Geology of the Sandhill zinc-copper-lead-silver prospect and economic potential of the Gibson-MacQuoid Greenstone Belt, District of Keewatin, Northwest Territories

The study area is approximately 120 km north-west of the community of Rankin Inlet, and 40 km SW of the tidal waters of Cross Bay in Chesterfield Inlet. Geological mapping from 1993-1995 in this area covered 350 km{dollar}sp2{dollar} of parts of the Gibson Lake (55N/12)-MacQuoid Lake (55M/9) maps. This area is underlain by a polydeformed sequence of mafic to felsic metavolcanic rocks and related clastic and chemical metasedimentary rocks, all of the Archean Gibson-MacQuoid greenstone Belt. Granitic gneiss is interlayered with the metavolcanic and metasedimentary rocks, and forms the northern and southern boundary to the greenstone belt. Archean granitic intrusions are common in the western parts of the map area, and younger gabbro intrusions and lamprophyre and diabase dykes are common throughout the map area.; The Archean stratigraphy in study area was deposited within a shallow subaquous environment of deposition in a continental marginal arc environment, near the boundary of the back-acr basin and sialic craton. deposition of the supracrustal rocks was accompanied by the formation of the sandhill volcanic-hosted massive sulphide prospect.; The Sandhill prospect, located in the central part of the map area, is comprised of a zone of stratiform base metal sulphide mineralization hosted within an extensive concordant horizon of pyritic quartz-muscovite schist. This schist horizon is stratabound to a felsic-intermediate metavolcaniclastic unit.; In the main Sandhill zone, massive and disseminated sphalerite occurs within multiple 1-2 m horizons in the upper 15-20 m of the quartz-muscovite schist. Surface samples assayed up to 9.3% Zn and 160 g/tonne Ag.; Mineralogy and whole rock geochemistry indicates the quartz-muscovite schist represents the metamorphosed equivalent of intense sericite alteration of the host metavolcaniclastic unit. This hydrothermal alteration resulted in the loss of Ca, Na and Mg as well as Sr, Ba and the LREE, and a gain in Mn and Fe as well as Zn, Pb, Cu and S. This schist horizon is enclosed in a much broader envelope of less intensely altered metavolcaniclastic rocks.; The Suluk base metal sulphide occurrence was discovered during the 1994 field season. Four surface samples of massive sulphide were found to contain anomalous concentrations of Ni, Cu and Co. These four samples averaged 2.2% Ni, 1.7% Cu and 0.14% Co. The Suluk occurrence is a 045-050{dollar}spcirc{dollar} striking zone of massive to semi-massive sulphides that can be traced discontinuously over a strike length of 650 m.; The Suluk occurrence is spatially associated with a ca 2.2 Ga gabbroic intrusion, referred to as the Suluk gabbro, immediately to the west and may be genetically related.; A unique diamond-bearing lamprophyre dyke, the Akluilak dyke was discovered approximately 1.5 km south-west of the Sandhill prospect.; The regionally extensive mineralization and alteration associated with the Sandhill prospect, the newly discovered Suluk Ni-Cu-Co occurrence and diamondiferous Akluilak lamprophyre dyke indicates the promising resource potential of this region. (Abstract shortened by UMI.)...