1914] Whitman : Notes on the Copper Ores at Ely, Nevada 313 



appeared to be chalcocite on the outside, when broken up, are seen to 

 be pyrite or ehalcopyrite within. Molybdenite occurs among the 

 secondary sulfids and seems to have been deposited by the same 

 solutions. It is worthy of note also, that pyrite occurs along with the 

 secondary sulfids in precisely the same manner, and is evidently 

 secondary with them. It was found chiefly as cubes in the ore proper, 

 and as dodecahedrons in the limestone inclusions. Gypsum and calcite 

 also enter into the composition of the ore, and alum incrustations 

 containing cubes of pyrite were found on surfaces where seepage had 

 occurred, indicating that sulphuric acid, liberated by the oxidation of 

 pyrite at the surface, had had a solvent effect upon the kaolin or 

 serieite of the rock, producing a basic sulphate of aluminum, and 

 that this substance coexisted in solution with the pyrite or with ferrous 

 sulphate which, without a recognized reducing agent, was transformed 

 into pyrite, upon the evaporation of the solvent. Perhaps, since 

 there are no carbonaceous or ferromagnesian substances present and 

 aluminum compounds are the chief active agents, some reaction may 

 have occurred with the aluminum minerals during the migration of 

 the mixed ferrous sulphate and sulphuric acid, by which oxygen was 

 taken from the sulphate, producing sulfid which was kept in an 

 ionized state by the presence of the basic sulphate of aluminum or the 

 potassium silicate or sulphate resulting from the reaction. Perhaps 

 colloidal kaolin might have supplied infinitesimal centers of crystal- 

 lization, causing the mechanical precipitation of ionized pyrite. 



LOCI OF GEEATEST ALTERATION AND ENRICHMENT COINCIDENT 



Neither the alteration of the ore-porphyry nor its mineralization 

 can be discussed separately, for the factors involved in one process 

 were evidently involved in the other also. If hydrothermal agencies 

 were factors in this process, it could only have been to initiate it by 

 producing the first kaolinization, thus rendering such portions more 

 susceptible to vadose alteration. It may be that in the vagaries of 

 their attack they were diverted along the underside of the contact 

 in 33 W winze, rendering the ore-porphyry more susceptible to the 

 subsequent action of the vadose waters, which were responsible for the 

 final alteration, supplementing it by mineralization. 



In a general way the extreme alteration and the greatest enrich- 

 ment, are distributed along the main axes of the ore-porphyry ex- 

 posures, and penetrate to the greatest depths along those axes, and, 



