Abstract
Exploration under thick glacial sediment cover is an important facet of modern mineral exploration in Canada and northern Europe. Till heavy mineral concentrate (HMC) indicator mineral methods are well established in exploration for diamonds, gold, and base metals in glaciated terrain. Traditional methods rely on visual examination of >250 µm HMC material, however this study applies modern automated mineralogical methods (mineral liberation analysis (MLA)) to investigate the finer (<250 µm) fraction of till HMC. Automated mineralogy of finer material allows for rapid collection of precise compositional and morphological data from a large number (10,000–100,000) of heavy mineral grains in a single sample. The Izok Lake volcanogenic massive sulfide (VMS) deposit, one of the largest undeveloped Zn–Cu resources in North America, has a well-documented fan-shaped indicator mineral dispersal train and was used as a test site for this study. Axinite, a VMS indicator mineral difficult to identify optically in HMC, is identified in till samples up to 8 km down ice. Epidote and Fe-oxide minerals are identified, with concentrations peaking proximal to mineralization. Corundum and gahnite are intergrown in till samples immediately down ice of mineralization. Till samples also contain chalcopyrite and galena up to 8 km down ice of mineralization, an increase from 1.3 km for sulfide minerals in till previously reported for coarse HMC fractions. Some of these sulfide grains occur as inclusions within chemically and physically robust mineral grains and would not be identified visually in the coarse HMC visual counts. Best practices for epoxy mineral grain mounting and abundance reporting are presented along with the automated mineralogy of till samples down ice of the deposit.
Highlights
Indicator mineral methods applied to sediment samples are important exploration tools in glaciated terrain for diamonds [1] and gold [2,3,4,5]
Indicator minerals are recovered from these large samples at specialized commercial laboratories using a combination of sizing, magnetic and density concentration methods to reduce the volume of material into a non-ferromagnetic heavy mineral concentrate (HMC)
[18,31] were were chosen chosen for for use use in in this this study. They were were selected based on their locations relative to mineralization and the indicator minerals identified in their selected based on their locations relative to mineralization and the indicator minerals identified in coarse fraction of HMC, in particular gahnite
Summary
Indicator mineral methods applied to sediment samples are important exploration tools in glaciated terrain for diamonds [1] and gold [2,3,4,5]. Their potential to aid porphyry Cu [6,7,8], magmatic Ni–Cu-PGE [5,9], carbonate-hosted Pb–Zn [10] and volcanogenic massive sulfide (VMS). The resulting HMC is composed of dense mineral grains (specific gravity (SG) >3.2) displaying varying levels of physical and chemical weathering, and the degree of abrasion and wear can be used to infer the transport distance of certain minerals [3]
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