Chemical Mapping of Trace Elements in Pyrite Provides Insight into Mineralizing Processes: the Example of the Neoarchean Cu–Au Porphyry System of the Chibougamau Area, Canada
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Abstract
Archean porphyry-style mineralization is one of the sources of Au and Cu in greenstone belts. Archean porphyries have been modified by regional deformation and late fluid circulation, and questions remain on the timing of Au mineralization. Indeed, Au may have been introduced at the magmatic-hydrothermal (porphyry) stage, or by a post-magmatic hydrothermal fluid (overprinting orogenic gold system), or a combination of these two processes. Using the Cu–Au Corner Bay deposit as a case study and high-quality chemical mapping performed using laser ablation coupled to a time-of-flight mass spectrometer (LA-FF-ICP-ToF-MS), this study demonstrates that pyrite chemistry has the potential to reconstitute the metallogenic model for Archean porphyry systems. The Corner Bay deposit is associated with the ~2718–2715 Ma Chibougamau pluton, located in the northeastern corner of the gold-endowed Abitibi greenstone belt. Pyrite chemistry points to the following succession of events at Corner Bay: (1) an early porphyry stage that produced pyrite-mineralized quartz-anhydrite veins associated to chloritization and sericitization; (2) followed by a porphyry stage that includes brecciation in response to fluid overpressure and deposition of Cu-Au mineralization by magmatic-hydrothermal fluids with a multi-metal signature (Cu, Ag, Bi, Te, etc.); and (3) a post-porphyry deformation event(s) that induced parallel fracturing and minor carbonatization. This study proposes that, at Corner Bay, Au was introduced during the porphyry-stage of mineralization and was neither remobilized, nor further introduced, during the ~2700 Ma regional deformation stage that is coeval with most orogenic gold-style of mineralization in the southern part of the Abitibi greenstone belt.
期刊介绍：
Geology of Ore Deposits is a periodical covering the topic of metallic and nonmetallic mineral deposits, their formation conditions, and spatial and temporal distribution. The journal publishes original scientific articles and reviews on a wide range of problems in theoretical and applied geology. The journal focuses on the following problems: deep geological structure and geodynamic environment of ore formation; distribution pattern of metallogenic zones and mineral deposits; geology and formation environment of large and unique metallic and nonmetallic deposits; mineralogy of metallic and nonmetallic deposits; physicochemical and isotopic characteristics and geochemical environment of ore deposition; evolution of ore-forming systems; radiogeology and radioecology, economic problems in exploring, developing, and mining of ore commodities.
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