The Mineral resources of the Philippine Islands

 
9781235949302: The Mineral resources of the Philippine Islands

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1908 Excerpt: ...cases means below sea level. Tunnels as a rule give very shallow depths in comparison with their length, so shaft work generally will be necessary. THE NALASVETAN, AMBOS CAMARINES, GOLD DISTRICT. By Wallace E. Pratt. Location.--Nalasvetan, a barrio of Labo, Ambos Camarines, is situated on a branch of the Bosigon River (also called the Labo River) and is about 21 kilometers in an air line southwest of Mambulao. It can be reached from Mambulao by means of a very poor trail. History.--Nalasvetan was the site of a considerable amount of early mining. The ruins of the few underground workings in this place, perhaps, are more extensive than any others in the Camarines gold field. There is no record of extensive Spanish mining at Nalasvetan, and the caved excavations have been attributed to Chinese miners working at a time earlier than the Spanish occupation. No direct evidence supports this supposition. Geologic.--The district lies at the center of the great area of extrusive and intrusive rocks which form the cordillera in this portion of Luzon. The prevailing type is porphyritic andesite, black in color grading into basalt and occurring generally as volcanic agglomerate or breccia. In the streams, boulders of diorite are not unusual, showing that the older, coarsely crystalline rocks, with which gold is commonly associated in the Philippines, occur here also, but no exposure in place could be found in the immediate vicinity. Isolated patches of metamorphosed sedimentary (Tertiary?) rocks were observed also at several places along the trail from Mambulao to Nalasvetan. Evidently, before the advent of the volcanics, this was an area of older crystalline rocks, at least partly covered with sedimentaries. Ore body.--The gold-bearing deposit at Nalasvetan can scarce...

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