Download Department of Geology and Geological Engineering

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
[email protected]
“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. 2720 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.