Composition of the mine waters ____________ _ Porosity of the gossan iron ore ___ _: __________ _ Distribution and character •of the gossan iron ore_ Distribution of the secondary copper ore-~-Texture of the secondary copper ore _________ _ Chemistry of alteration and enrichment ______ _ Segregation of iron ore and copper sulphide ore_ Silver and gold ___________________________ _ Solution of zinc ___________________________ _ T~nor of the ore beneath the chalcocite zone __ Enrichment below the chalcocite zone _______ _ Relation of chalcocitization to erosion _______ _ Comparisons with chalcocite zones elsewhere __ Summary of metasomatic processes_. ____________ _ Summary of genesis of the ores _________________ _ Future of the district_ _________________________ _ CHAPTER VI. Detailed descriptions of mines, by w. H.
Forthe structural observations and the dis-. In the spring of 1915, while engaged in a cussion of the•mine waters the senior author is study of silver emichment for the United responsible; for the detailed mineralogic and States Geological Survey, Mr. Bastin spent a inicroscopic 'studies both authors are remonth at Tonopah, Nev., in studying the ores• sponsible. They are •indebted to Mr. Chase and their mode of occurrence. At. about the Palmer, of the United States Geological Sursame time Mr. Laney was directed by the vey, for careful analyses of samples• of the United States Bureau of Mines to make collec-mine waters and for chemical and mineralogic .. tions of Tonopah ores and to study their studies, and to Messrs. F. L. Ransome and •mineralogy in connection with the researches Adolph Knopf, also_ of the .Survey,•for valuable ~f that Bureau on their metallurgic treatment~ criticisms and suggestions.
~To avoid duplication of effort and to secure the The mine operators and others in Tonopah added fruitfulness which should follow the con-gave generously of their time and their knowleentration of more than one mind on a scientific edge and contributed many choice specimens problem, it :was decided to ccmbine these efforts in furtherance• of the work. To them the. in so far as the two fields of research overlapped. writers' sincere thanks are offered. The paper accordingly presents the results of informal cooperation between the Geological Survey and the Bureau o~ Mines.The investigation . was intended to supplement the impqrtant work of Spurr 1 and Burgess. 2 t>y applying to the ores methods of microscopic study which were not in general use by economic geologists at the time their reports were prepared, but which, in other districts, have proved of 111aterial assistance in the interpretation of ore genesis.
THE TONOPAH DISTRICT.The Tonopah mining district is too well known to require an extended description. From the discovery of its ores in 1900, its output h~s increased year by year until in 1915 its production of silver was exceeded in the United States only by that of Butte. Its metal output since 1904 is shown in the following t•able, compiled by V. C. Heikes, 3 of the Geological Survey:
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