The Rosebery pyritic zinc-lead-copper-silver-gold orebody occurs in dominantly felsic volcanic rocks of Cambrian age in western Tasmania. Ore formation occurred in a marine environment following eruption of a thick pyroclastic unit consisting mainly of welded, ashflow tuffs, and subsequent subsidence. The main orebody consists of a discontinuous massive sulfide horizon and in the southern part of the mine there is a generalized metal zonation with a lower and central Cu-Fe-rich zone surrounded and overlain by Zn-Pb-Ag-rich ore. Barite-sulfide ore occurs as separate lenses higher in the sequence separated from the sulfide orebody by unmineralized, cleaved siltstone. The orebody is underlain by an extensive zone of alteration marked by depletion of Na and Sr and enrichment in Rb, K, Mg, Mn, and H20. The pyrite and chalcopyrite content of the altered footwall tuff and the Co content of the pyrite is highest beneath the Fe-and Cu-rich zones in the sulfide orebody and a feeder is inferred in this area.The •a4S values for sulfides in the sulfide orebody are higher in the richest Zn-Pb-Ag ore (>14.1%0) than the Fe-Cu ore (>7.8•), a pattern paralleled by a decrease in the Fe/Fe + Mg + Mn ratio of chlorite and a decrease in the FeS content of sphalerite. The •$48 values for sulfides in the barite ore are even higher (14.5 to 19.8%0) and the FeS content of sphalerite lower. Barite throughout the barite and sulfide orebodies is fairly constant between 84.6 and 41.2 per mil, but that in the sulfide ore appears to be epigenetic. The/i34S values for baritesulfide pairs indicate a temperature range of 255 ø to 298øC for the barite orebody, but the temperature of barite ore formation was probably about 250øC.The use of $a4S values for sulfides as stratigraphic markers indicates that the sulfide orebody is diachronous. It is possible to account for the metal and $a4S distribution by assuming that the ore solutions are buoyant on reaching the sea floor during the Fe-and Cu-rich phases but show reversing buoyancy during the PboZn-rich phase.The coexisting arsenopyrite-pyrite-chlorite-quartz assemblage in the sulfide orebody defines a range of aO2-T conditions using the six-component solid solution chlorite model of Walshe and Solomon (1981). The maximum indicated temperature of $00øC is consistent with the minimum temperature required by iron and copper solubilities. However, the chlorite compositions may be postdepositional, as seems to be the case for the FeS contents of sphalerite. The $a4Szs for the sulfide orebody is probably derived by almost complete reduction of Cambrian seawater sulfate mixed with sulfur leached from underlying rocks. The/ia4S values for the barite orebody may represent partial reduction of seawater sulfate.The ore fluid is supposed to have been generated by convective circulation of seawater in a rock pile heated by a Cambrian granitoid pluton.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.