Sulfide evolution in komatiite-hosted nickel deposits
Final Report Abstract
Samples from the Archaean komatiite-hosted Ni-sulfide deposits as well as from the komatiites itself were investigated to understand processes involved in komatiite emplacement and the sulfide ore evolution. Results of this study concerning komatiite emplacement are: (1) Remnants of vents of komatiite eruption fissures (dykes) are rare due to komatiite melt properties. A very low viscosity, laminar flow and eruption above the liquidus temperature causes the eruption fissure to close after eruption without leaving a trace of its former existence. (2) High-MgO komatiites rarely form pillow lavas (as known from basaltic lavas) as they need a low flow rate only possible a flow edges. The observed pillows are one to two orders of magnitude smaller than the basaltic counterparts. (3) Interspinifex ore formed during injection of younger komatiite melt into older sulfide melt causing an emulsion between them. Upon cooling olivine crystallized and thus destabilized the emulsion causing both melts to separate and leaving olivine crystals in sulfide behind. Results for the sulfide evolution are: (1) Most of the economical upgrading of the sulfide melt by the silicate melt occurred prior to the formation of a sulfide melt pool at the base of the komatiite channel based on 33S data. (2) Trace element data of massive sulfides suggest that the crystallization started at the edge and the crystallization front pushed a boundary layer liquid, containing incompatible elements, towards the center. In the central area droplets of an immiscible Co-As-Te-Bi melt exsolved from the last sulfide melt. (3) Combining textures from Moran with other magmatic sulfide deposits showed that the loop texture can be regarded as igneous texture. (4) Two net-textured ore layers were identified at Moran. Textures and trace element chemistry of sufides suggests that the basal layer formed by olivine sinking into and floating on top of the sulfide melt, whereas the second layer formed by sulfide melt infiltrating olivine cumulate and replacing interstitial silicate melt. (5) Younger hydrothermal activity can mobilize the magmatic Ni to form rare hydrothermal pentlandite under very reduced conditions at temperatures > 450 °C. The source of the sulfur to form the ore deposits were investigated using 33S data confirming the sedimentary sulfides were molten and entrained into the komatiite melt and subsequently enriched in magmatic S and economic metals.
Publications
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(2019) Remnant lenses of komatiitic dykes in Kambalda (Western Australia): Occurrences, textural variations, emplacement model, and implications for other komatiite provinces. Lithos 342-343, 206-222
Staude, S., Markl, G.
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(2020). The occurrence and origin of pentlandite-chalcopyrite-pyrrhotite loop textures in magmatic Ni-Cu sulphide ores. Economic Geology 115, 1777-1798
Barnes, S.J., Taranovic, V., Schoneveld, L.E., Mansur, E.T., Le Vaillant, M., Dare, S., Staude, S., Evans, N.J., Blanks, D.
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(2020). The textures, formation and dynamics of rare high-MgO komatiite pillow lavas. Precambrian Research 343, 105729
Staude, S., Jones, T.J., Markl, G.
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(2021) Multi-stage sulfide evolution of the Moran Ni sulfide ore, Kambalda, Western Australia: Insights into the dynamics of ore forming processes of komatiite-hosted deposits. Mineralium Deposita
Staude, S., Oelze, M., Markl, G.
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(2021). Interspinifex Ni sulfide ore from Victor South-McLeay, Kambalda, Western Australia. Mineralium Deposita 56, 125-142
Staude, S., Barnes, S.J., Markl, G.
