Metallogenic and Regulatory Inequalities Around the Northern Pacific Rim: Implications for Discovery
Published:January 01, 2013
Richard H. Sillitoe, 2013. "Metallogenic and Regulatory Inequalities Around the Northern Pacific Rim: Implications for Discovery", 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 northern Pacific Rim, defined as stretching from southern China to southern Mexico, displays profound differences in both metallogenic character and regulatory environment. The largest Mesozoic and Cenozoic ore deposits of the northwestern Pacific quadrant contain principally tin, tungsten, molybdenum, or gold, whereas those in the northeastern quadrant are dominated by copper, silver, molybdenum, or gold. The regulatory environments of the northwestern Pacific Rim countries are generally considered less attractive for equity-financed exploration than those of the northeastern Pacific, as witnessed by the far fewer active companies and projects in the former compared to the latter. Furthermore, there is little western company exploration anywhere for tin, tungsten, and molybdenum, arguably some of the prime targets in the northwestern Pacific quadrant. Therefore, notwithstanding greater state funding of exploration in the northwestern Pacific quadrant, particularly in eastern China and the Russian Far East, the northeastern Pacific region has been the subject of far more effective exploration during the past two decades.
More than two-thirds of the 67 principal metal deposits around the northern Pacific Rim are confined to and help define 20 spatially restricted metallogenic provinces, many the products of several discrete metallogenic epochs. The positions of these provinces may reflect the character of the underlying lithosphere. Nearly 40% of these major deposits had been discovered by the early decades of the 20th century, either accidentally or, chiefly in the western Americas, as a result of traditional prospecting. Since the 1940s, geologic, geochemical, and, to a lesser degree, geophysical techniques became progressively more widely employed. Geologic observation, mapping, and conventional geochemical exploration techniques led to most major discoveries before the mid-1990s. Application of broadly similar methods also resulted in the 15 more recent discoveries, 11 of which are located in the northeastern Pacific quadrant; all except four in the previously known metallogenic provinces. Most of the major discoveries from the mid-1990s onward were near known mineralization, seven of those in the northeastern quadrant involving junior exploration companies and four in the northwestern quadrant by semiautonomous provincial agencies. Eleven of the deposits discovered since the early 1990s were wholly or partly exposed, with the remainder completely concealed beneath pre- and/or postmineralization cover.
It is predicted that the northeastern Pacific quadrant will continue to attract the majority of effective exploration attention and, as a consequence, will continue to dominate the northern Pacific Rim discovery record into the foreseeable future. Most major new deposits are likely to be located in the defined metallogenic provinces and to result from conventional exploration programs increasingly underpinned by conceptual geology and robust drilling budgets.
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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.