Master of Science
Linnen, Robert L.
The Orenada Zone 4 deposit is an Archean orogenic gold deposit situated southeast of Val d’Or, Québec in the southeastern Abitibi Greenstone Belt. It is located directly within the Cadillac-Larder-Lake Deformation Zone. Mineralization is hosted within a volcanoclastic horizon of the Cadillac Group where two distinct facies were defined. Both facies underwent a pervasive sericite-chlorite-carbonate±albite alteration assemblage that predates gold mineralization. Gold is associated with two generation of auriferous quartz-carbonate-tourmaline veins and within fractures of corroded arsenopyrite grains, located proximal to the vein walls. A LA-ICP-MS study determined that neither textural type of arsenopyrite displayed refractory gold. Therefore, gold was not remobilized from arsenopyrite but instead, likely precipitated during formation of the quartz-carbonate veins. Gold precipitation is likely related to electrochemistry gold deportment where As-rich fractures within the corroded arsenopyrite acted as p-type conductors which attract the gold particles for precipitation.
Summary for Lay Audience
The Orenada Zone 4 deposit is an Archean orogenic gold deposit situated southeast of Val d’Or, Québec in the southeastern Abitibi Greenstone Belt. The Abitibi greenstone belt is a structurally controlled region, widely recognized for gold production where it produces 81% of the gold in Canada. The Orenada deposit is associated with one of these gold producing structures, the Cadillac-Larder-Lake Deformation Zone where, mineralization is hosted within a felsic rock unit of the Cadillac Group rocks. Two distinct rock types have been identified, one is quartz rich and the other feldspar rich. Geochemical results determined that both rock types underwent the same pervasive alteration that predates gold mineralization. Mineralization is associated with two generations of quartz-carbonate-tourmaline veins and arsenopyrite, an arsenic-rich sulfide mineral that is associated gold within the selected study area. . However, there are two different textures of arsenopyrite however, gold is only observed within fractures of large deformed grains observed proximal to vein emplacement. Both textures display zonations of differing arsenic and sulphur concentrations. In the literature, mineralization associated with arsenopyrite exists commonly as refractory gold, where gold cations are trapped within the arsenopyrite mineral structure. However, chemical analyses of arsenopyrite in this study determined that neither textural type contains refractory gold. Therefore, the gold likely precipitated during the formation of the quartz-carbonate veins. It is proposed that gold was deposited by an electrochemical reaction where, arsenic-rich fractures within the arsenopyrite act as electron recipients which attract the gold particles. After examining all the visible gold particles within the investigated arsenopyrite grains, 86% of gold grains are observed within arsenic-rich regions, which supports the electrochemical deposition hypothesis. There is a lack of published articles on non-refractory gold associated with arsenopyrite, thus this thesis makes a very important contribution that can be applied to examining other arsenopyrite-rich gold deposits and used as a guideline for similar deposits within the Abitibi and on a global scale.
Powell, Cassandra, "The relationship between visible gold and arsenopyrite at the Orenada Zone 4 deposit, Val d'Or, Quebec" (2020). Electronic Thesis and Dissertation Repository. 7160.