Reconstructing the Magmatic and Hydrothermal Evolution of the Au-rich, Cu-Poor Dorado Porphyry Deposit, Chile: Implications for Cu/Au Ratios in Porphyry Deposits Worldwide

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Globally, society consumes about 300 percent more copper and 100 percent more gold every year than in the year 1960. Production of copper and gold over the next several decades must increase significantly to achieve the United Nations Sustainable Development Goals of providing electricity to nearly one billion people on Earth for whom the lack of electricity contributes to economic impoverishment, as well as building renewable energy infrastructure to replace fossil fuels globally. To meet this demand at a scale and speed never before accomplished by humans, geologists must refine the models used to explore for and locate new copper and gold deposits. Currently, one mineral deposit type, referred to by geologists as a porphyry copper gold deposit, supplies the majority of the world's copper and about 15 percent of the world's gold. This project will investigate the formation of gold-rich porphyry deposits in the Maricunga belt of Chile, the world's leading producer of copper. These gold-rich porphyry deposits are poorly understood and finding new deposits requires a better understanding of the geologic processes that form them. The anticipated results will help constrain how the gold-rich deposits in Chile formed and allow geologists to improve their exploration strategies for new, undiscovered deposits. Porphyry-mineral deposits formed in subduction zone environments are society’s most important source of copper and an important source of gold. There is consensus for the general geologic model that explains the formation of porphyry mineral deposits. However, there is no consensus on why the ratio of metals such as copper to gold varies by several orders of magnitude among these deposits. Existing hypotheses to explain the variability of copper to gold ratios invoke: 1) the depth of emplacement of the upper crustal source magma and its impact on the evolution of the magmatic-hydrothermal ore fluid; 2) the composition of the source magma that represents a first order control on the partitioning of ore metals and their fluid-soluble ligands between melt and magmatic-hydrothermal ore fluid; 3) the redox conditions attending the evolution of magmatic systems that play a role in the relative mobility of copper vs. gold. The project outcomes will help clarify the evolution of the Dorado Au-porphyry system from magma emplacement to Au-rich, Cu-poor porphyry formation. This project has the potential to significantly change our understanding of the variability of copper to gold ratios in porphyry mineral systems and help guide exploration for Au-rich systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.