IAS Benjamin Meaker Visiting Professor Robert Loucks, University of Western Australia

R LoucksExperimental determination of copper and chlorine partitioning between granitic silicate melt and aqueous fluid at lower-crustal pressures

1 September - 28 November 2017

Biography

Robert Loucks is one of the world’s leading economic geologists. He obtained a PhD in geochemistry/metallogeny at Harvard University in 1984 and joined the faculty of Purdue University in Indiana in 1984 where he did research on epithermal Au-Ag ore deposits and on the petrology of lowercrustal layered ultramafic-mafic cumulate complexes in arc terranes. He transferred to the Research School of Earth Sciences at the Australian National University in 1992 and remained there through 2003, researching topics related to arc magmatism and metallogeny. Since returning to his boyhood home in Colorado in 2004, he founded a mineral exploration consultancy, Geoscience Research, LLC, and has continued research on arc magmatism and metallogeny in collaboratios with numerous major multinational mineral exploration companies. He joined the adjunct faculty of the Centre for Exploration Targeting at the University of Western Australia in 2009 and is an active researcher and supervisor of post-graduate student research on topics related to arc magmatism and related magmatic and magmatic-hydrothermal ore-forming processes.

Summary

Dr Loucks has established that the PCD-ore-forming granitoid magmas are not enriched in copper relative to ordinary, barren plate-margin granitoid magmas (they have only a few tens of parts per million Cu), but PCD-ore-forming magmas are exceptionally enriched in dissolved H2O (and probably in chlorine and sulfate), compared to barren, ordinary granitoid magmas—so much so that the 10-15 wt% H2O typical of PCD-ore-forming silicate melts cannot remain dissolved in the silicate melt at depths less than ~19km. This means that silicate melts ascending from storage chambers at 20-35 km depth begin to exsolve (unmix) aqueous fluid at high pressure; the aqueous fluid scavenges copper and chlorine and other chemical components from the silicate melt and should be distilled to the top of the rising magma column.

The planned experiments will test whether hydrothermal fluid segregating from silicate melt at high pressure has greater efficiency in scavenging Cu from the conjugate silicate melt than fluids segregating from silicate melt at upper-crustal pressures. If so, then the experiments will help explain how Cu-poor silicate melts can produce giant, high-grade copper ore deposits—currently an enigma.

During his stay Dr Loucks will be hosted by Professor Jon Blundy (Earth Sciences)

Dr Loucks will be giving the following semianrs (times and dates tbc)