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Abstract:
Our most important Zn resources occur within clastic-dominated (CD-type)
deposits, which are located in a small number of Proterozoic and Phanerozoic
sedimentary basins. The most common model for CD-type mineralisation
involves sedimentary exhalative (SEDEX) processes, i.e. the venting of metal
bearing fluids into a restricted, anoxic H2S-bearing (euxinic) water column. In
the Carpentaria Zn Province (Australia), multiple world class deposits are hosted
in Proterozoic (1.6 Ga) stratigraphy, where models of the ancient sulfur cycle have also been developed. Focusing on the most recent discovery – the Teena deposit – we report bulk rock and isotopic data (δ34Spyrite values) that provide information on the sulfur cycle during the diagenetic and hydrothermal evolution of the Teena sub-basin. In contrast to the SEDEX model, intervals containing abundant pyrite with highly positive δ34S values (>25 ‰) correspond with euxinic conditions that developed due to high organic loading (i.e. productivity) and not basin restriction.
This basin wide feature, which can also be mistaken as a hydrothermal pyrite halo, is genetically unrelated to the subsequent hydrothermal mineralisation that formed beneath the palaeo-seafloor. The formation of CD-type deposits in the Proterozoic does not, therefore, require euxinic conditions.
