The Mantoverde iron oxide Cu-Au deposit (Chile): Characteristics, genesis and relationship with Andean magnetite(-apatite) systems
Final Report Abstract
A metallogenetic study on the Mantoverde IOCG system and selected magnetite(-apatite) deposits of the Chilean Iron Belt, and their geologic context has been conducted. The Mantoverde IOCG district is located in the Chilean Coastal Cordillera about 100 km north of Copiapó. The IOCG bodies are mainly Cu-Au-bearing specularite or magnetite-cemented breccias and associated stockworks. The hypogene sulfide mineralization is represented mainly by chalcopyrite and pyrite and associated by variably intense K-feldspar alteration, chloritization, sericitization, silicification, and/or carbonatization. There is a positive correlation of Cu and gold grades. Elevated concentrations of light rare-earth elements detected locally may result from redistribution within the deposit rather than by introduction from external sources during the mineralization. The Cu-Au ores in the Mantoverde district are low in U, and have relatively low contents in heavy metals, which are potentially hazardous to the environment such as As, Hg, or Cd. Mineralization occurred in three hydrothermal stages: an early Iron Oxide Stage, a Sulfide Stage, and a Late Stage and evolved from an early hypersaline, high to moderate temperature fluid to a moderate saline, moderate temperature fluid, and, finally, a low saline, moderate to low temperature fluid. Boiling occurs only locally and is of no relevance for the ore formation. Sulfur isotope ratios of chalcopyrites show systematic variations within the district, which are interpreted to reflect relative distance to inferred fluid conduits and the level of deposition within the hydrothermal system. Most initial 87Sr/86Sr of altered volcanic rocks and hydrothermal calcite from the Mantoverde district are between those of contemporaneous igneous and seawater Sr reservoirs. Lead isotope ratios of chalcopyrite suggest that the Pb (and by inference the Cu) is derived from Early Cretaceous magmatism. The microthermometric, stable and radiogenic isotope data are consistent with a genetic model, in which cooling Cu and sulfur-bearing magmatic-hydrothermal fluids that mix with basin derived non-magmatic fluids at relatively shallow crustal levels are responsible for the bulk of the IOCG mineralization in the Mantoverde district. The non-magmatic hydrothermal fluids may have contributed with exotic (seawater, evaporitic) sulfur. Iron oxide Cu-Au deposits in northern Chile show remarkable similarities with magnetite(-apatite) deposits of the Chilean Iron Belt. Both occur in close spatial proximity and are broadly of same age. They show also a similar paragenetic sequence. Most altered host rocks of magnetite(-apatite) deposits have initial 87Sr/86Sr as contemporaneous magmatic-arc igneous rocks of northern Chile. Sulfur isotope signatures of magnetite-rich IOCG and magnetite(-apatite) ores are essentially identical. Similarly, the Pb isotope signatures of these sulfides are indistinguishable among these deposit types.
Publications
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2010. The Mantoverde district: An example of distal portions of zoned IOCG systems. In: Porter, T. M., ed., Hydrothermal iron-oxide copper-gold & related deposits: Advances in the understanding of IOCG deposits. Adelaide, Australian Mineral Foundation, v. 3; 273-284
Rieger, A.A., Marschik, R., & Diaz, M.
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2008, The Mantoverde district: example of the distal chlorite-sericite-carbonate facies of zoned IOCG systems33. International Geological Congress, Oslo, Norway, August 6.-14., Compact Disk, 1303446
Rieger, A., Marschik, R., Diaz, M., Chiaradia, M., & Spangenberg, J.
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2008. Iron oxide Cu-Au vs. magnetite(-apatite) deposits: Examples from northern Chile. 33. International Geological Congress, Oslo, Norway, August 6.-14., Compact Disk, 1323721
Marschik, R., Chiaradia, M., Spangenberg, J.E. Rieger, A.A., & Mathur, R.
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2008. The Mantoverde district: Example of the distal chlorite-sericite-carbonate facies of zoned IOCG systems. 33. International Geological Congress, Oslo, Norway, August 6.-14., Compact Disk, 1303446
Rieger, A.A., Marschik, R., Diaz, M., Chiaradia M., & Spangenberg, J.E.
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2009. IOCG mineralization in the Mantoverde District, Chile: Sr and S isotope signatures. XII Congreso Geológico Chileno, Santiago, November 22-26, 2009, Actas, S11_036
Rieger, A.A., Marschik, R., Diaz, M., Akker, B., Hölzl, S., & Spangenberg, J.E.
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2009. Iron oxide-copper-gold deposits in Chile: Characteristics of the Mantoverde district. 6th European Congress on Regional Geoscientific Cartography and Information Systems (EUREGEO), Munich, Germany, June 9-12, v. 2, p. 156-159
Rieger, A.A., Marschik, R., & Diaz, M.
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2009. Strontium and sulfur isotope signatures related to Chilean magnetite(-apatite) mineralization. XII Congreso Geológico Chileno, Santiago, November 22-26, 2009, Actas, S11_037
Marschik, R., Akker, B., Rieger, A.A., Spangenberg, J.E., & Hölzl, S.
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2009. Sulphur and lead isotope characteristics of sulphides of the Mantoverde IOCG district, Chile. In: Williams, P.J. et al. (eds). Smart Science for Exploration and Mining, Proceedings of the 10th Biennial SGA Meeting of the Society for Geology Applied to Mineral Deposits Townsville Australia, 17th - 20th August, v. 2, p. 653-655
Rieger, A.A., Marschik, R., Chiaradia, M., Spangenberg, J.E., & Diaz, M.
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2009. The Cerro Negro Norte magnetite(-apatite) deposit, northern Chile: sulphur, lead, and strontium isotope characteristics. In: Williams, P.J. et al. (eds). Smart Science for Exploration and Mining, Proceedings of the 10th Biennial SGA Meeting of the Society for Geology Applied to Mineral Deposits Townsville Australia, 17th - 20th August, v. 2, p. 641-643
Marschik, R., Akker, B., Rieger, A.A., Chiaradia, M., Spangenberg, J.E., & Hölzl, S.
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2010. The hypogene ores of the Mantoverde IOCG district, northern Chile. Economic Geology, v. 105, p. 1271-1299
Rieger, A.A., Marschik, R., Diaz, M., Hölzl, S., Chiaradia, M. Akker, B., & Jorge E. Spangenberg, J.E.
