|Résumé||(disponible en anglais seulement)|
Indicator minerals methods for intrusion-hosted Sn and W deposits were tested at the intrusion-hosted Sisson W-Mo and Mount Pleasant Sn-W-Mo-Bi-In deposits in
eastern Canada as part of the Geological Survey of Canada's (GSC) Targeted Geoscience Initiative 4 (TGI 4). The program was a collaborative federal geoscience program with a mandate to provide industry with the next generation of geoscience knowledge
and innovative techniques that will result in more effective targeting of buried mineral deposits. The case studies are a collaborative effort between the GSC, the New Brunswick Department of Energy and Mines (NBDEM), and the holders of the Sisson
(Northcliff Resources Limited, Hunter Dickinson Inc.) and the Mount Pleasant (Adex Mining Inc.) deposits, and Laurentian University.
The detailed till mineralogical + geochemical study described here is one of the first reported for major Sn-W
deposits in glaciated terrain. Indicator minerals were examined in heavy mineral (>3.2 specific gravity) concentrates of bedrock and till samples from both deposits, as well as in stream sediment samples from the Sisson deposit area. The <0.063 mm
fraction of till samples from both deposits was analysed geochemically using modified aqua regia (partial) and borate fusion (total) digestions.
Indicator/pathfinder trace elements in till at the Sisson W-Mo deposit includes W, Mo, Cu, Zn, Pb,
Ag, Bi, In, As, Cd, Zn, and Te. Indicator/pathfinder trace elements in till at the Mount Pleasant Sn-W-Mo-Bi-In deposit includes Sn, W, Mo, Bi, In, Ag, As, Cd, Cu, Pb, Re, Te, Tl, and Zn. These element suites reflect the polymetallic nature of these
deposits and the broader suite of elements that is now available using modern analytical methods such as inductively coupled plasma - mass spectrometry. The Mount Pleasant deposit is a significant source of indium and till down ice of the deposit
contains some of the highest indium values (13 ppm) ever reported for till, indicating that till geochemistry can be an important exploration tool for In-bearing deposits. Indicator/pathfinder elements in stream sediment downstream of the Sisson
deposit include W, Mo, Ag, As, Bi, Cd, Cu, In, Tl, and Zn.
Indicator/pathfinder elements in stream water around the Sisson deposit include W, Mo, As, Cd, Cu, Cs, and Zn. Indicator minerals of the Sisson deposit identified in the 0.25-0.5 mm
fraction of mineralised bedrock, till, and stream sediments include scheelite, wolframite, molybdenite, chalcopyrite, Bi minerals (joseite, native Bi, bismutite, bismuthinite), galena, sphalerite, arsenopyrite, spessartine, pyrrhotite, and pyrite.
Indicator minerals of the Mount Pleasant deposit identified in the 0.25-0.5 mm fraction of mineralised bedrock and till include cassiterite, wolframite, molybdenite, topaz, fluorite, galena, sphalerite, chalcopyrite, galena, arsenopyrite, pyrite, and
loellingite. Additional but rare secondary indicator minerals of the Mount Pleasant deposit include beudantite, anglesite, and plumbogummite which formed by oxidation and weathering of the galena.
The extensive suite of indicator minerals for
both deposits reflects their polymetallic natures and the ability of modern indicator mineral methods to recover these minerals. Indicator minerals present in the coarse (0.5-2.0 mm) heavy mineral fraction of till indicate proximity to the
mineralised source. A commercial service is now available to systematically determine the scheelite contents of heavy mineral concentrates using its short wave ultraviolet light fluorescence. This service will provide consistent scheelite results
within, and between, heavy mineral sampling surveys. Fluorite abundance was shown to be most abundant in the 3.0-3.2 SG (mid-density) fraction of till and can be readily recovered by including a mid-density heavy liquid separation as part of the