Charles George Warnford Lock.

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

. (page 71 of 76)
Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 71 of 76)
Font size
QR-code for this ebook

is then lifted, by a pair of tongs on wheels, placed upon the platform
of the elevating gear, and raised to its position in the heating chamber
of the main distilling furnace. The cover, which remains stationary
in the famace, has a convex edge, while the crucible has a groove
round the edge, into which the edge of the oover fits. A little
powdered lime is placed in the crucible groove just before it is raised,
so that when the edges of the cover and crucible come together, they
form a tight joint, and, at the same time, will allow the crucible to be
lowered easily from the chamber when the operation is finished, to
give place to another containing a fresh charge. From the cover
projects a slanting tube connected with the condenser. The con-
denser is provided with a small opening at the farther end, to allov
the escape of hydrogen, and has also a rod by means of which any
obstruction which may form in the tube during distillation may be
removed. After raising a crucible in its place in the fdmaoe, the
hydrogen escaping from the condenser is lighted, and serves to show
by the size of the flame how the operation is progressing in the
crucible, the sodium actually distilling soon after the crucible is in
its plaoe. The temperature of the reduction and distillation has been
^'oiir.a to be about 1510*^ F.

"i been found advisable to use a little more ^* carbide " than
on absolutely requires, and this accounts for the presence
1 quantity of carbonic oxide in the expelled gas, the free
ing upon the carbonate formed bv the reaction, thus giving
oxide, and leaving a very small percentage of the r^idne
a of sodium peroxide. This small amount of carbonic oxide

Digitized by VjOOQIC


rarely combines with any of the soditiin in the tube, and so the metal
obtained in the condensers is pure, and the tubes never become ohoked
with tbe black compound* In the preparation ofpotassium, a little less
*' carbide" is used than the reaction requires. Tnus no carbonic oxide
is given off, and all danger attached to the making of potassium is
removed. After the reduction and distillation, the crucible is lowered
from the furnace, and the contents are poured out, leaving the crucible
ready to be rediarged. The average weight of the residues ft-om
operating upon charges of 15 lb. caustic s^a and 5^ lb. carbide is
16 lb. These residues are treated either to produce pure crystallised
soda carbonate or caustic soda, and tbe iron is recovered and used
again with pitch in the formation of the "carbide," From this
residue, weighing 16 lb., is obtained 13 lb. anhydrous soda carbonate,
equivalent to 9*4 lb. caustic soda of 76 per cent. The practical yield
of sodium is 2*6 lb., when, theoretically it should be 2 '86. The
average duration of distillation is \\^ hours, and a furnace arranged
for 3 crucibles treats 45 lb. caustic soda every 90 minutes, producing
7^ lb. sodium and 89 lb. soda carbonate. The famace is heated by
gas from a Wilson producer consuming 1 cwt. fuel per hour ; and the
small auxiliary furnace for heating the crucibles requires a further
J cwt. The estimated cost is : —

720 lb. canstio soda at IH. a ton 3 10 10

150 lb. carbide at i<2. per lb 6 4

Labour 10

Fuel 17

Be-oonvetnon of carbonate into caustic .. .. 1

Total 6 14 2

Lees value 475 lb. caustic recovered .. ..268

Kett cost 120 lb. sodium 4 7 6

)r 8fcl. a lb. The life of crucibles is found to be about 200 operations,
»r less than Id. a lb. on the sodium made ; and oast-iron is as suitable
A steel.

These metals find their chief application in laboratory reagents*
lodium was at one time largely used in making aluminium (see p. 389),
nd considerable quantities are still consum^ in preparing sodium-
malgam for gold mills.

Digitized by




Thouoh widely distribiited geographicftlly, oommercial sappliee of tin
are obtained from roRtrioted areas. Geologically tin is umost con-
fined to graoitic rocks, and mineralogioally it is remarkable for
occurring practically exclosively in the one form of cassiterite, SdO^
binoxide, carrying 78^ per cent, metal, though a sulphide called
stannite is encountered as a rarity.

Cornish tin->miDing goes back 2000, if not 4000, years^ and is
entitled to first consideration if only on that account. Formerly
large quantities of alluvial tin (*' stream tin **) were collected in the
watercourses, having been derived from the erosion of stanniferDin
veins ; and such tin stone was always purer than vein tin, beosnse
associated pyrites had been oxidised and washed away from it. All
Cornish tin is now derived from veins, which occur principally in
granite ; they are also found in the slate (or '^ killos "), which usuallj
rests on the granite at a high angle. In 8ome cases the juncticm of
these two rocks is nearly vertical ; again they are considerably broken
and mixed at the point where they come together ; and sometimefl *t
these points they are also altered in texture, the granite becoming
very fine-grained, and the slate hard and massive. In addititm to
these rocks are numerous dykes of quartz-piorphyry, known as '' elran
courses," sometimes only a few feet in widtn, but generally much
wider; they traverse tne granite as well as the slate without in-
terruption. The mineral veins penetrate the granite, slate, and elvan
courses, showing that they were formed since the elvans. It is 4
common occurrence for the mineral veins to carry copper ores in tbe
slate, tin appearing as the eranite which underlies the slate ifl
approached, and eventually, where the main body of granite is pene-
trated by the vein, tbe copper ore gives out entirely, and tin takes iti
place. Every mineral vein or lode throws off branches and stringers
into the adjoining country rock, sometimes to such an extent that tbe
main lode becomes divided into a complex network of veins. A lode
will also dwindle to a mere line, while some of the stringers become
enlarged, exceeding in bize the parent vein. Near Bedruth are alte^
nations of granite and slate. At the Tincroft mine, granite goes
down to 156 ft. below surface, when slate appears, and continues to s
depth of 500 ft., at which point the main body of granite reappeam
At the Dolcoath mine a large mass of slate rock was mot with 2^ ft
below surface ; this slate is included in the granite 1440 ft. below the
point where that rock was first cut into by the workings, and 1860 ft
below sea-level. The average yield of tin from the rock mined ii
about 3-4 per cent., or 65-90 lb. per ton. In the Dolcoath mine a*
2400 ft. the produce is 300 lb. a ton. Enormous profits have beet
made in the past from such mineral. Much of the mining is noir

Digitized by



'Carried on aotnallj beneath the sea, presenting many difficulties, and
in no place can nnderground work be better studied.

In Spain are considerable deposits of stream and vein tin, in the
province of Orense, the rocks closely resembling the granites, mica-
schistSy and killas of Cornwall. The alluvials are extensive, 4-12 ft.
deep, and carry 3 lb. tin per ton. The veins strike 30° N. of E.,
averaging 5-8 ft. vnde, and dip S., but have not yet been developed.

Burma is the great source of Indian tin supplies. In the Tenas-
ferim division, tin stone is very plentiful, every stream bed near
Jfaliwun in Mergui yielding the metal when washed. Dr. Oldham
Btates Hiat the main source of all the Tenasserim tin is the granite
range separating that province from Siam, where it exists as an
essential ingredient of the mass of rock, occurring disseminated
through the granite in small crystals, and being similarly arranged to
the quartz and felspar. The degradation of this granite by weathering
through an enormous period of time has suppbed the sand which is
now so abundantly impregnated with stream tin . At Mergui it used to
he worked in the very gardens of the town, and in the Thawbawleck
river there have been iBxtensive stream washings for years ; the fine
sand being sorted out with a cane shovel that acts like a large sieve,
9sA finally washed in wooden dishes, in which the tin sinks by its
own weight on the water being revolved. The only European
attempt to work Burmese tin on a considerable scale was made
between 1873 and 1877, when they not only washed the stream tin,
hut opened out veins of ore in the hills. During the cold weather of
1874-75 some 7 tons of metal and 14 tons of cleaned picked ore were
exported. The works were, however, closed in 1877. It is worthy
of note, however, that since the European workers failed, the Ohinese
have found the mines remunerative, and are still at work there, though
th^ pay a ground-rent and a royalty of 5 per cent. Warth places
the average yield at *04 per cent, impure wash tin. Hughes has
reported officially on a so-called reef, which he says is '* rather a zone
of metamorpbic rocks through which runs of varying ore-bearing
quartzites can be traced. Many of the smaller seams, of a reddish-
brown colour, are heavily weignted with tin ore, giving as high a
proportion as 60 per cent. The point on which there can be no
dispute is that there is a large mineralised zone of rock exposed in the
form of a prominent, well-defined hill, which is free from any specu-
lative doubts as to its existence. At the spot known as Khow Muang
tiiere are at least 60,000 tons of reef within sight."

Straits tin * forms about a third of the world's production, and
the bulk of this is derived from an area 20 miles square in Perak,
the Kinta district, from a belt of Ij^ sq. miles, having yielded over a
million sterling worth of tin in 4 years. The N.-S. mountain ridge
traversing Perak consists chiefly of palaeozoic rocks, granite, lime-
stone, and syenite constituting the greater part. The granite is
porphyritic, containing felspar in large proportions. The limestone

• J. H. HamptoD, « Tin Deposits of the State of Perak." Trans. Min. Inst.
Cornwall, 1886; E B. Pike, "Mining in Perak," Trans. Min. Assoc, and Inst.
Cornwall, iii. 194; Becher, **Tin Mining in the Malay Peninsula," Trans. Inst.
Min. and Met., L

Digitized by



is a wbite orystalline mass, the relative age of which is diffidlt to
determine (variously called Devonian, Silurian, and LameDUaD), u
all evidence of organism has become obliterated. The aUayial tin
deposits which rest on these palasozoic rooks exist in the pkins,
valleys, and sullies, and are of I'ertiary age, being tm aocumnlatioa of
disintegrated rock. The beds of allnvium vary in extent and thin-
ness, and are composed of beds of sand and clay resting on tli6 tin
*' wash," and in which are found numerous trees and stamps in % good
state of preservation. The tin wash is found at depths vaiying from
2 to 35 ft, and vr^th a variable thickness of a few inches to 15 fU
producing at different points ver^ different percentages of tin ore,
from J^ to 30 per cent. The wash is composed of pebble-shaped Pig-
ments of quartz and granite, and it is this water^wom appeannoe of
the constituents that characterises the tin-producing layers. Tour-
maline in large proportions is one of the constitnents, and is jraait
in greater quantities than is usual in Cornwall or Tasmania. Wi& i
few exceptions the cassiterite is free from pyrites, and each gvun of
the mineral having a distinct existence, is easily sepaimted fiom tk
minerals of inferior specific gravity, and prepared for smelting. The
largest grains are found on the tops of some of the hills, while ti»
next largest are in the valleys near the hills, and so a diminntioD b
size is noticeable as distance from the hills is attained. Besides tb«
black tin ore, white cassiterite is of frequent occurrence, and oooasioDilij
red or ruby ore. The water in the deposits is in some cases ooc-
siderable, and the quantity experienced depends on the points tt
which the shafts are sunk, for in sinking the shaft keeps dry whik
piercing the clay, and until the sand is reached, when the oonfined
water, finding an outlet, rises to its hydrostatic surfiioe, and neoew-
tates the application of considerable pumping power until the stnti
are drained. Next to, or underneath the '* wash," is a bed of kaoiio,
or the bedrock, either granite, limcHtone, or syenite. Pockets ii^
crevices in the limestone are often found filled with tin-prodnobf
gravel, but in no case has limestone been discovered to be the matni-

In Becher's opinion, 1 per cent, of ore is a high average riohneei
for the gravel, as this represents 22 lb. to the ton, or about 40 lb.
black tin to the cubic yard ; and he considers the average pn>portii»
of gravel to overburden to be 10 per cent, of the total aUunmo,
which would thus contain ' 1 per cent, of its weight of tin or& At
the lowest computation a Chinese coolie will dig and raise 1 cab. ji
(say 3000 lb.) of ground per day. A yield of '1 per oeni or 3lh.
tin ore from this would be worth Is. ^d., which is double the ordi&sij
Chinese coolie's wage or the contract price for the job, and at titf
rate his year's work of 250 days would produce 18l. worth of 0n»
whilst he actually gets only about 02. As a m<&tter of fftct, a oooik
raises 2 cub. yd. a daj, and his average production is 800 lb. of on
per annum ; and taking it that he is actually employed 200 days ii
the year on this work only, this yield represents only 2 lb. per cob.
yd., or • 06 per cent, of tin ore in the total material, which may ^
taken as a near approach to the actual yield of the deposits togc^
with their overburden.

By the Chinese, these deposits are always worked in opoica^

Digitized by



and never by blooking ont with shafts and levels, the whole work of
mining and the treatment of the ore being a matter of the most
primitive application of manual labour. The valleys, where the
Chinese mostly work, are generally very swampy, so a big trench is
first dug, some 6 ft. deep, to drain off the surface water. The timber
is then feUed, and the paddock is marked off. The overburden is
taken off by contractors, who get paid about II. per ^' chang '* (30 ft.
square by \\ ft. deep). The size of a mine is measured by these
(^angs, 80 that if a mine is 30 changs in size and 30 ft deep it will
cost 6002. to remove the overburden. When this has been done, men
on daily wages are engaged at about 13d. a day to bring up the wash.
The overburden and rubbish firom each successive paddock is methodi-
cally filled back into those last exhausted, llius the overburden is
first entirely removed from each section, and the pay-gravel is then
separately excavated and raised to the most convenient and lowest
available place for free drainage in the workings, where it is washed
in rough sluice boxes, the largest stones in the gravel being separated
and left in the bottom. Botn overburden and pay-dirt are simply
dng by a numerous gang of men at the face, using long-handled hoes,
vho fill the stuff into small flat baskets, which are slung by rattans
b pairs, and carried on shoulder sticks by a still more numerous gang
of coolies along a gentle incline or up notched pole ladders to the
iomp. According to the distance of the latter from the face, it takes
2 or 3 to a dozen carriers to each digger. When working for him-
self^ a Chinaman will bring up 180 lb. in one journey ; on the other
band, if working on day wages, it takes a lot of persuasion to make
the same man carry 30 lb. even in the Ohinese mines.

The workings mostly carry much water, and are usually drained
rj water-wheels and Chinese pumps. The water-wheels used are
ibout 5 ft diam. and are always overHshot wheels. There is not
mly a waste of power, but also of level, as each wheel drops the
vater at least 6 ft. The Chinese pump (** kinchew *') consists of an
indless wooden chain, with wooden blades, working through a
vooden frame, and over a pulley at each end ; the whole framework
s placed at an angle, subject to alteration as t^e mine gets deeper.

This ingenious though cumbrous machine will, when in good
•rder and worked full speed, throw as much water as a 6-in. centri-
ogal, but only to a height of about 30 ft., for which maximum effect
he pump has to be about 100 ft. long, and inclined at an angle of
bout 25 . Small pumps of this form are worked bv man-power, the
mallest with hand cranks, and others by treadmills. A wheel and
^ump about 60 ft. long costs about 602., and the monthly keep
rould run to quite 102. In places where water is plentiful, they are
heaper than engines. There is an instance of one of these chain
umps having been run by a steam-engine in Perak with great suc-
ess. Where water-power is not avaUable, or the water is all required
ift sluicing, steam-engines are used for pumping, and consequently
nable the mines to be worked during seasons of drought, when the
^ater-wheels cannot be used. There are now some 300 such plants
1 use, consisting of engines of 4-10 nom. h.p. and pumps up to
in. discharge. The Malay miners confine themselves to the side-

2 8

Digitized by VjOOQIC


Hill or " lampan " workings, whicli need no (draining or machinory.
They begin by diverting a stream, and, when it is possible, nwDingit
at a height and allowing it to drop on to the fece they want to work.
The water falling on the soil disintegrates it, the stuff then ronnin^
into long sluices with riffles, and being continually stirred up witii
spades to prevent caking. When the gravel is nearly run off, the
residue is taken out and washed, sometimes in pans and sometimeB in
short boxes. This system has led to the suggestion that modem
hydraulicing methods might be applied to the less rich gravels lying
at lower levels, such as the valley deposits now worked by stripping;
but it seems very doubtful whether the flat, forested, or agricnltunl
country would admit of any such operation on a large scale.

Lodes have been recently discovered in the State. In Einta, tiiev
mostly occur in the limestone, and yield copper, sulphur, iron, aiBSuc,
and tin. Up to the present no great depth has been reached, bat
from the sniface down to 30 ft. most of the lodes give great pronuse
of being rich in tin. At the Mahlembu Co.'s claim, large quanti^
of ore are being shipped to Glermany, for which the Company are
receiving in some cases 13 per oent. for white tin.

The great preponderance of small mine owners and petty workings
is one of the features of backwardness and limitation of profit in ^
development of this field. Not only is the ontput less per head of ^e
mining population, owing to the lesser efficiency of small partw
without adequate appliances, but much ground is spoilt, and a laife
proportion of the mineral it might afford is wasted by desultory and
unsystematic operations.

Land can be obtained from Government on a 21 years' lease, and
hand fide work must be commenced within 6 months, an average o^
2 men per acre to be employed, unless the land is too poor to wamnt
such expense. All water and water-courses are the proper^ of
Government, and on new land sufficient water to wash with is giveti
out by the Inspector of mines. The duty on tin, coUected by tbe
Government, is 10 per cent.

The tin deposits of Banca, Billiton, Singkep, and other points in
the Dutch East Indies, are mainly alluvial, although some lodee
supposed to be 6f recent origin have been worked. The bed-rock ef
the country comprises granite, metamorphic slates, qnartzitee, and
sandstones. The cross-section of the Banca deposits would shov,
following from the bed-rock upward, an average of 3 ft. of tin ore over-
laid with coarse sand, followed by red, white, and black day ; then
coarse sand with pockets of clay, and layers of fine sand carrying »
little tin ore; then humus. The average overburden is 25-30 ft
thick, and the yield from the pay streak about • 1 per cent The tin
of Banca and Billiton has been traced to its original sources — ^tbe
veins in the granite and gneiss. Veins are also found cutting thrtmg^
the overlying quartz-schists, clay-slates, and clay-sandstones, bit
very little lode mining has been profitably done. Only about oaje-
quarter of the Banca and Billiton tin requires refining; the "bl*<i
tin " averages 71 per cent, in white metal, and the loss in smeltiiig i*
given at about 3 per cent.

Stream tin has recently been found in some quantify in the S^

Digitized by



distriot of Sumatra, in oreek beds overlying granite, with 26-30 ft. of
oTerbnrden, the pay streak yielding about 1 per cent, metallic tin.

The tin deposits of Tasmania * may be grouped as : {a\ alluvial
deposits ; (b) lodes and veins ; fc) impregnations or stockworKS. They
are generally confined to districts composed of granite or penetrated
by quartz-porphyry dykes, but at Mount Lyons tin ore is found in
Silurian strata, 18 nules from the nearest known granite, though
probably the granite lies below at no great depth. The principal
alluvial workings are in the north-eastern district, along the vallevs
of the Bingarooma and George's rivers and their branches; the
deposits are of different ages, from Miocene to recent. Some of the
older drifts are capped with basalt, and are worked by underground
mining, but the most tin has been got from shallow workings by
ground sluicing. The easily-obtained ore ( • 75 per cent.) is now pretty
well worked out, and hydraulic sluicing of the larger and poorer
deposits is being more and more resorted to. There are still large
areas of deep ground to be worked, and tin should be produced from
these for the next century at least. In this part of the country the
ore appears to be derived from small veins in the granite, and from
stockworks rather than from true lodes, for only^a very few of the
latter have been found, and none has yet been profitably worked.
On the Blue Tier the stockworks have been attacked with some
Boccess; in these the tin ore impregnates a much altered quartz-
porphyry, which appears to be intrusive through the main country
granite (felspar-porphvry). The average value of the rock is quite
low (i-lj per cent, black tin), but as the stuff is in very large
quantities, and can be worked in open quarries, it is possible to make
it pay. The Anchor mine has opened its deposit over an area of 8-9
acres, and has made profits with only a small and inefficient plant
from rock yielding on an average *94 per cent, black tin. With
^Tge plant and good appliances, there would be a very large pro-
iuction of tin from these deposits. True lode mining nas been but
Little attempted as yet, and with poor success, though lately the out-
look has become more promising, owing to the discovery of richer
uid larger veins. The celebrated Mt. Bischoff deposit, which yields
learly one-half of the product of the Colony, is partly an alluvial
Irift and partly a lode, while tin ore also occurs in it impregnating a
topaz-porphyry ; it therefore combines features of all three classes of
in ore deposits. A dyke of eurite and topaz-porphyry has been
ntruded through metamorphic slates and sandstones of Silurian or
^jrchsean age, and along the contacts and in fissures produced by the
jitrusion, tin ore, associated with much arsenical and iron pyrites
Lnd pyrrhotite, has been deposited. In the lower levels the unaltered
mlphides are met with, and require to be roasted to set free the tin
)re ; on the surface, however, the ore is quite oxidised. The Brown
?*aoe is an immense mass of gossan containing tin ; it is worked as
in open quarry 1000 ft. wide and 100 ft. high at very low cost. The
ode, which in the underground workings appears as quite a small
rein, seems to have widened out to a great size at the present surface

^ J. Bowe, ^ Tin Mining m Tasmania,*' Trana. Min. Inst Cornwall, 1886 ;
i. Montgomery, '* The Minem Indnstry of Tasmania," En. and Min. Jl.

2 s 2

Digitized by VjOOQIC


workinj^. Important discoveries of tin ore have lately been made at
North Dundas, the Meredith Bange, and at Bell Monnt, and it seems
likely that the tin-mining industry will increase in importance ratlttr
than fall off- At Bell Mount it may be noted that the tin orB is
closely associated with bismuth carbonate, specimens being obUin-
able containing both minerals intermixed, an nnnsnal oombinatian.
Miners' wages run high — 8Z.-10Z. a month, and driving ordisarilj
costs 4I.-5I. a fathom.

Australian* tin is generally found in connection with euritic
granites, though sometimes the stanniferous granite passes into a

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 71 of 76)