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. 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.
Highlights
Indicator mineral methods applied to sediment samples are important exploration tools for diamonds [1] and gold [2,3,4,5,6] in glaciated terrain
Scheelite is resistant to both physical and chemical weathering, and its presence in the coarse (250–2000 μm) fraction of till at Sisson was reported in all samples observed by this study
The presence of scheelite in the fine (
Summary
Indicator mineral methods applied to sediment samples are important exploration tools for diamonds [1] and gold [2,3,4,5,6] in glaciated terrain. A large till or stream-sediment sample (10–20 kg) is necessary to recover detectable and meaningful numbers of indicator mineral grains for analysis [14]. Indicator minerals are recovered from these large samples at specialized commercial laboratories using a combination of sizing, density, and magnetic concentration methods to reduce the volume of material into a nonferromagnetic heavy mineral concentrate, (HMC), for examination. The coarse fraction (250–2000 μm; medium to very coarse sand) of the HMC is visually examined using a binocular microscope to identify and count indicator mineral species [6,17]. Current methods focus on the medium to coarse sand-sized HMC fraction because it is the most cost-effective to recover and visually examine. The method is well established, having been used in mineral exploration and research for more than 30 years
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