Charles George Warnford Lock.

Economic mining: a practical handbook for the miner, the metallurgist and ... online

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emarks, the ore-bodies might be mistaken for ore-beds and not bed-
^eins, were it not for the presence of spurs into the walls." The
purs in these ore-deposits usually follow the planes of bedding of the
unestone. The limestone generally occurs in blocks, and the ore
hen follows the plane of beading until it comes to a cross-seam from
ne bed to the other, when the ore will sometimes jump to the next
earn. In places these seams are several inches or even a foot wide,
nd oompletelv surround blocks of limestone; and the vein then
ssumes the character of a stockwerk. In other places, what have
vidently been vugs and caves in the limestone have been filled by
he ore. Fig. 115 illustrates the formation: a, ore-bodies ; &, lime-
tone ; c, felsite-porphyry.

Wendt doubts * whether the ores of this district have ever been
olphurets in their present position. The whole deposition tends to
Tove that the ores are not a secondary decomposition or alteration of
rhat was formerly sulphurets, but have been precipitated as car-
onatee from an acid solution which carried them from the depths
elow. The origin is probably in the eruptive rock, which contains
onsiderable quantities of disseminated particles of pyrites.

The mining of the great ore-bodies of the Bisbee (Warren) district,
otably those of the Copper Queen and Copper Prince mines, has been
arried out in a very systematic manner, entirely difierent from that
f the Clifton district, where the Mexican imtem of mining ruled for
lany years. The plan adopted generally is underhand stoping and
imDering in square sets (see p. 86). Sawed Oregon or Huachuoa
ine, usually 10 or 12 in. square, is used, and the sets are made 7 ft
♦ A. F. 'WcncU, op. cii.



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426 ECONOMIC MINING.

high and 5 ft. from oeutre to centre. Even with this heavy timberiii|
occasional crushing takes place. In 1883 the cost of mining— iS'
eluding all expenses, such as timbering — was about 8*50 dol. (3^]
per ton. The cost of smelting amounted to about 10 dol. (42«.) p^
ton of ore treated, and the yield of the ore was about Vl\ per cent
Since then the yield of the ore has fallen below 10 per cent. ; but tin
cost of mining has come down to 6 or 7 dol., and of smelting to 8 doL
so that the cost of metal on the spot from 10 per cent^ ore should no^
exceed 7^ c. rsfd.) a lb.

In the Globe district, the Old Dominion mine is in a fissure ii
bedded sandstone dipping 15°-20° S., the vein striking N.E.— S.W.
dipping vertically, and measuring 2 ft. wide, with many barrel
patches. The sorted ore carries 20 per cent, copper, with considerable
arsenic and antimony, and some gold and silver ; it is silicioos, an<
requires much flux.

1'he vein of the Globe mine is in a fissure crossing Carboniferom
limestone, near an upheaval of diorite, which forms the foot wall o
the ore-body in part. Near the contact of diorite and limestone, tlv
rock 18 decomposed, kaolinised, and very soft and unctuous. Whei
the great ore-body is entirely in limestone, the latter is discoloured
The diorite is undoubtedly eruptive, and the ore found entirely in t
(copper glance) pinches out rapidly in depth. Wendt considers it i
true fissure vein, of chimney-like form, dipping almost parallel wit!
the contact of diorite and limestone, and pitching 45^ S. Timbering

is done by square sell
(12 X 12 in.), and ded
work is minimised. TiM
mine is illustrated in Fi^
116: a, ore; &, limestonej
e, diorite; d, incline shaft
c, levels.

The Black Coppfl
group of veins occur in i
belt of gneiss rock, cut b]
a dyke of diorite, oooasioa
ally intersected by a subse
quent in trusion of trachytt
The gneiss for a width cj
some 40 ft. is cut by iii
Fio. 116.— GoPFEB DEPosrrs, Globe. numerable small veins aiM

strings of copper-ore, fol
lowing generally the strike of the gneiss, and dipping, a little fa8t«|
than that rock, towards the diorite dyke close by. The shaft sunk '
the gneiss, shown in Fig. 117, exhibits the system of veinlets
clearly. The ore in the shaft and on the surface is malachite imd
socolla. The widest of the seams is only 2 in., and the whole
forms a atockwerk too poor to pay for working. Down the hill from
system of veins or stockwerk, and below the diorite dyke, a vein of
is found lying almost horizontally in the drift. Analyses prove it
be a typical chrysocolla. It is undoubtedly of secondary origin, al
<lerived from the veins up the hill near the diorite. It has befl

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METALLIFEROUS MINERALS, 427

itripped in a number of places, and has been found, by cuts sunk
hrough it, to have a thickness of 4 ft. of pure chrysocolla. The occur-
•ence is remarkable, as showing the formation of a bed of copper ore
n very recent times, and in the wash. In Fig. 1 17, a is the shaft ; 6,
rorface copper ; c, diorite ; d, gneiss ; e, wash ; /, chrysocolla.



Fio. 117. — Ck)PPEB Depospts, Black Coppeb.

Copper Basin is a region of cupriferous impregnation covering
bout 40 acres, and geologically simple. The foundation rock is
>ar8e-grained granite and gneiss, with soda-felspar predominating ;
lere are also porphyritio dykes and a large pyritiferous quartz vein,
aperimposed on these are horizontal beds of conglomerates, breccias,
id sandjstones, largely consisting of fragments of the plutonic rocks,
id forming repositories for copper ores, which are the cementing
igredient. The ores are azurite and malachite, and they coat the
agments of rock as well as forming the matrix. The beds are 3 to
)ft. thick, and yield up to 12 or 15 per cent, copper. These copper-
^positions are clearly the result * of the gradual percolation of copper
lutioDs (probably sulphate) passing through the porous sand-rock ;
id the copper carbonate is a deposit of incrustation, not of replace-
ent, for, so far as the sandstones and the conglomerates have in-
lenced the deposition, the action appears to have been mechanical
ther than chemical. The surface, rather than the chemical com-
eition of the strata, appears to have determined the deposition,
ar does it appear that the copper carbonate has replaced any
IcareouB or silicious cement. The absence of a cementing material
ems to have, favoured the infiltration and distribution of the cupri-
rouB solution, which may have been gradually concentrated by
aporation on the surface of the coarse grains of rock. Now as to
e source of such extensive depositions of copper. The granite
low the cupriferous beds, and throughout the copper area, is very
Qch decomposed and softened. Numerous veinlets and thin seams

red oxide of copper, accompanied by malachite, and malachite
^«eminated in small nodular or concretionary masses not much
rger than kernels of maize, occur in the soft ferruginous clay resulting
)m the decay of the granite. These little button-like discs of mala-
ite are so abundant that they could be washed out with profit if
iter could be led upon the ground. Also considerable quantities

• W. P. Blake, "Copper Deposits of Copper Basin,*' Trans. Araer. Inst Min.
tpi., xvii. 479.



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428 ECONOMIC MINING.

of red oxide of copper in tbin sheets, with malachite on each side;, forn
nmnerons small veinlets (j^l in.) traversing the granite ; the ni
oxide is in the middle and the malachite on each side next to
granite walls, and the central oxide is sometimes replaced by solpl
At Copperopolis, Califomia, laige beds of copper pyrites are 1<
in Jurassic slates, showing no trace of gold or eolver. At Spencei
a vein 230 ft. long, 40 ft wide, and worked to 150 ft. deep, oocari
diabase near its contact with granite. The Tiptop mine is on a
of parallel faults in qnartz-porphyry ; the ore was much oi
(iron) at surface, and carried 80 oz. silver per ton, but at 80 ft.
entirely copper pyrites and silicious rock low in silver, with
times masses of native sulphur.

In Moleje, Lower Califomia, extensive deposits oocnf in rock (
very recent origin, overlying a bed of trachyte of unknown depti
While the ore-beds extend over a very large territory, the valuaU
portions cover a comparatively limited area, and the pay-ore oocutb i
shutes or chimneys in the beds, having a width of 75 to 150 fL,aQd
general N.W.-^.E. course. The stratum carrying the ore is a sd
ferruginous clay, mixed in many places with oxide of manganese, ai^
in others intersected in every possible direction by small seams k
gypsum. The foot-wall or floor of the different ore-beds is always
conglomerate. The hanging-wall or roof is either day or soaj
or more generally a mixture of both, which readily crumbles
exposed to the air. The ores differ very widely in composition
appearance ; in fact, a great many of the ores have not the charac
istic appearance of ore at all, but look like yellow clay. True copi
ores varying from copper glance to green and blue carbonates
however, occur. Malachite forms the bulk of the ore; and wad
cupriferous oxide of manganese occurs in the next largest qnantil
The thickness of the ore-beds varies considerably, from a mere
to 3 ft.

At Oilpin county, Colorado, occur veins of pyrite and chaloopyTil
following the cleavage joints of the gneiss (or granite), and re^
the country rock on each side of them ; they are highly aimf<
and worked primarily for gold, the concentrates from the stamj
being afterwsurds treated for copper.

At St. Qenevieve, Missouri, large beds of chalcopyrite
with chert occur in magnesian limestone of Lower SUurian age.
In Tintic District, Utah, three great ore belts occur in vc
beds of magnesian limestone, apparently deposited along the bedi
planes, though often cutting across them ; the productive a
irregular in size, diape and frequency. (See Silver.)

Deposits at the contact between Triassic sandstone and
seem to be always lacking industrial value, and the same
would seem to apply to contact beds with gneiss and schistose rod
reple^dng the diabase.

Treatment. — Hardly any copper ores raised now-a-days are so ric
as to be at once treated for the extraction of the metal, and all hai
to undergo a preliminary enriching process by removal of waste.

Concentration. — The character of the ore determines the metlio
and degree of concentration needed.



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METALLIFEROUS MINERALS,



429



Hand sorting is simple and effective but rarely applicable. At
Vigsnaes it is adopted, boys being employed to separate the ore as
raised into three grades :— -(o) Clean lump pyrites, carrying 2-2^ per
cent, copper ; (6) pyrites mixed with waste ; (c) waste.

Crashing ordinarily has to be resorted to in the first place to
prepare the mineral for separation, and should be so adjusted that the
requisite fineness is attained but not exceeded. Breakers and rolls
^dry) are generally employed, though fine reduction with stamps is
often used on sulphides, but would produce too much slime with the
wfter (oxidised) ores.

Dry winnowing or "dousting" is useful where the ore is more
*riable than the gangue, e.g. the chalcopyrite and erubescite at the
3ape copper-mines, Namaqualand. The ore is first cobbed and classed
nto (a) prile, (6) best dredge, and (c) crusher dredge ; a is finished
product; c is crushed, jigged, and huddled; 6 is dousted, or, after
Cueing in rolls to 8-mesh, dry-sifted in fine mesh hand sieyes,
thereby the bulk of the ore is separated as fine powder, the coarser
^due being subsequently re-crashed, jigged, and huddled. About
>ne-third of the 700 tons monthly of 30 per cent, ore there produced
B thus obtained.

Wet concentration embraces sizing in trommels and hydraulic
eparators, jigging, huddling, vanning, (&c. In Japan, hand washing
n wooden bowls by women at 3^. a day is found cheaper and more
borough than machine work, but of limited capacity.

At the Lake mines the pmcess followed is briefly this. Dressing
eally commences underground. On reaching surface, the ore is
lumped on to grizzles or gratinu;8 lying at 45°, the bars of 1^ in. iron
leing 4-6 in. apart. The portion falling through goes to the stamp
fins; that passing over is hand-fed into a 14^ in. Blake. Lump
opper when encountered must be picked out before entering the
freakers. The stamps are fed automatically by a shaking tray,
rhich, however, requires constant supervision. The annexed figures
ompare results at throe of the important Lake mills : —



rumber of stamps
"attem of stamp .
'(xmdations ..



LP. per stam^ about

' ore© of blow in foot-tons, about
'ons cmsbed per day per stamp

Jharaeter of rock

V'ater ttted per ton

Mfeofahoe



Jfe of screen, about
Ibaracter of screen



Atlantic.



5

Bull

Solid nnd

spring.

140

21

210

Amygdaloid

7200 gal.

3000 tons

or 14} days

8820 tons,

or 42 days

4 cast steel

plates, 9^ X 48

in, X Mo. 11;

slot holes

^ in. long.



Tamarack.



5
Allis
Solid



21-4

300

Conglomerate

35-40 tons

3-4 days worn

from 700-200 lb.

3-5 weeks

4 plates steel

9 X 25 X A

in. ; A in.

punched holes



Calumet and
HecU.



22

Leayitt

Solid

150
20

Gonglomerute

5-6 days

1 month

Steel plates ;

Tff in-
round holes



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430 ECONOMIC MINING.

Three patterns of steam stamps are used at the present time— -tl
Ball, the Leavitt, and the AUis, the first being the old^t Tl
character of the rock from the different mines varies so much Uh
unless there were various stamps in the same mill, and working t
the same rocks, a comparison would be valueless. The capacity 4
the steam stamps is enormous, and the amount of water required 1
remove the crushed rock from the mortar is also very large.

The rock is crushed to pHss holes varying in diameter from ^\ i
to -f^ in., depending upon the character of the rock under treatmen
Crushing thus fine does not liberate all the copper from its gangii
In fact, it would be almost impossible to crush the conglomerate &
enough to do so. The size of the opening in the screens used at U
various mills has been determined by experiment to be the mo
economical for that particular ore. Crushing finer would, of ooun
decrease the capacity of the stamp, hence it is best to use as coarse
sci-een as the ore will permit. The copper that yet remains attach*
to particles of rock is not lost. A large portion of this materii
calif d the ragging, is caught on the jigs and either returned to ti
stamps or treated in some grinding machine.

The wear of the shoes, made of chilled cast iron, though it appea
very rapid, is actually very small when compared with the amount
work done by them.

As the ore passes through the screens of the stamp it is coUecti
by a splashbox, and drops into a launder leading to the separatoi
I'his launder divides the ore stream into 3 equal portions, one beix
delivered to e^ach of the separators. The separator at the Atland
mill consists of a V trotigh about 15 ft. long, 18 in. wide and 18 b
deep. Near the bottom, and at the front of each separator, are 4 snJ
pipes discharging upon the screens of 4 jigs just opposite them. 1
the axis of the separator and opposite to each outlet is a vertical l^i
pipe, supplied with water from above and opening downward abw
2 in. from the bottom of the separator. Between each of these ]iip
lies a bed of copper, deposited in the regular working, and allowed
remain there. As the ore enters the separator it passes over tha
beds of copper, coming successively in contact with the rising curren
generated by the supply pipes mentioned. The head of water in e»«
successive pipe is less, so that the heavy particles of o<>pper m
gangae will fall into the cavity around the first, and pass thronji
the small opening in the front and spread themselves upon ti
roughing jig. In the second cavity less heavy particles will fall ; i
the third, still smaller grains. The ore which passes the fouri
division of the separator is classed as slime, and goes to the settlin
tanks. The separation is very incomplete. Following each separate
are 4 roughing jigs, each having 2 screens; thus the ore from eac
separator is treated from a set of 8 screens, each set doing exactiy tl
same work. The hutch -work from the roughing jigs passes to 1
finishing jigs, placed at a lower level, all of which do different work

The product may generally be classified as 50 per cent coan
(over ^ in.) sand, 15 medium, 10 fine, and 25 slimes.

The Anaconda mill, Montana (capacity 3000 tons a day), uk
14 steam stamps. The concentrating plant is in a building 262 ft )



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METALLIFEROUS MINERALS. 431

36 ft., Bteam-heated by 150 h.p. boilers ; it consists of two 20 X 10 in.
md four 10 x 7 in. breakers, and three sets of 26 x 15 in. rolls. The
)ulp is concentrated on Collom jigs, the middlings are re-crushed in
uUs, the fines are dressed on double buddies 16 ft. diam., and the
limes go to Frue vanners.

Solution. — Wet methods of extracting copper are applicable
^-hen : —

(a) The percentage of metal is very low.

(6) Injurious impurities (as antimony and arsenic) are present.

ic) Associated metals would be lost by smelting.

(a) Dissolving and precipitating agents are obtainable at low
ost.

The first step \a oxidation, unless the ore is alreadj' a carbonate or
xide. In its simplest form, this consists in exposing the raw
yritous ore in a moist state to the influence of the air, and is often
astened by pumping water with some force (thus carrying entrapped
ir) into the ore heaps. But the process requires years for it^com-
letion with most ores. Considerable copper is recovered from mine
raters in which the operation has taken plaoe naturally, the copper
ontents varying from '08 to 50 gr. per gal. in cases where they are
tilised.* Such waters are well adapted for moistening ore heaps,
ometimes about 1 per cent, of salt is added to the heaps, to hasten
xidation, render the copper more holuble, and chloridise small traces
f silver ; heat aids the operation very much. Adding manganese
xide is a doubtful benefit. Occasionally acid liquors may be used on
arbonate and oxide ores contained in rook not attacked by the solvent,
nd where the acid is a waste product or very cheap, e. g. as recom-
lended by Blake at Copper Basin, Arizona.

Oxidation by heat T" burning ") is much more rapid, and is appli-
able to ores rich in sulphur and poor in copper, the sulphur forming
he fuel. It is done in two distinct ways — (a) in kilns, with the
bject of utilising the sulphurous acid generated, the ** cinders '* being
fterward« treated for their copper; (6) in open-air heaps or telercis
8 at Bio Tiuto, by which much SO2 is wasted and creates a nuisance.
"he telera consists of rude stone flues built on the ground, 15-18 in.
jgh, 12—15 in. wide, extending to stone chimneys at their inter-
tx^tions, and covered loosely with flat stones. Upon these are piled
amps of pyrites progressively decreasing in size as the height grows,
111 at 12-15 ft. the heap is coated with a layer of smalls. Ignition
* produced by lighting brushwood and logs in the flues, and com-
ujstion proceeds for 6-12 months. A single telera may contain 800*
3 1500 tons. The cost of the operation ranges between Is. 3d. and
Iff. a ton, and the product is a mixture of copper and iron sulphates,
rbich are extracted by washing either in the mass or in tanks. By
he latter method, f of the metal in a 2^ per cent ore can be recovered
t once and the bulk of the rest by repeated washings at yearly
utervals.

Maidenpec (Servia) ores are too small, and contain too much

• The most important contribution to recent literature is a paper by J. H.
>ollms on " Economic Treatment of Low-gnuie Copper Ores," in Trana. Inni. Min.
ad Met, ii. 5.



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432 ECONOMIC MINING.

silica and too little sulpliQr for the Xdera method, but by mtldnf
briquettes, duly dried and hardened, they can be burned in 900 ta
heaps, though consuming more fuel and taking more time.

Open-air burning is only applicable to ores containing a limited
proportion of fines, but little ridi sulphide (as ohalcopyiite), not unda
20 per cent, sulphur, and not over 20 per cent, silica.

Chemical methods of hastening oxidation have received mud
attention, being led up to by observing that ferric liquors obtains
by washing burned ore aid in oxidising and rendering 8<iluble tii
copper in raw ores, on prolonged or repeated contact.

The Joly (Doetsch) process aimed at replacing the ferric liqno
from burned ore by (a) calcined sulphate of iron, (&) by saturBtiiu
spent liquor from copper tanks with condensed fumes of roasted sal
and iron sulphate, or (c) bv the same operation, only adding man^
nese peroxide to the roasr, the two latter modifications being designs
(with small success) to generate chlorine. In its simple form tlu
method is now much used at Rio Tinto, though the action of tfa
liquor is very slow.

Roasting with addition of chemicals (chiefly salt) is best illoii
trated by the Longmaid (Henderson) method, which is applicable t
very silicious (90 per cent, even, when crushed to ^ in. or lees) ort
and to chalcopyrite. It has been used in Cornwall on ore containinj
much sulphur, silica, and iron, besides 1^ per cent, copper and 9 pe
cent, arsenic, with 9 lb. tin, 5 oz. silver, and a few gr. gold per toi
This ore required a preliminary oxidising roast (in reverberatory 9
Oxiand calciner) to remove mont of the sulphur and all the arseni(
the latter being condensed and caught in flues (see p. 158). For tb
second roast, 10-12 per cent, salt is added, whereby any remainiDj
sulphur becomes soda sulphate, and the copper, gold and silver ai
sume the form of chlorides (easily soluble), the solutions becominj
very concentrated in due course, and allowing the precious metals t
be recovered before the oopper is thrown down, while the tin \
separated from the solid residues left by the chloride solution.

The Hunt-Douglas process, successfully employed in America
low grade ores, has gone through three stages. In its earliest fbra
patented in 1869, ferrous chloride is dissolved in strong brine, and b
its action nith cupric oxide gives rise to a mixture of cnpric an
cuprous chlorides, the latter, though nearly insoluble in water, bein
held dissolved by the sodium chloride. The dissolved iron is sepi
rated as hydrous ferric oxide, retaining a small portion of fern
chloride. To prevent loss of chlorine, the use of sulphurous acid t
reduce and dissolve this iron oxychloride was propoised, but it wi
found in practice with roasted sulphuretted ores that the ferro*
salt formed in the reduction by metallic iron of the cupric sulphu^
thus obtained renders unnecessary the use of sulphurous acid. %
this method with ferrous chloride, the resulting solution being neutiv
absence of arsenic is ensured. Any silver contained in the ores i
chloridised by the acti(m of the copper salts, and made soluble in tb
bath of sodium chloride, from which, however, its separation preeeDt
considerable difficulties, precipitation of silver by metallic copper ii
presence of chlorides requiring that the whole of the dissolved ooppJ



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METALLIFEROUS MINERALS. 433

treeent sbould be in the cnprotis form. For the rest, the copper is
ery readily precipitated from these solutions by metallic iron, with
tincb reduced consumption of iron.

In the second form, heginning with a neutral solution of copper
ulpbate, there is added so mu(£ of common salt or other soluble
hloride as will serve to convert the copper present into cuprous chlo-
ide f58'6 parts sodium chloride to 63*4 copper). Through the
lear, hot solution is drawn or driven sulphurous acid gas, cot from
oasting sulphiuretted ores, which serves to convert the dissolved
opper into insoluble cuprous chloride, with liberation of the previ-
iiftly combined sulphuric acid, and the generation of half as much
lore of the same acid by oxidation of the absorbed sulphurous gas.
'be dear acid liquid drawn from the cuprous chloride is then satu-
ftted with copper from oxidised ores, and the precipitation by
alpbnroas gas is repeated indefinitely. The insoluble cuprous
hloride obtained in this process may be either reduced to the
letallic state by iron, under water, or decomposed by milk of lime
rith formation of cuprous oxide and calcium chloride ; the resulting
hlorides in either case serving for the chloridation of the further
ortions of dissolved copper. By the use of a solvent containing
nly small portions of soluble chloride, any silver present in the ores
\ cbloridised, but remains undissolved in the residue, and may be
xtracted by solution, by amalgamation, or by smelting ; whereas, in



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 48 of 76)