411 



University of California Publications. 



[Geology 



seams of barite, carrying gold and silver, distributed through a 

 kaolinized zone in diabase and diabase porphyrite. " Since 1892 

 more development work has been done, but at present the mine 

 is tied up by litigation, and the shafts flooded with water. 



Pine Hill itself consists of augite andesites, ophitic diabases, 

 amygdaloids, and tuffs. Intercalated with the porphyries is a 

 lens of fissile black slate 50 feet thick. Near the summit of Pine 

 Hill the tuffs have been crumpled and brecciated. This has been 

 the locus of most intense mineralizing activity. Extensive gossan 

 croppings often containing much heavy spar have formed. Large 

 masses of pure solid barite occur. The gossan when panned yields 

 numerous coarse colors of gold. The pure barite assays $2 per 

 ton. 



Tunnels run into the hill show that the porphyries have been 

 thoroughly leached by sulphuric acid. They still retain their 

 porphyritic aspect, but are soft enough to be kneaded. A very 

 white kaolin, theoretically pure,* is of frequent occurrence, but 

 seems limited to zones of movement. This movement may be 

 correlated with the arching upward of the floors of abandoned 

 drifts — 1 foot rise in 44 feet. The tunnels show that the 

 porphyry has been fractured and stained with iron oxide along 

 the cracks and fissures. At open spaces porous platy masses of 

 limonite have formed, and lying loosely upon these are numerous 

 small glassy crystals of barite. 



The gossan has long been mined as a free milling gold ore. 

 At 75 to 100 feet in depth oxides, carbonates, and native copper 

 were encountered, and the barite disappeared. The copper ore 

 below this consists of a crumbly mass of bluish black sulphide 

 in which the frequent glint of pyrite can be detected. A thin 

 section of leaner ore shows grains of pyrite surrounded by per- 

 ipheral coatings of copper sulphide. The gangue is fine grained 

 quartz. Unfortunately, the flooding of the mine did not admit 

 of a closer investigation of the extent of the secondary enrich- 

 ment. 



THE VALLEY VIEW GROUP. 



Dairy Farm Mine. — A large lens of solid pyrite 60 feet thick, 

 carrying 2 per cent, copper, parallel to the foliation of the enclos- 



* W. Lindgren, loc. cit. 



