GEOCHEMICAL STUDIES OF GOLD MINERALIZATION OF THE DISCOVERY-ORMSBY AND CLAN LAKE AREAS, YELLOWKNIFE GREENSTONE BELT, CANADA

Discovery-Ormsby and Clan Lake are areas of active gold exploration in the north end of the Yellowknife greenstone belt of western Canada. Gold occurs principally within sulfidized metavolcanic rocks of the Archean Banting Group (2.69-2.66 Ga). Discovery-Ormsby is hosted within a narrow, elongate mafic unit, which is surrounded by voluminous metasedimentary rocks. Clan Lake is hosted in a larger, intermediate to felsic, metavolcanic-volcaniclastic complex. Mineralization in both areas is characterized by arsenopyrite followed by pyrrhotite ± native gold. The deposits occur along a N-NE trend associated with regional faulting and present an opportunity to determine if their ores are related to similar hydrothermal systems whose chemistry differed as a function of host lithology, or instead indicate chemically distinct hydrothermal systems.

In summer 2011, 153 samples were collected to reflect the spatial distribution of quartz veins, sulfides, wall rocks, and alteration. The δ¹⁸O values of quartz veins and host rocks were used to identify areas dominated by hydrothermal fluids. A large lithogeochemical data set for 150 drill cores was provided by Tyhee Gold Corp. that permits us to link δ¹⁸O values with host rock chemistry. Quartz veins from Discovery-Ormsby have δ¹⁸O values of 13.0-15.1‰ V-SMOW (n=10), which are interpreted to reflect dominance of metasedimentary-derived fluids that reacted with the mafic metavolcanic host rocks.

In contrast, Clan Lake’s quartz veins and wall rocks have δ¹⁸O values of 11.3-15.2‰ (n=19) and 8.2-12.8‰ (n=14), respectively, indicating both metavolcanic and metasedimentary fluid sources. 3-D modeling of the spatial distribution of δ¹⁸O values defines a volume of rock with higher values that coincides with elevated gold concentrations. Thus, δ¹⁸O values may be useful in defining the size of the Clan Lake mineralizing system and may be helpful as an exploration tool and ore guide. By this reasoning, based on drilling to date, we have defined the northern edge of the economically mineralized portion of the alteration zone. To the south-southwest, the high-δ¹⁸O, high-gold trend appears to continue, indicating a potential vector for future exploration and drilling efforts. Ongoing studies are addressing the reaction(s) responsible for gold deposition within the mineralized zone.