Grant: Collaborative Research and Development Grants

Porphyry copper deposits are major global sources of copper (as well as gold and molybdenum) to industry and society, and are premier targets for exploration by mining companies. The general mode of formation and occurrence of these deposits is now well understood by geologists, and involves the exsolution of hot metalliferous fluids from crystallizing magma in the upper crust (magmatic-hydrothermal fluids); the ""fertile"" magma that releases these fluids is typically formed above subduction zones at convergent plate boundaries, such as the Andes of South America, and the Cordillera of western North America. However, the ultimate controls on whether an economic deposit of metals is formed (as opposed to a low-grade deposit or barren system) are not well constrained, and indeed may be stochastic (inasmuch as they may not be predictable except in a probabilistic sense). It is noticeable that ore formation in porphyry systems occurs over short and singular periods of time (~100,000 years) in the overall history of the source magmatic system (1 to 5 million years), and commonly involves explosive brecciation and shallow magma emplacement, and yet many magmatic systems to not show evidence of such events. This suggests that a dramatic, perhaps catastrophic change occasionally affects otherwise passively crystallizing arc magmatic systems, leading to ore-formation. The nature of large ore deposits is that they display extensive overprinting and alteration, such that early textures that might reveal these triggering processes are destroyed. Therefore, we plan to study the relatively small Titiribi and La Mina porphyry deposits in Colombia, where the degree of overprinting is less, and early breccia and magmatic textures are well preserved. This will enable us to tightly constrain the interplay between magma emplacement, hydrothermal fluid release, and ore deposition, with the objective of identifying the underlying triggers for these processes. Although, ore formation may still be stochastic, understanding the key controls will improve predictability, thereby improving the ability to target exploration.