470 II. W. Turner — Gold Ores of California. 



and in radiating tufts, and is presumably an altered dike rock, 

 perhaps a fine grained diorite. There is also a fine grained 

 dike? rock next to the vein of the Piatt and Gilsen mine, 

 which contains a good deal of a brownish mica, specks of iron 

 disulphide and chlorite in minute veins. This rock is also 

 called " slate " by the miners. The ore of the Hyde mine 

 which is also in granite in the Soulsby ville district, is free mill- 

 ing. It contains the same sulphurets as the other mines above 

 mentioned but in smaller amount. 



In the West Point mining district, the ore contains abund- 

 antly ordinary iron and copper sulphides and magnetic iron 

 pyrite or pyrrhotite. Cutting the vein of the Lockwood mine 

 are dikes of a fine grained diorite of the camptonite series. 

 The vein was said to have been richer where cut by these 

 dikes. 



To the north of Merrimac in Butte County, similar dikes 

 accompany some of the gold quartz veins in the granite. 



Gold in albite. — As is well known free gold usually occurs 

 associated with quartz as a gangue. Instances are on record, 

 however, of its occurrence in various materials, as talc, calcite, 

 etc. Recently a series of specimens was sent to the writer by 

 Mr. Leo Yon Rosenberg of New York city, from the Shaw 

 mine in Eldorado county, about four miles southwest of 

 Placerville. This deposit occurs in clay slates associated with 

 a dike or dikes of a feldspathic rock, which appears to be 

 devoid of bisilicates. Judging from the specimens forwarded, 

 the dike rock is more or less decomposed, and is at some points 

 replaced by secondary white feldspar, which at other points 

 cuts the dike rock in little seams. This feldspar is well crys- 

 tallized, and with the aid of a lens striations may be noted on 

 the crystals. In thin section these feldspars are seen to be 

 twinned polysynthetically with extinctions proper to albite, 

 and a partial chemical analysis by Dr. Hillebrand of the IT. S. 

 Geological Survey shows that it contains soda, no lime, and 

 about 19 per cent of alumina. It is therefore albite. In two 

 specimens of this crystallized albite there is free gold. Another 

 interesting specimen is of a dark fine grained rock which 

 appears to be an aphanitic form of the dike-rock in a seam of 

 which free gold with a little calcite has been deposited. 



The following is a partial analysis by George Steiger of the 

 feldspar of the grayish-green dike rock forming part of the 

 Shaw mine lode. 



(No. 452 Sierra Nevada collection.) 



Alumina . . - about 20-00 



Lime '49 



Potassa.. -. 1 - 15 



Soda .- 8-72 



