Characterization and dispersal of indicator minerals associated with the Pine Point Mississippi Valley-type (MVT) district, Northwest Territories, Canada

Abstract

A glacial dispersal study was conducted around a subcropping Pb-Zn deposit (O28) in the Pine Point Mississippi Valley-type (MVT) district, Northwest Territories, Canada, with the intent of characterizing and documenting the indicator minerals and their dispersal from a known orebody. Mapping of striations adjacent to deposit O28, and throughout the Pine Point district, along with observed glacial stratigraphy, indicate that there are three phases of ice flow that have affected the Pine Point district. Sphalerite, galena, and pyrite were identified in mineralized bedrock samples at deposit O28, and sphalerite and galena were recovered from the sand fraction of till samples up to 500 m from the mineralized subcrop. The majority of sphalerite and galena grains recovered from till samples down-ice of deposit O28 were 0.25-0.5 mm in size. Size and morphology of sphalerite grains in till demonstrate relative proximity to their bedrock source, with the largest and more angular grains being closer to the ore zone (<50 m) whereas smaller and more rounded grains occur further down-ice (ϳ250 m). The paragenesis, textures, major-element concentrations, and S and Pb isotopic compositions of bedrock samples from deposit O28 and from newly drilled core from four other deposits were characterized. Concentrations of Zn in bedrock sphalerite grains range from 43.95 to 67.48 wt.%, concentrations of S range from 32.03 to 34.01 wt.%, and concentrations of Fe range from 0.02 to 16.94 wt.%. The Fe concentration in bedrock sphalerite decreases from east to west across the district. Concentrations of S in galena grains in bedrock range from 12.50 to 14.00 wt.% and have a bimodal distribution. Generally, the geochemistry of sphalerite grains recovered from till were statistically similar to bedrock grains recovered from deposits O28 and L65. Major-element concentrations were statistically the same between the sphalerite grains recovered from till and the honey-brown and cleiophane varieties in the bedrock samples. Galena grains recovered from till samples were similar to the cubic and fracture-fill varieties of grains recovered from bedrock in the R190 and M67 deposits. Sulphur isotopic values for sphalerite grains from bedrock range from 20.6‰ to 24.2‰, while those from till samples range from −5.3‰ to 24.4‰. Lead isotopic ratios for galena grains from bedrock and till samples had very little variation, which is a characteristic of the Pine Point district. The S and Pb isotopic studies as well as major-element geochemistry suggest that indicator minerals derived from Pine Point-type mineralization can be distinguished from those sourced from other types of carbonate-hosted mineralized systems (e.g., Cordilleran zinc-lead deposits) and that the methods here can be used as exploration tools for identifying MVT deposit provenance or potential. The results of this study present criteria and highlights additional methods for exploration of MVT deposits in glaciated terrain.Résumé : La dispersion glaciaire a été étudiée autour d'un gisement su...

Microsedimentological evidence of vertical fluctuations in subglacial stress from the northwest sector of the Laurentide Ice Sheet, Northwest Territories, Canada

“…Four ice-flow phases were identified through till macrofabric analysis that correlates well with the erosional record around the Pine Point mining district (Table 4; Oviatt and Paulen 2013;Oviatt et al 2015). This confirms the glacial history of the Pine Point region is much more complex than previously reported (Lemmen et al 1994).…”

“…Subsequent work, using visual observations, grain size, till-matrix geochemistry, indicator mineral abundance, and pebble lithologies, identified four distinct till units at open-pit K-62 (Rice et al 2013). Oviatt and Paulen (2013) and Oviatt et al (2015) mapped striae exposed on the bedrock shoulders of the open-pits and identified three main ice flow phases which correlated with the regional ice flow pattern established from the geomorphological record in the area (Rice et al 2013). These investigations identified the earliest flow phase was to the southwest (ϳ230°), followed by a dominant flow phase to the northwest (ϳ300°), and finally, a west-southwestward flow phase associated with ice streaming during deglaciation (ϳ250°) (Fig.…”

Deformation ‘boundary front’ movements in subglacial tills—A microsedimentological perspective from till sequences near Pine Point, NWT, Canada

“…Fieldwork conducted by the Geological Survey of Canada in 2010 documented cross‐striated bedrock surfaces on the shoulders (i.e. bedrock benches) of several exposed open pits (McClenaghan, Paulen, & Oviatt, ; Oviatt, ; Oviatt et al, ; Oviatt, Paulen, McClenaghan, Gleeson, & Paradis, ). Striation measurements and cross‐cutting relationships (Figure ), combined with aerial‐photograph and satellite‐imagery landform analyses, have determined a minimum of three ice‐flow trajectories (McClenaghan et al, ; Oviatt et al, ).…”

“…bedrock benches) of several exposed open pits (McClenaghan, Paulen, & Oviatt, ; Oviatt, ; Oviatt et al, ; Oviatt, Paulen, McClenaghan, Gleeson, & Paradis, ). Striation measurements and cross‐cutting relationships (Figure ), combined with aerial‐photograph and satellite‐imagery landform analyses, have determined a minimum of three ice‐flow trajectories (McClenaghan et al, ; Oviatt et al, ). The earliest flow phase was to the south‐west (~230°), a subsequent significant flow phase to the northwest (~300°) and a final west south‐westward (~250°) deglacial flow were identified in several pits, including O‐28.…”

“…Broader studies of tills at Pine Point have indicated that a considerable thickness (>20 m) of till was emplaced beneath an active soft sediment deforming bed (Rice, Paulen, Menzies, & McClenaghan, ; Rice, Paulen, Menzies, McClenaghan, & Oviatt, ). The tills were deposited under various ice‐flow trajectories of the Laurentide Ice Sheet (LIS), and potentially represent successive accretion through three main glacial phases (Oviatt, Gleeson, Paulen, McClenaghan, & Paradis, ). This paper focusses on the microsedimentological findings from till exposures in Pit O‐28 to determine stress fluctuations within the subglacial sediment deforming layer during till deposition and the progression of an active deformation front as subglacial till is being emplaced.…”