SMEDG - Notice of Meeting

DATE: Thursday 21st October 1999 - 5.30pm for 6pm VENUE: 1st Floor, Rugby Club, Rugby (Crane) Place, Sydney SPEAKER: Dr. Rich Goldfarb TOPIC: "Orogenic Gold Deposits: A perspective through space and time" Orogenic gold deposits have formed over more than 3 b.y. of Earth's history, episodically during the Archean to Paleoproterozoic, and continuously throughout the Phanerozoic. This class of gold deposit is characteristically associated with deformed and metamorphosed mid-crustal blocks, particularly in spatial association with major crustal structures. The temporal distribution of the most important gold deposits, excluding the still controversial Witwatersrand ores, indicates most vein formation at about 3.1 Ga, 2.7-2.5 Ga, 2.1-1.7 Ga, and 0.6-0.0 Ga. The pattern of ages for Precambrian gold deposits is, in part, remarkably similar to that of the episodic growth of juvenile continental crust reflecting discrete periods of mantle overturning and extreme heating of the base of the lithosphere. Patterns subsequent to 1.7 Ga reflect the decreasing influence of such plume activity on plate tectonics and the increasing impact of modern-style plate tectonics on crustal evolution and ore deposition. Detailed study of some of the younger gold deposits around the Circum-Pacific rim provide for a better understanding of the tectonic controls on gold veining in orogenic belts of all ages. Rich Goldfarb has been a research geologist in the Minerals U.S. Geological Survey in Denver for the past twenty years. During that time, he has been very involved with the Survey's mineral resource assessment program in Alaska, including serving as the coordinator of geochemical exploration activities in Alaska for many years. He recently authored parts and edited Economic Geology Monograph 9 on "Mineral Deposits of Alaska". Rich's main research interests include global gold metallogeny with an emphasis on the temporal/spatial distribution of deposits, the geology of ore deposits in the North American Cordillera with emphasis on orogenic gold and collisional tectonics, and fluid inclusion/stable isotope applications to the understanding of ore genesis. Rich is also chief editor of Mineralium Deposita* , adjunct professor in economic geology at the University of Colorado, and active collaborator at the Centre for Teaching and Research in Strategic Mineral deposits at UWA. *Journal of the SGA