of observers, to have that character is (or.was) truly lode material, of a peculiar character ‘in situ.’ ”’

The associated porphyry dikes at Bischoff were noted in the earliest papers of Wintle*® and Gould.** Von Groddeck” was the first to show that these porphyries were topazized quartz por- phyries, comparable with the topaz-quartz porphyry in the Schneckenstein, Germany. Twelvetrees and Petterd** have also described the petrographical characters of the topaz porphyries.

Apart from Herman’s work no clear understanding of the true character of the actual tin deposits is recorded. The present writer, although agreeing with Herman that the greater part of the stanniferous deposit is a product of the alteration and replace- ment of the porphyries, also believes that the slate and sandstone country and some old basic igneous rocks have played a part in the tin deposition.

GENERAL DESCRIPTIONS. Physiography.

The Waratah area is characterized by a precipitous and rugged topography of recent age. Mount Bischoff is a residual conical eminence rising some 500 feet above the level of a great dis- sected peneplain. The two main streams, the Arthur and Waratah Rivers, have scored-deep gorges in the peneplaned sur-

to

7 Twelvetrees and Petterd, Proc. Roy. Soc. Tas., 1897, p. 1 Twelvetrees, Rep. Sec. for Mines, Tas., 1899-1900, p. cxi. 8J. D. Millen, The Mining Journal, London, 1910, p. 300. 9H. Herman, “ Australian Tin Lodes and Tin Mills,” Proc. Aust. Inst. Min. Eng., n. s, No. 14, 1914, p. 301. 10S. H. Wintle, op. cit., pp. 88-go. 11 C, Gould, op. cit., p. 100. 12 A, von Groddeck, Proc. Roy. Soc. Tas., 1865, p. 388 et seq. 18 Twelvetrees and Petterd, of. cit.

5; and W. N.

156 J. G. Weston-Dunn.

face so that the beds of the streams are now over 500 feet below the old peneplain. Mount Bischoff lies in that portion of the area situated in the angle formed by the junction of the two rivers.

South of the Mount the old peneplain has been covered by a late Tertiary basalt flow, so that here the country has a flatter surface. North and West, however, the rugged topography con- tinues almost to the coast. The Mount, rising 2,598 feet above sea level, owes its elevation in large part to a series of porphyry dikes. In places these dikes stand out from the hill slope as steep precipitous cliffs.

On the Don Hill are the remains of an old river valley, evi- dently the pre-basaltic Waratah River. This old river bed is represented by alluvium; great boulders of porphyry shed from the Don and Southern Dikes, incorporated with tourmalin- ized porphyry, quartzite and slate pebbles, in a hard matrix of fine grit. This is overlain by a sandy clay which is rich in vegetable matter. Above this is the basalt. These alluvial beds were probably laid down on a valley slope, as they dip to the South at 30 degrees; this tilting may, however, have been pro- duced by faulting. This old alluvium is probably of Upper Pliocene age; it has been worked for tin, and it appears probable that a deep tin lead may be continuous with it beneath the basalt to the South.

Rock Formations.

Stratified Rocks —The dominant rock type of Mount Bischoff is a highly inclined, contorted, and faulted slate with beds of sandstone, quartzite, and pyroclastic breccia.** These were orig- inally correlated as Lower Silurian,” but later as probably Cambro-Ordovician.** Mr. Loftus Hills states’’ that they are evidently members of the Dundas and Leven series of slates and breccias, porphyrites, and granite porphyries which constitute

14 W. H. Twelvetrees, op. cit., p. cxliii.

15 W. H. Twelvetrees, loc. cit.

167... K. Ward, Geol. Surv. Rep. No. 2, Tas., 1911, p. 3.

17 Personal communication.

—

THE MOUNT BISCHOFF TIN DEPOSITS. 157 the base of the Tasmanian Cambro-Ordovician. These are largely of pyroclastic origin and formed under submarine vol- canic conditions.

At Mount Bischoff, the slates, sandstones and quartzites are

aye ee

the important rock types of this period. So far as the writer is aware the only igneous representative is a rock evidently orig- inally high in olivine (apparently a dunite), now serpentinized.

a

It is not abundant, but occurs associated with the tin deposits.

wremer er

Its field relations are obscure, so that its position here is only tentative. It is older than the porphyries.

Porphyries—Southwest of Mount Bischoff is the outcrop of a large granite intrusion of Devonian age.** Between this point and the Mount the country is covered by the basalt, and it is quite probable that the granite approaches (beneath the basalt) close to the tin-bearing area. Twelvetrees and Petterd conclude’® “that the quartz porphyry is not a marginal portion of the main granite mass, but belongs to dikes running through the granite and having a slightly different composition from the latter ’’— that is, the porphyries belong to a later stage in the differentia- tion of the granitic magma, as is generally accepted elsewhere.

The great series of porphyry dikes forms perhaps the most striking feature of the Mount Bischoff area. Of these the Western Dike (see Fig. 14) is apparently the main one; it con- tinues northeast to form first the Stanhope Dike, then the North- eastern Dike, and apparently dying out on the northern slope of the Waratah Valley. On the western side of the Mount, its out- crop cannot be traced, but it is again met with in the underground workings of the Mount Bischoff Extend Corp., on the Giblin Lode. Here the dike is nearly vertical.

The Northern Dike and its southern extension, the Ringtail Dike, appear to have a steep southwesternly dip, and the Radio Dike a steep northerly dip. These dikes consist of fine-grained porphyry, which carries few quartz phenocrysts, but much pyrite.

The Queen Dike strikes approximately northwest, but towards

18 W. H. Twelvetrees, Rep. Sec. for Mines, Tas., 1899-1900, p. cxlviii. 19 Twelvetrees and Petterd, op. cit., p. 125.

Qeieslry 4. AS % me on . 99S) f a ai wat 24 PE) !

Z My NE Ae J158 J. G. WESTON-DUNN.

its western end trends nearly due west. Westward, the dike dips 70 to 80 degrees into the hill, but eastward it flattens to 30 degrees. The Queen Dike has been worked in places for tin.

Test Trois Ts

1S00'N Pros whey H I hd eS stp LOE ae

+

D Gu yt, yy Ono’, le 41) STANHOPE SLAUGHTER-,DETRITALZ/£ La ry ml WN SS - et SIVARD/FACE Set \1) i © “ A fooo's Zit]. VE(MTIGDAWAR> MT BISCHOFF FExTD. “i +V Jz, A a Tin MIN. Co. ul /w 2 ¢ 1 ee Ie O /r/ec i rar + + 2000'S 4

Pe oS zseo Scale . 2 at “ ri 2 at “i 2 4 2] : ° a ° 9] of D0 s 68) 3 8 8 8 8 3000's o g 1] 8 se Feet Fic. 14. Mount Bischoff. Plan of workings and dikes. (Compiled from plans by H. Sommerville, H. B. Schell, and A. D. Mackey, and from author’s n¢ tes. )

The Southern Dike and White Face Dike are huge porphyry masses, sill-like in character. The Wheal Dike and North Al- luvial Dike are both sills, their northern extensions taking on the character of dikes; possibly they are both tongues from the Queen Dike,

The Little Wheal Dike is practically vertical. In its southern extension isolated patches and splashes of porphyry may be noted in the fault rock, giving the impression that the porphyry

a a & y

The Mount Bischoff Tin Deposits. 159

also has been faulted, but as the outcrop is traced farther south the dike tails out, the patches of porphyry become less and finally give out, and the line of strike is then represented by a fault rock. The apparently isolated splashes of porphyry are evidently due to the squeezing of the molten magma into the fault rock; often a thin connecting thread of porphyry may be traced between the patches. The fault rock is a hard breccia of quartzite and slate in a fine silicified matrix.

The contention that the Western Dike, and its northeastern continuation, is the main dike of the area seems to be upheld, then, by a comparison with the structural characteristics of the other dikes of the area. Its continuation in depth is proved as well as its persistence in strike. The writer believes that this Western Dike in depth was connected with the granite magma below, that it was the channel up which first the porphyries of the area and then the ore solutions ascended.

In addition to these main dikes occupying fault fissures and those occurring as sills, there are numerous irregular and tongue- like masses distributed throughout the tin-bearing area, and often apparently isolated from other porphyry masses. For the most part these irregular porphyries

they may be compared with an irregular lit-par-lit injection into a highly fractured zone—have been subjected to extreme alteration. The Brown Face, White Face, Slaughter Yard Face and Gossan Face, the principal tin- bearing areas of the Mount, are practically made up of these highly altered porphyries, with the inclusion of large and occa- sionally highly replaced “ horses” of slate, and the association of altered basic igneous rocks. The slate is generally replaced by marcasite; the basic igneous rock is often completely altered to talc, with often the formation of tremolite (showing alteration to asbestos), or the alteration is less complete—merely serpentiniza- tion, or part replacement by calcite. The altered basic igneous rock is not tin-bearing as a rule.

In the Mount Bischoff Extended underground workings a

large “ boss ” of porphyry is met with, but does not outcrop. It

160 J. G. Weston-Dunn.

is apparently a bulge in the Western Dike, as in depth it appears to decrease where cut through. Faulting.

The Cambro-Ordovician series have been disturbed to such an extent within the area of the Mount that there does not appear to be any regular strike of the country. Still, a northeasterly strike predominates, particularly in areas of least disturbance on the east side of the Mount, while on the west side a northwesterly strike is the rule. These variations of the strike in different parts of the area are the result of great thrust faults, some of which have played perhaps the most important part in the sub- sequent localization of the tin deposits. The main direction of thrust movement was apparently almost east and west, as in- dicated by the three most important faults—the North and South Walls of the Brown Face, and the irregular south dipping “wall”? on which the Gossan Faces rest. ;

Subsequent normal faulting just prior to, or contemporaneous with, the period of igneous intrusion has still further disturbed the country. These normal faults have been the main passages of ascent of the porphyries. As shown by the often almost microscopic injection of porphyry, the fault rock was still in a soft and easily permeable state at the period of intrusion, so that the porphyries are closely related in time to the faulting.

A still later series of faults formed the original lode channels; these cut the earlier faults.

At Mount Bischoff, then, the important series of faults may be summarized as follows:

(1) Thrust faults, probably associated with the folding and crushing of the Cambro-Ordovician,

(2) Normal faults occupied by the porphyries and probably con- temporaneous with the earlier stage of igneous intrusions, and

(3) A regular series of southwesterly to westerly dipping faults forming the lode channels, and evidently associated with the later stage of igneous activity, later even than the formation of the main tin deposits.

The Mount Bischoff Tin Deposits.

Irregular Tin Deposits. The Brown Face and Gossan Benches are the main deposits now being worked at Mount Bischoff?® (Plate III a). Their structural relations may be noted from Figs. 15 and 16. A little

Rise

NE : Slate z O\b Sulphide &Porphyry-, )--—5/F Quartz &Tin S.E. eh. 150’ Level [ . el phd Goartz &Tin

J_N° 2 Level ‘Diab la Variation in Sectio ( Mein Tunnel Brown Face

going West

Detail Section, Fioor of

Brown Face

2 a w ae ia eco 1500'S 1000'S 500'S co §=6(Datum~ 2000’ above S.L. Scale ~Vertical=Horizontal am —20° Feet Fic. 15. Sketch section across Brown and Gossan faces to show approximate

structural features. (F probable fault wall.)

rock is still won from the bottom of the White Face; the North Alluvial and Summit Faces are now abandoned.

The Brown Face.—This deposit is confined north and south between two strong fault walls which converge west to form the apex or end of the deposit. The South Wall (or fault) ap- parently extends downward with little change in dip, whereas the North Wall flattens in depth and apparently becomes horizontal beneath the deposit before abutting against the South Wall; this change in dip may be noted on the “5o ft. level,” just below the Open Cut, and is shown in Fig. 15. The floor of the deposit is ‘generally a vuggy crystalline quartz-tin “make,” up to 2 feet

20 At the time of the writer’s visit, prior to the temporary closing down ot work in October last.

162 J. G. Weston-Dunn.

in width. Above this is generally a dense marcasite which passes into a soft decomposed porphyry above. Both the marcasite and porphyry may carry tin. Large horses of slate occur through- out, and these often show replacement by sulphides and may be impregnated with tin.

The slate country immediately beneath the “floor” on No. 2 level is, for the most part, practically horizontal. The level is driven on a “flat make” running almost parallel with the true floor, and this flat “‘ make” carries good tin in places. The slate country here is so saturated with water that it is quite soft and clay-like in places. It is noticeable that the South Wall acts as a watercourse, the slates in its vicinity also being soft and sat- urated.

Along the South Wall, and to a lesser extent the North Wall, excellent slickensided surfaces may be met with, as well as much fault rock. The striations vary greatly in direction. On the whole the movement was along the fault, and was essentially a thrust movement.

The North Wall is much more irregular than the South Wall and appears to have been only a minor plane of movement— probably merely a kind of relief fracture. Between these two walls the ground is severely crushed and shattered.

The eastern boundary is irregular; it may be a fault wall, but it appears more likely that the boundary is a more gradual one, and formed by the diminution in crushing and fracturing of the country farther from the fault junctions.

Into the crushed area enclosed between the North and South Walls came the porphyry, as tongues, dikes and irregular masses. These have, for the most part, been much altered subsequent to being impregnated and veined by tin, and they have in places been severely sheared and crushed: The alteration of the por- phyries is a replacement by sulphides, sericite, pyrophyllite or talc, and these replacements are of such an extent that all signs of the original porphyry may be (and generally are) quite lost. Other alterations are to a coarse sharp gritty sand, or to a soft mass of clay or sericite in which secondary sulpiides (as mar-

THE MOUNT BISCHOFF TIN DEPOSITS. 163 casite and chalcocite) and sulphates (as cyanosite and copperas) may be abundant. Impure secondary copper sulphides, black, and of a pitchy lustre, may abound in the clay and sericite, or when in the white decomposed porphyry they often produce a black or brown stain against which patches of the white porphyry stand out sharply. This is particularly striking along No. 2 level.

Isolated in the sulphide, numerous round and lenticular pockets of white coarse sharp sand are met with, often rich in tin.

The sulphides oxidize irregularly to gossan, the oxidation in different places apparently being governed by the presence of lines of water percolation, joint faces, and the junction of dis- similar rocks, such as slate and sulphide. It is only within the last few years that the pyritic zone has been reached. Above, the Brown Face was entirely of gossan, highly ferruginous, mainly of limonite, but in part of siderite. In the early days the “cap” formed a small subsidiary eminence as represented

by the surface profile in Fig. 16. Locally, it is said that the tin aS Ricy, f Pinnacle~2598 : ¢ 2 indurated Slate gs : MAY above Porphyry ft e 1 24 199 x gina) Suny C+ Vo i: & orid- SAtcn eos ox

NeA hey: Datum 2000’ above s.i.-]/Western Xcut Dyke

500'w oo 500°'E looo'E ISoo'E ZoodvE Scale Vertical =Horizontal Fe tOC 239, Soc 400 Feet

Fic. 16. Sketch section.C-D, E-IV. (See Plan, Fig. 14.)

ore in this upper zone often occurred in huge masses of pure cassiterite, and the ground was often so rich that it cculd be shovelled into bags and sent to the smelters without dressing. In those days the tin ore is said to have been so abundant that it was stacked on the spot more quickly than it could be removed to the smelters. The exceptional richness and coarseness of the

164 J. G. Weston-Dunn.

tin in that upper zone, now removed, can only be accounted for by secondary downward enrichment by leaching probably keeping pace with denudation.

The best values at the present day are generally within a ten-foot zone around the walls of the deposit. The fault breccia along the walls, where silicified, often carries tin, while small lenticular tin veins occasionally penetrate the country; for this reason the wall is in many places removed for a few feet back.

On the eastern side of the South Wall, fresh unaltered porphyry intersects it, showing that the porphyry is definitely later than the formation of the walls. Below the Brown Face a dike is met with in No. 2 Level West, and continuing down below the West- ern Crosscut. This dike may be one of the channels up which the porphyries forming the deposit ascended.

In the northeast corner of the Brown Face masses of tale are met with, associated with a highly altered basic igneous rock, from which probably most of it was altered. Veins of tremolite (altering to asbestos) are also associated and are evidently de- rived from the basic igneous rock. This appears to have been an olivine rich rock, much serpentinized, but pyroxene was evi- dently abundant in places as bastite may be noted altering to talc. This section of the Brown Face carries little or no tin.

The Gossan Benches—These occupy part of the southern slope of the Mount. At intervals along and up the slope an irreg- ular North Wall is met with along the benches, often with

horizontal strie—evidently another line of fault movement. The structure here is still obscure. Possibly it may be as indicated in Section 4-B, Fig. 15.

The crushed material evidently associated with the faulting in the Gossan Faces has been injected with porphyry dikes, masses, and tongues in the same way as the Brown Face. There have been similar alterations, but the main one has been to a pyritic material, weathering to ferruginous sands and clays (originally thought to be detrital), and to gossan. Along the walls the country is so crushed and decomposed that it cannot be

The Mount Bischoff Tin Deposits. 165

determined if the pyrite was originally contained in porphyry or in slate (Plate III b).

Occasionally, apparently isolated masses of comparatively fresh porphyry may be found throughout the benches. Only in rare instances do they penetrate the wall, as in No. 6 bench.

Siderite is a common mineral in the Gossan Faces, and is often associated with galena and sphalerite. Occasionally it is con- cretionary, a shell of siderite enclosing crystals of galena, sphal- erite and pyrites; these were regarded as water-worn pebbles in the early days.

Talcose rocks similar-to those in the northeasterly part of the Brown Face are met with, but are quite rare. Beneath the No. 5 Bench, in the Main Tunnel, is a hard massive dolomite carrying a little green talc (apparently residual) or serpentine, and often “making” into almost pure sulphide. It may have resulted from the total replacement of some basic intrusive. If this is correct the presence of the magnesia is explained, but it may be pointed out that the ore solutions at Mount Bischoff were quite high in magnesia. Throughout the West Coast of Tasmania the association of magnesia with ore solutions is noticeable.

In the Gossan Faces the best values occur in a 20-ft. zone along the wall. Within this zone veins of tin penetrate the deposit in all directions. Veins of coarse fluorite (carrying no tin) are common also, as well as much secondary vuggy quartz. The Gossan Faces are, on the whole, low grade. As in the Brown Face, the more siliceous parts are higher grade than the clayey or talcose.

The White Face.—This deposit lies to the east of the Gossan Faces, and differs from the ones previously discussed. As will be noted from Fig. 14, it is in part intimately associated with the junction of the White Face Dike, Stanhope Dike and Little Stan- hope Dike. Evidently the deposit was originally a huge bulge or “boss” of porphyry resting on a slate floor. As practically the whole deposit is now removed, whatever evidence there was as to any structural similarity to the Brown Face or Gossan Faces can no longer be observed. The only part of the deposit remain-

166 J. G. Weston-Dunn.

ing is a fine marcasite at the bottom of the open cut, and this

evidently goes down for at least another 20 feet. In the past

the pyrite was never worked. According to Herman,” the mate- rials worked at the White Face were friable sands and clays, often overlain by slates and sandstones, and were apparently the complete decomposition and disintegration product of porphyry im situ. The clays are really a white decomposition product of topaz and tourmaline. Herman, by watching the workings closely for some months, noted the gradations of the clays and sands “ through all stages of friability to an adhesive granular quartz rock, then to a hard stanniferous porphyry.” In Nos. 1 and 2 benches of the White Face East, Herman watched an open cut which “was in rounded and sub-angular boulders of gray porphyry in a matrix principally of sand. The whole pre- sented a striking appearance of fluviatile origin; but at intervals, as the work progressed from week to week, this loose aggrega- tion occasionally merged into and from undoubted more or less decomposed porphyry in situ. The steep dip of the slate and sandstone wall terminating the material was strong corroborative evidence that it was really a wall of a lode and not the ‘ bottom’ of an alluvial or any detrital deposit.” In places, a fine im- palpable powder mixed with fine gray tin was met with, and carried 30 to 40 per cent. tin. Herman points out in addition that the “sedimentary rocks also, in places, have a tendency, when stanniferous, to assume a loose granular character, but not nearly to the same extent as the porphyry dikes.”

It appears, then, that the White Face possessed practically none of the characteristics of a gossan, it consisted mainly of a peculiar white, loose sand and clay, and appears to have carried very little ferric oxide. This is peculiar in view of the pyrite lying at the bottom of the deposit. Either the replacement of the original porphyry by sulphides has only taken place at the lower limits of the deposit, or leaching has gone on to such an extent as to totally remove all iron.

21 Op. cit., p. 204.

22 Herman, op. cit., p.

23 Herman, op. cit., p. 2

PLATE Ill. Economic GeoLocy. VoL. XVII.

a. Brown face “Glory Hole” looking west to the apex at convergence of the two walls.

b. Oxidation and leached zones in porphyry; central pyritic zone surrounded by brown oxidized zone, and by leached zone.

c. Radial topaz (pycnite) being replaced by prosopite (showing cleavage) and replaced and veined by pyrrhotite. 20.

th an

pe ch pe

de pc er at lu

The Mount Bischoff Tin Deposits. 167

Perhaps one of the most persistently rich parts of the whole mine was worked in the White Face where a 15-inch seam of tin-bearing sand was met with, traversing decomposed porphyry, and along the walls of which was radial topaz or pycnite-rock. This seam was remarkably rich, the values constant throughout, and maintained the mine returns at a high level for some years.

In the tunnel beneath the White Face lenticular patches of a cellular, sintery quartz are met with in the sulphide

evidently a product of leaching. At the mouth of the tunnel, south of the open cut, is an extremely fine-grained porphyry in which phenocrysts are so few that the rock may at first sight be erro- neously regarded as a fine-grained sandstone.

The North Alluvial Face-—This deposit, on the north side of the Mount, is now abandoned. Originally it consisted of tongues and irregular masses of partly decomposed and disintegrated porphyry, in slate country. Herman records that “it had the character of the ‘wash’ of the White and Brown Faces, with perhaps an unusually large proportion of clay.” Much of the porphyry still remains practically unaltered, so that the undoubted derivation of the sands and clays from the alteration of the porphyry “in situ’? may be traced out. Herman states that the erroneous idea held at the time, as to the origin of these sands and clays, was responsible for the misleading name North Al- luvial. This Face proved a prolific source of tin for some years.

The Slaughter Yard Face.—This deposit, situated between the Brown and Gossan Faces, is identical in origin with them. Very little pyrite has been met with as it has been mainly worked in the oxidized zone. Although now abandoned, the deposit still goes down below the bottom of the open cut, except in places (as in the north part of the cut), where slate forms the floor.

The structure is obscure; no records have been kept, and the faces of the open cut are irregular and broken, so that nothing definite can be made out. To the writer, it appears that the structure resembles the character of the Gossan Faces, as shown

24 Herman, op. cit., p. 200.

168 J. G. Weston-Dunn.

in Section d—B, Fig. 15, the deposit occupying what was orig- inally a broken and shattered zone.

The best values were in the upper gossan, downward leaching evidently having brought about secondary enrichment.

The Stanhope Face-—This face, now abandoned, shows a rather fresh porphyry which originally carried considerable tin, disseminated and crystallized along joint planes. The porphyry is well jointed, large blocks of it carry good tin towards their boundaries, the tin content becoming poorer inwards so that generally the center is barren. This often coincides with. a bleached outer shell of white porphyry, and an inner kernel of hard, dark fresh porphyry. Within the outer shell of bleached porphyry is often a concentric zone of oxidized, ferruginous por- phyry, generally with tin content intermediate between the outer bleached porphyry and the barren central pyritic porphyry. The ferruginous band represents the zone of oxidation of the por- phyry working inwards from the joint planes, the bleached outer band represents the zone of leaching following oxidation.

The coincidence of values with these zones may perhaps be due to lateral enrichment caused by surface waters leaching and concentrating the tin towards the joint planes. On the other hand, it seems more probable that the concentration of the best tin content towards the bounding joint faces was essen- tially _primary—the ascending tin vapors or solutions traversed the rock along the joint planes, then permeated inwards from each joint, so that the best values would be closer to the joint faces; in those cases where the tin was unable to reach the center, the inner zone would be barren. This seems to be in some meas- ure confirmed by the tin selvage often found along joint planes, associated generally with quartz, pyrites, sphalerite, galena, bis- muthinite, arsenopyrite, chalcopyrite and sometimes tourmaline. The secondary oxidation and bleached zones are therefore super- posed on the primary zonal distribution of tin.

In the earlier days, the outer shells of huge porphyry blocks were spalled off, the fragments sent to the battery, the hard pyritic barren kernel picked up by crane and dumped.

The Mount Bischoff Tin Deposits. 169

The Summit Face (or Wheal Face).—This is an open cut on a sill-like mass of porphyry (continuous with the porphyry at the pinnacle of the Mount, just above). The porphyry is irregular, but on the whole lies practically horizontal; at the edge of the cut on the east side, however, the porphyry turns and lies nearly vertical, then apparently continuing down the hillside as a more normal dike.

Both the porphyry and associated slate country carried tin. Often fine facings of tin and quartz are met with in the joint faces of porphyry and slate. Pyrite is absent. The slate is rather indurated and silicified in parts, often producing a banded slate by selective silicification. Silicification and banding is not associated particularly with the tin; it often occurs in quite barren parts of the Mount. Neither is it associated exclusively with the presence of porphyries.

This face is now abandoned; at one time it was an excellent tin producer.

The Lodes.

Apart from the Queen and Giblin Lodes, veins have not been worked extensively at Mount Bischoff. up to the present. The Queen Lode is now abandoned, and practically no records have been kept. It lies to the north of the Brown Face; a plan of some of the levels is shown in Fig. 14. The strike is approx- imately northwest and it cuts across the Queen Dike, in places following along the walls of the dike. The dip is southwest and much flatter than that of the dike so that the lode and dike intersect in both dip and strike. In the past, the Queen Lode was an important feature in the ore reserves.

The Brown Face Lode evidently lies almost parallel to the Queen Lode in both dip and strike. A short level from the Main Tunnel beneath the Brown Face has been developed. It carries good values, but is merely in the prospecting stage as yet. The levels on the North East Lode (S. E. corner), the South West Lode (S. of pinnacle), and the winzes on the Thompson’s Lode (S. of Gossan Faces) are shown in Fig. 14.

170 J. G. Weston-Dunn.

These generally show a good tin content, but have as yet been only prospected. Their dip is always westerly.

From Fig. 14 it will be noted that the lodes appear to radiate from some point in the northwest of the Mount, the variation in strike being quite regular. The dip is always in the same relative direction, varying of course with the strike, the lodes with northwesterly strike dipping southwest, those with almost due northerly strike dipping west.

The Giblin Lode is worked by the Mount Bischoff Extended Tin Mining Company. A short description of this lode will serve for all the lodes of the area.

The Giblin Lode has been excellently described by C. W. Gudgeon.* It is a typical tin lode, “ making” and “ pinching ” in strike and dip. The average width is about 2 feet, occasionally widening to 15 feet or pinching to a mere film. On the whole, the widest parts are in slate, the pinching generally oecurring in quartzite. Associated with the wider parts of the lode, there is almost universally a large amount of gouge, while the thinner and more average parts are of dense and vuggy quartz often highly stanniferous throughout the width. The lode walls are occasionally polished and slickensided.

Generally along either the footwall or hanging wall, but more often the former, the lode is highly pyritic, containing pyrite, arsenopyrite, marcasite, pyrrhotite, galena, stibnite, sphalerite, and bismuthinite. In depth the galene-sphalerite content in- creases, the tin diminishes, the sphalerite becomes the dominant mineral, until the lode is characteristically a lead-zinc one. These sulphides also are sometimes scattered throughout the lode, and often in what appear to be transverse fissures across it. Still, although a large part of the sulphides seem undoubtedly later than the great bulk of the lode filling, much was definitely con- temporaneous with the main veinstone. The tin, in places, is intimately associated with the sulphides both mechanically and chemically (probably as stannite).

23 C. W. Gudgeon, “ The Giblin Lode of Tasmania,” Bull. Inst. Min, and Met., January, 1919.

The Mount Bischoff Tin Deposits. 171

Wolfram was occasionally found in small pockets in the upper parts of the lode, generally along the hanging wall and apparently only in the wider “ makes.” Its relation to the other minerals remains obscure.

Below level No. 5 there are two large “ droppers,” or subsid- iary lodes, and dipping at a much steeper angle than the main lode. The walls of these “droppers” are also slickensided. These “ droppers” are similar in structure to the main lode, but the tin content is unpayable and they carry more sulphides. There was an enrichment of tin where they junction with the main lode. These “droppers” apparently go up the footwall. and as Gudgeon pointed out,”° introduced the lead-zinc minerals.

First “makes” of quartz. containing a little tin often occur in the footwall between the lode and “droppers.” In the lode, horses of large dimensions often occur. Between levels No. 5 and 6 a large one of slate, quartzite and porphyry occurs, the hanging wall carrying the payable ore.

The ore solutions in places appear to have altered the slate walls, generally the hanging wall. This alteration is mainly a slight silicification. The walls are often impregnated with tin for a few feet on either side of the lode. In the neighborhood of small veins and fractures running off from the lode, there is often a slight replacement of the country by fluorite.

The mineral sequence appears to be tin and quartz, pyritic sulphides and fluorite, lead-zinc.

The lower limit of the oxidized zone is irregular, and the tin appears to have migrated, enriching the upper zone and often forming coarse masses of cassiterite.*

REPLACEMENT AND ORE GENESIS. The Porphyries. Mechanics of Intrusion.—lIt has been shown that the intrusion

of the porphyries was preceded by much faulting. The magma

26 Gudgeon, Joc. cit., p. 6. 27 Gudgeon, loc. cit., p. 9.

172 J. G. Weston-Dunn.

was intruded under great pressure as is shown by the forcing of “splashes” of the porphyry into the fault rock. This great pressure was probably the means by which the dike walls were forced apart, and it was also evidently the cause of the irregular tongue-like masses which formed the various faces.

It would appear that while the dikes were still molten, and probably even accompanying the ascension of the magma, the fluorite and other vapors commenced to ascend. The quartz phenocrysts, which in the deep-seated magma had grown to clear idiomorphic crystals, continued their growth after intrusion. But with this later growth was included much fine topaz in the quartz, the inner border of the inclusions still retaining the sharp outline of the original deep-seated phenocryst. Where magmatic resorption had corroded and embayed part of the phenocryst, the inner border of the topaz inclusions follows the corroded out- line. Under ordinary light this outer zone of inclusions is confused with the quartz topaz groundmass, except that the topaz is rather finer grained, but with crossed nicols the outer border of quartz is in optical continuity with the original quartz pheno- cryst. Every quartz phenocryst examined in the topaz-quartz porphyries of Bischoff shows this peculiarity. The writer accepts it as evidence that the fluoride vapors ascended while the dikes were still molten so that topaz was included in the quartz which grew around the phenocrysts when they reached their present position in the dike.

An alternative explanation may be that the fluoride vapours ascended subsequent to the consolidation of the dike, and replac- ing feldspars by topaz, threw out excess quartz, which crystallized around the quartz phenocrysts. If this were so, it could hardly be expected that the whole of this border of later quartz would show such optical continuity with the older magmatic phenocryst. Also, in this case, the topaz enclosed in the border would be ex- pected to be similar to that in the groundmass, whereas it is actually much finer. Also, it would be necessary to postulate that the phenocryst, once it was intruded with the magma, did not grow further, that is, there was no more free quartz available.

The Mount Bischoff Tin Deposits. 173

But the abundance of quartz in the groundmass shows that much free quartz was still present, and some of this would certainly have still further enlarged the phenocryst. Again, if the topaz replaced the feldspars subsequent to the consolidation of the magma, it would be expected that the topaz replacing the feldspar phenocrysts would be precisely similar to that replacing the feld- spar of the groundmass. But the topaz replacing the feldspars is often an aggregate of topaz laths, that replacing the ground- mass is generally either very fine-grained and felted, or more definitely crystalline. That little or no quartz was thrown down during topazization is indicated by the almost total absence of quartz with the topaz replacing feldspar phenocrysts; all excess quartz is apparently removed.

The evidence, then, favors the opinion that the fluoride (topaz) vapors ascended while the dikes were still molten, replaced the feldspar phenocrysts as aggregates of laths, replaced all feldspar in the groundmass coincident with its crystallization, and topaz was enclosed in some of the quartz which enlarged the older deep-seated phenocrysts.

The porphyries in general consist of quartz phenocrysts and topaz pseudomorphs after feldspar phenocrysts, in a groundmass of quartz and topaz. The groundmass may vary from extremely cryptocrystalline to coarse grained. Occasionally muscovite is met with, and generally shows alteration to a sericitic aggregate. Pseudomorphs of tourmaline after feldspar (blue and green) are often met with; occasionally the whole rock may show tourmalinization close to joint planes. A little cassiterite is gen- erally present. Practically all the porphyries of Bischoff are pyritic, the pyritic minerals being secondary.

The replacement of the porphyries has gone on in a definite sequence, apparently commencing, as indicated above, while the dikes were still molten. This replacement sequence is probably governed by temperature considerations, and may be taken under two general headings—Pneumatolytic Replacement and Hydro- thermal Replacement.

174 J. G. Weston-Dunn.

Pneumatolysis.

The pneumatolytic stage at Mount Bischoff is represented by topazization, tourmalinization and cassiteritization. It is possible that some sericitization commenced during this period, but the main bulk of sericite came in early in the hydrothermal stage.

An extreme result of pneumatolytic action subsequent to con- solidation is the removal of all alkalies and evidently alumina as soluble fluorides, leaving the silica as an insoluble residue. In the White Face, a 15-inch seam of tin-bearing sand was evidently formed in this way. The excess fluorides liberated by the dep- osition of much tin along a master joint plane converted the porphyry to angular sand particles, the excess fluorides evidently removing all alkalies and alumina. Either side of this, where the action of the liberated fluorides was not quite so severe, the por- phyry was converted into a pycnite rock; the presence of tour- maline in this indicates also the accompaniment of boron vapors. Still further from the wall of the seam of tin-bearing sand, the porphyry was the more normal topaz porphyry, but rather weath- ered. This same action of the pneumatolytic vapors has also taken place on the slate and sandstone at Bischoff, all feldspathic and other minerals being removed, leaving a clear, sharp, angular, “etched” quartz sand. The lenticular tin-bearing sand pockets in the deposits at Bischoff appear to owe their origin to this acute phase of pneumatolysis.

In Cornwall a similar phenomenon has been observed. J. H. Collins has recorded** that in places the stanniferous solutions have carried away the feldspathic ingredients of the granite “leaving the quartz in loose grains so producing the sand lodes,” as at Wheal Coates and the Great Beam Mine.

Topasization.—Topazization of the porphyries is practically universal throughout the area, unreplaced feldspars occurring only on the north side of the Mount away from the tin deposits, as recorded by Twelvetrees and Petterd.*

°8 J. H. Collins, “On Some Cornish Tin-Stones and Tin Caxels,” 1888, p.

29 Twelvetrees and Petterd, op. cit., p. 120

Lott

THE MOUNT BISCHOFF TIN DEPOSITS. 175 Topazization was the first alteration of the porphyries to take place and apparently commenced while the porphyries were still molten and continued after the consolidation of the dikes. For the most part, only the feldspars are replaced, but occasionally (as along the wall of the previously mentioned tin-sand seam of the White Face) the whole of the quartz is also replaced, and a topaz (or pycnite) rock results. In such cases the topaz occurs as spherulitic aggregates; the central portion of each spherulite is generally fine-grained to granular, and surrounded by radiating prisms and needles of topaz (or pycnite). Apparently the cen- tral granular aggregate represents the replaced phenocryst, the radiating prisms and needles the recrystallized groundmass. Pyc- nite rock is particularly abundant where tin is also abundant. (At the present day there is none to be found at Bischoff, all of it having been put through the battery long since; only specimens in museums can now be examined.) The pycnite rock has gen- erally associated with it some radial blue tourmaline, and is often stanniferous. Contrary to the usual stability of topaz, the pyc- nite variety easily weathers and alters either to sericite or a clayey material. It is also easily replaced by later minerals, particularly sericite (or damourite) and iron sulphides. It may be here noted that the whole of the topaz of Mount Bischoff is the pycnite variety; pycnite embraces the spherulitic, radial, co- lumnar and compact varieties of topaz. Tourmalinization—Tourmalinization commenced rather later than topazization. There is no evidence that boron vapors were active during the crystallization of the porphyries. It is possible that boron was associated with the early fluoride vapors, but the temperature was still too high for stable boron minerals to form. Spherulitic tourmaline aggregates are intimately associated with the radial pycnite rock; the two minerals, pycnite and tourmaline, appear to be simultaneous in growth. In some cases the whole of the porphyry is replaced by radial aggregates of tourmaline with which is often associated much tin. These radial aggregates of tourmaline are somewhat similar to those of topaz

a gran- ular to fine-grained central aggregate (often with a brownish

176 J. G. Weston-Dunn.

tint) surrounded by radiating blue or green prisms or fieedles. In places where only the feldspar phenocrysts have been replaced, the tourmaline is a fine-grained prismatic or lath-shaped aggre- gate. Tourmalinization is always confined to the neighborhood of joint planes or contacts of porphyry and country, and never replaces the whole rock mass in bulk.

Tourmalinization apparently continued long after topazization. It evidently continued (but with very diminished activity). to the crystallization of pyrrhotite, as one thin vein of blue tour- maline was noted in pyrrhotite. The mineral is rather common at Bischoff, but it is by no means as extensively distributed as topaz.

Cassiterization.—The replacement of the porphyries by cas- siterite is, of course, slight compared with topazization and tour- malinization, and is in fact almost confined to the occasional re- placement of feldspar phenocrysts by tin. Topaz and tourmaline also show occasional replacement by cassiterite. From the fact that all of the porphyry always carries at least .oo5 per cent. Sn, it would appear that at least a little tin accompanied the early vapors and crystallized while the rock was still molten. Most of the tin deposition commenced with the topaz and tourmaline. The stanniferous vapors moved up and along joints and fissures in the porphyry, impregnating the rock mass from the joints inward, with resulting zonal distribution already indicated. In the Brown and Gossan Faces, the walls of the deposits formed the easiest passage or line of weakness along which stanniferous vapors (and later solutions) could ascend, so that in these de- posits the best values are in the neighborhood of the walls.

The extreme result of pneumatolytic activity noted under “‘ Pneumatolysis ” as the total removal of all alkalies and alumina

from the porphyry, leaving only an angular “ etched” sand, is evidently a result of cassiterite replacement. It is always as- sociated with remarkably high tin (gray) values (often as much as 40 or 50 per cent. Sn), and appears to be the result of the excess fluorine liberated during the deposition of cassiterite.

The association of cassiterite with pycnite rock has already

Drt Ere Tt

THE MOUNT BISCHOFF TIN DEPOSITS. 197 been noted. Occasionally the tin appears to have accompanied excess boron vapors, coverting the porphyry into a tourmaline- tin rock, in the immediate vicinity of joint planes or other lines of weakness.

The ascension of tin appears to have been prolonged to the hydrothermal stage as in the quartz lodes of the area. The cassiterite occurs as both the gray and very dark amber or black varieties, the dark colored being by far the most common.

Hydrothermal Replacement.

The alteration of the topaz-quartz porphyries by hydrothermal replacement is not so widely distributed as topazization. It is practically confined to the main tin zone, and here the original character of the porphyries has, in the main, been lost. In fact, hydrothermal replacement is a more distinctly special feature of the crushed zones forming the tin deposits, than is pneumatolysis, in that whereas pneumatolytic replacement of the porphyries may extend throughout the area traversed by the dikes, total hydro- thermal replacement is confined to the actual tin deposits.

There appear to be certain temperature stages in the hydro- thermal period, producing an apparent mineral succession:

(1) Sericite, gilbertite, and damourite; with probably tale and pyrophyllite.

) Quartz, tin and chlorite (?).

) Prosopite, pyrrhotite, calcite, fluorite (?).

4) Arsenopyrite, marcasite (?), pyrite (?), chalcopyrite.

5) Galena, sphalerite; fluorite continuing with dolomite and siderite.

The minerals of each stage are more closely associated with one another than with those of later stages, but within each stage there appears to be a mineral sequence. The minerals of an earlier stage may transcend those of a later stage. Quartz evi- dently continued to the early part of stage 5; fluorite continued

through to 5; probably sericite continued to the stage 4. It may

178 J. G. Weston-Dunn.

be pointed out that these stages are not intermittent, they over- lap to a large extent, and appear wholly governed by gradual lowering of temperature. The stages will only represent, then, the temperature at which each mineral commenced to crystallize.

—— Hydrothermal Preumatelytic

: a Topaz r

——

Cassilerite

TT Tourmaline

Secondary Micas

4

(

Quartz

rm 2 i ='2 Frosopite Py

th Pyrrhotite

As-pyrite

Marcasite

Pyrite 4

Cu- pyrite _-!!!T “=a iGalena- Sphalerite

wy Fluorite

Talc

Fic, 17. Apparent sequence of important minerals at Bischoft.

The sequential positions of tale and pyrophyllite are doubtful, it can only be said that they are earlier than all the sulphides. The age of chlorite is also doubtful—it is earlier than the sul- phides, but apparently rather intimately associated with the tin in quartz veins. Chlorite is by no means a common mineral in this area.

Sericite, Gilbertite or Damourite; Talc and Pyrophyllite (?).— The secondary muscovites appear to be the earliest of the hydro- thermal minerals. There can be made out no definite line of demarcation between sericite and gilbertite, fairly coarse-grained gilbertite merging into extremely cryptocrystalline sericite, which when compact and dense becomes rather of the nature of damourite.

It appears evident that some of these secondary micas are es-

aCe

THE MOUNT BISCHOFF TIN DEPOSITS. 179 sentially pneumatolytic in origin, and may even have existed prior to topaz. Occasionally the porphyry shows no sign whatever of topazization, in which case the feldspar is altered to sericite or gilbertite. It is known that sometimes the action of fluoride vapors on feldspar results in the formation of muscovites. In the Brown and Gossan Faces where this type of alteration occurs, the porphyries concerned are isolated tongues. They are gen- erally rather low grade, and would appear to be away from the main path of ascension of pneumatolytic vapors. On the Don Hill numerous nodules of sericite-gilbertite-quartz porphyry occur in the more normal topaz porphyry. These nodules would appear to be segregation nodules formed before the consolida- tion of the main bulk of the porphyry, so that fluorine vapors would not have as great an action on them as on the still molten porphyry.

[t would appear, then, that where the fluoride vapors were not sufficiently in excess at Bischoff to form topaz, the feldspars were merely altered to muscovite. Where the porphyries show only sericitization, first the feldspar phenocrysts are replaced by sericite, then the groundmass is replaced until almost the whole rock, including much of the quartz, may be altered to a mass of sericite; the outline of the original phenocrysts is quite lost. During this process of replacement, the fine sericite may be recrystallized into a coarser gilbertite. In cases where the sericitized porphyry has been silicified, the secondary muscovites are left in the secondary quartz as ghosts of the original seric- itized phenocrysts.

Much of the secondary micas, therefore, may be pneumatolytic, and may precede or accompany topazization as representing a stage of only partial pneumatolytic activity. More abundant fluorine would form topaz, while subsequent to consolidation, excess vapors would remove all feldspathic constituents, leaving only a sharp angular “ etched ” sand.

Compact and occasionally banded masses of cryptocrystalline muscovite (damourite) are occasionally met with, closely as-

sociated with a massive topaz-pyrrhotite-prosopite rock after

180 J. G. Weston-Dunn.

porphyry, the damourite apparently being a product left after the leaching of practically all sulphides. The damourite is the result of alteration of the topaz—a type of alteration also recorded by Clarke,*® who shows that it may be brought about by the action of percolating alkaline waters on topaz. ‘Within this compact fine damourite, unaltered patches of prosopite may still be noted. This variety of muscovite is formed at least at a later date than the prosopite; it is probably due in part to weathering, as many large massive boulders show this surface alteration.

Within the Brown Face, large masses of saturated, clay-like, pyritic, brownish muscovite are met with, which on breaking possess the radial structure reminiscent of pycnite rock. This muscovite is so decomposed and saturated with groundwater that it is quite soft, unctuous and clay-like. It is possible that it may have resulted from the alteration of pycnite rock whose struc- ture it retained

an alteration due to percolating alkaline ground- waters. On the other hand, it may be due to the alteration of porphyry by the solutions accompanying the sulphides which also replaced the porphyry. It is highly pyritic, often merging into pure marcasite. It is quite saturated with surface waters and besides carrying secondary sulphides, as chalcocite, often contains much ferrous and copper sulphates from the breakdown of mar- casite and chalcopyrite. These clay-like masses of secondary muscovite do not carry good tin, except close to the walls of the deposit. .

Talc appears to have been derived by the action of magnesia- bearing solutions. It is met with in the northeast portion of the Brown Face and along the Gossan Benches. No definite gradation in the alteration of porphyry by tale is met with, as the mineral is not generally associated with other minerals. However, some of the talc is so closely associated with masses of porphyry that there would appear no doubt of the replacement of porphyry by tale through the action of magnesia-bearing

solutions. 80 F. W. Clarke, “ Data of Geochemistry,” p. 388. Also, U. S. G. S. Bull. 27, 1886, p. 9.

a

; F g

Rts

The Mount Bischoff Tin Deposits. 181

Occasionally, tourmaline spherulites may be seen to have been replaced by talc and this in turn by fluorite. The talc replaces the tourmaline from the edge of the spherulite inwards, at the same time assuming the radial habit of the tourmaline.

In the Brown Face, the tale occurs close to a basic olivine- bearing igneous rock. It is possible that the magnesia has been derived from the igneous rock by percolating waters which then replaced the neighboring porphyry. Much of the igneous rock has been converted into tale in situ. On the other hand, the abundance of magnesia has been recognized in the ore solutions of other areas on the West Coast of Tasmania, and talc, dolomite and other magnesia-bearing minerals are common associates of ore bodies in this mineral belt.**

Pyrophyllite, the aluminous talc, was originally recorded by Twelvetrees and Petterd,* as an alteration product of muscovite and also of feldspar. McIntosh Reid** believes it to be formed by the action of carbonic acid on feldspars, and shows that it often accompanies sulphides. It may therefore be formed at the same time as some of the secondary muscovites at Bischoff.

The age of both talc and pyrophyllite is very doubtful. They are occasionally replaced by sulphides, but apart from that nothing definite can be said as to their age. Although probably accompanying the sulphide solutions, they appear to have sep- arated out before the pyritic minerals.

The secondary muscovites are of widely varying ages, some probably pneumatolytic, others hydrothermal, and others again possibly products of weathering. The greater quantity formed prior to the sulphides, and before silicification.

Quartz, Tin, Chlorite—The period of silicification was evi- dently coincident with the commencement of formation of the lodes. The tin indicated at this stage is that accompanying the quartz, and represents the last of the tin deposition; the ascen-

81 A. McIntosh Reid, Geol. Surv. Bull., No. 28, Dept. Mines Tasmania, 1918, p. 50.

82 Twelvetrees and Petterd, of. cit., p. 122.

33 A, McIntosh Reid, op. cit., pp. 39 and 59.

182 J. G. Weston-Dunn.

sion of stanniferous vapors and solutions had been practically continuous down to this period.

Quartz occasionally replaces the porphyries, sometimes re- placing the whole of the topaz and leaving only an apparent quartzite in which not even any sign of the phenocrysts can be detected. In cases where the porphyry has been previously sericitized, unreplaced sericite in the quartz may represent the “ghost”? of original phenocrysts. The quartz is generally im- mediately followed by the crystallization of sulphides, and if these were abundant, but later removed, the rock becomes quite cellular.

The silicification of the country evidently took place at this period. Around the walls of the Brown Face, tin often ac- companied the silicification, forming a tin “make” similar to the “make” forming the floor of the Brown Face, and the “ flat make ” immediately below that again.

The chlorite is found accompanying the tin in the lodes, as is occasionally a little blue tourmaline—tourmaline was still slightly active at this phase. In some of the tourmaline porphyries, chlorite may be noted replacing both tourmaline and muscovite. Chlorite is not an abundant mineral in the area.

This group is quite well-defined. It represents the last stage of the deposition of cassiterite, and the commencement of quartz crystallization; quartz continues down through the next group. Tourmaline becomes more scarce, but continues into the next group to just later than pyrrhotite. Chlorite possibly represents the cooler stages of tourmaline, with absence of boron.

Prosopite, Pyrrhotite, Fluorite, Calcite-——The occurrence of prosopite [Ca(FOH).2A1(FOH).] in the porphyries at Mount Bischoff had been noted by von Groddeck. Twelvetrees and Pet- terd™ referred to the conversion of topaz to prosopite and pointed out that this pseudomorphous alteration product had been mis- taken for kaolin. Crystalline prosopite, however, may be found definitely replacing the radial pyenite. It is nearly always ac-

34 Twelvetrees and Petterd, op. cit., p. 123.

rey

THE MOUNT BISCHOFF TIN DEPOSITS. 183 companied by pyrrhotite, fluorite, and calcite, but these latter appear to have crystallized a little later (Plate III c).

The prosopite replacing the topaz at Bischoff has a very small axial angle and is almost pseudo-uniaxial. Dana records axial angles for prosopite up to 2E= 104° 14’, so that it is variable. Its constant association with fluorite at Bischoff would lead to the inference that it was the result of the reaction of CaF, on topaz. The curious combination in prosopite of fluorite with the cleav- age, birefringence colors, and positive sign of topaz is striking; the mineral is, however, monoclinic. It is a hydrothermal re- placement of topaz, and not the result of surface waters, as was supposed by Twelvetrees and Petterd.

Pyrrhotite veins and replaces the earlier minerals (topaz, prosopite, quartz, tourmaline and sericite), and is quite a common mineral at Bischoff. If its alteration product, marcasite, is in- cluded, it is one of the commonest minerals of the area. Occa- sionally it entirely replaces the porphyry, when a massive pyrrho- tite results. Pyrrhotite elsewhere is often a magmatic mineral. segregating or liquating out while the parent rock is still molten; such deposits are typically associated with basic rocks.** At Bischoff, however, the mineral is much later than the consolida- tion of the porphyries and is essentially a hydrothermal mineral. At Bischoff pyrrhotite was earlier than pyrite and marcasite and its separation out from the ore solutions was apparently so rapid as to inhibit the formation of pyrite. The mineral is found throughout the majority of lodes in the West Coast of Tasmania.

The fluorite is included in this period only because of its association with the pyrrhotite and prosopite. In other parts of the deposit, the fluorite is later than the sulphides, but where it was noted in the thin sections associated with prosopite and pyrrhotite, none of the later sulphides occurred. The fluorite replaces calcite in part.

Arsenopyrite, Marcasite, Pyrite, Chalcopyrite. arsenopyrite is undoubtedly the earliest ; the later minerals are oc-

Of this group,

85 Tolman and Rogers, “Characteristics of Magmatic Sulphide Ores,” Min. and Sci. Press, 114, 1917,

). 550.

184 J. G. Weston-Dunn.

casionally moulded around it or vein it. The mineral may con- ceivably be of the same age as the pyrrhotite, but no definite relation between these two could be made out. It is rather a common mineral and as in the case of pyrrhotite, replaces quartz, topaz, tourmaline and muscovite. Often marcasite is intimately associated with arsenopyrite, although the latter would appear to be usually earlier. Both arsenopyrite and marcasite are quite definitely earlier than pyrite, but marcasite is commonly moulded on pyrrhotite.

Although some marcasite is apparently primary and crystal- line, the greater bulk of it at Bischoff is secondary, botryoidal, and due to the alteration of pyrrhotite. This alteration may always be noted as a series of irregular “shells” of marcasite, concentrically arranged around a nucleus of pyrrhotite. The alteration of pyrrhotite to marcasite is always from the outside inwards, and the action is apparently perfectly pseudomorphic. Later minerals to pyrrhotite, therefore, appear later than the marcasite, with the result that it is difficult to estimate the true age of the botryoidal marcasite—whether it is due essentially to the action of surface water, or to the action of sulphide solutions on the pyrrhotite.

At the bottom of the Brown Face, the deposit is in places practically of pure marcasite, from the often botryoidal char- acter of which it would appear to be after pyrrhotite. This part of the deposit is quite saturated with surface waters—in fact the upper limit of this dense marcasite zone seems rather to coin- cide with the top of the saturated zone. The association of max- imum marcasite with surface waters would perhaps tend to point to the secondary character of the mineral as being due to the action of surface waters on pyrrhotite.

On the other hand, Allen** has shown that pyrite or marcasite may be formed by the action of sulphuretted hydrogen or alkaline polysulphides on pyrrhotite at a temperature above 575°. The ore solutions carrying the metallic sulphides very probably carry

36 E, T. Allen, “Genesis of Iron Sulphides—General -Principles,” Journ. Chem. Met. Min. Soc. South Africa, 12, 1911-12, p. 287 et seq.

THE MOUNT BISCHOFF TIN DEPOSITS. 185 dissolved alkaline polysulphides which reacting on the pyrrhotite give up their sulphur, forming marcasite and probable pyrite. Allen has also demonstrated the laboratory conditions under which pyrite or marcasite will form, indicating that marcasite cannot be formed in nature at a temperature above 450° C. In the presence of H.SO, marcasite shows greater tendency to form than pyrite.

The formation of marcasite by the action of alkaline poly- sulphides on pyrrhotite would also provide an explanation of the massive and occasionally compact sericite with which these sulphides are often associated. Clark** has shown that secondary muscovites may be formed by the action of alkaline waters on topaz. The alkalies liberated from the alkaline polysulphides subsequent to their giving up sulphur to pyrrhotite may react on the topaz, with the formation of sericite.

Pyrite is generally found in the porphyry dikes replacing first topaz, then muscovites, tourmaline and quartz in order of prefer- ence. It is met with in the porphyries, slates and sandstones over a mile from the Brown Face. Its position in this group is not clear, the writer has seen sections in which chalcopyrite veins, and is moulded on the pyrite, but its position in regard to the other minerals of the group remains doubtful. Although the greater

‘part of the sulphide in the tin deposits is marcasite, there is evi-

dently much pyrite present also. The general soft loose char- acter of the material prevents a decisive determination of relative ages.

Chalcopyrite has been occasionally noted moulded on marcasite and less often on pyrite. As a general rule, it is in small quan- tities throughout the whole deposit, generally altering to chal- cocite or other secondary sulphides, and to sulphate.

The formation of these sulphide deposits may be said to be the main feature of the hydrothermal phase in the replacement of the porphyries. Although at the present day the maximum replacement by these sulphides is to be found at the bottom of the several faces, it is quite probable that actual replacement

87 F. W. Clarke, U. S. G. S. Bull. 27, 1886, p. 9 et seq.

186 J. G. Weston-Dunn.

reached a considerable higher level, oxidation and leaching hav- ing removed them. The gossans of the Brown Face, Slaughter Yard Face and Gossan Face are evidently the oxidized zones of these pyritic replaced porphyries.

Galena, Sphalerite, Fluorite, Dolomite, Siderite—These form the last group of the hydrothermal stage. Galena and sphalerite may be said to form the end phase of the pyritic sulphide group, and accompanied the last of those minerals.

Fluorite, dolomite and siderite are occasionally notable as important replacements of porphyry. Fluorite replaces topaz, tourmaline, talc and perhaps sericite, and occasionally replaces pyritic sulphides. It also accompanied galena and sphalerite and occasionally replaced them. Fluorite is often accompanied by carbonates (dolomite) and is often veined by them. Dolomite is not a common replacement of porphyry. Siderite, however, may be noted replacing large masses of porphyry as a jointed crystalline siderite in which the only sign of earlier minerals is the occasional outline of replaced sulphides or a few plates of muscovite. This siderite often carries unreplaced cassiterite.

Carbonates may be sometimes noted replacing pseudomorphic topaz aggregates.

Weathering and Denudation.

One effect of the weathering of the porphyry has been de- scribed—the zoning of blocks of porphyry, producing an outer white bleached and often cellular porphyry, beneath which is an iron-stained oxidized band surrounding an unaltered kernel of hard pyritic porphyry. A normal pyritic topaz-porphyry shows, then, first oxidation of the pyrite which may then be removed, leaving a slightly cellular and somewhat soft white porphyry. Further alteration of this by weathering is to a crumbly disintegrating material of sand and clay. In one in- stance, the alteration of the porphyry to a shale-like clay was noted along joint planes, the laminze of the pseudo-shale lying parallel to the joint plane; this was in the White Face, close to where there had been a considerable amount of pycnite rock and

THE MOUNT BISCHOFF TIN DEPOSITS. 187 where the porphyry was fairly high in sulphide. The unaltered porphyry was mainly topaz carrying very few quartz pheno- crysts, and these phenocrysts were removed during the alteration along the joints. The only explanation of the occurrence appears to be that the reaction of H.SO, (resulting from the oxidation of pyrites) on the topaz liberated hydrofluoric, leaving kaolin; the hydrofluoric reacting on the little quartz present forms a hydrofluosilic acid which may be either removed or perhaps further dissociated with deposition of cryptocrystalline quartz. The “shale” is very fine grained, the laminz faces quite smooth and almost polished.

Where the porphyry has been replaced in part by considerable quantities of sulphide without any other alteration, the sulphide on removal may leave a coarse sandy residue or a cellular quartz, depending on the extent of the original sulphide replacement (in general there will be little or no residual topaz, as during replacement sulphides show a preference for topaz before quartz so that the rock would become a sulphide-quartz rock). This is evidently the origin of much of the coarse sand deposits of Bischoff, but these are quite distinct from the sands formed by the pneumatolytic action of fluoride vapors on the porphyry.

The action of surface waters on pyrrhotite may have been in part the cause of its alteration to marcasite. Chalcopyrite is altered to secondary copper sulphides, some of which have a black pitch-like appearance and occur in pockets and streaks in the brown sericite masses. These black copper sulphides may also stain irregularly the soft saturated white decomposed por- phyries beneath the Brown Face. In warm weather the decom- position of the marcasite provides in places a sticky plastic mass of sulphur on the surface of the cut. Impure arsenic salts also often form on the exposed surface of pyritic masses. In dry weather, ferrous sulphate is quite abundant in the sulphide. Often in opening up the marcasite it fires, igniting the timbers, in which case it has to be quickly sealed up again.

The oxidation of the sulphides has been the cause of the huge gossan deposits. The denudation of the upper limits of these

188 J. G. Weston-Dunn.

with the concurrent downward enrichment of the tin resulted in the huge masses of tin found in the early days.

To the east of the Brown Face and within the semicircle formed by the Queen and Stanhope Dikes a depression was formed during denudation, with an outlet to the south down the side of the Mount. Within this drainage area a thin detrital deposit accumulated, and was sluiced off by the old Stanhope Company. This, with the workings on the Don Hill, formed the only detrital deposit at Bischoff. 3

Other Replacements.

Slate and Sandstone.—The alteration of the country rock is for the most part confined to silicification, impregnation, by tin, and replacement by sulphides.

Silicification and impregnation by tin take place mainly in the vicinity of dikes, or along the walls of the deposits. During silicification, the slate or sandstone is converted into a quartzite, and may become quite vuggy. Sometimes minute topaz may form in the quartzite along the walls.

Occasionally slight tourmalinization of the slate and sand- stone may take place close to the walls, with formation of brown tourmaline. At other times the sandstone is altered to a biotite hornfels with considerable silicification.

Within the Brown and Gossan Faces, the crushed masses of slate and sandstone country often show entire replacement by pyritic sulphides and where this takes place, it cannot be dis- tinguished from the pyritic replacement of porphyries. It is quite conceivable that much of the sericite may be a result of the action of hydrothermal solutions on slate.

Herman** has noted that the country rock may show an alteration to coarse sands similar to the porphyries. This may be a result of pneumatolysis as in the porphyries, or the sands may represent the residue after the removal of sulphides from replaced slate and sandstone country.

In rare cases, the replacement of slate by fluorite may be noted,

38 Herman, op. cit., p. 205.

The Mount Bischoff Tin Deposits. 1&9

both in the various faces, and along the walls of the Giblin Lode.

Basic Igneous Rocks.—V ery little is known about these rocks; outcrops are small and difficult to distinguish from the altered porphyry. Their determination rests mainly on microscopical evidence. Specimens showing least alteration are fine-grained, in part greenish, in part brownish in color, and carry a little magnetite. Thin sections show a variable grained rock, mainly of rather fine-grained olivine, altering to, and in a base of, green to brownish serpentine, and containing secondary fibrous am- phibole and tale. Carbonate (probably dolomite) appears to have filled vugs into which well-developed crystals of olivine project. The carbonate also replaces serpentine and is in places traversed by veins of secondary tale. Magnetite occurs in fine dust in the serpentine. These specimens evidently represent a serpentinized olivine-rich rock, probably dunite.

In the northeast part of the Brown Face, specimens of fibrous amphibole (tremolite) altering to asbestos and talc are met with in large massive pieces and evidently representing alteration of the olivine-rock along joint planes. Occasionally thin sections of talc show an alteration from fibrous amphibole of short stumpy habit—probably bastite.

The dolomite containing a little residual serpentine that occurs in the main tunnel beneath the Gossan Benches may be a replaced basic igneous rock. This dolomite contains a good deal of sul- hide, which appears to replace the carbonate.

The relation of the period of alteration of these basic igneous rocks to that of the mineralization of the porphyries is doubtful. If the talc is associated with the same period as the formation of the Brown Face deposit, then the alteration of the rock by calcite and serpentine is prior to the tin deposits. This supposi- tion would be confirmed if the dolomite beneath the Gossan Faces represents a replaced basic igneous rock, as the dolomite in its turn is replaced by sulphides. On the other hand, the alteration of the olivine-rich rock in the northeast of the Brown Face is quite conceivably due to the action of surface waters. These rocks carry little tin.

190 J. G. Weston-Dunn.

Conclusions.

The direct association of the deposits with the porphyries indicates that the mineralization period represents the end phase of magmatic intrusion and differentiation. Subsequent to the intrusion of the granite batholith to the south of Waratah, pro- gressive differentiation gave first the porphyry dikes and later the mineral deposits.

The concentration of such mineralizers as fluorine and boron by abstraction from the granite magma continued down to the stage of the differentiation of the porphyries from the metallic minerals. Relief of pressure during the intrusion of the porphyry dikes was probably responsible for the release of the fluorine and boron mineralizers, so the pneumatolytic phase immediately followed the intrusion by the dikes while the latter were still molten.

The commencement of topazization, cassiteritization, and tour- malinization took place in that order, and was probably governed by lowering of temperature rather than progressive alteration in the pneumatolytic vapors. At the commencement when fluoride vapors were not abundant, secondary micas would appear to have preceded some topaz, and were incorporated in segrega- tion nodules as on Don Hill. The pneumatolytic phase continued after the consolidation of the porphyries. Where pneumatolytic activity was excessively severe, feldspathic constituents were removed, leaving a coarse etched sand, while where the pneuma- tolytic vapors were a little less active pycnite-rock was formed. Excessive pneumatolytic activity accompanied high tin values, and was probably the result of fluorine liberated during the deposition of SnQ,.

Topazization was the first of the pneumatolytic replacements to be completed; cassiterite and tourmaline continued into the hydrothermal stage.

In the hydrothermal phase, it is difficult to separate the mineral periods; they evidently succeeded each other in rapid succession with much overlapping.

Peper mee nT

The Mount Bischoff Tin Deposits. 191

Sericitization to some extent probably belongs to the pneuma- tolytic phase. But a large part is evidently directly associated with the pyritic sulphides, and represents the action of alkaline polysulphides on the replaced rock.

Perhaps the first definite stage in the hydrothermal phase is the formation of the lodes. In these, cassiterite appears to have been the first mineral to crystallize, often forming seams of prac- tically pure tin oxide along the walls. This was followed by quartz and cassiterite, which in turn were followed by the pyritic sulphides, then galena, sphalerite and fluorite—each of these stages being coincident with its equivalent replacements in the deposits.

The formation of the quartz lodes was of the same period as the silicification of some of the porphyry and of the country. Silicification was followed in places by alteration of the topaz to prosopite accompanied by pyrrhotite, calcite and perhaps fluorite. Alteration of topaz to prosopite appears to be due to the action of CaF, on topaz, but in general the free CaF, did not crystallize out till later at a slightly lower temperature.

Pyrrhotite replaced large masses of the porphyry in the crushed zone, and probably also the slate and sandstone country. This pyrrhotite was apparently later altered by alkaline polysulphide solutions to marcasite. This preferential alteration to marcasite instead of to pyrite may indicate a low temperature of alteration (below 450°) with perhaps the presence of free H.SO,. Away from the tin deposits where probably no free H,SO, was present, disseminated pyrite crystallized in the dikes and country.

The pyritic sulphides were succeeded by galena-sphalerite, and the final phase of mineralization was the replacement by fluorite and carbonates.

A graphic attempt at depicting the mineral sequence is made in Fig. 17.

Mineralogically, little of practical use can be said of the local- ization of tin values. The sharp “etched” quartz sands, repre- senting severe pneumatolytic activity, carry high tin; and in the early days when pycnite rock was abundant, this was also as-

192 J. G. Weston-Dunn.

sociated with tin. As practically the whole of the porphyry at Bischoff is topazized, there appears to be no other relation be- tween topaz and tin. Where diminished pneumatolysis resulted only in the formation of secondary micas, the tin content is always low.

Structurally, the best tin is in the neighborhood of the walls of the several deposits; the tin bearing vapors and solutions evi- dently followed the line of least resistance along the fault walls and joint planes.

The tin content in the lodes show a depth limit. In the Giblin Lode this limit is about the No. 9 level. The tin of the dikes is mainly of an earlier period than in the lodes, so that owing to the higher temperature tin values in the dikes are not likely to continue down to the same depth as in the lodes. For this reason, there is little possibility that any similar crushed zones that may occur in depth are likely to carry tin.

The large masses of tin and the exceptional richness of the upper part of the huge gossans would suggest that there has been secondary enrichment by leaching by surface waters, keep- ing pace with denudation.

Acknowledgments.

The writer wishes to acknowledge here his indebtedness to the following gentlemen :—to C. W. Gudgeon, general mine man- ager of the Mount Bischoff Tin Mining Corp., for great help, courteous and useful criticism and discussion, and kindly welcome during his stay at Waratah; to A. Tilly, mine superintendent, for useful assistance and critical discussion; to H. Sommerville for excellent help in going over mine plans; to Senator J. D. Millen and A. D. Mackey for the loan of numerous rock sections and photographs; to H. B. Schell for kindly assistance while at the Mount Bischoff Extended Tin Mine; to Professor E. W. Skeats for helpful criticism and discussion while in Melbourne; to Loftus Hills (government geologist of Tasmania), K. K. Ward (government geologist of South Australia), A. Gibbs Maitland

THE MOUNT BISCHOFF TIN DEPOSITS. 193 (government geologist of West Australia), H. Baragwanath (director Geological Survey, Victoria), B. Dunstan (govern- ment geologist of Queensland), J. E. Carne (government geol- ogist of N. S. W.), and Professor L. A. Cotton for literature received on Australian tin mining; and to Mr. Tallin, of the Royal School of Mines, for a large number of rock sections.

Finally, the writer wishes to thank Professor C. G. Cullis for his helpful advice and interest, and the Frecheville Fellowship Committee for the opportunity to carry out the work. The interest and criticism of Professor Wm. Frecheville have been of inestimable value throughout the work.

GEOLOGICAL SURVEY OF INDIA, CHOWRINGHEE Roap, CALcuTtTa.

POSSIBLE ORIGIN OF SOME OF THE STRUCTURES OF THE MID-CONTINENT OIL FIELD.

V. E. Monnett.

Introduction.—The productive rock folds of the Oklahoma- Kansas portion of the Mid-Continent oil field are usually of limited areal extent and have dips of less than 100 feet per mile. Many of them are not more than a mile and a half in length and the average inclination of the beds will not exceed fifty feet per mile. The common type of fold is that of a more or less elliptical dome, although some are extremely irregular in outline with a number of “noses” or subsidiary domes on the sides of the main structure. There is a noticeable lack of parallelism of the axes, and similar lack of alignment of the folds themselves. This is clearly shown by the rock folds of the Osage County, Oklahoma, field as mapped by the U. S. Geological Survey.* Fath called attention to this lack of arrangement but attempted to classify the folds of the Osage area into three or more zones of occurrence.” A definite zonal arrangement is to be noticed in the folds above the buried granite ridge of Kansas, but very little evidence of alignment is to be seen elsewhere. In Fig. 18 the trend of the principal folds of thirteen oil pools of Oklahoma is shown. It will be noticed that two pools which are in the same part of the state may have their structural axes nearly parallel, as for example Newkirk and Ponca City. Two other pools equally close to each other, as Cushing and Creek County, may lie nearly at right angles.

Well Logs.—Well logs from most of the Oklahoma fields show a great preponderance of shale with small amounts of limestone and numerous sandstone lenses, some of which are

1U. S. G. S. Bulletins 686 and 6091.

-2U.S. G. S. Prof. Paper, 128c, p. 80.

The Mid-Continent Oil Field. 195

from fifty to sixty feet in thickness. The Permian and Upper Pennsylvanian form the surface rocks of the entire area and are largely represented by shales with sand lenses. The Lower Pennsylvanian and the Mississippian formations are principally limestone. A larger percentage of limestone is found above the Mississippian in Kansas than is present in Oklahoma. Some un- conformities occur in the section but the increase of dip with

Fic. 18. Trend of axes of principal folds of thirteen oil pools of Oklahoma. Data obtained from maps in Bull. 19, part 2, Okla. Geol. Survey. (1) Gar- ber, (2) Jefferson County (north part), (3) Jefferson County (south part), (4) Newkirk, (5) Blackwell, (6) Ponca City, (7) Boynton, (8) Billings, (9) Loco, (10) Duncan, (11) Creek County, (12) Cushing, (13) Grandfield.

depth, which is so marked in some pools, is generally attributed to a thickening and thinning of the shale. Deep wells in northern Oklahoma and around the margin of the Wichita Mountains, of the same state, have encountered granite, without intrusive rela- tionship at comparatively shallow depths. Since most of these wells were located on anticlinal or dome structure, some relation- ship between the granite and the structure seems probable. Like the buried granite ridge of Kansas, the granite masses of Okla- homa may have served merely as agents in the localization of the folding, or they may have been in part the cause of the folds.

196 V. E. Monnett.

Cause of Folding.—Blackwelder® showed that such folds as have been described can not reasonably be explained on the basis of lateral thrust or by isostatic adjustment, and he suggested differential settling or compaction as the origin. Certainly the lithologic character of the upper 2,000 to 3,000 feet of the geologic section is not favorable to the transmission of thrusts over any considerable distance. There are areas of mountain structure in southern Oklahoma and in eastern Oklahoma and Kansas but some of the oil pool structures are nearly two hundred miles distant from either of these areas. Fath* explains the Osage County: folds as the surficial results of deep seated thrusts in the more consolidated and older Paleozoics underlying the Osage and extending from the mountain areas to the east and south. Such an origin does not explain the irregularity of form and arrangement which is characteristic of these folds.

Most geologists are agreed that all sediments lose a considerable percentage of their original volume as the water content is re- duced, and the grains are rearranged by the weight of the over- lying sediments. As to the exact amount of shrinkage, only an approximation can be made as very little experimental data is available and the sedimentation conditions no doubt have a pro- nounced effect. Sands will suffer less loss of volume than clays on account of the larger size and more rounded shape of the sand grains. Calcareous muds and oozes will likewise suffer a considerable shrinkage. Bleininger® found that bond clay from Bavaria had a shrinkage water volume of 65 per cent. of the true clay volume. This clay probably does not represent an average clay, but it gives some idea of the amount of shrinkage that clay undergoes by the loss of excess water at room tem- peratures and without pressure.

Effects of Shrinkage——The possible effects of shrinkage upon the attitude of sediments is illustrated in Figs. 19 and 20. In Fig. 19 the shrinkage of clay is taken as 35 per cent. and that of sand

8 Amer. Assoc. Pet. Geol. Bull., vol. 4, pp. 89-94, 1920.

4Loc. cit.

5 Trans. Amer. Elect. Chem. Soc., 1911.

The Mid-Continent Oil Field. 197

as 15 percent. It is believed that both of these arbitrary estimates are far too low, but the purpose is to illustrate the results which may be obtained with even the minimum estimates. The sedi-

Fic. 19. Results of compaction when sand lenses are interbedded with shales

and the sediments deposited on a horizontal surface.

ments are assumed to have been deposited on a horizontal surface and the amount of shrinkage was computed and is indicated along each of the vertical lines a, b, c, d, e, and f. The broken line 1-1 indicates the position of the upper layer after compac- tion. It is, of course, realized that consolidation and compaction of the lower layers will be in progress from the time of their deposition, and that the upper layers may thereby have an initial dip of deposition. In Fig. 20, regularly stratified sands and clays

are assumed to have been deposited upon an uneven surfac

oO

whose slopes may or may not have been too steep to permit of

4+

+

' a Se

' ! !

!

! ee

1— q. 199 a & j 600 x x x x ‘ , S ba x x x x x x x ™ :

Fic. 20. Results of compaction when sediments are laid down on an un- even surface.

198 V. E. Monnett.

initial dip. The shrinkage is taken as 25 per cent. since both sands and clays are included. The position of the broken line 4x is determined by the difference in thickness of the sediment instead of the differences in composition as in Fig. 19. The two illustrations might be combined to show the effects of lenticular sands and clays on an uneven surface, in which case the tendency might be to counteract each other or else to give still greater dips by a favorable grouping of sand lenses over the high points of the old surface. Blackwelder’s objection that a lens was not large enough to form a rock fold may thus be easily met by a series of overlapping lenses such as is found in nearly all oil districts.

Garber Field.—In an attempt to determine the possible relation between surface structure and differences in lithological composi- tion, the Garber field of Oklahoma was studied by the writer. The surface structure of this field, as mapped by Dorsey Hager and others, is that of a dome. The geologic section consists of a series of shales and sands of Permian and Pennsylvanian age totaling at least two or three thousand feet in thekness. Well logs from sections 13, 24, and 25 of T. 22 N. and R. 4 E. were examined and the percentage of the total depth represented by sand was computed. Only those beds which the driller recog- nized as sand were included in the percentage calculations. Most of the wells studied range from 1,000 feet to 1,600 feet in depth although a few deeper wells were included. A larger number of well logs were available but lack of detailed location limited the number actually used to sixty. These were fairly well dis- stributed over the area, no more than twelve being from the same quarter section. The percentages of sand in the wells. or each quarter section were averaged and the results are shown in Fig. 21 which also shows the structural contour map of the area. It will be noted that the differences in the percentage figures are very small and it was found that wells in the same quarter section usually differed far more than the averages of the quarter sections. By comparing the percentage figures with the location of the structural contour lines, it will be seen that there is a

oS EEE

——Ee

Er Eere

Sep

a

The Mid-Continent Oil Field. 199

general increase in percentage of sand towards the higher parts of the structure. Unfortunately well data was not available for points very far down on the structure but it is significant that the individual wells showing the lowest percentage of sand are located in the northwest quarter of the northwest quarter of section 25, while the highest percentage for individual wells was found in the northeast quarter of the southeast quarter of section 24.

Pg TW

Fic. 21. Structural contours after Dorsey Hager. The average percentage of sand to total depth in part of the Garber field, Oklahoma.

It would be presuming too much to suggest, from this meager evidence, that the structure was due solely, or even partially, to this difference in sand content. The evidence is given with the hope that other areas may be studied with the same idea in mind. In wells of but 1,500 feet depth, a difference of 2 per cent. in sand content is not sufficient to produce folds of the magnitude observed here, but when the added thickness of similar sediments underlying the oil horizon is considered, these percentage dif- ferences may be increased until they are important factors in the localization if not actual causes of folding.

200 V. E. Monnett.

Accumulation and Folding—Some difficulty has been expe- rienced by petroleum geologists in explaining the occurrence of oil in folds of such low degree of dip as frequently are found in the Mid-Continent field. It is argued by many that gravitational sorting is non-effective on rock slopes of very low dip. Munn,’ Johnson,‘ Shaw,* Mills,° and more recently Rich,*® have empha- sized the role of moving waters in causing the migration of oil and gas up and down the dip to points where it may be entrapped. If some of the rock folds are due to differential settling, the movement of the water, as it was slowly expelled from the ac- cumulating sediments, would tend to carry the oil and gas par- ticles both upward and laterally to points of greater porosity, such as the sand lenses, and to those places where further move- ment would be hindered, as in the anticlinal crests. If the sedi- ments contain the necessary organic material to furnish the source of the oil, the accumulation and the folding may take place con- temporaneously.

Conclusions—The writer has attempted to bring out the fol- lowing points :

1. The gentle folds of the north Mid-Continent oil field suggest a different origin from that commonly attributed to them.

2. Folds of similar magnitude and arrangement may be pro- duced under favorable conditions by differential settling of sedi- ments upon either an irregular surface or a horizontal surface.

3. Well data from one typical fold of this area suggest that there is a relation between folding and differences in lithological composition.

4. Such an origin permits folds to act as oil reservoirs even though the dips are too low to permit of gravitational sorting and although there is little movement of water after consolidation.

Irnaca, N. Y.

6 Econ. GEOL., vol. 4, pp. 509-529, 1909. 7A. I. M. E. Bull., 98, pp. 221-226, 1915. 8 Econ. GEoL., vol. 12, pp. 610-628, 1917. 9 Econ. GEOL., vol. 15, pp. 398-421, 1920. 10 Econ. GEOL., vol. 16, pp. 347-371, 1921.

Se nee

A Recent Deposit Of A Thermal Spring In Bolivia.*

Waldemar Lindgren.

Introduction.—During a recent visit to the Uncia tin mines in the Eastern Cordillera of Central Bolivia the manager, Mr. Maximo Nava, called my attention to a hot spring and its re- markable deposit in the valley two miles below the mine. He stated that the deposit was said to contain tungsten and this interesting statement was found to be fully correct.

The Uncia mine, property of Mr. Patiiio, is situated just east of the main Cordilleran divide, which here scarcely reaches 15,000 feet in elevation and the springs issue at an elevation of about 12,000 feet in a broad open valley. Both main ridge and valley are in the black folded Paleozoic slate so abundant in this part of Bolivia. Near the mine smaller bodies of rhyolite por- phyry appear. There are no mines or prospects on veins in the vicinity of the springs.

The Springs——The hot water issues from several vents a few meters above the valley bottom in which a small water course flows over slate bedrock. The quantity of water is, at least, 150 gallons per minute, perhaps considerably more. At one place a small geyser cone about 0.8 meter high and one meter in diameter has been built up of calcareous tufa. The water has a temperature of about 60° C., and is slightly salty to the taste. It appears to contain a little H,S but not much CO.,. The water is clearly of the sodium chloride type. I regret that no analysis of it has so far been made. The Indians from the neighboring villages use the water for bathing purposes, al fresco.

The Deposits—The deposits of the springs are predominat-

1 Read before the Society of Economic Geologists, Amherst Meeting, De- cember 29, 1921.

202 Waldemar Lindgren.

ingly calcareous and extend from the creek upward over the gentle valley slope for quite an area

at least 10 acres and pos- sibly more, and reach an elevation of at least 30 meters above the creek. It is evident, therefore, that the springs have occupied this position for a long time and that the orifice has been lowered as the erosion proceeded.

The larger part of the spring deposit consists of a rather com- pact light yellowish gray calcareous tufa in rude horizontal beds. This material has been used for burning lime as indicated by some old ruined kilns. Lime is a scarce article in this part of Bolivia, so that the tufa has been found valuable.

There are also minor beds and lenses of flinty brown streaked opal (not chalcedony). This material contains small dark brown masses of manganese dioxide and small streaks of crystalline barite and calcite.

The tufa in many places contains patches of dark brown to black earthy matter also rich in manganese and these sometimes form larger lenses of porous black manganese ore, rarely more than a meter in thickness. This is often rudely bedded by the intercalation of thin streaks of a white crystalline material which proved to be barite; it occurs in irregular grains or stout prisms and in the cavities thick prisms of the same mineral also project. Mixed with the barite are grains of calcite.

The little geyser cone mentioned above consists of a porous and cellular calcite, stained a dirty grayish brown. It also con- tains considerable silica probably in the form of opal. The brownish stains gave strong reaction for manganese, but contain little or no iron. The spectroscope showed a strong reaction for lithia.

The bedded material of barite, calcite and manganese ore was examined in thin sections and polished sections. The latter show the maganese mineral to be normal psilomelane in rounded mam- millary forms; this evidently is a colloidal deposit, which has now become hardened and has acquired a fibrous structure.

No other minerals were found. A careful qualitative analysis made by Miss Helen E. Vassar, the Analyst of this Department,

Deposit Of A Thermal Spring. 203

showed a little silica, not much lime but large quantities of barium oxide, sulphur trioxide and manganese. There were also traces of copper and lithium. A notable quantity of tungsten, at least 0.5 per cent. WOs, was present.

Assays for silver and gold proved negative except in the case of the brown opaline sinter which gave a fraction of an ounce of silver to the ton.

The definite discovery of tungsten led to many further tests for this element. There was little or no tungsten in the purer cal- careous and siliceous materials, and it was soon found that the metal was dependent upon the quantity of psilomelane present. Pure pieces of this mineral always gave a strong test for tungsten, but apparently this metal is not uniformly distributed. One specimen gave an amount of tungsten which must have repre- sented several per cent. It is concluded that the tungsten is not present as any definite mineral but was precipitated as a colloid together with the manganese dioxide. If this is true it follows that concentration processes will be of no avail and that the only way to utilize the material would be by aid of chemical processes similar to those followed by the qualitative analysis. It would, therefore, séem that in spite of a noteworthy amount of tungsten present, perhaps averaging 0.5 per cent., the ore has no economic value—certainly not at present.

Probable Mineral Combinations in Depth.—At the surface, then, we have this combination : Calcite, barite, psilomelane (with tungsten) and opal. In depth where colloids no longer easily form we might find quartz, calcite, barite, rhodochrosite and scheelite or hubnerite.

Barite is not common in the tin and tungsten deposits of

30livia. Probably it could not be formed at the temperature and pressure prevailing when these ores were crystallized.*

It is an interesting fact, however, that barite is frequently found on the surface, for instance, near Oruro according to H. F. Grondijs and at Potosi according to my own observation. It

1Stelzner states that barite occurs at Huanuni, Putocayo and Avicaya.

204 Waldemar Lindgren.

is said not to be contained in the regular ores of Potosi. Per- haps this barite is a younger deposit made nearer to the surface by thermal waters of more recent age but of a similar type to those which formed the tin, silver and tungsten deposits now worked.

Other Hot Springs in Bolivia—The geological map of the de- partments issued by the Bolivian government shows the location of many hot springs. Their locations appear to correspond roughly to the extent of the great rhyolitic flows in the depart- ments of Oruro and Potosi. Among the more northerly are the hot springs of Huanuni and Uncia. Another group is located about fifty miles further south near the mines of Avicaya. Still another group are situated in the vicinity of Potosi. Considering the scarcity of hot springs elsewhere it is well permissible to see in this arrangement a genetic relationship with the rhyolite erup- tions and further investigations of the deposits of these springs might produce interesting results.

Tungsten is now definitely added to the metals carried by hot springs. As is well known the tungsten and tin deposits of Bolivia are intimately associated as to genesis. Thus far no tin has been reported in the waters or tufas from Bolivia, but traces of this metal have been shown to exist in the waters of certain thermal springs of the Rhine region. It will also be re- called that Meunier reported tin from a sinter deposited by a spring in Malaya, though from some sources doubt has been cast on this occurrence.

Confirmatory Statements.—I am indebted to my friend H. F. Grondijs of Santiago who was with me at Uncia for a translation from the manuscript of a private mine report by Dr. Koeberlin.

In this it is stated that the springs issue from a fault plane which passes close by the Catavi bridge and which has a vertical throw of more than 1,000 meters; this probably extends to great depth and may establish some form of connection between the surface and the rhyolitic magma. The deposits, Dr. Koeberlin says, consist of alternating layers of tufa and siliceous material, especially the calcareous layers are strongly colored by manganese

a

Deposit Of A Thermal Spring. 205

oxide; in these manganiferous lime rocks tungsten has been found up to 4 per cent. of WO;. The thickness of the deposit is at most three meters.

The total area in the valley covered by lime and tungsten deposits is at least 100 hectares. The average tungsten content is 0.5 per cent. WO,. It has not been possible to identify any tungsten mineral, nor can the ore be concentrated by mechanical means. As far as I know these statements by Dr. Koeberlin have never been published.

Similar Deposits ——There are many accounts in the literature of the deposition of manganese dioxide by waters but most cases refer to the action of meteoric waters, in bog-manganese ores or in the pipes of water supply systems. Apparently manganese is rarely deposited in large volume by hot springs.

An instance analogous to the occurrence here described is furnished by the Luxeuil hot springs in the department of Haute Saone, France.* These waters, which have a temperature of 46° C., are probably not wholly of deepseated origin, and are similar in this respect to the waters of Plombiéres, the zeolitic deposits of which have been described by Daubrée. The Luxeuil springs deposit an abundance of earthy manganese containing some barium and a little arsenic. Zeolites are also formed by these waters. Apparently tungsten has not been looked for.

Another occurrence of much more striking similarity to the Uncia deposits has been described by R. A. F. Penrose, Jr.,* from near Golconda, Nevada. It is remarkable that this article has been overlooked in most accounts of hot spring activity; it is probably because the author expresses some uncertainty as to whether this occurrence really was formed by hot springs, none appearing at the precise locality now. However, Dr. Penrose mentions hot springs depositing maganese close to Golconda sta- tion and his final conclusion is that the deposits are of thermal

2E, Jaquot et Willm, “Le eaux minerales de la France,” Paris, 1894, p. 217.

3“ A Pleistocene Manganese Deposit near Golconda, Nevada,” Jour. Geo- logy, vol. 1, 1893, pp. 275-282.

206 Waldemar Lindgren.

origin. The careful description leaves no room for doubt of the genesis of the deposit. It is essentially a calcareous tufa with lenticular masses of wad or pyrolusite. An analysis of this manganese ore showed several per cent. of BaO and 2.78 per cent. WO,. It will be recalled that in this part of Nevada there are many occurrences of scheelite mostly in contact metamorphic deposits.

In conclusion, it may be said that the deposition of tungsten, precipitated in colloidal form with psilomelane by hot springs, seems now to be established beyond doubt.

LABORATORY OF Economic GEOLocy,

MaAssAcHusETts INSTITUTE OF TECHNOLOGY, CAMBRIDGE, Mass.

ta

The Determination Of Dip And Strike.

W. S. Tangier Smith.

A recent paper’ in Economic GEo.ocy described a method for determining the dip and strike of a plane when the inclination from the horizontal of the trace of the plane (apparent dip) in two different vertical sections is known. The following different methods of solving the same problem may also be of interest:

I. If a purely geometrical solution is desired, one which re- quires no special scales, protractors or tables, that offered by W. H. Dalton,’ and repeated in Cole’s “ Aids in Practical Geol- ogy,” and more recently by the writer,* is perhaps as simple as any. By using an ordinary tangent-cotangent scale, however, this solution may be considerably shortened, as follows.

Let CX and CY (Fig. 22) represent the two directions in

) which the apparent dip of a bed has been determined, as, for

' . B D

Fic. 22. 1 Longwell, C. R., and Waters, E. O., “A Practical Method for Determin- ing Dip and Strike,” Econ. GEoL., vol. 16, pp. 405-409, 1921. é 2 Dalton, W. H., “ Geological Problems,” Geol. Mag., vol. 10, pp. 332-333, 3 Cole, Grenville A. J., “ Aids in Practical Geology,” pp. 6-7, London, 1801. 4Smith, W. S. Tangier, “Some Graphic Methods for the Solution of Geologic Problems,” Econ, GErot., vol. 9, pp. 38-39, 1914.

208 W. S. Tangier Smith.

example, the directions of two walls of a quarry. Suppose the dip on both walls to be in the direction of C, as indicated by the arrows of the figure, the value of that on CX being represented by a, and of that on CY by b, the true dip being represented by c.

On CX lay off CA equal to the cotangent of a as obtained from the cotangent scale, and on CY lay off CB equal to the cotangent of b. If B and A are then joined by a straight line, this line, BA, is the required strike. The perpendicular distance, CD, from C to BA, when determined in degrees by the cotangent scale, will give the required dip (c).

By a slight modification of this method, the tangent of the angle of dip (both apparent and true) may be used instead of the cotangent, except for very large angles; and in the case of small angles its use is essential, on account of the large values of the cotangent. Since

cota tanb

’ cotb tana

the plotting on the two arms of the figures is reversed. That is, the tangent of a is laid off on CB, and that of b on CA, as indi- cated in Fig. 23. BA, as before, is the required strike.

To determine the dip, produce the perpendicular, CD, and on this line lay off CB’ equal to CB; through B’ draw a line parallel

The Determination Of Dip And Strike. 209

to BA, intersecting CX at D’. The line CD’, thus obtained, when measured on the tangent scale will give the required dip.

If the directions of apparent dip are different on the two walls (CA and CB), one being toward C and the other away from C, either CA or CB should be produced beyond C, and the deter- mination of dip and strike made in the adjacent supplementary angle thus formed, in which both apparent dips are either toward or away from C.

Instead of using a tangent-cotangent scale for the solution shown in Figs. 22 and 23, the values of a and b may be determined from trigonometric tables and laid off according to any scale suited to the problem and to the degree of accuracy required. This method has the advantage of not calling for a special scale, of permitting a variation in the size of the scale according to the particular problem to be solved, and of being usable wherever trigonometric tables and a scale of small, equal parts (e.g., milli- meters or fiftieths of an inch) are available. Moreover, it takes but little more time than the method with a fixed scale.

II. Another method, a little less simple than the foregoing, but giving results for the determination of strike directly in de- grees, instead of by geometrical construction, is based on the equations

tana _tand_ tanec

sinA sin B sin 90° or cota sinB cota — sin 90° and

cotb sinA cotc sind

In this solution, a horizontal line, SE, Fig. 24, is first drawn, and a second line, HK, perpendicular to SE and intersecting it at G. GE and GF are then laid off equal to the tangents of @ and b, respectively, as determined from a tangent scale. In the case of large angles, the cotangents instead of the tangents are used, the cotangents being laid off on opposite sides of G from the tangents, as indicated in the figure.

210 W. S. Tangier Smith.

From any suitable point K, on the line HK, the lines KE and KF are drawn and produced indefinitely. A right and left sine scale (that is, one reading in both directions from a central zero point) is then placed parallel to SE, with its central or zero point

w o w @

, S tan G tena /,v /E

(cot a) (cot 6) 2 / / / / / oh 4 / / a : / / /

4 j Fic. 24

on the line HK; and, still maintaining this parallelism and loca- tion of the zero point, is moved along the line HK until some point H is reached at which the total number of degrees, MN, cut off on the scale by the lines KAZ and KN, is equal to the known angle, the supplement of the angle formed by the direc- tions of apparent dip (that is, 180° —BCA, in Fig. 22). HM will then give the value of B and HN that of A, from either of which the strike may be determined.

The value of a and A (or of b and B) being known, the true dip c may readily be determined from the Wright geological protractor, the Brunton slope chart, or other device for the same purpose. Or the dip may be determined from the figure, as follows: With the sine scale in the position MN, mark at R, either to the right or left of H, the position of 90° on the scale.

The Determination Of Dip And Strike. 211

If the tangents of a and b are being used, RK is next drawn. The distance GS which this line cuts off on the line EF will give, when measured on the tangent scale, the required dip. If instead of the tangents the cotangents of a and b are being used, draw RF and produce to T, its intersection with HK, then draw TN. The intersection of this with GE will cut off GV, which, meas- ured on the cotangent scale, will give the true dip.

In this general solution of the problem, the position of MN with respect to FE will, of course, vary with the size of the dif- ferent angles, with the location of K, and with the use of tangent or cotangent of a and b. MN may therefore be above or below FE, or even coincide with it. The coincidence of the two lines in the tangent solution simplifies the determination, the true dip then being 45°. If these lines coincide when the cotangents are used, however, only an indefinite result is obtained. The tan- gents of a and b, therefore, should be used when the sum of their cotangents is equal or nearly equal to the sum of the sines of A and B.

Charts.—Charts may readily be constructed for the general solution of this problem of dip and strike. One type of chart for this purpose may be based on the equations given under the last solution. Charts of this type are relatively simple in both construction and use, but have the disadvantage that the angles A and B must be determined by a method of trial. Taking the graphic solution last given (that of Fig. 24) as the basis for a chart of this sort, the right and left halves of the chart would be symmetrical with respect to the median line between them (corresponding to HK of Fig. 24), the right half being identical with the dip chart described by Wright® a number of years ago.

A second type of chart, of which that given in the paper by Longwell and Waters (already referred to) is an example, is based on the equations

sin BCA ; tan A : and cct ¢ cota sin A. tan b : — cos BCA tan @ Wright, F. E., “A New Dip Chart,” Journ. Wash, Acad. Sci., vol. 4, pp.

440-444, 1914.

212 W. S. Tangier Smith.

Charts of this type are less simple in construction and use than those of the first sort, their only advantage over the latter being that the determination of the angle A (or B) is direct.

III. The values of A and B and the true dip, c, could all be determined with the Wright geological protractor, if there was added to it a second rotating arm exactly like the one with which if is already equipped. The protractor modified in this way would correspond to a chart of the first type. Referring to figure 25, the values of a and b are first read on the vertical scale CP.

The two protractor arms, opened to make an angle equal to the divergence angle BCA (which is the same as the corresponding angle in Fig. 22), are rotated, preserving this angle, until a position is reached in which horizontal lines from the determined positions of a and b on CP cut off equal values on the two pro- tractor arms. This value (as read on either arm) gives the true dip, while the angles A and B are read on the marginal scale of the protractor, as indicated in the figure.

The above determination is used when a, b and c are each less than 45°. When these angles are all greater than 45°, a and b are read on the left and right arms, respectively, as indicated in Fig. 26, and these arms, making an angle with each other equal to BCA, are rotated until a and b on the two arms are at the

The Determination Of Dip And Strike.

same height. This height read on the vertical scale (CP of the figure) gives the true dip.

Fic. 26.

By inverting Fig. 26, and comparing the lettering, it will be seen that this solution follows the method given for Fig. 22. The solution shown in Fig. 25, however, is different from that of Fig. 23, although the latter solution might just as readily be ap- plied in the case to which Fig. 25 refers.

If a or both a and D are less than 45°, while b and c or c alone is greater than 45°, the determination by means of the protractor is somewhat more complicated, and a description of the methods would unduly prolong this article. They may readily be worked out, however, from Dr. Wright’s explanation® of his protractor and its use.

Pato ALTO, CALIFORNIA,

6 Wright, F. E., “A Geological Protractor,’ Journ. Wash. Acad. Sci., vol. 6, Pp. 5-7, 1916.

Editorial

Editorial. Economic Geologists And Literature.

One of the noteworthy trends of geology is the great advance during recent years in the application of geology to the industries. The number of economic geologists has increased many fold and new societies have been organized in order that they may gather together for their scientific interests and exchange of ideas. We may consider economic geologists as falling into three large classes—those employed by governmental geological surveys and institutions of research, those associated with universities, and those engaged in the commercial application of the science to the industries, such as mining and petroleum. The last mentioned group has grown most rapidly, even at the expense of the others, and their members are scattered to all parts of the globe. It is of them, particularly, that we wish to speak.

Coincident with their growth in numbers and more widespread fields of observation we do not find a corresponding increase in the enrichment of the literature pertaining to economic geology. We do notice, however, an enormous increase in the demand for geological literature and knowledge. This is to be seen in active society meetings, in the increase of subscription lists for geolog- ical journals, and in numerous letters of inquiry which we re- ceive. Textbooks of geology are selling on an unprecedented scale. The present tendency, then, is rather one of obtaining geological data than giving.

For a healthy growth of any science there must be contribution or recording of new data, as well as extraction, and new knowl- edge added when old is discarded, else a subject will not keep abreast of the times or will tend to become out of date. Much has been discarded and much also has been added, but in economic geology, we do not believe the additions are commensurate with

re

—E

Editorial.

the growth in numbers and opportunities of observation, par- ticularly on the part of those engaged in the commercial applica- tion of geology. The latter, more than ever before, are being afforded opportunity for world-wide observations and field study, both on the surface and beneath the surface. The field is the geologist’s laboratory and yet the results of much of this labora- tory work are being lost.

We appreciate the limitations imposed on economic geologists both of time and permission which tend to restrict their oppor- tunities to record their observations on the printed page, for we ourselves have been subject to the same restrictions. Neverthe- less, we feel that there is much geologic knowledge of scientific value which may be readily separated from confidential data and published without prejudice. The paucity of this is largely the fault of the geologist himself. Few can fall back on the excuse that they are unable to write, for most geologists are highly trained. A recent publication of the National Research Council shows that of the present geologists in the United States, 87 per cent. have received collegiate degrees, and out of every 100 men who'received collegiate training, 50 went forward to a master’s degree and 39 to a doctorate. Neither should the economic geologist hesitate to enter the field of publication for fear that his subject does not deal with broad principles. The latter can be founded securely only on accurate records of careful observation, for, in most cases, it is beyond any one person to build broad principles without recourse to records of others. Our object would be defeated, however, were there a flood of publication repeating merely what others had done before, or submitted only for the vanity of seeing one’s name before an article.

To you, then, who have accumulated geologic knowledge of value, and are assiduous users of the other man’s data, is it fair continually to take and not to give!

Alan M. Bateman.

1“ Geology and Geography in the United States,” Edward B. Mathews and H. P. Little, No. 17, 1921.

Discussion

And

Informal Communications

This department is maintained in order to afford to those interested in questions relating to economic geology an opportunity for informal discus- sion or communication. Contributions are cordially invited either in the form of discussion of more formal papers appearing in earlier numbers or bearing upon matters of geologic interest not previously treated. Letters should be directed to Alan M. Bateman, Editor, Yale University, New Haven, Conn. The full name of the author should be attached to all communications.

Announcement.

We wish to call attention to the change inaugurated with this number in the heading of this department of the Journal. Pre- viously it was designated as “ Discussion”? to which is now added, “ Informal Communications.” It is not to be assumed that discussion is no longer desired. On the contrary, we hope and expect that it will increase. Our purpose is to encourage and to afford opportunity for publication of another type of com- munication in addition to more formal discussions of previous papers, namely, informal letters dealing with phases of interest in economic geology which do not necessarily relate to matters pre- viously published.

We recognize that every economic geologist in the course of his work frequently obtains some interesting geologic data, be it an unusual occurrence of mineral or structure, a new thought, or a new trick in the technique of methods, which he would not deem worthy of a separate article but would be glad to submit as an informal communication. Such contributions would bring to light many interesting minor points pertaining to economic geology which otherwise might sink into oblivion. Each reader would then profit more by observations of his fellow workers and the Journal will become of greater interest to its subscribers.

aitiicheiil

Discussion And Informal

Communications. .217

In broadening this department of the Journal it is our hope that it will be made use of freely by our readers and particularly by those who previously have not been contributors.

Editor.

Moving Underground Water In The Accumu Lation Of Oil And Gas.

Sir: The instructive article by Dr. John L. Rich on “ Moving Underground Water as a Primary Cause of the Migration and Accumulation of Oil and Gas” in a recent number of this journal. recalls the earlier experiments by Mr. R. Van A. Mills and by Dr. William H. Emmons. The former showed that currents of water moving through beds of sand were capable of displacing and rearranging oil and gas in the direction of the hydraulic flow. The experiments by Emmons showed that a current of gas readily caused the upward movement of oil which would otherwise remain stationary in a water-saturated sand, being held there by the capillary forces.

The general principle which may be deduced from these several investigations is that currents, either of fluid or of gas, are very effective in carrying petroleum greater or less distances through the rocks according to local circumstances. Such currents may be produced by hydraulic differential, as in the case of artesian water circulation, by the expansive force of gas being generated, by the compression of loosely deposited sediments, by tangential thrusts, and in other ways.

The student of a particular oil field must therefore try to visualize a complex set of conditions and processes in which the most important factors are the original presence of oil, the ar- rangement and porosity of beds, the nature and causes of the fluid and gas currents, and the areal distribution of these factors in his local province, and, finally, the structure of the beds.

Extot BLACKWELDER. DENVER, COLORADO.

218 Discussion And Informal Communications.

The Origin Of Graphite.

Sir: I am indebted to Mr. T. H. Clark for his comments in the September—October number of your journal on the origin of the graphite in the Sleaford Bay area of South Australia. A word in reply may perhaps not be out of place. . Mr. Clark is of the opinion that “

certain associations” described by me “seem to show that the graphite need not be wholly organic in origin.”

The associations leading Mr. Clark to this opinion have, how- ever, been incorrectly interpreted by him. Their interpretation, in fact, is based on an erroneous view of the original nature of the sediments now carrying graphite. The first case is that of the garnet showing inclusions of graphite zonally arranged. Mr. Clark is here in error in supposing that the garnet is a product of the silication of the dolomites, and from a little closer inspection of the original paper he would have seen that the garnet is an almandine type, and not a grossular or andradite. The original sediment I consider to have been a siliceous shale, and the garnet to have been derived from biotite, as in the associated para- gneisses, or in certain cases more probably derived from iron oxide in the original sediment (cf. pp. 196-7). Carbon dioxide can not be considered as a by-product in the synthesis of these zoned garnets.

It is to be noted that the majority of the graphite at Sleaford Bay is concentrated in rocks which were originally carbonate-free types and formed distinct stratigraphic units in an original sedi- mentary series. The assumption of an inorganic origin for the graphite necessitate the migration of CO. from the carbonate sediments to the siliceous and shaly types. While this is perhaps not to be regarded as a strong objection, it can scarcely be per- mitted to be used in support of an inorganic origin.

The facts brought forward in the original paper, and here in part restated, the absence of the vein type of graphite from this particular locality, are, in my opinion, more in harmony with an organic derivation than with one in which the reduction of CO, of an original carbonate molecule is involved. Alluding to the

f

Discussion And Informal Communications. 219

reactions which I have discussed, it may be emphasized again that in one of these only is experimental evidence available hith- erto for the deoxidation of the oxides of carbon, namely, in the reversible system 2CO@CO.+C. Even in the work of Du- brunfaut, which I have quoted, the carbon can be interpreted as derived from decomposition cf carbon monoxide without inter- vention of hydrogen.

As has been noted in the original paper, wnen excavation work has proceeded further in the South Australian area, examination may show that more than one method of derivation of graphite is involved. Be that as it may, it is not improbable that the prob- lem of graphite genesis, like not a few other vexed questions in petrology, will await its ultimate solution in high pressure experi- mental work in the laboratory.

Cecit E. TILtey. CAMBRIDGE, ENGLAND,

A Field Method Of Reducing Maps To Scale.

Two years ago, while engaged on some field work, the writer was called upon to reduce a geological map of a special area to a smaller scale in order to incorporate it in the general district map, then in the course of preparation. The usual method of locating the various points of the large scale map on the one of smaller scale by means of squares was found too slow and tedious and what was thought to be a new method, described in detail below, was devised which accomplished the work more quickly without loss in accuracy. It is based on the theorem of similar triangles and its very simplicity would suggest that it is already known and in use; but a diligent search in handbooks of Field Geology and verbal enquiry amongst a number of geologists would indicate that the application of this theorem to the reduc- tion of maps to scale, while not new to some, at least has never been described. A brief note on its use may therefore be justified.

Let the upper polygon of Fig. 27 represent a closed plane table traverse which it is desired to transfer to a correlation sheet

220 Discussion And Informal Communications.

drawn to a smaller scale. Two points on the traverse, A’ and B’, correspond to points A and B, definitely located on the sheet and lying the distance A—B apart. With A’B’ as radius describe

arcs about A’ and B’, intersecting at O. Radii from all the sta- tion points of the traverse are then drawn to O and the distances OA and OB equal to AB are laid off. Then, by similar triangles,

Ob Ab

Ob! Ab!

Beginning at 4’, by means of two set squares or a parallel ruler a line is drawn parallel to 4’C’ through A, the point of inter- section of radius OA’ and the arc, described about O with AB as radius. This line cuts OC’ at C. Then, by similar triangles, A‘'C' OA‘ AC OA In the same manner CD is drawn parallel to C’D’ through D, intersecting radius OD’ in D. Continuing thus around the trav- erse, with careful work the line drawn through G parallel to G’A’ should intersect point 4, thus giving a check on accuracy.

Discussion

And Informal Communications. 221

The reduced traverse is then oriented over the correlation sheet by means of 4 and B and the various station points pricked through with a needle. In reducing side shots, such as shown in the figure, it must be borne in mind that the smaller the angle between NO and MO the greater the danger of error, hence the need for accuracy. This method may likewise be employed in distributing the error of closure of a traverse between two known points over its component courses. The procedure is the same as in the case of the closed traverse, one of the two radii employed here being the distance between the known points as taken from the traverse to be adjusted, the other being the actual distance to which the traverse must be reduced. As will be seen from the figure, maps may be enlarged as well as reduced by this method.

It should be remembered that this is only a quick field method and in no way, of course, intended to supplant more accurate methods, such as photography.

P. ARMSTRONG. LABORATORY OF Economic GEOLOGY, YALE UNIVERSITY, New Haven, Conn.

Reviews

A Textbook of Geology. By AmMaApEus W. Grapav. Part I. General Geology, pp. 864, Figs. 1-734, with tables of the most important min- erals. Boston, 1920. Part II. Historical Geology, pp. 976, Figs. 735- 1980, with table of Tertiary correlations. 1921. D.C. Heath and Co. In the preparation of this notable work the author has purposely

departed somewhat widely from the order and method of treatment most

commonly adopted in textbooks of geology. Instead of making the first volume declaredly a treatise on geologic processes, he has made the materials of the lithosphere the thread which holds everything together.

The keynote of the first volume is clearly the rocks, and of the second

the sediments and their fossils. After three preliminary chapters intro-

ducing the scope of geology, its subdivisions, and a brief sketch of the early rise of the science, Chapter IV. plunges into the materials of the earth and imparts in condensed form some of the more essential facts and principles of mineralogy. Petrology follows. Objecting to the time-honored classification of rocks into igneous, sedimentary, and metamorphic groups, which he calls artificial, the author offers the fol- lowing classification: A, Endogenetic (Non-Fragmental) Rocks, divided into (1) Pyrogenic or igneous, (2) Hydrogenic or aqueous, (3) At- mogenic or atmospheric, and (4) Biogenic or organic. B, Exogenic

(Clastic) Rocks, comprising (1) Atmoclastic, (1a) Anemoclastic, (2)

Hydroclastic, (3) Pyroclastic, (4) Autoclastic, and (5) Bioclastic rocks. This classification becomes the governing outline and framework for

more than half of the first volume. The treatment of igneous rocks is followed by chapters on vulcanism and volcanic phenomena; and they in turn lead on to the form and structure of older igneous masses and to contact metamorphism. The descriptions and discussions of hydrogenic and biogenic rocks are very thorough, reflecting various special re- searches of the author. In particular, the eighty-five pages devoted to biogenic rocks impart a wealth of detailed information which will be very welcome to teachers and advanced students. The author is at his best here.

After a transitional chapter on Atmospheric Precipitates and their Derivatives, which is devoted largely to descriptions of glaciers, the thread of clastic rocks is taken up. There follow in succession the

REVIEWS. 223 destructive work of the hydrosphere, pyrosphere, glaciers, and organisms, each of which is set forth as the parent of clastic material. Then comes the transportation, assorting, and deposition of clastic rock material by winds, rivers, glaciers, and the sea, the treatment of each subject cen- tering on sedimentary action. The physiographic processes also receive considerable attention aside from their clastic work, but the prime emphasis is not upon these processes as such.

Deformation of the rocks of the earth’s crust is well handled from the descriptive standpoint, though the chapter on movements is divorced from that on deformation and covers only earthquakes and slow changes of level, particularly of strand lines. One looks in vain for the under- lving dynamics, or a full discussion of the forces that produced the deformed features so well described. Thirteen pages only are devoted to metamorphism, which seems to the reviewer too brief for so far- reaching and profound a subject. Two chapters on the sculpturing of the earth’s surface close Volume I.

In Volume II. the author has undertaken to give his students a good working knowledge of the essential characteristics of plants and animals, with a peep into the doctrine of organic evolution, before setting forth to understand the history of the earth. One hundred and forty pages are very profitably given to this preparatory work, although essentially bio- logical. in his delineation of earth history, the base of the Cambrian is taken as a line of demarkation and starting point. From the base of the Cambrian the chronologic record is read first backward toward the be- ginning and then forward toward the present, instead of reading from the beginning to the present in an ever forward sweep as is done in most texts. The stages of earth history before the recognized Archean are designated pre-geological and are stated to belong to the domain of astronomy. The reviewer strongly dissents from this view, believing that if geology is to be regarded as essentially a history of the earth, the birth of the earth was an important event of that history, while its youthful and adolescent stages are strictly geologic, and not astronomic, and are important because they shaped its subsequent career.

In developing the geologic periods, the author has placed the emphasis upon stratigraphic rather than biologic development, believing that the former is more readily grasped by the student and will have greater interest. But the biologic aspect is by no means neglected. In describ- ing each period the general scheme is to present, at the outset, char- acteristic sections and to put before the student the tangible features of the evidence from which generalizations and deductions are to spring. The stratigraphy and physical events are treated with fullness. One of the notable features is the large number of original paleogeographic

224 Reviews.

maps. These make no distinction between the abysmal depths and shal- low submergences of the continental platforms, recalling certain Euro- pean works whose maps create the impression that the continents and ocean basins were singularly unstable and reversible. These maps are drawn with great freedom and pay no attention to whether the bottoms of the ocean basins show signs of such features or not, nor do the possible alternatives or the dynamics involved seem to have been con- sidered.

A brief description of the essential characteristics of the faunas and floras, illustrated by an unusual number of figures, closes each period chapter. At the close of the Paleozoic, and again following the Meso- zoic, chapters are introduced treating in a consecutive manner the prog- ress of life development which has taken place during these eras. These summaries are very commendable features of the book.

The economic aspects of the science have been sadly slighted. In the historical part only the briefest mention is made of coal, iron, copper, and oil, incidentally and without headings. Lead, zinc, tin, and gold are not even listed in the index of Volume IT.

An unfortunate feature of the work is the paucity of footnote refer- ences for collateral reading and further inquiry. For example, the statement of theories of the cause of the glacial period is quite imperfect, and on top of this the student is left without a single reference. There is a very scanty citation of authors in the index, even when recognized in the text. Among those whose names do not appear in the index of either volume are the two Geikies, DeLapparent, and Van Hise, while Suess, Gilbert, and J. D. Dana are cited but once in the two volumes. But, on the other hand, the portraits of many of the pioneers and leaders in the development of geology are a happy feature.

In general, one feels that Grabau’s “ Textbook of Geology ” is a book of marked individuality, in which the special leanings of the author appear strongly. If he prefers to put aside the causes and nature of glacier motion with the assertion that they belong to physics rather than geology, he abundantly makes up for it by a full and excellent presenta- tion of the stratigraphic and biologic phases. What constitutes the ideally balanced textbook is largely a matter of individual judgment, and will probably always be a debated question. That an author gives nota- ble preference to the phases of the subject upon which he is best qualified to write is natural and has its advantages. In thus giving to the pro- fession and to students so full an expression of the products of his long study of geologic problems, Dr. Grabau has placed his readers under distinct obligations.

R. T. Chamberlin.

Reviews.

to ty wn

A Manual of Determinative Mineralogy with tables for the determination of minerals by means of: I. Their physical characters, II. Blowpipe and chemical properties. By J. Vorney Lewis. 3d edition. Wiley & Sons, Inc., 1921. Price $3.

The present edition of Lewis’s well-known manual has been thoroughty revised throughout and a set of new tables for the determination of minerals without the use of the blowpipe has been added, making the work particularly useful to geologists and engineers. These tables are well arranged and contain a great deal of information in a small space.

A noticeable feature of the blowpipe tables and particularly of the pages devoted to apparatus and operations is the exceptional care taken to warn the student against any conditions that may obscure a given reaction or of appearances that might be mistaken for a confirmative test. The language throughout is unusually clear and concise, is aided by effective illustrations, and there is scarcely a page of the general text that does not contain one or more helpful little wrinkles in manip- ulation that are additional to those found in most determinative min- eralogies.

)

The volume contains 298 octavo pages, appears to be practically free from typographic errors, and in its general make-up is very creditable to both author and publisher.

F, L. Ransome.

The Economics of Petroleum. By JosepH E. PoGur. 375 pp., including index; 151 figs.; 124 statistical tables. John Wiley & Sons, Inc. New York. 1921. Price, $6.0c

postpaid.

Everyone interested in oil has been studying statistics. They are essen- tial to an understanding of the industry and to prediction of its future. The oil man needs them in forecasting the immediate future price of crude and of refined products. The investor wants the same data to give him a clue of the probable future change in market value of his securities. The engineer appraising oil properties needs them as a basis of his calcu- lation of future earnings. The economist and diplomat need them in pre- dicting the future world shortage of oil and its international effects.

This book satisfies all these needs at the moment, and if brought up to date with annual new editions or supplements it will remain the best au- thority on the subject.

One does not here find merely the bald dry statistics as issued by the Government and by oil journals. Most of the statistics have been digested by the author before publication. They are presented in significant ana- lytical form. For instance, the production of various products is given

226 Reviews.

in some diagrams in terms of the annual or monthly rate of consumption.

As thus interpreted, the great production and enormous stocks of oil now on hand can not frighten the investor. In terms of consumption the production and stocks are much smaller than in some past periods of rising prices. They are not too large to’satisfy the probable needs of the immediate future.

Analytic studies of this kind, so fully and logically interpreted, carry a significance not otherwise appreciated. For instance, they show how the production, consumption, and price of petroleum is largely independent of the course taken by other commodities. Until he has digested this book it doubtless will be hard for the engineer working in copper, iron, coal, etc., to understand why the consumption of crude oil during the year 1921 decreased only 1 per cent. below the consumption of 1920, when it reached a maximum. The industrial depression had greater percentage effect on the price of crude, but much less than on the price of most other essential commodities. It did not materially affect the volume of consumption of crude oil. Its effects on consumption of refined products are shown by the increase of refined stocks at refineries, which is a serious matter for the small refiner. Yet all these figures lose their terror to the industry at large when interpreted as so many months’ supply at current rate of consumption.

Some of the figures recently published by the Petroleum Institute are given in similar analytic form, but without diagrams, and they do not cover nearly all the matters analyzed by Mr. Pogue. A fine feature of his diagrams is the use of semi-logarithmic paper which brings out per- centage changes very clearly.

Everyone interested in the oil business should study the book. It is not light reading. The language in places is unnecessarily heavy and tech- nical, but the diagrams are simple and easily understood. It rings true and there is no escape from its logic on most points.

Chester W. Washburne.

Society Of Economic Geologists

This department has been established for the official communications of the Society of Economic Geologists whereby the affairs of the Society such as notices, minutes, titles of papers, elections, etc., may be brought regularly to the attention of its members.

The royalties on Political and Commercial Geology, edited by J. E. Spurr and published by the McGraw-Hill Book Company, are to be as- signed to further the work along the same lines as the volume, in accord- ance with the statement on the ttile page, as follows: “ Royalties received irom the sale of this book will be assigned to an institution of learning to finance further studies along the lines followed in the volume.”

The thirty or more authors, whose work make up the volume, have asked the Society of Economic Geologists to determine the use of these royalties in the above provision. The funds are already sufficient for one or more scholarships, or fellowships, for one year. The awarding of the scholarship carries an obligation of tangible results to appear in the form of a publication. The President of the Society has appointed the follow- ing to administer the funds: E. C. Harder, J. E. Spurr, C. K. Leith and G. H. Garrey. Applications for this fund should be sent to the chair- man of the Committee on Royalties, Mr. E. C. Harder, Republic Mining & Mfg. Co., 1111 Harrison Bldg., Philadelphia, Pa.

F, L. Ransome has been re-appointed as one of the two delegates of the Society to the Division of Geology and Geography of the National Re- search Council.

The members of the Society are indebted to ex-President Penrose for the pin emblems of the Society which were officially adopted by the Coun- cil at the meeting of December 7, 1921. The emblem has been sent to the members who did not attend the Amherst meeting.

The membership has been requested to transmit to the Secretary any discussion it may desire to add to the report of the Committee on Foreign Mineral Policy of the Mining and Metallurgical Society of America which is published in Bulletin No. 151, Nov. 15, 1921.

228 Society Of Economic Geologists.

The membership has also been requested to further the passage of the Temple Bill which provides for the completion of the topographic map of the United States within twenty years.

An invitation has been extended to the Society to attend an Interna- tional Scientific Congress to be held at Liege, Belgium, by the University of Liege Association of Engineers, from June 11th to 16th, 1922.

We regret to record the death of John Casper Branner, March rst, at Palo Alto, California. Dr. Branner, who for many years was Professor of Geology at Stanford University, was later made President. He was a charter member of the Society.

A Committee on Publication has been appointed by the Society whose duty it shall be to decide which of the papers presented before the Society are suitable for publication. They are:

)

B. S. Butler, Calumet & Hecla Mining Co., Box 22 E. DeGolyer, 65 Broadway, New York City. Willis T. Lee, U. S. Geological Survey, Washington,

7, Calumet, Mich.

—

Ge

Approximately a year ago, the first publication of the Society was sent to its members. It is entitled “The Relation of Economic Geology to the General Principles of Geology,” by R. A. F. Penrose, Jr., and is to be known as Publication No. 1. Subsequently there has been sent to each member the following:

‘Plain Geology,’ by George Otis Smith, Publication No. 2. ‘The Geology of the Braden Mine, Rancagua, Chile,” by Waldemar Lind-

gren and Edson S. Bastin, Publication No. 3.

‘Society of Economic Geologists: Its Sphere and Future,” by R. A. F.

Penrose, Jr., Publication No. 4.

Hereafter all publications of the Society will be numbered serially; the next to be known as Society of Economic Geologists, Publication No. 5, “A Recent Deposit of a Thermal Spring in Bolivia,” by Waldemar Lindgren.

Scientific Notes And News'

D. F. Hewett, of the U. S. Geological Survey, has completed his field work at Goodsprings, Nev., and has gone to Atlanta and Pioche, Nev., to make brief reconnaissance examinations of these districts. From Pioche he will go to Fallon, Nev., and later to Searchlight, Nev., to re- port on the underground water supply of that town.

Chester W. Washburne spent the first week in April lecturing on the principles of oil geology at Harvard University.

Basil Prescott is in Chihuahua, Mexico.

C. K. Leith has returned from South America to resume his work at the University of Wisconsin.

A. C. Seward has been elected president of the Geological Society, England.

Willet G. Miller sailed from New York for England on March 23.

G. V. Colchester has been appointed to the Geological Survey of the Anglo-Egyptian Sudan.

Myron L. Fuller, Consulting Geologist, sailed from New York for England on March 11, to be gone about eight months, during which time he plans to visit France, Switzerland, Germany, Belgium, Netherlands, and Norway, in addition to Great Britain and Ireland.

J. Coggin Brown has returned to India from London.

W. C. Phalen, geologist of the Solvay Process Co., delivered a lecture on geologic mapping in the nearly horizontal rocks of the Coal Measures to the Geologica] Club, at Syracuse University, March 16. Earlier, he presented a paper on “A Possible Cause of the Red Color of Certain

Potash Salts” at the same institution.

Charles Schuchert has returned to Yale University after a trip extend- ing through some of the oil regions of Oklahoma.

C. W. Purington has returned from Vladivostok to Yokohama.

Geologists, mining engineers and others interested in applied geology are invited to keep the editor informed of new investigations of mining districts

or scientific studies undertaken by them, together with such other scientific and personal items as may come to their notice

230 Scientific

Notes And News.

H. Foster Bain, director of the Bureau of Mines, was elected president of the Joseph A. Holmes Safety Association, at the annual meeting held recently in Washington, D. C.

J. R. Finlay has returned to Redlands, Cal., having finished his work for the State Tax Commission in New Mexico.

D. D. Irwin has recently been made General Superintendent of the Copper Queen Mine, at Bisbee and Douglas.

G. H. Clark, who has been studying the fuller’s earth mining projects of the Standard Oil and other companies in Georgia and Florida, has re- turned to Birmingham, Ala.

H. P. Barrett, State Geologist of Michigan, completed an annual inspec- tion of mining properties in the Lake Superior district for appraisal pur- poses.

George Hironao Nishihara, who left the University of Minnesota seven years ago, has opened an office in the Murai Bank Building, Nihonbashi, Tokio, Japan, as consulting geologist. He has recently made an in- vestigation of a bismuth mine in Canton, China.

Frank Ayers has been made General Superintendent of the Moctezuma Copper Co., of the Phelps Dodge Corp., at Nacozari, Mexico.

C. P. Ross, of the U. S. Geological Survey, has left for Tucson, Ariz., to study the economic geology of the Christmas quadrangle and later to make a reconnaissance examination in the neighborhood of Arivaipa.

F, J. Katz has returned to the U. S. Geological Survey at Washing- ton.

C. L. Nelson and Roscoe Reeves have returned to the United States and are now in the New York office of the Sinclair Exploration Co.

O. E. Meinzer has received the doctorate degree in geology from the University of Chicago, his thesis being entitled “Occurrence of ground water in the United States, with a discussion of principles.”

Ernest W. Dean, who has specialized on chemistry related to petroleum, has resigned his position with the Bureau of Mines and is now with the Standard Oil Company of New Jersey.

H. W. Wheeler, of the Petro Oil and Gas Co., is working out inter- esting structural conditions which led to the discovery of the new Wamac Oil pool, near Centralia, in western Illinois.

The U. S. Geological Survey reports that the World’s production of

graphite for 1920 was less than for any year since 1902. The abnormal

Scientific Notes And News.

demand during the war period resulted in overproduction of graphite in 1917. This surplus has tended to reduce the price per ton of graphite throughout the world and especially in Madagascar where the supply on hand was greatest. The result is that a general depression in the graphite industry has been felt in Europe, the United States and Canada.

At the annual meeting of the Engineers’ Society of Western Penn- sylvania, held on March 21st, Roswell H. Johnson gave a paper on the Appraisal of Oil and Gas Properties, and Paul ‘Ruedemann presented a paper on the Application of Appraisal Methods to Rate Making, Federal Taxation and Commercial Purposes.

The Geological Society of America will hold its next annual meetings at Ann Arbor, Mich., Dec. 28-30, 1922. The Geological, Society of America presents the following names for officers of the Society for 1923: for President, David White; for Vice-Presidents, William A. Hobbes, William H. Emmons, T. Wayland Vaughan (from the Pale- ontological Society), and Edgar T. Wherry (from the Mineralogical So- ciety of America); for Secretary, Charles P. Berkey; for Treasurer, Edward Mathews; for Editor, Joseph Stanley-Brown; for Councilors 1923-1925, Edmund Otis Hovey, Alfred H. Brooks.

The seventh annual meeting of the American Association of Petro- leum Geologists was held in Oklahoma City on March 9, 10 and 11. The following papers were presented: C. W. Shannon, Pre-Pennsyl- vanian Rocks Encountered in Wells in Okla.; A Geologic Map of Okla.; Besse Mills, Percentage of Square Mile Production in Okla.; C. M. Bennett, A New Geological Survey; E. Bloesch, Remarks on Sub-Surface Contouring; H. Fukuda, The Relative Role of Strike, Streak and Faults in Determining the Long Axis of the Osage Pool; B. Hartley, Relation of Structure to Oil and Gas in Northeastern Osage, Okla.; R. S. McFarland, Structure of the Burbank Pool, Osage County, Okla.; R. H. Johnson, A Standard Persistence Index and Coefficient of Per- sistence for Oil Well Decline Curves; R. H. Johnson and W. H. Osgood, The Mechanical Error in Constructing Decline Curves on Logarithmic Paper; P. Reudemann, Some Graphic Methods of Appraising Oil Wells; P. Reudemann and I. I. Gardescu, Estimating Reserves of Natural Gas Wells by Relationship of Production to Closed Pressure; F. A. Edson, Diamond Drilling for Production; R. D. Longyear, The Diamond Drill in Oil Ex- ploration; F. L. Aurin and G. C. Clark, The Lower Permian of Northern Okla.; S. Powers, Age of the Oil-Bearing Sands of Southern Okla.; R. D. Reed, Some Suggestions’ in Regard to Pennsylvanian Paleogeography in the Henryetta District; J. V. Howell, Some Notes on the Lithology of the Pre-Permian Paleozoics of the Wichita Mountain Region, Okla.; L.

Scientific Notes And News.

English, A. Meyer, and R. Denison, Robberson Oil Field; C. T. Lupton, W. Lee, and B. R. Van Burgh, Oil Possibilities of Western Kansas; E. F. Shea, Water Conditions in the Urchel Pool, Kansas; A. C. Trow- bridge, Tertiary Stratigraphy in the Lower Rio Grande Region of South- west Texas; J. Y. Snyder, Three Unmapped Salt Domes in the Black Lake Area of Red River, Natchitoches and Winn Parishes, Louisiana; J. P. D. Hull, L. P. Teas, and W. C. Spooner, Status of Development of Oil and Gas Pools in North Louisiana Territory; A. F. Crider, The Eldorado, Arkansas, Structure and its Relation to Producing Areas in Northern Louisiana; H. D. Easton, The Possibilities of Mississippi as an Oil Producing State; R. C. Moore, Stratigraphy of a Part of Southern Utah; M. W. Ball, The Oil Possibilities of the Tertiary of Utah; R. A. Wilson, The Relation of Geologic Features of South Dakota to Petro- leum Possibilities; E. M. Spieker, Petroleum Geology of a Part of Western Peace River District, British Columbia; G. C. Martin, Natural Coal Tar Mistaken for Oil Residue; A. R. Castile, A Recent Fissure near Terrill, Texas; F. G. Clapp, Oil Possibilities in China; J. H. Gardner, Epiclinal Distortion; J. W. Bostick, The Importance of Microscopic Work on Well-Cuttings; V. V. Waite, Microscopic Study as an Aid to Shooting Dry Holes into Production; L. G. Huntley, Geological Features Illustrated by Models; B. K. Stroud, The Necessity for Engineering in Developing Oil and Gas Properties; M. J. Mann, Restatement of the Hydraulic Theory of Oil and Gas Accumulation; W. R. Jillson, Deple- tion of Kentucky Crude Oils; V. E. Monnett, Topographical Criteria for Oil Structures; L. Franklin, A Preliminary Study on the Recovery of Oil by Sinking Shafts and Driving Galleries; W. C. Thompson, The Midway Limestone of Northeast Texas; S. Weidman, Source of the Red Color of the Permo-Carboniferous Red Beds; J. L. Ferguson, The Oil Boom at Spokane, Washington; W. T. Thom, Jr., The Relation of Deep- seated Faults to Surface Structural Features of Central Montana.