Dinah Quaye, MSc
D. Quaye1, C. Yakymchuk1, S. Lin1
1Earth Sciences Department, University of Waterloo, Waterloo, Ontario, Canada
The Young-Davidson (YD) 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 YD gold mine, syenite hosts the majority of gold mineralization; however, the potential of gold in the metasedimentary rocks and conglomerates is underexplored, although mineralization has been discovered to extend into them. Previous work on metasedimentary rocks has identified phengite as one of the main alteration minerals; however, the origin and formation of this phengitic alteration assemblage remain understudied. This study aims to expand the understanding of mineralization in metasedimentary rocks at YD by increasing knowledge of the origin of alteration minerals responsible for mineralization.
Hyperspectral imaging and electron probe microanalysis confirm the white-mica as phengitic (i.e., a series between the muscovite and celadonite solid solution with notably higher Si, Fe, and Mg contents and lower Al values), suggesting that the white-mica chemistry is primarily controlled by the Tschermak substitution mechanism, AlIV + AlVI ↔ SiIV + (Fe+Mg)VI, where an increase in Fe and Mg in the octahedral sites is balanced by increased SiIV, simultaneously resulting in a decrease in total aluminium contents.
Non-mineralized metasedimentary samples generally have higher modal abundances of quartz and feldspar, specifically plagioclase, and exhibit weak to negligible sericitic to chloritic alteration. Mineralized samples show more pronounced alteration signatures characterized by an increased proportion of chlorite relative to sericite, with medium-grade mineralized samples having the strongest sericitic overprint. The presence of pyrite and magnetite typically increases with increasing alteration intensity and higher gold grade. A spatial association between chlorite and pyrite with anhedral biotite suggests biotite breakdown contributed to pyrite growth (i.e., 2K (Mg,Fe)3AlSi3O10(OH)2 + 2H2S ⟶ (Mg,Fe)5Al2Si3O10(OH)8 + FeS2 + 2K+ + 3SiO2) with an increased intensity of biotite alteration indicative of gold mineralization.
Future work will involve characterizing the main controls of the phengitic series and other alteration minerals using further petrographic and lithogeochemical data. Incorporating hyperspectral imaging with geochemical and petrographic techniques will contribute to the knowledge of alteration minerals in metasedimentary rocks while assessing the relevance of hyperspectral imaging at YD and other orogenic gold terranes.