328 The Philippine Journal of Science wis 



geologist has published a description of the Bato-bolani ore de- 

 posit from which the following extract is quoted : 



It might be thought that the magnetite masses here are a segregation 

 from an igneous rock, probably from the diorite found between the masses 

 of ore. It is surprising, however, in explaining the magnetite as a magmatic 

 segregation that nowhere was the contact between the diorite and the ore 

 to be seen. The ore masses were encountered everywhere without any 

 adhering or inclosed pieces of diorite. This circumstance indicates strongly 

 that the once existing rock with which the present blocks were associated 

 was comparatively easily destroyed, so that the ore, freed through weather- 

 ing, is now nowhere in continuity with it. In this connection the occurrence 

 of a dark-colored limestone, of which several pieces were found at a place 

 on the same slope, is interesting. It is possible that the ore masses were 

 enveloped in this easily soluble limestone. It appears to me very plausible 

 that the magnetite blocks at Bato-bolani were formed by contact phenomena 

 between diorite and the limestone, which is still found in traces over the 

 former surface of the igneous rocks. * * * Qne could suppose that 

 the ore formed in the limestone under the influence of the solutions and 

 gases coming from the cooling diorite magma. I did not observe other 

 contact minerals such as garnet, at the place, but in complete accordance 

 with this theory is the occurrence of nests of yellowish white, needlelike 

 quartz which are found sparingly in the magnetite. In places the ore 

 particles build a sort of frame or skeleton, the spaces of which are filled 

 with quartz. 



CHAEACTER OF THE ORE 



The iron ore on Calambayanga Island and on the adjacent 

 mainland is almost pure hematite with only traces of magnetite. 

 The hematite is massive or granular, and the ore is moderately 

 soft and very porous, or vesicular. At places over the exposure 

 a small proportion of pyrite in fresh crystals may be detected in 

 the hematite, and likewise quartz is found sparingly in scattered 

 grains or in veinlets. Copper stains were found in the slightly 

 pyritiferous ore at two places, indicating that some chalcopyrite 

 occurs with the pyrite. 



The Bato-bolani ore contains much more magnetite than the 

 ore on Calambayanga Island; it is also harder and shows more 

 pyrite and quartz, but otherwise the ores are similar. 



The composition of the ore is shown in Table I. Analysis 1 is 

 to be given greater weight than any of the others because of the 

 larger quantity of ore which it represents. Apparently the 

 average ore carries about 60 per cent of iron and is reasonably 

 free from objectionable constituents. In only one analysis is the 

 phosphorus above the Bessemer limit. 



GENESIS OF ORE DEPOSIT 



' The observations set forth in this report have led to the con- 

 clusion that the ore on Calambayanga Island is related in origin 



