Charles George Warnford Lock.

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

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machine to assist in forming a '* puddle '* of sufficient density to flott
the lighter stones in the pan, and allow only the heaviest gravel to
accumulate at the bottom. At the end of the day's work the machine
is stopped, and the contents of the pan are taken out to be submitted
to a cleaning process by means of the pulsator, cradle, or small gravi-
tating machine. It is then brought to the sorting table. Great caie
must be taken in fixing the pans truly leveL To test the efficiency
of the machines, it is the practice to put in a few inferior or curiously
shaped diamonds which may be easily recognised by the watchers.
These are called tent stones, and, if the machine is working well, are
invariably found again amongst the residue in the pan.

The cradle machine consists of a tier of 2 or 3 square sieves on a
pair of rockers. The top sieve is the coarsest and retains the largest
stones, whilst the mud and sand are washed through.

The river diggings may be said to be all in alluvium, which con-
sists of a heavy deposit of ferruginous gravel mixed with red sand and
boulders. The same, no doubt, was washed and imbedded in the
crevices of the rock by floods, as a large number of river diamonds are
found coated with oxide of iron, and, if cracked, it will be found that
this has penetrated. As a natural consequence the stone is discoloured,
and this has a tendency to interfere with its value, but notwithstand-
ing this, they are generally free from faults and flaws.

Sometimes a portion of the old river bed is found, where the stones
as a rule are very good. Explosives are seldom used. The boulders
and large stones are thrown aside, and the diamantiferous gravel is
excavated with pick, shovel, and crowbars in the ordinary way. Tliis
gravel varies at various diggings. The average will be found to be
in something like the following proportions : one of boulders, which
must be thrown away, one of rough stones, to be served likewise, one
of fine sand, and finally, the productive gravel which remains to be
treated. The following is the chief mode of their working and
washing. There is a sifting machine termed " baby " which oonsists
of an oblong sieve, about 5 ft. long, and of very fine mesh. It swings
by 4 ropes, or thongs, sometimes by small chains. It is fixed, as a
rule, with 4 nearly upright poles, slightly inclined, so that the gravel
may roll over it. At the top, or feeding end, a sieve about 2 ft. square
is fixed over the baby, and this will admit of small pebbles passing
through. The ground taken from the claims is put into the square
sieve ; the native or boy standing at the head swings it to and fro,
and thus makes the separation, the roughs and finest being thrown
away as refuse. The medium size gravel which has been caught at
the bottom end of the baby, as a rule, contains the diamonds. If
there should be a large stone it ought to be immediately noticed by
the man who is placed at the head or top of the machine, and whose
duty it is to continually throw the rough stones out in order to make
room for the other ground to be treated. Any diamond so small a?

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to pa88 thnmgh the sieve with the fine sand is not worth the trouble
of searching for. This process is called dry sorting. In the next
(" wet " or " gravitating ") use is made of a round sieve, similar to
those used in copper mining, with the handles taken off, so that when
the serving is settled by its operator, it is taken up out of the water,
and turned upside down on the sorting table. If he has managed his
work properly, all the heavy deposits will appear on the surface of
the mould or bottom contents of the sieve, and consequently, at a
glance, the diamonds, if there should be any, would be discovered.
To guard against the risk of losing any, he dissects the whole of the
contents of the sieve with what we should call a scraper, known to
him as a sorting knife. After a careful examination the whole is
hrnshed off from the table to continue the treatment of a fresh supply.
An ezperienoed sorter can tell from the appearance of the deposit
whether there is a chance of finding or not; finding the heaviest
itones that occur in diamond-bearing gravel is a sure sign of the
presence of these precious stones. This is particularly the case if a
peculiarly marked pebble, streaked with a succession of parallel rings,
known by the name of " Banddoom," the specific gravity of which is
almost the same as the diamond, is present, and where the former is
/bund the latter may be confidently expected. The average quantity
of maiden ground that a man can excavate per day is about \\ loads
of rough gravel and sand, which, after being put through the machine
ur baby, yields \ load of pebbles to be washed, costing for picking,
sifting, and vrashing, 2<. 6kl. per load of 22^ cub. ft., or thereabouts.

PBODucnoN OP Diamonds at thb De Beebs Consolidated Mines.









Value per


on Floors,


of Year.

•9 , 944,706
» 5,192,226
a 1,978,153
n 3,338,553






£ «. d.

901,118 5
2,330,179 16 3
2,974,670 9
3,931,512 11 1





£ «. d.

19 8j

1 12 61
I 9 6
1 5 6

«. d
9 10}
8 10}
8 8
7 4f


• And Du Toil's Pan and Bultfonteln 454.278.
Touk. 7^430,722 cftralB, valued at 10,148.3102. \U. Od. Dividends paid since 1888, 2.840,9361. ISi .

Dividends Paid.





Jane 30


£ i.

188,329 10
394,786 10
394,895 10
394.895 10
394,895 10
394,895 10
493,619 7
493.619 7



Equal to


10 I
10 \
10 \





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Seoond in importanoe among diamond-producing oonntries is
India, where, according to Ball,* are 3 extensive tracts, widely sepa-
rated from one another, in which the diamond is known to occur ; and
others where, although the fact of the oocnrrence of diamonds his
been recorded, information in reference to the circumstances connected
therewith is less perfect.

The most southern of these tracts, or part of it, has long home a
familiar name, which, however, must be characterised as being, to a
certain extent, a misnomer. Goloonda (Eala-Eandar), itself neTer
produced diamonds ; it was, in fcujt, merely the mart where they were
bought and sold. The districts included in this southern tract, in the
Madras PresideDcy, where are or have been diamond mines, are Eada-
pah (Cuddapah), Bellary, Eamul, Eistna, and Godavari.

The second great tract occupies a considerable area between th«
Mahanadi and Godavari rivers. Although diamonds are known but
from two neighbourhoods within it, still it is not improbable that the
diamond-bearing strata may have a wide range. The two neighhonr-
hoods referred to are Sambalpur, with the bed of the Mahanadi for
many miles above it, and Wairagarh or Weiragud, 80 mil^ to the
south-east of Nagpur. Again, as an outlier to this seoond tract, aia
two or ttiree localities within the province of Chutia Nagpur, where
diamonds have been found.

The third great tract is situated in Bundelkhand, near one of the
chief towns in which, Panna, some of the principal mines are situated;
but there are others scattered about in various parts of that province.

At Panna diamonds are only known certainly to occur ui Mte in a
conglomerate which is referred to the Bewah group (Upper Tin-
dhyan). There, however, as elsewhere, are numerous workings ia
alluvial or superficial deposits ; but the greatest amount of labour is
spent in mining in this the bottom bed of the group, which, thou^
it has a wide extension, has onlv as yet been ascertained to be diamoE^
bearing in the neighbourhood of Panna town. Although diamonds
have not been obtained directly from any lower group, it wooli
appear that this conglomerate is largely made up of pebbles derived
from the lowest or Semri sandstone group (Lower Yindhyan), and
since it is stated by the native miners that diamonds are sometimea
found in these pebbles when broken up, it would seem that tJie lattac
mnst include an earlier, if not the original matrix of the gem. Thif
point is of great interest, since it brings us to a horizon, the base ol
the formation, which is strictly comparable with that of the Banagao-
pilly group (Eamul), which includes the lowest known matrix ii
Southern India.

The ordeY of succession of the rooks in the Mahanadi-Gk>davaii
tract has not yet been fully ascertained ; but from the fact of the onlj
known localities where the diamond occurs being situated on thi
margins of the area, it may with a considerable degree of probi^liQ
be assumed that the matrix is in a bed dose to the base of the fomi*

Some interesting remarks by Griesbach have been published njMi
the correlation of the Vindhyan rocks of India with certain
♦ * Economic Geology of India/

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occnrriBg in South Africa, to one of which the sandstones of the
Table Mountain belong. The possibility of the original matrix of
the Cape diamonds belonging to a period or horizon directly com-
parable to that which includes the Indian diamonds, is a subject
worthy of fdture investigation. It is noteworthy that a rock very
similar to Indian laterite appears to occur in the same parts of Africa,
and that the Glondwana rocks are also represented in that country.
A comparison of the geology of Borneo with that of India may also
prore productive of interesting results in this respect.

According to King, the quartzites of the Banaganpilly group
form a cap, resting unoonformably on the denuded sunace of a much
older set of shales and traps with some limestone bands. The
quartzite covering is 20-30 ft. thick, and it is pierced here and there
»ver the Banaganpilly end of the hill by shafts of 15 ft. or less, from
the bottoms of which nearly horizontal galleries are run to get at the
earns of diamond gangue. The capping is composed of compact grits
md sandstones in thickish beds above, and somewhat thinner bedded
towards the bottom.

Externally the rocks are hard and vitreous. At the level of the
Series there are beds of coarse pebbly conglomerate, occasionally a
breccia, which are sandy and clayey, and with these run seams of
Qore shaly and clayey stuff. There is no trace of the clayey
onstitation on the outside along the outcrop, nor are there any
iistinct bands of shales ; there are only some sandy shales down at, or
ear, the bottom of the series.

In the mines the coolies pick out a seam about 6 or 8 in. thick,
ocnrring with thicker and harder beds of sandstone, as the diamond
ijer; this rock is an easily broken-up, damp, clayey conglomerate,
id partly breociated, of small rounded fragments and pebbles of
lack, red, green, and pale coloured shales and cherts, and of quartzite
ith large and small grains of dirty and pellucid quartz. The
mgne is pounded up, washed, sifted, and laid out to dry on prepared
)or8, after which the residue of clean sand is carefully examined in
le hand, by the women and children of the working parties, for the

With r^ard to the origin of the Sambalpur diamonds, the
)ological structure of the country leaves but little room for doubt
to the source from whence they are derived. Coincident with
eir oocurrenoe is that of a group of rocks, referable to the Lower
bdhyan or Eamul series, certain members of which series are now
and, or are believed to have formerly existed, in the vicinity of all
e known diamond-yielding localities in India, and in the case of
toal rock-working include the matrix of the gems.
The fact tiiat &e place (Hira Ehund) where the diamonds were
i«hed for is on metamorphic rocks, may be readily explained by the
jsical features of the ground. The rocky nature of the bed there,
d the double channel caused by the island, afforded unusual
:ilities for, in the first place, the retention of the diamonds brought
wn by the river, and secondly, for the operations by which the bed
[lid on one side be laid bare, and the gravel washed by the simple
atrivanoes known to the natives.

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It 18 impossible to say at present whioh the actual bed or beds
rock may be whence the diamonds have been derived, as there is i
record or appearance of the rock matrix ever having been Tvorkec
but from the general lithological resemblance of the sandstonee ai
shales of the Barapahar hills, with the diamond-bearing beds, az
their associates in other parts of India, it seems not improbable th
they include the matrix.

The diamond stratum at Eamariya, locally called ItdkrUy oonak
of a conglomeratic sandstone made up of pebbles, \-\^ in. diao
imbedded in a rather fine matrix, which ako includes clay gal
The lower Bewah sandstone here stretches out a oonaiderab
distance in front of the scarp, and the pit was just on the northe
edge of this terrace, some 20 ft below the summit, and itself abo
10 ft deep. On the top of the diamond bed was 1 ft or so of ha
thin flaggy sandstone, and about 7 ft of the same mixed with sha
A little farther to the south and west, on this terrace, was an old {
between 30 and 40 ft deep, but the bottom was filled with ^water,
that the rocks immediately above the diamond bed could not be sea
there were, however, certainly 10-15 ft of shale between it and ti
lower Bewah sandstone. In all the pits examined there mnst ha
been 10-20 ft of intermediate shale. The Faunas are here very thi
80 that this position is not much above the top of the Kaimurs (ti
lowest group of the Upper Vindhyans).

So far as can be ascertained, the Panna mines have never yields
any diamond of remarkable size. But there can be little doubt th
vast quantities of diamonds have been produced there which ha
commanded relatively a higher price than Brazilian and Cai
diamonds. The influx of the latter into the Indian market of la
years has, however, seriously depreciated the selling value of Indii
stones, and but few find their way to the Calcutta market Accordii
to Dr. Hamilton, in lus time, 1813, a good many stones were foui
worth from Rs. 500 to Bs. 1000, and he says that the Haja had oa
supposed to be worth Rs. 50,000.

It would almost seem that except under a system of slavery tl
diamond cannot be worked for profitably in India. The pree^
svstem, though not so called, practically amounts to much the saa
thing ; the actual operatives are by advances bound hand and foot
the farmers of the mines, who are content to wait for monti
together without any return ; their outlay too is very small, no heai
expenditure of capital being involved. But no particular str^
according to Ball, need be laid on the fact that the several attemp
in Southern India, at Sambalpur, and at Panna, to work min
under European management have hitherto failed.

In Brazil, diamonds were discovered at Tejuco, now known \
Diamantina, in Minas Gbraes, in 1746, and at Jacobina, in Bahia, i
1755. The diamonds are found both in old river gravels and in ti
beds of rivers in whose bott(Hns numerous pot-holes are found, i
San Juan de Ohapada the diamonds occur imbedded in clay traveTsis
itaoolumite and itabirite (a hydromicanschist containing specuh
iron). At Corrego diamonds have been found in solid conglomerat
At Tibagy they are found in ancient and recent alluvium, and appe«

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have been derived from a Devonian sandstone. In 1772 the
h>v6mment began to work the mines, but the cost was too great,
ad in 1832 the monopoly was abolished. Nevertheless the ontpnt
D 1850 is estimated at over 10 million carats, value 15 million

Since 1867 the production has rapidly dwindled, and at present
oes not amount to over 15,000 carats a year, worlh about 20,000/.
Phe rich placers of Diamantina and of the Ouro and Parag^y rivers
isoame exhausted about 1840 ; the laws prohibiting the introduction
F new slaves and providing for the gradual emancipation of the old
bes, caused a scarcity of cheap labour, without which the mines could
toi be -worked; the financial crisis of 1858 in Brazil caused an
tamenee idling off in the value of diamonds, which in turn caused
\tb abandonment of many mines ; and the discovery of the great
lamond mines in South Africa ruined the market for the sii^dler
lonea of BraziL

A sabatanoe known as carbonado, carbonate, or carbon, was
Bnovered at Chapada, Brazil, in 1845. It is an allotropic form of
brbon, oloaely related to the diamond, and is found in small irregular
kypto-orystalline masses of a dark grey or black colour. Although
|i density ia not so great as the diamond, it is ver^ much harder ; in
hct, it is the hardest substance known. It is found in small

Etities in Borneo, but has not yet been discovered in the diamond
I of India or of South Africa. At first it was used only in cutting
onds, but since the invention of the core-drill for boring in rocks
\ baa found a greatly extended use, and is now employed for the
Hsalled *' diamond crown " of this drill. In 1850 it was worth only
a per carat, and the demand was limited ; but at present it is worth
nmt 32. per carat, and the production has increased to 20,000 carats
Mr annum. The " bort " of the South African mines finds a similar
Uustrial application, being worthless as a gem.

"BmeraXd. — The composition of the emerald is 65 per cent, silica,
14 alumina, 13 gludna, 3*5 chromium oride, 2*5 lime; hardness,
r*5 ; sp. gr., 2*7 ; colour, rich deep ^reen ; somewhat brittle, trans-
Urrait to subtranslucent. Europe is said to possess emeralds in
fcrway and Austria. In Asia, they have been found in the Urals
lad Altai Mountains, in Burma, and on the Siberian frontier of
[Aana. A&ican emeralds are found in mica-slate beds in the Sahara,
Bid at the junction of the Harrach and Oued Boaman rivers, in
Ugeria. The principal modem source of the gem is in S. America,
between the mountains of New Granada (Colombia) and Popayfui.
the mines of Muzo, in the Tunka Valley, about 75 miles from Bogota,
the capital of Colombia, and classed by all writere on gems as the
boat mmous mines in the world, were discovered by Lanchero in
1555. Work was commenced in 1568, and although no exact data
•re to be obtained, it is known that for many years the output of
tne etonea was so great that they ceased to be rare. The mines were
abandoned about 1740, and so remained until 1844, when they were
fe-opened. Soon afterwards a French company was formed, and the
taines were leased from the Government at an annual rental of 1600iL
Tbia company sent many fine stones to Paris ; but the work evidently

B 2

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did not pay, for the mines were abandoned in 1868. They are wf
leased by a company paying 5000/. annually, the lease to run mit

The gems are found in a bituminous limestone, said to be of Lowi
Cretaceous age, which lies upon red sandstone (Triassic) and cU;
slate. The emeralds occur either in isolated crystals or in geodi
with calcite, iron pyrites, and parisite. Streeter describes the gra
Muzo mine and metiiod of working as follows : —

" The mine has the form of a tunnel about 100 yd. deep, wil
very inclined walls. Near the mouth are several liu-ge reserroi
whose waters are shut oflF by gates. The overlying barren rock
cut out in benches and falls to the bottom of the tunneL Wh^i th
begins to fill, the water is turned on and the rock is carried awj
through an underground tunnel into a basin below. This operatic
is repeated until the stratum containing the gems is laid bare.*"

Jade, — The jade-producing districts of Burma are partly endoeed \
the Chindwin and Uru rivers, and lie between tne 25th and 26i
parallels of latitude. Jade is also found in the Myadaung distric
and the most celebrated of all jade deposits is reported to be a lar|
cliff overhanging the Chindwin, or a branch of that river, and distu
8 or 9 days' journey from the confluence of the Uru and Chindwii
Of this cliff, called by the Chinese traders " Nantclung," or '* difficn
of access," nothing is really known, as no traders have gone there f(
at least 20 years. Within the jade tract described above small qua^
tities of stone have been found at many places, and abandoned quarri^
are numerous. The last old quarry of any size is Sanka, situated 7
miles north-west of Mogaung. The largest quarries now being workti
are situated in the country of the Merip Eachins. The largest mi^
is about 50 yd. long, 40 broad, and 20 deep. The season for ja^
operations begins in November and lasts till May. The most pK
ductive quarries are generally flooded, and the labour of quarrying i
much increased thereby. In February and March, when the floor <
the pit can be kept dry for a few hours by baling, immense fires al
lighted at the base of the stone. A careful watch is then kept in |
tremendous heat, to detect the first signs of splitting. When thi
occurs the Eachins attack the stone with pickaxes and hammers, c
detach portions by hauling on levers inserted in the cracks. The hei
is almost insupportable, the labour severe, and the mortally amoz^
the workers is nigh. The Eachins claim the exclusive right of won
ing the quarries, and there is not much disposition on the part of othei
to interfere ; traders content themselves with buying the stone froi
the Eachins. All payments are made in rupees, and Burman or BumM
Shan brokers are employed to settle the price. The jade is then ti^^
by Shan and Eachin coolies to Namia Eyankseik, one long daj^
journey from Tomo. Thence it is carried by dug-outs down a smal
stream, which flows into the l\idaw river, about 3 miles below Sakai«
and down the Tudaw river itself to Mogaung. The Sawbwa of tb
jade-producing tract, Eansi, levies 5«. on every load of jade that IcstJ
his country, the local chief at Namia Eyankseik takes another 2»., aw
the farmer of the duties obtains an ad vcUorem duty of 33 per cent
The Eachins and Chinese-Shan coolies who work in the mines pay t<

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the Sawbwa, Eansi, 10 per cent, of the price they get from the jade
merchants. The farming of the jade dnty of 33 per cent, od valorem^
for the year ending June 30th, 1888, sold for 5000Z.

LapMazuU. — The composition of this gem is 45-50 per cent, silica,
3(^2 almnina, 9 soda, 6 sulphuric acid, with minor quantities of lime,
iron, chlorine, and sulphur ; hardness, 5*5; sp. gr. 2 * 4 ; colour, ultra-
marine or fine azure-blue of varying intensity, depending, it would
Mem, upon the proportion of iron and sulphur. The stone occurs in
Asia and S. America. A celebrated mine is in the valley of the Eokcha
m BadakhBhan ; here it is met with in an unstratified limestone, and
is extracted by heating the surface of the rock so that it can be flaked
off by smart blows till the stone is exposed. Another source is the
ihores of the Shudank, near the Baikal Lake ; also in many parts of
CSiina, and reputedly on the Indus. In the Cordillera of the Andes,
near the sources of the Oazadero and Yias, tributaries of the Bio
Gbande, the gem is found in a thick stratum of limestone, accompanied
by small quantities of iron pyrites.

The Badakhshan miners distinguish three varieties, called mli
^indigo-ooloured), atmaim (sky-blue), and Boibzi (green). The mines
ire bat little worked now, though at one time they produced hundreds
>f pounds weight of the gems.

Op<d, — Composition, 90-95 per cent, silica, 5-10 water, with traces
)f iron, potash, soda, lime, alumina, &c. ; of various colours and many
rarieties ; the noble or precious opal, the only one to be considered
bere, exhibits a beautiral play of colour by refracted and reflected
light. The only two sources of precious opal are Hungary and Mexico,
^ product of uie former being by far the more valuable. The Hun-
jparian mines are situated at Dubrick and Cservenicza, on the eastern
hlopes of the Labanka^ Mountains, the workings and waste heaps
stretching for a distance of nearly 1 j^ miles.

The interstices of the andesite (a trachytic lava that forms the
natrix of the precious mineral) are filled up with opal and hyalite,
rhe felspathio ingredient of the rock is mostly in a metamorphosed
condition, being changed partly into kaolin and partly into opal. The

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 27 of 76)