IX, A, 3 



Dalhurg and Pratt: Iron Ores of Bulacan 



223 



and composed of plagioclase feldspar and pyroxene or horn- 

 blende, are prominent near the ore deposit but in undetermined 

 relations. The general structure is shown in fig. 5. 



The ore consists of soft massive magnetite with quartz and 

 pyrite. It grades into the walls which are composed of the 

 usual complex of silicates among which amphibole, pyroxene, 

 epidote, and chlorite were identified by Eddingfield, together 

 with much magnetite, quartz, and pyrite. As revealed in this 

 pit, the ore appears to form a vein 1 to 2 meters in thickness. 

 The outcrop can be traced over a length of 50 meters. The 

 strike appears to be northwest and the pitch northeast at an 

 angle of about 45°, but the presence of two strike faults with 

 evident displacement makes the true attitude of the ore body a 

 matter of doubt. In the hanging wall is a small parallel quartz 

 vein carrying magnetite and pyrite. Eddingfield found by the 



Fig. 5. Geologic section through ore body at Montamorong, along a northeast-southwest line ; 

 diagrammatic in part: (a) Granite; (6) intrusives ; (c) altered wall rock; (d) iron ore; 

 (e) effusives ; length of section, about 100 meters. 



study of thin sections that the original quartz in this vein had 

 been shattered and recemented by quartz and magnetite. 



THE HISON-SANTA LUTGARDA-CONSTANCIA ORE DEPOSIT 



About 9 kilometers south-southwest of Camaching and on the 

 line of the strike of that ore body are three adjacent outcrops of 

 iron ore. The central and largest of these outcrops is known as 

 Hison. About 300 meters south-southwest of Hison is the Maa- 

 rat or Santa Lutgarda outcrop, and 500 meters north-northeast 

 of Hison is a smaller outcrop called Constancia. Each outcrop 

 is revealed by a small eastward-flowing tributary of Maon Creek. 

 Although the ore cannot be traced in continuity from one out- 

 crop to another, yet the exposures appear to be closely related 

 and are probably situated on the same structural line if not 

 actually continuous. 



These outcrops lie just outside the eastern limit of the granite 



