Abstract

Pb isotope analyses, combined with sensitive high-resolution ion-microprobe U-Pb zircon dating, suggest that the giant Broken Hill orebody formed over an ∼6 m.y. period, coincident with a number of small Broken Hill–type deposits lower in the stratigraphic sequence. The formation of the smaller, but significant, Pinnacles deposit was also episodic over ∼7 m.y. and up to ∼10 m.y. prior to the formation of Broken Hill. Using relative ages and stratigraphic position, together with lithologic and isotopic variation, a subsea floor origin for the deposits, including the Broken Hill Pb-Zn-Ag orebody, is proposed. Mn-P–rich banded iron formation stratigraphically above the orebody may have been derived from spent ore-forming fluids exhaled onto the seafloor. Extensive magnetite disseminations in metasedimentary rocks at the same level as the banded iron formation probably represent distal signatures of the same hot springs.

You do not currently have access to this article.