PLUME-RELATED OCEANIC PLATEAUS AS A POTENTIAL SOURCE OF GOLD MINERALIZATION?

There are several publications considering mantle plumes, originated at the core-mantle boundary and consequently enriched in the siderophile elements, as a potential source for gold mineralization in accretionary margins. In the global tectonic context, these studies usually consider the interaction of hot spots with subduction zones. We argue here that an alternative way of involving plume material into the mineralization process in accretional orogens may be linked to the transfer and incorporation of an oceanic plateau into subduction zones. Formation of an intrinsically gold-enriched oceanic plateau proximal to a mid-oceanic rise or triple junction implies a long cooling history and reduced buoyancy. Consequently, at least a part of the plateau material could subduct like normal oceanic crust. We speculate that some particularly well-endowed gold provinces may be related to the arrival of fragments of a large oceanic plateau. Metamorphic devolatilization during subduction would have allowed for the gold to be released into the overlying crust, thereby ‘fertilizing' the convective hydrothermal system, which, in turn, gave rise to gold mineralization. Importantly, this process describes a mechanism that allows for the complete temporal (~ 100 My) and spatial (thousands of kilometers) decoupling of the initial mantle plume activity, formation of a fertile primitive oceanic source rock and the establishment of a highly-endowed gold province at an accretionary margin. A plume that gave rise to the fertile source rock can be much older than the age of gold mineralization, with any direct evidence long obliterated from the geological record. The recognition of this separation between first-order cause and effect on the development and geographic location of an anomalously gold-enriched province should be of major significance to the formulation of conceptual exploration strategies, as well as target area selection. We also speculate that the nearly coeval, ca. 120 Ma Sierra Nevada Foothills (California) and Jiaodong (Shandong Province, China) gold provinces may be related to the simultaneous arrival of the fragments of a common, ancestral oceanic plateau that originated from the arrival of a plume head to the Early Permian mid-oceanic ridge in the proto-Pacific.