220 ^^6 Philippine Journal of Science i9w 



practically no fines. The magnetites are so soft that a consider- 

 able proportion, perhaps 20 per cent of the ore mined, would be 

 objectionably fine. 



GENERAL CHARACTER OF THE ORE DEPOSITS 



The ore deposits are revealed by the presence of bowlders of 

 iron ore which are found most frequently in streams and on the 

 hillsides adjacent to streams. Such masses weighing from 50 

 to 100 tons are common in the vicinity of the principal deposits, 

 Hison and Camaching. Bowlders and large blocks of iron- 

 stained quartz are also found in profusion near the ore bodies, 

 and, as has been noted, the adjacent effusive rocks are highly 

 silicified. In a general way, the deposits are arranged along 

 a line which marks the base of the sedimentary series and the 

 strike of the ore bodies at Camaching and Hison is parallel to 

 that of adjacent sedimentary beds. The form of the deposits 

 cannot be accurately determined because of the obscure geologic 

 relations and the absence of development; but, as is brought 

 out in the subsequent descriptions of individual ore deposits, 

 the ore appears to occur both as a filling in cavities or veins and 

 as an extensive replacement of the adjacent rocks. The inevit- 

 able alteration of the walls renders it impossible to define their 

 original character, but here again in a general way it may be 

 said that the ores occur in proximity to intrusive dikes and 

 sills and are located in sedimentaries or in granite or other 

 igneous rocks near their contact with the sedimentaries. Ed- 

 dingfield concluded from a microscopic study of the ores and 

 wall rocks that much of the altered wall rock was originally a 

 diorite. Hematite was observed replacing limestones, coarsely 

 fragmental rocks, and volcanic breccias; likewise small veins 

 of magnetite in limestone (Plate HI) and blocks of limestone 

 inclosed in bodies of magnetite-hematite ore were noted. 



At no place were veins or lodes with sharply defined walls of 

 fresh rock noted. Invariably the walls are a soft, dark green 

 rock composed of basic silicates, commonly fibrous, and carrying 

 varying proportions of magnetite and hematite. The associa- 

 tion of this greenish, altered wall rock with the iron ore is a 

 matter of general observation with the Filipino miners, and is 

 so nearly universal that they have learned to know it as camisa 

 de bacal (the shirt or cloak of the iron ore). The suggestion 

 at once arises that this rock with which the iron ore occurs may 

 be analogous to the skarn of the Scandinavian iron-ore deposits. 

 Skarn is defined " as a rock of varying composition, consisting 



"Sjogren, Hjalmar, Trans. Am. Inst. Eng. (1907), 38, 766. 



