326 The Philippine Journal of Science 1915 



which were formed in the granite during metamorphism were 

 filled by gold-bearing quartz. One of the products of the min- 

 eralization associated with the intrusion of the dike rocks into 

 the sedimentaries is the iron ore in question. 



CHARACTER OF THE IRON-ORE DEPOSITS 



The ore body on Calambayanga Island appears to be irregular 

 in shape, but to conform more or less closely to the strike and 

 dip of the sedimentary beds in which it occurs. It outcrops on 

 the western part of the island and is roughly oval or lens-shaped 

 in plan. Ore of exactly the same character is encountered on 

 the mainland to the south, where exposures are seen at intervals 

 for a distance of at least 2 kilometers (1.2 miles) inland. A 

 small island south-southwest of Calambayanga Island and con- 

 siderably to the west of a line between it and the outcrops on 

 the mainland is composed wholly of iron ore of the same 

 character. Again, at Bato-bolani, 12 kilometers (7.5 miles) 

 southeast of Calambayanga Island and still near the line of 

 contact between the sedimentaries and the older igneous rocks, 

 iron ore similar in character to the Calambayanga ore is found. 



At each of these places the outcrops are marked by great 

 blocks of black ore, angular in form and with pitted, irregular 

 surfaces. These blocks have been designated as bowlders by 

 several observers, but the term bowlder conveys a wrong im- 

 pression, inasmuch as the masses of ore at the outcrops show 

 no evidence of having been transported, but have the appearance 

 of disintegration products in place. They vary in size up to 

 masses of many tons' weight. At the prominent outcrops they 

 occur to the exclusion of all other rocks, but elsewhere they 

 are isolated from each other and are embedded in yellow, residual 

 clay. 



Only the Calambayanga ore body has been examined closely 

 by me. The western half of the island is strewn with blocks 

 of ore. The northeastern part is made up of sedimentary rocks, 

 principally sandstones, or iine-grained elastics, shales, and con- 

 glomerates. At the northern extremity of the island the beds 

 strike north 20° east and dip 45° to the west, but toward the 

 south, along the east coast, the strike changes gradually until it 

 is north 60° west with the dip to the south. A bed of crystalline 

 limestone outcrops in the sedimentaries halfway along the eastern 

 coast, and some of the other sedimentary beds are calcareous. 

 Minor outcrops of stratified rocks are found on the eastern coast, 

 but here the strike is north 60° west, and tuffs, agglomerates, 



