X, A, 5 Pratt: Iron Ore on Calambayanga Island 327 



and fragmental rocks predominate over other types. These 

 volcanic rocks are less indurated than the sedimentaries on the 

 eastern shore of the island, and there is a consequent suggestion 

 that they belong to a separate younger formation. 



Extending north-northwest into the mass of the island from 

 the southeastern point is a great outstanding body of quartz, a 

 lode or vein, with a width of possibly 100 meters. This quartz 

 is mineralized and contains numerous veinlets of iron ore. A 

 shallow pit has been sunk in the quartz near the center of the 

 island, and a sample taken from the wall of this pit showed upon 

 assay a trace of gold. The sedimentary rocks to the east are 

 highly silicified near the contact with the quartz. 



The outcrop of the quartz becomes concealed toward the north- 

 northwest by a mantle of clay, but on the northwest shore, ap- 

 proximately at the point where the quartz should reappear, if 

 it continued so far, there is encountered a dike of dark-colored 

 gabbro between agglomeratic tuff and sedimentaries. This dike 

 is vertical and strikes north 60° west. A small vein of quartz 

 carrying unaltered fresh pyrite was observed in it. Under the 

 microscope the dike rock is seen to be holocrystalline and to 

 consist principally of plagioclase feldspar and pyroxene. The 

 feldspar predominates and occurs in large lath-shaped crystals 

 with a parallel arrangement. The pyroxene appears to be much 

 decomposed, and associated with it throughout the section is 

 magnetite in considerable abundance. 



Along the western and northern shore line of the island the 

 blocks of iron ore are present in great abundance and lie one 

 upon another with no intervening foreign material. Farther 

 up the slopes, however, and at the summit of the island the 

 blocks are scattered over the surface, embedded in residual clay. 



Fanning - studied the ore on the mainland ; he traced the out- 

 crop of the ore for a total distance of 3 kilometers (including 

 the outcrop on the island?). The width as revealed to him by 

 occasional outcrops in place varied up to 15 meters. Sedi- 

 mentary rocks are found on the mainland, as on the island, and 

 similarly are indurated, tilted at various angles, and pierced by 

 dikes. Volcanic tuffs, agglomerates, and flows are prominent 

 on the mainland and on the neighboring small islands. 



At Bato-bolani the iron ore occurs in large blocks scattered 

 over the side of a hill. The ore is magnetite with some hematite 

 and carries also fresh quartz and pyrite. F. Rinne,^ a German 



' Smith, W. D., and Fanning, P. R., Min. Res. P. I. 1910 (1911), 58. 

 ' Zeitschr. f. prak. Geol (1902), 10, 117. 



