Exploration of Small Mines

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ARIZONA BUREAU OF MINES

MINERAL TECHNOLOGY SERIES No. 48

BULLETIN No. 164

EXPLORATION AND DEVELOPMENT

OF SMALL MINES

ARIZONA BUREAU OF MINES

January, 1954

PUBLISHED BY

~ n i 6 e r 1 5 i t v n£ :i\ril!omtTUCSON, ARIZONA

By H. E. KRUMLAUF

~ u i & £ r z i t ~ of ~ r i ~ o u n~ u l l £ t i u

TWENTY-FIVE CENTS(Free to Residents of Arizona)

Vol . XXV, No.1



TABLE OF CONTENTS

PAGE

INTRODUCTION ...........................................................•................................ 5

PART I - PREPARATION AND COSTS ..........................•............................. 5

Primary Appraisal 5

Surface Exploration 6

General Program 6

Trench Sampling 6

Pi t Sampling . 6

Diamond Drilling 6

Wagon Drilling 7

Ore Values for Small Mines.................................................. 7

Underground Exploration 8

Labor ...............................................................................•.................. 8

Pay Scale 8

Labor Costs 9

Mine Surface Plant 10

Shaft Sinking 11

Cost of Shaft Sinking 11

Drifting ...............................•..............................................................12

Cost of Drifting 13

Raising 13

Cost of Raising c·... . . . . . . . . . . . . . . . . . . 14

Equipment 14

General List 14

Suppl ies to be Purchased 15

Rent 15

Summary of Costs 16

P ART II. MINING METHODS FOR SMAL L MI NE S 17

Factors Governing Choice of Method 17

General Statement 17

Strength or Physical Characteristics ......•......................... 17

Value of th e Or e 17

Dip 17

Length of Ore Body :...................... 17

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PAGE'

Width of Ore Body _ _ _. 18

Capital Available _ _ _ _ _.............. 18

Experience _ _._ _._ __ _......... 18

Particular Methods ._ _ _ _ _. __ _ __ 18

Gophering or Gouging _._ _._ _._..... 18

Star t ing the Stope _ _ _ _ _._.. 18

Stoping on Drift Sets _ """ 21

Starting the Stope on Drift Pillars _ _ _ 21

Room-and-Pillar Method _ ,.._.,_ 22

Cut-and-Fill Stoping - _ 25

Stull Stoping in Narrow Veins _._._ _........... 26

Shrinkage Stoping _ .._ _ _ _ __ 28

Square-Set Stoping _. __ _ __ _ 30

PART III. - WHY MANY SMALL MINES PROVE UNPROFITABLE ...._.. 33

PART IV. - MILLS FOR SMALL MINES . ._. _._ .._ _ _ __ ._ .. 34

ILLUSTRATIONS

FIGURE l.-Starting th e s tope on drift sets _ __ .__ ._.... 19

FIGURE 2.-Starting th e stope on drift pillars _ __ _... 20

FIGURE 3.-Room-and-pillar stoping _ _. 23

FIGURE 4.- '-Horizontal cut-and-fill s toping on drift sets 24

FIGURE 5.-Inclined cut-and-fill stoping on drift pillars 25

FIGURE 6.-Stull stoping in narrow veins .. _. 27

FIGURE 7.-Shrinkage s toping on drift sets _............ 29

FIGURE8.-Squale-set

stopinginnarrow veins 31

EXPLORATION AND DEVELOPMENT OF SMALL MINES

By H. E. Krumlauf*INTRODUCTION

The information given in t he following discussion is f or sma llmine operators and those who might become interested in smallmines. Seldom will th e cost figures, as shown, fit exactly a givenmine; they ar e presented here to help th e potential operatormake reasonable estimates of th e capi ta l needs and operating

expenses involved in exploration and development of small mines.

PART I - PREPARATION AND COSTS

PRIMARY APPRAISAL

Assume that th e prospector has found a promising outcrop,mineralized zone, or geological structure, indicating th e possibility of an ore deposit, and that he has properly located a nd r ecorded a claim or c la ims to cover th e area. The prospector thenshould sample th e outcrop or zone by t ak ing samples f romtrenches or test pits that h av e b een d ug into th e solid r oc k o fthe outcrop or zone of mineralization.

I f th e samples show that ore ha s been fo und, a developmentprogram can be planned, and, if capital is available, t hi s p lancan be pu t into operation. At t hi s point many prospectors makea serious e rror by believing that the material found i s ore . The

United States Geological Survey defines ore as fol lows: "Oreis a natural aggregation of one o r mor e miner al s f rom whichuseful metals may be profitably extracted." I t requires considerable mining and metallurgical experience to determine if th evaluabl e miner al s f ound can be "profitably extrac ted" and tode termine i f th e material found is actually "ore."At t hi s point th e wise prospector wi ll obta in th e services of

a competent consult ing mining engineer either t o d ir ec t th eoperation or advise him on th e best procedure for h is proper ty.Such an engineer should be well and favorably known in hisprofession and registered i n t he St at e w her e he practices. Thecos t of obtaining th e services of a competent consultant is about$100 pe r day and expenses if employed on a short-term daily rateor, if the consultant is to plan and direct th e operations duringthe development stage, he would b e p ai d a monthly salary of

about $500, more or less, depending upon th e amount of workinvolved. These costs are g iv en onl y a s a gener al guide to th eprospector and may v ar y f rom one d is tr ic t t o ano ther .

I f th e sampl ing result s are encouraging , a lthough indica tingmaterial too low in g rade for "or e" as previously defined, or ifthe prospector believes that he has found a promising geologicalstructure, he then should obtain th e advice of a competent mininggeologist. This man should be well and favorably known in hisfield, Such a geologi st probably would be emp loyed only on ashort-term basis, and h is s ervi ce s w il l cos t about $100 pe r d ay

'Professor o f Min ing Enginee ri ng , C o l l e g ~ of Mines, University of Arizona.

5



plus expenses. The cos t of the geological examination is moneywel l spent , and the prospector would do well to follow thegeologist's advice. The char ge s made by consulting geologistsmay vary considerably.The cost of obtaining professional services may seem to be

high, bu t in most cases the advice given th e operator wil l savemany t imes th e cos t o f this service.

SURFACE EXPLORATION

GENERAL P R O G R A ~the report that has been submitted by the consulting geologist

wIll recommend one of several courses which generally may besummarized as follows:

1. Abandon the property for lack of sufficient evidence towarrant the .cost of additional exploration. The prospector shouldfollow this advice.

2. .A.dditional trenching and test pitting along th e outcrop todetermIne the extent of mineralization, or fo r additional informat ion on th e structure.

3.. Dri ll in g t o d et ermi ne v al ue s or geological s tr uc tu re a tdepth.

Trench Sampling: Trenching can be done with pick and shovelt o dep ths of 6 or 7 feet and 2 to 3 feet in width, dependingupon the depth. Its cost will d ep end t o a considerable extentu ~ o n the type of material in which the t rench is dug. In soilwIth some rocks but .no large boulders, the average cost is $3to $4 per cubic yard of material removed.Fo r la rge amounts of trenching, a bul ldozer should be used.This machine also will handle rocky soil at a much lower costt han may be achieved by pick and shovel. The cost pe r f oo t oftren ch may be about the same for each method, b ut the jobca n be done in.a much shorter t ime wi th a bul ldozer . Also th ewide b lade on th e dozer Will expose more of the bedrock forexamination. A bulldozer of sufficient power to handle the job~ i l l c ~ s t $75 to $100 per. d ay or $300 to $350 per week o f 6 days ,mcludIng operator, servIce, fuel, and repairs. In addit ion to thisamount is th e cos t of trucking the equipment to the prospect

and return, which should no t exceed $25.Pi t Sampling: Test pi tt ing is necessary where overburden is

too thick for t renching. Tes t pi tt ing is s imi lar to the sinking ofdiscovery ~ h a f t . Test pit s are usually 4 by 4 ft. or 4 by 5 ft.

In cross sectIOn and may be 30 to 40ft. deep. Test p it s d ownto 10 fee t deep in soil or gravel will cost from $5 to $7 pe r footwithout timbering, but t he cost pe r foot will increase with depthand.amount of timber necessary. These costs are for dry ground.Diamond Drilling: I f the consulting geologist recommends adiamond dril l ing program, he should determine the location foreach hole together with it s direction, angle, and depth. The init ial dril l ing program fo r the prospect rarely exceeds a total of1,000 feet of hole, which is considered by th e driller as a small

*Includes railroad freIght t o sme lt er o r o re buyer .tZlnc o re c an b e s ol d only to a custom mill, an d at a market p ri ce o f lOc pe r poundIs of little value to t h e smal l mine operator. No payment for zinc Is received froma copper smelter or lead smelter if s om e z in c i s i nc lu ded in a lead , copper, gold.or silver ore.

:j:Does not include development or haulage allowances an d production bonus.

The ta bl e above gives a rough estimation of t he " br ea k

7

Value pe rlb. or oz.25c/lb.12%c/lb.10e/lb.$35/oz.

90.5icf/oz.$3.50/lb.

Grade ofpe r ton

5lf2%15 %25 %0.6 oz.

24 oz.0.20%


Type ofore

CopperLead

ZinctGold ( flux)Silver (flux)Uranium oxide

contract. Since th e condition of the rock to be drilled is unknown,and the amount of drilling i s small , the contract price for th ejob may range from $4 to $6 pe r foot, with possible extra chargesfor cementing holes where necessary and f or cas ing i f needed.Under certain cirCUmstances it may be better for the claimowner to pay for dr il ling on a "cost plus" basis. With a contractof this type, th e claim owner pays the drilling costs plus an

additional amount per foot. This additional amount may rangefrom 75 cents to $1 pe r foot. The claim owner should determinein advance just what i tems wil l be inc luded in the cost.Wagon Drilling: In areas where the mineral bodies ar e of considerable horizontal extent and at shallow depths, a wagon drillhlay be used successfully for explora tion . This type of rig inc ludes a standard wagon dri l l equipped with a 4-inch air-drivendril l ing machine and a compressor of 315 c.f .m. (cubic feet perminute) capacity. Drill r ods 1% inches to 1% inches in diameterwith %-inch hole i n t he center, and a 2%-inch to 3-inch tungstencarbide bit, are emplOYed. Drilling is done without water; air,forced down through the hollow rods, brings up t he cuttings andcools the bit. A 4-inch collar with side outlet is placed overthe hole. The collar has a bushing at th e top through which thedrill rods pass, and t he a ir and cuttings flow through the side

outlet to a dust collector, which may be of simple cone design.This type of drilling is particularly suited to shallow deposit swhere the depth does not exceed 100 to 125 feet. However, undervery favorable conditions, holes as much as 200 f ee t deep maybe drilled. The rock mus t b e dry.For a drilling program of approximately 2,000 feet, th e cQstper foot should be less than $2. With greater total footage, th ecost can be reduced; i f 20,000 feet, it m ay be as low as $1 pe rfoot.

Ore Values for SmaI1 Mines: At th is point in an explorationprogram, the operator must appraise carefully th e informationobtained. I f drilling has shown that no valuable minerals arelikely to be found, th e claims should be abandoned. Only if theresults indicate ore, may h e plan t he nex t step in exploration.

Ore buyers*Gross returnValue (approx.)

$27.50 $1437.50 1450.00 1421.50 1421.75 1414.00t 14

UNIVERSITY OF ARIZONA BULLETIN



--------------------- -------------------------,

!

UNDERGROUND EXPLORATION

Trenching, test-pitting, and drilling may indicate the presenceof valuable ore; however the physical characteristics of theindicated ore and the wall rocks can not be det ermined by thesemethods of exploration. To obtain this additional information,

it will be necessary to examine the ore and wall rocks and samplethe ore at some distance below the outcrop.General p lans for the underground exploration may be out

lined as fol lows:1. Appraisal of the labor situation in the district whe re t he

prospect is located.2. Estimation of the size and cost of the surface plant.3. Shaft-sinking costs.4. Drifting costs.5. Estimating the size and cos t o f equipment necessary to do

t he wor k successfully.

LABOR

Pay Scale: The following table is approximately the union pay

even" grade of material for smal l mines. I f the exploration indi

cates material of better grade for any single metal than is shownin th e table, th e min e m igh t be profitable.

Complex ores containing combinations of the aforementionedmetals may b e s en t t o a cus tom mill or smelter . For example, anore containing 12 pe r cen t lead an d 3 pe r cent copper, with agross value of $45 pe r ton, can be shipp ed to a lead smelter,

where payment for coppe r at a reduced price, combined withthe payment for lead, will return a total of about $14 pe r ton tothe shipper.

The "break even" grade of o re f or the smal l mine opera tor,a s shown in th e above table, must return $10 pe r t on to coverdirect mining costs; $1.40 for royalty at 10 pe r cent of the smelteror ore buyer's return; approximately $1.50 for trucking from mine

, to railroad; and a balance of $1.10 ou t of the total of $14 maybe u&ed for such items as taxes, insurance, exploration, legalcosts, and surveying.

Under very favorable condit ions, a small mine operator maybe able to produce and ship ore for less than $14 pe r ton, whereasth e cost for other operations having less favorable conditionsmay exceed $14 pe r ton. The f inal cos t f igure will depend uponsuch i tems as width of vein, strength of the ore and wall rocks,

cost of transportation, royalty, ability of th e mine operator, typeof labor, and cos t of suppl ies. The values g iven above a re fo restimating only, and an ore buyer or sme lt er r ep re sent at iveshould be con&ulted for more detailed information.

If , however, the gross value of the material discovered by t heexploration thus fa r is e qu al t o or greater than shown in thetable on page 7, after adjust ing for changes in market value,t he n ex t step in the explora tion program can be planned andexecuted.

9XPLORATION AND DEVELOPMENT OF SMALL MINES

scale effective in Arizona a s o f May , 1954.Classification Base pa y p er shift

Miner $15.44Mucker 13.88Topman 14.24Hoistman 15.44

Since small mines commonly are located distant f rom larger

mines, the pay scale t ends to be less. For t he example to be dis-cussed,the following pay scale wil l b e used:Classificatiort Base pa y p er shift

Foreman $15Miner 14Mucker i2Hoistman 14

The small -mine foreman should be in immediate charge of th eworkmen, and he also should be ready to do or help wit h anyjob from mi ning to hoisting. The sma ll mine cannot a ffo rd alazy foreman.

The amoun t of material t o b e hoi ste d per shi ft f rom a smallmine wil l require only part of th e hoistman's time. The balanceof h is t ime will be spent in t ramming ore or waste to placesof disposal, framing timber, sharpening picksand moils, operat

i ng t he compressor, and doing other odd jobs as needed.The miner and tnucker wi ll do the drilling, mucking, timber

ing, and t rack laying as the job progresses.Labor Costs: The base pay shown i n t he foregoing table is only

part of th e cost of l abor to th e operator. Substantial amountsin the form of insurance and t axes mus t be added to th e basepay, as fol lows:

1. Overtime: I f th e mine is ope ra te d f or s ix d ay s pe r weekat eight hours p er d ay a rate of 1% times th e base p ay mus tb e paid for t he s ix th day. This over time is then distributedequally to each of the s ix d ay s t o obt ai n the so called "payrollwage." All insurance a nd t ax es a re computed from th e payrollwag e an d n ot the base pay.

2. Old Age and Survivors' Insurance (O.A.S.!.) in i ts variousforms is commonly called Social Secur ity. The O.A.S.I. r at e, a s

of January 1, 1954, was 2 per cent of the payroll wage. Thi s i sa Federal insurance.

3. Industrial Insurance r equi red by t he S ta te of Arizona is in

two par ts .a. Industrial accident insurance for mining is 8.30 pe r c en t o f

the payroll wage.b. Occupational disease insurance for mining i s 0.58 pe t cent

of the payroll wage.4. Unemployment compensation tax is part S ta te a nd part

Federal. This ta x is a percentage of the payrol l wage of anyworkman and is paid a ft er he h as b ee n employed for a periodof twenty weeks. However, it is retroactive to th e beginningof the employment period.




EXPLORATION AND DEVELOPMENT OF SMALL MINES 11

Estimated CostHeadframe, including the shaft collar $700

Buildings:12 ft. x 35 ft. for hoist , changeroom, shop, andstorage - frame construction @$3.00 pe r squaref oo t o f floor area 1,250

Compressor shed 150

Powder house and outhouse 200Leveling ground, installing surface equipment, lay-ing track, fitting pipe 200

Water tank (used) installed 100Air receiver (used) installed 200

Total $2,800

The above co st o f $2,800 is for a semipermanent installationwhich can be used, with some additions, for production. A temporary plant could be installed at a lower cost b ut must be re

placed i f t he mine produces. Also the co st of roads for accessand other purposes mus t b e added to th e total.

SHAFT SINKING

The next step in the exploration program is th e sinking ofan exploration shaft to examine. th e mineralized area.at depth.This shaft should be pu t down m the ore body or mmeralIzedzone wherever pos sib le . A shaft outside th e mineralized zonewil l f urni sh no informa tion of v al ue t o the operator. In someplaces the topography may no t permit the building of a surfacep la nt n ea r t he outcrop or the sinking of a shaft in the vein.For example, a cliff or steep mountain side may re qu ir e t he

surface p lant and sha ft to be located away from the outcrop.Also a shaft should not be put down in the outcrop i f it is inthe bottom of a wash. Too frequently the inexperienced operator drives a long tunnel to intersect t he v ein at depth , onlyto f ind t ha t i t h as b ee n faulted o r h as p in ch ed out. This information could have been obtained at a fraction of the cost, hadhe sunk a shaft on the vein. Wherever possible, all explorationwork should be done in th e vein or mineralized zone.

I t is customary t o s in k the prospect shaft about 110 feet andestablish the first level a t about t he 100-foot d ep th i n t he shaft.The lower 10 feet of shaft will be used as a sump and fo rloading a skip where one is used

Cost of Shaft Sinking: A satisfactory small mine shaft, whethervertical or inc lined, i s 6 feet by 9' feet in rock cross section. Thisshaft when timbered with wall plates and lagged, can be dividedinto hoisting compartment 4 ft. by 4 ft. in cross section anda manway 3 f t. by 4 ft . in cross section. Guides for a cage wouldbe installed in a vertical shaft" and stringers rather than tiesshould b e used in an inclined shaft to car ry the rails. Stringers4 in. by 6 in. or 6 in. by 6 in. , fas tened to the sills, will give a

\ .

Total cost pe r shift

$18.5217.2814.8117.28

UNIVERSITY OF ARIZONA BULLETIN0

Total cost per shif t to operator ~ $ 1 7 . 2 8The actual cost to th e operator for labor, including t axes and

insurance, is as follows:Classification Base pay

Foreman $15Miner 14Mucker 12Hoistman 14

a . S ta te unemployment compensation is 2.7 pe r cent of thepayroll wage.

b. Federal unemployment compensation is 0.3 pe r cent of thepayroll wage.

The Sta te rate may be reduced after one or two years if thecompany furni shes s teady employmen t to i ts employees.

5. In addition to the above taxes and insurance, an established

company may be required to pay for shif t differentials, vacationslholidays, group insurance, transportation, and o ther items.

Example: The total daily cost per miner for a six-day week iscomputed as follows:

Miner 's base p ay p er shift $14.00Weekly overtime distribution = $14 x lf2 x 1/6........ 1.17

Payroll wage pe r shift $15.17Payroll insurance and taxes:

O.A.S.I. @2.0 pe r cent x 15.17 = $0.30Industrial Accident Ins.

@8.30 pe r cent x 15.17 = 1.26Occupational disease Ins.

@0.58 pe r cent x 15.17 .09

State unemployment [email protected] pe r cent x 15.17 = .41

Federal unemployment tax

@0.3 pe r cent x 15.17 = .05

Total ta x and insurance $2.11 2.11

MINE SURFACE PLANT

The type and s iz e o f surface plant will vary somewhat. Forexample, if th e headframe t o b e built is for sinking and exploringwith a sinking bucket, it would cost less than one des igned forsinking and inclined shaft with a skip. However, this latter typeof headframe can be used more efficiently for production.An ore bin may be included as part of th e init ial surface

plant t o handl e ore that may be found dur ing the exploration,or this o re cou ld be stockpiled in some convenient place, andth e ore bi n m ight b e bu ilt later. A bin to hol d 15 tons of orewould cost about $600.

r



s tr on ge r s up po rt t o t he rails than ties and also wil l keep th et ra ck in alignment.

The l abor d is tr ibut ion and costs are shown as follows:Number Classification Cost per shift

1 Working foreman $18.521 Miner 17.281 Mucker 14.81

1 Hoistman 17.28

Labor cost per shift , $67.89

A detailed list of th e cos t o f supplies, tools, possible repairs,pumping, compressed a ir , i nsurance, transportation, sampling,

assaying, accounting, and managemen t wou ld vary so much foreach operation that only a n estimate ca n b e made. However ,

th e cost sheets of a large number of underground mines indicate that these costs range f rom 30 pe r cent to 50 pe r cent of

the total . cos t of th e operation. The higher figure should be ap

pli ed for mines where considerable timber is r equi red, and thel ower v al ue may b e u se d for mining under very favorable conditions. This percentage is for direct costs on ly a nd does no tinclude th e castor rental of equipment. Hence, for est imatesof operations such as shaft sinking, drifting, and stoping, th e

total cost may be divided on th e basis of 60 pe r c,ent f or l aborand 40 pe r c en t f or a ll other direct costs. There wil l be excep

tions t o this divis ion of costs, and, if they can be anticipated,allowances should be made. For example, labor eff iciency isreduced when water is encountered in a shaft, and if a shaftis to be s unk i n solid, bu t wet, ground th e co st o f l abor wouldbe higher . Inexperienced labor also may cause an increase inthe labor cost.

I f th e c os t o f labor as shown in the foregoing table amountsto 60 per cent of th e total cost of shaft sinking, t hen the overallcost pe r shift w il l b e $67.89 divided by 60 pe r c en t o r $113.15.The cost of suppl ies and other i tems at 40 pe r cen t w il l b e $45.26.Assume the average advance per shift of th e completed shaft

for th e crew of four is as follows:Advance, Labor cost Supplies, etc. Total cost

feet pe r shift pe r foot cost per foot pe r foot1 $67.89 $45.26 $113.152 33.95 22.62 56.583 22.63 15.09 37.72

Shaft sinking for uranium o re on th e Colorado Plateau is gen

e ra ll y i n very favorable g round and to shal low depths; hence it s

cost pe r foot in some cases may be less than shown h er e. D ee p

shafts cost more pe r foot than shal low shafts.

DRIFTING

The usual size of drift fo r th e small mine is 5 ft. wide by 7ft. high, which wil l a llow for a t rack with 18- inch gage, a ditch,

and pipes for a ir , water, an d ventilation. In bad ground th e drift


should be dr iven 6 ft. by 8 f t. in rock sec tion to a llow for timbers.The l abor d is tr ibut ion and costs a re shown as follows:

Number of men Classification Cost per shift

1 Working foreman $18.521 Miner 17.281 (or 2) Mucker 14.811 Hoistman 17.28

$67.8945.26

Labor cost per shiftSupplies, etc. at 40 pe r cent of total cost

Total cost pe r shift $113.15

In reasonably good ground, th e crew should advance 4 feetper shift, which wou ld amoun t t o dri ll ing, breaking, mucking,

an d hoisting 10 to 12 tons of rock. In ground requi ring t imber ,th e advance pe r shi ft wou ld be 3 feet or less. However , i f twodr if ts a re be ing advanced, an ext ra mucker can be used advantageously, as a mucking crew of tw o men c an b e wo rking i n one

drift, while th e miner, with th e foreman's help i f needed, canbe dri ll ing in th e other drift.

Cost of Drifting: The cost of drifting, including th e l ay ing o ftrack and pipe, under various conditions is shown in th e following table:

RAISING

Raising may be done t o explore ore shoot s for development of

ore, or for venti lat ion. Long ra ises for development or ventilation may be 4 feet high by 7 f ee t wide. A line of s tu ll s w il l b eplaced a long t he cen te r line of th e raise, an d lagging will b enailed onto one side of th e s tul ls, dividing th e r ai se i nt o two

compartments of which one is to be used as an ore pass, th eother w il l b e a manway with ladders.

Advance pe r Approx. cos tNumber of men Kind of ground shift (feet) per foot

4 Requires timber 3 $37.754 No timber 4 28.305 No timber 5% 25.00

The amount of drift ing needed to prove or disprove th e valueof t he p rope rt y wil l vary greatly. In some instances it will be

necessary only t o check diamond dril l ing results; in case of smallbu t high-grade ore shoots, considerable dr if ting may be requi redto determine th e amount of ore ava il able . Unle ss a definite

amount of d ri ft in g c an b e d et ermi ne d i n th e beginning of th eunderground exploration, about 300 feet t en ta ti ve ly may b e

planned.

As no information regarding grade and characteristics of th eo re can be obt ai ned f rom dri ft s in th e footwall or hanging wall,

th e drift ing should be done in or along th e vein whenever pos

sible.

,.-)




Fo r some types of s tope development , short raises about 4feet by 4 feet in cross sect ion wil l co nne ct t he d ri ft with thebottom of th e stope. These raises are 12 to 15 feet long.Cost of Raising: Raising is usually done while other phases of

mining are being carr ied on. Thus the cost per foot i s materiallyreduced, since supervi si on and hoi st ing a re ava il ab le withoutmuch additional cost. Also, mucking is necessary only at the

start, as a chu te should be ins ta ll ed after the raise has bee nadvanced 10 or 12 feet.In good ground a two-man crew should advance a 4-foot by

7-foot raise 3 feet pe r day. This work should include all drilling,blasting, t imbering, and tramming. The total cost per day wouldbe about $54 or about $18 per foot. For long raises, over 75 or100 feet, the cost wil l be h ighe r. The 4 feet by 4 feet chute-raises

will cost $10 to $12 per foot, not including cos t o f th e chute.


Total. $2,064

Rent: Ren t paid dur ing the exploration period is part of th ecapital investment. I f the equipment is obtained on a rentalpurchase contract, and if the exploration i s successful, only aportion of th e r en t is chargeable direc tly to the exploration.

TotaL $2,425The prices l is ted are for good used equipment a nd may v ar y

somewhat in different localities. New equipment would cost abouttwice the amount shown.

Supplies to be Purchased: Supplies, such as powder, fuse, detonators, bits, drill rods, and timber, that are consumed duringthe operations, have been included in the cos t o f shaft sinking,

drifting, and raising, as shown in preceding computations. Thefollowing supplies listed ar e p ar t of the capital expendituresand have not been included in th e previous costs:

Item Estimated cost

Track:16-lb. rai ls for an inclined shaft $ 120

About one ton (used); not needed for

vertical shaft.12-lb. rai ls for surface and underground 240About 2 t ons (used ).

Spikes, bolts, f ish plates, and t ies estimated at...... 150Pipe:

500 feet of 2-inch, black iron, @40c pe r

foot (new) for compressed a ir l ine ...,.................. 200500 feet of %-inch, galvanized, @16c pe rfoot ( new ) f or water pipe 80

Miscellaneous pipe fittings estimated at 100Ventilation:

450 feet of lO-inch galvanized pipe @1.00 per foot.. 450Ventilation pipe fittings 50

Hose:2 50-foot lengths of I -i nch a ir hose with

fittings @$40.00 each 802 50-foot lengths of lf2-inch water hose withfittings @$25.00 each 50

2 line oilers for dri ll ing machines @$22.00 each.... 44General tools:

P icks , s hove ls, s aws, axes, wrenches, anvil,forge, and other tools estimated at 500

Item Estimated cost3 mine cars (used) 16 to 18 cu. ft. capacity at $100 each $ 3001 t ruck-1 ton (used) ,.......................... 1,5001 pump (used)-small ai r dr iven duplex 751 mine fan-gasoline engine driven' (used) 250Auxiliary hoisting equipment-skip, sheave, rope 300

..\

60

150

100

$140185235260298

4,000

2,300

1,600

$3,4004;7006,0005,9007,300


EQUIPMENT

General List: The major equipment i tems for small mines maybe e it he r rented or purchased. Dur ing the exploration stage itis advisable to rent this equipment arid t h u ~ materially reducethe init ial capital outlay. Furthermore, equipment may be ob

tained on a rental-purchase agreement in which 75 pe r cent oft he r en t may be applied on the purchase price. This methodpermits a small mine operator to obtain equipment on a type ofinstallment ,plan.

The following is a list of equipment that may be rented:

Item of Cost Cost RentEquipment used new pe r monthCompressors:

105 c.f .m.-gasoline driven $2,250160 c.f .m.-gasoline driven , 2,850160 c . f . m . ~ d i e s e l driven 3,500210 c.f.m.-gasoline driven 3,750210 c.f.m.-diesel driven 4,500

Hoist:

Fo r cage with 4,000-to 4,500-pound rope pul l (gasoline) .. 2,600

For' skip with 2,000-to 2,500-pound rope pull (gasoline) .. 1,500

Fo r bucket with 1,000-to 1,200pound rope pull (gasoline) .. 1,000

Ai r drills:45-pound ai r leg drill, complete 400 585 6055-pound ai r leg drill, complete 450 605 602% inch stoper 375 735 65

The used equ ipment l is ted in the above table must be of a latemodel and in good reliable condition.

The f ol lowi ng i s a list of equipment that must be purchased:



$25,139

Under good supervIsIOn and favorable conditions, th e totalcost may be r educ ed as much as 25 per cent. However, underpoor supervision or adverse conditions, the cost wil l be substantially higher.

The cost figures shown here a re on ly to gu id e the small mineope ra to r o r the investor in. small mine explora tion . No twoexplorations are exactly alike, and no two ope ra to rs have identical costs; therefore the above cost figures, although derived inpart f rom act ua l sma ll m in e operations, will correspond to agiven explora tion only by chance.

PART II - MINING METHODS FOR SMALL MINES

FACTORS GOVERNING CHOICE OF METHOD

GENERAL STATEMENT

From information obtained dur ing the exploration programa mining method may be selec ted for. removal of the ore. If:h ? ~ e v e r ,

the exploration consisted only of drilling and testpIttmg, a method cannot be selec ted until a shaft h as b ee n pu tdown, or ad it driven, and enough drift ing and cross-cutting hasb een don e t o d et ermi ne the physical characteristics of the oreand wal l docks. This mining method should be the most suitable

as well as th e most economical one that will fit th e conditionsfound.

Of t he many factors or conditions that may influence choiceof a mining method, the more impor tant a re listed as follows:

1. Strength or physical characteristics of the ore and wall rocks.2. Value of the ore.3. Dip, length, and width of the ore body.4. Amount of capital available.5. Experience.

The above conditions a re not necessarily listed i n t he ir o rder

of importance, since under cer ta in circumstances some othercondition may be .of greater importance. For.example, a miningmethod that reqUIres a considerable amount of t imbe r may not

be the most economical, if t imber must be t ransported greatdistances at a very h igh cost.

Strength or Physical Characteristics: The s tr engt h o r physicalcharacteristics of the ore and wal l rock, such as texture, hardness, jointing, and faulting, indicate the' ability of th e ground

~ stand unsupported over a given span. This unsupported spanIS generally the principal factor that indicates the most suitablemining method to be used for a given ore body.

Value of the Ore: High-grade ores should be mined by a methodthat permits a high percentage of ore recovery. Such methodstend to be relatively expensive, bu t the value of the additional

ore' recovered should more than pay for the additional cost.Conversely, low-grade'ores mus t be mined by low-cost methods,even though th e percentage of recovered ore i s lower .

Dip: The ore f rom flat-dipping veins must be removed by mechanical or hand means, whereas ore f rom steeply dipping veinswill move to the haulage levels by f or ce o f gravity. Certain

mining methods do not lend themselves to successful operationson f lat dips.

Lengt h o f o re body: A regular method of support can be des igned for or e bodies of substantial length, bu t those shorterthan 50 feet may no t require regular support, or they may bemined by "gophering." In the cas e o f the small or e body, noregular method of mining is used


$ 840600720

$140100120


Allow for miscellaneous cost, such assampling and assaying 1,000

$2,160

*1£ -oompl'essed ai r is, to be used to ope ra te equ ipment o ther than drills,a larger compressor should be provided.

tA spare drilling machine is necessary.

Summary of Costs:

Item Estimated costSurface plant $2,800Shaft sinking 110 feet at $56.58 per foot 6,200Drifting 300 feet at $28.30 pe r foot 8,490Equipment t o b e pur ch as ed 2,425Suppl ies to be purchased 2,064Rent 2,160

24,139

Since, however, the mine operator must provide for payment oft he r en t d urin g th is period, it is usual ly more conveni en t fore st imat ing purpose s to inc lude a ll the rent in the explorationcosts; ,The time required to complete th e exploration outlined is as

follows:Shaft sinking at 2 feet per day will require fifty-five days to

complete 110 feet of shaft .Dri ft ing a t 4 feet p er d ay will require seventy-five days tocomplete 300 feet of drift.

Allowing twenty-four shifts p er mon th a nd a f ew sh if ts f ora safety factor, si x months would be required to complete theexploration. Therefore the renta l costs would be as follows:Item pf Ren t per Total cost

Equipment month f or s ix mon th s

*105 c.f.m. compressor(gasoline) .

Hoi st for skip .t2 air-leg drills .

16



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Width of ore body: An ore body of 10 or more feet wide maybe m in ed by one of several methods, the choice of which maydepend upon some condition other than width. For removingthe ore f rom a vein 5 feet wide, only two'methods are available,and one of t hem depends p rimari ly upon a physical characteri st ic of the ore or wall rock ra ther than upon width.

Capital available: I f t he amoun t of capital available is sma ll ,

only those mining methods that require a small amount ofdevelopment work may be considered. Sub-level stoping is avery low-cost method of mining, but it requires a substantialamount of capital for development. Hence , a small amount ofcapital will prevent use of this method and necessitates a lesseconomical metho·d.Experience: 'There is no substitute for mining experience. I t is

improbable. that a person with l it tl e o r no mining experiencecould s el ec t a sui table mining method or develop a mine forproduction. Inexperienced people generally mine by "gophering"or "gouging," and unless the ore is high grade, the operation isapt to fail.Each mining method described i n th e following discussion has

been devised to fit a particular se t of conditions and when properl y used should be the most economical and safe method for those

conditions. In some instances there will be a choice of one ormbre methods, bu t the final selection should be based upon economical production with safety.

As used in this discussion, a "strong" ore or wall rock in general is one that will s tand unsupported over a width of at least10 or 15 feet and a length of 100 feet; a "weak" ore or wall rockis one that will not stand unsupported over an area of approximately 6 feet by 6 f ee t f or mor e than a shor t period of t ime.Some ores and wal l rocks belong between these two extremes,bu t methods have been devised for the mining of ore under almost any se t of conditions.

PARTICULAR METHOD

GOPHERING OR GOUGING

Some ores are mined without any regular procedure or sup

port. Such a .method, i f t he t erm "me thod " c an b e appl ied, isused to mine irregular stringers or shoots of ore . I n many cases,however, its use result s f rom inexperience. This method, i f applied to a larger and more uniform ore body, would soon renderthe mine a rea dange rous for workmen to ent er , and t he remaining ore might be lost. Since gophering or gouging has only avery limited application, it will not be discussed further.

STARTING THE STOPE

When the physica l character is tics of the ore and wall rocks

ar e known, and a min ing met hod h as b ee n chosen, it w ill benecessary to prepare the ore body for mining. Raises should bedriven at each end of the planned stope, if th e ore shoot is more

18




than 50 to 75 feet long; otherwise only one raise may be used,and i t should be at one end of the s tope. Raises are to be usedfor ventilation and to permit access to the stope. I f adequatemechanical ventilation is available, the raises can be driven asthe s tope is advanced; otherwise they should be driven beforethe s tope i s started.

Stoping ma y be started directly on drift sets as show n in

Figure 1, or above drift pillars as shown in Figure 2. Each of thesemethods has certain advantages and disadvantages as given insubsequent paragraphs.

Stoping on drift sets: (Fig. 1 )

Advantages: 1. Full product ion can be at ta ined almost imme-diately.

2. No chute raises necessary for shrinkage stoping.3. No o re l os t in drift pillars.4. Best for level intervals of 75 f ee t o r less.Disadvantages: 1. Cost of drift sets.2. Where dip is 60 degrees or more, t he weigh t of broken ore

o r was te may c rush the d ri ft sets.3. Not recommended for veins over 10 feet thick.

4. T im be re d d ri ft m us t b e k ep t in repair.

The stope is opened by first taking a cut about 6 fee t h igh outof the back of the drift, from foot to hanging. This ar e is removed, and regular 3-piece drift sets are pu t in at about 5-footintervals. The drift sets ar e l agged on th e sides and doublelagged on top. Chutes are built into th e drift sets at about 15foot intervals, if th e shrinkage stoping method is to be used.When the drift is completely timbered, a second cut is takenfrom the back. This second cut should n ot be m or e than 2 or3 feet t hi ck and should be blas ted l ight ly to prevent breakingthe lagging on top of the sets. This are is left on top of thetimber to act as a cushion, if the shrinkage method is used; orth e a re is removed, and was te f il ling is pu t in its place, if thecut-and-fill method i s used. The stope is then carried upwardeither on broken are as shown in Figure 7 or on waste fill asshown in F igure 4.

Starting t h stope on dri ft pil lars : (Fig. 2)Advantages: 1. Better protect ion for the drift.

2. Bes t for l evel i nt erva ls ove r 75 feet.3. Very l it tle costly timber used.4. No r ep ai r w or k on timber.5. Not limited by the dip of the vein .Disadvantages: 1. R eq ui re s m or e d ev el op me nt w or k fo r f ul l

production.2. Chute raises necessary for shr inkage stoping.3. Some a re may b e l os t i n d ri ft pillars.Opening th e stope on drift pillars is probably the safest and

most sat is factory method to use. I f mining or explorat ion is tobe done beyond the stoped area, t he d ri ft will remain open. In

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the long run, th e cost wil l p robably be lower with drift pillars.The stope is opened by driving a small drift parallel to the maindrift and from 10 to 25 feet above it. This sub-drift is drivenfrom the r ais e on one end of th e stope to the ra is e on theother end.I n t he shrinkage stoping method (Fig. 7)-, chute raises at inter

vals of about 15 feet are dr iven from the h au la ge d ri ft t o t he

sub-drift, and their tops are funneled out to cut the vein offfrom foot-to-hanging wall for the full length of the stope.I n the cut-and-fill method, the s tope is started from the sub

drift, and the broken ore is t rammed or s cr aped to the nea re store pass. The fill then is placed direc tly on top of the drift pillar.

ROOM-AND-PILLAR METHOD

The room-and-pillar method is used extensively for mining offlat-lying deposits or for veins or beds of ore which d ip lessthan 35 or 40 degrees from the horizontal. It is a very simplemethod of mining. (Fig. 3)

The width of the rooms (stopes) and the s ize of the supporting pillars depend upon the strength of the wall rocks, especiallythe hanging wall, the strength of the ore, and t he distance below th e surface. Pillars 8 to 10 f ee t t hi ck with rooms 15 to 20

fee t wide are common in metal mining. With s t rong ore and astrong hanging wall, 10-foot pil lars and 30-to 35-foot rooms ar epossible. With a weak hanging wall, 15- to 20-foot rooms may bepossible if two rows of stulls ar e placed in the stope, parallel tothe pillars, f or added support of th e hanging wall . Openings

a re m ad e through the pillars where n ee ded t o permi t bet te rventilation of the rooms.The first mining, that is, the removal of ore f rom t he drifts

and rooms, will give a 60 to 70 pe r cent extraction of the ore,and the balance remains in th e pillars. When a secti on o f theore above one drift has been mined, th e p il la rs can be robbed(mined). It is usually impossible t o r emove all th e ore fromthe pillars, but in most cases enough can be removed to give anover-all extraction up to 90 pe r cent.In horizontal or nearly horizontal deposits, th e mine c ar s c an

be loaded at the f ace o f the room. For dips exceeding 5 or 10degrees, either scrapers or conveyors are used to move th e oreto c ars i n the haulage drift. Fo r d ips of more than 20 degrees,the scraper is most commonly used.Advantages of the method: 1. A simple method of mining.

2. Well sui ted to veins o r bedded deposits which dip less than40 degrees.

3. Full production possible in a short time.4. Small amount of capital tied up in development.

5. Small amount of timber necessary in most cases.Disadvantages: 1. Canno t be used on steeply dipping deposits.2. Considerable ore l ef t in p il la rs t o be robbed later.

3. Additional equipment as scraper hoists and scrapers needed.



l

25

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ORE

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VERTICAL LONGITUDINAL SECTION

Figure 5.-Inclined cut -and-fil l s toping on drif t pillars;(After U.S. Bur. Mines Bull . 419).

Accident record: Fairly l ow for deposits less than 8 feet thick,bu t th e rate is higher for thick deposits.

Cost per ton: For small mines th e cost should be f rom $5 to$10 per ton, except for very thin deposits.

CUT-AND-FILL STOPING

In th e cut-and-fill method, a 4- to 6-foot cu t of ore , from footto hanging wal l and the length of the stope or panel, is blastedfrom the back of th e stope and transferred to the haulage level.A volume of waste material is then brought into the stope tofill a space equal to th e volume of ore removed. I t is from thisprocedure that th e name "Cut-and-Fill" was derived.

The method is divided into two types, although th e generalprocedure is about th e same for both. The,principal type is called"Horizontal" or "Flat Back" cut-and-fill stoping because th emining faces in th e stopes are horizontal or nearly so, as shownin Figure 4. The other type is called "Inclined" or "Rill" cut-andfill stoping, because th e mining face is inclined at an angle thatwill cause th e br oken or e t o flow to the o re pas s by f or ce o f

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24



STULL STOPING IN NARROW VEINS

A stull is a single piece of timber that is s et between the footand hanging wall of the vein as shown in Figure 6. I f the timbe r is vertical or nearly vertical, it is usually called a post ratherthan a stull. As shown in Figure 6, a great many s tu ll s are usedin this method, which gives rise to th e name, "Stull Stoping."

The stul l s toping method is used in veins 6 feet t hi ck o r less,

gravity, and the waste filling will flow into the stope from the

waste raises as shown in Figure 5.By this method, stoping may be done on drift sets as shown

in Figure 4 and 1, or on d ri ft p il la rs as shown in Figure 5. Thechoice will d ep end upon t he width and dip of the ore body asexplained before, the cos t of timber, and the experience of th eoperator.

The method is used in ore bodies where the ore is s trong andwil l s tand unsuppor ted over the width of the o re body and the

length of the stope. One o r b oth walls may be weak and require support. The supporting material is waste rock that hasbeen obt ained f rom development work in the mine or fromsome source outside the mine.

This method may be used in either narrow o r w id e o re bodieswhich dip at least 40 degrees or steeper.

Advantages: a. Caving is reduced by the filling.b. Irregular extensions of ore can be mined.

c. Waste can be sorted from ore in the stope.d. Ore is removed from the stope soon after it has been mined.e. Oxidation of the ore is reduced to a minimum.f. Large pieces of ore can be broken in the stope.g. Horses of waste can b e le ft in place.h. Less dilution of ore with waste.i. Stope can be w ell ventilated.Disadvantages: a. High cos t o f mining.

b.Low production per man-shift.c. Difficulty in obtaining filling.d. Mining is stopped while fil l i s being placed.e. Fill must be covered by flooring.f. Some los s o f fines through flooring.g. Considerable amourrt of timber used.h. Timbered raises through the filling g et o ut of line due to

settlement of filling.

Safety Features: The accident rate is fairly low.

Cost: The cos t p er to n for small mines may be from $10 to$15.

The inclined o r "Ri ll " stoping method should be less cost lythan the horizontal or "flat back" method, bu t the accident rateis much higher. Rocks roll ing down the inclined flooring or fillingcause many injuries, especially in narrow and steeply dippingveins.


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EXPLORATION AND DEVELOPMENT OF SMALL MINES 29UNIVERSITY OF ARIZONA BULLETIN8

SHRINKAGE STOPING

In t hi s method about two-thirds of the broken ore is l ef t i nthe s tope to ac t as a plat form from which th e miner s can d ri ll

above. One-third of the ore is removed ei ther through chutesat th e bottom of th e stope or by scraping to raises a t the endsof the stope. This one-third must be removed, since broken oreoccupies about one-th ird more space than s oli d ore .

The stope may b e st ar te d on drift sets a s s ho wn i n F ig ur es7 and 1, or on drift pillars as shown in Figure 2. Wide s tapes

ar e usually started on drift pillars, because the weight of brokenare i n t he stope may be greater than drift sets could hold. However, narrow ore bodies, less than 8 feet or so in width, may besafely. started on d:dft sets.

Vertical holes, drilled with a s to pe r, generally ar e used tobreak the are. In some places, however, the vertical holes tendto shatter t he b ac k a nd m ak e the stope unsafe; under these circumstances air-leg drills are used t o d ri ll horizontal o r nea rl y

horizontal holes. Both methods are shown in Figure 7.I f the broken o re is removed through chutes placed at the

bottom of the stope, the trammers should check with the minersto see that the top of the broken ore moves down evenly while

being drawn. I f th e vein is narrow, less than 5 or 6 f ee t, or ifthe walls of the stope are irregular, the broken ore may arch

where the ore is s tr on g a nd t he w al l rocks a re s tr on g o r f ai rl ystrong. T he d ip of the ore body should be 40 degrees o r m or eso that th e are wil l move along the slides a nd a re passes bythe force of gravity. I t can be used on f la tter veins, bu t theare must then be moved to the main haulage levels by mechanical means or wheelbarrows.

Advantages: a. Smal l amount of capital is required to bringthe mine into production.

b. Mine can be brought into product ion in a very short time.c. O re c an b e s or te d in the s tope if necessary.

d. Miners' work under l ow , s oli d back that can be examinedeasily for l oose r oc k.

e. G oo d ventilation is possible.f. I t i s, a simple method o f m in in g:Disadvantages: a. Production per man shift is low because th e

vein is narrow, and because of the t ime used in sett ing timber s and bui ld ing slides and platforms.

b. A large amount of timber is necessary.

c. Dangerous to work on platforms.

d. Valuable fine ore may be lost through the pla tforms andslides.

Safety features: The accident rate is fairly high because of thedanger of fal ling from platforms.

Cost: The cost varies with the thickness and hardness of theare bu t .should be between $7 and $12 pe r ton.



across from foot-to-hanging wall, forming an open pocket between. the top of the broken ore and th e chutes. The vibrationcaused by a drill ing machine may break this arch; t he minermay be drawn into the pocket and covered with broken ore.Accidents of this type are usually fatal.In ore bodies that are narrow or have irregular wal ls t he

b roken o re should be removed by scr ap ing to r ai se s a t th e ends

of the stope. This change in the method requires more equipment but removes a safety hazard.The method may be used where the ore is strong, and where

the wal l rocks wil l not slab off and dilute th e ore. Also the dipmust be sufficiently steep, 45 degrees or more, to cause the oreto slide down the footwall.Advantages: 1. Low cos t of mining.2. Some product ion can be obta ined immedia te ly .3. Small amount of capital in development work.4. Large number of men can wor k i n a small area.5. High production pe r man-shift.6. Broken ore gives some suppor t to wall rocks.7. Large chunks of o re c an be broken in th e stope.8. Small amount of timber used.9. Very common method of mining.

10. Experienced workers are usually available.11. Good ventilation of s topes is possible.Disadvantages: 1. Two-thirds of ore remains in stope until

completed.2. Considerable cap it al t ied up in broken ore.3. Possible dilution by wall rock.4. No sorting of waste f rom ore in stopes.5. Arching of broken ore is dangerous.

6. Ores with 25 pe r cent or more of sulphides may burn.7. Oxidation of broken ore may reduce mill recovery.Safety features: Accident rate is f ai rl y h igh because:a. Method is sometimes used in unsui table ground.b. Careless drawing of ore by trammers.c. Poor supervision.Cost per ton: The cost will vary from $6 to $12, depending

upon width of the ore.

SQUARE-SET STOPING

As the ore is removed from the vein in the square-set methodof mining it is replaced by a framework of t imbers . These t imbers offer temporary support to the ground and when t he mininghas advanced fa r enough the framework is fil led with waste.This framework consists of rectangular box-like sections calledsquare sets consist ing of four posts, two caps and two girts.Each timber is f ramed to fit into it s proper place, a nd e ac h s etwill fit into the adjacent se t or sets. See Figure 8.The method is used where the ore or the ore and wall rocks

ar e h ea vy a nd w il l s tan d unsupport ed ove r only very small

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areas, usual ly not much ove r 6 by 6 feet or so. A secti on of orethe size of a square se t is removed and a se t is placed in theopening, lagged and blocked into place. The method is veryflexible as the sets can be ext ended in a ny d ire ct io n or c an b e

l ef t o ut whi le m in in g a ro und a block (horse) of wast e or inmining a narrow part of the vein. Sets may also be added tot he r egul ar se ts , so that stringers of ore extending into the

foot or hanging wall may be mined.I t is a very high-cost method of mining and can not be used

for the -. mining of low gra de ore bodies. Thi s method should

be adopt ed only after al l other methods have been consideredor tried. It is possible to obta in 100 per cent extraction of th eore with t hi s met hod and h en ce it is somet imes used for th emining of high grade ore bodies that could be mined by cheapermethods; because the high percentage of ore r ecovered wil lmore than pay for the high cos t of mining.

Advantages of the method: 1. Irregular ore bodies can bemined.

2. Horses of was te can be left in place.3. Waste may be sor ted f rom the o re a nd l ef t in the stope.4. Different grades of ore may be handled separately.

5. High percentage of extraction.6. Very little caving or settling of the hanging wall.7. Very flexible.

Disadvantages: 1. The most cos tly of a ll min ing methods.

2. Production pe r man-shift is very low.3. Rate of mining i s s low.4. A la rge amount of costly framed timber is used

(about 20 board-feet pe r ton of ore removed).5. Well t ra ined workmen are necessary.6. Very close supervision is required.7. Use of mechanical equipment is l imited.8. Danger of mine fires because of th e timber.9. Stopes ar e difficult to ventilate.

Accident record: This method has the highest accident rateof any mining method, although its rate of fatal accidents islower than that of some other methods. The high accident rateis caused in part by the la rge amount of timber that must be

handled.

Cost per ton: The cost pe r ton for the square-set stoping variesmore than that for any other met hod and fo r sma ll m in es wi ll

probably be $15 or more.I

Square-set stoping is one of the more complicated methodsof mining and should be directed only by experienced personnel.


There a re many reasons why smal l mines prove unprofitable.

The mos t common are as follows:

3.Lack of capital4. Premature erection of a mill

1. Lackof

ore

2. Poor management

In many cases large sums of money are spent for th e construction of a mil l before explora t ion or development h ave b ee ncompleted. The operators may th en find insufficient ore to bet rea ted in the mill, and that not enough capital is left to complete

the mine development, or that the mill w as not designed totreat the ore found. This situation results from inexperience orpoor management.

Many good smal l mines fai l because there is not enough capital available for development, equipment, payroll , and supplies,whereby the' mine might car ry through the early s tages to th eperiod of profitable returns . Adequate financing should be assured before explora tion or mining starts.

The exploration program may be unsuccessful or may indi<;ateonly a small quantity of ore; when this ore h as b een m in edout, the mine must be closed. There are also many instanceswhere a tt empts have been made to mine material that was toolow in g ra de t o return the cost o f production. Failures of thisty pe are due primarily to poor management . I t h as be en saidthat 90 pe r cent of the success of a venture depends upon management. This is true f or m in in g as wel l as for any o ther k indof bus iness. Good management may make a profi t on low-gradeore, bu t poor management must have a bonanza mine to makea profit. I t is advantageous for both the owner and the investorto see that the mine is well managed.

PART III. WHY MANY SMALL MINES PROVE

UNPROFITABLE

The re a re many o ther reasons why small mines fail. Mo stof them result indirectlyfrom poor management or lack of capital.The mos t common one is misunderstanding among those whoare interested in the property. Other causes include excessiveamount of water in the mine workings, changes in the- markEitprice of metals or minera ls produced and disasters such as firesor caving.




The operation of a concentrator requires substantial quantitiesof wat er , whi ch mus t be assured before a dec is ion is made toerect a concentrator.

In order to assist small operators, The Arizona Bureau ofMines pl,'ovides an ore-testing service for ores originating withinthe State of Arizona. The charge for this work is nominal. Fulldetails will be furnished upon request.

A considerable knowledge of ore concentration is necessaryto determine the proper flow sheet for the ore. Unless the operator is thoroughly trained in this field, he should obtain theservices of a consulting metallurgist to t es t the ore and to designthe mill properly. Such a man should be well and favorablyknown in his profession. A correctly designed mill may meanthe difference between a profitable operation and failure.


PART IV MILLS FOR SMALL MINES

34

Mills are expensive, and the simplest type of gravity concentration plant, including crushing and grinding, will cost $1,000per ton of daily capacity, if good used equipment is used. Thus

a mill of this. t ype wit h a dai ly capaci ty of 25 t on s wil l cos tapproximately $25,000. Using new equipment will add to thecost. If the mill is not located near a public utility power line,the cost of a power unit will be additional. A mill using selective flotation will cost substantially more than the gravity type,and a fine-grind cyanide plant wil l cost twice as much as a f lotation mill.

Comparatively few small mines have sufficient ore reservesto justify the cos t of erecting a mill for concentrating the ore.The amount of this reserve will depend upon the cost of custommilling or smelting plus the cost of transporting the raw oreas compared wi th the cost of concentration in a sma ll mill plusthe

cost oftransporting and smelting the

concentrates.The

reserves must be large enough so t ha t t he savings on their t reat-ment will pay for the mill. The cost of operating a smal l milli s h igh, and frequently the recovery is lower t han tha t for alarger mill. Labor costs alone will be a minimum of $3 pe r tonof ore treated, to which must be added the cost of supplies,power, repairs , taxes, and miscellaneous costs.



SERVICES OFFERED BY THE ARJZONA BUREAU OF MINES(Continued from inside front cover)

3. Geologic investigat ions of mining dist r ic ts and counties and th emaking of topographic and geologic maps an d reports. In cooperation withthe United States Geological Survey a la rge-scale base map, a reconnaissance geologic map, an d a topographic map (lOO-meter contours) of theentire S',ate have been pub li shed . Geologic r epor ts on various mineralresources of t he S ta te a re prepared.

4. The Bureau provides an ore-testing service fo r ores or igina t ingwithin the State of Arizona. Full deta i ls wi l l be furnished on request.

5. Semitechnical meetings with miners and prospectors ar e heldthroughout the State.

6. The collection and dissemination of statistics relating to the mineralindustries of th e State.

7. The collecting and filing of al l i tems relating to Arizona mines andminerals that appear in Arizona newspapers an d in many technicalperiodicals.

MAPS OF ARIZONA

The Arizona Bureau of Mines now has avai lable for distribution th efollowing map s o f the S ta te:

A. Base map of Arizona on a scale of about 17 miles to th e i nch. Thi smap i s s t ric tly geographic , indicat ing th e posi tions of towns, ra il roads,rivers, surveyed lands, national forests, national p ar ks and monuments,

etc., r ev i sed to 1939. I t is pr in ted in b la ck on one sheet 22x36 inchesand sells fo r 30c unmounted.

C. Geologic map of Arizona in one sheet o f many colors. I t wa s is;medin 1924 on th e same scale as the topographic map, b ut i t is now out ofprint, and i ts l i thographic plates a re wor n beyond repair.

The Bureau is now prepared to supply s et s o f 44 kodachrome slides,2x2 inches in size, covering the en ti re map. The slides may b e used wi theither a low-cost pocket v iewer o r a projector. The pri ce of t he s et is$9.00 which includes mailing charges.

D. Metallic Minera l Map of Arizona, 25x27 inches. This map consistsof a re d overprint made on Map A, and shows the p rinc ipal knownlocalities of metallic minerals by means of representative symbols. Roadsar e indicated. This map vvas revised in May, 1953, and sells fo r 30c whendelivered w it hout t ub e i n t he offices of the Bureau of Mines. I f mailed,the cost, including mailing tube, is 45 cents.

E. Nonme ta ll ic ,M iner al Map of Arizona, 25x27 inches, similar to

Map D bu t devoted to nonmetallic minerals. This map sells fo r 30c whendelivered without tube in th e offices of the Bureau of Mines . If mailed,the cost including mailing tube, is 45 cents.

F. Map of Ari zona Min ing Districts, 25x27 inches. This map consistsof a re d overprint made on Map A and s hows t he p ri nc ip al m in ingdistricts of mining localities by mean s of numera ls and index. Roadsare also indicated. This map is sold for 30c when delivered without tubei n t he offices of the Bureau of Mines. I f mailed the cost, including mailingtube is 45 cents.

All communications should be addressed and remittances made payableto the Arizona Bureau of Mines, University of Arizona, Tucson, Arizona.

Documents

Exploration of Small Mines