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Abstract:

The geological processes responsible for the formation of hydrothermal gold deposits are often equivocal. For example, gold-bearing, shear zone-hosted laminated quartz veins in the Missanabie-Renabie gold district (Archean Wawa subprovince, Ontario, Canada) have been interpreted as both intrusion-related and metamorphic-hydrothermal in origin.<br/>The veins were mined at the past-producing Renabie mine, which yielded ~1.1 Moz of gold during production from 1941-1991. Whereas the intrusion-related interpretation links the veins to magmatic-hydrothermal fluids released during the crystallization and solidification of their hosting tonalitic pluton, the metamorphic interpretation suggests the veins were deposited from hydrothermal fluids produced during greenschist-facies metamorphism. This study integrates detailed structural field mapping with a number of geochemical techniques to unravel the evolution of the historically controversial ore zones. Results suggest that: (1) the laminated veins and their alteration envelopes pre-date regional deformation, and spatially localized later shear zones, which subsequently focused hydrothermal activity resulting in the formation multistage, composite ore zones; (2) the laminated veins formed during an early, intrusion-related gold event, and the later, co-spatial hydrothermal events are orogenic in nature, and thus more likely to be the products of metamorphic fluids; and (3) discriminating intrusion-related from orogenic events requires constraints provided by geological field mapping. Whereas pressure-temperature information from fluid inclusions and U-Pb geochronology facilitate discrimination, the geochemical signatures of the different hydrothermal events are largely overlapping and do not aid in classification.