Figure 4
(A) View of the L1 gossan looking North. The hill rises approximately 75 m above the surrounding tundra and is 400 m long at the base (Peterson et al., 2014). The deposit consists of loosely-consolidated pyritic sands capped by gossanous soil. The contact between these two units is shown by the dashed line. The yellow square shows the approximate size of circular alteration zones. (B) Close-up view of one of several alteration zones mapped in the L1 gossan. The dashed line shows the contact between grey pyritic sand and the oxidized, yellow to rust-coloured material at the periphery. The scale at centre is 7.62 cm long.
Citations
... The Voisey's Bay Ni-Cu-Co orthomagmatic sulphide deposits ( Figure 1) were discovered in 1993 when a small gossan (Discovery Hill) was sampled by prospectors [1][2][3][4][5][6][7][8]. The Ovoid deposit was discovered in a valley below Discovery Hill through geophysical surveys, buried beneath 10-20 m of glacial till [9]. The Ovoid deposit consists of a bowlshaped body of massive sulphide approximately 200-300 m in diameter [3]. ...
... The following descriptions of the Voisey's Bay deposit are based on [1][2][3][4][5][6][7][8][9]11]. The Voisey's Bay mineralization consists of orthomagmatic sulphides hosted by troctolite feeder dykes of the Nain Plutonic Suite (NPS). ...
The Voisey’s Bay nickel-copper-cobalt (Ni-Cu-Co) sulphide deposits constitute a significant resource of orthomagmatic mineralization. The deposits are not exposed at the surface except for in a small ferruginous gossan (Discovery Hill). The subsequent geophysical surveys and diamond drilling led to the discovery of the Ovoid ore body, buried beneath 20 m of till, and other deeper deposits in the bedrock. This study was initiated to characterize the sulphide mineralogy of these deposits through various stages of weathering, erosion, and transport. Because the samples ranged from bedrock through to a variety of surficial sediment types, the automated SEM-based identification provided by the MLA-SEM system was the ideal technique to quantitatively evaluate mineral distributions in the different media. The derived MLA-SEM data indicate that, aside from the Discovery Hill gossan, the surface sulphide mineralization at Voisey’s Bay was weathered in a pre-glaciation regolith at the Mini-Ovoid deposit and, on the surface of the Ovoid deposit, the massive sulphide was unoxidized due to a thin calcite-cemented clay cover. Pentlandite is very preferentially oxidized compared to other sulphides in the Voisey’s Bay ore, to depths of up to 10 m in bedrock. Conversely, within the coarse reject samples of crushed drill cores stored in sealed plastic bags, pyrrhotite was altered, whereas pentlandite and chalcopyrite are stable, presumably due to anaerobic reactions. The MLA-SEM detected trace amounts of minute sulphide grains in surficial sediments, but their contents abruptly decreased with distance from the sulphide mineralization. Microtextures such as troilite and pentlandite exsolution or twinning in pyrrhotite, however, could be observed in the fine sulphide grains from till, suggesting a derivation from orthomagmatic sulphide material, such as the Voisey’s Bay mineralization.
... The shape of the space occupied by the Ovoid Deposit is broadly an elongate west-east trough with a dyke connected to the base as a keel which dips to the north. The north wall of the Ovoid curves towards the south at the east end of the trough, and the south wall curves towards the north at the west end, so the geometry is broadly consistent with the space created by both rifting (Cruden et al., 2008) and at a cross-linking structure along a right-stepping dextral fault system (Lightfoot and Evans-Lamswood, 2014). ...
Models for the disruption of supercontinents have considered mantle plumes as potential triggers for continental extension and the formation of large igneous provinces (LIPs). An alternative hypothesis of top-down tectonics links large volcanic eruptions to lithospheric delamination. Here we argue that the formation of several LIPs in Tarim, Yangtze, Lhasa and other terranes on the Eurasian continent was coeval with the assembly of the Pangean supercontinent, in the absence of plumes rising up from the mantle transition zone or super-plumes from the core–mantle boundary. The formation of these LIPs was accompanied by subduction and convergence of continents and micro-continents, with no obvious relation to major continental rifting or mantle plume activity. Our model correlates LIPs with lithospheric extension caused by asthenospheric flow triggered by multiple convergent systems associated with supercontinent formation.
