GSA Connects 2021 in Portland, Oregon

Paper No. 195-1
Presentation Time: 2:30 PM-6:30 PM


SUHEY, Jane1, REGAN, Sean2, HOLLAND, Mark E.3, PICKETT, Jessica4 and REAUME, Michelle1, (1)Dept of Geosciences, University of Alaska Fairbanks, 900 Yukon Dr, Fairbanks, AK 99775-9702, (2)Geophysical Institute, University of Alaska Fairbanks, 900 Yukon Dr, Fairbanks, AK 99775-9702, (3)Department of Life, Earth, and Environmental Sciences, West Texas A&M University, 2403 Russell Long Blvd., Canyon, AK 79015, (4)Valdez Creek Mining Camp, 900 Yukon Dr, Fairbanks, AK 99775-9702

Gold deposits located within the accretionary and subduction-related tectonic environment of south-central Alaska are generated by either devolatilization of hydrous assemblages through regional metamorphism (orogenic model) or by intrusion hosted devolatilization processes (porphyry model). The Valdez Creek mining district, southern Clearwater Mountains of south-central Alaska, is located within a complex geologic setting where the North American-derived Maclaren schist was emplaced structurally above lower greenschist-facies rocks of the basinal Kahiltna assemblage by south-vergent thrusting across the ca. 60 Ma Valdez Creek shear zone during the terminal collision of the Wrangellia composite terrane. Placer gold mining and lode gold exploration is currently focused within the footwall of the Valdez Creek shear zone. The region also contains abundant, and texturally variable, intrusive rocks associated with gold anomalies. Here, we test competing gold-models in the Valdez Creek drainage.

Constraining mechanisms of gold mineralization through a geochronological and geochemical framework with structural analysis provides a robust tool to determine dominant ore-forming mechanisms and provenances. We hypothesize a system model in which metamorphic fluids generated from the dehydroxylation of chlorite occurred simultaneously with shearing along the Valdez Creek shear zone. Preliminary 206Pb/238U zircon data collected from the alkali pluton suite and the placer system indicates gold deposition was localized above alkaline plutons in the region. These data suggest the placer gold has a spatial association with the ca. 89 Ma plutonic suite in the footwall but is temporally related to crustal thickening 30 Myr later. We posit auriferous fluids were concentrated within or proximal to rigid intrusion(s), coinciding with vein development and fluid channelization, similar in process to the Juneau gold belt. White mica 40Ar/39Ar geochronology from gold-bearing quartz veins will be vital to strengthen the proposed link between the origins of gold enrichment and the Valdez Creek shear zone’s influence on economically viable gold system models.