RARE-EARTH AND MAJOR ELEMENT CHEMISTRY OF GARNET-RICH ROCKS IN THE SOUTHERN CURNAMONA PROVINCE, AUSTRALIA: IMPLICATIONS FOR THE EXPLORATION OF BROKEN HILL-TYPE PB-ZN-AG DEPOSITS

Mn garnet-rich rocks are spatially associated with the giant Paleoproterozoic, Broken Hill Pb-Zn-Ag deposit and hundreds of minor Broken Hill-type deposits throughout the Southern Curnamona Province. Garnet-rich rocks, metamorphosed to granulite facies at Broken Hill and conformable to bedding in surrounding metasedimentary rocks, are interpreted as metamorphosed exhalites. Quartz garnetites at Broken Hill (up to 19 wt. % MnO) and garnet-rich rocks interlayered with metasedimentary rocks metamorphosed from lower amphibolite to granulite facies at Cathedral Rock (up to 7 wt. % MnO), Thunderdome (up to 14 wt. % MnO), Mutooroo, and Iron Blow show similar Fe/Ti vs. Al/(Al+Fe+Mn) compositions suggesting approximately the same input of detrital and hydrothermal components. Garnet-rich rocks from the Mundi Mundi Plain show a relative high contribution of detrital components whereas garnet-grunerite rocks from Weekeroo and Meningie Well (up to 16 wt. % MnO) possess a high hydrothermal component. Rare earth element (REE) patterns of garnetite and quartz garnetite from the Broken Hill deposit show strong chondrite normalized positive and negative Eu anomalies, respectively. Similarly, plots of individual garnets in garnetites and quartz garnetites from the Broken Hill deposit by LA-ICP-MS exhibit positive and negative Eu anomalies, respectively. Garnet-rich rocks distal to the Broken Hill lodes and from minor Broken Hill-type deposits or horizons unrelated to mineralization show high light REE (LREE)/heavy REE (HREE) ratios and negative Eu anomalies. REE patterns (>200 analyses) of individual garnets from these sites show low LREE/HREE ratios and negative Eu anomalies, except for those from Cathedral Rock that show small positive to no Eu anomalies. The REE signature of garnet-rich rocks and garnet, in conjunction with hydrothermal and detrital chemical indicators, suggest that the protoliths of garnet-rich rocks from the Southern Curnamona Province away from the Broken Hill deposit contained a high detrital component. The fluids that formed these rocks could have had similar temperatures and/or fO₂ conditions to those that were responsible for the formation of quartz garnetites at Broken Hill. REE and major element compositions are potentially valuable in the exploration for Broken Hill-type deposits.