in this rock, and it is generally known to contain various metallic veins, as gold, silver, and copper. "Subordinate to the former is green-stone slate, in mighty layers, often as to appearance constituting the principal rock of a district for many miles. This is the case about Guramanypenta and the other mining places. The layers or stratification of the latter rock I have as yet always found in a horizontal position. "The green-stone slate is often approaching to green-stone; it occurs then only obscurely slaty, has a jet black color, strong glossy lustre, foliated fracture, hard in a small degree; in this state it seems here barren of metals of any kind. The real green-stone slate is of a bluish black color, with small white spots of decomposed felspar, half hard; and when exposed to the air, it crumbles soon to pieces, and takes a green color. The rock is reckoned one of the richest' mothers of ores' of any in the world. In it are found silver and copper in rich beds or layers, as is the case here; but never in veins, as in other formations*. "The layers of copper are of different thickness, and distances from each other the general run of the pieces of ore, constituting the layers, is two inches in thickness; but they have been found also of several feet. The pieces are in general flat, as if compressed, and coated with ochre. The vertical distance between the layers is 4 to 8 feet, and the horizontal is even more uncertain. : "A corroded honey-combed quartz is found in great abundance in the greenstone slate, particularly along with the copper ore. It appears often on the surface, in such places where the water has washed the earth away. It looks then like indurated marl, which in other parts of the country is very common. "The rockt is covered with a red coarse gravel, which is the superficial soil of this part of the country. In my opinion, this is formed from the decomposition of the green-stone slate, and its quartzoze and ferruginous contents; for copper ore is often found in it in considerable quantity, and in the same situation, as in the slate rock. "At Yerrapillay, in a new mine, which I opened, I found two layers of ore in it, at distances of four feet asunder. "The thickness of this stratum of gravel differs according to its situation, whether it is on a high or low ground. I have found it from 4 to 6 feet, and more. "The copper ore which Dr. THOMSON calls Anhydrous, the most common kind, is in flat pieces, externally, of a brown ochry color; internally, of a black iron color, which often passes into green; when moistened with water, it becomes almost immediately throughout green; in some places, it is bluish grey throughout. Lustre, in some places, where it is black, semi-metallic; and in the bluish grey, metallic‡. The copper indeed * One of my specimens from Nellore is abundantly curious and interesting. It consists of distinct layers of the carbonate, alternating with black micaceous schist, or rather green-stone, affording exactly the appearance of gradual deposition from a liquid at this earliest period of geological formations. The angle formed by the strata of this striated rock with the horizon is stated by Mr. KERR to be about 45o.-J. P. + See Dr. BENZA's observations on veins of quartz pervading decomposed pegmatite, J. A. S. iv, 421.-ED. This description accords so completely with that of No. 3, in the subjoined analysis, that I have no doubt Dr. HAYNE has mistaken the sulphuret for Dr. THOмSON'S ore.-J. P. is in an almost metallic state in it. Fracture approaching to even fine grained streak; of the black, brighter metallic; powder, "greenish;" not very hard, except the iron black and bluish grey part; which is with difficulty scratched by quartz; brittle; not particularly heavy. Specific gravity, 3.09. Some pieces are found of a nut brown color, and some with conchoidal fracture. The foreign admixtures are various, as white and green quartz, mica, iron ore;' mountain blue and malachite are in some places found with it. In other places, I suspect the admixture of silver. For the analysis, I must refer to that of Dr. THOMSON, in a paper laid before the Royal Society of London, which I was permitted to publish as an appendix to my "Tracts on India." I will only mention here, that on an average, he procured 50 per cent. of pure copper. In the dry way, or by simply smelting the ore, we have received the metal in greater proportion, which may be easily accounted for by the quantity of iron, which the ore contains, that cannot be separated, as when the analysis is carried on by acids and other re-agents." Mr. HAYNE seems to have been wrong in imagining, that the natives had only discovered these mines 50 or 60 years before (about 1750). Mr. KERR, who has since visited the whole of the mining district, and examined all the formations, and the old works, with great care, states, that the former excavations are of prodigious magnitude, many of them occupying several hundred feet square, and having a depth of 50 or 60 feet. The matrix rock and rubbish are now accumulated in these immense tanks; but on clearing them away, the mouths of the galleries extending into the rocks were discovered; blocks of the ore, (perhaps some that had been gathered previous to the discontinuance of working the mines from some political convulsion or oppression,) have been used to mend the village tank at Guramanypenta; and Mr. KERR imagines, that any quantity of the richest ore* may be obtained at a trifling expence, and within 100 feet of the surface. Extensive hills, formed of lumps of ferruginous slag, now covered with vegetation, point out the situation of the ancient smelting houses. A piece of this slag (which was at first mistaken for a volcanic product) was analysed by myself. It yielded but faint traces of copper, shewing that the native processes of extraction, however rude, were effectual in completely separating the metal. But I must now proceed to observe upon the actual specimens of the ore submitted to my examination, purposely avoiding all allusion to the mercantile value of the mines, the estimates of the expence of working them, and the invitations to join in an association for this purpose:-objects which are highly interesting to the community, connected with so laudable a measure for developing the natural riches of * The "steel-grained, crystallized silvery ore, invariably found in green-stone slate, and partly imbedded in quartz, the richest ore met with," is doubtless No. 3, the sulphuret.-J. P. the country; but which cannot with propriety be entered upon work devoted exclusively to literature and science. in a The ores now presented to me are from three different localities. They differ considerably in quality one from the other, and all from the former ore, which Dr. THOMSON pronounced to be an anhydrous carbonate, new to mineralogy. No. 1. A parcel, weighing 90 lbs. of roughly-picked and cleaned ore, has a quartzose matrix, in some parts colored green, or appearing so from the malachite beneath the transparent crystal. It contains much iron, which, on solution in an acid, appears in the form of a yellow ochre. Ten per cent. of quartz was separated from this specimen on pounding it roughly, before setting it apart for analysis. No. 2. A parcel of the same weight is labelled “ Bungeral Mettah," and is the species stated to be found in clustered nodules in the alluvium, of rounded exterior, as though they had been detached from their original site, and reburied here. The ferruginous matrix of this ore, on solution, assumes the appearance of a dark-red oxide. It is the same probably as that of Dr. THOMSON'S specimen. The carbonate of copper runs through it in veins, but the mixture of sulphuret of iron and perhaps of copper with the oxide, gives the whole a dark arenaceous texture. No. 3. The richest ore of the three is at the same time the most abundant, and promises to yield the safest return, as it runs in unbroken veins. This ore is a combination of carbonate and sulphuret, the former intermixed with the latter, but readily distinguishable from it, as the sulphuret is crystallized, and has the grey metallic lustre of galena. The specific gravity of this ore is 3.77, being intermediate between that of the carbonate, 3.2, and the sulphuret, 4.5. The analysis was conducted for the sake of expedition on separate parcels of 100 grains each, in lieu of attempting the separation of the ingredients from a single parcel. Some variation may thus be induced from the irregularity of the ore; but, on the whole, the results ought to be more trust-worthy. Thus the carbonic acid was estimated by the loss of weight on digesting 100 grains, finely pounded, in dilute nitric acid. The water, (for none of these ores was found to be anhydrous,) by heating in a glass tube, removing the aqueous vapour by bibulous paper, and ascertaining the loss. As the ore generally lost its green colour by this operation, it is possible that a portion of carbonic acid was also driven off. Calcination in an open dish, in the muffle of an assay furnace, gave a loss, which was compounded of that of the carbonic acid and the water. Calcination drives off the sulphur also, but the equivalent of oxygen, which replaces it, being of precisely equal weight, this operation affords no test of the quantity of sulphur present. In fact, not expecting from Dr. THOMSON's analysis, to find sulphur in the Nellore copper ore, I at first neglected the precautions necessary for its separation. This was accordingly effected on other samples, by boiling in strong nitric acid, which, from its heat, caused part of the sulphur in a pure state to rise in fused globules to the surface while a portion, being oxygenated, was afterwards separated by precipitation with barytes. : The quantity of copper was most conveniently estimated from the black oxide taken up from the calx by dilute nitric acid. It was also obtained directly from other samples by reduction of the oxide with charcoal and borax.-The iron and pyrites were deduced from the difference between the residue in the cold solution, and that from the hot dissolution in strong acid of another parcel, before calcination. Collecting together the results of the above operations, we have the following data, whence to deduce the composition of the three specimens. a. Loss of carbonic acid by digestion in dilute nitric acid, No. 1. No. 2. No. 3. 12.0 14.6 7.0 ..... b. Loss of water (and some carb, acid?) by heating without air in a glass tube,..... C. Total loss on calcination with access of air, c2. Ditto average of two other trials (more carbonate,) d. Oxide of copper taken up from calx c by dilute acid, e. Residue of insoluble earths and ox. iron, after d, f. Residue from digestion of crude ore in boiling nitric acid, ...... ..... 20.0? 8.5 0.0 9.0 28.5 .... g. The same, after burning off the sulphur and redigesting in do. ...... h. Sulphur, separated on boiling in strong acid, i. Sulphate of barytes precipitated afterwards, k. Weight of metallic copper actually recovered from c 2, 28.5 52.2 59.0 In regard to d, No. 3, it was observed on digestion in cold nitric acid, that a very considerable portion of the calx of copper was of a red color, or in the state of protoxide, or perhaps in a metallic state, and was not taken up without disengagement of nitrous gas;-the weight 73.7 must therefore be increased, to give the true weight in terms of the peroxide. This is also proved by the amount of loss in c, 21.0, which is considerably in excess; and it was remarked on removing the calx from the fire that it was agglutinated, so as per * This residue may have consisted partly of sulphuret of copper that had escaped decomposition in the fire; for another specimen was wholly soluble, and little iron was present in the solution. haps to have prevented the access of air to oxidate the interior.→ The sulphur enables us to approximate the correction of this item; for 12.8 requires 51.5 copper, 64.3 black or peroxide; and this, added to 22.8, the peroxide of the carbonate, would give 87.7; which is 14.0 greater than the actual return from the fire.—Again, deducting the deficiency after calcination (c.) 21.0, from the sum of the three volatile ingredients-sulphur, 12.8; carbonic acid, 7.0; and water 3.0 =22.8, there remains but 1.8 for the weight of oxygen absorbed in place of the sulphur; whereas 12.8 are required.-Adding the difference 11.0 to d, we shall have 84.7. This number will be found to be a little in defect from the subsequent results; while 87.7 is a little too great; a mean may therefore be adopted. 9 From the above data, we may now proceed to extract the simple elements of each specimen of ore : 69.0 4.5 12.8 6.3 n. Carbonic acid, less th for hygrometric moisture,.. 10.8 13.1 The carbonic acid being supposed to be wholly combined with copper, while the sulphur may be partly united with iron, we may calculate the proportions of the carbonates and sulphurets by means of the scale of chemical equivalents, thus: .......... No. 1. No. 2. No. 3. 31.4 38.6 18.3 0. The carbonic acid will require copper, Now in the first two of these, the copper required so nearly agrees with the calculated weight of metal, 7, that the latter may be looked upon as existing here wholly in the form of carbonate, and the sulphur as united entirely with iron*. In No. 3, however, we find that the majority of the copper remains; and knowing the nearly total absence of iron in this specimen, we may conclude it to be a mixture of nearly two parts sulphuret, with one of carbonate. The miner would rest content with the determination of the pure metal in the ore, and would have good reason to be satisfied with the 60 per cent." actual yield" of No. 3, or even with the 30 per cent. of the poorest of the three ores; but the mineralogist will prefer an exhibition of the component salts of the ores, according to the usual synthetical formula. I may here remark, that the water separated (b) is more than is required to convert the carbonate into a hydrate or ordinary malachite: thus, *In the second Analysis of No. 2, however, the copper actually recovered, k, so much exceeds this quantity, that it is evident this ore frequently contains sulphuret, or is of very variable quality. |