viii, a, 2 Edding field: Ores of the Philippines 87 



one case alternations of these two classes of solutions have taken 

 place, producing banding of calcite and quartz. The country- 

 rock seems to have had but little chemical effect upon these 

 deposits, and the predominance of veins in the andesite is due 

 entirely to its more fractured condition. 



The most characteristic feature in regard to the ore deposits 

 of the Philippines is the abundance of quartz-calcite-manga- 

 nese veins. Quartz-manganese veins are very common in Ter- 

 tiary deposits of the United States, some of which also contain 

 calcite, but the occurrence of large amounts of calcite associated 

 with the quartz and manganese is unusual. 



The primary manganese ore is probably either manganiferous 

 calcite or rhodonite; in one mine rhodochrosite was found. It 

 is probable that, where the manganese and quartz were deposited 

 together, the primary ore would contain some alabandite. In 

 the zone of oxidation are found the oxides, manganite, and wad. 

 These oxides are found in streaks in the veins, and usually 

 contain the highest gold values found in the deposit. 



The characteristic section of this type of vein in the zone 

 of oxidation consists of: (1) A band of solid compact calcite, 

 varying in width from 0.5 to 6 meters, often lying next to the 

 foot wall; (2) bands of black, soft manganese, usually mixed 

 with quartz fragments or honeycomb quartz, and often con- 

 taining pockets of white quartz crystals which in some mines 

 indicate high values; these bands are found in some cases next 

 to the calcite, in some cases next to the foot wall, and almost 

 always next to the hanging wall ; they vary in width from 0.2 to 

 4 meters; (3) a band of massive quartz, carrying sulphides and 

 varying in width from 0.1 to 4 meters, usually separated from 

 the calcite by a manganese band. 



ALTERATION IN THE VEINS 



Alteration has taken place in the veins due to oxidation, leach- 

 ing, and enrichment. These elements have in some cases entirely 

 changed the character of the ore above the lowest level of ground 

 water, so that very little remains to indicate the true character 

 of the primary ore. 



The zone of oxidation in the veins in many cases is deep on 

 account of the mountainous condition of the regions and the 

 resulting low limit of ground-water level. The ground-water 

 level varies from a plane near the surface during the rainy 

 season to a plane near or possibly below the level of the bottom 



