16 Penfidd and Pearce — Polybasite and Tennantite 



for the most part was taken from an area of about one half 

 acre of territory, with a maximum depth of but 300 feet. lN r et 

 weight of ore 9,080,570 lbs., carrying 2,053,149 ounces of 

 silver, an average of 452 2 ounces per ton. 



The rich ore occurs between a hanging wall of black car- 

 bonaceous shale and a foot wall of gray magnesian limestone, 

 which is probably of lower carboniferous age. The ore is 

 richest and most abundant immediately under the black shales. 

 The minerals which have been observed at the mine are poly- 

 basite, tennantite, native silver (sometimes in very beautiful 

 specimens), argentite, galena, sphalerite, siderite, barite and 

 calcite. 



Polybasite or "brittle silver" of the miners. 



This is the most abundant silver mineral at the mine and 

 occurs massive, with grayish black color and irregular fracture. 

 Large quantities of it, nearly free from gangue, have been 

 mined, assaying from 10,000 to 16,000 ounces of silver to the 

 ton. A very abundant and conspicuous ore is a pink barite 

 ("pink spar") with the polybasite disseminated, quite uni- 

 formly through it and assaying from 1800 to 2700 ounces of 

 silver to the ton. The mineral also occurs as streaks and par- 

 ticles in the shales and limestones on the borders of the deposit, 

 and even some seams of impure coal, above the shales, are quite 

 rich in silver. 



The massive polybasite is not a pure mineral as it appears at 

 first sight to be. The analyses show a wide variation in the 

 percentage of lead and do not yield a satisfactory formula until 

 this metal is deducted in the form of galena, although the lat- 

 ter is no where visible in the material which was analyzed. 

 The remaining impurity consists of a carbonate of iron and 

 manganese, which is very evenly distributed, is black from car- 

 bonaceous material and not conspicuous in the metallic sulphide. 

 The analysis is given beyond. 



Some of the specimens consist of a fine grained, crystalline 

 carbonate of iron, manganese and zinc, having a brown color 

 and probably a variety of siderite. This seems to have been 

 deposited over tabular crystals of polybasite, but it can not be 

 broken away so as to show the crystalline form of the latter as 

 it adheres quite tenaciously. Some of the polybasite crystals 

 are surrounded first by a layer of siderite, then by a narrow 

 zone of metallic mineral and then again by siderite. As this 

 seemed to be the nearest approach to the pure crystallized silver 

 mineral, which we were likely to obtain, great pains was taken 

 to pick out a sufficient quantity for the following analysis. 



