DIAMOND IN INDIA
At Condapetta the mines are from 4 to 12 feet deep. Here there is a bed of earthy sand, 3 to 10 feet thick, resting on a bed of pebbles, which vary in size between that of a nut and that of a cobble, and among which the diamonds are found, usually loose, but sometimes cemented to the pebbles. The latter usually consist of ferruginous sandstone or conglomerate, among these being others of quartz, chert, and jasper, the latter being sometimes blue with red veins; also porphyry containing crystals of feldspar. The greater number of these pebbles have been derived from the surrounding mountains, but some for example, those of porphyry-have been transported by water from greater distances. The mines here, as at Chennur, are only worked in the dry season, since in the rainy season they become filled with water, the removal of which would entail too much labor.
The mines at Woblapully were opened somewhere about the year 1750. The diamonds found here are flat and much worn and rounded, so that they show no definite crystalline form. They are especially hard and have a high luster. In color they are clear white or clear honey-yellow, also cream-colored and grayish-white. They are found in alluvial deposits of varying widths which follow the course of the river, and consist chiefly of much rounded nodules of limonite of about the size of a nut. This district has not been systematically explored, the mines, of which the average depth is 16 feet, are very irregularly scattered about, and have apparently never been of any great importance. Following up the Penner valley and then turning to the north we reach Munimadagu and Wajra Karur, two important diamond localities in the Bellary district.
The first of these, Munimadagu, is sixteen miles west of Banaganapalli and forty-one miles east of Wajra Karur. Here, in a circular area some twenty miles in circumference are a number of mines, which in former times especially during the period between the beginning of last century and the year 1833, supplied the important market, and cutting works of Bellary with the bulk of their material. The systematic working of the mines on the particular diamantiferous bed has, however, now been given up, although a few stones are occasionally still found in the neighborhood. The diamond-bearing stratum is of small thickness and rests upon granite, gneiss and similar rocks.
Wajra Karur is another locality from which a more abundant yield of diamonds was obtained in former times than is the case at the present day. To emphasize the fact that diamonds are still to be found here, we may mention the stone of 67 3/8 carats discovered in 1881, from which was cut a beautiful brilliant of 24 5/8 carats, valued at £12,000 ($1,335,000). Some of the largest and most famous of Indian diamonds are said to have been found here. The occurrence of diamonds at this place is peculiar: they lie loosely scattered about on the surface of the ground, and there is no definite diamond-bearing bed. The rocks at the surface are granite and gneiss, and the diamantiferous Banaganapalli sandstone has not been detected in the district. The diamonds are often washed out of the soil by heavy rains, and are then picked up casually, or the people of the district may make an organized search for them.
In order to explain the peculiar mode of occurrence of diamond at this locality, it has been supposed that in earlier geological times a diamantiferous bed covered a large area in the neighborhood of Wajra Karur, and that this has since been entirely removed by denudation, leaving the diamonds behind as an unalterable residue. Although there is nothing impossible about this view, it is supported by no definite facts.
Later investigators have attempted to explain the mode of occurrence of diamond in this district in other ways. To the west of the town of Wajra Karur a pipe of blue rock, similar in character to volcanic tuff, was found in the granite or gneiss. This closely resembles the richly diamantiferous rock of Kimberley, in South Africa, and was therefore supposed to be the original mother-rock of the Wajra Karur diamonds. An English company with absolutely no success worked this bluish-green, tuffaceous rock, with interspersed blocks of granite and gneiss, on a large scale, not a single diamond having been found.
More recently the French traveler, M. Chaper, who searched the district for diamonds in 1882, has offered another solution of the problem. This explorer found that numerous veins of various igneous rocks penetrate the surface rock lying just beneath the soil, which in the neighborhood of Wajra Karur is gneiss. These veins very frequently consist of a coarse-grained, rose-red or salmon-colored pegmatite containing epidote (pegmatite being a special variety of granite). In the upper, much-weathered portion of such pegmatite veins M. Chaper himself collected two small diamonds, which were accompanied by irregularly bounded grains of blue and red corundum (sapphire and ruby) as well as by other minerals. The two diamond crystals were octahedral in form with perfectly sharp edges, and showed no signs of having been water-worn. Numerous diamonds are said to have been found under the same conditions by the natives. Chaper was convinced that the diamonds he collected had been originally formed in the pegmatite, and had been loosened from it only by the weathering of the matrix. This theory would of course apply equally well to all the other regularly developed crystals of diamond found at the same place.
The Indian geologist, Mr. R. B. Foote, has raised a doubt as to the correctness of Chaper's observation, and especially of the deduction he drew there from, suggesting that his native attendant deceived the French traveler. A confirmation of Chaper's statement is much to be desired, since it would be of considerable help in elucidating the general problem connected with the identity of the original mother-rock of Indian diamonds. The original matrix of all Indian diamonds may possibly have been similar in character to the rock in the neighborhood of Wajra Karur, the weathering and breaking down of which has given rise to the sandstones and conglomerates in which the diamonds are now found, but which cannot under any circumstances be regarded as their place of origin. In support of Chaper's view may be mentioned the fact that diamonds in the lower Penner district are sometimes associated with the minerals which Chaper observed at Wajra Karur - namely, ruby, sapphire, and epidote. Foote meets this argument with the statement that ruby and sapphire have never been found at Wajra Karur except with the two specimens found by Chaper, and these, moreover, he considers show signs of workmanship. Were it further confirmed, the reported occurrence of diamond in pegmatitic rocks, both in Lapland and in Brazil (Serra da Chapada, in the State of Bahia), would afford support to Chaper's views.
2. The Nandial Group between the Penner and Kistna Rivers.
This group lies near the town of Banaganapalli, and only about seventeen miles north of the last group. It is situated on the northern margin of the plain, which extends from the western slopes of the Nallamalais as far as the town of Nandial (lat. 15º 30' N., long. 78º 30' E.). The mines of this group, which are sometimes referred to, for example, by V. Ball, as the Karnul diamond mines, lie to the east, southeast, and west of Nandial, and are partly in the diamantiferous bed itself and partly in the sands. This group, of which a few only of the more important workings can here be mentioned, includes some of the most famous mines ever worked in India, the majority of which, however, are now abandoned.
Rafal Swiecki, geological engineer email contact
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