Geological Notes, Tasmania. 121 



The lode which the Mount Lyell Company are working con- 

 sists essentially of pyrites. According to Dr. Peters, whose 

 rejort on the mine was published last year, the great bulk of the 

 ore mass consists of iron and copper pyrites, with a little heavy 

 spar (barium sulphate), and silica, and traces of antimony, 

 arsenic, lead and zinc. This ore also contains about 3 oz. of 

 silver and 2^ dwt. of gold to the ton. Besides this main body of 

 ore, pockets of argentifei'ous copper pyrites and silver-copper 

 glance occur. This class of ore has proved enormously rich, 

 yielding several thousand ounces of silver to the ton, besides a 

 large percentage of copper. 



Several theories have been put forth to account for the forma- 

 tion of the ore, but the most satisfactory is that proposed by 

 Dr. Peters and Mr. Montgomery. According to these gentlemen, 

 the mass of pyrites is an ore-bed contemporaneous with the 

 enclosing country rock, having been probably deposited in a 

 swamp or lagoon of the period. The ore-bed has a thickness of 

 300 ft. at the surface, this thickness representing, on the above 

 theory, the original depth of the deposit, which may therefore 

 be pretty confidently expected to be of very large extent. 



Resting unconformably on the older schistose rocks, with their 

 accompanying sandstones and conglomerates, are massive beds of 

 conglomerate intei^stratified with sandstones, which are very 

 characteristic of the West Coast Range as a whole. These beds 

 may be traced from the level of the Linda Valley to the summits 

 of both Owen and Lyell. They have in general a south-westerly 

 dip at an inclination of about 40" to 45°; but at the top of Mount 

 Lyell, where they constitute the plateau on which the trigono- 

 metrical station was erected, they are dipping to the N.W. at an 

 angle of 15°. They are much jointed, and show a tendency 

 to foliated structure. The included stones, which are almost 

 invariably quartz and quartzites, vary in size from small pebbles 

 to boulder's of at least two feet in diameter, thus giving the rock 

 a very striking appearance. The beds are pierced by quartz- 

 veins, which traverse both matrix and included pebble, and the 

 jointing planes, in dividing the rock, also cut right through the 

 quartz pebbles. The foliated structure, which causes the quartz 

 to flake off in thin sections, would appear to show the intense 

 compression to which the beds have been subjected. The matrix 



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