DIAMOND IN INDIA
The diamond-bearing strata, together with the sands derived from them by weathering, are everywhere exposed to the action of streams and rivers, which transport the material to lower levels. The next resting-place of the diamond is therefore the sands and gravels of the riverbed or its alluvial deposits. The most recent of these alluvial deposits lies at the present level of the river; others are found at higher levels on the sides of the valley, having been formed before the valley had been cut down to its present depth. These diamond-bearing alluvial deposits have a close connection with the diamond-bearing beds from which they have been derived. In any district where diamonds occur in the strata they will also be found in the beds of the streams and rivers, although not always in numbers sufficiently great to repay work on a large scale.
The mining of diamonds is at the present day, just as in former times almost entirely in the hands of natives of the lower castes. Attempts on the part of British to work the diamond-bearing deposits on a large scale, and according to modern methods, have never been attended with success. The work in many cases is tedious and difficult, and, moreover, the methods used must be altered to suit the conditions in different localities, which vary considerably. The same methods are for the most part now employed as were in use in the oldest times of which records exist; at any rate, they are identical with those seen and described by Tavernier, the French traveler and dealer in precious stones, in 1665.
The working of the surface layer of sands, that is the loose, weathered product of the sandstone beds, and of the river alluvium, is easy. It consists essentially in removing the larger masses of rock and in washing away the finer earthy material with water. From the sandy residue thus obtained the diamonds are picked out, usually by the women and children of the workers who dig out the gravels.
The working of the sandstone beds is more arduous, and is only attempted where they lie on the surface or at a very small depth beneath it. Where they are overlain by younger beds of any thickness, they are inaccessible to the natives, whose appliances for the sinking of shafts and other ruining operations are few and primitive moreover, in such eases the cost of working would be prohibitive, and the mining of the diamonds can only be effected where the strata crop out on the surface of hill-sides, the workings penetrating to only a very small depth even in these more favorable situations. Where the diamond bearing bed lies at a small depth below the surface, a pit or shaft of a few square feet or yards in section is sunk to meet the desired bed, the shaft being usually about 20 feet, rarely 30 feet, and in a few cases 50 feet in depth. The workings at the bottom of the pit extend only to such distances, as the stability of the material overhead will permit. The diamantiferous rock so obtained is, when necessary, carefully broken up, and the diamonds obtained from it by washing and sorting in the same manner as from the loose sands and gravels.
The excavation of the hard, solid beds of sandstone, which often overlie the diamantiferous stratum, is a matter of no small difficulty to the worker whose tools are inadequate for the purpose. In a few districts the difficulty is somewhat lessened by the employment of a device often made use of by the old German miners. A large fire is kindled on the spot at which it is desired to sink a shaft, and when the rock below is strongly heated, it is suddenly cooled by the application of cold water. This causes the rock to crack in many places, and thus the work of excavation is rendered less arduous. Diamantiferous sandstone, which has been removed from its natural bed, and from which diamonds have been extricated, is often allowed to be exposed to the various atmospheric weathering agencies for sonic time, and is then again worked over, when a further yield of diamonds may be given, this being sometimes repeated several times. This fact has given rise to a belief among the natives that this second crop of diamonds has originated iii the waste rock, or that it is the result of a fusion together of the smaller diamonds originally left behind; similar beliefs are also met with in South Africa. The actual explanation, of course, lies in the fact that during the interval in which the waste rock is exposed to the air, weathering takes place, and any stones which may have been embedded in the larger fragments of rock are thus set free and easily picked out by the searchers. A mass of rock, which has once been worked over, will naturally be the poorer both in the number and the size of the diamonds it contains. In spite of this, however, the refuse heaps from old diamond mines are in many places at the present time being continually turned over and diamonds as continually found.
C. Ritter arranged the Indian diamond mines known to him in five groups, according to their geographical distribution, and described them in order from south to north. In what follow, this grouping will be adopted, the smaller mining districts not mentioned by Ritter being introduced in appropriate places, and information derived from later reports, especially those of V. Ball, incorporated with the matter given by Ritter. Ball gives a rather different grouping of the mines. The map shows the distribution of the diamond-fields in India.
1. The Cuddapah Group on the Penner River.
This group includes the most southerly mines; those furthest to the east are in the neighborhood of Cuddapah on the river Penner, where numerous mines have been worked for several centuries with varying success. At the present time the majority of the mines in this group - perhaps, at times, the whole of them - are abandoned, but this by no means indicates that the supply of diamonds has been completely exhausted. The spot at which diamonds have been most abundantly found is Chennur (Chinon), near Cuddapah, on the right or southern bank of the Penner River. Westward of this, that is, up the river and on the same bank, mines are situated at Woblapully (Obalumpally). On the other bank of the river are the mines of Condapetta, referred to by the travellers who formerly visited and described this district, and which probably corresponds to Cunnapurty of the present day. West of Chennur, diamonds have also been found at Lamdur and Pinchetgapadu, and at a few other places, of which Hussanapur (Dupand) may be mentioned as having at the beginning of the nineteenth century yielded many stones. Still higher up the valley of the Penner diamonds were formerly sought at Gandicotta, but with little success.
All these mines are referred to as the Chennur mines. At Chennur itself the abandoned mines are in the Banaganapalli sandstone or in the weathered products of this rock. Many stories, some of very fine quality, have been found here. In two particular cases £5,000 and £3,000 ($556,000 and $334,000) were obtained for single specimens. After a long period of idleness, mining operations were, in 1869, again commenced, but without success. Under the surface soil of this neighborhood is a stratum1 1/2 feet thick of sand and gravel with clay, beneath this a tenacious blue or black clay, 4 feet thick, and underlying all, the diamantiferous layer 2 to 2 1/2 feet in thickness, and differing from the clay above only in that it contains many large pebbles and boulders. The pebbles thus included in the diamantiferous clay consist of various minerals; among others there are yellowish transparent quartz, epidote, red, blue and brown jaspery quartz, round nodules of limonite the size of a hazel-nut, and corundum. The boulders are often the size of a man's head, and consist of sandstone, basalt, often of hornstone, as well as fragments of felsite (?), a rock of which the hills standing 1000 feet above Cuddapah are constituted.
Rafal Swiecki, geological engineer email contact
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