84 
ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
for chemical analysis can not be obtained. They are nearly all lead- 
gray in color, with hardness varying from 2.5 to 4. 
The argentiferous galenobismuthite named by Koenig 1 ^ilaskaite 
occurs abundantly in the Alaska mine and in the Acapulco claim 
adjoining it on the east. Its occurrence and accompanying minerals 
are described on page 195. 
Cosalite, from the Yankee Girl mine, with more or less of the lead 
replaced by silver, has been analyzed by Low, 2 and probably occurs 
in other mines of the vicinity. It has been reported also from the 
Alaska mine. Kobellite has been analyzed and described by Keller 3 
from the Silver Bell mine, and beegerite, from Poughkeepsie Gulch, 
by Koenig. 4 The naming and identification of these species from the 
Silverton quadrangle rests upon chemical analysis of massive, more 
or less impure material, and these results have not yet been confirmed 
b} T any investigation of crystal form. 
In the course of the present investigation sulphobismuthites have 
been met with in many of the ores, but never with external crystal 
form nor in such amount or purity as would warrant complete chem- 
ical analysis, whereby alone they can be specifically determined. 
At the Barstow mine the richest ore is a bright lead-gray mineral, 
of hardness 3 to 3.5 and specific gravity 7.04 at 30° C. (Hillebrand). 
It shows indistinct crystal forms, suggestive of isometric symmetry, 
and is very intimately intergrown with pyrite. 
The purest material that could be picked out proved to be a mixture 
of a lead sulphobismuthite with pyrite and a teliuride. According 
to Dr. Hillebrand the following may be taken as a rough approxima- 
tion to the chemical composition of this mixture : 
Approximate chemical composition of material from Barstow mine. 
Constituent. 
Per cent. 
Constituent. 
Per cent. 
Pb „.. 
45. 5 
22.5 
6.0 
.06 
.3 
Fe '. 
2.8 
Bi 
Te 
3.5 
Ag 
s 
14.1 
Au - 
1.5-2.0 
Cn 
Had pj^rite been the only mineral present with the sulphobismuthite 
it might have been easily deducted from the completed analysis. 
But the presence of tellurium shows that there is present also some 
teliuride of unknown composition which can not be thus allowed for. 
The idea of a quantitative anatysis was therefore abandoned. The 
above rough approximation indicates the probable presence of a min- 
eral of the composition of beegerite, mixed with pyrite and perhaps 
an auriferous hessite (teliuride of silver). 
1 Proc. Am. Philos. Soc, Vol. XIX, 1881, pp. 
472-177. 
2 Proc. Colo. Sci. Soc, Vol. I, 1883-84, p. 111. 
3 Zeitschr. fiir Kryst., Vol. XVII, 1890, pp. 67-72. 
4 Loc. cil. 
