134 The Philippine Journal of Science 1913 



is plentiful; but judging from the fairly constant proportion of gold to 

 silver (about 1 to 100 by weight) there has been little selective migration 

 of gold and silver during oxidation, although the vein has been enriched 

 to some degree by downward penetration of minerals leached from the out- 

 crop as it was eroded. 



XXII. Manhattan, Nev. — Although the schists contain stringers of gold 

 of uncertain genesis, the principal deposits are steeply-dipping lodes of 

 quartz and calcite, stained with iron and manganese oxides. Some placers 

 are developed. Rich ore was found very near the surface, but it was 

 richer a few feet below the outcrop than at the surface. * * * In 

 many instances the gold of the pockets of rich ore is intimately associated 

 with iron and manganese oxides. 



XXIV. Bullfrog District, Nevada. — The minerals include pyrite, quartz, 

 and manganiferous calcite. Enough manganese is present in the calcite 

 to stain much of the oxidized ore chocolate-brown or black. No placers 

 are developed. The outcrops are comparatively poor, but within a few 

 feet of the surface good ore was encountered, and some of the deposits 

 were worked by open-cut. Some of the deposits decreased in value below 

 the 400-ft. level, where ore carrying less than $5 per ton is encountered. 

 Since the ore above this level carried many times this value, it appears 

 that there has been a secondary concentration by surface-waters, and that 

 the rich ore is related to the present topographic surface. 



