Orogenic Gold mineralization at 3Ace and Geochemical Characteristics of Quartz Monzonite Dikes at Sprogge, South-east Yukon

Abstract

3Ace and Sprogge are two Au occurrences in the southeast Yukon, Selwyn Basin. Gold mineralization at 3Ace was previously believed to be intrusion-related, however, recent petrography and geochemical analysis show mineralization to be associated with mid- Cretaceous orogenesis. Gold occurs along fractures within quartz veins hosted in metasediments of the Neoproterozoic Yusezyu Formation of the Selwyn Basin, and precipitated from low salinity, CO2-rich acidic fluids at temperatures around 300°C. Stable isotopes show evidence of fluid mixing and a significant meteoric water component in the system, but a magmatic contribution cannot be ruled out. X-ray diffraction was used to define alteration assemblages associated with Au. Geochemical analysis was also carried out at Sprogge to garner a better understanding of the regional geology and potential for mineralization. Radiogenic isotopic compositions of quartz monzonite dikes at Sprogge yielded estimated ages between 95.7 ± 2.0 Ma and 103.5 ± 1.2 Ma. Whole rock geochemical analyses indicate the quartz monzonite dikes were produced from similar petrogenetic processes to the Hyland and Tungsten plutonic suites.