H. W. Turner — Gold Ores of California. 467 



Art. LIX. — Notes on the Gold Ores of California y by 

 H. W. Turner. 



As is well known gold occurs chiefly in quartz veins and 

 these in California have been found to be largest and richest 

 in the slate series of the Sierra Nevada, but gold occurs in a 

 great variety of rocks and associated with very different min- 

 erals. 



The occurrences will be grouped geologically. 

 Veins in the auriferous slate series. — Most of the richest 

 gold mines of California occur in the auriferous slates, and in 

 the associated greenstone slates which are, to a considerable 

 extent, metamorphic forms of diabases and porphyrites. The 

 richest single belt of mines is that along the Mother lode, 

 which consists of a series of quartz veins chiefly in a belt of 

 clay slates of Jurassic age, which are designated on the maps 

 of the United States Geological Survey as the " Mariposa 

 slates." The quartz veins are not, however, entirely in these. 

 clay slates. In the southern part of Calaveras county and in 

 part of Tuolumne county, the lode lies to the east of this clay 

 slate belt, chiefly in amphibolite-schists. At many points, as 

 at Carson hill in Calaveras county and at Quartz mountain in 

 Tuolumne county, the quartz masses are very large. At other 

 points the quartz occurs in little veins and stringers, through a 

 mineralized zone of the black slate, which then forms part of 

 the vein. In some such occurrences the iron sulphurets con- 

 taining gold are found both in the slate and in the quartz, and 

 all the material is treated as ore. 



Accompanying the Mother lode quartz veins at many points 

 is a green micaceous mineral, containing chromium and called 

 mariposite by Silliman,* who states that so far as he observed, 

 this mineral accompanied the quartz veins only in the neigh- 

 borhood of magnesian and chloritic rocks. 



Prof. Silliman also states that the white magnesian mineral 

 associated with the mariposite is ankerite. Other minerals 

 found by the same author along the Mother lode are ordinary 

 iron and copper sulphides, antimonial copper sulphides, anti- 

 monial lead sulphides, and various tellurites. Prof. Silliman 

 also identified somewhat doubtfully tetrahedrite or gray copper 

 ore at the Rawhide mine in Tuolumne county. 



Prof. F. A. Genthf states that petzite, telluride of gold 

 and silver ; calaverite, telluride of gold ; altaite, telluride of 

 lead; and melonite, telluride of nickel, occur at various mines 

 of the Mother lode in the area of the Stanislaus drainage. 



*Proc. Cala. Acad. Sci., vol. iii, p. 381. 

 fThis Journal, vol. xlv, IT, p. 321. 



