Subseafloor origin for Broken Hill Pb-Zn-Ag mineralization, New South Wales, Australia

• Published in: Geology (Boulder) 2004-07, Vol.32 (7), p.589-592
• Main Authors: Parr, Joanna M, Stevens, Brian P. J, Carr, Graham R, Page, Rodney W
• Format: Article
• Language: English
• Subjects: absolute age; Australasia; Australia; banded iron formations; base metals; Broken Hill; chemically precipitated rocks; dates; disseminated deposits; Economic geology; exhalative processes; Geochronology; Geology; giant deposits; gneisses; Hores Gneiss; hydrothermal conditions; ion probe data; iron formations; iron ores; lead-zinc deposits; magnetite; marine environment; mass spectra; metal ores; metamorphic rocks; mineral deposits, genesis; Minerals; New South Wales Australia; Oceans; ore bodies; oxides; Paleoproterozoic; Pb/Pb; periodicity; Precambrian; Proterozoic; sedimentary rocks; silver ores; Southern Cross Deposit; spectra; submarine environment; U/Pb; upper Precambrian
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/G20358.1

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.