Tectonomagmatic Controls on Porphyry Mineralization: Geochemical Evidence from the Black Mountain Porphyry System, Philippines
Published:January 01, 2013
Pete Hollings, Gabriel Sweet, Mike Baker, David R. Cooke, Richard Friedman, 2013. "Tectonomagmatic Controls on Porphyry Mineralization: Geochemical Evidence from the Black Mountain Porphyry System, Philippines", Tectonics, Metallogeny, and Discovery: The North American Cordillera and Similar Accretionary Settings, M. Colpron, T. Bissig, B. G. Rusk, J. F. H. Thompson
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The Black Mountain Southeast Cu-Au-(Mo) porphyry system of the Baguio district, Northern Luzon, consists of two orebodies with a total resource of 65 Mt @ 0.40% Cu and 0.38 g/t Au. Detailed mapping, petrography, and geochemistry have identified six intrusive phases within the Black Mountain area. From oldest to youngest these are as follows: the Liw-Liw Creek hornblende megacrystic mafic dikes (Liw-Liw Creek; 3.20 ± 0.02 and 4.73 ± 0.17 Ma), the early mineralization quartz diorite, the plagioclase- and variably hornblende-phyric diorite (2.87 ± 0.08, 2.98 ± 0.02 and 2.83 ± 0.23 Ma), the hornblende megacrystic gabbro (2.81 ± 0.15 Ma), the hornblende-phyric basalt, and the aphanitic to plagioclase microphenocrystic fine-grained mafic dikes. The rocks of the Black Mountain area are low to medium K calc-alkaline intrusions; however, the intrusive history of the Black Mountain Southeast intrusive suite demonstrates an abrupt shift from megacrystic mafic dikes to voluminous stocks and plugs of relatively felsic equigranular and porphyritic intrusions, followed by a gradual transition to mafic fine-grained dikes. Hornblendes from the intrusive rocks fall into two groups: one formed at depth in a mafic magma and the other at shallower levels in a felsic magma. The presence of both groups within a single sample suggests mixing of a mafic and felsic magma. Porphyry mineralization in the Black Mountain area is interpreted to have formed as a result of underplating of a felsic magma chamber by a mafic magma that formed as a result of mantle recharge related to the subduction of the aseismic Scarborough Ridge.
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Tectonics, Metallogeny, and Discovery: The North American Cordillera and Similar Accretionary Settings
The northern Pacific Rim—for the purposes of this contribution—comprises the Mesozoic and Cenozoic magmatic-arc and associated terranes of eastern China, Korea, Japan, the Russian Far East, Alaska, Yukon, British Columbia, the western United States, and Mexico. This ~1,800-km-long segment of the Pacific Rim is marked by a broad spectrum of metallogenic environments and mining jurisdictions, which combine to dictate where and how exploration is conducted and the overriding character of any resulting discoveries.
This summary report commences with a brief metallogenic overview of the northern Pacific Rim, with particular attention paid to the world-class Mesozoic and Cenozoic ore deposits that define the region’s premier metallogenic provinces. This is followed by a summary of the relative attractiveness of the region’s various mining jurisdictions, as recorded by recent exploration activity. The major discoveries made along the northern Pacific Rim, particularly during the past half century, are then placed in this metallogenic and regulatory context as a basis for determining the successful exploration methodologies employed. This discovery track record is then used to predict what the future of exploration in this vast and varied region may hold.
Much of the northern Pacific Rim, from eastern China and the Russian Far East in the northwest through Alaska to western parts of Canada, the United States, and Mexico in the southeast (Fig. 1), is characterized by a complex array of oceanic, accretionary prism, magmatic arc, and back-arc basin terranes and associated microcontinental blocks accreted to the North China, Siberian, Hyperborean, and North American cratons, mainly during Mesozoic times (Coney et al., 1980; Campa and Coney, 1983; Kojima, 1989; Nokleberg et al., 2005; Yakubchuk, 2009). The metallogeny of these tectonic collages is dictated by various combinations of pre-, syn-, and postaccretion ore-forming events, the last of which are generally preeminent, except in British Columbia (Nokleberg et al., 2005; Nelson and Colpron, 2007).
Although the Meso-Cenozoic metallogeny of the northwestern and northeastern Pacific quadrants displays some similarities, it is the contrasts that are most marked. The main contrasts stem from the preeminence of tin, tungsten, and antimony in eastern China, Korea, Japan, and the Russian Far East and of copper and silver in Western Canada, the conterminous United States, and Mexico. Nonetheless, both the northwestern and northeastern Pacific quadrants are exceptionally well endowed with gold and molybdenum deposits. The northeasternmost Russian Far East, Alaska, and Yukon Territory display elements of both northwestern and northeastern Pacific metallogeny (Fig. 1). These metallogenic contrasts between the northwestern and northeastern quadrants result in China being the world’s leading producer of tungsten, tin, bismuth, and antimony, mostly from its eastern Mesozoic metallogenic province.