Charles George Warnford Lock.

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

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quartz. In rich specimens, fluid or gaseous inclusions of what
probably carbonic acid are abundant.! Some quartz shows evidencl
of dynamic disturbances. The walls of the veins are themselv^
impregnated with the precious metal and attendant sulphides, Tlj
rich portions of the veins occur in shutes to a large degree. Tlj
great Mother Lode extends 112 miles in a general N.W. direetio^
it is not strictly continuous, nor is it one single lode, but rather
succession of related ones, which branch, pinch out, run off in strbgei^
and are thus complex in their general grouping. It is regarded u\
great series of veins along a fissured strip. The veins are often 1^
in strong relief by the erosion of the wall rock, and thus are call^
ledges or reefs. The gold in the pyrite in most cases is native meti
mechanically mixed, and not an isomorphous sulphide. The veil
are younger than any of the igneous dykes with them. They ma
have been filled, as thought by Whitney, during the metamorphia
of the rocks attendant upon their upheaval in post-^Jurassio tin
Certain it is that a very extensive circulation of silicious solution
was in progress.

• J. F. Kemp, ' Ore Deposits.' t W. M. Courtis.

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In tbe Stunmit district of Colorado are a number of rich mines
rhere the gold occurs native in quartz on the contact between a
hyolite and trachyte breccia and andesite. The deposits are probably
ue* to a silicification of the rhyolite along those lines; oxidation
Bd impoYerishment of the npper parts led to bonanzas below.

In the Black Hills, South Dakota, gold occurs f under diverse
onditions : — (a) in Quaternary and Eecent placers, from the degra-
lation of h and c ; (5) in ancient gravels, cemented, obviously due to
oarine action on the exposed edges of the veius c, and only found in
oxtaposition to tbem ; (c) in bedded veins of pyritous quartz in the
ilted (almost vertical) Archsean schists, formmg an enormous ore
lody several miles long and often 50-200 ft. thick, locally known as
he "free-milling belt"; (d) in silicious impregnations which have
eplaced the calcareous cement of the Potsdam sandstones over an
jea of about 30-40 square miles, sometimes still pyritous, sometimes
oddised, always associated with " porphyry " dykes and sheets, and
ODstitntin^ the " refractory belt " ; (e) as an ingredient of argen-
iferoos galena, limonite, and iron pyrites, in beds of Carboniferous
imestone ; (/) in the porphyry itself.

The free-milling ores are very low grade, seldom exceeding 10 dwt,
the ton, but, being in gigantic bodies, admit of mining and milling
n a grand scale, and profitably. The major part of the annual out-
rat of 150,000 oz. is from this source, and mainly the product of one
;roap of mines. The recent placers are practically exhausted. The
emented gravels are limited in area, and afford an average of only
iboat 3 dwt. per ton, which, however, they yield readily. The Pots-
lam beds are exceedingly irregular, being very much faulted and
ointed, making systematic mining a matter of cost and difficulty, and
necessitating much expense for prospecting ; moreover, the degree of
titriferous impregnation is most erratic, iSways decreasing more or
ess rapidly on leaving the fissures through which the infiltration
aktered ^ verticals " of the local miners), so that a great portion of
iach ore body uncovered is not worth removing, the gold assay
imging from traces up to 2-3 oz. per ton. They require treatment
yj chlorine or cyanide for extraction of the gold, so that nothing
)elow 12-15 dwt. rock can be dealt with, while there are millions of
ons ranging between 5 and 10 dwt. Almost all the porphyry dykes
^eld traces of gold on assay, and occasional samples go very high
5-10 oz. and more per ton), but they cannot be said to afford any
snconragement for industrial mining.

Montana possesses remarkable quartz veins with auriferous pyrite
m the contact between limestone and granite, near Bannack ; bodies
if gold quartz in gneiss, porphyry, or limestone, in Jefferson County ;
mS auriferous silver ore in a true fissure vein in granite, near

In Utah, limestones regarded by Blake as Carboniferous, and other
ledimentary rocks, have been broken through by great outflows of
ipranite, andesite, hypersthene-andesite, &c. The ore bodies appear

• B. O. Hill*.

t C. G. Wamfoid Lock, **Gold Mining and Milling in the Black HUls,
3. Dakota,** Trans. Inst Min. and Met, iii.

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to be contact deposits in limestone near igneous rocks, and canj miu
free gold.

In the Sontliem States, segregated veins oocnr in metamorpli
slates, talcose schists, &a, of late Archaean or early Palieozoic ag
with numerons associated trap (diabase) dykes ; also auriferons be^
of slate, gneiss, felspathic and hjdromicaceous schists, and limestoo
Gold has even been found in a trap dyke.* It is generally in pyrit
and the rock, where productive, is heavily charged with that minen
The trap dykes have exerted an important influence ; at the E&i
mines, Sonth Carolina, the rock is rich only near them. They ba^
probably stimulated the ore-bearing solutions. The country jook i
the un^laciated regions is often covered to a great depth \f9 tl
residual clays and other products of its alteration, as mudi as ibo f
in places. This material is sometimes called laterite, and wbfffs ^
original rocks have been auriferous, it has furnished loose mateiiilf<
panning and washing, essentially different from ordinary placeai,ao
called '' frost drifb.'\t "^^^ ores of the Southern States are guienll
low grade.

Lq the metamorphic rocks of the Lake Superior iron oomtr]
several good auriferous quartz veins have been opened. {

Douglass Island, Alaska, is remarkable for the Treadwell mini
This is located in a boss or dyj^e of granite 400 ft. wide, pHraii^
Triassic slates § and impregnated with auriferous pyrites. :l^ or
body consists in great part of a mass of quartz, felspar, calcitflb vu
pyrite, and is supposed || to have been originally a hornblende gn&iti
afterwards subjected to solfataric action, which introduced the gold.

Placer mining. — The formation and peculiarities of placers aad ^
various appliances used by the alluvial miner have received fnl
treatment in an earlier volume,ir and the following remarks must b
regarded only as supplementary.

The prohibition of hydraulic mining in Califomia has led to
great extension of drifting, or tunnelling and breasting on the pa^
streak, thus obviating the removal of vast quantities of siqieni]
cumbent poor or valueless material. In river mining, the ooDinot
practice on the Klamath is to build wing-dams of rock-filled cril» c
poles, faced inside and out with 1-in. planking. Some lOjOOO-SO.OO'
sq. ft of the river bottom is thus enclosed, and the water is remored
Then a pit is sunk in the exposed river bottom, the top gravel azH
sand containing no gold are stripped away by derricks down to paj
gravel, and the latter is washed. In this connection the ** stratxuf
tester " shown in Fig. 137 is a simple and efficient machine. It ood
prises an " Invincible " portable centrifugal pumping engine workii
in connection with a hydraulic disintegrator. The latter is placed
inlet of suction pipe of centrifugal pump, and its function is to bi<
up the ground in such a manner that it will readily pa^ through I
pump, which is of the same type as those used for dredging. 11
disintegrator is very simple in construction, and is provided with
series of small jets, from which water under pressure acts upon i
stratum to be broken up. A telescopic pipe is provided in the sncti

♦ F. A. Genth. f W. C. Kerr. % 0. D. Lawton. § G. M. Dana

• F. D. Adama. 1 C. G. Wamfonl Lock, * Practical Gofd Mining'

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lain, so that the diBintegrator can lower itself automatically as the
ork proceeds, and, to enable the appliance to work over a certain
-ea, a ball-and-socket joint is fixed in the same pipe. When the
aterial is broken up, it mixes with a quantity of water, is then
tfised through the pump, and deposited at any convenient site, the
ater being allowed to return to the pit for use over again. The
Invincible" centrifugal dredging pumping engine is employed in
ising auriferous river and sea sand ; the operation is much the same
explained in regard to the stratum tester, but the plant is, of course,
ted on board a barge or other suitable craft, and, if necessary, the

Fig. 137. — Gwyn^es Stkatum Testek.

Igings are forced ashore through pipes. In dealing with sand
rel, or other loose material, no disintegrator is required, and
ling whatever is used beyond a specially designed mouthpiece for
t of suction. Fig. 138 represents one of these appliances at work
vering ashore, as explained. The great trouble experienced by
ing engineers in finding pumps suitable for moving such material,
Arell as tailings in some instances, is avoided to the utmost by
ie centrifugal dredging pumps, which are designed and constructed
uch a way as to minimise the unavoidable friction. Both appli-
es just described are made by John and Henry Gwynne, of
nmerMniith Iron Works, and 89 Cannon Street, London.

2 I

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In the milling of cemented gravel modem practice is disoaidiai
the stamp battery in favour of the simpler and cheaper arrastnL TIm






arrastras in use at Smartsville and Moone}' Flat contain the princi{
of the original arrastra, adapted to its operation and handling

y Google

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water or steam power. They are 12 ft. diam. and 3 ft. deep ; bottoms

paved with hard rock ronghly dressed, and in such manner as to

present as even a surface as possible, and laid in cement, the paving

being 16 in. deep. The post in the centre is 14 in. square and 18 in.

high, carrying the mast with 4 arms, to each of which a heavy drag,

is attached. The motive power is transmitted either by means of a

large horizontal pulley, through whose centre the mast passes and

upon which a belt runs ; or by means of a toothed gear fixed in a

circle around the mast, and into which a pinion works — a preferable

arrangement. The drags are heavy blocks of diabase hung to the

arms by means of chains and clamps, and so arranged that all portions

of the pit are traversed by them when they are rotated ; they weigh

600 to 1200 lb. To charge the arrastra, gravel is run in from a car,

or, better, from a shute ; 5 to 9 tons constitute a charge. While the

charge is being introduced, the speed is lowered, water being added

from time to time in order to prevent the charge from caking. A

large quantity of water is taken up, and the charge finally has the

consistency of thin paste. The arrastra is speeded up to 14 rev. a

minute ; in the case of hard cement this is kept up 1 hour. It is

discharged by opening a gate in the arrastra, which empties directly

into the sluice containing the riffles. The charge runs itself out,

water being added to facilitate the discharge. By a judicious mixture

of •* sharp " or crushed gravel and the ordinary gravel that has gone

through the grizzly and has not required crushing, it is remarkable

what a thorough grinding and pulping the gravel receives from the

process. About one tablespoonful of mercury is added to each charge,

the loss falling below 10 per cent. The sluice run is nearly 200 ft.

long, the boxes containing for the most part ordinary longitudinal

riffles. The sets nearest the arrastra, however, have cross riffles, and

likewise the last sets in the run. The sluices are cleaned up once a

week. Almost the whole of the amalgam will be found in the first

t cross riffles near the arrastra, very little getting farther down the sluice.

^When running off the charge, about 30 '' inches" of water is required.

Drags last 6 weeks, and cost about 5 doL (1{.) apiece. A new bottom

I xwts 40 dol., and lasts about 6 months. The capacity of one arrastra

I m hard cement is 60 tons per day ; on soft " top gravel," 75 to 90 tons

^)er day. The advantages of this process consist in the low first cost

k)f the plant, in its simplicity and that of its mechanical devices, in

he extreme cheapness of the cost of treatment, and in the apparent

jiffectiveness of the process itself. When suitably arranged, as in the

Mieaton plant in Mooney Flat, the cravel is dumped upon the

grizzlies, the coarse going through the Gates crusher, which is

uperior for this work. The ** sharp " and •* dull " gravels are then

n two separate bins, centrally situated, from which they can be

lumped into the arrastras by means of shuter<. One man per shift

an thus fill, run, and discharge 4 arrastras, being the only man in

he mill, with the exception of a rock-breaker. The cost amounts to

ut 3/i.-4d. per t<m.

• Quartz reduction. — The pulverising of auriferous rock is governed

X general by the same conditions and principles involved in the

sduction of any other mineral, with these essential differences: — t

2 I 2

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(a) that the material is not homogeneous, the richer portion bemg
often moi e pulverulent than the barren rock ; (5) that amalgamatioD
of the metal is often made a simultaneous operation with the rednciog.
After passing through some form of coarse breaker, aa already described
(p. 121), the rook is conveyed either to rolls for dry cruiiing, or to
stamp batteries for wet crushing. Fig. 139 illustrates the latest type
of stamp battery as made by Robey and Co., Lincoln. It ib in
2 sections of 5 heads each working in one mortar box, mounted on one
frame, driven independently by a pulley on each side. Its special

Fig. 139.— Stamp Battery.

feature is lightness combined with strength, the form of framing
lending itself well to bracing and staging. All bearings are provided
with automatic lubricators, preventing leakage of oil into the pnlp.
Abundant room is provided for access to working parts, everything is
made handy and well-fitting, and the materials selected are in
accordance with most recent experience in various climates.

The free gold contained in the pulp is caught by mercury applied
in various forms of amalgamating apparatus ; and the gold enveloped
in pyrites and other refractory bodies is recovered by chlorinatios,
cyanidoi &c.

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This scarce metal is quite widely distribnted geographically, — ^in
California, Oregon, Russia, India, Borneo, Sonth America, Canada,
Australia, and in certain parts of France, Germany, and Spain. The
prindpal sources of snpply are Bnssia and California ; it is nearly
always associated with either platinum or gold, is recovered as a
bje-prodnct, and is always found in small grains or fine powder, the
largest pieces being about the size*of a grain of rice. In nature it is
generally alloyed with other metals, most commonly platinum and
osmium ; the platinum alloy is called platin-iridium, and the osmium
alloy osmiridium or iridosmine. Platin-iridium grains are sometimes
found as small cubes with rounded edges, while iridosmine usually
cTists in the form of flat irregular grains, and occasionally as hexagonal
prisms. The Bussian supply of uib metal is generally obtained from
platinom mines, in the tJral Mountains; while in California it is
found principally in the placer gold-washings. The ores of iridium
are a source of great annoyance when mixed with gold-dust, on
account of its specific gravity being nearly the same as that of gold ;
oonseqnently, it is impossible to separate the gold from the iridium
by washing, though it may be made either by the amalgamation of
the gold (as neither iridium nor its ores combine with mercury), or
by dissolving out the gold in aqua regia. In the mints, these metals
are frequently separate by melting the gold-dust, and allowing the
molten mass to remain in the crucible for some time, during which
the iridium slowly settles to the bottom, as it does not alloy with the
gold under such circumstances. The gold is then poured off from
the top, and the dregs in the bottom of the crucible are found to
contain the greater quantity of the iridium ; the gold therewith is
then dissolved, and the iridium is found in the residue. In Bussia it
is contrary to law to possess or deal in iridium ore, because it has
been used to adulterate gold-dust, with disastrous results to the
coinine machinery, owing to its great hardness. Iridium possesses a
white lustre, resembling that of steel ; its hardness is about equal to
that of the ruby ; in the cold, it is quite brittle ; at a white heat, it
is somewhat malleable. It is one of the heaviest metals, having a
Bp. gr. of 22*88. Heated in the air to redness, it is very slowly
oxidised. It is insoluble in all single acids, and in the massive state
even aqua regia does not attack it. Its leading application has been
for pointing gold pens. The iridium point consists simply of a small
gram of iridosmine, selected bjr first removing from the ore, with a
inagnet, the magnetic oxide of iron which always accompanies it, and
then dissolving out, by means of adds, the other impurities which
may be present ; the ore is then washed with water, dried and sifted
in order to remove the fine dust, and the sifted ore is then ready for
the selection of points, by an operator who rolls the grains of iridium

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around with a needle point, examining them under a magnifying
glass, and selecting those which are solid, compact, and of the proper
size and shape. These points are usaally selected in three grades-
small, medium, and large — depending upon the size of the pen for
which they are intended to be used. The grain of iridium having
been soldered on to the end of the pen, it is sawed in two (whi<£
makes the two nibs of the pen), and ground up in the proper diape.

By heating the ore in a Hessian crucible to white heat, adding
phosphorus, and continuing the heating for a few minutes, perfect
fusion ensues, and the metal can be poured and cast, but the presence
of 7^ per cent, phosphorus is an obstacle in the way of its use for
electrical purposes. On heating the meted in a bed of lime, the
phosphorus is completely removed. In this operation, the metal is
first heated in an ordinary furnace \p white heat, and finally, after no
more phosphorus makes its appearance, it is removed and placed in an
electric famace with a lime crucible, and there heated until the last
traces of phosphorus are removed ; the metal which then remains
will resist as much heat without fusion as the native metaL For
mechanical applications, where the metal is not subject to great hett,
it is melted with phosphorus and cast into the shape desired, and
then ground or worked, as the application may require. Its hardness
is now finding it many useful spheres, both in the solid form and in

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This metal is one of the most abundant and widely disseminated ele*
ments of the earth's crnst, its distribution being materially aided by
the &ct of its forming two oxides of different chemical quanti valence.
Apart from the accumulations of the metal in the form of ores, more
or less pure, it is found in large proportions in many igneous and
metamorphio rocks, notably as oxides in basi^ts (12-20 per cent.\
dioritee and diabases (4-16 per cent), andesites (3-15 per cent),
porphyries (0-14 per cent), rhyolites (0-8 per cent), and granites
(0-7 per cent). In the sedimentary rocks it is less marked, but all
limestones and sandstones may be said to contain it, as well as sands,
daya, and gravels. The industrial sources of iron are the following
ores: —

Magnetite, or magnetic iron ore, Fe804 — 72 per cent iron.

Hematite, in two forms, red hematite, and specular iron ore or iron
glance (also micaceous iron ore), FejOs — 70 per cent

Idmonite, or brown hematite (also bog ore, lake ore, and black brush
ore), 2 FejjO,, 3HaO— 60 per cent

Siderite or spathic iron ore (also clay ironstone, sparry iron, clay
band, black band, coal measure iron, argillaceous iron ore), FeCOg —
48 per cent

ryrite, pyrites, or mundic, FeSj — 46 per cent

These percentages refer to pure ores, but they never occur pure in
large quantities. The best known output of magnetite was 40,000 tons
averaging 68J per cent, while the Lake Champlain mines afford much
at 6^-65 per cent when dressed, but as low as 60 per cent when
mined. The specular hematites of the Lake Superior mines reach
60-65 per cent, and the red hematite of New York about 44 per
cent The limonites vary between 40 and 50 per cent. ; and the
crude spathic ores reach as low as 20 per cent, or even less, being
largely €X)ntaminated with clay and bituminous matters. The usual
impurities of all iron ores are the common elements or oxides that
enter most largely into rocks, and those which make up the walls of
the deposit are usually the ones that appear most abundantly in the
ore. Silica (SiOj), alumina (AljOj), lime (CaO), magnesia (MgO),
titanium oxide (TiOa), carbonic acid (CO^), and water (HjO) occur in
large amounts, and determine to a great extent the character, fluxing
properties, Ac, of the ore. With these, and of superior influence, are
sm^er amounts of sulphur and phosphorus. The last two and
titanium chiefly decide the character of the iron which is yielded in
the furnace, and are the first foreign ingredients considered. The
solphur is present in pyrite, the phosphorus in apatite. For Bessemer
pig irons, which command the best market, the extreme allowable
timit of phosphorus is • 1 per cent. ; thus a 65 • 3 per cent ore should


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not have over • 066 per cent phoepboras to be ranked as Beeiemer,
and if, combined with sufficiently low phosphorus, the gangae is
highly siiicious, even low grade ores may be of value, though remotely
situated. Thus the lump magnetite of the Chateaugay mines, afford-
ing but 50 per cent iron, is mined and transported over 400 miles w
the furnaces; it has 18 '44 per cent. SiOj and only '029 phosphorus
and ' 052 sulphur. A moderate amount of phosphorus is not only dC'
drawback for ordinary foundry irons, and such as are to be subjwted
to tool treatment, but it is a prime necessity ; excessive amounts ai?
desired only for weak but very fluid irons. Considerations like tboe
help largely to determine the value of a deposit of iron ore.

The annual production of iron ores in the United Eingd<xn is
about 14 million ton^, classified approximately as 8 million carhootte,
3^ brown ironstone, 2^ red hematite, and 150,000 tons alumifion
hematite. The Cumberland ores give 53>60 per cent metal in the
furnace, and the N. Lancashire 51-55.

For all practical purposes, our home production of ore mtybe
divided into the two categories of hematite and lias, the former repre-
sented by Cumberland and Lancashire, and the latter by ClevelM
Lincolnshire, and Northamptonshire. The three latter districts jm)-
duce more than 50 per cent, and the former 18 per cent of all Uieirai
ore raised in the United Kingdom. Of the lias iron ore there i»
practically an unlimited supply. Of hematite, however, the quantitT
available is more uncertain ; and although it has recently been prtmit
by new discoveries to be more abundant than was at one time m^
posed, it is doubtful whether the present annual output of abwt
2\ million tons could be largely augmented or indeed be quite maifi*
tabed. As it is this description of home ore that is insufficient ^
our requirements, the sources of external supply become not only a
important but a pressing question.*

The day band deposits of N. Sta£fordshire are a valuable swud
of supplv for blast furnaces, and contain only traces of phospboH
and sulphur. Some of them yield 90 per cent metal after caldnAtiiJ
at the mine mouth.

The iron ores of the United Kingdom are mined under
advantageous conditions, as regards cost, than those of most oi
countries. According to official returns, the average quantity of ir*
ore produced per miner is about 631 tons per annum in Luxembm^
559 tons in England and Wales, 352 tons m France, 228 tons in tbi
United States, and 213 tons in Germany. If we take into account^
fact that the average quality of the iron produced in England is mwfc

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 54 of 76)