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Application of apatite (U-Th)/He thermochronometry to the determination of the sense and amount of vertical fault displacement at the Chuquicamata porphyry copper deposit, Chile

McInnes, Brent I. A. and Farley, Kenneth A. and Sillitoe, Richard H. and Kohn, Barry P. (1999) Application of apatite (U-Th)/He thermochronometry to the determination of the sense and amount of vertical fault displacement at the Chuquicamata porphyry copper deposit, Chile. Economic Geology, 94 (6). pp. 937-947. ISSN 0361-0128. https://resolver.caltech.edu/CaltechAUTHORS:20130130-105254249

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Abstract

Chuquicamata is the world's largest porphyry copper deposit, notwithstanding the fact that a portion of the orebody has been faulted off by postmineralization movement along the West fault. In order to locate the missing portion of the orebody in the vertical dimension, a study was designed to estimate the sense and amount of vertical displacement along this major structure by measuring the (U-Th)/He and fission-track ages of vertically distributed apatite samples from each of the crustal blocks (Fortuna and Chuquicamata Intrusive Complexes) bordering the fault. Apatite (U-Th)/He ages range from 32 to 16 Ma, whereas apatite fission-track ages range from 33 to 28 Ma, reflecting the lower closure temperature of the (U-Th)/He thermochronology method ( approximately 75 degrees vs. approximately 125 degrees C for cooling rates of approximately 10 degrees C/m.y.). The (U-Th)/He ages decrease systematically with depth in both blocks, however, the age-elevation curve for the western Fortuna block is shifted vertically with respect to the eastern Chuquicamata block, indicating that the postmineralization denudation was significantly greater to the west. The minimum vertical displacement along the West fault is estimated to be 600 + or - 100 m, implying that the missing portion of the Chuquicamata deposit should be located at a present-day elevation of at least 3,600 m. The new apatite ages, combined with previous thermochronometric data (Rb-Sr, U-Pb, Ar-Ar), reveal rapid cooling rates ( approximately 100 degrees C/m.y.) for the Chuquicamata deposit following emplacement at about 35 Ma, thereby indicating that the Cu mineralization took place at a depth of less than 4 km.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.2113/gsecongeo.94.6.937DOIUNSPECIFIED
http://econgeol.geoscienceworld.org/content/94/6/937.abstractPublisherUNSPECIFIED
ORCID:
AuthorORCID
Farley, Kenneth A.0000-0002-7846-7546
Additional Information:© 1999 Society of Economic Geologists. June 29, 1998; February 24, 1999. This study was supported jointly by CODELCO-Chile and the Department of Industry, Science and Tourism Australia-USA Bilateral Science and Technology Collaboration program. KAF acknowledges funds from a David and Lucille Packard Foundation Fellowship Francisco Camus approved the study on behalf of CODELCO-Chile and facilitated the participation of RHS. Guillermo Ossandόn provided valuable background information regarding previous geochronologic and structural studies in the region. Roberto Fréraut assisted in the collection of assessment samples during an initial visit to Chuquicamata, and Irene Aracena participated in the main sampling program. BIAM is grateful to Noel White and BHP Minerals for supporting his participation on a field trip to the study area in 1995. Chris Ryan is thanked for producing the PIXE trace element maps of apatite High-quality mineral separates were provided by Jeff Davis. Irradiation costs for fission-track work were met through a grant from the Australian Institute of Nuclear Science and Engineering. This study was partly financed by the Australian Research Council and the Australian Geodynamic Cooperative Research Centre, and this paper is published with the permission of the Director, Australian Geodynamics Cooperative Research Centre. Comments on earlier drafts by Jorge Skarmeta Fracisco Camus, Andy Tomlinson, Noreen Evans, and Kai Yang led to significant improvements. We thank Andrew Warnock for a helpful review.
Funders:
Funding AgencyGrant Number
CODELCO-ChileUNSPECIFIED
Department of Industry Science and Tourism Australia-USA Bilateral Science and Technology programUNSPECIFIED
David and Lucile Packard Foundation FellowshipUNSPECIFIED
Australian Institute of Nuclear Science and Engineering (AINSE)UNSPECIFIED
Australian Research CouncilUNSPECIFIED
Australian Geodynamic Cooperative Research CentreUNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20130130-105254249
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20130130-105254249
Official Citation: Brent I. A. McInnes, Kenneth A. Farley, Richard H. Sillitoe, and Barry P. Kohn Application of apatite (U-Th)/He thermochronometry to the determination of the sense and amount of vertical fault displacement at the Chuquicamata porphyry copper deposit, Chile Economic Geology, September 1999, v. 94, p. 937-947, doi:10.2113/gsecongeo.94.6.937
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36687
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:30 Jan 2013 19:48
Last Modified:03 Mar 2020 13:01

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