338 University of California Publications. [Geology 



probable that the porphyry on the north side of the dyke below 

 the zone of oxidation is impregnated with chaleoeite just as it 

 is on the south side. In fact, the general conditions of deposition 

 lend much support to the belief that a large part of the por- 

 phyry mass below the zone of oxidation will be found to carry 

 more or less copper and will be well worth prospecting, particu- 

 larly where the capping of quartz blout is strongly developed. 



At Copper Flat the general conditions are analogous to those 

 at the Ruth. There is the same porphyry intrusive in Carbonif- 

 erous limestones, and although, as the map shows, this area of 

 porphyry is separate from that of the Ruth yet the two may be 

 continuous in depth. The fact that, on its western border, the 

 porphyry of the Ruth area plunges beneath the limestone, while 

 that of the Copper Flat on its eastern border passes similarly 

 beneath the limestones in the opposite direction, renders this 

 subterranean continuity of the porphyry of the two areas quite 

 probable. On the hills about Copper Flat there are remnants 

 of a once extensive body of quartz blout. In general it is diffi- 

 cult to specify any significant difference in the general condi- 

 tions affecting the porphyry and those which prevail at the Ruth. 

 Yet in one important particular the porphyry regarded as an 

 ore of copper is very different from that at the Ruth. This 

 difference lies in the fact that, in the zone of oxidation, the 

 copper ores, over a very considerable acreage at least, have not 

 been leached out of the porphyry but have been fixed in the 

 form of carbonates. Over an area of perhaps 10 acres numerous 

 prospect pits have been sunk in the porphyry and show a very 

 general impregnation of the rock with green and blue carbonates 

 and carrying on the average an attractive percentage of copper 

 said to range up to 7 per cent. Many of these pits are fairly 

 deep and the dumps about them show that the copper carbonate 

 extends to their bottom. Not having had access to the record of 

 these prospect pits or to the assays of the samples taken from 

 them the writer can form no very exact idea as to the depth and 

 value of the ore. The exposures are, however, excellent and 

 enough is apparent at the surface to warrant the statement that 

 there is a vast tonnage in sight, both of unoxidized and of oxi- 

 dized ore, that could be mined by steam shovel methods. Unfortu- 



