86 . The Philippine Journal of Science 1913 



in some places cross Assuring, which strongly suggests pressure 

 fracturing. 



In as much as mining has been done only comparatively near 

 the surface, it is impossible to tell how deep the ore deposits 

 can be expected to go. Depths from 30 to 100 meters have been 

 explored, and at this depth no apparent decrease in width has 

 been found. The fissures in general are strong, and can be traced 

 for over 500 meters along the strike. In Mambulao it was noted 

 that the veins in the granite gneiss were wide and strong, but 

 where they passed from the gneiss to the schist they became 

 very irregular, splitting into stringers, and finally pinched 

 out entirely. In the San Mauricio mine the veins near the shaft 

 in the schist, which overlies the gneiss at that point, are very 

 irregular in dip and strike, but when the gneiss is reached with 

 depth these veins are united into one uniform vein. This is 

 probably due more to the physical condition of the schist than 

 to chemical action. The schist offers great resistance to As- 

 suring, except parallel to the planes of compression. This has 

 resulted in a resistance to transverse Assuring and a tendency 

 to change the fissure parallel to the schistosity. 



In Benguet, the Fianza vein is either cut off at the diorite or 

 the Assuring in the andesite does not extend into the diorite. 

 In another section of Benguet on the Ascension group, a vein 

 was found varying in width from 1 to 5 meters in a distance 

 of 1 kilometer along the strike. These cases are the only ones 

 so far found where marked irregularities occur, except in cases 

 of lateral enrichment or in contact deposits between igneous 

 and sedimentary rocks. These veins are small, unimportant, 

 and presumably limited in extent. No veins are found cut- 

 ting across sedimentaries. 



VEIN FILLING 



The difference in the mineralization of the veins of any one 

 district is very marked, and indicates clearly that the ascending 

 solutions must have taken up minerals from different formations 

 in their path. It is apparent in Suyoc, Benguet, and in Aroroy 

 that solutions from at least two different sources have produced 

 most of the vein matter, each one dissolving different minerals 

 in its ascent. At one period, solutions deposited silica, silica 

 and manganese, silica and copper, or silica and lead, depending 

 upon the minerals encountered in their passage. At another 

 period, they deposited calcite and calcite and manganese. In 



