204 The Philippine Journal of Science i9i4 



each outcrop, but these surveys yielded no data which could 

 be used in quantitative determinations. 



McCaskey's work, already referred to, is the most important 

 publication on the Bulacan iron ores and iron mining. McCaskey 

 mapped the region and described in detail the smelting process, 

 but was unable to devote much time to the geology of the 

 ore deposits. A report by Maurice Goodman ^ contains accurate 

 cost and production data for the mining industry, together with 

 a design for an improved blast furnace. Warren D. Smith * 

 has published brief notes on the geology of the region, and 

 has ventured an opinion on the genesis of the ore. The other 

 published references are brief general descriptions, the value 

 of which is principally historical, or reports of the former annual 

 mine inspections of the Spanish Government. 



SUMMARY OF PRINCIPAL RESULTS OBTAINED 



The iron ores of Bulacan are situated in the edge of the 

 Eastern Cordillera of Luzon in an inaccessible and undeveloped 

 region; the ore bodies are not continuous, but are found at 

 intervals over a distance of about 15 kilometers. They occur 

 at the base of the Miocene sedimentary rocks in the overlap 

 of these beds on the older complex of deep-seated and effusive 

 igneous rocks of the cordillera. Intrusive rocks in the form 

 of dikes are found in proximity to the ore deposits, and are 

 probably genetically related to the ores. The largest ore body 

 is at Camaching in the northern part of the region, but other 

 deposits which may be of commercial importance are situated 

 at Hizon, Santol, and Montamorong. 



The ores consist of magnetite and hematite in intimate 

 mixture ; quartz is the most abundant gangue mineral, but pyrite 

 is also common. Magnetite, hematite, and pyrite occur as 

 primary minerals in quartz; quartz and pyrite also occur as 

 secondary minerals. The ore occurs in veins and as replace- 

 ments, the latter class of ores being more important. The largest 

 deposit is in sedimentary rocks with which it conforms in strike 

 and dip; it replaces limestone and clastic sediments. Some of 

 the ore bodies are probably in igneous rocks. The walls of the 

 ore bodies are uniformly composed of a soft dark green rock 

 made up of complex silicate minerals which is comparable with 

 the "skarn" characteristic of some of the Scandinavian iron-ore 

 deposits. 



" 6th Annual Rep. P. I. Min. Bur. (1905), 48-56. 



'Min. Resources P. I. for 1909 (1910), 32; ihid. for 1910 (1911), 57. 



