Alteration of Metasedimentary Rocks Associated with Gold Mineralization at Young-Davidson Gold Mine

Abstract

The Young-Davidson gold mine is situated within the southwestern part of the Abitibi greenstone belt in Northeastern Ontario. It is part of the Western Cadillac-Larder Lake region, known for its lithological complexities and hydrothermal alteration. Within the Young-Davidson gold mine, syenite hosts the majority of gold mineralization; however, the potential of gold in the metasedimentary rocks are underexplored, although gold mineralization does extend into them. This study integrated hyperspectral imaging, petrography, electron probe microanalysis (EPMA), and lithogeochemical data to understand the alteration and its relationship to gold mineralization in the metasedimentary rocks at Young-Davidson. Hyperspectral imaging and EPMA show that alteration-related white mica is phengitic and can be compositionally divided into two groups; one of these is associated with higher gold grades. Gold mineralization is also associated with chlorite and pyrite, with higher bulk rock Fe contents generally associated with elevated gold grades. The presence of pyrite typically increases with increasing alteration intensity and higher gold grade. A spatial association between chlorite and pyrite with anhedral biotite suggests that biotite breakdown contributed to pyrite growth, and an increased intensity of biotite alteration is indicative of gold mineralization. Both the syenite and the metasedimentary rocks have pyrite as the dominant sulfide phase however; a clear contrast in the oxide phase is noted. Overall, these findings highlight sulfidation and the availability of Fe-rich assemblages as an important control on gold mineralization in the metasedimentary rocks at Young-Davidson, and the importance of incorporating a variety of methods to understand gold mineralization, as well as the relevance of hyperspectral imaging as a recently adapted tool in mineral exploration.