266 The Philippine Journal of Science i9i4 



THE VEIN MINERALS 



In all cases, the magnetite and crystalline hematite were the 

 first to solidify in the deposit; a few slides show magnetite and 

 hematite together, but so intimately associated that their rela- 

 tion could not be determined. Following or overlapping this 

 period was the period of crystallization of the pyroxene and 

 amphibole minerals, which seemed to be segregated near the 

 walls and even to attack the walls. This was followed by the 

 quartz period which not only filled all the crevices in the fissure 

 but attacked the walls and, continuing upward, attacked the 

 capping of the district. 



In a few cases a pyrite period occurred accompanied by a 

 little chalcopyrite. This came in between the iron oxide period 

 and the quartz period. 



Where magnetite or hematite is associated with quartz alone 

 is found the beautiful treelike growth of crystals, mentioned 

 above as needle- and fan-shaped groups. These indicate very 

 clearly the jellylike condition of the quartz which supported the 

 iron oxides during crystallization. These fanlike growths occur 

 only with the quartz, and are not found with the pyroxene or 

 amphibole or in the wall rocks. Rounded grains and masses of 

 magnetite are also found associated with quartz, but the tabular 

 shapes are found almost entirely in the pyroxene and amphibole 

 portions of the deposits. 



THE WALLS 



The principal wall rock, according to the samples submitted, 

 is a diorite of varying texture and crystallization. It has under- 

 gone considerable metamorphic action near the contact, being 

 attacked principally by the iron, quartz, and to a lesser degree 

 by the amphibole and pyroxene. It contains generally large 

 amounts of pyroxene (or of amphibole), plagioclase, orthoclase, 

 and quartz and frequently epidote as the chief constituents. The 

 new minerals formed .during metamorphism are magnetite, 

 quartz, titanite, epidote, possibly zoisite and pyrite, and an added 

 amount of amphibole or pyroxene. There appears to be no orig- 

 inal quartz in this rock. If there ever had been, it was replaced 

 during metamorphism. 



Epidote is abundantly distributed in the andesites and diorites 

 throughout the mineralized belt. 



Titanite was probably derived from the iron ore. In one 

 locality only, titanium is abundant in the ore, but chemical anal- 



