Transcript Archean Greenstone Belts: What are they?

Van Tuyl Lecture Series - Spring 2016
4:00-5:00p.m. in Berthoud 241
Thursday, March 31, 2016
Robert W. D. Lodge
University of Wisconsin – Eau Claire
“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
For More Information Visit:
mineral deposits.
geology.mines.edu/GE_Lecture-Series
Image: Red rock formations at Garden of the Gods Park in Colorado Springs, CO, http://imgur.com/9ugrm2L