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fault: east of it the strata are inclined S.E. to N.N.E., whereas west of it the strata exhibit the normal dip of these parts, viz. N.W. The workings extend for about 100 yards on the east side of the ravine, pretty nearly along the strike of the strata. The main drifts run parallel to the bedding; but meandering passages across it in all directions also exist. The ore here appears to occur in segregated veins parallel to bedding, and there did not appear to be any indication of a true lode. Still, the oriferous beds may, I think, be advantageously followed deeper down. The difficulty of drainage has led to their abandonment; and at present the miners burrow here and there on a small scale.
Masses of quartz rock containing copper pyrites are found in the bed of the Rátho, a short distance below the mine. An average sample yielded on analysis 6°38 per cent. of copper.
§ 3. Summary and Concluding Observations. The following is a summary of the copper localities mentioned above :
(A) In the Dalings.
s Old Pachikháni.
(B) In the Gneissic rocks.
(Lindok. Localities not yet tried . . . Lingui.
(Ronglichu. The Nepalese miners have a very keen eye for copper ores; and the localities where they have been mining or rather burrowing-Tuk, Bhotáng, Rátho and Páchi-are certainly the most promising in all Sikkim. They work, however, in a primitive fashion; and the depth of the drifts which they run for the ore is limited by the water level of the nearest streamlet. As soon as a drift fills in with water which cannot be easily let out, it is abandoned. The deepest mine scarcely ever goes down below 60 feet from the surface; that at Páchikháni has scarcely reached this depth, and the miners intend abandoning it already, owing to the difficulty of draining it, though the ore is found to get richer with depth. It was chiefly this difficulty of drainage that led to the abandonment of Tul: kháni, Bhotangkháni, and partly also of Ráthok háni. I have no doubt, Páchikháni also will be deserted as soon as the surface ores have been worked out. Deep mining on modern methods at these places, especially at Páchikháni, is likely to yield a very fair return.
Of the four places just mentioned Pachikháni appeared to me the most promis. ing. This may partly be due to the fact that owing to the works here being in progress I could see for myself the exact mode of occurrence of the ore. However as the existence of at least one rich deposit here is known, this place ought to be tried first, in case Sikkim should attract mining enterprise, which it is likely to do in the near future. A sample taken at random from the deposit just mentioned yielded 20-31 per cent. of copper; and, from what the miners told me, the average yield from the entire mine is about 12 per cent. (5 seers of copper from one maund of ore). On the other hand, the picked ore from Ráthokháni was found by Mr. Nallet to contain not more than 8 or 9 per cent. of copper. At Bhotáng the ore contains rather too much of mundic. From what the miners who had worked at Tukkháni told me, the ore there at the point where it was given up appears to have been richer even than that of Páchikháni. I would not place much reliance upon such a statement uncorroborated by samples. Still, from all accounts, Tukkháni would be a very favourable place for trial, after Páchikháni.
Of the other localities the surface indications at Rhenock appear to be rather favourable.
IRON. Occurs chiefly as pyrites in association with chalcopyrite. It is most plentiful at Bhotang, where magnetite also occurs. The iron ores have nowhere been put to any economic use.
There is a vein of calcite in the gneiss at Lingtam about 3 miles north-east of the Ronglichu rest-bungalow. Lime was experimentally made from it, but it did not turn out quite satisfactory, being rather dark-coloured. There are beds of limestone in the Dalings, north-east and north-west of Námchi, but it is, as a rule, too impure to yield good lime. Lime in Sikkim is invariably made from tufaceous deposits, which abound in the vicinity of these beds, especially at Vok, near Námchi, whence large quantities of lime used at one time to go to Darjiling.
Is abundant in the gneiss and mica schists at places. But it does not appear to be good enough for the market.
NOTE ON A CUPRIFEROUS LATÉRITIC ROCK IN SIKKIM. Mr. Lake in his excellent discussion on Laterite (“Memoirs," Vol. xxiv, pt. 3) observed that the general absence of laterite in the Himalayas “may be partly due to the want of continuous heat, and partly to the nature of the rocks, which are probably not so ferruginous as the traps and gneisses of the Peninsula.”! There may be want of continuous heat at high elevations ; but the climate of the deep valleys is essentially one of damp heat. There are also rocks in the Himalaya which are not less ferruginous than those which, in the Peninsula, have been decomposed in situ into lateritic rocks. If damp heat, aided by decomposing vegetation, be the chief cause of this lateritisation, as I believe it very likely is, laterite
1 Op. cit., p. 46.
ought to be found specially developed in the damp hot Himalaran valleys, clothed with exuberant vegetation. I think the reasons why the case is otherwise are,- ist, excessive rainfall; and secondly, steepness of the valley slopes. Before the rocks get sufficiently decomposed to be lateritised, they are clean washed away. The conditions, besides damp heat, which are favourable to the formation of laterite, viz. moderate rainfall, and the existence of plateau or gently undulating land—are absent in the Sikkim Himalaya.
I found a tendency towards lateritisation on a small scale at places; and I may here notice a perfect lateritic rock which has been formed in a somewhat sheltered spot at Páchik háni, south of Pakyang. There are here heaps of débris from the copper mines by the side of a watercourse which have been lateritised at the surface. As the mines at this spot have only been worked for the last 2 or 3 years, the laterite must have been formed within that time. At Ráthokháni I found lateritisation had commenced at the surface of a heap of dressed ore not many weeks old ready for the furnace.
The Páchikháni laterite contains abundant concretions, from 'ath of an inch or less to 14th of an inch in diameter, of which the lining is of green carbonate of copper, and the interior is filled by a mottled brown ferruginous substance. The fine débris which have been lateritised contain copper and iron sulphides; and the laterite is evidently the result of complicated chemical re-actions by which the iron has been separated, and the cupreous sulphide has been converted into the green carbonate,
Chemical and Physical notes on Rocks from the Salt Range, Punjab, by
THOMAS H. HOLLAND, A.R.C.S., F.G.S., Geological Survey of
INTRODUCTION. Before Mr. Wynne in 18781 published an account of his detailed survey of the geological structure of the Punjab Salt Range, the district had, from its remarkable physical characters and from the value of its economic products, received a considerable amount of attention at the hands of both official and private observers. Since that year numerous facts in the geological structure of this district have been recorded; but a special interest in the question has lately been aroused by the interesting account Mr. C. S. Middlemiss has given of his re-examination of the area, and the hypothesis he puts forward to account for the remarkable position and origin of the salt-marl.2
At the request of several workers who are interested in this question of both scientific and economic importance, I have undertaken to devote a portion of my leisure to the study of the specimens which have been coliected in the Salt-Range area by officers of the Geological Survey of India. In the notes appearing in this part of the Records I give what I hope to be only a first instalment of the investigations into this subject which I propose to pursue. I hope to follow the examination of the bi-pyramidal quartz-crystals and preliminary investigation of its gypseous matrix with some notes on the chemical and physical characters of the dolomite, salt and associated minerals, as well as the Khewra trap.
1 Wynne. Mem., Geol. Surv., Ind , vol. xiv.
9 "Notes on the Geology of the Salt Range of the Punjab with a re-considered theory of the Origin and Age of the Salt-Marl.” Records, Geol. Suro., Ind. vol xxiv (1891), pp 19-42.
Besides the light these specimens throw on the problems of local interest, the results so far obtained seem to offer some pertinent evidence on one or two questions of general mineralogical interest.
1.-On the Bi-Pyrumidai Guarts-Crystals. The mode of occurrence of these crystals, which have been used by the natives
of the district for ornamental purposes under the name of Mode of occurrence.
beco “Márf diamonds," has received the attention of Mr. A. B. Wynne, Dr. H. Warth,” Mr. B. H. Powell, and others.
The crystals are found embedded in the gypsum near Marí, at the western end of the Salt Range ; Kálábágh, on the west side of the Indus; and at Sardi, Kusak and Kaiha in the Salt Range. They weather out from their soft and partly soluble matrix in a manner which at once arrests the attention of the observer from the brilliant lustre of the crystal-facets. In size they vary from that of a millet-seed to that of a walnut; in colour from
white, through shades of pink, to brick-red. They are often Physical characters.
e transparent on the exterior, but in the centre of each crystal there is invariably a white or pink translucent core. In some cases, where the inclusions are of sufficient dimensions, the light reflected from their faces produces an avanturine appearance. The suspicion that these translucent cores might be due to inclusions of the matrix led me to expect that a careful investigation of the specimens might afford some evidence as to their origin and their decidedly remarkable form and mode of occurrence. The crystals almost invariably present combinations of the hexagonal prism and
pyramid. Of over three hundred which I have examined, Crystalline form.
I failed in three cases only to detect a development of the prism form. Their bi-pyramidal nature and comparative regularity of their faces recall at once the quartz of like form found in many acid volcanic rocks, where a yielding liquid magma has probably allowed a symmetrical development of the faces. Mr. Middlemiss has remarked that crystals so perfect and exhibiting no trace of rounding are certainly not characteristic of sub-aerial sedimentary formations; and their occurrence, therefore, in gypsums, which are generally regarded as aqueous in origin, is a fact worthy of notice.
The prism-faces in these crystals are almost invariably pitted and marked, but in the absence of any definite shape to these markings it is impossible to say whether the blemishes are due to “etching."
* Mem. Geul. Surv., Ind., vol. xiv (1878), pp. 13, 180, 268 and 300.
Inland Customs Administration Report, 1870-71. “Report on the Salt Mines of the Punjab Salt Range west of Pind Dadun Khán.” Appendix D, P. 189.
8 Handbook of Punjab Economic Products (1868), pp. 41, 48, 59.
Specimens dropped into a platinum crucible previously raised to a white heat
invariably become traversed with cracks, and pieces fre. Cleavage.
quently fly off. In this way I have, in a few cases, developed the rhombohedral cleavage of quartz with a lustre of cleavage-face sufficiently perfect to allow of measurement with the reflecting goniometer, the results agreeing so closely with the angle for R. as to leave no doubt about the form. Crystals, when broken, exhibit a fracture whose surface is composed of a series of
zonal ridges and furrows. This is the case both with fracFracture.
tures at right angles and parallel to the vertical axis, and a corresponding zonal arrangement of inclusions is sometimes seen in thin slices under the microscope. Finding from a preliminary qualitative analysis that sulphate of lime in some
form existed in the crystals, sections were made by grinding Microscopic characters,
* in oil instead of in water. Under the microscope the centres of the quartzes are seen to be crowded with small plates (of less than 35 mm. edge) of a colourless and highly doubly refracting mineral in approximately square
or irregularly-shaped plates, which, on chemical examit anhydrite nation, proved to be anhydrite (Plate I, Fig. 2). The anhyin quartz.
drite-crystals seldom exhibit cleavage-cracks and never, as far as I have observed, any twinning. In the centres of the quartzes they often exceed their host in bulk; but towards the exterior the fragments are more widely separated from one another, and there is generally an external border of clear quartz. I selected three crystals for chemical examination, having previously determined
the specific gravity of each specimen. The following results Chemical analysis. have been obtained :
'15 99997 9997
Neglecting the loss and impurities, which are very small, and calculating the results to 100, we obtain a mineralogical composition of
29*75 13:04 12:15
| The method employed in determining the specific gravity I hope to describe in a sueceeding note. For the present it is safe to say that the limit of accuracy in these results is well within 'ooi (sp. gr.).