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The Distribution and Timing of Molybdenite Mineralization at the El Teniente Cu-Mo Porphyry Deposit, Chile

2015; Volume: 110; Issue: 2 Linguagem: Inglês

10.2113/econgeo.110.2.387

1554-0774

Edward T. Spencer, Jamie J. Wilkinson, Robert A. Creaser, J. Seguel,

earthquake and tectonic studies

Research Article| March 01, 2015 The Distribution and Timing of Molybdenite Mineralization at the El Teniente Cu-Mo Porphyry Deposit, Chile Edward T. Spencer; Edward T. Spencer † 1Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, United Kingdom †Corresponding author: e-mail, es406@imperial.ac.uk Search for other works by this author on: GSW Google Scholar Jamie J. Wilkinson; Jamie J. Wilkinson 1Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, United Kingdom2Geology Department, Natural History Museum, London SW7 5BD, United Kingdom Search for other works by this author on: GSW Google Scholar Robert A. Creaser; Robert A. Creaser 3Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar Jose Seguel Jose Seguel 4CODELCO División El Teniente, Rancagua, Chile Search for other works by this author on: GSW Google Scholar Economic Geology (2015) 110 (2): 387–421. https://doi.org/10.2113/econgeo.110.2.387 Article history received: 13 Mar 2014 accepted: 28 Jul 2014 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Edward T. Spencer, Jamie J. Wilkinson, Robert A. Creaser, Jose Seguel; The Distribution and Timing of Molybdenite Mineralization at the El Teniente Cu-Mo Porphyry Deposit, Chile. Economic Geology 2015;; 110 (2): 387–421. doi: https://doi.org/10.2113/econgeo.110.2.387 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The El Teniente Cu-Mo porphyry deposit, Chile, is one of the world's largest and most complex porphyry ore systems, containing an estimated premining resource of approximately 95 Mt Cu and 2.5 Mt Mo. Although Cu mineralization at the deposit is quite well studied, little work has focused specifically on the distribution and timing of Mo mineralization. Combined grade, vein, and breccia distribution analysis reveals that deposit-wide Mo grades of 0.01 to 0.06 wt % are strongly controlled by the abundance of main mineralization (type 6a) quartz ± molybdenite veins. These show a clear spatial relationship with several felsic-intermediate intrusions and appear to develop outward and upward into Cu-rich (type 6b–7b) quartz-chalcopyrite veins and (type 8) chalcopyrite-anhydrite ± bornite veins with sericitic alteration halos. High-precision Re-Os molybdenite dating reveals that these linked vein types did not develop in a single, deposit-wide evolution, but are diachronous, related to distinct episodes of hydrothermal activity associated with the emplacement of diorite finger porphyries and the composite Teniente Dacite Porphyry. These units acted as effective, short-lived (<100,000 years) conduits for pulses of Mo- and Cu-bearing hydrothermal fluids between 6.3 and 4.6 Ma. The rapid thermal contraction of each system during mineralization led to extensive overprinting of Mo-rich veins by their lower-temperature, Cu-rich equivalents. Separate pulses in magmatic-hydrothermal activity are separated by distinct gaps of up to 300,000 years, during which Mo-mineralizing activity appears to have gone into quiescence.Mo grades exceeding 0.06 wt % correspond to the presence of molybdenite-bearing, late mineralization-stage, tourmaline-cemented (type 9), and anhydrite-carbonate ± gypsum (type 10) veins and breccias. These are abundant at shallow mine levels and show a close spatial relationship with a series of concentric faults associated with the Braden Breccia Pipe. Mineralization in this paragenetic stage is relatively short-lived and occurs in all parts of the deposit between 4.80 and 4.58 Ma. The generally Cu poor nature of the late mineralization stage is attributed to the prior preferential extraction of Cu from the underlying magma chamber in earlier mineralizing events. This led to the late exsolution of oxidized, Mo-rich fluids that may have undergone further enrichment by remobilizing Mo from main mineralization-type veins associated with the Teniente Dacite Porphyry. The formation of the Braden Breccia Pipe is likely to have occurred in a single cataclysmic event at approximately 4.58 Ma, which cut the Mo-rich tourmaline breccias and created a distinct Mo-rich grade halo at shallow mine levels. With the exception of minor mineralization associated with small dacitic dikes at approximately 4.42 Ma, the Braden event marked the termination of Mo deposition. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.