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The geology, geochemistry, and petrogenesis of the Huckleberry Cu-Ni-PGE prospect in the Labrador Trough, Canada: Perspectives for regional prospectivity

Smith, W. D., Maier, W. D. and Bliss, I. 2021. The geology, geochemistry, and petrogenesis of the Huckleberry Cu-Ni-PGE prospect in the Labrador Trough, Canada: Perspectives for regional prospectivity. Ore Geology Reviews 128 , 103905. 10.1016/j.oregeorev.2020.103905

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Abstract

The Palaeoproterozoic Huckleberry Cu-Ni-(PGE) prospect in the Labrador Trough, northern Québec, represents a ∼ 400-m-thick, out-of-sequence sill complex that comprises a ∼ 200-m-thick glomeroporphyritic gabbro, intruded in its centre by a ∼ 200-m-thick differentiated gabbro-peridotite sill and in its gabbroic footwall, several thinner (< 30 m) ultramafic sills. Globular sulphides are present at the base of the sill complex, whereas disseminated to net-textured sulphides occur in the ultramafic units (Cu/Ni = 0.1-0.8) as well as their gabbroic footwall (Cu/Ni = 1-3). The glomeroporphyritic gabbro sill stack (MgO ∼ 4 wt.%, TiO2 ∼ 0.6 wt.%, Na2O+K2O ∼ 2-3%, Eu/Eu* ∼ 1.2, Anplg ∼ 70-60) comprises several sills characterised by sharp changes in size and abundance of plagioclase glomerocrysts. We hypothesise that the glomerocrysts represent remobilised crystal mushes that were dislodged from a floatation cumulate in a staging chamber during episodic expulsion of magma. In the central gabbro-peridotite sill, mineral compositions (Foolv ∼ 75-75, Mg#opx ≈ 78-68, Anplg ≈ 78-70) and whole-rock data (MgO ≈ 22 – 27%, TiO2 ≈ 0.4%) suggest that the parent magma was an olivine-saturated basalt containing 8-9 wt.% MgO. Whole-rock geochemical data further suggests that the parent magmas did not undergo any significant contamination (La/SmN < 2, S/Se < 4,000). The Cu/Pd values of ultramafic units (> 10,000) suggest sulphide melt saturation was attained before their final emplacement in magma feeder conduits or staging chambers at relatively low R factors (1,000-5,000). Downward decreasing concentrations of chalcophile elements in the drill cores suggests that sulphide melt percolated downward from the ultramafic cumulate units into the glomeroporphyritic gabbro footwall. We propose that the footwall ultramafic sills represent downward injections of olivine + sulphide melt from the overlying gabbro-peridotite sill, which mechanically concentrated high volumes of sulphide in narrow sills.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Additional Information: This is an open access article under the CC BY license http://creativecommons.org/licenses/by/4.0/).
Publisher: Elsevier
ISSN: 0169-1368
Funders: NERC
Date of First Compliant Deposit: 3 December 2020
Date of Acceptance: 28 November 2020
Last Modified: 15 Jan 2021 16:00
URI: http://orca.cf.ac.uk/id/eprint/136778

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