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Geology and Mineral Characteristics of Manila Mining's Placer Mine
Regional scale Geology
Surigao del Norte is the northernmost end of the Eastern Mindanao Ridge or the Eastern Mindanao Island Arc System (EMIAS). Most workers interpret the Eastern Mindanao Ridge as an inactive west-facing arc related to the eastward subduction with the paleo-trench lying west of the Agusan-Davao trough. The Agusan Davao trough is a NNW- SSE trending basin of Eocene Pleistocene sediments of about 50 km wide and 6 km thick. To the west of the arc lie several NNE trending splays of the Philippine Fault. The EMIAS area consists of three (3) distinct Physiographic-Tectonic-Stratigraphic units namely; the Eastern Highlands, the Central Lowlands, and the Western Range. These units trend NNW (Fig. 4).
Upper Cretaceous basement rocks and Miocene volcano-sedimentary series dominated by volcanic centers of the Pliocene Mabuhay Andesitic principally underlie the Eastern Highlands together with the offshore islands. Placer Mine of MMC is located within this Tectonic Unit.
The Central Lowlands including the area of Lake Mainit are apparently a graben structure bounded by splays of the Philippine Fault and filled mainly by Quaternary and Pliocene deposits. The Surigao Valley Fault and the Mainit Fault, respectively, control the graben on the east and west (Figs. 4 & 5).
The Western Range is an uplifted block between the Mainit Fault splay and the major fault of the Philippine Fault System, extending offshore the Surigao peninsula. Quaternary andesite and local occurrences of tectonic mélange of basement rocks dominate this block.
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| Volcanic, Volcaniclastic & Sedimentary Rocks |
| Intrusive Rocks |
| Structures |
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