W. Lindgren — Auriferous Veins of California. 205 



soon replaced by the sulphides mentioned and in which the 

 gold occurs in extremely line distribution. 



Auriferous copper ores prevail at the Keystone, with cuprite, 

 chrysocolla and other secondary minerals. At the most devel- 

 oped mine, Excelsior, iron pyrite is the most abundant ore. 

 Silver does not occur to any notable extent in the ores. 



Gangue. — While some white quartz with admixed sul- 

 phides occur, the usual gangue is a black, hard and dense 

 rock of sometimes almost basaltic appearance, in which the 

 ores are disseminated.* In more coarse-grained specimens 

 yellow epidote, quartz grains and small radiating aggregates of 

 a dark brown tourmaline are visible. Under the microscope 

 the black veinstone is resolved into an interlocking aggregate 

 of quartz grains, occasionally traversed by cracks along which 

 comminution and crushing has taken place ; gas and fluid 

 inclusions are plentiful ; epidote and sometimes zoisite form 

 aggregates in places ; tourmaline occurs as irregular grains 

 with the quartz but much more commonly as slender crystals 

 and radial aggregates intimately and plentifully imbedded in 

 the quartz. The tourmaline has pleochroic colors varying 

 from bright brown to dark bluish or greenish gray. Skeleton 

 crystals are common, the interior being tilled with quartz 

 grains and bunches of radial chlorite. This latter mineral is 

 quite common in some slides, sometimes traversing the tourma- 

 line in small veins. Brown mica occurs in aggregates, together 

 with the tourmaline. A colorless mica, titanite, ilmenite and 

 some caicite were also observed. The ores occur intimately 

 intergrown with this gangue. In one case pyrite was observed 

 surrounded by a ring of pyrrhotite. 



In a small vein occurring where the trail to Meadow Lake 

 crosses Fordyce creek grains of a faintly greenish monoclinic 

 pyroxene and probably also a little albite occur together with 

 abundant quartz, tourmaline, epidote and pyrite. . The occur- 

 rence of pyroxene in veins of this class is certainly not usual. 

 Pyroxene is however not exclusively an igneous mineral ; Dau- 

 bree has long ago shown that it may be formed by the action 

 of superheated water on glass containing iron, and according 

 to Broggerf it sometimes occurs in the veins of the syenite of 

 southern Norway together with zeolites and caicite in such a 

 way that it must be regarded as having been formed contem- 

 poraneously or even later than the zeolites. 



*Mr. Alfred R. Conkling, who for some time was engaged as a geologist of the 

 Wheeler Survey, makes indeed the startling statement that "the ore deposits at 

 Meadow Lake are generally found in a mass of basalt enclosed in the country- 

 rock, gray granite." Annual Report of Chief Engineer, 1878, Appendix NN, 

 p. 183. 



f Zeitschr. Kryst. u Min., xvi, p. 329. 



