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A.G. Loudon






Marcopper porphyry copper deposit is located in the Philippines near the center of the island of Marinduque, 180 km south of Manila. The islands' tectonic history is dominated by northwesterly trending elements of the Philippine mobile belt. Mineralization is related to differentiated intermediate intrusives which occupy the core of a northwesterly trending
regional anticline. The deposit occurs on the western margin of a middle Miocene quartz diorite stock with the majority of the copper rnineralization within a granodiorite porphyry phase. Eocene and Oligocene metasediment and metavolcanic wall rocks are locally brecciated and mineralized.

The orebody contains 102,000,000 tons averaging 0.58 percent copper. It is 1,400 m long, up to 600 m wide, and has been drilled over a vertical extent of 450 m.

Leaching, oxidation, and secondary enrichment have taken place within the top 30 to 90 meters. Primary mineralization is largely vein and fracture filling with some dissemination. Chalcopyrite, pyrite, and magnetite are ubiquitous together with minor amounts of bornite, covellite, molybdenite, gold, and silver.

An irregular alteration/mineralization zoning accompanies the primary orebody. A central core of the highest grade copper mineralization is accompanied by potassic alteration and heavy quartz stockwork locally intensified to complete silica flooding. Phyllic followed by propylitic
alteration zones surround the potassic zone. Irregular argillic alteration zones occur between the inner propylitic and inner zones. The plus 0.25 percent copper contour approximately follows the phyllic-propylitic alteration zone boundary.




Geological Society of the Philippines

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