0361-0128/09/3832/687-26 687 Introduction MANGANESE-RICH garnet-rich rocks are spatially related to a variety of strata-bound massive base-metal sulfide deposits that have been metamorphosed from the upper greenschist to the granulite facies, including the Broken Hill deposit, Australia; the Sullivan Pb-Zn deposit, British Columbia (Slack et al., 2000); the Gamsberg Zn deposit, South Africa (Rozen- daal and Stalder, 2001); the Cannington Pb-Zn-Ag deposit, Australia (Bodon, 1996); and the Broken Hill Pb-Zn-Cu de- posit, South Africa (Spry et al., 2000). This spatial relationship constitutes an exploration guide to ore (e.g., Spry et al., 2000). Garnet-rich rocks, some highly manganiferous, are known from all but the youngest units of the Willyama Supergroup throughout the Paleoproterozoic southern Curnamona Pro- vince, Australia. However, such rocks are most abundant in the Broken Hill domain (Figs. 1) where they are spatially as- sociated with the giant Broken Hill deposit (280 Mt @ 20 wt % Pb + Zn and 100 g/t Ag; Spry and Wonder, 1989; Spry et al., 2000; Plimer, 2006), the small Pinnacles deposit (2 Mt @ 6–11 wt % Pb, 2.5 wt % Zn, 300–500 g/t Ag; Parr, 1992), and with hundreds of minor Broken Hill-type deposits (Barnes et al., 1983; Conor, 2006a, b; Conor and Preiss, 2008). Broken Hill-type deposits are metamorphosed, strata- bound accumulations of Pb-Zn-Ag sulfides characterized by a spatial association with various Fe-, Mn-, Ca-, Si-, and Zn-rich rocks including garnetite (>80% garnet; Spry and Wonder, 1989), quartz garnetite, pyroxenoid-rich rocks, gahnite-rich rocks, and iron formation (e.g., Stanton, 1976a; Walters, 2001; Walters et al., 2002). The origin of these rocks remains a Geochemistry of Garnet-Rich Rocks in the Southern Curnamona Province, Australia, and Their Genetic Relationship to Broken Hill-Type Pb-Zn-Ag Mineralization* ADRIANA HEIMANN, 1,†, ** PAUL G. SPRY, 1 GRAHAM S. TEALE, 2 COLIN H.H. CONOR, 3 AND WOLFGANG R. LEYH 4 1 Department of Geological and Atmospheric Sciences, 253 Science I, Iowa State University, Ames, Iowa 50011-3212 2 Teale and Associates, P.O. Box 740, North Adelaide, South Australia 5006, Australia 3 Geological Survey Branch, Primary Industries and Resources South Australia, 101 Grenfell Street, Adelaide, South Australia 5001, Australia 4 Eaglehawk Geological Consulting Pty. Ltd., P.O. Box 965, Broken Hill, New South Wales 2880, Australia Abstract Garnet-rich rocks are locally associated with the giant Paleoproterozoic Broken Hill Pb-Zn-Ag deposit and hundreds of smaller Broken Hill-type occurrences in the southern Curnamona Province, Australia; however, others are present unrelated to sulfides. Mn-bearing garnet-rich rocks are conformable to bedding in metased- imentary rocks of the Paleoproterozoic Willyama Supergroup and, together with sulfide-bearing zones, are spa- tially related to amphibolite and/or felsic volcanic rocks or shallow granite intrusions. The stratiform garnet- rich rocks can be subdivided into two groups: Mn-rich varieties typical of the stratigraphic hanging wall of the Broken Hill deposit and Mn-poor and Fe-rich varieties that are typical of the footwall and are regionally wide- spread. These garnet-rich rocks formed on the floor of a rifted basin as a mixture of chemical precipitates and detrital sediments and were subsequently metamorphosed to the amphibolite or granulite facies during the Olarian orogeny. A plot of Fe/Ti versus Al/(Al + Fe + Mn) ratios of these rocks suggests equal proportions of hydrothermal and detrital components in the precursor phases. Low Co + Cu + Ni contents are consistent with the input of a small hydrogenous component. Quartz garnetite and garnet-gahnite rocks in the stratigraphic footwall of the Broken Hill deposit (Zn-rich, Cu-poor B and C lodes), and garnet-rich rocks elsewhere in the southern Curnamona Province that are Mn poor and Fe rich, exhibit chondrite-normalized rare earth element (REE) patterns with negative Eu anomalies, which indicate that the precursor minerals formed from hydro- thermal fluids at <300°C and under relatively low fO 2 conditions. Garnetite and hedenbergite-, bustamite-, and rhodonite-bearing garnet-rich rocks from the stratigraphic hanging wall of the Broken Hill deposit (Pb-rich 2 and 3 lenses and the A lode) are Mn and Ca rich, Fe poor, and have positive Eu anomalies. Precursors to these Mn-rich rocks formed from relatively cool hydrothermal fluids (~250°C) at fO 2 conditions higher than those that formed Mn-poor, Fe-rich garnet- and gahnite-rich rocks at Broken Hill. Correlations among various ele- ments show that the presence of positive or negative Eu anomalies in garnet-rich rocks depends on the com- position of the precipitate (Fe, Mn, and trace metal content) as well as the chemical, crystallographic, or sorp- tion control that the precursor Fe-Mn oxyhydroxides/oxides/carbonates had upon the incorporation of Eu. Garnet-rich rocks from the Broken Hill deposit have higher average Mn, K, Rb, Eu, Ga, Cs, Cu, Pb, Zn, As, Cd, Sb, Ag, W, and Au contents than those from other locations in the southern Curnamona Province, and these are more enriched in Fe, Mg, Ni, P, V, Co, Sc, Sr, Y, and U, which indicates a larger hydrogenetic com- ponent to their precursor minerals. Enrichments in Mn, S, Ga, Eu, Cu, Pb, Zn, As, Cd, Sb, Ag, and Au, and a positive Eu anomaly in garnetite can be used as exploration guides in the search for Broken Hill-type deposits by indicating close proximity to mineralization. *A digital supplement to this paper is available at http://www.geoscience- world.org/> or, for subscribers, on the SEG website, http://www.segweb.org. † Corresponding author: e-mail, aheimann@geology.wisc.edu **Current address: Department of Geology and Geophysics, 1215 W. Dayton Street, University of Wisconsin-Madison, Madison, Wisconsin 53706. ©2009 Society of Economic Geologists, Inc. Economic Geology, v. 104, pp. 687–712 Submitted: August 28, 2008 Accepted: June 24, 2009