REPLACEMENT ORE DEPOSITS IN THE SIERRAS 395 



be quite poor, showing only about $14 per ton. The gold seems 

 to lie largely along the seams and joints of the mass. The 

 unweathered dike rock carries about y 2 per cent, of pyrite in 

 little cubes from 0.5 to 1 mm in diameter. 



In Eldorado county similar dikes form the lodes of gold 

 deposits. Two of these have been worked with some profit. 1 

 The claims are known as the Shaw and Big Canyon (Orofina) 

 mines, and are indicated on the economic geological map of the 

 Placerville folio. My attention was first called to the Shaw 

 mine lode by Mr. Leo von Rosenberg who transmitted specimens 

 of the rock showing the porphyry dike rock, and other specimens 

 containing veins of quartz and veins of albite with free gold. 

 The dike rock of the Shaw mine and also that of the Big Canyon 

 mine contain iron pyrite rather abundantly in places. Calcite 

 is scattered through the dike rock in little rhombs. The evidence 

 at the Shaw and Big Canyon mines is that mineral waters have 

 percolated through the dike rock and deposited the iron pyrite 

 and calcite with some gold throughout portions of the dike, 

 while the quartz has largely been deposited in little veins along 

 with most of the gold. The veins of white albite in the Shaw 

 mine rock are undoubtedly secondary, but probably represent 

 the material of the dike leached out and redeposited. This in 

 itself suggests that albite is a mineral which is readily dissolved, 

 and Lindgren has found sodium one of the elements most readily 

 removed from the wall rocks of quartz veins. 



The Bachelor lode on the north bank of the Tuolumne River 



lies at the contact of a mass of serpentine with a lens of argillite 



supposed to belong to the Calaveras formation. Just east of 



the vein, in the clay schists within a width of thirty feet, are 



six or eight dikes, which usually run parallel with the strike of 



the schists, but at two points cut across the schistosity. Such 



a series of dikes might be called a multiple dike, following 



1 Am. Jour. Sci. Third Series, Vol. XLVII, 1894, pp. 470-471. 

 Engr. and Mining Jour., Nov. 19, 1892, article by C. A. Aaron on the Shaw mine 

 lode. 



Am. Geol. Vol. XVII, 1S96, p. 3S0. 



Kemp; Ore Deposits of the U. S., New Vork 1S96, p. 287. 



