Open AccessIndicator mineral signatures of magmatic Ni-Cu deposits, Thompson Nickel Belt, Manitoba: Part 2 - till data
Author(s) -
M B McClenaghan,
I M Kjarsgaard,
S A Averill,
D Layton-Matthews,
D Crabtree,
G Matile,
I McMartin,
M Pyne
Publication year - 2013
Language(s) - English
Resource type - Reports
DOI - 10.4095/292543
Subject(s) - geology , pentlandite , geochemistry , chromite , mineral , heavy mineral , pyrite , chalcopyrite , arsenopyrite , mineralization (soil science) , sulfide minerals , mineral exploration , mineralogy , pyrrhotite , provenance , chemistry , copper , organic chemistry , soil science , soil water
The Geological Survey of Canada (GSC) conducted an indicator mineral study around the komatiite-associated Ni-Cu deposits in the northern Thompson Nickel Belt, northern Manitoba, to document the indicator mineral signatures of the Ni-Cu deposits. Samples used inthis study include archived till heavy mineral concentrates from 1996, till and bedrock samples collected in 2005 and 2006, and till samples collected in 2007 as part of another GSC study. The Laurentide Ice Sheet flowed across the Thompson Nickel Belt southwestward, and subsequently westward, andstriations from both ice-flow events are readily apparent on outcrops along the Belt. Till samples were collected to evaluate glacial dispersal along both ice-flow trends. Till and bedrock samples were processed to recover heavy (specific gravity>3.2) mineral concentrates. Potentialindicator minerals picked from heavy mineral concentrates included Cr-diopside, olivine, chromite, spinel, gahnite, rutile, pink corundum, and sapphirine, as well as metallic minerals such as pyrrhotite, pentlandite, chalcopyrite, pyrite, arsenopyrite, gold, and sperrylite. Elevated chromite abundances combined with the presence of Ni-Cu sulphide minerals are strong indicators of potential magmatic Ni-Cu mineralization in till down ice of the Ni-Cu deposits in the Belt. Chalcopyrite and sperrylite are the most useful metallic indicator minerals as they are the mostlikely to survive glacial transport and postglacial weathering. Elevated Zn content (>2 wt.% ZnO) in chromite is only found in strongly mineralized rocks and is the strongest indicator for mineralization other than the actual ore minerals. The Zn content in chromite from Ni-depositsmight be considerabley lower in regions with lower metamorphic grade and thus this feature does not have universal application. The distribution of Cr-diopside, olivine, enstatite, and chromite are similar and are most abundant just east of the Thompson Nickel Belt, at the Thompson deposit andsouth of the Pipe deposit. Their mafic Cr- or Ni-rich compositions reflect the abundance of ultramafic rocks in the area. Chemical variations in Cr-diopside (higher Cr, Na) and olivine (variable Ni) and the occurrence of high-grade metamorphic minerals, such as corundum, sapphirine, rutile, andspinel, reflect the higher metamorphic grades in certain areas, rather than presence or absence of mineralization. Exploration along the Thompson Nickel Belt and in the surrounding terranes should consider both the older southwest and younger westward ice-flow events when interpreting and followingup till indicator mineral results.