Tectonics, fluids and ore deposits: Mobilization and remobilization

Abstract

The mobilization of metals leading to the formation of many known types of metallic resource involves the focussed flow of very large (km 3) fluid volumes. Different types of fluids, such as sea water, and metamorphic and meteoric fluids, with or without biomolecules, may be specific for certain metals or suites of metals. Where large fluid volumes are part of a geologic process there is potential for local metal enrichment. Examples of such processes, within the context of plate tectonics, include: convective flow of sea water at ocean ridges in relation to ophiolite CuZn mineralization and “black smokers”; subduction of metal-enriched sediments and the tectonic recycling of SnW mineralization; metamorphic dewatering of subducted oceanic crust in the context of Au deposits; metamorphic degassing around high-level granitic plutons; and metamorphic re-equilibration of the underthrust plate in relation to continental thrusting. In addition, during weathering processes, short-term leaching produces fertile soils, whereas long-term leaching can result in lateritic ores. The large-scale remobilization of ore deposits, or of mineralization where metal-enrichment is currently sub-economic, is improbable unless large fluid volumes are involved or the crust undergoes major tectonic re-arrangement. But it is perhaps possible that these situations are more common than we suppose, and that such multistage events are indicated by the long-term persistence of metallogenic provinces.