Charles George Warnford Lock.

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

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Rn>ridngs are quite extensive, &e total length of the several galleries
)eing about 2 miles. The opal-bearing rock is not disposed in vein or
led form ; on the contrary, the precious stone is found in nests or
>ock6t8, and it not unfrequently happens that a considerable distance
oay be passed in workings without uiowing a sign of an opal.

Although the iridescent varietv alone possesses a commercial value,
t is of interest, from a mineralogical standpoint, to note the fact that
11 the varieties, milk opal, wax opal, fire opal, and hyalite, occur here
n abundance. The last-named mineral is often found in most graceful
talactitic forms. The origin of the opal by the infiltration of water
)oiktaining silica in solution, is here demonstrated in the most con-
rrncing manner. Large precious opals, it is said, are now rarely found ;
10 specimens of the size of a hazel-nut have been found for a number
tf years. Formerly the mines were worked by private individuals,
•nt since the year 1788 the proprietorship has been assumed by the
Jrcvemment, and the workings are conducted under Government super-
k-ision, affording at present a yearly revenue of about 15,000 florins



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246 ECONOMIC MINING.

(1200t). These opals vary in value from IZ. to 6/. a carat, and even
higher, and are almost the only ones employed by jewellers.

The Mexican and Honduras stones come from Esperanza, Amealeo,
and Beal del Monte, oocnrring in a porphyritic formation. They are
beautiful when new, but soon lose their beauty, and are worth only a
few penoe a carat. S. Auslralia is said to afford a few specimens re-
sembling the Hungarian ; and some of particular beauty are reported
from B^chworth, Victoria. A few have been found near Col&x,
Washington, in a much altered basalt.

JBtiby. — In composition the ruby varies from almost pure alumina
to a compound containing 10-20 per cent, of magnesia, and always
about 1 per cent, of iron oxide; hardness, 9; sp. gr., 4* 6-4-8;
colour, various shades of red. The ruby is essentially an Eastern
ffem. One celebrated mine is situated about 20 miles from Ish-
kashm, in a district called Gharan, on the right bank of the Oxus.
The formation is either red sandstone or magnesian limestone, easOj
worked ; the stones occur encased in nodules in seams and spots in the
rock. Superior gems are found at Mo-gast and Eyat-pyan, 5 days
8.E. of Ava, the workings being a monopoly of the King of Burma.
Perhaps the finest come from a district between the north-east of
Mandalay and the west of the Upper Solween river. Another noted
locality is at the foot of the Capelan Mountains, near Sirian, in Pegu,
where fine rubies are not rare ; also near Eandy, in Ceylon, where
good stones are very scarce. One has been found near Mount Eliia^
on Port Philip Bay, Victoria ; also one in Queensland ; and another
in New Zealand. Bubies of pure colour and &ir size are the most
valuable of all gems.

The search for these gems in Ceylon centres around Batnapura. inj
a district 20 to 80 miles square, in almost all of which a stratum of
gravel 6 ft. to 20 ft. under the surface exists. Throughout this area
gem-pits are to be seen near the villages, some being worked now.
others being abandoned. The natives work there in companies of oj
to 8, and pay 1 rupee per man per month for the privilege of working
a certain allotment where they begin by marking off a square of abont
10 ft. After removing about 3 ft. of soil, the sounding rod, a piec^
of iron about \ in. diam. and 6 ft. long, is used to sound for the gravel
If successful, the digging is begun in earnest till about 4 ft. deep. Oc
the second day gravel is taken out by means of baskets handed frooj
one man to another till all within the square is excavated. Shonld
the miners find the soil fairly firm at the bottom of the pit they tunne
all round for about 2 ft., drawing out the gravel and sending it oj
also to be heaped with the rest, which usuaUy completes the work (^
the second day, a watchman remaining near it all night. On the thirt
day^ it is all washed in wicker baskets by a circular jerking motioi]
which throws out all the surplus light stone and rubbishy till a go^j
quantity of heavy gravel is left in the bottom, which is oare^
examined. There is hardly a basketful that does not contain so
gems of inferior value, which are usually sold by the lb. for ab<
9 rupees. Should no valuable stones be found, another pit is sv
and so on till one or perhaps two or three really valuable guns
unearthed. A lower stratum of gravel is said to be richer in ga



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NON-METALLIFEROUS MINERALS. 247

Imt is raroly worked on aooount of the difficulty of removing the
rater.

In Siam, the method of obtaining the precious stones is identical
it all the diggings in the region of Bangkok, and is as follows : — The
intending digger, on entering the district, pays 3 ticals {hi. 3d.) to the
Uadman, a Burmese British subject appointed by the British Legation,
nd responsible to the governors of Battambong and Chantubong,
kooording as the fees received are derived from the Phailin or Krat
nines. Beyond this tax there is no further fee exacted. The Siamese
Sovemment claim no right to pre-empt gems found, or to purchase at
Mrket value all stones above a certain carat weight, as was the case
EA Burma. The Tongsoo digger's first object is to discover a layer
|f soft, yellowish sand, in which both rubies and sapphires are de-
iDtited. This stratum lies at depths varying from a few inches to

10 ft on a bed of subsoil, on which no precious stones are found. A
hit 18 dng until this corundum is exhausted, and the soil removed is
jkea taken to a neighbouring canal or stream, one of which runs in
ibB proximity of the mines, both at Phailin and Krat, where it is mixed
rith water, and passed through an ordinary hand-sieve. In his search
br this peculiar alluvial deposit, which is generally free from any ad-
loxture of clayey earth, the digger has often to penetrate into the
jangle that grows thickly around, and to combine the work of clearing
■ith the occupation of gem-digging. The Tongsoos do not appear to
brm themselves into companies for mutual assistance or division of
Ifofits. They work principally in twos and threes, and if chance lead
ikem to discover a gem of any value, they either undertake a sea voyage
k> Bangoon or Calcutta for the purpose of obtaining a good price for it
Ibemsdfves, with the dealers in precious stones at these places, or oon-
ign their acquisitions to an agent, while they themselves continue to
^Nurch for more. A process of migration is continually ^ing on
toongst the Tongsoos of the different mines, the workers passing from
ice to the other, according to the reputation of a particular mine at
■tttain periods. No artificial or mechanical processes for the washing
■ the soil have as yet been introduced, nor have gems been discovered
^ fissoi^ veins of soft material imbedded in crevices of hard rock, or

11 crystal form. Bubies and sapphires are found at all the digging,
iften deposited side by side in the same layer or stratum of sand. The
f»by of " pigeons' blood " colour is rarely, if ever, met with. The
llkmr of the Siam ruby is usually light red of a dull hue. The sap-
ilnre is of a dark, dull blue,, without any of the silken gloss which is
pe distinctive mark of the^fBurma and Ceylon stone. Stones resem-
bliBg garnets rather than rubies are found in the dried beds of water-
leaxses at Baheng, 200 miles north of Bangkok, and there is every
g S Mon to believe that rubies also equal, if not superior, to those dis-
ivrered in the south-east, exist throughout the Baheng district Those
ktkerto obtained are the result merely of surface scratchings by Tong-
IDO seekers.

I Sof^lwre. — Composition, about 98*5 per cent, of alumina, with
jnde of iron and other colouring matter; hardness, 9; sq. gr.,
4* 6-4- 8; colour, from translucent yellow or white to violet. Sap-
fikoes of great beauty are found in and near the Iser Mountains, in



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248 ECONOMIC MINING.

Bohemia, and in ilie bed of the river Iser, mostly in qnartz-sand sim
granite detritos. In Ceylon, good sapphires are not rare. Quite i
msh recently took place to the mines of Battambong and Chantn
bong, in Siam, whence a stone of the finest water, weighing 370 cant
in &e rongh, is credibly reported. Bine and white stones of som
▼alne have been found in IXuidenong Creek, Yictoria; at Balluai
S. Australia ; and in the Hanging-n^ caves, near the Pearl Biva
New South Wales.

Most of what has been said about rubies refers also to sapphiia
the two gems being intimately related and generally found t(^etliei;

Tcfoz. — Composition, 34 per cent, silica, 57 alumina, 15 fiuonse
hardness, 8 ; sp. gr., 3*5; colours, yellow, blue, and white. In Saxon]
is found a pale-violet variety ; and in Bohemia, a sea-green. Hur
occur in the Urals, north of Katharinburg, in granite and albite ; as
in E. Siberia. In the Brazilian province of Minas Geraes, nunb^
are met with in the auriferous gravels, especially at Capao. Son
fine specimens have been got at Beechworth, Victoria, in Flindei
Island, and in Tasmania.

Twtqwjue, — Composition, 47 alumina,^ 27 phosphoric acid, 3 lin
phosphate, 2 copper oxide, 1 iron oxide, 19 water ; hardness, 6 ; 8p.g1
2 * 6-2 * 8 ; colour, blue to blue-green. The Land of Midian possess^
three turquoise mines : one at Aynuneh, a second near Ziba, and
third, known to the Bedouins as Jebelshehayk. But the stones cob]
principally from the motmtainous district of Nishabor (Neshapore), i
N.E. Persia ; the oldest mine is in the Bari Mad&n btiMl:, and a seoos
has recently been discovered in the hills to the south, separating Nisi
abor from Turshiz. Mashhad is the headquarters of the trade. BetU
stones at lower figures are said to be procurable at Shikapur, in SiiM

The number of small or seed turquoises of light tint found in tb
Persian mines is enormous. Becently 1} lb. of the better grade (
second-class stones were sold in Teheran for about 7/. sterling. Stoine
of a dark sky-blue tint are comparatively scarce. All the mines (
Ehora£san are farmed by officials connected with the Gov^mmen
For this privilege they pay 18,000 tomans annually to the Shah, a bid
equivalent to 6000/. The best stones are sent to Europe, and thei
is at present no evidence of exhaustion in the Persian mines.

During the past two years turquoise has been actively mined i
New Mexico, at Los CeriUos and in Grant County. The latter miiM
produce stones having a faint greenish tinge, which is either due 1
a partial change or metamorphism which has taken place while tli
turquoise was in the rock, or may be a local peculiarity, but it i
claimed by the owners of the mine that they are not subject to
change of colour. Turquoise has always been known as an unstal^
gem. Even the finest Persian stones are likely to change occasionall
with scarcely any warning, the alteration probably being due to tli
turquoise coming in contact with add exhalations from the skin, c
fatty acids or alkalies in the soap used to wash the hands.

The sale of turquoise during the year 1891 from the New Mexica
localities probably amounted to 25,000^.



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NON METALLIFEROUS MINERALS. 249



GBAPHTTE.

Ths mineralised snbstanoe popularly known as blacklead or plumbago,
ftnd more correctly as graphite, is generally conceded to be of organic
origin, the result of ^e metamorphism of some of the products of
destraotiYe distillation of vegetable tissue. It consists essentially
of carbon, in mechanical admixture with varying proportions of
ulioioiis matter, as clay, sand, or limestone. Gleologically it occurs in
fonnations ranging from the Carboniferous back to the oldest rocks,
4nd notably in dose relation to gneiss. Sometimes it is found in beds
and in tme fissure veins, at other times disseminated through schists.
Tein graphite is usually associated with calcite and quartz, and less
frequently with apatite, mica, and pyroxene. Bed graphite is com-
monly amorphous.

By far the greater proportion of the yearly product of graphite
DOW comes from Ceylon. Analysis shows the following composition : —

Per cent.

Carbon 98-817 to 99-792

ABh -05 „ -415

Volatile matter '108 „ -9

But the quality and commercial value of graphite depend more
apon physical structure than upon chemical composition. Thus the
LTystallised graphite of Ceylon, in which only 1*2 to 6 per cent, of
\ormffi ingredients exists, is not fit for pencHs ; while the '* black-
lead " from Borrowdale, in England, with 13 per cent, of impurities,
\ijhs been found to be very well suited for their manufacture. For
Lhe making of pencils, only a compact, grain v kind is suitable ; while
for cmcibTes, the loose mould, with grapnite appearing in shiny
icales, is preferable. This kind generally occurs with an enormous
unount of mineral matter, unequally diffased through the mass, and
producing thus, even in small hand-pieces, respective dififerenoes in
tA mecific weight.

The most valuable kind of graphite is, of course, that which is
kp|>licable for the manufacture of pencils ; but it is seldom found. A
^markable example was the Borrowdale mine, Cumberland, now
warkbdi out. With the diminished supply of Cumberland graphite,
■rhich needed next to no treatment, have come improvements in pre-
lAration whereby inferior grades have been reudered available. This
uainly consists in separa^g, by grinding and levigating, the hard
.od impure portions of the rock. The commercial value of a new
Ample of graphite cannot be appraised without actual trial of its
inafities for tne specific purposes aimed at. The market values of
lie article cover such a wide range as from 9/. to 5000Z. a ton. The
ordinary product, adapted for crucibles, pencils, stove-polish, bearings,
^c^ as imported from Ceylon, is divided into four grades. " Large



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25© ECONOMIC MINING,

Inmp" and ''ordinary lump" are worth abont 18Z. to 20Z. a ton;
"chip," about 15L; and "dust," about \2h The exports amount to
about 10,000 tons yearly.

A large proportion of the Ceylon graphite, on which the world's
supply really depends, is mined by small native owners in a most
primitive and wasteful manner.

The influx of water into the workings, even in small quantity,
causes a cessation of operations and is soon followed by a caving of
the walls and roofs of the tunnels and shafts, whereby in many
cases the unworked portion of the deposit is buried from view and
probably altogether lost. It is a very great pity that the whole
graphite mining industry of the island is not placed under proper
control, so that while advantage is taken of the cheap local mining
labour, yet that operations may be conducted systematically and
economically, and to far greater depths than is possible to the unaided
native miner.

Crermany possesses several graphite deposits. A variety about
equal in purity to that of Cumbenand, but somewhat more amor-
phous and friable, occurs in considerable quantities at Griesbach, neai
Passau, in Bavaria. It is not refractory, and is therefore valueless for
crucible-making, and is of little use as a lubricator ; but for pencils
it is largely employed, and is imported into England, for making
domestic blacklead (stove-polish). In the Adelheids-Gluck coal-mine,
at Kybnik, Prussian Silesia, an important layer of graphite earth bAs
been foimd, in thickness exceeding 40 ft. Trials are said to hare
proved it well fitted for luting, muffles, hearths, <&c. A specimen of
graphite from Styria exhibited coarsely foliated structure, strong
metallic lustre, and sp. gr. 2*1443. Its composition was: — ^Uarbon,
82*4; silica (belonging to the ash\ 12 '38; alumina, 3*9; iron per-
oxide 0*53; manganese protosesquioxide, 0*62; lime, 0*02; alkalies,
traces. The production of graphite in the Austro-Hungarian Empire
is about 20,000 metric tons yearly, half of which is raised in
Bohemia. Spain has lately sent some graphite of fair quality to
this country. An analysis of Portuguese graphite gave: — Water
(including hygroscopic), 10*21 ; carbon, 38*47 ; ash, 50*81. A sample
from Upemavik, Greenland, hard and of pale colour, useless fo^
pencils, showed: — Carbon, 96*6; ash, 3*4 per cent. An occurrence
of graphite with quartz is reported from Arendal, Norway. Tin
mineral has also been found in Finland.

The distribution of graphite in Asia is by no means inconsiderj
able. A deposit, said to be very abundant, has been discovered iJ
the Bagoutal mountains of S. Siberia, near the Chinese frontier, «
which great things are predicted. Seebohm, in 1879, brought abonl
20 tons of almost pure graphite from the banks of the Eiireijka. Th^
deposit is leased by a Bussian from his Gk>vemment, and has not ye^
been the scene of anything like scientific working. Two samples oj
Siberian graphite from Stephanovsky respectively revealed on analysti
the following composition: — Carbon, 36*06, 33*20; silica, 37*72
43*20; ferric oxide, 4*02, 3*05; alumina, 17*80, 16*42; lime aa^
magnesia, 1*20, 1*06; volatile matters, 3*20, 4*03; sulphur, trac«
0*04. English graphite is said to be imported into Busaa, W



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NON-METALLIFEROUS MINERALS. 251

admixture with the low-grade native produce. Deposits of lamellar
gnphite have been found in several parts of India. In 1862 a new
mine was discovered at Sonah, near Goorgaon. The mineral is found
in niamee of variable size, and generally quite detached. In some
cases Uie surrounding rook is impregnated with graphite, mixed with
snail micaceous particles. It yields on analysis: — Carbon, 78*45;
silica and alumina, 12 * 98 ; iron peroxide, 3 * 30 ; lime carbonate, * 84 ;
watw", 4« 35 ; alkaline sulphates and chlorides, • 08. Japan produced
about 3500 tons in 1889, and 4500 in 1890.

The American production of graphite is almost entirely from the
mines at Ticonderoga, N.Y., and its neighbourhood. The output had
not much exceeded 200 tons of refined graphite in any year before
1891, when it reached about 700 tons, with an approximate average
Tilue of 352. a ton. The old mines by which the place is best known
are on a series of elliptical chimneys in gneiss which are filled with
cftlcite and graphite. They were long since exhausted. The present
aouroe is a graphitic quartzite or schist in the town of Hague, N.Y.,
some 5 miles west of Lake George. There are crystalline limestones
near Lake Champlain which also contain graphite, and might furnish
the mineral. Any rock employed for this purpose must be free
from mica, for it is impossible to separate two s(^y minerals in the



A crude graphite, adapted for the manufacture of crucibles, stove
tracking, <&a, is found in conjunction with anthracite coal in Bhode
bland. Graphite is also mined in Pennsylvania, Michigan, and
Wyoming. Other deposits are known, but none is worked. Most
of the graphite used in America comes from Ceylon.

The rock consisting of about 10 per cent, graphite and the re-
Eoaindor quartz, which is worked at Lake George, is crushed in a
battery of California stamps and then washed with buddies and
lettlers, the percentage of graphite being thus raised to 40 or 50 per
sent. This product is further treated at Ticonderoga by a secret
vaabing process, whereby the grade is raised to 99 per cent.

The Styrian graphite undergoes no preparation for market beyond
nmple screening, which suffices to produce an article containing 73-
^ per cent, of the actual mineral, the bulk of the impurity being
dUica, which renders it refractory and well adapted for crucible
naking.

The Bohemian article is softer, and is partially sorted underground
nio three classes. The first and second grades only need hand-picking
tnd drying to be ready for packing in barrels. The third grade,
prhich is harder and less pure, is ground in excess of water, and
settled to get rid of the heavy gangue ; the graphite slimes are after-
irardB pumped into filter presses, and the cakes taken from the presses
kre dried for market.

Graphite is largely used for pencils, and as a lubricant, for both
>f which purposes it must be soft and of high grade. Lower grades
kre used for crucibles, stove blacking, foundry facings, and as a
mbstitute for redlead in pipe-fitting. It is also being extensively
smplqyed as a paint for covering smoke-stacks, boilers, tin roofs, &a,
saving been proved to be very durable. Eecent experiments have



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252 ECONOMIC MINING.

shown that a graphitic lining for Bessemer converters is specially
adapted to withstand the cutting action of acid slag, and a large
demand for graphite has come from steel works in consequence, espe-
cially in Germany,^ where this material has been adopted by the Kmpp
Works. Thus, the imports of graphite into Germany, from Ceylon,
are said to have increased from alx>ut 3100 cwt. in me year endiog
June 1, 1889, to 14,215 cwt. in 1890, and 11,000 cwt in 1891.



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NON'MEIALLIFEROUS MINERALS. 253



GYPSUM.

. TERT oommoD mineral product is the rock Icnown as gypsum or
tftster, which occurs in two forms, the more familiar being a hydrated
dphate of lime containing about 32^ per cent, lime, 46}^ sulphurio
nd, and 21 water, while the other is an anhydrous variety (called
ihydrite) consisting of over 41 per cent, lime and 58 sulphuric add.
oth forms are encountered in most geological formations, but are
rpecially prominent in the Triassic salt-bearing series. The mineral

applied chiefly to two purposes — the preparation of plaster or
noco, and as a fertiliser (called " land plaster " in America). For
te latter application, all samples may be said to serve equally well,
id only require grinding, which, indeed, is often dispensed with,
or use as plaster, however, the value of the article depends on its
nlity, after calcination, to " set " very rapidly on admixture with
ater, and consequently anhydrite is not applicable, being cdready
ee firom water. Puri^ of colour is a desideratum.

The beds of gypsum of most importance in the plaster manu-
cture occur in 5ie neighbourhood of Paris, in the Lower Tertiary
nnation. Different beds vary in respect of character and quantity
' admixed materials, and in the structure of the gypsum itself.
Tith regard to the first point, some deposits contain a notable pro-
xtion of lime carbonate, a fact which under certain circumstances
ay considerably influence the character of the plaster. In the
atter of structure two principal varieties occur: grantilar and
tn^os. Further, hardness of the granular kind varies considerably,
bese differences of structure in the original material appear to exer-
ie an influence on the properties of the plaster. Thus plaster formed
cmi the granular variety sets more gradually than that derived from
le fibrous, and forms a denser mass. The so^r kinds of the granular
fpsom are those principally used in the production of plaster for the
cmlds of potteries.

In the old-fiashioned process which is still employed for making
le common kinds of plaster, the material is exposed to the direct
iion of flame. Large lumps are placed in tlie lower part of the fur-
ioe« above them smaller lumps, and, after the heating has been
OTied on for some time, finely divided material is filled in at the top.
he outer portion of the larger lumps is always overbumt, and in the
pper part of the fa mace the presence of shining crystalline particles
a&erally indicates the fact that some gypsum has remained un-
umged. Provided that the amount of unbumt and of overbumt
aterial does not exceed about 30 per cent, of the total, the plaster is
dtable for many applications.

Bo^ the differences in time of setting and in hardness of the
jsulting material are affected by the mode of baking. The hardest
aterial is frequently obtained from the quick-setting plasters, but

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2S4 ECONOMIC MINING.

for certam purposes tliifl rapidity in setting is of great practical in-
oonvenience. The moulder in pottery work must have leisure to fill
in every detail of a design, often complicated and intricate, before the
material with which he is working becomes intractable. Thus, for
many of the more refined purposes to which plaster is applied, extreme
hardness in the set plaster is of less vital importanoe than a oonyenient
period of setting. On the other hand, plasters which set very dowly
give, as a rule, too soft a material, as well as being inconvenient is



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 28 of 76)