Charles George Warnford Lock.

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

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In England a few owt of the metal are yearly produced in Com-
wall, but the chief European sources are the 6axon Erzgebir^
where it is commonly encountered with cobalt and silver ores ; the
Erzgebirge of Bohemia, in connection with silver and tin.; the silver
ores of Styria and Carinthia; and the gold mines of Cziklova in tiw
Banat and Rezbanya in Transylvania, associated with tellurium, pdd,
and rilver. The yearly production of bismuth ores in Austria is
800-1000 tons, aifording 1200-1400 lb. metal. In Norway it oocwb
with copper. The auriferous deposits of the Yeniseisk, Siberia,
contain bismuth. It is associated with gold in Charlotte County,
New Brunswick, the rock giving 10 per cent, bismuth and 5 dwl gold
per ton. Bismuth occurs with certain silver ores in the San Jota
district, Colorado, where it is produced commercially ; and Lane's
mine at Monroe, Connecticut, has furnished specimens of native bia^
muth in quartz. Bismutite has been met with in conjunction with
gold at Chesterfield, S. Carolina. The sulphide is found at Cato
Branca, Minas Geraes, Brazil. A large deposit of bismuth ore is
worked at Quechisla (Chorolque), Bolivia, associated with silw vA
tin, the monthly output reaching 25 tons. Both metallic bismnth
and bismutite are products of the auriferous deep leads of VictcHia;
and at Nuggety Reef, Maldon, Victoria, both in the neighbourhood oC
the granite veins and a few inches deep in the granite itself, are en-
countered quantities of maldonite, the gold from this district being
largely alloyed with bismuth. In Queensland, bismuth ore aoown-
panies magnetite, and the mixture, after wet concentration, is P*^
through a magnetic concentrator, by which the percentage ol
bismuth is raised from 10 or 12 to 20. Tasmania also affords some
bismuth.

The metallurgy of bismuth possesses but littie general interest m
the industry is a monopoly. Producers of bismuth ore content the®-
selves with concentrating the mineral as eflficientiy as mav be, to «^
freight, and shipping to London. Nearly all commercial bismuth and
bismuth ores carry notable amounts of the precious metals, enhancing
their value but complicating their treatment.*

The low fusing point of the metal, 476° F., gives it a ^^^^
alloying purposes, and it is employed to some extent as a drug; wt
the demand is always limited, and the market is closely controDei
Shipments of 20 per cent, ore from Australia have fetched lOOi. atos*
but probably the gold contents influenced the value.

♦ Consult E. A. Smith, Jl. Soc. Cham. Ind., 1893, p. 318; E. Mattliey, aia*
1889, p. 286, and Chem. News, 1893, pp. 63, 67 ; and * Mineral Industrj.' u. 69.

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METALLIFEROUS MINERALS. 409



CHROMIDM.

^ mineral cbromite, which is a mixture of the oxides of iron and
hrominin, is the nniversal source of chromium. Chromite is a
lember of the spinel series, and resembles magnetite very dosely.
lie theoretical chromite FeO, Cr^Oj, with 68 per cent, chromic oxide,
fien has magnesia (MgO) replacing a portion of the FeO, and ferrio
ode (Fe^O,) and alumina (AI2O9J replacing a part of the Gtjdi.
liefle other oxides lower the grade of the ore. About 50 per cent,
liromic oxide is the general market standard.

Chromite is always found in association with serpentine. This
)ck has usually resulted from the alteration of rocks consisting
^ly of olivine, hornblende, and pyroxene ; the chromic oxide has
iparated from these minerals and from a chrome spinel (picotite,
[gO, FeO, AljOj, FcjOs, Qtjd^ often found with them. The chromite

thus scattered through the serpentine in irregular masses, which
Id often of considerable size. Although known as a mineral in many
q)entines, chromite has only been pi*oduced commercially in Queens-
ttd. New Zealand, New Caledonia, Asia Minor, Eussia, and the
nited States. Individual mines are seldom large on account of the
)ckety nature of the deposit.

Wood's mine, in Pennsylvania, was a notable exception, but it is
)w exhausted. Certain others in the Bare Hills north of Baltimore
ere also quite productive in their day. California is at present the
inoipal commercial source of chrome ore in the United States,
reat areas of serpentine occur on the flanks of the Sierras and in the
xwt Range. These afford chromite in Del Norte, San Luis Obispo,
Aoer, Shasta, and many other counties of the State, but the four
aned send Ae greater portion to market. A mine on Shotgun
reek, in Shasta County, produced in 1889 the exceptional yield of
KK) tons; the general yield is much less. In San Luis Obispo
)Tmty the mineral is gathered from the surface of the serpentine,
bere it has been left as '* float" by the weathering of the rock. It

also mined underground. At the skipping point an ore with
> per cent, chrome oxide brought d5«. per ton. No ore less than
^ per cent, chromic oxide is accepted, at present conditions, but ores
^er 50 per cent, bring higher prices. There is great uncertainty in
te mining on account of the irregular distribution of the ore, and
;cau8e it grows less rich as depth is attained. Traces of nickel
inerals frequently occur in connection with chrome ore. The mining
carried on in a desultory manner, the greater part of the ore being
carried by timers in dull times and sold to dealers in small lots,
ily one mine being exploited systematically. Much of the chrome
'6 existing in California assays less than 47*5 per cent. Cr^Oj, and
IS no commercial value at present, while many of the richer deposits
e in localities whence the cost of transport to market is prohibitory.



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4IO ECONOMIC MINING.

It is stated that so ore with less than 50 per oent. chromio oxide oal
be sent east in competition with ores from the Mediterranean.

Ohromite has been mined at Cnrpur, in the Shevaroy Hills* India
sinoe 1833. The principal roclos where the mines are sitiiated aii
homblendio, mioaoeoas, and talcose schists, penetrated by dykes <i
basalt and layers of serpentine, whioh last is intersected by a porfed
network of veins of magnesite. The ohromite occurs very irregnlarl;
in these veins in lenticular masses of various shapes and sizes ;
block was said to weigh a couple of tons.

There are many places where chrome ore is produced which
handicapped by transportation charges, and in this connection it
interesting to quote recent figures relating to cost of one month'
concentration in California,* where a 42 per cent, ore is omshed *
breakers and Huntington mills, and dreraed by Woodbury vannei
and settling tanks : —

£

900 tons (2240 lb.) ore at 22«. 990

10,000 bags at 4H 180

60 oords oak at 200 , 60

80 oords willow at 16«. 24

1 millman at 16f. a day 24

1 „ at 14s. „ 20

5 labourera at 6s. «, 45

MisoellaneouB expenses '.. .. 40

Product : 700 tons (2000 lb.) of 50 per cent, concentrates, oostiiij
36«. 6d. for material and fuel, and 39. 6(2. for labour, total 40t.
ton.

Placet, a French chemist, is said to have succeeded in producing
perfectly pure chromium by means of electrolysis, which will allow
the metal Doing placed on the market in sufiGlcient quantities to
all industrial requirements. The pure chromium differs £ram
metal produced in the ordinary way. It has a beautiftil white
that is unaffected by exposure to the air or by contact with adds,
it has the further quali^ of being exceedingly tough, and less fiosil
even than platinum. Until chromium was produced in its pure st
its scope as an alloy was strictly limited to the manufacture of ehroi
sibeel, as the presence of iron and carbon prevented its being alio)
with other metals. The pure chromium nas practically no limit
its application as an allov. A very small quantity will suffice to gi'
great toughness and malleability to almost any metal, which is
rendered capable of bearing a very high polislL The toug^
of copper, for instance, will be nearly doubled by an alloy of 5
cent, pure chromium; and the possibilities of aluminium are in
same way enormously increased, as any deeree of hardness and tougl
ness can be secured by a more or less addition of chromium as ai
alloy.

* < Mineral Industries,* a. 154.



s



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METALLIFEROUS MINERALS. 4"



COBALT.

^BALT ooonrs in many forms, and all cobalt minerals are associated
Qtimatelj with those of nickel, especially with the arseniate, the
rsenide, and the sulphide. The chief ores of cobalt are (1) the arse-
late, cobalt bloom, carrying 37^ per cent, cobalt oxide; (2) the
lack oxide, asbolane, or earthy cobalt, with 24 per cent, cobalt oxide
nd 76 per cent, manganese oxide ; (3) the arsenide, smaltine, or tin
rhite cobalt, giving 18 to 25 per cent, cobalt; and (4) the snlph-
rsenide, cobaltine, yielding 33 to 37 per cent, cobalt Mention may
Ibo be made of the cobaltiferous wad or " cobalt terra," carrying 3-5
er cent, cobalt oxide, raised in New Caledonia.

Near Bhyl, Flintshire, is the only productiYe British cobalt mine,
hirioas irregular cavities called ** swallows" here occur in the
lount&in limestone, and are filled up with a red ferruginous clay,
ontaining deposits of hsamatite, asbolane, and manganese oxide.
amples of clean ore vary from 20 to 37 per cent, cobalt sesquioxide,
to 10 per cent, nickel sesquioxide, and 23 to 40 per cent, manganese
inoxide ; but the mineral as mined does not afford over 1 per cent.
[>balt and ^ to 1 per cent, nickel, yet the search is profitable, and has
een carried on for some years, yielding 50-150 tons annually, worth
bout 62. a ton.

Norway possesses important cobalt deposits at Skutterud, where
be ore is chiefly cobaltine, associated with arsenical and iron pyrites,
1 bands of quartz-schist and mica-schist, which Prof. Le Neve Foster
efines as beds in altered sedimentary strata, while others describe
tie formation as gneissic. The bands are nearly vertical, with a
f.-S. strike, generally 12-18 ft. wide, and richest where the quartz
redominates. In 1882 this mine was producing at the rate of 8000
ms of ore per annum.

The Swedish mines at Tunaberg are similar. The country rock
I gneiss, and the vein carries bunches of cobaltine and copper pyrites,
ith a little galena and limestone. The ore yields 36 per cent, cobalt
rhen sorted and cleaned. Much more important are the Gladhammar
dnee, a network of veins carrying cobaltine and cobalt bloom asso-
iated with copper pyrites, salena, blende, stibnite, molybdenum, and
magnetic iron pyrites, in chloritic, homblendic and micaceous schists.

Other European sources of minor importance are located in France,
rermany, Austria, and Spain.

CobiJt is widely distributed in Nova Scotia, and is frequently
3nnd in wad (bog manganese), mispickel, copper, and magnetic iron
yrites, but has not been mined commercially.

In the United States it is sometimes associated with the ores of
ickel, sometimes with Uiose of copper. At Silver Islet, the mineral
^acfarlanite, found with the silver ores, yields a small percentage of



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412 ECONOMIC MINING.

cobalt. In Missouri, at Mine la Motte and at the Saint Joe lead mineB,
oobalt-bearing minerals are found associated with the galena and with
nickel in the form of millerite ; the cobalt as siegenite, in brilliant
octahedral crystals. At the Gap mine, in Lancaster County, Penn-
Bvlyania, cobalt is found replacing part of the iron in the pyrrhotite;
the percentage is exceedingly small, and the ore cotdd not be worked
for cobalt alone. Smaltite occurs in Gunnison County, Colorado, &t
the mines of the Sterling Mining Company, analysis showing 11*59
per cent, cobalt. Some of the copper ores of western Nevada are also
reported to contain cobalt ; and it is found in traces in many of tbe
iron ores of Pennsylvania and Virginia. The speiss formed in smelt-
ing certain Utah lead ores also contains appreciable quantities of
cobalt. But no American ore is worked for cobalt alone, the small
amount produced being obtained as a by-product in the reduction of
the nickel ores of the Gap mine. These ores are smelted to a mattd
at the mine, and further treated at the Camden Nickel Works ; the
small amount of cobalt obtained is worked up into oxide. At Mineh
Motte, the cobalt is obtained in a matte produced in smelting the lead
ores, liie matte being shipped to England and (Jermany for reductioiL

In New Caledonia are found quantities of cobaltiferous manganese
ore. Both the cobalt and the manganese occur as hydrated oxides in
fragments scattered through a red clay filling pockets in serpentine,
the percentage of cobalt in the cleaned nodules oeing 1\ to 3.

Several methods of treatment are adopted for cobalt ores.

At the Gladhammar mines the ore is hand-picked and then redaced
to apple-size in a Blake crusher. After mixing it with slack ooal and
calcining slowly and at a low temperature for removal of arsenic and
sulphur, it is ground very fine in a mortar mill, mixed with alkali,
and again roasted at a gradually increasing temperature. What
roasted and cooled, it is leached with hot water in a series of tanks.
In the uppermost group, the contained iron is precipitated ; in the
next, the copper is thrown down by adding scrap iron; itod fimally,
the cobalt is removed by powerful filter presses.

Dr. W. Stahl adopts a process which enables him to work up veij
low grade materials. His method of treatment consists in roasting'
the powdered ore with salt and pyrites, by which means the cobalt,
also copper and manganese if present, are converted into chlorides,
whilst the iron is only chlorinated to a very small extent. After thaj
roasting, the ore is extracted with water without any difficulty, and
the liquors obtained are treated first with sulphuretted hydrogen, to
remove copper, and then from the filtrate the cobalt is precipitated by
means of sodium sulphide. The small quantity of manganese and
iron thrown down with the cobalt is dissolved from the mixed
sulphides by means of a mixture of dilute sulphuric and hydrochlorie
acids. The following equations represent the changes 'which tab
place in the roasting process : —

4NaCl -h 2SO3 + O2 -h 2HaO = 2^9.^0^ + 4HC1

2C03O4 + 12HC1 = eCoCTa + GH^O -f O^

C03O4 -t- 6NaCl-f 3SO2 + 02 = 8C0CI2 + 3 NaaSO*

2C03O4 + 12NaCl -f 6SO3 = 6Na2S04 + OCoaj + O^



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J



METALLIFEROUS MINERALS. 413

At the works of the Maletra Chemical Company, at Petit Qu^rilly,
tear Boaen, Prance, a new process for the treatment of the cobaltio
oaDganeee ore from New Csdedonia has been successfully introduced
»y Herrenschmidt The composition of the ore, subject to variation in
ertain of the less valuable constituents, averages : manganese per-
xide, 18 per cent. ; cobalt protoxide, 3 per cent. ; nickel protoxide,
•25 per cent; iron peroxide, 30 per cent; alumina, 6 per cent;
Ime and magnesia, 2 percent ; silica, 8 per cent ; loss in calcination,
2*75 per cent The operations are entirely performed by the wet
raj, and the reagents used are to a large extent waste products,
risbg in the treatment of the ore. The order of operation is as
)llows : —

The ore, which is comparatively soft, is ground to a fine powder
nder edge-rollers, and is tnrown into large pans containing a strong
)liition of ferrous sulphate, which is boiled by blowing steam through
* This dissolves manganese, cobalt, and nickel as sulphates, while
le whole of the iron, including that in the ore, goes down as basic
Trie sulphate together with the silica and alumina. The action
mtinnes for some hours, fresh ore being added as required, until
le liquor when tested with permanganate is found to be free from
fisolved iron. The contents of the pan are then blown over to a
ttling tank, where the clear liquor is separated from the ferruginous
•ecipitate. The latter is then filtered off, dried, and calcined, giving
powder which is sold as colcothar.

The ferrous sulphate employed in the above operation is prepared
\ the spot from scrap iron and nitre cake, or the residue (consisting

sodium sulphate and sulphuric acid) obtained in the manufacture

nitric acid. This gives, in addition to the green vitriol, sodium
Ipbate, which salts are separated by crystallising ; the latter may
so be utilised at another stage of the process.

The liquors oontaining cobalt, nickel, and manganese sulphates
? transferred to stills made of slabs of the lava from Volvic, in
ivergiie, and sodium sulphide is added. This precipitates cobalt
d nickel as sulphides, with only a small proportion of manganese,
3 balk of the latter metal remaining in solution by reason of the
dity of the liquor. The mixed sulphides when separated are
ated with a solution of ferric chloride, which dissolves the man-
oeee, giving a mixture of sulphide of nickel and cobalt nearly free
m foreign matters. The manganese in the still liquors is cou-
rted into chloride by calcium chloride, and precipitated by lime to
Twed in the Weldon process.

The sodium sulphide used in this operation is obtained by decom-
dng the sodium sulphate remaining from the ferrous sulphate with
lali waste in a dosed vessel under pressure, the final residue of
& operation being calcium sulphate.

The precipitate of mixed sulphides, after the removal of the man-
leee, is subjected to a very careful roasting in a reverberatory
nace, which, if the operation is successful, results in its complete
nsformation into sulpnates of cobalt and nickel soluble in water.

The product of the last operation, when dissolved in boiling
ter, is treated with calcium chloride to convert the sulphates into



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414 ECONOMIC MINING.

chlorides, after which the liquor is divided. In one portion fa) the
metals are precipitated as hydrated protoxides with lime, ana sftei
washing to remove the calcium salts, the precipitate is difiPdsed throogb
water and subjected to the joint action of a current of chlorme and of
air under pressure, with the result of forming peroxides of nickd tnd
cobalt. A second portion (&) of the original protochloride is th«
added, and the whole is energetically mixed by blowing it n]^ witk
steam. This has the result of reducing the nickel peroxide m the
a precipitate, which redissolves as protocmloride with tiie peioxidatuio
and precipitation of an equivalent proportion of cobalt from b, bo thit
only nickel remains in solution, while the cobalt is entirely sepantei
The proportion of & is so chosen that the whole of the precipitated
nickel is not dissolved, in order to ensure that the liquors contaia
no cobalt. Further additions of the solution are made in graduated
quantities until the oobalt precipitate is oompletely free from nickel
when it is filtered, dried, and calcined for sale. The various liquon
containing nickel are finally collected and treated with lime, ^
nickel protoxide precipitated is separated by a filter-press, and afte
drying and calcination is readv for reduction.

The chlorine required in the operation is obtained from a poitioi
of the ore which is used in the stills with hydrochloric acid, in tii
same way as an ordinary manganese ore. Cobalt, nickel, and iro(
paslB into solution at the same time ; the first two metals are re
covered, while the ferric chloride is used in the treatment of ib
mixed sulphides.

The works treat about 150 tons of ore a month and yield aboa
5 tons of cobalt oxide. The ore being very bulky, it hais been pn
posed, in order to save freight, to convert it into regulus at the misa
Experiments in this' direction have been made at the same work
running down the ore with silica and iron pyrites in a water-jacb
blast furnace, with the result of producing a regulus with 8 per oe&
cobalt, in addition to iron and sulphur, and slags containing all ti
manganese and only * 02 per cent, oobalt. This concentrated mat^
it is proposed to treat in the same way, commencing, however, wil
the calcination of the mixed sulphide.

The world's production of oobalt is estimated at about ^to
yearly. New Caledonia alone exporting annually 2600-4000 tons
3-6 per cent. ore. It is almost exclusively used in the form of Hai
oxide as a pigment, and is worth 9«. to 12«. a lb.

See also Hgments, p. 309.



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METALLIFEROUS MINERALS.



415



COPPEB.



IfoT only is copper fotind in the Bative state almost pure (a little
lilver being generally the most important impnrity), but its natural
oombinations are almost endless. Not less than a hundred mineral
ipedes may be regarded as copper ores from the practical miner's
point of yiew, L e. possessing economic value, and there are probably
\& many more which are not yet utilised. As might be expected, the
in^ of chemical associations is equally wide, embracbg sulphides,
ffitmionides, arsenides, oxides, chlorides, bromides, iodides, carbonates,
mlphates, phosphates, silicates, arseniates, simple and compound,
lydiated and annydrous, in almost every degree of variety.

In point of richness in copper the most important may be tabu-
atedthus: —



Copper, natlTe

inprite, CiijO

attksodte, Cu^

[eltconite, OnO

^)nixte« CuaFeSt .. ..
[•lachite, 20aO,Ga,H,0
sorifte, SCaO,CO,AO ..
kttidte, Ca«AB8« .. ..
Hishedrite, 40ii»,,8b,8,
hnraocdla, CoO,8iO,4HaO
bflJoopyrite, CnFeS,



Cu.



100
88
79
79
61
57
55
48
86
86
84



/



/•



/



Fe.



11

i

30



19



Sb.



26



20
25



82

26

84



But these rich minerals are by no means the most important as
igards the commercial supplies of the metal ; in fact, in that light
ley may almost be disregarded so far as affoiding any considerable
roportion of the total yearly output, thongb, of course, deposits of
lese rich ores are profitable. The duUc of the world's consumption of
)pper is famished by ores of the lowest grade, ranging from little more
lan 1 to perhaps 5 ^r cent., though rarely more &an 3 to 3^ per -cent,
or the most part, if not entirely, they may be considered as rocks
' sedimentary origin impr^nated to a sli^t degree with particles

native copper or copper ores. Thus the ores ^yritous, arsenical,
id silicious) of Devon and Cornwall are worked for li to 2 per cent,
pper ; those of Cheshire (oxidised copper disseminated in sandstone)
r less than 1^ per cent; those of Mansfeid, Germany (pyritous
ipregnations in bituminous schists), for little over 2^ per cent.;
ose of Bio Tinto, Spain (pyrites), for 2^ to 3^ per cent. ; those of
aidenpeo, Servia (various), for 2 to 3 per cent. ; and, overwhelmingly
6 most abundant producers, those of the Lake Superior region



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4i6 ECONOMIC MINING.

(native metal scattered through conglomerates and am jgdaloids), k
as little as ' 65 per cent.

Formerly the world's supply of copper was drawn froni rich ora
containing up to 40 per cent, metal as mined, and further exploratkn
may again reveal in the future similar deposits to replace thoee no^
exhausted ; but at present and in the immediate future reliance miE
be placed on the enormous low-grade ore bodies now being workei
especially in North America.

As to the geological conditions under which the varions deposii
occur, and the manner in which they are worked, it will perhaps \
most convenient to adopt a geographical arrangement, in alphabet!
order, omitting unimportant cases.

Bolivia. — The well-known mines of Corocoro, worked since tiB
immemorial, are situated in red sandstones of Permian or Truss
age. The mode of occurrence is shown in the sketch section. Fig. 110
The copper is found as metallic grains or larger masses disseminate
irregularly in the sandstone bedis, those which are known and workc



Fig. 110. — GoFPEB Deposits, Ck)BoooBO.



being shown as solid black lines (as : a, Yeta del Buen Pastor ; hy Ye
de Bejo ; c, Yeta Umacoia), while broken lines represent snppoR
additional veins. In the centre, a great fault d divides the wb(
metalliferous district into two parts, and has produced both vc
and horizontal disturbance. The fine grained sandstone of the
Pastor is impregnated with grains of metallic copper and mi
silver, the latter predominating in value. In the Kejo, the oo]
is associated with arsenic and sulphur, much of it being as arsen^
On the east side of the line of fault much thinner metallifextms be4
(^^ramos^*) are found, tolerably constant in strike, but increa8in|
rapidly in dip as the fault is approached. I

The ore obtained from the ramos is very different and in a mud
finer state of aggregation than that from the vetas ; this pxobablj
arises from the latter being situated in the midst of much coaxBeor an
more porous beds of grit and conglomerates of small pebbles. In boti



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 46 of 76)