Technical Paper 95: Mining and Milling of Lead and Zinc Ores in the Wisconsin District, Wisconsin

United States Department of the Interior Bureau of Mines · 1915 · Historical

Technical Paper 95: Mining and Milling of Lead and Zinc Ores in the Wisconsin District, Wisconsin by United States Department of the Interior Bureau of Mines…

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

REEE LOGE FRIAGETON, NA. Technical Paper 95 DEPARTMENT OF THE INTERIOR BUREAU OF MINES

JOSEPH A. HOLMES, Drrector

MINING AND MILLING OF LEAD AND ZINC ORES IN THE WISCONSIN DISTRICT WISCONSIN

By

Clarence A. Wright

Washington Government Printing Office

sateen once

The Bureau of Mines, in carrying out one of the provisions of its organic act—to disseminate information concerning investigations made—prints a limited free edition of each of its publications. When this edition is exhausted copies may be obtained at cost price only through the Superintendent of Documents, Government Printing Office, Washington, D. C. The Superintendent of Documents is not an official of the Bureau of Mines. His is an entirely separate office and he should be addressed: SUPERINTENDENT OF DOCUMENTS, Government Printing O ffice, Washington, D. C. The general law under which publications are distributed prohibits the giving of more than one copy of a publication to one person. The cost of this publication is 10 cents. First edition. January, 1915.

Contents.

Page.

INGO UCTIONY Sadan aavdaies scisteianlamninen va seecls oawunas sgh ban wediees eames asad 5 Acknowledgments i.e sce Veccss cose poche iene ye loo seis See sks FaeSndwee ses 6 Mining and milling in the Wisconsin district 2-2--222 6 Situation of chief producing areas 2--2-2-20- eee eee eee eee eee 7 Zinc production in the district 2- 222202 e ee ee eee eee eee eee eee 8 Field relations of ores: $so.2% 2.07.35 setsaetsasees,2og0b3.4etenasomtapvosaesanaee 9 Ore Cepowita :.2.. ie sisatiae a afew Walaind arabes eye eleran SOS LE helen owsy cee yes 1l OCeuITenGe ssi sisees ie iS oetex saci ee ye siwesasscteae esses censaseoses 11 Mineral: constituanta..522 spe 2ece Ye csede sis leg Sac ease ese GsG ee ee 12 Prospecting methods :.c< i.e. scsce2sclaS224254558 bRerceeiteasteepaweaenes 13 Mining methods..5:..c.ssicarscae sn eess tne he Sete eco F 5s Gee see eeloe sear 14 Underground) work 2 0 tie balsineia'gas sh eiedgalamee sea o oka eer 14 Shafts 6- 2525 hcade oe heehee Sowa sone eae Pics wae e ey sales snesew aves 15 Drilling pracheess. si Jose rsicdheloiies 38 bree IS ace pe Osos nbeeseigseics 15 Blasting co22 ietieetes dice sca secis teary ccasbess Soraass padseasecetoues 16 Shoveling and underground tramming +--+--+-+-- 17

THO DEN Ig oo obit eu shes fargo need beds ceeteicasaasd Boueeesepotesseis 18 PUMPING oleicadats ose wise darele osisseigus ead gace tet coesasa steers tee ssics 18 Surisee: workyecess os coher seth et eseteis uch ste es sgeasast ieee geese 19 Hoisting and surface tramming 2---2-2---2-2-e- eee 19 POWGEs:20sscccestabes saad vad atin isashahas ame sed aes Sainte akanpacas wale 19 Ore-dressing practic. s...522.<22 22s scecansodssinad $29 SSseiSreices tase He88 20 Concetitrating mills ans 3.0'scsdsciire pos canoes semanssaese cess anaes 20 Method of concentration... . 2.2.22. 62 jcc cee ee eset eee ee eee eees 20 Crushing 'sseacks yee paewP aes eae uasa ogee serene eae de pe Soe eeeeeeS 21 DIVING seeds teats sea sb esa Dohad song st oaispeudswnsseseclbesepore 21 Rougher-and-cleaner system 22e eee eee cece eee 22 Oné-jis system. st ooteasccss co insenteses fo tues as sonaacassersesenses 22 Concentration of fine material 2-22-2--2-2-202220+- 25 Handling and treatment of concentrates +--+ ++-++-- 27 Source and quantity of waste 222: - eee e ee eee eee eee eee eee 28 Mill tepta.;occcssccoscieescls scacincamet sag peancseetwied csessametbasssedacass 30 Comments on results of tests 2 2-- 22-22 eee ee eee ee eee eee eee en 33 Labor in the Wisconsin district + Se re 33 Cost data. feos cos cassie ns woah se mossy certs cco eean rane cee scat smacaesea ne kis 34 Accidents and safety precautions 2--2-2- 22-22 2ee cece eee eee eee 35 Health conditions at the mines 2222-20- 2-22 cece eee eee eee eee 36 Regu: seas och sce getda serene teas £5.54 45 2a sae eeysaeeae ee a 37 Publications on mineral technology + e-2eee- eee sees 38

Puate I.

Fiaure 1.

a

Illustrations.

A, Tramways connecting shafts at mine near Livingston, Wis.; B, Endless rope haulage system between shafts

A, Mill near Cuba City, Wis.; B, Mill near Platteville, Wis Curves showing spelter produc tion in Wisconsin lead and zinc dis- THIGH, TIOC 91S en a5 sesh sce es ewe pete nisla's spielen gare ate ciamplaw ele aiaaens

. Generalized geologic section of the Lancaster and Mineral Point

quadrangles: o22.a23 te cdesecesesasasiesecscwsoasscasgosea anne

. Diagrammatic cross section of a series of flats and pitches . Arrangement of a representative lead and zine concentrating mill

in the Wisconsin district, one-jig system

. Arrangement of a representative lead and zinc concentrating mill

in the Wisconsin district, rougher-and-cleaner system

MINING AND MILLING OF LEAD AND ZINC ORES IN THE WISCONSIN DISTRICT, WISCONSIN.

By Criarence A. WRiGarT.

Introduction.

The Wisconsin lead and zinc district includes not only mines in the State of Wisconsin, but also mines in those parts of Illinois and Iowa directly adjacent to southwestern Wisconsin. This district has long been known as a lead producer, but only within recent years has it been considered an important producer of zinc.

The geological occurrence of the lead and zinc ores of the district has been described in numerous reports by several geologists. Some of the more important recent publications are those of the United States Geological Survey, by Bain,* and by Grant and Burchard,® and those published by the Wisconsin Geological and Natural History Survey.¢

In this report no attempt has been made to describe, except incidentally, the geology of the district, the author's aim being to give a general outline of the methods used in mining and milling and to show in some detail the general conditions affecting the efficiency of those methods. The report indicates certain improvements that can be made and emphasizes the importance of safety and health conditions at the mines. The authordid not visit all the minesof the district, but this report is based on an inspection of most of the more important representative mines.

Only the mines and mills actually examined are discussed in detail, and statements of results cover those mines in general, with no special reference to any one mine.

The lead and zinc ores are closely associated, but the proportion of zine ore mined is far greater at present than in former years. For this reason, and because the losses in milling zinc ores are proportionately greater than in milling lead ores, the zinc ores are here considered more especially. The author made a few mill tests in order to

a Bain, H. F., Zinc and lead deposits of northwestern Illinois: U. 8. Geol. Survey Bull. 246, 1905, 56 pp.; Zinc and lead deposits of the upper Mississippi Valley: U.S. Geol. Survey Bull. 294, 1906, 155 pp.

Grant, U. 8., and Burchard, E. F., Lancaster-Mineral Point Folio Geol. Atlas 145, U.S. Geol. Survey,

¢ Lead and zine deposits of Wisconsin: Bull. 14, Economic Series No. 9., Wisconsin Geol. and Nat. Hist. Survey, 1906, 100 pp.

6 Mining And Milling Of Lead And Zinc Ores.

determine in a general way the efficiency of the milling practice, but there are few concentrating plants at which systematic mill testing and sampling can be done, owing to the arrangement of the mills and to the necessity of estimating the tonnage of the ore treated. However, much time could profitably be spent in the Wisconsin district in studying the milling conditions and in devising means of lessening the loss of zinc, especially in the treatment of fines.

The author has made several comparisons between conditions in the Wisconsin district and those in the Joplin district, on which the bureau has issued a report.

Acknowledgments.

The writer is greatly indebted to the operators and mine superintendents for furnishing much information, for extending many courtesies, and for giving assistance in many other ways.

Mining And Milling In The Wisconsin District.

In the Wisconsin district simple methods are used in both mining and milling, the mines are shallow, and most of the plants are small and simply equipped. To one accustomed to the elaborate methods used in some mining districts elsewhere, and to districts in which everything is done on a much larger scalethe practice in this district may seem crude and wasteful, but after a careful study of the ore bodies it will be evident that the methods used here are in general well adapted to the existing conditions. The ore bodies vary greatly in shape, and it is difficult to calculate the yield of an ore body from the records of the drill holes. Often, however, the amount of drilling and preliminary development work is too small, an attempt to block out the ore being seldom made, except by the larger operating companies.

The generally small size and irregularly varying shape of the ore bodies have not encouraged the building of large and expensive plants. The loss of time occasioned by an insufficient or irregular ore supply is more costly with a large mill than with a small one, so that large central mills have not been considered feasible in this district.

Although the controlling conditions mentioned persist with little change, the methods used in both mining and milling are being constantly improved and the general conditions at the mines are being bettered each year. The operators are making every effort to improve the milling methods and to effect any possible saving of ore.

On the whole the ore is richer in mineral content than that mined in southwestern Missouri, so that a somewhat higher recovery is

@ Wright, C. A., Mining and treatment of lead and zinc ores in the Joplin district, Missouri, a preliminary report: Technical Paper 41, Bureau of Mines, 1913, 43 pp.

Mining And Milling Of Lead And Zinc Ores. 7

possible, but the content of iron is so high that the concentrates produced are of much lower grade, and most of them have to be re-treated by roasting and magnetic separation.

Situation Of Chief Producing Areas.

The chief producing areas of the Wisconsin lead and zinc district at present are included in Grant, Lafayette, and Iowa Counties of southwestern Wisconsin, and in Jo Daviess County in the adjacent corner of Illinois. Formerly mining extended into Dubuque and Clayton Counties of northeastern Iowa, just across the State line, but for the past few years mining has been at a standstill in those counties.

The district is divided into mining camps, or distinct groups of mines, separated by areas that so far have been nonproductive. The names of the camps, together with the names of the more important mines included in them, are tabulated below:

Producing mines of the Wisconsin lead and zinc district during the year 1913.

Location.

Name of mine. Name of mine.

Section. aes Range. Section. TOW" Range.

ship. Benton Camp, Wis. meee Camp, is, 30 IN. 2E. COMO... 355 since an 29 5N 1E. ot ee 1E- Ellsworth. 2227) 29| 5N 1E. 8 iN. 1E, Rundell 30 5N 1E. 16 IN, LE. yigtin Camp, Wis. Lucky Six. 25 5N 1E. Peacock... 25 5N 1E. : 2 N. LW. Shamrock. . 34 5N 1E. 8 ce ¥ Montfort Camp, 32 2N. 1E. or Pane O. P. David 30 6N. 1E 27N. 1E. P 22| 29N. LE, "Pesterle Comp, 21 29 N. 1E. wi East End 29 3.N. lw. Hazel Green Camp, Empire S85 15 3N. 1w. Wis. Enterprise. . . 15 3N. 1W. Grant County ll 3N. lw. Cleveland 30 1N. 1E. Homestead... ll 3N. 1W. Federal. . . 533 32 1N. 1E. Klar-Pigett.. 4 29 3N. 1Ww. Kennedy. 29 IN. 1E. Potosi Camp, Wis. es Camp, Wilsons ...2. 0.50 35 and 36 3N, 3W is. Shullsburg Camp, Highland-Franklin. 28 7N, 1E. Wis. Linden Camp, Wis. Milwaukee - Shulls- Ly ae 30 2N. 3E. Optimo No. 1 8 and 9 5N. 2E. Rodham... 25 2N 2E. Optimo No, 2 17 5N. 2E. Winskill... 19 1N 2E.

In addition to the mines mentioned above, some prospecting is being done and new developments will no doubt be commenced in the near future, so that the production ef the district as a whole should gradually increase within the next few years.

8 Mining And Milling Of Lead And Zinc Ores.

Nearly all the camps are within a short distance of some railroad, so that the shipment of the ores is an easy matter, although the hauling of coal, supplies, and ore to and from the mines could be facilitated by better roads in many parts of the district.

Zinc Production In The District.

The production of spelter from the ores of the Wisconsin district has increased considerably since 1906, as shown by the production curves in figure 1. As a zine producer Wisconsin stands third among the States, with about 10 per cent of the total production of spelter

Year 1909 1910 1911 1912 1918

FicurE 1,—Curves showing spelter production in Wisconsin lead and zine district, 1906-1913.

in the United States. The bulk of the zinc produced from this region comes from the mines in the State of Wisconsin. Although the zinc production of Illinois has been on the increase during the past few years, except in 1913, the production in Illinois is small compared to that of Wisconsin. Both lead and zine mining in the State of Iowa have been practically at a standstill since 1909.

In comparison with their standing as zine producers, both Wisconsin and Illinois are to-day far less important as lead producers than they were formerly, the lead production being at present about onetenth that of zine.

Mining And Milling Of Lead And Zinc Ores. 9

The prospects for an increase in the zine production from this district in the near future look favorable, as new ore bodies have been

discovered during the past year. Tabulated data regarding spelter production in the district during the past eight years are presented below.

Spelter production in the Wisconsin district, apportioned according to source of ore,

1906-19183 .@ State. 1906 1907 1908 1909 1910 1911 1912 1913 SET i Aaa Fh RR SET Sa) VAR, OREN

Short tons.|Short tons. Short tons. Short tons. Short tons. Short tons. Short tons.'Short tons. Wisconsin 11,057 15,273 17,538 20, 381 19, 752 31, 809 34, 137 33, 743 Mnols.55. ste edsceses 282 1,446 298 675 1,551 2,834 3,952 1,345 IGWA vias css ce cens 201 BIG lepeci enone r OY eee oe pera) Grey ec ies

a Siebenthal, C. E., Zinc: Mineral Resources of United States, 1913, U. S. Geol. Survey, 1914, p. 623. FIELD RELATIONS OF ORES.

According to the United States Geological Survey," the geologic succession of the rocks of the upper Mississippi Valley is relatively simple. The rocks are sedimentary deposits of Paleozoic age and comprise beds of sandstone, limestone, dolomite, andshale. A general section of the district is shown in figure 2.?

The formations that occur in the ore-bearing district belong to the Ordovician and Silurian systems, the rocks of the former being the more important, as regards mining, within the limited area.

The chief ore-bearing rocks of the mining district are found in the Platteville formation and at the base of the overlying Galena formation, the ores occurring in much greater abundance in the latter. A better idea can be obtained from the generalized sections of these two formations, as given by Bain,° which are presented below:

Generalized section of the Platteville limestone in the upper Mississippi Valley. 4, Thin beds of limestone and shale 2.2 10-15

. Thin-bedded, brittle limestone, breaking with conchoidal fracture. 25-30 2. Buff to blue magnesian limestone, heavy bedded, in many places a

wo

1. Shale, blue, in some places sandy +-2--2--+ 1- 5

a See Grant, U. S., and Burchard, E. F., Lancaster-Mineral Point Folio Geol. Atlas 145, U. S. Geol. Survey, 1907, p. 1.

+ See Grant, U.8., and Burchard, E. F., Op. cit., p. 14.

¢ Bain, H. F., Zinc and lead deposits of the upper Mississippi Valley: U.S. Geol. Survey Bull. 294, 1906, pp. 20 and 25,

67213°—15 2

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10 Mining And Milling Of Lead And Zinc Ores.

[Scale: 1 inch—=125 feet.)

Sys-

Tem. Formation Name. Section Ness In

CHARACTER OF ROcKs.

Niagara limestone. . . 150+ Light-buff to dolomite. Basal beds massive pom ro Gent succeeded

Silurian.

Maquoketa shale... . 160-225 Gray argillaceous and calcareous shale, locally "a fossiliferous and magnesian at the top.

Plastic blue and green shale and clay with indurated fossiliferous bands near the a

Drab and blue, thin, fissile shale and iferous, thin, us limestone. Fine conglomerate near base.

Galena limestone 235 ed gra dolomi thick iddle top.

ite, c] and portion, thin bedded at fine-grained limestone and fossiliferous. Basal n lly con zinc and lead ores. ee nee

Ordovician.

Platteville limestone. . 55 Fine-grained limestone and very fossiliferous reous shale. Thin, wavy-bedded, fine s fossiliferous limestone. Thick-bedded magne-

sian limestone with thin sandy shale at base.

St. Peter sandstone... 35-175 White or iron-stained quartz sandstone, massive and usually poorly cemented, Thin sandy

clay-shale at base.

Prairie du Chien for-

100+ Irregularly bedded, rough-weathering dolomite, mation, thin

cherty in places and locally con beds and lenses of sandstone. A few Base not exposed.

Figure 2.—Generalized geologic section of the Lancaster and Mineral Point quadrangles.

Original from

Princeton University

Mining And Milling Of Lead And Zinc Ores. 11

Generalized section of the Galena dolomite.

Feet. . Dolomite, earthy, thin bedded ere 30 . Dolomite, coarsely crystalline, massive to thick bedded 60

. Dolomite, thick to thin bedded, coarsely crystalline, chert bearing. 90 . Dolomite, thick bedded, coarsely crystalline; locally the lower por-

tion is nondolomitic and thin bedded + 50 1. Thin-bedded limestone, with shaly partings which are highly fossiliferous and, in part, at least, carbonaceous—the ''oil rock" of the miners, usually with a well-defined clay bed at the base 2-10

tO w eR Ot

Generalized section of basal Galena beds.

4. Thin-bedded magnesian limestone, variable in thickness, which Feet.

depends upon the extent of dolomitization 0-15 3. Thin-bedded limestone or dolomite, with partings of oil rock.. ... 5- 8 2. Brown, shaly material, with minor lenses of limestone; the main

oilsrock horizon'? ead dows aude nh iote tae wen areas 4-2 1. Shale or blue clay containing black phosphatic pebbles +3

The limestone in No. 3 and No. 4 of the Platteville section, when composed of a fine-grained gray to light-brown limestone, and having a more or less conchoidal fracture, is known by the miners as "glass rock.'' Much of the glass rock is ore bearing, but the main bulk of the ores, as has already been stated, is found in the basal part of the Galena limestone. The ores are not found in the underlying Cambrian beds. The beds of all the formations in the district dip slightly to the southwest.

Ore Deposits.

Occurrence.

The important ores found in the Wisconsin district are those of lead, zinc, and iron, and comprise mainly galena, the sulphide of lead, sphalerite and smithsonite, the sulphide and carbonate of zinc, and marcasite, a sulphide of iron. Sulphides, carbonates, and oxides, other than the above, are found, such as pyrite, chalcopyrite, cerussite, and malachite, but these are of less common occurrence, and commercially less important.

The ores may be divided into two main classes, according to the manner in which they are deposited—those that occur in crevices, joints, or openings, and those that occur disseminated through the ore-bearing rock. Under the first division are included all deposits found in fissures, joints, and openings.

The fissures or crevices are in many places parallel, and some are of considerable length, and collectively are generally known as "ranges.'"' Most of them have a direction nearly east and west, known as east-and-west runs; at right angles to these are north-andsouth runs. The main crevices are best developed in the upper orebearing beds, and contain chiefly galena and the carbonate of zinc.

12 Mining And Milling Of Lead And Zinc Ores.

Immediately below water level are ore bodies consisting of open spaces or cavities in the rock lined, or partly filled, with metallic sulphides. The open spaces are said to have been formed by the action of water after the brecciation of the beds. Most of them are lined with a thin layer of marcasite, and in the larger ones the marcasite is overlain with blende and galena. Where these cavities are above water level, and when the ores have become oxidized, or partly so, the carbonate of zinc is then more common.

"Pitches and flats'' (fig. 3%),-are characteristic of this district, the bulk of zine sulphide ore and its associated minerals occurring in this type of deposit. The pitches and flats consist of horizontal sheets known as " flats'? connected by a series of dipping fissures or joints called "pitches." The ores deposited in the pitches spread along the horizontal bedding planes on both sides of the joints that connect the main beds. The ore-bearing pitches and flats are found principally in the lower beds of the Galena dolomite, just above the top of the Platteville formation.

Below the pitches and flats lies the disseminated ore. This occurs as small crystals of blende, and in places of galena, scattered through the country rock.

FIGURE 3.—Diagrammatic cross section of a series of flats It is found chiefly at the and pitches. a, flats; b, pitches; c, vertical crevice. bottom of the Galena formation and in the upper part of the Platteville. Usually where this form of deposit occurs, the country rock contains a considerable proportion of clay or shale.

In regard to the vertical distribution of the ores mined, above and near the level of the ground waters are found galena and the oxidized ores of zine and other minerals; below that level the sulphides of zine and iron become dominant and little galena is present. The sulphide of iron is usually associated in such quantities with zine blende that even a fairly clean blende concentrate is obtained with diflficulty through wet methods of milling, the specific gravity of the two minerals being so near alike. Marcasite, with minor proportions of blende, is so abundant in places that it is being mined and sent to plants that manufacture sulphuric acid.

Mineral Constituents.

The most important minerals of commercial value occurring in the Wisconsin district are galena, sphalerite, smithsonite, and marcasite. Here, as in other districts, these minerals are known by local terms,

@ From Grant, U. 8., and Burchard, E. F., op. cit., p. 11.

Pelt

Mining And Milling Of Lead And Zinc Ores. 13

such as "Jead'' for galena, "jack'' for sphalerite, "carbonate ore"' for smithsonite, and "sulphur" for the iron sulphides—marcasite and pyrite. Closely associated with these ores, including the gangue minerals, are chalcopyrite, calcite, dolomite, and barite, and in places small quantities of other minerals.

The ores are relatively simple in composition, practically none being complex. The country rock is mainly the dolomite of the Galena formation, which has a gray to blue color, turning brown when oxidized. The other constituents of the country rock are shale, oil rock, "glass rock," and some fuss in the upper parts of the orebearing formation.

Prospecting Methods.

Prospecting is commonly done with a churn drill, the ore bodies not lying deep enough to hinder its being used to good advantage. Six-inch holes are drilled, and from the cuttings a fairly representative sample of the rock and ore penetrated can be obtained. The holes are spaced 100 to 300 feet apart, with intermediate holes for locating more definitely the flats and pitches and indicating the general size and shape of the ore bodies. When an ore body of considerable length is found, the holes are placed near its outer edges and are advanced in the general direction of its length. Drilling is usually done by contract at 75 cents to $1 a foot.

Because of the many crevices and open cavities and the considerable quantities of flint often encountered in this district the diamond drill has been little used, the reasons being the difficulty of obtaining a representative core. Where it is possible to obtain a core with the diamond drill the sample is more accurate and the results more certain, but the higher cost would probably not be offset by the better sample obtained from a diamond drill core in this district. Another consideration of importance is that usually the diamond-drill core has a diameter of 14 to 24 inches only, whereas the hole cut by the churn drill has a diameter of 6 to 7 inches.

It is a fact that blende is often found below the level of the ground water in localities where lead and the carbonate of zinc have been known to occur above. In other words, when an area for prospecting is being selected, the chances of finding a body of zinc ore are greater in areas where lead has already been found above the water level than in areas where lead is not known to exist above the water level. In this connection Grant makes the following comments:

In the matter of prospecting, it is wise to carry in mind the fact that, other things

being equal, the ranges and the districts which produced in early days close to the surface of the ground large quantities of lead, or lead and zinc, are the most favorable

@ Grant, U. S., Lead and zine deposits of Wisconsin: Bull. 14, Economic Series 9, Wisconsin Geol. and Nat. Hist. Survey, 1906, pp. 85-86.

14 Mining And Milling Of Lead And Zinc Ores.

locations. The chancesare thata range which has borne considerable quantities of these materials in its upper part will continue to bear large quantities in its lower part, the main difference being that below the level of ground water there will be less lead, practically no smithsonite, and probably much sphalerite. In selecting an area for prospecting, however, one should be taken in which there is below the level of ground water a considerable thickness of the Galena limestone—that is, a considerable thickness of rock which may carry ore, for the deposits in many cases are limited by the base of the Galena limestone, and in nearly all other cases are limited by the oil-rock bands at the base of the main glass-rock horizon of the Platteville formation.

Bearing in mind the two points just mentioned a third should be added, and that is that a range, or a series of ranges, or a district, which can be shown to lie in a synclinal basin, isa more favorable place for prospecting than one which is not so situated.

Mining Methods. Underground Work.

Mining practice in the Wisconsin district is similar to that in the Joplin district, except that in Wisconsin everything is on a somewhat smaller scale. In other words, the tonnage of ore mined and treated is less and the mills are built with a proportionately smaller capacity.

In general, the ore bodies are reached by vertical shafts, 100 to 200 feet deep and as a rule are mined from only one level, as few of the deposits are over 40 feet thick. The usual method of mining is by underhand stoping, one or two benches being left below the heading, depending on the height of the working face. The ore is generally followed to its upper limits, the broken ore being allowed to work itself to the bottom, where it can be shoveled into the cars or tubs. When the breast or heading has been advanced far enough ahead, usually 15 to 20 feet, the lower part is drilled and blasted.

Toward the top of some of the deposits the ore-bearing rock is rather soft so that many of the raises have to be abandoned temporarily to prevent the roof, or part of it, from caving. Most of the soft deposits lying above the main ore body are lead-bearing and pockety. Although the roof is trimmed after each round of shots, special care has to be taken by the men who work beneath or near these soft deposits to guard against falls of roof. Little timbering is done in the mines, pillars 10 to 20 feet thick being left at intervals of 20 to 50 feet, depending on the nature of the deposit, the height of the face, and the firmness of the roof and overlying strata.

The broken ore is shoveled into cars on narrow-gage tracks and trammed to the shafts, where it is hoisted and dumped into the hopper. In many places there is considerable barren rock between the ore-bearing strata, but on account of the irregularity of the ore bodies this is trammed and hoisted while mixed with the ore, so that the quantity of "dead rock" is often large. The larger pieces are

Eh a

Mining And Milling Of Lead And Zinc Ores. 15

sorted on the grizzly on which the ore is dumped, and are trammed to the waste-rock pile. SHAFTS.

Except at one or two mines that have inclines, the ore bodies are reached by vertical shafts. Most of the shafts have single compartments only, although some of the larger properties have doublecompartment shafts. At most of the mines, hoisting is possible from more than one shaft, but at many mines only one shaft is in use. The main shaft is usually connected directly to the mill hopper, with which other shafts are connected by inclined or aerial tramways. It is customary to sink the shafts a few feet deeper than the lower level from which the ore bodies are worked, so as to form a sump into which the water in the mine may drain, the depth of the sump depending on the quantity of water to be handled. Over the sump a platform is built for handling the tubs and ore cars. From the collar down, the upper part of the shaft is cribbed to prevent any loose ground from falling. The cribbing is extended through the surface and the less firm ground until hard rock is reached, the depth depending upon the nature of the rock and the quantity of water coming from the rock beds. In some of the shafts the cribbing extends to the bottom.

A few of the shafts are provided with ladders, but as a rule the miners are lowered in the tubs or cages used for hoisting the ore. It is obvious that for safety, ladders should be provided in at least one shaft of a mine, if only for use in emergencies, especially when new properties are being opened and the working face of the ore body is still near the shaft. At such a time men may be hit by pieces of rock from blasting, if the hoists are not in good working order at the time of firing to enable the men to get out of danger promptly. The average distance between shafts is about 300 feet, but is considerably greater at two or three of the larger mines. The sinking of shafts is more difficult than in the Joplin district because more water is encountered.

Drilling Practice.

As the methods of mining in this district are so similar to those found in the Joplin district, there are certain features ¢ommon in the latter district that can be well applied here, without much change. In all methods of rock drilling certain questions have to be considered before choosing the kind of drill or the method of drilling. First of allis the nature of the rock in which the ore bodies are found— whether it is hard or soft, brittle or tough. The form of deposition of the ore—whether massive or in stratified layers—is also important.' Some rocks are full of crevices and others contain large cavities, variations that make it necessary for the drill man to use judgment in placing the holes so that the effect of the powder in break-

16 Mining And Milling Of Lead And Zinc Ores.

ing ground will be greatest. The chief object in mining, aside from the safety and health of the miners, is to excavate the most ore at the lowest cost. Too much emphasis can not be placed upon the need of ascertaining in advance the nature of the rock to be handled. Lack of definite knowledge is apt to cause much dissatisfaction between the mine superintendent and drill men by reason of the high cost of breaking ground. The preliminary attention to the probable nature of the rock to be handled would tend to eliminate the possibility of the miner arguing, for instance, that the powder is at fault and another grade or brand should be used.

The main rock is limestone, fairly hard and compact, which breaks into a rather fine powder. This powdered rock is apt to accumulate in the holes during drilling and to make the footage less than what might be obtained. However, this difficulty is largely overcome by using water-type hammer drills, which keep the hole washed out as the drilling advances.

In places crevices and pockets are encountered, causing the holes to be lost so that drilling has to be started from another point or at a different angle. The rock does not wear the bits down as fast as does the flint in the Joplin mines, but in places it is tough and is then penetrated with difficulty.

The length of the holes varies according to the height of the face and the method of mining used. Where the face of the ore is only about 10 feet high, and no stoping is used, the holes are drilled 6 to 8 feet. In driving stopes the holes for advancing the heading are usually 6 to 7 feet long, whereas those drilled in the underlying bench or benches are 10 to 14 feet in length. At afew of the mines the lower portion below the breast is broken by vertical holes 6 to 8 feet deep.

Several makes of machine drills are in use; they are operated by compressed air. The average capacity of the compressors is about 600 cubic feet per minute, and the pressure is about 90 to 100 pounds. The air distributed to the drills has a pressure of about 80 pounds, the difference being due to leakage and other losses in transmission. The tendency at present seems to be toward the use of the one-man drills, which so far have given satisfactory results.

Blasting.

In blasting, as in drilling holes for explosives, careful attention to details is necessary to insure efficiency in mining. The miner or machine man should be familiar with the nature of the rock that is to be blasted in order to arrange his drill holes to the best advantage. He should drill each hole in a direction nearly at right angles to the line of least resistance of the shot, and arrange the drill holes so that the number of holes necessary and the quantity of explosive used may be the least possible. Two other important factors that have to

Mining And Milling Of Lead And Zinc Ores, 17

be considered in breaking ground efficiently are irregularities of the face and the form in which the face will be left after the shot. The mine foreman or ground boss should constantly foresee the condition of the face after shooting, and should have the machine men follow a system that leaves the face more accessible for subsequent drilling and blasting. It is not to be understood that this lack of foresight is common in the Wisconsin district, but it is a detail that can bear close watching and in some instances might reduce the cost of breaking ground.

The powder most used in the Wisconsin district is 40 per cent strength gelatin dynamite, although ammonia dynamite is largely used where the holes are fairly dry. As a rule the cartridges are prepared and loaded into the holes for shooting by the machine men except in a few mines, where a powder man is employed purposely for this work. Preliminary chambering or ''squibbing" of holes is not generally practiced. The number of sticks or the quantity of explosive used in each hole varies according to the length of the hole, the strength of powder used, and the amount of rock to be broken.

The method of priming the holes differs somewhat in that the primer or cartridge containing the cap (detonator) and fuse is inserted in the central part of the charge or at the outer end, followed by one or two sticks of powder. Usually the miners prepare the primer by lacing the cap and fuse through the cartridge near one end and then inserting the cap into the cartridge at the side in the direction of the other end. The Bureau of Mines recommends that the detonator be inserted in the end of the primer. To lace the fuse through a cartridge of high explosive is dangerous because the explosive, ignited by side spitting of the fuse, may burn before exploding, with the result that poisonous gases will be produced.

The usual strength of detonator used is No.6. Tamping of holes is practiced little, if at all. A few companies in this district have tried it and abandoned it, but no systematic trial has been made to demonstrate the advantage or disadvantage from the use of stemming.*

The quantity of powder used averages about 1 pound per ton of rock broken.

Shoveling And Underground Tramming,

After the ground has been broken the ore is shoveled into cars or cylindrical tubs which are pushed by hand or hauled by mules to the shaft. The tubs, locally known as ''cans,"' usually measure 28 by 30 inches. For the convenience of the shovelers, a piece of sheet iron

a In the publications of the Bureau of Mines the word ''stemming"' is used to designate the material placed on a charge of explosive in a drill hole, the word "tamping"' to designate the act of placing and ramming the material. For an account of experiments showing the results of using stemming with high explosives, see Technical Paper 18, Bureau of Mines.

67213°—15——_3

18 Mining And Milling Of Lead And Zinc Ores.

is laid down so as to provide a flat and smooth surface from which to shovel. The bowlders and larger pieces of rock are lifted into the tubs, those too large for one man to handle being broken with sledges. Shovelers are paid either by the day or by the tub, but paying by the tub seems to be the more general custom. The amount paid is 6 to 10 cents per tub, depending on the size of car or tub and the distance from the shaft when the men are obliged to do their own tramming. This system tends to increase the tonnage, but at the same time has the drawback in that the men may not fill the tubs full in an effort to get a greater number of tubs to their credit. This defect can be overcome only by careful supervision. As a result of the tendency of the men to shovel scant tubfuls and of the fact that the filled tubs are rarely weighed, the reported tonnage of ore hoisted is apt to be somewhat higher than the actual amount. If the ore hoisted were weighed, some system could be devised by which the men would be paid by the ton, or would receive a daily wage combined with a bonus for extra tonnage above a required quantity of ore.

Each tub of ore is assumed to weigh 1,000 pounds, which is considered by some to be a little more than the actual average weight. At a few of the mines 30 by 30 inch tubs are used, and the average content of this size is thought to be nearer 1,000 pounds than is the average content of the smaller size, 28 by 30 inches, when the weight of dry ore and the point to which the tubs are usually filled are considered.

Where cars are used, these are hoisted in cages, except in one mine entered by an incline, where the ore is dumped from the mine cars into a larger car and hoisted up the incline to the hopper.

Timbering,

Few of the mines in the Wisconsin district are timbered, as most of the roofs are good. Pillars are left at intervals of 20 to 50 feet, according to the nature of the ground and the height of the roof above the floors. Now and then one finds posts placed wherever necessary to support slabs or loose rock in the roof.

Pumping,

The quantity of water pumped from the mines varies from 200 to 1,500 gallons per minute, and with efficient pumps it is easily handled. The different types of pumps in use are the Cornish crosshead, doubleacting lift pump, the usual small steam pumps, and electrically driven centrifugal pumps. few of the old walking-beam pumps are to be found, but they are now practically out of use. As the mines are shallow, most of the shafts are wet and some water is found in the mine workings as a result of the intermittent seepage.

Mining And Milling Of Lead And Zinc Ores. 19

The water is drained into a sump at the foot of some shaft either by means of ditches cut along the sides of the drifts or by some natural drainage course. From the sump it is pumped to the surface.

Surface Work. Hoisting And Surface Tramming.

In the Wisconsin district the system of hoisting most commonly used is that of direct winding without attempt to balance the load. The bucket or tub and its load are hoisted by power and lowered by gravity, and the hoisting engine is coupled or geared direct to the shaft of the drum, which is provided with friction devices or positive clutches and brakes. If cars are used they are placed in cages and hoisted in the usual manner. When the tub has been hoisted to the top of the headframe the hoistman covers the opening with a lid to prevent any loose material from falling back down the shaft, and then dumps the load on a chute leading directly to the grizzly over the hopper. Both electric and steam hoists are in use.

Signaling for raising and lowering both the men and the tubs and cars 1s done by a pull bell, although at a few mines electric bells have been installed. When men are hoisted, not more than four, as a rule, are permitted to ride in a bucket at once. Each man stands on one leg inside the tub, his other leg being outside. This way of riding is not without risk, for there is always danger of injuring the kneecap or leg if the tub bumps against the sides of the shaft.

Connected with each shaft is a storage bin or hopper, and with few exceptions the main shaft is connected directly with the mill hopper. If hoisting is done from more than one shaft, the ore is trammed to the mill hopper by inclined or horizontal tramways (Pl. I, A), or, as at two or three mines, by aerial tramways. The latter method is claimed to be satisfactory, both as regards cost and operation, but few mines use it. At one of the mines, where the distance between shafts is greater than the average, an endless-rope system (PI. I, B) is in use.

The tram cars used on the surface are self-dumping and have a capacity of 1 to 2 tons. The hoppers to which the ore is hoisted and trammed, inclusive of mill hoppers, are built of timber, their capacities varying from 100 to 300 tons.

Power.

Both electric and steam power are used for hoisting and for driving mill equipment, steam being generated by coal. Electricity is largely used, and a combination of electric and steam power is found at some of the properties.

20 Mining And Milling Of Lead And Zinc Ores. Ore-Dressing Practice.

The average zinc content of the concentrates produced from the mills in the Wisconsin zine district is below that of the Joplin district. The lower grade is due to the high percentage of iron sulphide in the ores, and the difficulty of separating zinc and iron sulphide by wet methods. For this reason the concentrates are, as a rule, lightly roasted and the iron sulphide is separated with magnetic separators.

Concentrating is commonly effected by the usual rougher-andcleaner system, with the use of the Cooley type of jig, which is so well known in the Joplin district. For low-grade zine ores the single-jig type of mill is used. The ore is crushed to about one-half inch but not below one-fourth inch, the object being to produce a minimum proportion of fine material and slimes, because of the great loss of fine material in the single-jig system.

Concentrating Mills.

The concentrating mills in the Wisconsin district are much alike in design and equipment and similar to those found in the Joplin district, but are smaller and have less capacity. The "dirt" treated contains more blende and iron sulphide, so that in order to obtain an efficient recovery the ore can not go through the jigs as fast as is the custom in southwest Missouri. The mills are built of wood with concrete foundations and are of the level-site type, elevators being used to raise and advance the ore from one treatment to the next. The average capacity is 75 to 150 tons per 10-hour shift, although it is somewhat greater at a few of the more recent mills. Pl. II, A and B are representative mills of the Wisconsin district.

As has already been mentioned, mills are commonly built adjacent to a shaft, usually the main shaft, so that the ore can be hoisted directly into the mill hopper. This construction simplifies the handling of the ore and reduces costs. The course of the treatment of ore, as outlined by the flow sheets shown in figures 4 and 5, is usually simple.

Method Of Concentration.

The ore hoisted is dumped on a chute leading to the grizzly, which consists of iron bars or pipes spaced about 4 inches apart. The undersize passes through to the hopper below. The oversize is caught on the grizzly, the larger mineralized pieces are broken with sledge hammers, and the bowlders that are practically barren are sorted out by hand and trammed to the waste pile. The proportion of waste rock thus sorted out is 5 to 25 per cent, depending on the nature of the rock. The sorting is done by screen men, better known locally as cull men, who are paid about $2.30 a day.

Bureau Of Mines Technical Paper 95 Plate

A. Tramways Connecting Shafts At A Mine Near Livingston, Wis.

B. Endless-Rope Haulage System Between Shafts.

aoe

Bureau Of Mines Technical Paper 95 Plate 1!

A, Mill Near Cuba City, Wis.

B. Mill Near Platteville, Wis.

Gor gle PRINCETON UNIVERSITY

Mining And Milling Of Lead And Zinc Ores. 21 Crushing.

The undersize material, 5 inches or less in diameter, from the ore dumped on the grizzly bars falls into the mill hopper. From the hopper the ore is fed to an incline leading to a crusher of the Blake type, which reduces the larger material to pieces about 2 inches or less in diameter, depending on the setting of the jaws of the crusher at their lower end.

Instead of an incline it might be possible to use a perforated shaking screen having three-fourths-inch holes, and play a stream of water on the material passing over the screen. The finer material would be washed through, thus eliminating much unnecessary crushing and increasing the capacity of the crusher. The plan would also reduce somewhat the proportion of fine material produced. The undersize from the coarse screen would go to a set of rolls or directly to the elevator to be raised to the trommel at the head of the rougher jig. The benefits obtainable from such a screen would have to be determined by actual trial, although most satisfactory results are known to have been obtained in some of the larger mills in this country and abroad.

In the Wisconsin district the material from the crusher is fed directly to a set of rolls and is largely reduced to three-fourths-inch size or finer. As a rule only one set of rolls is used for crushing the material to this size.

The ore next goes to an elevator, by which it is raised to a trommel. These elevators are of the usual gear-driven belt type, equipped with conveyor buckets spaced about 10 inches apart. The trommels are 6 to 12 feet long and 3 feet in diameter with one-half-inch holes. As the ore falls on the revolving screen, the undersize passes through the one-half-inch holes to the first jig and the oversize goes to a set of return rolls, by which it is further crushed, and is then carried by the elevator back to the trommel. In this manner all of the ore is reduced to one-half-inch size before it reaches the first jig.

Jigging.

As in the Joplin district, the jig most used is known as the Cooley jig, which is similar in principle to the Harz jig. It is of the fixedsieve type, with a plunger to force the water up and down through the screens or grates. The compartment containing the plunger is connected with the hutch below the grates. The plunger receives its motion from an eccentric on a shaft, which connects a battery of plungers. The jigs do excellent work if the large quantity of material passed over them be considered.

22 MINING AND MILLING OF LEAD AND ZINC ORES. ROUGHER-AND-CLEANER SYSTEM.

From the tromme!] the crushed ore, with considerable water, comes to the first cell of the jig. A bed 5 to 7 inches deep is formed on the screen, and by the pulsating action of the water the lighter material, such as flint, limestone, dolomite, and calcite, rises to the top and the lead and zine minerals, being heavier, work to the bottom. The suction stroke of the plunger causes the finer grains of mineral and some sand to pass through the openings into the hutch, and the proportion of gangue material drawn into the hutch depends on the strength of the suction. From the first cell, as well as from the second, is produced the first concentrate, usually lead concentrate, which goes direct to the concentrate bins. In some of the mills no finished products are obtained from the rougher jigs.

Between each two cells there is a fall of a few inches, so that the material gradually advances from one cell to the next until it reaches the last. As the material advances, its mineral content decreases until from the last cell the bulk of it flows off as tailings into the tailings elevator. The other products from the rougher jig are middlings and chats, which either go directly to the cleaner jig for re-treatment or are sent to a set of rolls for finer crushing.

The cells in use measure about 30 by 36 inches, and the shafts, directly connecting the plungers, are run at speed of about 140 to 160 revolutions per minute for the rougher jig and 180 to 200 revolutions per minute for the cleaner jig. At a few of the mills the recrushed chats and finer middlings are treated separately on a sand jig instead of being returned to the main system.

Diagrams representative of the milling systems used in this district are shown in figures 4 and 5, which show the flow of material from beginning to end.

One-Jig System.

The difference between the one-jig system and the rougher-andcleaner system is that the entire feed in the former is treated on one jig only, roughing and cleaning being done in one operation. The advantage of the single-jig type of mills is limited to the saving of labor, power, repairs, etc., and to low cost of installation, which are important items with low-grade ores or those with a high percentage of iron sulphide. The feasibility of this system of milling is also determined by the amount of crushing necessary to liberate the mineral from the gangue, as the losses in fine material are greater than in the two-jig or three-jig mills. In other words, the single-jig mill is suitable for ores with a high content of iron sulphide and which are coarsely disseminated.

On the other hand, it has certain disadvantages that have to be tuken into account. The single-jig system is not feasible for high-

Mining And Milling Of Lead And Zinc Ores. . 28

C-Pb= Lead concentrates C-Zn Zinc concentrates

M Middlings Ch= Chats

a

Return

a

Concentrates

Oversize e Fe g § iS) V2] Ch orM VAST Zen ora] YN chor at] Tailings ——] S—

ne s

Tailings

Pond

Figure 4.—Arrangement of a representative lead and zinc concentrating mill in the Wisconsin district, one-jig system. 1, hopper, capacity 150 tons; 2, crusher, 14-inch Blake type; 3, rolls, 24-inch; 4, elevator (feed); 5, trommel, 36 by 96 inches, with }-inch round perforations; 6, rolls, 24-inch; 7, jig, eight 30 by 42 inch cells; 8, elevator (middlings and chats); 9, rolls (for middlings and chats), 18-inch; 10, elevator (tailings).

ease

24 Mining And Milling Of Lead And Zinc Ores.

C-Pb=Lead concentrates C-Zn=Zinc concentrates M=Middlings

Ch= Chats

Concentrates

Return

return

é 2)

Overflow

Overflow

Return

5 Tallings

Pond

FiGURE 5.—Arrangement of a representative lead and zine concentrating mill in the Wisconsin district, rougher-and-cleanersystem. 1,hopper, capacity 150tons; 2, crusher, 14-inch Blake type; 8, rolls, 30-inch; 4, elevator (feed); 5, trommel, 36 by 96 inches, with }-inch round perforations; 6, rolls, 24-inch; 7, rougher jig, seven 30 by 42 inch cells; 8, elevator (middlings); 9, cleaner jig, seven 28 by 42 inch cells; 10, elevator (chats and middlings); 11, rolls, 24-inch; 12, elevator (tailings); 13, settling box.

TP ne

Mining And Milling Of Lead And Zinc Ores. 25

grade or finely disseminated ores, as the losses of fine material are too great. If the lead content is fairly high a good zine product is not easily possible with the single jig.

Most jigs used in the one-jig system have a battery of eight cells divided into two sections; that is, the shaft line connecting the eccentrics of the plungers is in two sections, the plungers of the first four cells being driven separately from those of the last four cells, so that the speeds of the two sections are different. Usually the speed of the shaft of the first section is about 180 revolutions per per minute, whereas that of the other shaft is about 200 revolutions per minute. The cells are about 30 by 36 inches.

In treating the material on the single jig the lead concentrate, if any, is obtained from the first cell, and the zinc concentrate from the third, fourth, fifth, and sixth cells and from the hutch of the seventh. - In order to obtain as clean concentrates as possible the suction is not as strong as when the rougher-and-cleaner system isused. The suction effect must be such that it will draw the proper quantity of fine material into the bed and the proper quantity of fine mineral into the hutch, but must not be strong enough to bring the fine gangue particles into the hutch. A closer jigging is therefore necessary. In the rougher-and-cleaner system the suction is greater as the material passes over the rougher, so that more fine mineral and also some of the gangue material is drawn into the bed and hutch. Consequently a greater quantity of middlings is produced and there is less fine mineral in the tailings. As the fine material is usually higher in zinc content and more of the mineral is drawn into the bed and hutch by strong suction, it would follow that the tailings would be lower in zinc content. The middlings and chats from the single-jig mill are recrushed and returned to the original feed of the one-jig system.

Concentration Of Fine Material.

In the concentration of the fine material the operators of this district have not been able to obtain a clean concentrate by the use of tables, so that tables are found in few of the mills. The practice is to obtain as much of the finer material as possible from the jigs, the overflow water being allowed to return to the pond. The difficulty in obtaining a good concentration on tables is due to the fact that the specific gravity of the iron mineral is so nearly like that of the zinc mineral that it is almost impossible to obtain a distinct line of separation on any table so far used in the district. Although a concentrate can be obtained from the table work it is of low grade as a zinc product and is of little if any profit to the operator. At one of the mills tables are used to advantage, but there the chief mineral is iron sulphide, and the object is to save the sulphide, which is shipped to sulphuric acid plants.

26 Mining And Milling Of Lead And Zinc Ores.

The results obtained from some tests with two Wilfley tables at one of the mills near Platterville, Wis., are shown below. The object was to determine whether a separation of the iron sulphide and the zine sulphide was possible, and to ascertain how clean a zine concentrate could be made from table work; and, secondly, whether tables could be run at a profit. The conditions under which the tests were made and the equipment used were as follows: The feed entered a spitzkasten or settling tank with three spigots. At the time of the tests, however, only one spigot was in use, the other two being choked. From the settling tank the feed flowed to a shaking screen with a screening area of about 550 square inches. Screens with different sized perforations were used, and it was found that the best results were obtained from the smallest size on hand, which had }-mm. round perforations. The undersize entered a V-shaped box, with water passing up through it, and then passed to table. Of the two tables one was used as a rougher and the other as cleaner. The length of stroke given to the tables was varied to determine the best results obtainable at a fixed speed. The foundations of the tables could have been considerably firmer. The results follow:

Results of tests with two Wilfley tables.

Assay of oversize c . on screen with Assay ol ied to Assay of tailings

; tables. from tables. mm. 0 Se Date. - roe Zine. Iron. Zinc. Iron, Zinc. Iron. Per cent. Per cent. Per cent.| Per cent.| Per cent. Per cent. Angiist 28: 55 tcsaehceclaeces sete dasaubests 2.4 4.2 8.4 6.6 3.8 4.0 Hoptembler IS cass ss0s Bors so re2ts es sae Ss ofoese reese seteeeeeese G'S, |hessacpascisecatcatce seceseseee . Assay of concentrate pro- Quantity Diameter] Shape of duced. at Date. of screen screen Galen Remarks ; perfora- perfora- nin uss 7 ons. Uons. Zine. Iron. Lime. per hour. Mm. Per cent. Percent. Percent.| Pounds.

August 12 1.5 Round.. 39.0 12,2 4.5 60 First trial.

August 13 1.5 Round... 37.2 15.2 bP eer eee Including more iron sulphide in concentrate.

August l4 1.0 Round.. 33.2 14.0 GiF ll sccsewececss Including more gangue in concentrate.

August 14 Oblong. 34.0 19.6 BL Asse nba Found screen to be inetlicient. Not enough feed.

August 28 2) Round.. 42.6 10.0 4.4 584 Round holes found to be more — ethcient. Plenty of feed.

August 29 2 Round.. 44.0 10.0 3.8 574 Cutting out more

gangue in concentrate and less feed to cleaner table.

September 1 Round.. 38.0 15.6 3.4 61 Crowded rougher table as much as possible. Too much feed.

@ Diagonal openings 1.27 cm. long and mm. wide.

viatizes by GOogle ane

Mining And Milling Of Lead And Zinc Ores. 27

As has been stated, the main object of the tests was to ascertain whether a separation could be made of the iron and zinc sulphides. From the results obtained it can be seen that a separation of the two minerals is possible, but there is a question as to whether a large enough quantity of zinc concentrate assaying 40 per cent zinc or better can be produced to run the tables at a profit. From the figures obtained from the first four tests it seems that the tables could not be run with a profit, especially when breakdowns and other drawbacks are taken into consideration. However, the average assay of the concentrates of the last three results (42.6, 44.0, and 38.0 per cent zinc), or 41.5 per cent zinc, indicates that a small profit might be possible, or if the table concentrate was mixed with the coarse concentrates from the mill, which at the time of the test were running about 46 per cent zinc, a profit might have been realized.

In order to insure a profit from tables in this mill, it would be necessary to make several changes. In the first place, there is feed enough for four or five tables when all three spigots are in use. By adding two more tables to the two already on hand and by using a larger screen 100 to 150 pounds of zinc concentrate per hour could probably be obtained, especially if a closer classification were made and the tables all put in proper order.

As the average assay of the concentrates produced by the mills is much lower than 46 per cent, any profit that could be made from tables at any of the mills would be possible only in the mills treating the higher grade ores; but so far the higher grade ores, or those whose concentrates do not need further treatment by roasting and magnetic separation, are the exception.

Handling And Treatment Of Concentrates.

As most of the concentrates from the mills assay 30 to 40 per cent zinc and have a high content of iron, it is necessary to increase the zinc content and decrease the iron content to a minimum before shipping the concentrates to smelters. The changes mentioned are accomplished by giving the concentrates a superficial roast and then passing them through magnetic separators. The customary roaster is a long, slowly revolving cylinder lined with fire brick. As the concentrates pass through, a flame is directed against them, the roasting being carried far enough to render the iron sulphides magnetic but not far enough to drive off all the sulphur. After being roasted the concentrates are passed under magnets, which remove the incompletely roastediron sulphides. This treatment brings the zinc content in the concentrates up to 57 to 60 per cent.

Some operators have a roasting plant directly connected to the mill, but as a rule each of the larger companies has only one plant

28 Mining And Milling Of Lead And Zinc Ores.

for all its mills. Operators that have no roasting equipment haul or ship their concentrates to a local custom roaster for further treatment. Besides the usual type of roaster found in this district, one company uses a patented process, which is claimed to necessitate only a slight roast, the iron sulphides being not only recovered but left in a proper condition for sale to acid manufacturers.

The concentrates produced from some of the mills are high enough in zinc content to allow shipping directly to the smelters. The common opinion seems to be that the owner of a small mine and mill should sell the green concentrates rather than to invest in a roasting plant, especially if the life of the mine is uncertain. The reasoning is good, but it also emphasizes the necessity of drilling preliminary to development in order to ascertain the extent of the ore body to be worked.

Representative averages from the treatment of concentrates by roasting and magnetic separation are as follows:

Per cent. Average zinc assay of concentrates treated. 33. 91 Average iron assay of concentrates treated 17. 85 Average zinc assay of concentrates after treatment. 59. 53 Average iron assay of concentrates after treatment. 1.99 Average zinc assay of middlings produced 2 '8:71 Average zinc assay of tailings from treatment. 4. 64 Average percentage of zinc recovery from treatment 91. 54

The cost of treatment is $2 to $3 per ton, which includes the total roasting costs, supervision of plant, and general expenses.

It has been found that by screening and crushing to make the material more uniform in size a better product and a higher recovery is possible. A closer classification of the material treated and the use of magnets with greater differences in strength, especially for re-treating middlings, have been suggested.

Source And Quantity Of Waste.

The sources of loss in the mining and treatment of ores in this district are as follows: In the pillars left in the mine, in the culling or sorting of waste rock before treatment in the mill, in the wet concentration of the ores, and in the treatment of concentrates by roasting and magnetic separation. Little timbering is done in the mines, pillars are left for the support of the roof or back, and the percentage of the deposit so left is 15 to 30 per cent, depending on the nature of the deposit and the firmness of the overlying strata. Although some trimming of the pillars is done after a mine has been practically worked out, the ore left in the pillars at many mines is a total loss.

Another source of loss is in the rock sorted out as waste before the ore enters the mill. This loss is comparatively small, the zine content of the waste rock being estimated at about 0.5 per cent. This culling

eek:

Mining And Milling Of Lead And Zinc Ores. 29

is the first step in the concentration of the ore and the proportion sorted out is 5 to 25 per cent. Culling has advantages that are well worth considering. It lessens the quantity of material treated and thus saves power, lessens wear on the machinery, and increases the relative capacity of the mill. Many operators believe that the sorting of waste rock easily pays for itself in many ways, and that even a closer sorting than is generally practiced at present would be advantageous.

The greatest loss, however, is in milling the zinc ores. Although the average zinc recovery from the mills is about 5 per cent higher than that from the mills in the Joplin district, the grade of the concentrates produced is considerably lower and the ores as a rule are richer in mineral content, making a higher saving possible. This higher recovery from the milling, however, is offset by the lower grade of the concentrates, which have to be re-treated by roasting and magnetic separation. The re-treatment means a further loss, probably equal to the difference in the average recoveries in the two districts. The average recovery of zinc in the milling of ore in the Wisconsin district is 70 to 75 per cent, whereas the recovery from the mills in the Joplin district is about 65 per cent, or perhaps a little higher at present.

The zinc recovery from the treatment of the concentrates by roasting and magnetic separation is about 90 to 95 per cent, so that the losses here together with those from the milling would bring the recovery of zinc from both treatments down to about 65 to 70 per cent, or about the same as that in the Joplin district. The average loss, therefore, in the treatment of the zinc ores in the Wisconsin district to produce concentrates for shipment to the smelters, is 25 to 35 per cent. When the losses in the smelting of zinc ores are included the total loss in the production of zinc, from the ore in the mine up to the commercial product of spelter, reaches nearly 40 to 50 per cent.

The larger operating companies in the district determine in a general way what results are being obtained from the milling operations by taking samples of the tailings, but few of them know the exact recoveries from the mills, for they do not include the overflow water and slimes in their sampling, and have as a basis for calculation only an estimated weight of the tonnage treated. In many instances it would be difficult to make any systematic mill test, but there are certain tests possible that would show more closely what results are being obtained and where the losses are greatest.

If the tailings alone are sampled it is necessary to take a representative sample, which should include ail slimes and water that are discarded with the coarser material as tailings, and not the coarse tailings only, the water and slimes being allowed to flow off, a method often used not only in this district but in the Joplin district as well.

30 Mining And Milling Of Lead And Zinc Ores.

Mill Tests.

In connection with the investigations in milling operations certain tests were made to show in what sizes the loss was greatest and to find out from representative mills the approximate zine recovery in the milling practice in the district. The various samples were also assayed for iron simply to show that a considerable quantity of iron sulphide is present, which the millman has to contend with. The sizing was done through such screens as were available. The results of the mill tests are tabulated below:

Results of mill tests of practice in the Wisconsin district.

Test 1.—MILL USING ONE-JIG SYSTEM.

Dey. Pro- gash. Weight S Quan- Weight : weight |portion tity of of zinc ine tity of ofiron) Iron Bize of tailings. of of zinc con- loss, iron con- loss. sample.) weight. |(assay).| tent. (assay).| tent. Grams.| Per ct. Per ct. |Grams.| Per ct. Per ct. |Grams.| Per ct. Through #-inch, on }-inch screen. 1,770 19.15 0.81) 14.33 7.9 3.67 64.96) 16.55 Through 4-inch, on §mesh screen 2,000 21.60 71 14.20 7.8 4.00 80.00; 20.40 Through &-mesh, on 10-mesh scree! 730 7.9 1.07 7.81 4.3 3.80 27.74) 7.10 Through 10-mesh, on 20-mesh screen 770 8.3 61 4.69 2.6 3.00 22.10 5.65 Through 20-mesh, on 40-mesh screen 70 8.1 2.44) 18.30] 10.1 4.00 30.00 7.65 Through 40-mesh, on 80-mesh scree! 1,050 11.35 3.82 40.11 22.1 3.70 38.85 9.90 Quantity of ore treated 2 oo cic e2.setesesccs ace dbalase ean aced tons.. 330 Quantity of zinc concentrates produced do 35.5 Quantity of tailings Pesicis Ayes geese ees sakes do 294.5 Zinc assay of concentrates 2.2220eeeeecee eens percent.. 32 Zinc assay of tailings i beeseedeawnassesbeeowseateed do 1.96 Quantity of zine in concentrates produced. tons.. 11.36 Quantity of-zine in: tailings , isccecca cd cece dees easaseass do 5.77 Total quantity of zinc in ore treated do. 17.13 Recovery of zine from mill percent.. 66.3 Test 2.—MILL USING ONE-JIG SYSTEM. Dry Pro- Quan- Wetent % Quan- Weight Sy na weight 'portion, tity of of zinc ine tity of ofiron| Iron Size of tailings. of of zinc con- loss, iron con- loss. sample. weight. |(assay).| tent. (assay).) tent, Grams., Perct,| Perct. |Grams.| Per ct. Per ct, ;Grams.| Per ct. Over 23-inch, on }-inch screen 520 3.85 0.71 3.69 1.6 3.40 17.68 2.85 Through j-inch, on 4-inch screen 4,020 29.7 61 24.52 10.5 3.85 154.77 24.05 Through }-inch, on 8-mesh sereen 2,630 19.4 87 22.88 9.8 3.70 7.31 15. 70 Through &mesh, on 1(-mesh screen... 600 4.4 93 5.58 24 3.70 22. 20 3.60 Through 10-mesh, on 20-mesh screen... 700 5.15 1.39 9.7. 4.1 3.60 25. 20 4.05 Through 20-mesh, on 40-mesh screen.. 760 5.6 1.63 12. 39 5.3 5.50 41.80 6.75 Through 40-mesh, on 80-mesh screen..| 1, 110 8.2 2.65} 29.41 12.5 4.15 46. 06 7.40

Mining And Milling Of Lead And Zinc Ores.

Quantity of ore treated : Quantity of zinc concentrates produced

do 226.00

Quantity.of tailings. ...5..35.ccdcsseacdeiccdeseaeesineslocay Zinc assay of tailings +-2 2--e--20ee-e percent... 1.72 verage zinc assay of concen OB. occ cc eee cess es swe eecs s Onn-- ° A f trat d 32. 47 Quantity of zinc in concentrates produced tons.. 18.48 Quantity of zinc in tailings 2 2 do...'.. 7.67 Total quantity of zinc in ore treated do 26.15 Recovery.Of 2G. os ses. cccccasiee se downs sagedese percent.. 70.6 Test 3.—MILL USING ONE-JIG SYSTEM. ay Pro- Gasp. Weigit Sheer Wale me weight portion tity of of zinc ic tity of of iron mn Size of tailings. of of sta eon Moan, Grou} oom loss. sample.| weight. |(assay).| tent. (assay).| tent. Grams.| Per ct. Per ct. |Grams.| Per ct. Per ct. |Grams.| Per ct. Through 8-mesh, on 10-mesh screen. 1,060 8.2 1.02] 10.81 6.2 3.25 34.45 5. 65 Through 10-mesh, on 20-mesh screen. . 900 6.9 1,07 9.63 5.5 3.50 31.50 5.15 Through 20-mesh, on 40-mesh screen. . 540 4.15 1.07 5.78 3.3 3.70 19.98 3.25 Through 40-mesh, on 80-mesh screen. . 700 5.4 2.04 14.28 8.2 4.20 29.40 4.80 Quantity of ore treated 2 2 eee eee ee cence eee eees tons.. 580.00 Quantity of zinc concentrates produced do 70.95 Quantity of tailings. 2. 2.22.0. e eee eee eee eee eee do 509. 05 Zinc assay of concentrates 2--2+2--2-5- percent.. 36.4 Zinc assay of tailings 2.00csce cece cece eececeees do 1.34 Quantity of zinc in concentrates produced tons.. 25. 826 Quantity of zinc in tailings 2.--+- do 6.820 Total quantity of zinc in ore treated tons.. 32. 646 Recovery Of 2iNG:. 23500522 seen. fees cease cess percent.. 79.1 Test 4.—MILL USING ROUGHER AND CLEANER. ne Pro- oat beth Fis siege Welehe i Anis weight |portion| tity of of zinc ce tity of of iron ron Size of tailings. 0 of zine con- loss. iron con- loss. sample.| weight. |(assay).| tent, (assay).) tent. Grams. Per ct. Per ct. Per ct. Grams.| Per ct. Through 3-inch on }-inch screen 3,840 29.75 28.1 5.33 204.67 44.00 Through }-ineh, on &-mesh screen 4,680 36.20 29.3 3.00 140. 40 30. 20 Through &mesh, on 10-mesh screen. . . 900 6.95 4.5 2.50 22,50 4.85 Through 10-mesh, on 20-mesh screen. . 670 5. 20 4.1 3.20 21.44 4.60 Through 20-mesh, on 40-mesh screen. . 270 2.10 1.7 2.70 7.29 1.55 Through 40-mesh, on 8-mesh screen. . 280 2.15 1,85 2.95 8. 26 1.80 Through 80-mesh screen 2,280 17.65 30. 45 2.65 60.42 13.00

Mining And Milling Of Lead And Zinc Ores.

Quantity: ford treated... cots ci s25563 cosede anise S253c8 62 tons.. 1,022 Quantity of zinc concentrate produced + ++- do.. 57 Quantity oftalings: os. 2 cace8s oso eottes set vecisedee ceils do 965 Zinc assay of concentrates 222+00ee-02 eee seen eee per cent.. 40.00 Zinc assay of tailings. . 2)... 2c scecscadecssateseeese srataneesdOsecs, 1618 Quantity of zine in concentrates. 62--- .--tons.. 22.80 Quantity of zine in tailings + do 11.38

Total quantity of zinc in ore treated do 34.18 ReCOVEFY OF ZING. assisiccsG2s essaewagent we em abews per cent.. 66.7

Test 5.—MILL USING ROUGHER AND CLEANER.

Weight

Dry Pro- beac Weight Quan- Fas weight |portion| tity of of zinc tity of of iron} Tron Size of tailings. of of zine con- iron con- loss. sample.| weight. |(assay).| tent. (assay).| tent. Grams.| Per ct. Per ct. |Grams. ct, |Grams.| Per ct. Over 10-mesh screen. 2,350] 42.4 0.7 16. 45 3 124.55 43.50 Through 10-mesh, on 20-mesh screen.| 1,122 20.2 1.3 14.58 2 2 58. 34 20. 40 Through 20-mesh, on 40-mesh screen. 532 9.6 i Lay 9.04 9 26. 07 9.10 Through 40-mesh, on 80-mesh screen. 460 8.3 1.5 6.90 4 20.24 7.10 Through 80-mesh screen 1,080 19.50 2.5 27.00 2 56. 96 19.90 Quantity of ore: treated .:2ss.scdidsosonrieedeldidilisisieides tons... 454 Quantity of zinc concentrates produced + do 43 Quantity of ype cd tony sine inr en ey eee do 411 Assay' of 'concentrates... s2s.2ss2es02 sce tse sea sceceassazess per cent. . 34 Assay Of taulngsss.<condqspowes aes tersal pe Pekar betes hada 5y 0% 322-433

Quantity of zinc in concentrates Quantity of zinc in tailings

tons.. 14. 62 do 5.

Total quantity of zinc in ore treated do 20.08

Size of tailings.

Through j-inch, on }-inch screen Through }-inch, on S-mesh screen... Through s-mesh, on 10-mesh screen .. 'Through 10-mesh, on 20-mesh screen. . Through 20-mesh, on 40-mesh screen. . Through 40-mesh, on 80-mesh screen. . Through 80-mesh screen

rites y GOOgle

zine

Weight Quanof zinc Zine tity of con- loss. iron tent. (assay). Grams.| Per ct. Per ct. 11.36 12.1 7.80 30. 00 31.9 4.70

9. 29 9.9 4.00 13.58 14.4 4.00 6. 60 7.0 3.20 6, 23 6.6 2.84 17.00 18.1 5.90 94.06 100.00 4.85

per cent.. 72.8

Weight ofiron| Iron con- loss. tent. Grams.| Per ct. 62. 40 19.15 112. 80 34. 60 28. 80 8.85 37. 00 11.35 16.00 4.90 9.94 3.05 59.00 18. 10 325. 94 100. 00

Mining And Milling Of Lead And Zinc Ores, 33

Quantity of ore treated. . z Satis ee eHesipscace 55s MODS iG 330 Quantity of zinc eoncentrates: produced... Sc udeipeialncthieaerctete oe do 36 Quantity of tailings 2.--20- 2222 eee eee eee eee do 294 Zinc assay of concentrates +--2-22-22--- percent.. 47.9 Zinc assay of tailings 0--.0- eee eee eee ee eee do 1.40 Quantity of zinc in concentrates 2 tons.. 17.244 Quantity of zinc in tailings 22.-+--- do 4.116 Total quantity of zinc in ore treated do 21.360 Recovery of zinc from mill percent.. 80.7

Comments On Results Of Tests.

In general, as the results show, the zinc content in the different sizes increased as the size of the material decreased. In other words the zinc assay of the tailings was highest in the material that passed an 80-mesh screen. The first three mill tests were made at mills where the one-jig system was in use, and in all three the percentage of loss was by far the greatest with the smallest size of material. The explanation has already been given. This loss is not as noticeable in the results for the other three mills in which the rougher-and-cleaner system was used.

It was noticed that the recovery in test 3 was considerably higher than in tests 1 and 2 representing the other two mills using the one-jig system. Spaced rolls were used in test 3, and the results would lead one to conclude that it would be better to use them in both systems. Itis to be regretted that so few mills with spaced rolls were in operation at the time, for more tests could have been made to prove more definitely the advantage from the use of spaced rolls used in test 3. Regarding the results of tests 1 to 3, if tables are not used for treating the fine material, it is the belief of the writer that the best recoveries can be obtained from the treatment of ore as practiced in the Wisconsin district by the use of the rougher-and-cleaner system in combination with spaced rolls (rolls set so that the faces do not touch).

The average recovery of zinc from the six mill tests was 72.7 per cent.

Labor In The Wisconsin District.

Labor conditions in this district are not unlike those in the Joplin district, except that men of various nationalities besides Americans are to be found, such as Bulgarians, Cornish, and Austrians. There are no unions, but each little band of foreigners has its leader who represents them in any disputes that may arise between the men and the operating company.

34 Mining And Milling Of Lead And Zinc Ores.

The length of the underground shifts in the mines is 8 to 9 hours, and the length of the shifts for surface and mill work is 9 to 10 hours, according to the nature of the work. Some of the larger companies run double shifts in both the mines and the mills, whereas others run double shifts in the mine and single shifts in the mill, but the practice varies with the size of the mill and of the underground workings.

The number of men and the average wage at 14 representative mines are given below:

Number of men and average wages at 14 representative mines in the Wisconsin district.

Wages. Designation of workmen. ara i 4 Average Total. per diem, Surface labor. Moistnttts 2005626025235 copdasazastbens cts aenecSas ele sent es teeeeesaeeae 21 $55.50 $2.64 Screenmen etek 3 61 141.25 2.32 Millmen 2.5.05-- 56 161.52 2.88 Engineers and helpers. 28 86. 22 3.08 Shopmen and helpers... eece 33 86.75 2.63 'Other'surface Mens so ..s 552555 aea5s cscs see tate ss sacs ood ceeadecasecaccspese 15 34.09 2.27 otal surlacslabors s.202.5 22 ss duties sedate vatecaksacesaausascaacd 214 565. 33 2.64 Underground labor.

Drillnon anid helper zs sac. 50.505.aceata le sciicgscemesade cepts ieeareet estat 121 295.35 2.44 Shovelers 170 468. 30 2.75 Tub hookers... . acme as 24 64.50 2.69 PrACKMOD 3.432 acssiedaccccssapysesesesacicace Secs eo Ze ll 29.25 2.66 Trammers and other underground men... nor ace of 64 154. 25 2.41 Total underground labor... 390 1,011.65 2.59 Total Mim ber of MON ss scs.ss ss sece ss sa sess bei ass iss bocce jas idecees 604 1,576.98 2. 61

The figures in the foregoing table show that the average wage per man is about $2.60 a day. This average is not as high as that in metal-mining districts of Rocky Mountain States, but living costs are lower in Wisconsin and there are fewer interruptions of work from labor troubles. A steady man is usually certain of holding his job.

Cost Data.

It is difficult to obtain average costs of mining and milling operations in a mining district as a whole, because each company has its own system of keeping costs, but at several of the representative mines in the Wisconsin lead and zinc district costs were being kept systematically, and the writer is greatly indebted to the companies that placed their cost sheets at his disposal.

The following figures represent the average costs of the different operations at the various mines and mills covered.

a

Mining And Milling Of Lead And Zinc Ores. 35

Costs per ton of ore mined.

Mining: 4 Drilling ais sasesarssse ccc chai ceedseseiees devacetensczaes sacs $0. 1296 SLANG 25'-= 2s cc nnet seers se abe egudcore aaldy eats SGanweceadar . 1243 Shoveling, hoisting, and tramming . 3426 otal tick he gas Sees Se Ree Doe aeR CCE SLA cadekausins . 5965 MANN F522 oes oes keno wnisad balan ea AMaTeae Geel en eawe ke benches . 1565 PUMPING. 2600 cas scant ase ccm sOsaneaseceaae edsos site a2 eupreea due - 0103 ROWGL 2. Giscacet soe ecculdes sameacevcraet'stt enews ws cage vox space: . 2804 General and administrative expenses 2---2---+--- . 2416 Total average cost per ton of ore mined and milled. 1. 2853 Average cost per ton of concentrates produced 15. 635

In the foregoing figures it will be noted that the cost of power for each operation is not included in the cost of that operation but that the power cost is kept separately as one item. It would have been interesting to show, if possible, the distribution of power cost under each item. This separation was not possible from the data on hand, so that the expenses for the different operations include everything except the power cost, which is given separately. The figures for the average costs given above were furnished by mines that were operating during the year 1913.

Accidents And Safety Precautions.

The causes of accidents in the Wisconsin district are various, but it is safe to state that more than half of the fatal and more serious injuries are caused by falls of slabs or pieces of rock from the roof of the underground workings. There are other important causes, such as the use of explosives, falls down shafts, the workings of machinery, and underground haulage. Although some accidents are unforeseen and unavoidable, yet many are due to carelessness on the part of the miners or to lack of proper inspection of the underground workings or lack of discipline over the miners on the part of the ground bosses or mine foremen. For more definite figures of both fatal and nonfatal accidents and their causes in the Wisconsin lead and zine district the reader is referred to Bureau of Mines Technical Papers 40, 61, and 94, for the years 1911, 1912, and 1913.° The figures presented in the reports mentioned are interesting in that they show the number killed or injured per 1,000 men employed for the number of days actually worked and also on a 300-day basis. Figures on the 300-day basis bring out the importance of safeguarding against acci-

@ Each operation includes labor, supplies, and repairs.

b Fay, A. H., Metal-mine accidents in the United States during the calendar year 1911: Technical Paper 40, 1913, 54 pp.; Metal-mine accidents in the United States during the calendar year 1912: Technical Paper 61, 1913, 76pp., 1 fig.; Metal-mine accidents in the United States during the calendar year 1913: Technical Paper 94, 1914, 73 pp. .

36 Mining And Milling Of Lead And Zinc Ores.

dents not only in the larger mines but also in the smaller mines and prospects, and Fay shows by the figures he presents that the hazards of prospecting are greater than those of mining.

As to the prevention of accidents at or in the mines, every item of a set of rules necessary for large mines would hardly apply to the smaller mines of the Wisconsin district, but many of the items would apply. After an accident has occurred, measures are usually taken to prevent another similar accident. If the miners or mine foremen could foresee the possibility of an accident as readily as they can observe the causes after one has occurred, the number of accidents would be considerably reduced. Closer supervision of the ground or shafts on the part of both the miners and mine foremen, and a careful study of conditions and application of precautions shown to be proper by accidents at other mines, would all help to increase safety.

Protection around the collar of shafts is important, and it is gratifying to note that at many of the mines shafts are protected effectively by gates or railings. However, there should be such protection at all the mines, and not at the mines of the larger companies only.

When ore is being hoisted in tubs or "'cans," men should not be allowed to stand directly at the bottom of the shaft, for the bumping of the tubs often causes pieces of rock to fall down the shaft. Straddling the side of the tub in riding, a dangerous but common practice in the Wisconsin and Joplin districts, may result in the miner's hitting his kneecap or foot against the sides of the shaft; consequently there should be strict regulation of the speed of hoisting or lowering men.

Every miner can do much to lessen the danger from falls of roof by examining carefully the roof and working face after each shot before starting to drill new holes or clearing away the place in which they have been working. There should be strict supervision of the use of explosives, especially if the miners or machine men load and fire holes. In other words, in each kind of work done by the men certain precautions are necessary, and each miner should cooperate in helping in every way to prevent possible accidents.

Health Conditions At The Mines.

ITealth conditions in a metal mine in general depend largely on the material mined, the depth of the mine, the gases present, and the character of the ventilation. Favorable conditions in the mines of the Wisconsin district are the shallow depth of the ore deposits, the lack of the injurious gases found in coal mines and in some deep metal mines, and the good ventilation. Fans are used wherever

Mining And Milling Of Lead And Zinc Ores. 37

necessary to blow fresh air through workings where natural ventilation is insufficient or can not be utilized.

The shafts and the ground underfoot in the mines are usually wet, so that the men are often obliged to wear rubber boots, and sometimes are compelled to wear slickers. At many of the mines there are change houses where the men have their own lockers. As many of the men drive or walk to and from the mines these change houses are necessary and are largely used. It has been stated that the mines in general are small, so that the change houses are not elaborate, but they at least serve the purpose of allowing the clothes to dry after each shift, and they guard the men against unnecessary exposure.

In most of the mines that are practically free from water and dampness dust is produced from the drilling and blasting. This dust, if inhaled by a miner every day for a considerable time, may cause lung trouble. The exact amount of harm done by inhaling the dust in different classes of metal mines is not definitely known, but it is believed that much of what is known as ''miners' consumption"' is caused by sharp particles of dust, in that the lungs, when affected, are more susceptible to disease. The injurious effect of rock dust is lessened by spraying the faces. Wetting of the face should be done in all mines where rock dust, especially siliceous dust, is prevalent. Water drills are used to some extent.

At some of the mines there are boarding houses, and at a few of the larger mines company houses are furnished in which the married men may live with their families, paying a nominal rent. The living conditions on the whole are being bettered, and still greater improvement will undoubtedly be made as new mines are opened.

Wherever improvements relating to the betterment of the health conditions of the men are possible they should be made, for too much importance can not be placed on the miner's health, not only for his own good, but also to promote the greater efficiency of his work for the operating company.

Resume.

The importance of certain features of mine and mill practice in the Wisconsin lead and zine district is realized by some operators but not by all. The main object of every operator is to make a mine pay, but whereas one operator is constantly seeking to improve methods or equipment in order to increase his profit through the greater efficiency of the plant, others attempt to make as close a saving as possible with the equipment on hand, and do not care to investigate possible improvements that would involve any changes. As regards the latter class, lack of funds often prevents investigations that the mine manager or superintendent might wish to undertake,

38 Mining And Milling Of Lead And Zinc Ores.

but if the mine has any future and there is a chance for improvement, experiments on a small scale should be made, for a slight saving here and there might mean the making of the mine. At all mills sampling should be done to show what results are being obtained. To be of value, however, the sampling should be careful and systematic. The sampling of tailings without including material in the overflow water from the jigs and settling tanks, an oversight frequently observed, is of little value. The richness of the ore varies, and to keep a check on the work, samples should be taken every day.

At many of the mines and mills excellent results were being obtained under the existing conditions. It is hoped that every operator will endeavor to effect greater saving, so far as is profitable, and take advantage of any experiments made by others that seem to show how his own practice may be improved.

The proper grade of explosive and the proper quantity to be used in breaking ground should be determined by test from time to time as the working faces advance and the character of the ground changes. A saving in the use of powder would be an important item in the reduction of mining costs.

The matter of hand sorting should be given closer attention at many of the mines. Close determination should be made as to how far discarding of waste rock can be carried advantageously. The greater the quantity of waste rock eliminated before the ore enters the mill, the richer will be the feed; a higher recovery will be possible; there will be an important saving in power and in the wear on rolls, etc.; and the relative capacity of the mill will be increased.

Possible improvement in many other details might be discussed. Each operating company should see that, in the development of its mine and in the operation of its mill, due effort is made to effect every major or minor improvement that will improve health and safety conditions.

Gor gle RINCETON UNIVEF

Mining And Milling Of Lead And Zinc Ores. 39

Publications On Mineral Technology.

A limited supply of the following publications of the Bureau of Mines is temporarily available for free distribution. Requests for all publications can not be granted, and to insure equitable distribution applicants are requested to limit their selection to publications that may be of especial interest to them. Requests for publications should be addressed to the Director, Bureau of Mines.

Buttetin 3. The coke industry of the United States as related to the foundry, by Richard Moldenke. 1910. 32 pp.

Buuetin 8. The flow of heat through furnace walls, by W. T. Ray and Henry Kreisinger. 32 pp., 19 figs.

Bu.etin 12. Apparatus and methods for the sampling and analysis of furnace gases, by J. C. W. Frazer and E. J. Hoffman. 1911. 22 pp., 6 figs.

BuLietin 47. Notes on mineral wastes, by C. L. Parsons. 1912. 44 pp.

Buiietin 53. Mining and treatment of feldspar and kaolin in the southern Appalachian region, by A. S. Watts. 1913. 170 pp., 16 pls., 12 figs.

Bu.etin 54. Foundry cupola gases and temperatures, by A. W. Belden. 1913. 29 pp., 3 pls., 16 figs.

Buuetin 64. The titaniferous iron ores in the United States, their composition and economic value, by J. T. Singewald, jr. 1913. 145 pp., 16 pls., 3 figs.

BuLietin 67. Electric furnaces for making iron and steel, by D. A. Lyon and R. M. Keeney. 1913. 142 pp., 36 figs.

Buuetin 70. A preliminary report on uranium, radium, and vanadium, by R. B. Moore and K. L. Kithil. 1913. 100 pp., 2 pls., 2 figs.

BuLvetin 71. Fuller's earth, by C. L. Parsons. 1913. 38 pp.

BuLLeETIN 73. Brass-furnace practice in the United States, by H. W. Gillett. 1914. 298 pp., 2 pls., 23 figs.

BuLetin 77. The electric furnace in metallurgical work, by D. A. Lyon, R. M. Keeney, and J. F. Cullen. 1914. 216 pp., 56 figs.

TECHNICAL ParER 31. Apparatus for the exact analysis of flue gas, by G. A. Burrell and F. M. Seibert. 1913. 12 pp., 1 fig.

TECHNICAL PapPER 36. The preparation of specifications for petroleum products, by I. C. Allen. 1913. 12 pp.

TECHNICAL Parer 41. The mining and treatment of lead and zinc ores in the Joplin district, Mo.; a preliminary report, by C. A. Wright. 1913. 43 pp., 5 figs.

TECHNICAL Parer 49. The flash point of oils, methods, and apparatus for its determination, by I. C. Allen and A. 8. Crossfield. 1913. 31 pp., 2 figs.

TECHNICAL Parer 54. Errors in gas analysis due to assuming that the molecular volumes of all gases are alike, by G. A. Burrell and F. M. Seibert. 1913. 16 pp.

TecHnicaL Paper 57. A preliminary report on the utilization of oil and natural gas in Wyoming, by W. R. Calvert, with a discussion of the suitability of natural gas for making gasoline, by G. A. Burrell. 1913. 23 pp.

TECHNICAL Parer 58. Action of acid mine water on the insulation of electric conductors, a preliminary report, by H. H. Clark and L. C. Ilsley. 1913. 26 pp., 1 fig.

TrecHNICAL Paper 60. The approximate melting points of some commercial copper alloys, by H. W. Gillett and A. B. Norton. 1913. 10 pp., 1 fig.

TeEcHNICAL PaPeER 81. The vapor pressure of arsenic trioxide, by H. V. Welch and L. H. Duschak. 1914.

O

seg ne