Trace Element Characteristics of Pyrite and Arsenopyrite from the Golden Ridge Gold Deposit, New Brunswick, Canada: Implications for Ore Genesis

Abstract

The Golden Ridge gold deposit is located in southwestern New Brunswick, in the Canadian Appalachians. Gold mineralization is consistently associated with acicular arsenopyrite, and to a lesser degree with pyrite, disseminated in host rocks, sulphide veinlets, quartz-carbonate veins, and the breccia matrix. According to petrographic-based textural differences, four types of pyrite and two types of arsenopyrite are recognized with associated assemblages. Based on SEM-BSE imaging and LA-ICP-MS spot analyses of the different types of pyrites and arsenopyrites, “invisible gold” (solid solution in the crystal lattice of pyrite and arsenopyrite or <100 nm nanoparticles) and micrometer-size inclusions were identified as the main forms of Au. Four syn-gold mineralization pulses of fluid are suggested. The initial hydrothermal fluid, which generated low-grade pyrite (Py-I) enriched in Sb, Pb, Cu, Co, Ni, and Bi, was followed by a second pulse of fluid enriched in arsenic and gold, generating coprecipitated Py-II and Asp-I. The third and fourth pulses were enriched in both arsenic and gold and precipitated Py-III, then coprecipitated Py-IV and Asp-II, which constitute the most important Au depositional episodes. The repeated occurrence of growth zones with Au enrichment in the arsenian pyrites (Py-II, Py-III, and Py-IV) indicate surface growth during metal deposition and disequilibrium crystallization processes.