204 W. Zindgren — Auriferous Veins of California. 



diabase-porphyrite ; at Fordyce dam, farther south, it is a bio- 

 tite-diabase. The relations of the diabase to the granodiorite 

 are not clear beyond doubt, but the latter appears to be the 

 younger rock. 



Andesite. — Several small masses of andesitic breccia of late 

 Tertiary age cover the older rocks to the west of Meadow 

 Lake ; north and east of it large masses of this volcanic rock 

 appear. 



Ore deposits. — The granodiorite area contains between Sig- 

 nal Peak and Meadow Lake a great number of black veins 



and seams composed of 

 quartz, tourmaline and epi- 

 dote, together with grains 

 and smaller masses of pyrite. 

 In certain places the latter 

 mineral, and other sul- 

 phides have been formed to 

 a large extent and are aurif- 

 erous enough to render 

 their exploitation possible. 

 A few of the veins which 

 have been worked from 

 time to time are indicatsd 

 on the figure. The strike 

 is northerly or northwest- 

 erly, the dip vertical 

 or at high angles to the 

 northeast ; the width of 

 the veins is variable ; some- 

 times, as at Excelsior, it 

 W/i'/'j/' y^S^r^i reaches twelve feet. The 



^b/i^/M^r^ ^\ """»• walls are frequently indis- 

 • tinct. The veins near 

 Meadow Lake do not seem 

 to be traceable for long dis- 

 tances, while some of those 

 of Old Man Mountain, 

 which is a rounded granitic dome, traversed in several directions 

 by fissure systems, appear to be continuous for half a mile or 

 more. The country rock is not extensively altered in the vicinity 

 of the veins. Many small veins occur at the contact of grano- 

 diorite and diabase near Meadow Lake and a few are also 

 found in the latter rock just south of the lake. 



Ores. — The ores consist of iron pyrite, arsenical pyrite, 

 pyrrhotite, zincblende, and rarely galena ; on the decomposed 

 surface much coarse free gold occurred which, however, was 



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