Information Circular 6186: Mining Methods and Costs, Alaska Juneau Gold Mining Company, Juneau, Alaska
Information Circular 6186: Mining Methods and Costs, Alaska Juneau Gold Mining Company, Juneau, Alaska by United States Department of Commerce Bureau of…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.
CiRCULAR 6186 OctTosBer, 1929
<tygo DEPARTMENT OF COMMERCE 4 aS eit” Er ee: c. ar’ of -- UNITED STATES BUREAU OF MINES yor gsh Scott TURNER, DIRECTOR ee i ——— oa,
Information Circular
MINING METHODS AND COSTS ALASKA JUNEAU GOLD MINING COMPANY, JUNEAU, ALASKA
By
P. R. Bradley
w Go gle UNIVERSITY C FM NNESOTA
Circular No.6186. Octobcr, 1929, INFORMATION CIRCULAR
Department Of Commerce Bureau Of Mines
MINING, METHODS AND costs. ALASKA JUNEAU GOLD MINING CO., JUNEAU, “Araseal -.
By &. R. Bradley“
“DyTRODUCTION tg -
This paper is one of a ‘series, dealing with mining mechoas on oe sponsored and oublished by the U. S. Bureau of Mines, Papers of this series are written by engineers and executives of mining companies, at the solici- tation of the Bureau, and in accordance with an outline prepared by Bureau engineers, for the purpose of . pace ear op esenray ale and conformable - data. - — , ’
The sees of the Alaska Juneau Gold Mining .Co. is situnated.near the city of Juneau, Alaska, in what is known as the Harris mining district. Whole- Sale mining operations have teen adopted on ‘a large 'scale .and:10,000 to 41,000 tons per day of gold-bearing ore are mined and ‘sent .to concentrators near. Juneau. In addition to gold, the ore Yields 0.6 ounce of silver and 13.0 pounds of lead to each ounce OS eon8 recovered.
Acknowledgments:
This paper is;a comilation and revision of an article by the author Which was published in the Transactions of the. American Institute of Mining and Metallurgical Engineers, -volume 72, and of an article by Joseph A. Williams, engineer of the company, which was published in the Explosive Engineer for November, 1926,
HISTORY OF THE DISTRICT Gold was first discovered in the district in 1650, and mining might be Said to have been continuous since that date. During the late eighties there
was a substantial production from DRoCeE work and from mumerous small mills of various types. . .
a
1 Tke Bureau of. Mines will welcome reprinting ‘of this paper provided tie fol- lowing footnote acknowledgment is used: "Reprinted from U. S. Byreau of Mines Information Circular 6186."
2 One ‘of the consulting engineers, U. 8. Bureau of Wines. “Consulting engi- neer, ‘Alaska Juneau. Gold Mining Co. se Se .
6477 ee
Inf .Car.Noe6186.
Spencer shows that the carly mills were:
Arrastres in the period to 1661 Ba oes oe A 5-stamp mill in 1682, Regia Pk ane A "newly devised grinding mill! in 1584, Two Huatington mills in 1586. A 10-stamp mill in-1889,. & see A revolving Dodge mill in 1890. A 5-stamp mill in 1891. Stee A 20-stamp mill in 1893. oo
In 1896 the owners of the iis ska Tens au property, having been encour- aged by results obtained from their own 5-stamp mill, as well as by results of neighboring operations, built a 30-stamp mill. In 1898 the Ebner Co. built a 15-stamp mill, and in 1907-08 the Perseverance Go. built a 100-stamp mill. These mills, which had been pioneered by the smaller mills preceding them, in their turn pioneered the later: ia amas in. the scale of operation that lead to PECSEnEr ~day pacha Ces er
Dyring the first ents years ‘of “Alaska Juneau operations the small mills were operated both: for conmercial and: for experimental purposes. At the same time a close study vas made of all local conditions and problems, and valuable economic and technical data were ores The conclusions obtained therefrom may be sueyreoo as’ follows’. -
le The Juneau gold belt is an integral portion of the coast range form- ations, and is of great length, variable width, and of irregular and erratic mineralization. a eg : A . :
&.e The belt itself is composed of slate and similar sedimentaries with intrusions of metagabbro.e a ee
The pene ae aire’: into bands of poor definitions
4, In the vicinity. of Juneau the various ‘bands converge to a limited width, become better defined, and constitute a broad lode.
Se The gold in the nee is due to the presence of quartze
6. The broad lode in the Juneau vicinity contains an enormous tonnage of low-grade Ore. 3
Te This grade of ore could be mined and milled at a commercial profit when operating on a large-scale all-year basis.
8. Large-scale all—year operations demand low-cost underground mining, Sea-level mills,.and a continuous supply of cheap powers
Climatic: and other conditions rendered all-year operations impossible at the high altitudes where the various’ early mills were situated. Therefore the proposal to change from seasonal water-power operation to all-year operation
involved the driving of low adit-level outlets from the mines to suitable mill a
é
6477 —-2-
Inf .Cir.No.6136.
sites.on the beach, these adits servine at the same time to tap the ore at depths aS much as 2,000 feet below the surface. ;
the first deep-level adit on the Alas’a Juneau. property was planned in 1896 ond started in 1699, brt it was not definitely arranged for until 1910. In that vear F. W. Bradley entcred into a contract with the Alaska Jutieau Co. whereby he was to drive a tunnel 420 fect above sen level for a distance of 6,500 feet to a point beneath ‘ths surface workings, and then to raise 800 feet to tne surface. Tris work started in 1911 and was comleted in about tivo years. In 1913-14 the Alaska Juicau Co. built a 50-stamp viiot mill on the hillside near Juneou, and in 1916 a rev mill was built, with a rated capacity of 8,000 tons per day; but, owing to the failure of some experimental features, the actual capacity of the mill proved to te less vehnan 4,000 tons per day. The milling costs proved to te about four times higher than the average milling costs in the district. a oo ua
The Juneau goid belt lies between the @iorite core of the coast range
mountains and the grsenstone and chloritic schists on the northeastern shore
of tne Gastineau Channel. The rocks occupying this interval consist of sedi- ments and their variovs derivatives, with irregular intrusions of metagaboro. ‘The sediments heave been folded, intensively plicated, and subjected to the com- pression that develoncd th: slaty cleavage. This cieavags is generally coin-. cident with inc stri-c but not with the dip. The rocks making up the sediment- ary scries coucist o, phyllite gray slates, granitic slates, laminated quart- gites, and sericitic schists. The metagabbro intrusions are fairly abundant ‘in the slates, and extend. to a lesser degree into the schists and See cus Oeen vane occur in ae four of s ills, small EagcOnstan and dylces.
Gold occurs chiefly, if not holly, a quartz stringers sna gash veins in the slate and metagabbro. .The quartz is irregular in form:and disposition, following the strike of the slate cleavage’ in a general way, but has a slightly
Strinces lodes. usually near the slate and gabhao contacts are found in a zone from 1,000 to 2,000 feet wide. These lodes are made-up of a network of quertz veinlets and tsolated Lenses varying in width from less. than I inch to 3 or 4 feet. The higher-~grade ore bands are not. over 300 feet wide, oe the lower-grade material between them varies from to 100 feet.
Cleen quartz will average $6 per ton within the areas of commercial ore wnile the rocl: outside of the quartz stringers is practically worthless. Out- side the commercial ore zone there is an Se erases of quartz carrying little or no gold. :
The gold itself is erratically distributed and of wide variation in size. The size of gold ranges from nuggets with a maximum dimension of 0.75 inches,.
as
to the finest dust.
6477 - Om
Trt Cir. No 06156 e
Associate minerals are galena, spHalerite, pyrrhotite, and pyrite. Galena and Sphalerite are usually highly aurifecrous; the pyrrhotite will assay about p6 pcr ton and the pyrite less. The run-of-mine ore avernses about 90 cents a
Exploration, Sampling, And Estizmlation Of Tonnages And Values
Preliminary knowledge of the charactor, extent, ond value of the ore de- posits was gained by the early operations in the district, the gradual expansion of which had a most importent Bearing on present-day operations. This is true to the extent that each succussive step in the progress was the result of the preceding step and the fin:l overations of the Alaska Juneau Gold Mining Co. were based on an accumulated fund of information rather than on a systematically de- veloped tonnaze of which the assay value had been determined by any of the hand- Semling practices commonly in use.
Theoretically, it shold be possible t:, hand-somyling to determine the average assay value of any gold ore, but on theduneca gold belt the gold is un- usually coarse for lode gold, its distribution in the quartz is erratic, and the quartz itself is irreczularly disposed througout the ore-bodies. Therefore, it is a dirficult problem to determine in advence, ty any. system of hand-sampling, the average gold content of these ores. Furthermore, the development work done in any one of the mines on tne belt, in advance of milling operations, wns not suf- ficient to permit a reliable determination of average assay values by hand- Sampling metnous exclusively.
Tho average assay value of the ore milled during the history of the Alaska Juncau mine is 39 cents per ton, but many samples taken from within stop- ing areas exceed this average by sevcral thousand per cent. <Any practical method of hand-sampling this ore will vroduce such a great variation of values.
Systematic channel-sampling in the Alaska Juneau. mine is considered an unnecessary expense and is not nov practiced.. The value of ground not already known through actual mining is gained by grab samples taken from tho-muck during the progress of development work. The assay results of such samples are inter- preted in light of experience and lmowledge of the ground. The chief purpose of sampling in the Alaska Juncau mine at all is to determine the grade of what is known to the miner's eye to-te ore, and to make a permanent record of the information. The results obtained by this method of sampling, or any other method, determine the high or low value of what the experienced eye already knows to be ore.
Final knowledge as to the value of the ore in the Alaska Juneau mine has been derived from muck samples, moil samples, and mill returns; in addition to the mill returns from normal operations, many tests have been made, not only on ore from various parts of the mine, but also from bands interveining between ore bands, and fromwaste. The conclusions arrived at have been supported by actual returns.
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Inf .Cir.No.6186, SELECTION OF STOPING METHOD
As previously sta ated, the Juneau gold belt is: ‘divided into ore bands of poor definition. The most easterly workings on the belt, those of the Alaska Gastineau Co.,. disclosed three separate ‘bands: The footwall or Ground- hog band, 70 feet wide; the Perseverence band on which the recent mining vas done, also 70 feet wide; and the No. 2 band, 100 feet wide. These bands, © aggregating 240 fect are found over width of 2,000 feet. Going toward the © west into the adjoining Alaska Juneau ground, four bands have been found which have a total right-angle thicl:ness of 755 feet. These bands. are convergent in their westerly trend. and terminate on the planc of Silver Bow fault.’ The four bands have better, definition at the fault plano than at the eastemm boundary line where they enter the property. Along the property line, the width of the bands and intervening country is 1,600 feet, and at the Silver Bow fault this
width is reduced to 1,300 feet. Me distance from the eastern property line
to Silver Bow fault is 2,400 feet. The bands are slate or Slate with metagab- bro intrusions, together with gold-bearing quartz masses, stringers, and ‘gash veins. The bands themselves are not all ore, but all ‘comercial ore is found within the vands. They have no uniform width either in horizontal or vertical section. The ore has no hard and fast boundary except where cut: by faults, and profitable mining ceases on a vague and indefinite line where the aurifer-_ ous stringers and gash veins become too fev.
The throw of Silver Bow fault was downward and westerly, the components of motion being about equal, and the apparent horizontal displacement is about 2,000 feet, ‘Being later than all the rocks and later than the ore, the fault has had the effect of dividing the mine into two parts. The occurrence of the ore bands on the eastern side of the fault has already been described. On the western side there apoarently has been a coalescence of the bands without the identity. of any one band being pronounced, unless it is the footwall or Nugget Gulch band.
For ining purposes a band can be considered as a definite channel of values, but actually this is not the case; the distribution of values through- out each channel or band if ‘byno means uniform. There is an abundance of evi- dence to this effect in all the mines on the belt, and the irregularity of values extends both vertically and horizontally. No general law has made itself evident; that is to say, there is no system of repeated ore bodies with- in the bands, no arrangenent of ‘horizons of characteristic leanness or rich- — ness, and no eeeee! of any kind that will indicate that a certain unknown part of a band will be good, bad, or indifferent. Some bands are known to be better than others, and parts of the same band are definitely lmnown to vary greatly in gold content. The gold values may diminish and the amount of quartz remain the same; but, as a general rule, quartz that is gold-bearing contains sulphides of lead, zinc and iron, and couversely the abserice of these sulphides denotes an absence of gold in the quartz, and marks it as low grade. Hence an intimate acquaintance will enable the eye to distinguish between payable areas and those. not payable.
the selection of a ‘mining method for the mines on the belt resolves
itself immediately into consideration of (1) selective mining, and (2) whole- sale mining.
Inf .Cyr.No.6186.
Selective Mining, - Small-scale selective mining on the Juneau gold belt has been tried in a number of instances, and.whereaS some of the enterprises have operated at a small, vrofit, none has been a commercial success, Larg:-Scale se- lective mining means a large number of Small stopes or a Smalier numter of large stopes;.in either case, stope control is necessary in order to avoid dilution. The result, however,, wi’l be and has ee failure, for the reason that control means prohibitive nna sHe costs, : 5
Wholesale ee Wholesale mining has ee be euea entirely in. terms of the effects of dilution, for no low-cost system can be worked without this inevitable result. Due consideration must be given to the amount of dilution, its effect on the mill feed, and what means, if any, can be used to overcome this effect. In order to determine the effect of dilution on the value of the ore mined, it is necessary toa know the value of the ore and the value and amount of dilution. Knowledge as to the value of the ore in the Alaska: Juneau mine has been derived. from muck samples, moil Samples, and mill returns; in addition .to the mill returns from-normal operations, many tests have been made, not only on ore from various parts of the mine but also from bands intervening betteen ore bands, and from. waste. All this accumlation of data is sufficient for. the de- termination of ore values, and the conclusions arrived at are supported by actual returns; the mill feed and mill returns have confirmed absolutely wnat all..data indicated.
In the Seino: hiases Gastineau esents the mine and mill operations were based on two assumptions: (1) That the ore bands were "continuous and uni- form’ and (2) that by a modified caving system of mining the stopes could be. con- fined to a single ore band. Neither of these assumptions were correct, and the combined effect of irregularly distributed values and inclusions of low-grade ma-— terial and waste reduced the mill feed so that the recovery instead of being $1.5 per ton, as estimated, was but 82 cents per ton, 7 cents of which was in silver and lead values.
The caving system adopted for mining the Alaska Juneau ore accepted dilu- tion, and the new mill has been so rebuilt as to avoid having an excess of waste rock submitted to the process of fine grinding at an excessive ball mill cost of 40 cents per ton. The elimination of waste is accomplished by sorting the ore from the waste at advantageous points in the mill; 53 per cent of the rock tram- med is rejected, and the remaining 47 per cent is fine-milled. The cost of sort- ing and disposing of waste is abomt oOcents per ton trommed and the final mill feed has nearly twice the assay ‘value ef the ore trammed,. 7
In deve lopine the mining system finally adopted, due consideration was Given to all physical conditions surrounding the ore todies. Full advantage was taken of the fault system, consisting chiefly of Silver Bow fault, and Nugget Creek fault, and a number of subparallel sympathetic faults, all being post- mineral, Silver Bow fault cuts the ore at a horizontal angle of 539, completely Severs all the ore bands, and divides the mine into two parts, locally called the "north half" of the mine and the "south half" of the mine. Nugget Gulch is a strike fault and for all practical purposes is the marker for the footwall of
tne ore; its dip varies from 55 to 60°. On each fault plant there is a consider- able amount of fault odreccia which sloughs away readily when underaut, The sys- tem as finally vorked out consists of;
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(1) Cutting out stopes cf larse arez., so located that the fortvall of the Stope is one of the faults.
(2) Driving raises from the back of the cut-out stope area, through to the next two levels above.
(3) Driving nemerous powder drifts Jrom and radial to these raises.
(4) Provision of bulldozing chambers for drawing ore out of the stopes into the loading chute, Figure l.
The system of mining is caving forced vy firing charges in powder drifts located over the back of the stopes. In preparing a Stope, two parallel drifts - 40 feet apart are advanced “ander the ground to be caved. From these loading drifts chute raises are extended 50 feet above to an intermediate level, where the ore is to be drawn from the stope through bulldozing chambers. From the vulldozing chambers a cut-out raise at 38° is driven toward the hanging wall on one Side and to the footwall on the other side; these tyro are then connected by a back cut-out raise from each. The undercutting then begins by worlting from these raises; one raise serves aS a manvay in cutting out the rest in a receding MANNEY Pillars, which between stopes are 80 feet wide, are left wherever necded,
addition semmorary pillars are frequently used to susport a weak roof dur- ing cutting-out work: these temporary pi’lars are shot out just before the stope is brought into production. While the undercutting is being done, stope raises about 100 feet apart are driven to the level above. The upper level is then used as a suooly level and for means of access to the powder drifts below. From these raises powder drifts are driven radially, usually being about 40 feet long with not over 50 fect of burden. When the area is completely undercut, blasting be- gins and the rock is drawn through the milldozing chambers into the chutes below. It. has been found by exserience the t to produce the best results from powder drift blasting and caving, the stope should have a horizontal cut-out area of not less than 50,000 eae feet. Figures 2a, 2b, and aCe
On the averags, 12,000 feet of tynneling and raising and 46,000 square feet of undercutting are Bonipleves in one year. No tinher is required, as the wor is in either medium hard slates or dense gabbro.
STOPING Powder Drift ost Powder drifts or coyote noles are driven fron
stope raises out over the back of the stope; they are 4 by S feet in section on a zrade of about 10°to facikitate mucking operations. These drifts are seldom over oO feet long; where they exc2ed this lersth, the first half is made big enough for a wacelbarrov. The muck from the last tvo rounds is left in tho bottom as stemnine for the powder charge. Ti.e nature of the ground, the dis- tance the rock Will have to fall, and the position of the rowder piles in rela- tion to the boundaries of the stope are the sain factors in determining the burden and the charge of exnlosives. Tice average depth of ground placed on a powder drift is 35 feet; this wovla recuire an average charee of 4,000 nounds of 40 per cent dynamite placed in two piles 35 or 40 feet apart. Three or four or even five such piles meke uy an ordinary blast. As a rile only one series of powder drifts on the same level in anyone Stone is blasted at a time,
Tie powder, a 1-1/4 ty € inch 40 pez cont ammonia dynamite, is taker from the cases at a convenient place, usually at the top of the stope raise, and transTerred to canvas pacir-sacks in which it is carricd down the raise to the mouth of the powder drift. Here the sack is made fast to the middle of a long rope and hauled into the face on a wooden slide; the emmty sacks are returned
in the same manner. The cartridges are pactzed tightly against: the solid rock, care being taken beforehand to remove all loose material. Prior to the pee tion of loading, double-countered Cordeau-Bickford detonating fuse is laid from pile to pile; each pile is then tamped for about. 15 feet with fine rock stemminz.
In some of the smaller blasts when the location. is favorable, the load- ing, tamping, and blasting are finished in one shift, but for all large blasts these operations require two shifts.
- The Bickford fuse is detonated by No. 8 blasting cans and two 30 foot lengths of single tape safety fuse. The fuse is spit in going off shift, and immediately after the shot the blast doors are closed. Enough broken ore is kept in the stopes to prevent any ill effects from air blasts due to caving; there has not vet been any trouble from this source.
Up to the end of 1928, 313 blasts have been made using a 632,959 younds of dynamite and averaging 20 tons of ore brotxen by each pound of explosive. In stopes and pits, where the blasting is not accompanied by caving, 5.56 tons are broken by a pound of explosive.
Bulldozing. - Bulldozing is the local name applied to the operation of delivering ore from the stope through the grizzly into the loading chute. The rock comes on to the grizzly through a raise called the draw, which slopes at , 880 from the horizontal. Here tne large ieces are blockholed with a Sullivan DP-33 drill using 7/8-inch hexagonal hollow steel. The holes are loaded with 1-1/4 ty 8 inch 40 per cent ammonia dynamite and blasted with No. 6 caps, on o-foot fuse; no stemming is provided. Mudcapping is resorted to only when the boulder can not be drilled with safety and then the charge is limited to three cartridges of explosive. Before firing, the "bulldozer" warns his neighbors and turns on an air jet which acts as a warning to those at the loading chute below if the chute is empty. When a big rock hangs up in the raise above the grizzly so that it can not be barred down it is left for the "bulldoze toss" to handle. If he considers it safe, the rock is drilled with a CC-11 Ingersoll Stoper; otherwise it is brought.down with powder charges on long blasting poles.
The grizzly bars formerly were 12 by 14 inch fir timbers strengthened with 100-pornd rails. For the last three years, however, a standard 15-inch 104—nound H beam 16 feet long has been satisfactorily used. The wide flange is stiffened by cast-iron fillers spaced 4. feet on each of the center grizzlies and on the inside of the side beams. A 13-inch channel inverted is riveted to the top; besides adding strength, this channel also makes the spacing between beams less at the top than at the bottom, which desirable. The opening be- tween the girders is 25 inches, Figures 4 ond
The beams slope 1-1/4 inches a foot aoa 6°) and are set on concrete foundations with the lower ends butting against solid rock. Wooden blocking, to maintain ‘the syacing, is wedged in between beams at both ends, U,gually the center girder, which gets most of the wear, will handle 47,000 tons of rock
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Inf .C,r.No.6186.
before it needs replacing. Often a worn center beam will still do for a side, or if bent too badly it can be cut into wearing plates for the loading chutes,
When the back of the drawhole from the stope wears so that rock drops vertically onto the grizzly, the beams are reset in a position which is rela- tively higher and farther away-from the opening. The bottom of the draw then fills in with fine material up to the angle of repose and the drawhole becomes as good as new, The nature of the ground has a great deal to do with how soon this grizzly charge is necessary; experience shows that over 250,000 tons are handled before the change is needed.
The amount of powder for secondary breaking varies with the age of the stope and the nature of the ground. During the first year of operation of a new stope in hard, tough rock, 2.85 tons of rock per pound. of powder is not umusual, while in. the older slate stopes 5.26 tons per pound is ordinary. The average is
4,54 tons a pound of explosive as
Explosives
Two days sueuie of powder is ee in the underground magazine. On the surface two miles from the mine, 3,000 cases are always stored in a non-heated, bullet, weather, and fire proof magazine. This magazine, located in compliance with the American Table of Distances, is constructed of weak cement mortar ac- cording to the recommendations of the Institute of Makers of Explosives.
Of the total powder consumption 13 per cent is used in development head- ings and stope preparatory work; 16 per cent in stoping (the blasting of powder drifts), and 71 per cent in secondary breaking or block haling, commonly called bulldozing. All drilling and blasting operations fall into one of these three large groups.
Underground Transportation
After passing the grizzly, the ore falls into chute raises which hold 200 tons of ore each. From these raises it is drawn through the chutes, which are equipped with an underslung arc-type gates, into the cars. The chute open- ing is 6 feet long by 3 feet high. The bulldozing chambers and chutes are spaced on 42-foot centers so that when a train is in the loading drift, every third car is under a chute, Figures 5 and 6.
A 10~ton flat-bottoned box car is aged in main haulage levels, and a 50-inch gauge track of 50-pound steel rail is used throughout the mine, except where a 40~pound rail is used for sidings.
The overhead trolley system is used in the haulage level and the ore is trammed to mill. 2 miles distant in trains of 44 cars each by 18-ton articu- lated Baldwin Westinghouse locomotives.
Storage—battery locomotives are used for development in advance of main jaulage work and also on the upper Tevels.
Inf .C3r.No.6186,
No mechanical mucking machines are used in the mine and there is 2rac- tically no hand-tranmming except in the. small. coyote drifts where wheelbarrows are sometimes eguaece es Eats hich : oe longer than the’ averag feo
Podee. is spre mee fron eo sais Joneau'Co.'s inydroclectric ee ee There is also a standby steam unit which is used only in cases of emergency or water shortage. The cost Bee kw.h. for 1928 was .00439,
fg 28 PERCENTAGE OF . EXTRACTION
“It is yet bee oa to Seice the euueenease of extenctiean ‘but a total extraction is expected in the northern half of the ore body plus-a slight dilu- tion from the lower—grade wall rock. A small loss ts expected on the . southern © ore body because of the pyramidal sections ‘between. the: cone-shaped stopes which ° it may not be sconomical to undercut and cave. This loss, plus the dilution, was calculated before Sonne cen of Sper aeaOues a
No. sorting or selective mining is attempted underground. Approximately o3 per cent of all ore is discarded in the mill: by hand and mechanical devices DenorS it is sent to the fine-grindiag department, i
a ae “DETAILS OF DEVELOPMENT
: The varieus sizes of opéenines are! aulag> tunnels, 9 by 9 feet, main levels, 7 by 7 feet; intermediate levels, 7 by 5 fcet; powder drifts, 4+ by 3 feet; oreway raises, 7 by 9 feets:cut Bue raises, 6 by 6 feet; stope raises, 5 by 5 feet; and stope cut out, 7 feet high. 3 eg :
Machines in use on tis: qork: are the medium weight wet Leyner a drifters, using the anvil block, and medium weight, hand-rotated stopers. The Leyner drill is used for cll work ‘except that in small, steep raises. The steel used is 1-1/8-inch hexagonal, hollow for drifters and 1-1/4-inch cruciform and l-inch quarter. octagon for stopers. The: standard cross bit with single 14~1/2° taper is employed with 1/4-inch SADR ES in gauge for eacn 20-inch: change in ies )
Rounds are drilled with from 8 to 24 si neer ei ance over 6~1/2 feet long. The center yramid cut is: customary and is blasted first, then the rest of the round is loaded and blasted. A 40 ver cent axmionia dynamite in a 1-1/4 by 8 inch cartridge has been adopted for all work; no stemming-is provided. No. - & blasting caps*and single tape safety fuse constitute the detonating agents. The average advance on all headings is 2.64 feet a machine a shift. In stope cut out work the average aren covered during each machine shift is 38.54 square feet; mz 118 area is taken out toa height - a a aes ,
Wage ,’ Contract Nd Bows Systems Employed
Bylldozing, loading, and ere and ‘all mine development as well as preparatory mining work, is done by contract. The wages paid out to the con- tractor and his laborers amounts to‘ 75 per cent of the total underground payroll. Briefly mentioned, some of the features that have made the contract system suc cessful, are:
6477 - 10 -
—
The guarantee of a acaicoaedi tal ia for contractor and mene
The division of all excess earnings or bonus after a certain stipulated amount among contractor and contractor's employees, Share and Share alike, in accordance with the number of shifts worked. —
The close supervision of work and the prompt adjustment of price when justified by changed conditions.
Tne careful selection of men for contractors, and the prompt elimination of such contractors as are unable e earn more than Bade wages at a reasonable contract price.
The withholding of a small amount of carnings as retained pay. This is usually retained when contractors! earnings are good. This retained pay may be forfeited by the contractors for unsatisfactory work or failure to complete the contract satisfactorily. I, has seldom been recessary to forfeit the contractors! retained pay on ‘account of poor work.
The furnishing of ood equipment and its ‘maintenance in good condition, with plenty of steel and good air pressure.
Maintaining the same price for explosives regardless of market change.
The inélusion of two or more working faces. in the same contract whenever practicable to obtain more nearly average drilling and breaking conditions.
The bulldozing and tramming contract as handled at present guarantees a good base wage to contractor and men, with a graduated bonus to all when ton~ nage exceeds a certain amount. This contract is really more of a bonus system than a contract, but. the working conditions are such, and so many men working in different parts of the mine are included in this contract, that it is not ‘practicable to make it as firm a contract as in.the case of development work.
In connection with and on account of the other contract and bonus work, the company >ays a bonus to all employees who are not in the development or bulldozing and tramming contracts. This bonus is based on tons ner man per day and payable on the twentieth of the month to employees who worked 26 days in the preceding month. It has been necessary to adjust the bonue rate from time to time owing to changed conditions. This bonus is based on the theory: that at those times of the year when help is searce and the plant may be somewhat under- manned, the employees who do ‘stay will automatically receive an increase in pay.
Outline Of Early Mine-Development Contracts
Gold Creck tunnel was started in August, 1911, and finished in August, 1913, during which time it-was driven 6,538 feet. The tunnel was driven 9 feet nigh and 7 feet wide at a total cost of $20.49 per coe
For the first few months , straight daily wages were sata the men. How- ever, in January, 1912, a bonus was added Which for several months amounted to $3.50 per shift per man.
6477 bie
‘Inf Cir.No.6186.
She bonus system was as follows: The month was divided into three periods on which bonus was paid; only those men who worked during a corplete period were entitled to the bonus earned during that period. The bonus started at 150 feet at the rate of $5 for every foot over 180 up to and including 240 feet. For every foot over 240 feet made during the month, the bonus was $10 per foot. The bonus was prorated among all the men according to the number of shifts worked, The base rates peid in 1912 are as follows;
Per shift Foremen $5.00 Machine men 5200 Machine men helpers. 3,25 Muckers 3200 Blacksmith — 4,50 B. 5. Helper 5200 Trarmers 300:
The driving of 450 Oreway Raise in 1915 was probably the next contract sob in the mine. The first set of contractors made 17 feet and then gave it up. The second group finished the raise for a slightly higher price per foot but made less than wages for themselves. The prices vere as follows:
First set (cancelled) Second set - First 200 ft. - - - - $6.00 per ft. First 100 ft. - - - - $8.50 per ft. c00 300 ft. 6.50 " 1 100: 200 tte So e-. 900° 300 - 400 ft. 7,00 " " 200 - 300 ft. 9,50 " "I A000 560 ft... 2 2d
“oo OM a. 300 - 400 ft. 10.00 " " : 400 - 580 ft. 10.50 " 4
Labor was $4.50 per day, powder $6 per case, and primers 8 cents each.
Two stope raises in 402 Stope were contracted for in August, 1915, for a price of $6.per foot. Then in Ajril, 1916, the south portal of No. 3 Tunnel was driven 9 by 9 feet for a contract price of $9.50 per foot. Up to this time no provisions were made regarding maximum or minimum earnings. In a contract October, 1916, let for the widening of No. 3 Tunnel for $5.50 ner foot a maxi~ mum earning of $250 per month and a guaranteed minimum of $5 per day was agreed upon. The surplus over $250 remained with the comany. Labor at that time was $3.50 per day and powder $7 per Case,
From 1918 to date nearly every: neading has teen advanced by contract work. Up until June, 1922, no maximum rate was providedfor, but at this time it was agreed that anything over $11 per day remained with the company. In November, 1922, it vas provided that the surplus over $11 ver day be divided among the contractor and his men according to the number of shifts workede Up to this time it was customary to deduct 25 per cent of the contractors! earn- ings each month. This was later changed so that the whole amount retained rarely excess $150 per contractor, depending on the length of the jobe
Aware scale without bonus for the various ‘years follows:
5477 -12-
Inf .CirNo.6186,
1915 1918 32920 1922 1924 1926: =1928
Shift boss $5.00 $5.50. $5.50 $5.50 $6.00 $6.50 $ 7.00 Blacksmith 5,00 6.00 5.00 5.00 5.50 5.50. 5450 Steel sharpener - - 4,00 4.50 5 200 2 00 5.00 5 200 500 Timberman - - - - - 4.00 4,50 4.50 5 00 DeLD Deed 5.50 Trackmen - - - - - 3.50 4.00 4.50 4.50 4.50 4.50 4.50 Pipemen - - - - - - 3.50 4.50 4,50 4,50 - 4,50 5.00 5 250 Hoistmen - - - - - 3.50 - 4.00 4.00 4.00 4,00 4.50 4.50 Machinemen 3.50 4.50 — 5.00. 5.00 5.00 5.50 5.50 Contr. mucker - - - 3.00 ° 4.50 4,50 4.50 5,00 5.00 5.00 Laborer 3.00 3.50 4,00 . 4.25 4,00- 4,00- 4,00- Bulldozer - - - - - 4.50° ~5.00 — 5,00 5.25 5.25 6.00. 4,00 4,25 4.50 4.75 4,75 5.00.
Present Mene-Development Contracts
Contract work in mine development such as driving a 500-foot drift is handled in the following manner; A call for bids on the work may be posted, the company reserving the right to reject any or all bids. When a bid. is finally accepted, a contract is drawn up and signed by both parties. The price per foot may be the same for the whole distance, or it may increase every So often as the distance from the face to the dump increases. The general nature of the ground is usuolly known, For short nieces of work bids are not always called pore but a certain miner is chosen and a nrice is sete 3
The contract price is so much a linear foot; out of this amount the con- tractor pays for his direct labor, including. liability insurance, and for his explosives, The explosives are bought from the company at the rate of $9 a case for powder and 8 cents each for primers,
. The contractors! labor consists of machinemen, muckers, and a steel- nipper. Aside from direct labor and explosives, the company supplies everything, including tools, compressed air, steel, pipe, track, etc. On the average the. contract price for explosives and direct labor amounts to 60 per cent of ‘he total cost of driving headings.
The contract price of headings of the same cross section varies with the hardness of the ground, length, accessibility, ventilation, etc. Wo timber is required, as all work is done in gabbro or medium-hard slates. one prenere prices run as eee
$12.50 to $14.50
Main Haulageways - - - - - - 9x9 ft
Drifts and crosscuts 7x5 ft 7.00 to 8.50 Powder drifts - - -- - - - 4x3ft 5.50 to 6.50 Stope raises - 5x5 fte--- 6.50 to 8.50 Oreway raises 7x7 ft, 10.00 to 12.00
Stope cut-outs which are 7 feet high are also done on contract. The price varies from 35 to 40 cents per square foot slope measurement, Liability
64°77 © 13 -
Inf .Cir.No.61&6,
.insurance is ‘figured at 3 per cent of the total; labor >aid, including the con- tractor himself, who is rated.at $5.50" er day.
It is customary to pring th LB tn tractoys! eariin;ss up to $6 per day advancing the necessary acidunt which? Day be deducted from future eamings. When- ever his earnings per shift exceed $11 the surglus asount is divided between con- tractors and laborers alike “according ‘to the Bale of shifts worked.
H -@
BULLDOZIIG,- LOADING," AND HAULING CONTRACT ) The’ sseeneay. work of - -ore prodiction,. ‘which iheiuaes bulldozing, loading, and hauling; is done by contraet. The’ early contracts were short lived, but in 1919 a new contract-a7as agreed upon which, by modifications made from time to ‘time, has developed into the existing arrangement. The 1919 contract =rovided fora payment of 13 cents per ton of ore tulldozed, loaded, and hauled to the mili, The. Con 1tractors -provided: all labor and explosives, and liability insur- ance; the coz rpansy provided all else,. Hauling was them, and is yet, handled as a subcontract under the main contract. . Cohtractors on bulldozing and loading Were limited to $8 per shift, and ail seir earnings in excess vere prorated anong the men and contractors according to the number of shifts worked; all earnings over $10 per shift for contractors, $7 per snift for bulldozers, 37 ser shift ior chute -yunchers, $5.50 for’ loaders, and 34.75 for. cleanuy men were to be held.as retained pay to be distributed in future months when the eamings fell below the schedule, The subcontractors on tranming were guaranteed $7 ver shift, ond earnings in excess of this amount were to ve divided between the contractors and their men on the basis of shifts forked. It was further provided that men uitting during the month were to be vaid at the base rate of $6 for contractors, $5.25 for bulldozers, and $4.75 for loaders. This provision was incorporated into tne contract as an inducenent for men to stay on the job, as at that time there WaS a Shortage of labor. In 1923 it was agreed-that if at the end of six months there was any retained pay that had not been absorbed in making up defic- lencies as provided for, it would be distributed. armon> all men in the mine work- ing on Straight day's nay and prorated among them on-the tasis of shifts worked; however, to participate in this distribution or toms a man must have worked an average of 26 shifts per month for four months previous to the time of pay- ment. In 1924 the distribution of the bonus was put on a monthly basis, with the same 26 days work,not including overtime, as a qualification, However, any man incapacitated by accident received the bonus for the time he did worl: even though that time was less than 26 days, Men >aid by the day were siven the benefit of the bonus on the theory that they, the timbermen, trackmen, plipemen, etc., by efficient work contributed to the efficiency of the contractors. Later tne timoermen's wages were charged: directly to the contract vecause their work consists chiefly of chute renairs, the amount of wnich depends on the loader*s care in handling chutes. In 1928 the rate for bulldozing, loading, and hauling was increased rrom
13 to 14 cents per ton; and the base wage increased as follows:
for contractors
$7.50 6.25 " chute sunchers 6.00 " bulldozers D200 i" loaders 5 290 ' motormen AS cleanim men 6477 -1]4-
Inf .Cir.No.6136. This. list gives an outline of the alterations in the original contracts made necessary by changing conditions. It also shows how the first contract, all the earnings of which were paid to a few, grew into a bases patents: bonus system for all men emsloyed on the contract.
A great many factors operate to change conditions so that it is neces- Sary to alter the contract from time to time. Some of these factors follow:
The weather affects tne flow of rock in the South ore body. Too rch rain-causes loading troubles, whereas a continued dry spell slows up bulldozing. Occasionally a cold winter will cause muck in low-drawn pits to freeze. North ore body muck generally runs more freely above the grizzly than that fror the South due to its more slaty nature. Rock in 4CO Stone, for instance, could be handled. much more cheaply than South ore. Old stopes are generally more ro- Cuctive than new ones. Gabbro ore does not run as freely as slate ore. In the South ore body with its long oreways below the grizzly the rock becores well broken so that the cars can be loaded to canacity. In the North frequently a car must be loaded light on account of large slabs,
At the end of each month the contract is credited with 14 cents per ton trammed out of the mine. From this amount is taken the cost of explosives and all direct labor, including the contractors, all at base rates. The balance, if any, 16 available for bonus and is divided emong the contractor's entire crew in proportion to a certain maximum bonus rate ;er shift. If after this first bonus has been declared there is still a surplus, it is divided so that every- one, including the contractor, receives the same amount per shift. If the con- tract fails to make wages at buse rates, the amount advanced to enable it to do so may be deducted from ruture earnings. The men who leave during the month are aid at their base rates. -
Explosives. are sold and dgiaiversa Bg the company as follows: 40 per cent Red Cross powder at $9 per case; 3-foot primers with ‘No. 6 Cap at 80-cents each.
Contract 58-A, which is a subcontract for the tra nsportation of ore from the mine to the mill, is charged to contract 100. The trainmen are paid $5 per day and receive a bonus of 50 cents per day Vases contract ay earns a bonus.
‘Liability insurance on contract 100 amounts to 3 per cent of the total labor at base rates, including contract 58-A.s It is charged to the contract Whenever there is a surplus available for bonus, exceeding the insurance by .$1,000. inclusive.
er day, 1925 1928
Bulldoze contractors average carninges
"raeae " Reeaiaar ices mi ed ede Pore cnie Gre a eras boar 1923 $9.10 6,860 7525 1924 9.88 8,476 63.4 1925 9.16 9,618 55.2 1926 8.17 10,579 65,4 1927 8.34 11,790 22,2 1928 7.29 10,243 6.4 6477 Ye
Inf .Cir.No.6186, ©
The contract system has proved highly satisfactory. The men make better wages and the unit costs are less than they would be under straight day's pay. Supervision is reduced to a minimum, and. the inclusion of day's-pay employees into the contracts indirectly, through a share of the earnings, swings them into the contractors! stride. The general result is an esprit de corps and a ecnuine: Ee enOer in the oe on the part. of the mngere oun. crew. 3
ae
The mine is. ventilated by natural draft stimulated in two re by Ventura fans. of 60-inch diameter... Raises and crosscuts are driven solely.for ventilation as required. a
By means of ventilation and blast doors, g2sses from blasting find a ready exit to the surface without.pclluting cther portions of. the mine. The ventilation is so good that after a shot of 200 cases of pouser: one can eeery venture to that locality within eight hours.
FIRE HAZARDS There are practically no fire hazards in the mine. _Timber is used only in the ore chutes and No. 4 main haulage level and in places where ground is heavy because of the promimity of fault plane. As timbers on this level fail a i are being ae by steel sections. .. :
Si ETY METHODS AND 3 FIRST-AID ORGANT ZATION
Bivdiaig. training is considered iasortant by the management, and a first-— class safety enginecr is employed. Local instruction is given to the men in both first-aid and helmet work, and as far as possible the first-aid spirit is in- Stilled into the organization, with the result that the accident rate is excep- tionally low.
FORM OF ADMINISTRATIVE CRGANI ZATION An organization chart is aateiaeds to define the authority and duties of every one in the organization; this chart shows not only lines of authority,
Suu lines of eooperat son as well.
Tyeteevieds from the management to superintendents and foremen or to other members of the staff are usually preceded by a discussion or conference. At such a Son eV ONee the ee in authority should be a leader in thoug oe
As most of the wae is done by contractors, the number of foremen and Shift bosses is reduced to a minimum. During 1928 the total numoer was five per day, or an average of 55-1/2 men underground to one boss.
6477 ee
Inf .Cire:]oe6186.6
Summary Of Ccsts
Tons of ore trammed during period: 3,670,910 Pericd covered: 1928
Mining method: Sublevel caving
Unaerground costs per ton of ore trammed
Labor Power Explosives Other Total Costs Supplies
Development: ; In ore’'- - - |,0375 0035 ,0095 0106 ~=60611
Mining ©0015 . 0000 ! 0069 e005 0090
os a
Transportation - - - - - 0821 ~0035 : 20290 1136 (undersround) !
sel pot yy ap 6477 17
Inf .Cir.No.6186,
Summary Of Mining Costs In Units Of Labor, Power And Supplies
Tons trammed: 3,670,910
Es Es A Ss —
A. Labor (man hours per ton): Underground § All labor charged . crew to mining Development - - 22 2030 048 Stopping - - O01 003 Bulldozing - 064 00835 Tramming + 064 2132 Total 2159 0255 Tons per man per shift - - - - 00.10 40.10 Tons per man per shift on surface Chargeable to underground - - - 75 4 B. Power and supplies: ixplosives, pounds per ton: Development 006 Stoping - 205 Bulldozing 029 Power, kw.h. per ton - - - - - - 1.61 Other supplies in percentage of total supplies and power 48.%
Supplies and power, percentage of total cost --- 19.1%
C. Percentage of Total Cost:
Devel coment. 8.6 ese es 20 5% Mining 79 .41% 100.00% 6477 -1l3-
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