Charles George Warnford Lock.

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

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32 per cent, on the average, which may be regarded as a very good
lult, as the mineral contains 83*36 per cent, carbonic acid.

The ore as broken in the mine contains much marble or barren
ktter; consequently cobbing and hand* picking, both before and
«r calcination, are resorted to. The picking ore before calcination
insufficiently done, owing to lack of water and mechanical appli-
3es. Most of the ore of *' walnut " size is not assorted at all, but
30 direct to the second class kiln. All large stuff is tipped on a
.tform and washed by hand pump or syringe. When the ore is of
»d quality, the sterile rock and second (uass ore are picked out, the
aainder going direct to the first class kilns. When of lower grade,
• barren rock and first class ore are picked out by hand, the rest
Dg seoond dass. All mineral having a preponderanoe of " smalls "
tipped on an iron grizzly (having spaces of 2 in. between bars), and
omall stuff which passes between the bars is then classified by a
tnmel (holes { in. square), worked by hand, from which tbe " coarse "
m direct to the second class kilns without assorting, and the '* fine "
>Aded direct into waggons and sold as '' raw product." The larger
see which fail to pass through the grizzly are hand-sorted into
bB, seconds, and waste. After calcination, the ore from the first
10 kilns (except the larger pieces, which are picked out and loaded
» waggons direct as firsts; is tipped on to inclined fioors and
iflrted — i. e. all that is waste, or doubts, or insufficiently calcined
i^ed out. The smaller stuff (maximum size, hazel nut) is put to
<bA class, the balance going to first class. The ore from the second
s kilns, after being watered in order to slake the lime that it cod-
m^ is dumped on to another part of the inclined floors, and the
0d lime and fines are taken out of it by a trommeL The ore as
cbd fi>T market purposes is : *' 1st class calcined," 50-54 per cent.
•Hie manganese; ''2nd class calcined," 43 - 45 per cent.; ''raw
taet," 33-36 per cent. The silica is 6-9 per cent. ; phosphorus,
L— ^MS per cent.

"WmmMTce, — The manganese ore trade has undergone great changes

I last few years. Until recently, its chief application was in the

"■ ire of chlorine, when the value depended • on (a) the avail-

ide ; (6) the absence of carbonates (of calcium, &c.), which

letter from F. Glaudet, Assayer to the Bank of England, Oct 5, 1891.

2 o

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would constiine hydrocUoric acid, and would evolve carbonic add-
which latter has a most deleterious effect in the manufacture of
bleaching powder; (c) the physical condition, hard ores reqniiing
excess of acid and steam for their solution. Now the consampdon i
manganese in the chemical trade is quite paltry compared with tk
quantity absorbed in making manganese steel. In this case, the
whole manganese contents are available, and the impurities to k
avoided are silica (English smelters demand under 7 per cent), aoi
phosphorus (not exceeding \ per cent.). In the United States pnfi«
are based on ores not containing more than 8 per cent, sitica and 1
per cent, phosphorus, and deductions are made of 7dL per ton for ead
unit of silica above 8 per cent., and* of ^ per unit of manganese far
each y\y per cent, in excess of • 1 per cent. Ores are bought as low as
12-16 per cent, manganese, at say 7jd. per unit ; at each 4 per cent
advance in manganese the price per unit rises 1(2., up to 40 per cent.:
above that it advances Id. for each 2 per cent, additional, up to ^
maximum of 49 per cent.

Covering the last 5 or 6 years, statistics show the productian of
manganese ores to be exceedingly irregular, and approximately u
follows : —

Tons Yearly.

Caucasufl 50,000-135,000

ChUi 20,000- 50,000

United States 4,000-30,000

France 500- 25.000

Cuba 1,500- 16,000

Japan 0- 15,000

Greece 400- 15,000

Great Britain 800-13,000

Spain 3,000- 10,000

Australia 800- 9,000

Turkey 200- 8,000

Portugal 2,000- 6,000

Sweden 1,000- 5,000

Bosnia 0- 4,000

India 0- 2,500

Italy 0- 1,600

New Zealand 0- 1,100

New Brunswick 0- 1,100

Holland 0- 1,100

Noya Scotia 0-200

Total 150,000-250,000

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Mrrcurt (qTUcksilver) is found to a limited extent i]
bat most commonly iu association with sulphur. '
phide, cinnabar, HgS, contains about 86 per cent
sulphur. There is also a black sulphide, called
found in one locality in California ; and, in Califom
snlphoselenide named guadalcazarite (81^ per cent
phor, 6^ selenium) is sometimes encountered. Ai
frequent companion, but not in chemical union. Cic
the only ore of industrial importance. It occurs as
porous rocks (especially sandstones) of various
owing its origin to the influence of basaltic or andoE

Mercury is not a widely diffused metal, and itc
dnction is somewhat restricted. Approximately, tl
consumption is supplied as follows, the figures refe
76J lb. each :— Spain, 48,000-52,000 ; Austria, 16,0C
12,000 ; United States, 23,000-33,000 ; total, 95,00(
additional quantities are obtained from Servia, Rus
Borneo, and Mexico. 'Peru was at one time an impo]
but has long ceased to famish any.

Spain's yearly product is almost entirely deriy<
brated Almaden mmes, situated on the northern si
Morena. The metal occurs as the common native su
impregnating sandstone beds of Silurian and Dei
principal deposits dip nearly vertical and have b
length of 600-700 ft and a width of 40 ft. From n
of mineral raised in 1892, the yield was 8 per ceni
ore of the El Porvenir mines at Mieres only affords
its yearly output of 5000-6000 tons. The workings
are now at a depth of over 1000 ft.

At the Imperial mines of Idiia, Camiola, Ausi
occurs in rocks of Triassic age both in veins and as
the beds of shale, conglomerate, and dolomitic bre
cover an area of over 100 acres. Much of the oi
before being crushed in breakers and stamps ready f

The Bussian mines near Bakhmont, Ekaterinosla
corial impr^nations of permeable sandstones. Tb
20,000 pouds (of 36 lb. each) annually. Considerab
reported from Daghestan, Caucasia.

American mercury deposits are found in woi
almost solely in the coast range of California, i
to have followed great basaltic and andesitic er
Pliocene age. At New Almaden, cinnabar occurs

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crystallised and cbaloedonio quartz, calcite, dolomite, and magnedtej

forming a " stockwork ** in shattered metamorphio rocks (sandstone,!

serpentine, psendo-diabase, and psendo-diorite). The two maiii

fissures form a sort of V, with a wedge of country rock betwe^; and

the ore is found in both fissures and wedge, associated with mud^

attrition clay and bitumen. A rhyolite dyke runs parallel to M

fissures and is thought by Becker * to be responsible for the depoatal

At New Idria, the ore is deposited in shattered

metamorphic rocks of Neooomian (Lowe<

Cretaceous) age, and in overlying Chico beds^

and is accompanied by bitumen. Other nuDe^

have been opened in regions of metamorphic

and unaltered sedimentary rocks pierced bj

basalt and andesite. Fig. 160 shows a aectioi^

of the Great Western mine: a, serpentise;

6, band of black opaline mineral called by tlu

miners " quicksilver rook " ; c, slightly altered

Neooomian sandstone ; (2, ore body. AtSteun*

boat Springs, Nevada, cinnabar aooompanid

by many other minerals is still in actual pn>

cess of formation. Granite is the principal

rock, overlaid by metamorphic Jura-Triai

deposits, with much andesite and basalt

Becker attributes the ore to the granital

whence it has come up in solution withsodind

Fig. 160. sulphide.

Mbbcuby Dbpobit, jq^^^ Almaden is a striking example ol

California. ^^ irregularity of the deposits. It has ofted

occurred in the history of the mine that ther«

was no ore, or scarcely any, in sight, and looked as though the mii^

must of necessity have been shut down ; it has only been by mosi

careful and continuous prospecting that it was possible to keepnptb^

production. Very frequently large bodies of ore will almost eon^

pletely run out, and there will l« visible in the face of the worq

only a slight colouration of vein matter, but by following out thii

little string of ore very carefully it may lead to a large deposit At

New Idria the mine timbers decay in an unusually short time, vA

two men are kept constantly employed in replacing the old ones b^

new. This rapid decay is more marked during sultry weather, wh«^

the draft in the tunnel is almost nil, and the atmosphere oppressiTej

Timbers immersed in water, or kept constantly wet, do not seem tq

be so affected. Dry, seasoned wood lasts longest. Timbers, a^

having stood in place for only 36 hours, accumulate a mildew 1 ii^


Statistics of Americanf mercury production show that the yi^l^
has decreased from 36 per cent, in 1850, to 20 in 1860, 10 in 1866^
6 in 1870, 3 in 1880, and 2 in 1890. The 11 mines working in 1889
obtained from *l^. to 2 '3 per cent, mercury per ton roasted, th^
average being only 1*088 per cent, on 93,000 tons or© roasted vsA

♦ G. P. Becker, "Quicksilver Deposits of the Pacific Slope," Monogiaph XHl
U.S. Geol. Sur. f J. B. Randol, Census Bulletin No. 10.

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26,600 flasks merotuy produced. The average cost of mining per ton
roasted has grown from about 82«. in 1880 to nearly 60«. in 1890 ;
v^hile the total cost per ton roasted has fluctuated between 50^. anc^
72«. ; and the cost per flask (76^ lb.) has risen from 48«. in 1880 to
5i. in 1889-91, and 9/. 10». in 1892.

Mexico possesses considerable resources in mercury, not yet
leveloped. Near Arichuivo occur five seams of cinnabar in poiphyry.
The Guadaloazar deposits occur mainly as layers in limestone, but
rregular networks of vein, or " stockworks," are also found. Much
)f the ore is said to yield 11-12 per cent. The chief ore is cinnabar,
)fteo hepatic, and sometimes accompanied by the seleno-sulphide
gaadalcazarite). Calcspar and fluorspar are the gangue minerals,
in the state of Guerro, cinnabar deposits are worked on a small scale
it Huitzuco, about 60 miles north of Tixtla. The deposits here are
)ocket6 of various dimensions and layers ; veins, however, are known
exist in disturbed metamorphic slates and limestones. The deposit
(f Teposcolula is a vein between metamorphosed limestone and slates,
rhe ore, which is also argentiferous, is livingstonite, a sulphide of
utimony containing mercury.

In Queensland and New South Wales, alluvial deposits of cinnabar
•ecur, those at Kilkivan* in the former colony being profitably
forked. The " lodes " which have furnished these alluvial " leads "
xist variously in mica and chlorite schists ; in beds of sandstone,
arbonaceous shale and conglomerate ; in coarse grained granite, and
lot far from the junction of the granite and an altered poi-phyritic
ock. Sometimes there is a regular " stockwork " of veins, the richest
f which run about N.W.-S.E. Some of the veins have little or no
latrix, but consist of small bunches of gre in the granite. Others
ontain a matrix of quartz and calcite. In one shaft, 30 ft. deep,
\ a distinct lode 2^^ ft. wide, consisting of a granitic material with
alcareous clay veins running through it. Near the surface were very
Lch patches of high-grade ore — that is to say, ore containing about
per cent- mercury— in bunches up to 6-7 in. wide. The ore is
ighly crystallised. The mercurial wash-dirt before alluded to consists
f a granite drift, with large pebbles of the altered porphyritic rock ;
t contains small waterwom pieces of cinnabar throughout it, and
coasional pieces of over 1 lb. in weight. The wash-dirt is about
ft. thick. Drives have been put in across the drift for a distance
f 25 ft, and cinnabar has been obtained throughout. While the dirt
dll not pay to carry away for treatment, it can be profitably sluiced.
Q 1891, 1 J tons of mercury was obtained from 28 tons veinstone
lined in the coarse-grained granite, or a yield of 5 * 3 per cent.

TrecAiMfnX, — The separation of the mercury from the associated
ilphnr is effected by roasting in kilns and condensing the mercurial
imee, effective condensation and prevention of loss in escaping
apours being the most troublesome operations. Furnaces of many
nrma and designs have at different times been introduced, and the
»oet recent model used at Almaden is shown in Fig. 161. Two are
nployed, one for rock up to 2 cc., and the other for mineral not
cceeding 10 cc. The hearth is an inclined plane constructed of fire-
• W. H. Rands, Queeusland Geol. Reports, 1886, 1892.

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brick, 7^ ft. wide by about 24 ft. long, the grade of which is equal to
or a little steeper than the natural elope of the fines. At every 13 in.
this floor has a rise of 1 in. It is divided by partitions, 10 in. higK
into 12 channels 4 in. wide, in which the ore runs ; these vertical
partitions are of firebrick. Transversely in the channels, and sup-
ported on their partitions, are placed some bricks called toeot
("stoppers") which are above the floor of the hearth about 1^ in.,
this being the thickness of the ore in each channel. Arranged in
the same way are others situated immediately at the bottom of the
rises and at the same distance from the hearth as the " stoppers,**
which serve to break up the fine ore on them so as not to present
invariably the same surface to the action of the heat. On the lower
part of the hearth is another inclined plane a at right angles to it,
from which, at the point where it commences, it is situated as many
centimetres as the thickness of the covering of ore ; this is also divid^
into channels, but is smooth. The ore, already calcined on the fint

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ore remaiiiB subjected to the action of the heat about 4 hourd ; for the
charge beiug made at 2 . 30 p.m., it passes in front of the bridge at
6.40, and leaves the second plane at 7.45 p.m., the capacity of the
channel admitting about 950 lb. The fines, now calcined, are ejected
by a hopper to a passage, whence they are taken out in cars. They
do not now contain more than '02- '04 per cent, mercury.

The condenser is formed by two series of chambers, the first of
which communicates with the furnace by a throat 0, in the shape of
a trunoated pyramid of iron plate protected with brick. The 6 cham-
bers d which constitute this first series are of brick, with thin walls,
and are divided by partitions which have openings arranged for the
passage of the fumes, so as to run in double zigzag. The bottom of
each division is farmed of two inclined planes, whose intersection has
a small incline towards a channel common to all the chambers, in
which is collected the mercury condensed in them. The bottoms are
of iron plate in the 3 chambers nearest to the furnace, and of slate in
thoae farthest away, this arrangement being in consequence of the
iron being attacked by the mercury in the latter. The last part of
the condenser is formed of wooden chambers A with glass, divided into
4 parts by vertical partitions. These chambers, like the former, are
arranged so that the air can circulate below and around the sides, and
allow of observation in case of any filtration of mercury through the
bottoms. The temperature of the fumes observed at different points
is shown to be, after travelling 850 ft. in tJie brick chambers, and
those of "wood and glass, the lowest possible in relation to the tempera-
ture of the surrounding air ; consequently the condensation is effected
under the best possible conditions, so that almost all the mercury is
deposited from the fumes in the chambers. The cost of calcination
is about 1«. a flask (Spanish) or 1^. a lb., half being for labour and
half for fueL

The New Idria furnaces are fashioned after those at Idria in
Austria, being square, about 30 ft. high, 10 ft. wide, and 12 ft. long,
fed at the top by a drop-hopper at the rate of 1 ton an hour, and
holding 24 tons when fulL They employ 2 men per shift of 12 hoiirs
on ea<£ furnace, and consume 1 cord of wood (manzanita and oak,
costing 26«. delivered) every 24 hours.

At the Oipsy works in Merced County, the old-fashioned retort
system is in vogue, treating 1200 lb. per 24 hours of 6 per cent,
dressed ore.

A great many new forms of furnace have been introduced at
various times in Oalifomia, the main features in which have been
arrangements to secure automatic working and the substitution of
fiins or blowers for tall chimneys. The operation demanding most
attention, however, is condensation, a loss of 10-15 per cent, taking
place even in well-equipped works through inefficient condensation of
the niercurial vapours. It has been laid down as an axiom that the
ratio of condenser volume to the furnace volume shall be as 24 to 1,
but it is difficult to see the value of such a formula, as much must
depend on the heat at which the vapours leave the furnace, the speed
at which they flow, and the opportunities provided for cooling them.
By controUing the draft with a fan instead of a chimney it is possible

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and obviously adyisable to prolong the condensers as long as they
oatoh anything.

Amonff the most sucoessfal American furnaces is that of B. J.
Enox, a uiaft furnace with fireplace at the side, shown in Fig. 162.
It is 39 ft. high, rectangular in shape, with the fireplace 17 J ft. from
the bottom. At top it is 2 ft. square, but widens to 7 ft at a deptk
of 4 ft, and at the fireplace the section is 7 ft. by 2 ft. Towards the
drawhole, the area is contracted till it is only 2 ft The fireplace b
fed with hot air. The walls are built 6 ft. thick, and tied. The
cubic contents of the furnace equals 75 tons of ore, of which 1 ton per
hour is drawn out, so that each ton is in the furnace 3 days, dnzioj^
part of which time it is cooling ready for being drawn. Feeding ii
done by an automatic car holding a ton, which removes and replaoef
the lid on the charging hole c. The flue d for exit of gases is of oast
iron, 18 in. diam., and 16 ft. high where it enters the oondensen e.
The calcined ore is drawn into cars that run on the rails/, andtk
mercury flows into the receptacles A. Two furnaces are usuadly Inilt

Fig. 162.— Enox Fubnacb.

together, as shown. The draft is produced by Boot's blowers. TIm

labour required is as follows: — A single ftirnaoe treating 24 tons a

day requires 6 men ; a double ftimace treating 48 tons needsjB nkeo;

a quadruple furnace treating 100 tons em]

densers are connected together by iron pii

floors are inclined at an angle of 15-20^ T

long, 2^ ft. wide, 5 ft. high at one end and

wooden frames on a cement floor ; they ar

transportation, &c. The top-piece is 36 in.

projection on the piece below the top ; its si

mg water. A manhole gives access for o

The acid liquors which condense flow to the

each set of condensers clamped wooden bo

30 in. square conduct the remaining vapoun

and 4 ft. square filled with stones over whi

solid soot collected from the condensers and

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)f the mercury recovered, and is treated with lime in retorts 9 ft
oDg, 30 in* wide, and 18 in. high. The total cost of calcining ore in
iie Knox fomace at the Redington mine, on a 2 years' run with a
lonble fdmaoe, including repairs, was about d«. 9(2. a ton. The cost
>f the double furnace and condensers was about 12,000Z. The cast-
ron condensers were afterwards replaced by wooden (1 J in. plonk)
itmctures of the same pattern but double the size, at much less cost,
Jid were foand equally efficient.

At the Abbott mine in Lake County the furnaces used are a Ejiox-
kbome of 6 tons capacity for coarse ore and a Hughes of similar
ispaoity for fines. The dimensions of the Enox-Osbome furnace are
approximately 14 by 20 by 31 ft. The firedoors, one of which is
itaated at each end, are about 15 ft. below the charging floor, and
he discharge for the roasted ore is about 15 ft below i£e firing doors.
Phis furnace consumes only \ cord of wood in 24 hours, the heat
teing maintained to a great extent by the roasting ore. The vapours
«88 into an iron-lined, brick condensing chaml^r, wherein a large
mount of soot accumulates, and thence into 6 iron and 2 wooden con-
tensers, cooled by water. Most of the mercury is caught in the first
' condensers. The cost of a 12-ton Enox-Osbome furnace is about
000/. In the Hughes furnace the fine ore descends an incline of
bout 45^. The flame from a fireplace at each end passes over the
orface of the ore. The roasted ore is discharged from a shute in the
ide between the fire-doors. This furnace consumes about 1} cords of
rood a day, and is not considered satisfactory. The vapour passes
nto an iron-lined dust chamber, where the soot principally collects,
nd thence into 4 iron and 2 wooden condensers, cooled by water. A
toot suction blower, running slowly, draws the vapours of both
omaoes from the condensers into a 50-ft wooden flue, uie escape pipe
f which extends about 60 yd. downhill at an an^e of about 60^.
lie sooty some 60 per cent of which is finely divided quicksilver, is
forked with caustic lime, which causes the tiny globules to collect
*he residue is returned to the furnace.

At the New Almaden mines, the ore is brought from the mines to
be reduction works in cars run by gravity pulleys, and is dumped
ito shutes, where screens set at an ancle of 45° separate it into three
Lzes — *• granza," coarse ore ; " granzita, medium-sized ; and ** tierras,**
ne ore* The last grade was formerly made into bricks, and treated
I ftn intermittent furnace togetiier witii coarse ore. A great
3onomy is now effected by wor&g the fine ore alone, in the tierras
omaoes. Such ore as needs drying is dried either by spreading out
od exposing to the sun, or in an upright chamber, heated by the
aponrs and hot air passing from the tierras furnace. The dry ore is
isoharged at the bottom of the drying chamber, and is elevated to
le oharffing floor by means of a water hoist, a tank of water being
lade to balance a car full of ore.

The dry fine ore is run by trucks from the elevator to the top of
le tierras furnace, where it is dumped into a hopper, the throat of
hioh closes with a sUde-vidve, whicm sustains the charge of the ore
[>pper until needed, and shuts off any vapours which might otherwise

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escape from the heated ore below. When this slide- valye is opened, a
charge of ore drops into the throat of the furnace, which, when filled
with ore, naturally assists in keeping down the vapours. From ben
the ore falls upon a series of tiles, set one above another in the brick-
work of the furnace, each one inclined toward the one below at ^
angle of about 45*^. Each hopper feeds two sets of such tiles, tnd
each furnace is partitioned ofif into 3 compartments. The firing fio(?
is about 12 ft below the charging floor. Here a fireplace runs acma
one side of the furnace, being fed at both ends with 4-ft. sticks of oaL
pine, or redwood. The flame reverberates on the arched roof of tk
fireplace, and passes through holes in a wall, which divides the fiI^
place from the main body of the furnace. Crosbing the or&-kd££
tiles to the opposite side, the flame enters a chamber, the arched rcKf
of which again causes it to reverberate across the furnace. TLis
reverberating process is repeated a third time. Each reverberatkn
heats a separate tier of ore-laden tiles. The vaporous product of tlic
furnace passes by means of an air pipe through the hollow walls of
the drier into the condenser. Each double set of inclined tiles ter-
minates in ** boshes," in which the roasted ore collects, to be finallr
discharged from 3 openings, regulated by a shaking table at cie
bottom of the furnace.

The granzita resembles the tierras furnace, except that the t£ei
are a little farther apart, and there is no shaking-table at the base.
The cool roasted ore is raked out from the places of discbarge at tbe
bottom of the furnace.

The hopper of the granza furnace, which protrudes aboTe tb
charging floor, is covered with a lid closing with a water-tight jcant,
the rim of this lid being submerged in a circular trough surroundiBf
the hopper, to prevent the escape of vapours. TlJough this bd
passes a rod connected with a plug, so fitted to the bottom of tbi
hopper that by depressing the rod the plug is lowered, and tbe os-

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 64 of 76)