TECTONIC CONTROLS ON GOLD MINERALIZATION IN ARCS OF SE ASIA AND THE SW PACIFIC

The magmatic arcs of SE Asia and SW Pacific contain some of the world’s major magmatic-hydrothermal gold deposits. Most gold deposits in SE Asian and SW Pacific arcs formed during periods of plate reorganization rather than during periods of normal or steady state subduction. We have superimposed a database of gold deposit ages and styles on the animated tectonic reconstruction of SE Asia and SW Pacific to evaluate tectonic controls on mineral deposit formation in that region. These plate reorganizations were caused initially by the collisions of the Australian Craton with the Philippines-Halmahera Arc and the Ontong Java Plateau with the Melanesian Arc at ~25 Ma. A second Mid-Miocene period of mineralization accompanied plate reorganization following maximum rotation or extrusion of Indochina and cessation of spreading in the South China Sea at ~17 Ma. However, the vast majority of deposits from New Zealand to Taiwan formed since 7 Ma during an important period of tectonic reorganization that accompanied and followed changes in the relative motion between the Indian-Australian and Pacific plates between ~8 and 3.5 Ma. Magmatism in unusual tectonic settings produced the most abundant and largest deposits with many deposits associated with high-K calc-alkaline, shoshonite, adakite and alkaline magmatism. In particular peak mineralization appears related to melting of sub-arc lithosphere that has been previously modified by subduction. During large-scale plate reorganization this can occur towards or at the end of a period of normal subduction, following arc collision or accompanying subduction reversal at approximately the same time in different parts of a complex system of arcs such as in SE Asia and the SW Pacific.