1. Department of Geology and Geological Engineering
Van Tuyl Lecture Series- Spring 2016
4:00-5:00 p.m. in Berthoud Hall Room 241   
Thursday, March 31, 2016
Robert W. D. Lodge
Department of Geology
University of Wisconsin – Eau Claire, WI  
“Archean Greenstone Belts: What are they? What were they? And What Does that Mean for their Metallogeny?”
Abstract: Archean greenstone belts are host to many world class precious and base metal mineral deposits and by association are very important to their local economies. The metallogeny of each greenstone belt is directly linked to their unique geodynamic settings and geological history. However, the geodynamic settings are more often than not poorly understood and the relatively prospectivity of a belt for a particular type of metal deposit is ambiguous if minimal exploration or mining activity has taken place. These ancient volcanic terranes are complexly deformed, metamorphosed, and hydrothermally altered which acts to obscure their original volcanic architecture and therefore their metallogenic setting.
This seminar examines several greenstone belts in the Lake Superior region of the Superior Province and compares and contrasts their reconstructed geodynamic settings using trace element and isotopic systematics. These belts vary greatly in their degree of deformation, metamorphism, and degree of textural preservation thus making primary field observations of their fundamental volcanic, tectonic, and metallogenic settings impossible. Many of the greenstone belts were formed ca Ma and were all previously broadly interpreted to be deposited in a rifted-arc to back-arc tectonic setting. While this interpreted tectonic setting should be prospective for synvolcanic Cu-Zn-Pb mineralization, the greenstone belts in this region show vastly different (discovered) endowments for these deposit types. Additionally, the prospectivity for magmatic Ni-Cu-PGE deposits also varies between these belts. Therefore, it is unlikely that that these belts represent similar tectonic and geodynamic settings. A combination of trace elements and isotopic systematics aids in deciphering differences in their geodynamic setting and crustal architecture at the time of volcanism and formation of mineral deposits.