CATHODOLUMINESCENCE-REVEALED PRIMARY DEPOSITIONAL TEXTURES IN ARCHEAN VMS-RELATED QUARTZ: NORANDA, BEN NEVIS AND MATAGAMI DISTRICTS, ABITIBI SUBPROVINCE, CANADA

Cathodoluminescence (CL), using the “hot cathode” technique (HC1-LM system), of quartz in ore, stockwork and veins from the Noranda, Ben Nevis and Matagami volcanogenic massive sulfide (VMS) districts, Abitibi Greenstone Belt (~2.7 Ga), reveals primary growth textures not apparent in transmitted light. The CL of quartz veins from Ben Nevis is characterized by a transient (t < 120 s) blue CL characteristic of hydrothermal quartz. Along host rock contacts, CL reveals weak concentric growth zoning. The zoning confirms that initial quartz precipitation within the vein occurred as open-space euhedral growths projecting outwards from the vein walls. In ore and stockwork material from the Matagami (Bell Allard and Isle Dieu deposits) and Noranda (Corbet deposit) districts, CL reveals primary concentric growth zoned quartz. Each zone is characterized by a slightly different CL color shade, defining the internal hexagonal crystal morphology. The quartz is characterized by an overall transient (t < 120 s) blue CL and is crosscut by sulfide mineralization – clear evidence that the quartz is undeformed and directly related to VMS mineralization. CL clearly reveals pseudo-hexagonal, strongly zoned structures in sulfide-mineralized breccia pipe quartz from Ben Nevis. These structures and their host quartz are characterized by an unstable (t < 20 s) bright yellow CL. The structures are interpreted as recrystallized quartz that has undergone rapid growth from a strongly supersaturated solution and non-crystalline precursor. The CL also reveals colloform/crustiform textures indicative of open-space filling. CL from quartz-epidote veins from Matagami and Ben Nevis, and quartz in vesicles and interstitial fillings between pillow lavas from Ben Nevis are characterized by a transient (t < 120 s) blue hydrothermal CL response. However, CL does not reveal primary growth zoning. Hence, there is a correlation between the intensity of CL zoning and the degree of inferred chemical and/or thermal fluctuations within the hydrothermal environment. This relationship between CL zoning and geological location supports a primary seafloor environment of formation. Thus, quartz CL is a powerful tool for identifying primary growth textures and primary mineralogies – a key distinction for correct textural interpretation of trapped fluids.