Short-wavelength infrared spectroscopy as a tool for characterising hydrothermal alteration at the Geita Hill gold deposit, Tanzania

Van Ryt, M.R., Sanislav, I.V., Dirks, P.H.G.M., Huizenga, J.M., Mturi, M.I, and Kolling, S.L. (2017) Short-wavelength infrared spectroscopy as a tool for characterising hydrothermal alteration at the Geita Hill gold deposit, Tanzania. In: EGRU Contribution (69) p. 120. From: FUTORES II Conference: future understanding of tectonics, resources, environment and sustainability, 4-7 June 2017, Townsville, QLD, Australia.

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Abstract

Geita Hill is a world-class gold deposit located in north-western Tanzania and hosted within an ironstone-dominated sedimentary package, intruded by diorite dykes and sills. The host rocks were metamorphosed to greenschist facies and show a complex deformation history comprising early ductile, and late brittle-ductile events. The regional metamorphic assemblage at the deposit is characterised by Bt + Chl + Act + Kfs ± Phg ± Mt ± Po ± Py. The gold-related alteration overprints the regional metamorphism, and manifests as a series of silicification and sulfidation fronts, and/or microfracture and vein networks. Gold is closely associated with secondary pyrite, and occurs as free-Au and gold tellurides. The mineralized vein/microfracture networks contain Bt and Kfs as primary accessory minerals. The mineralising alteration is overprinted by barren, multiphase quartz-carbonate and carbonate-chlorite veins, characterised by the assemblage Ca + Sd + Chl ± Qtz ± Py ± Ba. The close association between gold and biotite in the mineralized vein/microfracture networks and the scarcity of retrograde chlorite makes the Geita Hill deposit ideal to test the change of the biotite short-wave infrared (SWIR) spectral response with the proximity to the gold alteration. SWIR spectra were collected from three well-characterised drill holes that intercepted the gold mineralization and the results were compared to the gold grades. The SWIR data shows that there is a good correlation between the biotite spectral response and the gold grades. The position of the 2250 nm biotite absorption feature is changing systematically as a function of the ore proximity indicating that SWIR can be used to trace gold mineralization and has the potential to be a powerful exploration tool if used in conjunction with well characterised mineral paragenesis.

Item ID: 54659
Item Type: Conference Item (Abstract / Summary)
ISBN: 978-0-9954470-3-5
Keywords: short-wavelength infrared spectroscopy; hydrothermal alteration
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Date Deposited: 24 Jul 2018 02:55
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040201 Exploration Geochemistry @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840105 Precious (Noble) Metal Ore Exploration @ 100%
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