Information Circular 6149: Mining Methods of the Tennessee Copper Company, Ducktown, Tennessee
Information Circular 6149: Mining Methods of the Tennessee Copper Company, Ducktown, Tennessee by United States Department of Commerce Bureau of Mines…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.
Circucar 6149 JUNE, 1929
Information Circular
Department Of Commerce — Bureau Of Mines
Mining Methods Of The Tennessee Copper Company, Ducktown, Tenn.
By
Cc. H. MCNAUGHTON
Circular 6149 June, 1929.
TiWoRMart ot CTROVLAR -F es mEpanes OF — - “URE AY oF ines
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‘MINING METHODS OF THE TENNESSEE COPEER COMPANY, DUCKTOWE., PENNESSEE 1
Pisgah aie ee ‘By C. Ee “Motenghtone
ee 7 "INTRODUCTION, : a The Tennessee nr Co. sueeaee’ two mines in the Dicktown district dur-
ing 1928, The Burra Burra mine is much the larger operation and is the chief source of the ore smelted and treated in thé company's smelter and acid plant at Coppe rhi t1, ‘4,5 miles from Ducktown, This mine operates steadily and furnishes a regular‘ output ‘of : about 40, OOO tons per month, The Eureka mine is operated irregularity. and produces @ much smaller tonnage of high-sulpaur ore, the rate of output depending upon the demand for sulphur... During 1928 about: 60 per. cent of the combined output of. these mines was shipped directly to the smelter, and the balance was concentrated pert bay san in ae flotation plant located near the
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ote Be eg a soEIOMLEDEUENTS : The: athe adinobledges the sat stance ‘of Lamar Weaver, Assistant mine ‘superintendent of the Tennessee Copper. Co., and of C. F. Jackson, mining engineer, U. S. Bureau of Mines, in the preparation of this paper. U. S. Geological: Survey Professional Paper 139, ‘by W.°H,-Emmons and F,. 5. Laney, has been dram upon for information contained in’ the: en on history and evoloeS ae
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tee “tn ‘ea? secondary copper. ore “was ; mined from Burra barre lode and gossan ore from the Cherokee mine. Mining. tn. the district has been continuous’ since then except for three. years during the.6ivil War, and from 1877, when the rich secondary ores were exhausted, to 1891' when progress in the metallurgy of copoer and the Completion of the Marietta and North Georgia Railroad from Knoxville to. Atlanta made the treatment of lower-grade’ ores profitable. Up to 1891 there had been a number of small mines in‘the district, operated by {Individual Ccompanies.. The Tennessee Copper Co, w a8 organized in .1899 and acquired by purchase the Burra Burr: london, Boyd, and Chale ote properties and by lease ‘the: Pole County properties.
1 The Bureau of: Mines: will welcome reprinting of this article, but requests that the following footnote acknowledgment be used: "Printed by eral ssion of the Director, U. S. Bureau of Mines. (Not subject to copyright.
2 One of the consulting engineers, U. S. Bureau of Mines.
Inf, Cir. 6149
The smelting plant was built at Copoerhill on the Ocoee River, and a standard- guage railroad was built from Copperhill to Ducktoim with spurs extending to several mines, The works and shaft rere begun in 1899, and the first mining was: done in 1901. Although the company's ores were of lower grade than those pre- viously worked in the. district, the costs were low, In 1903, when this company produced 10,000,000 pounds of copper, the costs wete 8,2 cents per pound,
ee GEOLOGY The rocks of the distpict all belong to the Great Sidney fonmation of Lower Cambrian age and are almost wholly me tamoFpho sed sediments consisting mainl of graywacke with arkose, graywacke conglomerate, conglomerate, mica schist, slat staurolite schist, and garnet schist in the ordéinamed, The ore bodies are described as replacements of a limestone bed thickened in places by thrust folds and by strike faults in the ore bodies,
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ies ve oaks. PHYSICAL OUARACTERISTICS
s a: ieaen ore body: “has a ‘géneral © strike of: ¥. 62 7 and dips 75° SE, at gaefaces ‘flattened. to 50°. ak the sixteenth level with local dips as low as 35°, The oré body eccurs over a length of 2,300 feet oh the fourteenth, level of Burra mine where the mineable thicknéss’ varies’ from a few foet to a maximum of 180 fee’ The plans {fig.'1) show the géneral shape of the ore body on two levels 200 feet apart ‘vertically, and the cross sections (fig, 2) show the irregularities and chaniges.in shape. and dip from the surface to Lower levels,
The imsediate wall rocks are highly metamorphosed wenhges and graywackes the bedding p!.ases of which parallel the..qre.in dip and strike, The schistosity in general, but not always, parallels the bédd@ing. The terdency is to break along bedding planes rather ‘than parallel to the less prominent schistosity, Th Walls in general:may be said to stand well, and spans of 100 feet are usually i exeept whe re the; ground is fractured peceiee of folding.
The ore, itself is enarecteriod by but few stanivent’ slips and joints, which where they do appear are generally horizontal. ‘The spacing of prominent Slips and joints is measured by feet rather than by inches. The ore tends to adhere to the walls instead of breaking to them. It is not self-supporting ove: as long spans as’is the wall.rock, Haulage levels stand without artificial sup in both ore and:wall rock, In.the zone of primary ore; to which mining has beer confined since the present. Company started. operations, the principal ore minera’ are massive sulphides; pyrrhotite, pyrite, and’ chalcopyrite. The ores also con. tain small percentages of.zine in the form of sphalerite, ‘The gangue minerals are chiefly lime-bearing: silicates, quartz, and calcite; with which the sulphid minerals are intergrowm,:.: The ore tends to break ‘im large angular’blocks and sla which wedge in chutes and hang up on flat stopes. For further details regardin the' mineralization, the. reader is referred to U. S. Geological earrey Professio. Paper 139. acai
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Inf. Cir. 6149
The average grade of ore is 1.6 per cent copper, 24 per cent sulphur, and 32 per cent iron. However, there is considerable difference in the grade of the ore in the different sections of the mine. Ore from 16 to 24 per cent sulphur is shipped to the flotation plant for treatment, while that from 24° to 28 per cent sulphur goes directly to the’ blast “furnace. In order to produce the tonnages of the foregoing graces as required by each of the se plants it is necessary.to mine from more stopes than would be needed if only one grade of ore was demanded. This situation also complicates the handling, haulage, and hoisting problems,
Exploration.
Since the ore zone is piacticniiy continuous, ‘eienditen is eetueieaiay by sinking, crosscutting to the ore zone, and drifting on the strike of the ore body. The ore bodies are outlined by crosscutting holes from the exploratory drifts. Long holes are diamond drilled, whereas holes less than 150 feet long are drilled with a deep-hole hammer drill. The last diamond drilling was done by the company with its own equipment and cost $2.50 per: foot. Assay records, diamond- drill cores, and deep~hdle cuttings are filed; aaa file records are practically Complete for more than 20 years.
Sampling And Estimating Reserves
Burra Burra Mine is laid out in 100 foot blocks measured along the strike and from track to track of haulage levels. These blocks are designated by the level, direction, and distance from Burra Burra shaft. Tonnage is estimated by blocks after drifting through them on both levels and crosscutting the four corners with drill holes or drifts. A factor of 8.1 cubic feet per ton, is used in com- puting tonnages. Grab samples are taken twice weekly in the stopes and daily in development headings.. Assays. for copper and sulphur are recorded by blocks and used to control the grade of production. Assay values’ of ore reserves of the en- tire mine are computed yearly. Blocks containing active stopes are given the grade of the last 50 assays from the stopes in these yearly estimates. New blocks are given a weighted average grade based upon development and drill-hole assays.
In practice this method has proved accurate for all practical purposes. :
Development And Mining
The Burra Burra mine is develo ed from two shafts 2,200 feet apart measured along the strike of the lode (fig. 3 and fig. 3B)
The Burra shaft is an inclined shaft sunk in the footwall at an angle 740 30' from the horizontal, At the surface it is 100 feet from the footwall and at the bottom, or.1,600-foot level, it is 650 feet therefrom. The McPherson shaft is avertical shaft starting in the hanging wall at surface, cutting through tne vein at the sixth level, and eens on the sixteenth level at a distance of 650 feet from the footwall,
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ref. Cir, 6149 ie —. . % gfe ee gat
. The Burka shaft is a three commartment shaft 6 feet by uf feet é oe measured inside the timbers, Two compartzents are used for hoisting with skips in balance, and the third compartment serves as.a ladder, pipe, and power-cable . way. - The shaft is timbered with regular shaft sets‘ over most of its length, but: in part of it, where the ground is ospecially strong, only sills and eee are employed for support of the track. : :
The McPherson shaft is 6 feet 6 inches by 16 feet inside of timbers and has three icomoartnents ‘-.t70 for hoisting with cages in balance and the third ‘serving as a ladder, pipe, and cable way.
During 1928 - practice} ly all of the ore "wii hoisted at Burra shaft and the McPherson shaft was:used for.handling supplies aud waste from development work, During 1929 it is planned to equip the McPherson shaft with 4=ton skips and divide the hoisting.of ore. between. this and the Burra say ‘Mort cf ne supplie: will then be handled at Burra shaft,
Levels are opened from these. shafts at vertioal: int ervals of 196 feet. connect the two shafts. Because. of the irregular outline of the ore zone it has been found impracticable to follow either wall with these drifts, and they are driven to make the connect ing distance between shafts as short as possible and at ‘the same time keep them-in ore. These drifts serve for prospecting and are locally termed "exploratory drifts;" parts of them are ‘used later eos neu aee 7masre uae ore body is narrow.
bi There. the exploratory drilling donne a width oe ore s eansodine 40 feet, haulage drifts are afterward driven in the footwall 20 to 30 feet from the ae and are kept asstraight as possible, From these longitudinal exploratory and footwall drifts, crosscuts are then driven to the: hanging wall at 40-foot inter- vals along the strike. . Where. the ‘ore is less than 40 feet wide, the i taeda drifts are widened to the footwall - leaving pillars, however, where neces ssary keep the opening less than 18 feet wide. a
Development
Some years Aas padsed ‘since any shaft ee has ee ae. and no sha Sinking data comparable.with those for other classes of work now being done are evenran ar In recent: years the shafts’ have been he oy raising.: meee 4 x Exploratory drifts and haulage arifts are driven 8 by. 8 feet. Figure 4 ‘--"ghows a drift face and, tne’ standard drill round'employed. ‘Two center holes are drilled straight in but are not blasted. Tyo cut:holes,.1, and two easers, 2, are loaded and shot, using No. 8 caps on fuse. If these holes do not break bott they are reloaded and shot with the rest of the round. The usual round pulls 5 to 5% feet,
As a rule no effort is made to obtdam speed in drifting; experiance has proved that the lowest per-fodt cost of development is obtained by driving at rate of 100.to 140 feet per month. Drilling and blasting are done on the nignt shift by two contractors using two 144-pound Leyner-type drifting machines moun:
Inf. Cir. 6149
The average grade of ore is 1,6 per cent copper, 24 per cent sulphur, and $2 per cent iron. However, there is considerable difference in the grade of the ore in the different sections of the mine. Ore from 16 to 24 per cent sulphur is shipped to the flotation plant for treatment, while that from 24 to 28 per cent sulphur goes directly to.the blast. furnace, In order to produce the tonnages of the foregoing graces as required by each of these plants it is necessary to mine from more stopes than would be needed if only one grade of ore was demanded. This situation also complicates:the handling, haulage, and hoisting problems,
Exploration.
Since the ore zone is.practically contimuous, exploration is principally by sinking, crosscutting to the ore zone, and drifting on the strike of the ore cody. The ore bodies are outlined by crosscutting holes from the exploratory drifts. Long holes are diamond drilled, whereas holes less than 150 feet long are drilled with a deep-hole hammer drill. The last diamond drilling was done by the company with its own.equipment: and cost $2.50 per foot. Assay records, diamond- drill cores, and deep-hole cuttings are tiled; these file records are practically complete for more than 20 years.
SAMPLING AND Bos eeeTeNe RESERVES
‘eee Bere Mine is laid nat me “100 foot blocks aes weared: along the strike and from track to track of haulage levels.. These blocks are designated by the level, direction, and distance’ from Burra:Burra shaft. Tonnage is estimated by blocks after drifting through them on both levels and crosscutting the four corners with drill holes or drifts. factor of 8:1 cubic feet per ton, is used in com- puting tonnages. Grab samples are taken twice weekly in the stopes and daily in development headings. Assays. for copper and sulphur are recorded by blocks and used to control the grade of production. Assay values of ore reserves of the en- tire mine are computed yearly. Blocks containing active stopes are given the grade of the last 50 assays from the stopes in these yearly estimates. New blocks are given a weighted average grade based upon development and drill-hole assays. In practice this method has proved accurate for all practical purposes,
Tevelopment And Mining
The Burra Burra mine is developed from two shafts 2,200 feet apart measured along the strike of the lode (fig. 3 and fig. 3B)
The Burra shaft ia an inclined shaft sunk in the footwall at an angle 74° 30' from the horizontal, At the surface it is 100 feet from the footwall and at the bottom, or 1,600-foot level, it is 650 feet therefrom. The McPherson shaft is a vertical shaft starting in the hanging wall at surface, cutting through the vein at the sixth level, and bottoming on the sixteenth level at a avevence of 650 feet from the footwall.,
6042 7 -3-
Inf. cir. 6149
The Burra are is a three somaaeenent: shaft 6 feet by cE feet: 6 ee measured inside the ‘timbers, .Two comparttents are used for noisting-witn skips. in balance, ana the third compartment’ sétves as a ladder, pipe, and power-cable way. The shaft is-timbered with regular. shaft sets over most of its length, ‘but in part of .it, where the ground is espdclally strong, only sillsand divicers are employed for support of the track,
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The McPherson shaft is 6 feet 6 inches by 16 feet inside of timbers and has three compartments - to for hoisting with cages in balance ‘and the. third crane as a ladder, pipe, and cable way. iS
eer 1928: ‘practicelly all of the ore was hoisted at. Burra shaft and the McPhe rson shaft was used for handling supplies: and waste from development work. During 1929 it’ is planned to:equip the ‘McPherson shaft with: 4-ton skips and divide the hoisting:of vre‘ between this. and the: Burra shart. Most, cf the supplies will then be handled at Burra shaft. me i ee :
Levels are opened ftom these’ shafts at vertical intervals of 196 feet. Crosscuts are driven to the ore zone, and drifts are run therefrom in the ore to connect the two-shafts,:. Because of the irregular outline of the ore zone’ it has been found impracticable to.follow either wall with these drifts, and they. are ¢— . driven'to make the connecting: distance between shafts as short as possible and at the.same time keep'them in:ore, These drifts serve for prospecting and are locally termed "exploratory: drifts," . hom are usc peter for rama where tne ore ow os BAEEOM. ee
There the. axoloreeery drilling engae. a, width of ore exceoding 40 feat, nauiake drifts are afterward: driven in the. footwaitl 20 to 30 feet from the ore and are kept asstraight as possible. From these longitudinal exploratory and footwall drifts, crosscuts are then. driven. to the hanging wall at 40-foot inter- vals along the- strike, Where the ore,is-less than. 40 feet wide, the. exploratory. drifts are widened to the footwall - leaving pitiare, however, where necessary to keep the opening less than 18 feet wide...
seikanmccteas: cele Some years have oa since any shaft. ‘vokine has Geen ee and no ane sinking data comparable with those for other classes of work now being done are aecteecs -In recent gear the Bars have been Bee DepeG: bY: raising.
a oe “Spioretory drifts ene eee drifts are driven 8. by 3. feet. Figure 4 shows a drift face and tae; standard drill round employed. Tyo center holes are drilled straight in but are not blasted. Tyo cut holes, 1, and two easers, 2, are loaded and shot, using No. §& caps on fuse. If these holes do not break bott they are reloaded and shot with the reset of the round. The usual round pulls 5. to 54 feet,
As a rule no effort is made to obtan speed in drifting; experiance has proved that the lowest per-foot cost of development is obtained by driving at th rate of 100.to 140 feet per month, Drilling and blasting are done on the night shift by two contractors using two 144-pound Leyner-type drifting machines mount
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Inf. Cir. 6149
on colums with arms. The contract price for drilling and blasting is $5.50 per foot of advance for average ground-with a 50-cent decrease far soft ground and increase for hard ground, This price covers the drilling and blasting labor and the cost of dynamite, : . . ee a
The mick is hand-loaded on the day shift by two men in each heading, who are paid.at the rate of 20 to.30 cents per ton according to the length of tram, car service, and ventilation, :...:°°: :
Long Crosscut
At present a long crosscut of standard cross section (8 by 8 feet) is being driven to connect with the. Eureka mine, Speed is desired in this operation, and an advance of about 500 feet: per month is being made, A-scraper operated by a double-drum. 25h, electric hoist, mounted on.a portable frame of mine-track gauge unon which ig Supported a steel incline for loading into 4-ton mine cars, is used for mocking out the face. Cars are spotted by a cable-reel locomotive. Sidings lor emty cars are kept within 700 feet of the, face, ‘It. has been found that the few aimtes employed in switching cars does not: delay the operation, since this.
time is well employed in preparing. the muck pile for easy loading.
The drill crew comes in at 7-a.m. and, with a clean set up, starts drilling 1*4-pound drifting machines mounted on columns. At 9 a.m. the round is lled off, and it-is usually shot and smoke bloi out’ by 10 o'clock, © The
With two about dri
ar breaks better than the average ground, and gériérally the entire heading is ling gt OPeration., The mucking crew comes on at 9 o'clock and is occupied in
then and over-hauling the equipment in readiness for operation by 10 o'clock roa: starta. While the face is being mucked put, thé drill men overhaul saort “Tpment, send out dull steel, bring in and sort fresh steel, and take a Tound : ‘i Period, The round is usually mucked out by 12 o'clock noon. A second mickey. rilled off and shot by 3 o'clock, Two shifts each of drillers and
about 20 h 1 and mek four rounds, making an average advance of 18 feet per day of a. Ourg, we
leader got aril crew-oonsists of ‘two, drill, runners, one of whom acts as snift
are - Grill helpers, and one gteel nipper. The steel nipper assists the
steel), hd on his shift in addition to keeping the drill crew supplied with
ate ea mucking crew consists of a hoist operator, a helper who works at the sin, ¢ 2Otorman who spots and changes cars. The motorman also hauls and
responsibye ood cars while the drill. crew is working at, the. face 3 A foreman has
“mp8 the Charge of both shifts.
ach aos Job is organized. on the basis of two high-pressure work periods for he amie an intervening period of rest. The following’ rates are paid for
ion of two..complete rounds on each shift,
Inf.Cir.No. 6149
: Shift leaders ee © ee e © @ $8.16 Shovel operator Seo oes “S16 Drill helpers’... + es 6016. Steel nipper. . . . + 5el6 ee Scraper helper. . 516 ha ye e e e ® e 4.08
With the exception of the motorman's rate, which is the standard, these rates are 40 to 90 per cent above the standard daily wage. If the two — rounds are not completed, the men Eecenve ony the regular daily rate.
Sublevel Drifts aaa Raises
Sublevel drifts are driven 4 by 6 feet in cross section with one drill of the type used in driving inlevel headings. One driller and a helper are employed drilling in each drift. One or two mucksrs using wheelbarrows mick out on day epee These drifts are not timbered.
- Raises are usually 4 by 5 feet in cross section and are drilled with light, hand-rotated, wet, stoper drills. ‘The raises are not timbered, and ea bie is done from staging supported on sprags ae between the walls.
Development Data 8 by 6 foot drifts| Subdrifts Raises
Explosives 1/...pounds per ft. 11-2 9.5 8.8 Average advanca per day...feet . 4.84 520° 366 Number of men per day. 4 al 4 2
1/ Special bulky daz of 35 per cent bulk strength.
Mining
Barly Methods
Prior to 1910, ore above the sixth level was mined by inherband stopin, in open stopes with irregular pillars supporting back and walls. Spans of 50 feet or more were common between the pillars. A large percentage of the ore left in pillars hag since been sii i from drifts driven in the footwall close to the vein... @: ck
Later on, stiiniaes stoping was employed, first on timbered drifts and then on ore pillars above the haulage levels. Above the tenth level these stopes were carried longitudinally and practically the full width of the ore. Below this level transverse stopes 80 feet wide with 30-foct pillars between were employed in wide ore, and ‘longitudinal stopes were used in narrow ore. The stopes were pulled empty and filled with waste drawn frem caved levels above.
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Present Mining Method
In 1925 the sublevel stoping method was, introduced on the fourteenth level and is now the principal method employed,. although only. 32-6 per cent of. the total production during 1928 came from sublevel stopes.
eierager in 1928 divided as follows: .
ieee oe
From sublevel Stones. snstarterovanetata enero mieiaate G, sete ee see — S206 From ore pillars under old shrinkage stopes Seues 6 SOeO 2. 4 .From shrinkage stopes sc ie Oa atte talaga eae nase 9.0 From breaking floors and pillars, mostly on the ee
Upper Levels ..cscccsescsccscseccressecsvscoe 17.6 From flat stopes and pulling CAVES cccccccnccccene 1204 ©
poe eee in ore @° Ce gee atanciemasabers 4 5el)
. Sublevel Stoping ot
Where the ore tink is léss than 40 feet wide sublevel stopes are run longitudinally and the full width of the ore. Figure 5 shows the method of developing and mining a longitudinal sublevel stope.. The block to be stoped is developed by long raises driven on the footwall to the level above. In the block shown in the illustration, two of these raises were driven, one at each end of the block. An intermediate raise was driven to the third sublevel for the purpose of speeding the development of the sublevels. At 40-foot intervals along the haulage drift 4 by 5 foot raises, called "pull holes," are driven on the footwall to the first sublevel. Sublevel drifts are at vertical intervals
cf 40 feet connecting the long end-raises and driven from each raise to meet near the center of the block.
Before stoplie starts, ica chambers (fig: 6) are opened’ up over the hanlage drift at one end of the lock. The grizzlies are installed immediately over the drift timbers without the provision of storage capacity below.
The total amount of stope development, as distinguished from level
development, required for on a stope in ore 40 feet wide and 390 feet long is. as follows:
oc
Two long raises between levels 450 Four sublevels ..s+sssecssereeseceeceves, 14360 Eight pull holes cc.seccecscccccccecsees. 400 — Total development. . pos eeesecseeseesecesee 2,210 -
The tonnage developed in this. block, exclusive, of that in ore floor and in pillars over the haulage drift, is 206,000 tons. ‘Thus 1 foot of development is required for every 93 tons of ore prepared for first mining. This development also assists later in the extraction of the pillars which contain an additional
6042 nn rae
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Inf. Cir. No. 6149
103, 000 tne. 60 per cent or 62,000 bons of which can later be recovered in robbing operations. The total recoverable ore per foot of stope development is therefore 110 tons. : ,
Stoping is started at one end of the block, after first funneling out the pull holes by drilling downward from the bottom sublevel and at the same time slabbing off the hanging wall side of the subdrift exposing both walls (fig. 5). Beginning at the long raise and-on the second sub, the drift is slabbed to expose the walls, and the raise is benched out to the full width of the ore. A slab about 5 feet thick, 6 feet high, and extending from wall to wall is then shot off the sublevel, retreating fron the end of the block and thus providing a bench from which down holes may be drilled to form a second bench 6 feet lower down. Another slab is then shot off the sublevel, and the breaking operation is repeated, benching through to the back cf the first sub- level. This operation is carried out on successive sublevels; the work on a’ lower level is kept far enough ahead of that on the level eure that the men are always working under protection of solid ground. ; SO
The bench offsets are so proportioned that men working on the benches intermediate between sublevels are never under ‘ground that can not be tested from the sublevel with a 15~foot- bare :
At the Burra Burra mine the iecewing is done snticely with down holes. In this respect the practice differs from that in many other mines employing sublevel stoping in which the benches are drilled both up and down from the sublevel drifts and where intermediate benches are net employed.
The first bench below the sublevel is drilled to a depth of 6 feet and the following benches a depth of 10 feet. Usually two men work together on @ sublevel. Drifting machines are employed for cutting-in or slabbing on the sublevels and jackhammers for drilling the benches. Both types of machines are eperated as one-man machines. The slabbing rounds are drilled with three holes in a vertical row to a depth of 10 feet, with 2 feet to 24 feet of burden on each row of holes. Usually nine holes can be drilled in a shift.
Bench holes are drilled 4 to 5 feet pera: aleng the face of the stope with a burden of 23 feet. s-
Blasting in the stopes ig done seniokt on a blasting crew using a bulky 35 per cent powder and electric detonators -fired from the 250~volt mine circuit.
Drilling in stopes is done on contract at a price cf 7 cents per linear foot of hole drilled. The drilling is closely supervised to insure that the holes are properly placed. _&4n average of 48 tons per drill man-shift is broken in the stopes, with a powder consumption of 0.33 pounds per ton of ore. These figures include opening of the stope, cutting grizzly chambers, etc.
The ore broken in the stope falls to the funneled raises or pull holes above the grizzlies and is worked through the grizzlies directly into cars on the haulage level. An average of 72.5 tons per man shift is put through the
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Inf.CireNo. 6149
grizzlies, with a powder consumption’ of 0.167 pounds per ton of ore. Cars are spotted at the grizzlies in trips of .fcur. When a car is filled, the grizzly man goes to the, level ‘and moves another car into position.
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: Wide Stopes
‘Where the ore body is wide the sublevel stopes are opened up 40 feet wide, across the strike of the ore body, with 40-foot pillars between the stopes. These stopes are developed from the crosscuts or the haulage level in the same manner as the narrow longitudinal stopés are opened from the longitudinal drift. Figure 5 shows this development and method of mining. To date no pillars. between sublevel stopes have been extracted, but the method of recovery will be the’ same as that employed in recovering the pillars between the old shrinkage stopes, as will be described.
Robbing and Pillar Extraction, ;
‘Figure 7, an ideal longitudinal géction, ilustrates the method: of robbing and of extracting stope pillars, beginning at’ the upper levels with the pillars over the old. haulage drift beneath the Scio ec stopes.
Starting at the end of the block to be’ robbed, as at A, an 4nclined cut or slice is taken in the haulage-drift pillar from wall to.wall, at an angle corresponding to the angle of repose of the caved waste. After the slice is blasted, the broken ore is mucked out and trammed to the ore pocket. ‘The driller then goes back and drills a round from the face of the preceding break. This procedure is continued till the last round breaks through into the broken waste above, letting it down to fill the opening. Another slice is then started fur- ther back, and the cycle of operations is repeated. In this manner the entire pillar is robbed back from one end of the stope to the cther. When this is done the weight of the broken waste is carried on the floor pillar. 7 mee
The next step is the recovery of the pillars between the transverse
shrinkage stopes which had been mined from the next haulage ‘level below. ‘The pillar is first partly undercut at. an elevation about 50 feet above the level, blasting the broken ore into pull holes of the ald stope. Then, using deep-hole hammer drills set in stations cut from the footwall raise opposite ‘the middle
of the pillar, long holes were drilled as shown in figure 8. The holes tere
. from a few feet to a maximum of 120 feet in ‘depth. The ‘holes were drilled and shot several rounds beginning at. the’ botton. “fhe holes were charged with 60 per cent gelatin and detonated with cordemi. ° The charge was figured at 0.1 pound
Of explosives per, ‘ton of ore and the holes were charged two-thirds full and — stemmed to the collars with clay cartridges.” Tie explosive used was made up in 2 by 16 inch sticks. ‘The iain broke ‘well, but some large blocks broke off behind the holes,
The floor’ Bintes was recovered by aritting long slabbing holes from
stations on the footwall and blasting the ore into the pull holes. Slabbing was contimed until the floor pillar failed and broke into the stope, followed by broken waste. 7
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oe +. DRILLING PRACTICE .
Compressors. - The ‘air-compreasor: plant is ‘located: at McPherson shaft. There are three 2,500 cubic foot, electrically driven, two-stage air compressors maintaining a pressure of 100 to 110. Rounds at,the plant. This gives a pressure of about 90 pounds at the drills. This plant furnishes the air for Burra Burra mine, the Eureka mine, and the high-pressure air at the flotation plant. The air is metered to.each. operation, and the cost of compressing. the alr is pro- rated to each on the bagis of air actually consumed. Each. foreman is held responsible for:thejair-conswned in the operations under, his direction. The meters were. introduced.as payt of a drive to.roduce air congumption. ‘Prior to this drive.all: three compressors were required at times to maintain pressure. At present-only one:compressor-is employed. and the. rate of. ore. ‘Production’ is 40 per cent greater than formerly.
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Drills.- For all drifts, crosscuts, .and other horizontal hatte: & medium weizni Leyner-type drifting machine is employed. With this type of drill 14 inch, hollow, round. steel in lengths of. 30. inches. to 10, feet 8 inches is used Steel is made-up in 1~foot. changes, . but. 2-foot changes. are. ‘employed in drilling. The double taper (5° to 14°) cross bit ia standard at this mine. Starters have. a gauge of 1 7/8 inches, with one-sixteenth-inch decrease in gauge for each changs of steel. Thug. the bit on a 10-foot steel has a gauge of 1 3/8 inches. ? ee all benching, sinking, and other down-holes, medium-weight hanmer drills. equippec. with plugger shells are employed. These machines use sevén- eighths-inch }cilow, hexagon, collar-shank steel in lengths of 30 inches to 10 - feet 6.inches overall. The double-taper cross bit is employed with one-sixteent inch change in gauge for each change in steel, starting with I 3/ inch Ege.
In raising and other up holes, hand-rotated stopers are ‘eupLoyed with 1- Such hollow hexagon. steel having double-taper bits of the same sizes as those for the Jackhamers.
“Drifters and atepers are run ‘wet, and. Jackhammers ary.
rom
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; The deep~hole drills are of the heavy, drifter type ‘With Soleninid reversible. rotation. These drills employ “‘4-inch’ hollow round gteel with eae threads, made up in 3.and 6 foot lengths and with outside couplings. These - drills are:mounted on a crossbar secured tq.two columns with universal clamps. - Fhe double-taper crogs bit.is used, starting with 3 3/ 4-inch gauge. Twenty-fiv gauge changes are used between.3 3/4 and 2 1/4 inches. In medium ground and fc holes not more than 100 feet. in depth each bit is run until the hole size is down to that of the next: gauge. In harder. ground, or for ere holes, as many as three bits of each gauge are employed. -. . ee These machines do not work satisfactorily on flat or down holes. Tey give best results on holes above 15°. from the horizontal. Their operation re— @oires men of exceptional ability. . The drills: are. at run wet; the water ji.
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introduced through a swivel connection in the side of the first drill rod, which is of iced forged construction. ,
The crew consists of two men,.a runner and a helper, who drill on the average abdnt 25 feet per shift. ‘The total: cost. of deep~hole drilling is 80 cents per foot, including TAO Ee air, shop os and. steel. 7
All steel is handled in & central shop with two sharpening machines and three oil~fired forges. The forges are equipped with pyrometers, and an excess of oil is used to produce a‘minimum of oxidation and resultant scaling of steel. It has been found that ‘best ‘overall results are. obtained by careful work on the steel rather than wy endeavor ing to obtain high output, per Renner
UNDERGROUND TRANSPORT oN
Locomotive haulage is mpiecea on 1 all mins levels. "The production is handled by 4 and 6 ton trolley locomotives: with cable~reel. attachment and for development work 1 and 2 ton storage battery "trammers" are used. Main-haulage tracks are laid with 40-pound rails. All tracks are 24-inch gauge.
Sever-ton, end-dump, steel cars equipped with roller bearings are employed on the sixteenth level, dumping through chute or slide directly into ?7-ton skips at Burra shaft. These cars are 5 feet wide, 45 inches high, and 9 feet long and are equipped with journal springs. The cars are built in the comany'!s shops at Copperhill.
Storage for loaded and sane care. ays provided at the shaft bottom with convenient crossovers and turnouts. The care are moved by means of an overhead continuous rope system, driven by a small electric hoist and are dumped by power from the car mover. “The skip riders, two.in mumber, move and dump the cars without other assistance. Figure - shows the en at the shaft dottom.
‘On tiie’ fourteenth level 5~ton: Granby-type. cars are “ employed which dump into a storage pocket or directly into the.skip by means of an air jack. The storage pocket. has a capacity of 400. tons and.discharges into a measuring pocket. The discharge from the storage pocket into the measuring pocket. is regulated by a vertical, tiandercutting gate operated by a-double-acting air jack. The measuring pockst discharges into the skip through an le at door.
On the twelfth level both Granby cars and 2-ton rocker cars are in use. The former are used for loading ore from pull holes and the latter for hand- loading. These cars dump either into a pass leading to the fourteenth level pocket or directly into: bes skip, oo upon the kind of ore being handled.
On the tenth level: ‘and: stove,” 4eton end-dump cars are employed which dump either into pockets and oré passes leading to pockets or directly into skips, depending upon the kind or ere: being handled. -
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The necessity of keeping the two grades of ore separate on each level is responsible for the two methods of handling as above described. Pockets are located in the shaft below the sixth, tenth, and fourteenth levels; these pockets and the passes from the other levels, have a combined storage capacity of 7,000 tons.
The hoist at Burra shaft is a double-drum geared hoist driven by a 400- hp., 2£,300-volt, slip-ring motor. The drums are 6 feet in diameter by 4 foot face, grooved for 11/4-inch rope. Three layers of rope are run on the dmm. Hoisting speed is 700 feet per mimite. The hoist was installed in 1917.
The McPherson shaft hoist is a duplicate of the above. The skips are equipped with manganese-steel wheels and liner plates. PERCENTAGE OF EXTRACTION
It is estimated that 85 per cent of the ore is extracted, with a dilutic of about 5 per cent.
Comparison Of Stoping Methods
In comparing the shrinkage method with the sublevel method of stoping, it may be stated that: (1) Sublevel stoping is safer because of the fact that the men are not out under a wide back but are always under solid ground which can be and is tested daily. (2) The total breaking cost is less in sublevel stoping than in shrinkage stoping, largely because the ore is broken finer from the solid with less secondary breaking in the sublevel stopes; in the shrinkage stopes large slabs come down which must be drilled and blasted, but often they fall in such a position that it is dangerous to go out under the stope to break them up. (3) The drawing of the ore from sublevel stopes as compared to shrinkage stopes can be concentrated at fewer pull points to obtain the same rate of output, so that increased pulling and haulage efficiency results. (4) In sublevel stopes a greater percentage of the ore is recovered. In the shrink age stopes a considerable amount of ore was often left cn the footwall because of minor folding, and this ore can be recovered only by open stoping in which the footwall is exposed throughout the operation. (5) In the sublevel stopes very lean or barren parts of the ore body are left as pillars; this is usually very difficult to do in shrinkage stopes. (6) More development and stope prep: ration are required for sublevel stoping than for shrinkage stoping. The difference, however, is not as great as might first appear, because shrinkage stopes require closer spacing of pull holes. fFurthermore, it was found advisa to carry footwall or pillar raises in addition to cribbed manways through the broken ore for access to the shrinkage stopés. .
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Labor Costs Per Ton, 1928
Stope drilling |Blockine and loading Total
Sublevel stoping
$0.173
Shrinkage stoping 0272 Ore pillars under old
shrinkage stopes eool
) e174
Floors and pillars
In comparing the figures in the foregoing table it must be born in mind tht the shrinkage stoping was in somewhat narrower ore bodies and included more tan-loading than did the sublevel stoping. Ore from pillars under old shrink- age stopes was loaded entirely by hand and was also hand-sorted at the face.
Wage, Contract, And Bonus System
General.- All development work, with the single exception of the long crosscut to the Eureka mine, is driven on contract. The blocking (blockholing) and leading are partly done on contract and partly on day's pay. Thirty—nine. per cent of the total shifts under this classification in 1928 were paid on the contract basis. Thirty per cent of all stope drilling was done on contract.
Ml other mine labor was paid according to standard daily wage rates for each Classification of labor.’ —
Develonrent.- Drillers in standard 8 by 8 foot drifts receive a price of $5.50 per foot with a 50-cent variation either way for very hard or very soft ground.. The =cund classification is determined at the end of each pay period ly the mine éngineer, who is himself an experienced drill runner. The company bays for mucking these headings in the manner described later under "loading."
The sublevel drifts are contracted at the following rates: $6 per foot for the first 50 feet from dump point. $6.50 per foot for distances of 50 to 150 feet from dump.
Fitty cents is added to or taken from these prices for hard and soft ground, fespectively, The prices named cover drilling and mucking labor and dynamite. the drillers receive 60 per cent and the mckers 40 per cent of the net earnings.
For raises driven by two men, which is the usual practice, the price per foot ranges ‘from $5.25 for the first 25 feet above the level to $8.50 per foot for distances 200 feet or more from the level. Price changes are made every
feet. A 25-cent variation from these prices is made for hard and soft ground.
Stoping.- Drilling in stopes is contracted at a price of 7 to 10 cents Mr foot of hole drilled; the price is varied according to the hardness of the sround, The price is fixed for each stope and ‘is altered ‘only oceasionally as “ditions change. oF ae t 0's
Inf.Cir.No. 6149
Loading.- Loading includes blockholing on grizzlies, loading cars from grizzlies, and hand-loading from drifts, stopes, and robbing. The men employed on this work are shifted from one job to another as’ Occasion demands. Payment is made on a per-ton basis; the tonnage is figured from the car count.
Prices paid range’ from 4 to 30 cents per ton, depending upon the loading method, amount of blockholing required, and car service.
Labor for blocking and loading from grizzlies is eds for at the rate of 4 to 7 cents per ton.’ The 7~cent rate was paid at the first grizzlies installed where storage was provided below the grizzly and the ore had to be pulled throug @ chute. On account of the blocky nature of the ore it tended to wedge in the chute, and almost as much labor was required to pull the chute as to block the ore through the grizzly.
Hand-loading from development drifts is paia for at rates varying from 20 to 30 cents per ton, depending upon the material handled (waste or ore) and length of hand~tram.
The actual price paid for loading is set for each job and place upon recommendation of the mine foreman and authorization by the superintendent.
Company Rates and Contractors! Averag 6 Earnings for Principal Classifications, 1928
Classification Company rate Actual contract — per shift earnirss per shift —s_s—
1. Drillers:
a. Development $3.92 $7.17
b. Stoping B92 6.06 2. Trammers (loading). ae 3260 4.97 Se Timbermen cce0 3072 4. Motormen ieesee 3092 “— Se Skip conductors 4.88. oe —— 6. Hoist engineers 4-88 as
Ventilation
Natural ventilation is good except in dead ends, where small electrical driven blowers with flexible tubing are employed. The flexible tubing is being discarded in favor of 16-gauge steel pipes 8 and ke inches in diameter with - stove~pipe joints.
FIRE HAZARDS oe
Very little timber is employed in the bie: and all scrap timber is to surface for disposal. Although the ore contains 15 to 30 per cent sulphur it has never caught fire and has shown no signs of heating. Hlectric Wiring is installed in accordance with best practice for prevention of shorts and undergoes periodic inspection.
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The company employs a safety engineer on full time at the mine. This. engineer gives first-aid training to regular classes, makes inspections, checks engineering work for safety, and conducts educational work by personal contact — and classes. There has been a marked decrease in the frequency and severity of accidents. since safety.has been recognized as a major problem.
MINING COSTS Burra Burra Mine For Year 1928
Tons Ore Hoisted suveees 2S 298. 5 nee :
Underground costs per ton of. ore’ hoisted -
Labor |Super-| Compressed Power Teplice Timber Other Total 1/ vision|air,drills cost: |sives” supplies; —
and " steele/
$0.2295/
Development...,
Mining. ...c.seeee e216. BLOCKING s:o:00rs'a'in% e116 Transportation . (underground) 0386 General under- gtcund expense... 0145 Surface expense. ° - 043 (directly appli-- cable to under- © Jo fo fo fo tp pee ground operation)
Totals. eeseoe fj. Ps sao e118 —
1/ Guleterousk labor costs include surface labor employed in steel shop and other surfacé labor allocated to the several underground operations.
2/ Includes power for air compression and materials for drill repairs, air, and water lines. Labor repairing drills, operating a aa and laying air and water lines is included under "Labor.'
3/ Development cost is higher than normal, since more development work vas done during the year than was required to keep pace with the cre extraction.
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Tons of ore hoisted: 473,292...
A. Labor (man hours per ton:
Summary of Costs Per fon in n Units of Labor, Power, and Supplies
Burra Burra.
t
pos
Drilling and blasting e.. BLO CINE yc web-ose Sirsa bree ve been oe MUCH NP su bobaa Sw eres ee wear bees Transportation. ccecscsccees General... .cccseseseees jet, @eaeares
Supervision ese- oe eoevee ee. Surface labor eee a ‘
underground. . Cie eSNG wie ears
Total man hours per tons venicern. Tons per man-shift cceeee.
Labon per cent of total cost
Be. Power and supplie :
Explosives (lbs. per ton) - per cent ammonia ccecees
Timber (Board feet per —- ue Total tA (Kw. hr. per eae
Other seplsee in peseentate of. total supplies and power Power and supplies, - percentage
Of COtal. COS .s6sewisiwbccwwa.
C. Percentage of total cost ee.
‘Mining methods: Sublevel stoping and
shrinkage stoping.
Development Total
e132 e100
65.6%
42%
34. 4%
Notes: - Figures for Neckiaeaans are based on total mine output and not on ore
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from development headings only.
Drilling and blasting includes lator employed in sharpening steel on surface. Mucking includes all loading of cars.
Inf.Cir.No. 6149 Detail of Costs in Unite of Labor, Power and Supplies
Development
i Drifting Drifting Raising
t Size of Excavation. .cccccccevsercvecce 8 by 8 foot 4 by 6 foot 5 by 5 foot
Timbered or nOt...eseuwecee gNciave.wsnacetuecs No : No No Physical properties of rock Medium drilling, but rather difficult to break
1, Labor (man hours per ft. )s Breaking (drilling and blasting) Sed Sed 4.4 Mucking and hand-tramming 3.3 249 : Total labor (man hours per ft.). 6.6 6.2 4e4 Feet per 8-hour man-shift 1.21 1.30 1.83
B. Power and Supplies (per ft. ):
Explosives (lbs. por ft.)es.eves 8.8 Power (kw.h. per fto).ccsccceses 27 C. Labor (percentage of total cost): 50.5 Power and supplies (percentage Of total cost..ccecsecsecvecer 49.5
Jotes: - Labor for sharnening steel and advancing air lines is included in figurs for piwir ord suprliss. Haulaze and hoisting of Cevelopment muck and loading of raise muck are not included in development figures.
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