Charles George Warnford Lock.

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

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micaceous variety. While the tin granite of Australia appean
closely allied to that of other countries, and has even been described
as exactly corresponding to that of Cornwall, it contains more white
orthoclase in its composition and less schorl ; in fact, in many places
there is a total absence of this last mineral. It is also a mucn softer
rock, more easily eroded; and its easy disintegration is a veiy
important item, as on this greatly depends the extent of the stream
deposits. There appear to have been two outbursts of granite, both
highly felspathic ; the older, which has been the chief source of tin,
is euritic, and the second porphyritic, the crystals being white
orthoclase. The period between the emissions has not been great,
and all of them are tin-bearing. There is a very marked difference,
however, in the character of the tin stone from the euritic and the
micaceous granite, that from the former being more highly and more
generally crystallised and transparent, and that from the latter, when
crystalline, being less transparent, but more usually amorphous. The
difference is seen, not only in the mode of occurrence in the veins,
but also in the stream tin, where it is not derived partly from eadv
kind of granite. In the case of the euritic, the sides of the veioa an
generally covered with crystals of tin, very transparent; and evea
when these veins run together, as they often do, and form masses, the
ore is always of a more glistening hue when broken. In Uie
micaceous granite, although sometimes crystalline, the crystals are
not so perfectly developed, and are dull; while the masses consist of
dull irony-looking lumps, and the stream tin is of a dull dirty brown
colour. It does not appear, however, to have any effect on the
quality of the metal, the tin made from both refining equally wdl
and being as pure.

The sources of Australian tin are threefold : — (a) existing riter
and creek beds ; (6) buried drifts of the Miocene period ; and (c)
veins in the granites themselves. The first are sometimes enridwd
by erosions of the second system ; they extend for a length of 400
miles along a granite country. The " deep leads " occur wherever
basalt joins the granite, and are of enormous extent. V^taUe
Creek (Emmaville), New South Wales, has been worked for a distance
of about 5 miles along its course with usually great success. Somfr I
portions of the ground contained the tin at surface, and in other parts f
it has been obtained at various depths. The covering in some places '
is composed of granite detritus cemented together by infiltration d ; |
iron. In one mine, the lead has been proved payable for a width of

• S. S. Vale, " Australian Tin Deposits," Trans. Min. Inst Ck>nurall, 1884.



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METALLIFEROUS MINERALS. 629

300 ft., having an average thickness of wash-dirt of 3 ft, containing
about 80 lb. of ore to the load of 60 buckets. At Victoria Creek,
N.8.W., a tunnel has been driven for a distance of 2000 ft. along the
cotuse of the lead, the widtii being 18-400 ft., with an average thick-
ness of 3 ft. of excellent paying wash-dirt, and at a depth of 60 ft.
from surface. On one part of the workings a very hard layer of
cement was met with, 14 in. thick, and under it a splendid run of
wash was found 2-4 ft thick ; 16 ft. below this again the main lead
is worked. In one portion of the lead, tremendous volcanic heat has
passed through ; everything is charred, even the tin ore. In another
place, the phenomena led to a supposition that the tin was in siivk in
a hard el van rock, but later development showed it to be only a local
metamorphosis caused by a flow of basaltic lava, which had hardened
the bed. Small patches of tin in the chlorites are only of local occur-
rence. The permanent sources of tin will be the veins and segrega-
tions in the granites. They occur along the whole course of the
granite formations, wherever the alluvial ground is found, having a
uniform bearing of E.N.E. ; varying in thickness from a mere thread
to 1 ft ; and are rarely followed to a greater depth than 20-30 ft,
when iliey die out Occasionally these strings of ore run together
and form huge masses of ore ; at one place, lumps of solid ore were
obtained weighing 50 lb., but it proved to be only an irregular mass.
Frequently the ore is disseminated through the rock in fine grains,
osuidly highly crystallised, black, and compact in the euritic, and
less crystaUised, brown, and less compact in the micaceous, while the
tinstone from the former assays higher than that from the latter.
The matrix of the tin is principally quartz, and in all cases it is
bighly silicious; sometimes almost entirely white topaz. In some
aases the tin crystals are inside the quartz, and in others outside the
]nartz, thus showing that they were deposited simultaneously.

The most important tin mines in Queensland are near Goolgarra,
in the Herberton district ; others are at Cooktown, on the Annan
iod Bloomfield rivers; and at Stanthorpe, on the border of New
South Wales. Herberton is the chief tin-mining centre of Queensland,
md the tin is here obtained chiefly from lodes. A very noticeable
(iBature in the district is the occurrence of dykes of some altered
basic rock. These dykes are the main sources of the tin ore. They
ippear to be more prevalent among the sedimentary strata than
imongst the granitic rocks. As noticed by E. L. Jack, there exists
m intimate connection of the tin deposits with these metamorphosed
Igneous dykes. These tin-bearing dykes have no prevailing direction,
sometimes they intrude themselves along the planes of bedding of
the sedimentary rocks, and at other times they follow joint planes.
13asee were noticed in which it appeared as though they have even
penetrated quartz reefs. The percentage of tin in these dykes varies
rery much in different portions. Throughout the '' stone," the cas-
dterite occurs in an exceedingly irregular manner. There are no lodes
n the proper sense of the word. The tin ore occurs sometimes in fine
^strings " or *' leaders," often swelling out into large bunches ; at other
limes a-certain amount of the ore is disseminated through the body of
the dykes. Some stream tin has been obtained by washing the gullies.

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630 ECONOMIC MINING.

The yield of tin in Victoria is small, and nntil lately no field of
importance had been disooveied, bnt toward th^end of 1890 extennTe
deposits were reported to exist in the Gippsland district, at Omeo
and TarwiD. Small deposits have been fonnd in the Beechworth
district, at Indigo and Mitta Mitta. The formation in which the
lodes occur at Wombat Creek consists mainly of altered slates and
sandstones, converted in many places into nodular schists^ and ]^yl*
lites. These sedimentary rocks are probably Upper Silurian. They
are all highly inclined, and are apparently lithologically similar to
the supposed Upper Silurian sediments m the lower part of the
valley, which are there associated with limestone and conglomerate
beds. The sediments have been penetrated by extensive pegmatite
and aplite masses, which, together with other more silicious segrega-
tions, form outcrops along the ridges. It is in the former, or associated
with them, forming a sort of stockwork, that many of the tin lodes
occur. When the stanniferous materials are most abundant, the
matrix is a very distinct greisen. The mica (mxiscovite) is finequently
plumosely arranged, and the quartz glassy. In some localities wb^e
the lodes traverse the slates the matrix is granulitic. Manv of the
pegmatite masses are full of tourmaline crystals, and where the latter
are most abundant the micaceous materials are either wa n ting or is
smaller quantities. The granitic rock masses with which the tin ore is
associated are certainly* younger than the Silurian sediments they
invade, and are probably Devonian. The deposits are well situated
for economic mining and dressing ; yields of me stone vary firom 2*9
to 5*85 and average 4*8 per cent, metallic tin«

In Western Australia, tin is worked near Bridgetown. The
formation of the district is crystalline schistH, gneissic and granitic
rock, with numerous dykes of diorite, granite, and veins of tour-
maline. The tin-wash of the field varies greatly in thickness (6 in.
to 20 ft.^, and in richness. No lodes have been found, but from the
crystallme, un-waterwom character of the tin they must exist. The
field is in its infancy, and, up to the end of 1891, 576 tons of tin ore had
been exported. Tin has also been discovered in the alluvial workings
at Pilbarra, but the deposits could not be worked, as the mining
regulations for working gold and tin clash.

In the United Stat^ cassiterite occurs in small stringers and veins
on the borders of granite knobs or bosses, either in the granite itself
or in the adjacent rocks, in such relations that it is doubtless the result
of fumarole action consequent on the intrusion of the granite. It
appears that the tin oxide has probably been formed &om the fluoride.
A fovourite rock for the ore is iiie so-called " greisen," a mixture of
quartz and muscovite or lithia mica, and probably an original granite
altered by fumarole action. Topaz, tourmaline, and fluorite are
found with the cassiterite, indicating fluoric and boraoio fumaroles.
Cassiterite seems also to crystallise out of a granite magma with the
other component minerals. Narrow veins have been discovered ib
mica schists with lepidolite and fluorite.t

Of the many American mining ventures which have brought

• J. Stirling, *'The Tiu Lodes at Wombat Creek," Bep. Victoria Govt.
t Kemp, op. cit.



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METALLIFEROUS MINERALS, 631

fortnneB to their vendors and disaster to the British capitalist, Ihe
tin mines stand out prominently. The Cajaloo mine, belonging to
the San Jacinto Estate (Limited), in California, has cost approximately
200,0001. (including 90,0002. purchase money), and from it has been
milled about 6000 tons ore, yielding about 120 tons pig-tin (2 per
cent, say), value 11,0002. Of the Harney Peak mines. South
Dakota, it was officially reported in 1891 ^at there were about
500,000 tons of ore in sight, averaging 14 per cent., while selected
specimens gave 30-40 per cent., and that inexhaustible quantities
could be ^ot yielding 4 per cent. An expenditure of about 4 millions
sterling (mostly English) has not produced more than 10 tons of tin,
the fact being that Sie ore will nowhere average more than 40 lb. to
the ton (1*3 per cent.), and cannot be worked at a profit. So much
for the developed mines. Undeveloped deposits are reported in
Alabama, N. Carolina, and Virginia. At Broad Arrow, near Ashland,
Alabama, tin-ore is diisseminated in gneiss, the ore averaging about
\\ per cent, black tin, but being very much mixed with titaniferous
iron. At King's Mountain, N. Carolina, cassiterite occurs very
irregularly in a " greisen " or altered granite, and in limited alluvials
derived from the disintegration of the same. On Irish Creek,
Virginia, experimental parcels of veinstone taken from deposits in
granite have shown 3^3^ per cent, metallic tin, largely associated
with arsenical pyrites and ilmenite, which increase the difficulties of
concentration and lower the value of the product. The United States
virtually produce no commercial supplies of tin.

In Mexico, tinstone has been found at numerous widely separated
localities, among which may be mentioned Durango, Cacaria, Potrillos,
and Sain, in the State of Durango; Chalchiuites, in Zacatecas ; Bolanos,
in Jalisco ; Cerro de Zamorano, in Queretaro ; Cerro del Chiquihuite,
in Aguas Calientes; and some places in the State of Guanajuato.
None of these deposits has been systematically or extensively ex-
ploited, with the exception of those of Durango, where the ore is found
to occur in small but frequently very rich pockets in ill-defined veins
in trachyte-porphyry, which is the common country rock.

Bolivian tin occurs in association with silver. The veins are
encountered in porphyritic diorite traversing sandstones and con-
glomerates, in trachyte penetrating slates, and in slates and quartzites.
The silver veins of Potosi carry quantities of tin, the two metals
eometimes occurring in distinct bands in the same vein. At Chorolque,
bismuth accompanies the tin ; and iron pyrites is a common associate.
High cost of transportation (on llamas) to market is the chief
hindrance to development of the industry.

According to Strauss, very large quantities of alluvial tin exist in
Swaziland, South Africa, but are not immediately available on
account of lack of labour and difficulties of transportation.

Treaimeni, — The treatment of stanniferous material is twofold,
firstly a mechanical dressing to separate the tinstone or ore proper
from the refuse, and secondly, a metallurgical process by which
metallic tin is smelted out of the ore. In the case of stream tin the
material is already in a form fit for concentration, but vein tin
requires pulverising to reduce it to that condition. Nearly all the



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632 ECONOMIC MINING.

Oomish tin is won from veins, and nearly all the foreign tin is
alluvial.

The Oomish veinstone is mined and transported to the mill as any
other mineral. At the mill it first undergoes a preliminary hand
sorting to separate any lumps of copper ore which may be among it,
derived, in fact, from the same vein or lode. The first stage in
reduction is often accomplished by hammers wielded by women, also
by breakers. Next the tin ore passes to the stamps, which are for
the most part of simple if not rudimentary construction, as compared

with the modem forms JiJSf&^
in milling auriferous ro(^
Fig. 173 illustrates a pattern
possessing some novel featores
which are claimed * as im-
provements. The ore is sup-
plied to the feed launder a and
falls thence into the feed-box
b, whence it passes at c into
the mortar proper near the
bottom. The imoe and die
are made hemispherical in
section and the stamp d re-
volves, so that a grinding
as well as a crushing acticm
is obtained, and the shape
adopted gives twice as much
surface as the usual flat form.
The battery consists of 8 such
stamps, in 2 rows of 4 each.
The grating is at e. It is re-
corded that while the ^* battery
sand" or crushed ore of 20
years ago was considered fine
enough if it passed thraugh
a 30-me6h screen in the grating
e, now 40-mesh is commonly
employed, the reason given
being that the tin in the deeper
Fig. 173. — Tnr Stamp. workings is more oompletely

disseminated through the rock
in exceedingly fine particles, that in the ore known as *' blue peach,"
for instance, being almost invisible to the naked eye. Stampmg
is done wet, and the pulp flows from the stamps to a huddle, in which
it is settled, so that the heavier metallic particles are deposited
in the centre, while the refuse (called ''green stuff") is deposited
towards the circumference. So much of this central deposit as is
not merchantable is calcined (** burned "^ and then mixed with
water, by which means a large portion of the copper is carried off in
solution and precipitated ; the solid matter is carried into a second
* J. Hicks, *« Treatment of Slime Tin," Trans. Min. Inst, and Assoc CacnvaU.



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METALLIFEROUS MINERALS. 633

«'biiddle,"from which "black tin" is obtained. The "black tin"
concentrates contain an average of about 66 per cent, metallic tin ;
they are mixed with about 20 per cent, pulverised coal, and smelted
in reverberatory furnaces. The tin in the ore is reduced to a metallic
state by this treatment, and is tapped out of the furnace into a cast-
iron kettle, from which it is afterwards ladled into moulds ; the blocks
of metal thus obtained are known in commerce as '*pig tin." The
"burning" or calcining above alluded to expels the arsenic and
sulphnr carried by the pyrites which accompany the tinstone. The
arsenic is collected in separate receivers (see p. 158) and sold. The
calcining also affects the chemical condition of the copper, and enables
it by subsequent huddling to be further separated from liie tin. The
product is again huddled and stamped, sometimes several times.
The first water, containing copper in solution, is run into pits, and
the sediment, containing a large proportion of copper, is sold. By
reason of the chemical changes occurring in the " burning," certain
parts contain tin, chiefly in the form of oxide, while the outside por-
tioDS contain little tin, but a certain proportion of copper. So much
of the deposit in the buddies at this stage as the workmen think
worthless they send down the stream as waste. A certain portion,
substantially tin oxide with some copper, is shovelled out and
smelted. The residues or discarded portions are known as " leavings "
or " burnt leavings," as the case may be. They all carry considerable
metallic value, and afford a livelihood to numbers of " streamers,"
who catch more or less of the escaping metal on various contrivances
placed in the streams by which these tailings flow to the sea, the
usual harvest of the streamers amounting to about 17 per cent, on the
weight of tin saved in the mills. Besides this, an enormous quantity
yearly goes to waste, which could certainly be profitably saved bv
more efficient concentrating apparatus, such as the Linkenbacn
huddle.

The wash brought up in the Chinese diggings in Perak is
generally put in a big heap and left to dry in the sun. By this
means a lot of the clay becomes friable, and puddling, which is a
very expensive process, is avoided. When all the wash has been
brought to surface, a wooden box is made, about 30 ft. long, with a
&11 of about 1 in 10, according to the class of stuff to be washed.
The washing is performed by shovelling the stuff into the box, allow-
ing a stream of water to run over it, and agitating it by means of
long hoes. The clean mineral carries 66-67 per cent, tin, and goes to
the furnace. The smelting is carried on in a cupola furnace, about
5 ft. diam., made of well beaten day (supt)orted with stakes arranged
around it, and bound with iron lings), hollowed in the centre, into
which the tin ore and charcoal are put; the metal runs out of an
aperture in the bottom, and is caught in a small cell made on the
ground, from whence it is ladled into moulds well prepared in the
sand, and after cooling, is ready for the market. At the beusk of the
furnace is a hole made for the admission of air and for raking the
charge. The blast is furnished by l^and bellows and a bamboo.
Charcoal is universally used as fuel, and great damage is done to fine



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634 ECONOMIC MINING.

timber by the promlBCUOns burning of valuable wood. A company
recently are buying a great deal of ore firom the Chinese in Kinta,
and smelting it in Singapore.

The vein tin rais^ in Tasmania is treated first by sluicing in
boxes on the mine to get rid of clay and soft iron oxide and to get out
some free tin ore, and after this partial concentration, is sent to a
reduction mill, where it is crushed by stamps and conoentrated on &
very complete system of V classifiers, jigs, concave buddies, and eon-
vex slime tables. The proportion of slimes is about 33 per cent. The
clean ore is smelted in the Mount Bischoff Company's smelting works
in Launceston, in small reverberatory furnaces. Slack coal from
Newcastle, New South Wales, is used as fael, and a little lime as flnx.
The dressed ore received for smelting averages 72 per cent, metallic
tin, and the average yield is 67 • 73 per cent., the smelting loss being
therefore 4*27 per cent. The tin ingots are of good quality, averaging
99*85 per cent, pure tin.

At Kangaroo Flat, Au^tralia, the cemented wash-dirt is puddled as
well as sluiced, at a cost of 9<2.-10<2. a ton.

Commerce, — The annual production of black tin in ComwaU is
about 14,000-16,000 tons. The Malay Peninsula in 1866 exported
6692 tons; in 1874, 13,666 tons; in 1883, 17,196 tons; in 1889,
28,492 tons, showing a constant and steady increase. What is known
to the trade as ** Singapore " tin comes partly from Perak, partly from
Sungi, Ujong, Selangor, Kwalla Lumper, Jelubu, and Malacca;
" Penan^ " tin is all from Perak ; what is known as " Straits " tin in
London is Penang and Singapore tin; and what is known as *' Malacca"*
tin in the United States is also Penang and Singapore tin, specially
branded for the American buyer, who is every year taking an in-
creasinely large proportion of the total shipments (about 30 per cent
in 1891j. Banca and Billiton produce about 10,000 tons annually, of
which some 7600 tons go to Holland. Tasmania exports 3000-3500
tons yearly ; Queensland, 2500-3000 ; New South Wales, apparently
4000-6000 tons, but these are chiefly re-shipments of Tasmanian and
Queensland produce. California sometimes affords 60-60 Ums
Bolivia is a steady shipper of 1600-2000 tons a year, all to England.

The greatest consumption of tin is for making tinplate — exoer
ingly thin sheet iron covered with a tin coating — and the grea,
development of this industry of late years has been in the canned
provision trade. The market values of tin, and therefore of its ore,
fluctuate seriously, if not suddenly, say from SOI. to 90/. a ton for pig-
tin. The basis of valuation of tin ores is by chemical assay, the per-
centage of metallic tin being worked out as tin oxide (black tin).
Certcdn impurities or foreign substances detract from the market
value of the sample. Titamum is not of serious moment. Tungsten
lowers the standard, though, when a market can be found for the
product, the ore may be freed from tungsten by treating with Bodn
' sulphate, and washing out the soda tungstate. Tantalum and niobium
^^"0 found as the minerals columbite and tantalite in many samples of
"^^^•^ ore, and are injurious by alloying with and lowering the quality
* J'e tin during the smelting. All impurities, such as sulphur,
s (iron or copper), arsenic, &c., leiewi to deductions by the



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METALLIFEROUS MINERALS. 635

smelter, as they increase the oost of treatment. At Singapore, the
smelting charges are 5Z. 5«. a ton on ore assaying 70 per cent, and
upwards, 61. for 65-70 per cent., and 72. for 60-65 per cent. ; in addi-
tion to which, deductions are made of *2-'5 unit per cent of im-
purities, and further deductions for smelting losses, viz. 2 units on ore
assaying 70 per cent, and over, 3 units on 65-70 per cent., 4 units on
62-65 per oent., and 5 units^ on 60-62 per cent., so that an impure
and low-grade ore may suffer as much as 12^ per cent, discount.






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636 ECONOMIC MINING.



TUNGSTEN.

The element tungsten has the general characteristics of a mineral;
but it is also capable of acting as a non-metallic element, and can
form an acid — tungstic acid. It is in this r6le that it is always
found in nature, as the tungstic acid salt of iron, manganese, caldum,
or lead. The most abundant is wolfram, a mixture of tungstates of
iron and manganese in varying proportions. The tungstate of iron
may replace the manganese almost entirely, when the mineral receives
the name ferberite, or the manganese may replace all the iron, giving
the mineral hiibnerite. Besides these, scheelite, the tungstate of
calcium, scheelitine, tungstate of lead, and wolfhun ochre, the an-
hydrous acid itself, are found in small quantities. In Europe and
America, wolfram is almost the only ore raised ; in New Zealand, the
more important deposits are scheelite. The output is always exceed-
indy uncertain. Thus the production of wolfram in the United
Kingdom rose from 1 ton in 1880 to 380 tons in 1885, fell to ^ t(Hi
in 1889, and reached 140 tons in 1891. The two chief applications of
tungsten are in the metallic state for alloying with iron, and in the
state of soluble tungstates as a mordant and fire-proofing medium for
textile fabrics. In order to produce tungsten steel it is neceeaaiy ia
the first place to rid the wolfram of the impurities which it contains.
Accordingly it must, in the first place, be roasted, then treated by
dilute acid, and finally washed with water. In this manner the
sulphur and arsenic are eliminated. After being dried, the residue is
raised to a strong heat in crucibles lined with damp charcoal, the
tungstic acid is reduced to the metallic state, and a compouDd is
formed containing iron and manganese ; 5-25 per cent, is added to
the steel, according to the proportion of tungsten desired.

The preparation of soluble tungstates and bimultaneous purifica-



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 72 of 76)