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Targeted Geoscience Initiative (TGI-4)
The world-class Roberto gold deposit, Éléonore property, James Bay area, Superior province, Quebec; Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Programs with Abstracts vol. 34, 2011 p. 55-56, Earth Sciences Sector, Contribution Series
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The world-class Goldcorp Roberto gold deposit (9 Moz) is one of the most si...
The world-class Goldcorp Roberto gold deposit (9 Moz) is one of the most significant discoveries made in the last 10 years in Canada and is a new illustration of the diversity of styles and settings of major gold deposits in the Superior Province. Located in the relatively underexplored northern part of the Superior Province, it is a lower amphibolite sediment-hosted Au-As-Sb-B deposit mainly hosted by post-2675 Ma Timiskaming age turbiditic wackes but with ore also present within >2675 Ma paragneiss, local high-grade quartz veins and ca. 2620-2600 Ma LCT pegmatites. The deposit straddles the contact between the La Grande (Uchi) volcano-plutonic and the highly metamorphosed Opinaca (English River) metasedimentary subprovinces. It is located within a window of lower metamorphosed but polydeformed La Grande sedimentary rocks within a km-scale fold hinge that affects amphibolite-facies turbiditic metagreywacke and paragneiss. Gold mineralization is primarily confined to sub-parallel decameter-wide mineralized zones and is associated with calciumbearing veins, potassic alteration, and Mg-tourmaline (dravite). The principal mineralized zone (Roberto) consists of a stockwork of quartz ± actinolite ± diopside ± biotite-arsenopyrite-pyrrhotite veins and quartz-dravite-arsenopyrite veinlets, contained within microcline, phlogopite, dravite and arsenopyrite-pyrrhotite replacement zones. The alteration and mineralized zones are metamorphosed and deformed by structures attributed to D2, although some ore zones appear to be controlled by D2 structures. Timing of gold mineralization is interpreted as being pre- or early-D2. Chronology between deformation, stockwork-replacement, disseminations and high-grade vein-type mineralization, with dated pegmatites, and ages of monazite, titanite and arsenopyrite indicate that: 1- gold mineralization is younger than ca. 2675 Ma; 2- the main stage of deformation (D2) was still active by ca. 2616 Ma but is older than ca. 2603 Ma; 3- major metamorphic and deformation event(s) occurred between ca. 2621-2606 Ma; 4- part of the mineralization and/or the metamorphosed and remobilized product of an earlier bulk gold stage is dated at ca. 2620-2605 Ma suggesting much younger tectonic, metamorphic and gold-bearing event(s) compared to events documented in the Superior Province. The link between some of the Au-mineralization and magmatic fluids should be considered, as indicated by the presence of multiple generations of pegmatites, some of which are contemporaneous with part of the mineralization or its remobilization. The deposit shows a spatial association with an unconformity at or near the contact between two subprovinces. It also indicates that contact between the sediment-dominated Opinaca, English River, Quetico and Pontiac with the volcanic-dominated La Grande, Uchi, Wabigoon and Wawa-Abitibi subprovinces, may be underexplored.
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