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.

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. This study applies mineral liberation analysis (MLA) to investigate the finer (<250 µm) fraction of till HMC. Automated mineralogy (e.g., MLA) of finer material allows for the 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 Sisson W-Mo deposit has a previously documented dispersal train containing the ore minerals scheelite, wolframite, and molybdenite, along with sulfide and other accessory minerals, and was used as a test site for this study. Wolframite is identified in till samples up to 10 km down ice, whereas in previous work on the coarse fraction of till it was only identified directly overlying mineralization. Chalcopyrite and pyrite are found up to 10 km down ice, an increase over 2.5 and 5 km, respectively, achieved in previous work on the coarse fraction of the same HMC. Galena, sphalerite, arsenopyrite, and pyrrhotite are also found up to 10 km down ice after only being identified immediately overlying mineralization using the >250 µm fraction of HMC. Many of these sulfide grains are present only as inclusions in more chemically and robust minerals and would not be identified using optical methods. The extension of the wolframite dispersal train highlights the ability of MLA to identify minerals that lack distinguishing physical characteristics to aid visual identification.

Indicator minerals from heavy mineral concentrates have long been used in exploration for diamonds and gold, and more recently porphyry copper and volcanic massive sulphide deposits. This study is investigating the application of rapid automated mineralogy to identify and characterize indicator minerals in till and stream sediment samples. The fine (&amp;lt;0.250 mm) heavy mineral fraction is well suited to automated mineralogy as a large number of mineral grains can be analyzed from an individual sample. These small grains are difficult to visually recognize using traditional microscopic methods. The initial phase of this study has assessed methods to process and analyze the &amp;lt;0.250 mm heavy mineral concentrate using archived samples from three test sites. Investigations focused on identifying key areas of loss and contamination during processing and workflow, and establishing mitigating protocols. Concentrates were split into four size fractions to better represent the large number of grains in a sample. Single-use sieves were developed to reduce potential for cross-contamination. Fractions were mounted into an epoxy plug, which were quartered and remounted to capture both basal and cross-sectional planes to compensate for any density settling, prior to rapid automated scanning by mineral liberation analysis.

The authors set out to evaluate the use of three sieving methods when sieving the &amp;lt;250 micrometres heavy mineral concentrate (HMC) material. As the grain size to be evaluated decreases, unique concerns for sample loss and cross-contamination during processing arise and this study reports a methodology for sieving the &amp;lt;250 micrometres fraction of a HMC using disposable nylon mesh sieves. The disposable sieves result in a significant reduction in sample loss when tested against traditional stainless-steel sieves, and their single use nature eliminates the chance of sample cross-contamination of samples from reuse of a sieve and the need for sieve cleaning between samples.

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