138 W. H. Melville — Powellite : Calcium Molybdate. 



Art. XYII. — Powellite — Calcium Molybdate: A new min- 

 eral Species ; by W. H. Melville. 



Attention has been recently called in mining journals to a 

 locality in the western part of Idaho known as the " Seven 

 Devils" where mining operations for some time past have 

 been actively conducted. " The ' Seven Devils ' about ninety 

 miles dne north of Huntington and fifteen miles east of Snake 

 River form a high broken chain of mountains nearly 9,000 

 feet above the sea level. The mineral zone is about one mile 

 wide by four miles in length."* The ore is worked for copper 

 and silver, and is mainly the mineral bornite, a sulphide of 

 copjDer and iron. " The formation on the west of the vein of 

 ore is syenite and quartzite, while on the east wall is a soft 

 white granite. A short distance to the east is a lime contact 

 which extends south for some four miles, and forms a contact 

 with granite. Along this contact some very good chimneys of 

 ore have been discovered." 



This bornite carries silver varying in quantity from 12 to 

 20 ounces to the ton. In one sample of very pure bornite Mr. 

 E. L. Packard found by assay 14 ounces of silver to the ton. 

 A sample from which I had separated for the most part the 

 other mineral constituents gave me 15*65 ounces of silver to 

 the ton. It was this latter fragment of bornite, weighing 

 about 60 grams, which Mr. Packard picked up from a dump 

 before one of the tunnels in the mining claim called Peacock 

 and which through this gentleman's kindness furnished the 

 material for this paper. The specimen had evidently been 

 exposed to weathering processes and had become friable to 

 such an extent that between the fingers it could be crushed by 

 slight pressure. 



There were two . associated minerals, one of which was 

 identified by the following partial analysis as a lime-alumina 

 iron garnet. It was light brown, but not crystallized. It 

 fused easily to a black glass. 



Loss on ignition 0'06 per ct. 



Si0 2 -_ 38-67 



A1 2 3 . . _ _ 10-08 



Fe O s 16-00 



FeO 0-91 



CaO 33-35 



MgO ._. -. 0-77 



CuO trace 



99-84 

 * Quotations from Engineering and Mining Journal. Nov. 22, 1890. 



