Date of Award
Doctor of Philosophy
Geological and Atmospheric Sciences
Paul G. Spry
Sediment-hosted gold mineralization of Archean age is found in the Wyoming Province and is geologically and geochemically more similar to the Phanerozoic turbidite-hosted or mesothermal type of gold deposit than to the more typically Archean greenstone-hosted type. Approximately 335,000 oz of gold have been produced from the Atlantic City-South Pass district from quartz veins in shear zones localized along the contacts of metaigneous rocks of the Miners Delight Amphibolite Belt with the surrounding metagreywackes;Rare earth element patterns for Miners Delight metagreywackes have strong LREE enrichments, Eu depletions, and more closely resemble post-Archean than Archean sediments. The widespread occurrence of similar metasediments throughout the Wyoming Province indicates that a significant source of evolved continental material existed during the Archean. Trace element data for metaigneous rocks of the Miners Delight Amphibolite Belt also supports the presence of thick continental crust during formation of the South Pass Supracrustal Belt;Lode gold deposits were emplaced in zones of structural competence contrast at the contacts of metaigneous rocks with the surrounding metasediments by multiple generations of CO[subscript]2-CH[subscript]4-H[subscript]2O-NaCl-CaCl[subscript]2 fluids in which phase separation occurred. Deposition occurred post-peak metamorphism. Sulfur isotope data does not indicate an equivocal source, but does suggest leaching of sulfur from the older Goldman Meadows Formation by reduced fluids. Carbon isotopes indicate an organic carbon component, probably derived from graphitic sediments of the district. Oxygen and hydrogen isotope and fluid inclusion compositional data suggest that the ore fluids were probably evolved formation waters. The most likely source of gold was leaching of the sedimentary pile. The deposits were formed in a subduction-related tectonic environment similar to that responsible for younger turbidite-hosted gold deposits such as those of southern Alaska, and in contrast to the volcanic-dominated environment of greenstone-hosted deposits where thick, evolved continental crust was lacking.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Krista I. McGowan
McGowan, Krista I., "Thermochemical conditions for the formation of Archean lode gold mineralization at Atlantic City-South Pass, Wyoming " (1990). Retrospective Theses and Dissertations. 9457.