This chapter is tagged (labeled) with: 

Ch. 2: Gems in Ceylon

Ch. 2: Gems in Ceylon Page of 442 Ch. 2: Gems in Ceylon Text size:minus plus Restore normal size   Mail page  Print this page
150                                            GOLD IN INDIA.
E. to nearly east and west. The dip is southerly and south easterly from 60° to vertical.
Only an extended examination of the country, such as would be made in the course of a minute geological survey, would enable the observer to offer suggestions as to the probable origin of these metamorphic and metamor­phosed rocks. It is apparent wherever they are well exposed that there is one system of planes very like strike-joins which, but for the direction of the dip, might be supposed to represent planes of original deposition. The direction of these in some degree accords with the general direction of the main quartz veins, and it might be surmised on a first view that the forma­tion of the latter was due to the same forces which operated in altering the strata they intersect; that in other words, the quartz in the veins was segregated during the enormous period which elapsed from the time of the first slight alteration of the original sedimentary rocks until they were metamorphosed as we see them now.
In the Manual of the Geolopy of India it is stated that " this Nilgiri strike is noted as distinctly that of the lamination and bedding of the gneiss as well as of the foliation," and therefore it is the more difficult to conjec­ture to what forces the direction of the quartz veins is due, .coinciding as it does, not with the foliation, but rather with the system of joints- above referred to.
While the strike of the rocks over a large part of Australia is nearly meridional, the reefs also have generally a north and south direction.
The stronger and more persistent veins as they appear at present may represent what were once lines of least resistance, and some speculations of a strictly geological character might follow this suggestion if this report were not confined to questions of a practical character.
Much valuable information is to be obtained respecting these rocks from the reports and map prepared by Mr. King. A sketch of a geological map of South-East Wynaad on the scale of four miles to one inch, published with the records of the Geological Survey of India (May 1875), and which I had not the opportunity of seeing until after much of this report was written, shows alternating bands of felspathic gneiss and chlorite gneiss running north­easterly and south-westerly, as well as a large area occupied by quartzo-hornblendic gneiss (Nilgiris) and the smaller areas of granitoid gneiss at Yeddakilmullay and Munnaynvulla.
There is an absence of intrusive rocks in South-East Wynaad. There are no dykes or masses of porphyry, no basalts or recent volcanic rocks; and it is only at one point, as far as is known, where greenstone occurs, namely, on the Hamsluck estate. The rock consists mainly of hornblende with a small proportion of felspar (oligoclase).
Near the spot where this rock is exposed there are veins of granite, or perhaps, to speak more correctly, veins of quartz which are essentially granitic. In several places, more particularly at Giidalvir, Cherambiidi, Moopenaad, and Velliry-mulla there are masses of quartz with large transparent plates of mica. The micacisation of the quartz is observed most frequently (but not invariably) where the veins are very thick; and from the observations which have been made up to the present time it might be inferred that gold, in such proportions as it is found in veins which are free from mica, is rarely present in these micacised reefs.
It is not yet certain that the " country rock " is commonly less silicious in those places where the quartz veins are numerous, but this peculiarity is to be noted in the neighbourhood of Pevala.
General character of the auriferous quarts veins.—The quartz veins of the Wynaad differ in some respects from those intersecting the almost unaltered lower Silurian rock of Australia, but they are usually as thick, or thicker; and quite as persistent. The auriferous veins, those which have yielded well both on the large scale and by tests in the laboratory, are laminated and more or less pyritous, and those which up to the present time are regarded as less auriferous are com­posed of saccharoid, often snow-white opaque quartz with transparent particles
Ch. 2: Gems in Ceylon Page of 442 Ch. 2: Gems in Ceylon
Suggested Illustrations
Other Chapters you may find useful
Other Books on this topic
bullet Tag
This Page