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<title>UTas ePrints - 40Ar/39Ar and Re-Os Geochronology of Porphyry Copper-Molybdenum Deposits and Related Copper-Silver Veins in the Collahuasi District, Northern Chile</title>
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<meta content="40Ar/39Ar and Re-Os Geochronology of Porphyry Copper-Molybdenum Deposits and Related Copper-Silver Veins in the Collahuasi District, Northern Chile " name="eprints.title" />
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<meta content="The Rosario and Ujina porphyry Cu-Mo deposits, together with porphyry copper mineralization at the nearby Quebrada Blanca deposit, constitute the third-largest concentration of copper mineralization associated with the Domeyko fault system in northern Chile. At Rosario, fault-hosted Cu-Ag-rich massive sulfide veins are associated with pyrophyllite-alunite-quartz altered rocks. The Rosario massive sulfide veins cut biotitealbite-magnetite, K-feldspar and illite-chlorite altered rocks associated with porphyry-style copper-molybdenum mineralization. Similar massive sulfide veins occur in the La Grande area, 1 to 2 km south of Rosario. Copper ore at Ujina is associated with a K-feldspar-biotite-altered quartz monzonite intrusion. The
K-feldspar-biotite assemblage has been overprinted by white mica-chlorite alteration.
New geochronologic data presented in this paper constrain the ages of hydrothermal activity in the Rosario and Ujina deposits. The 40Ar/39Ar biotite, illite, and alunite dates (at 2 sigma error), and a Re-Os molybdenite date (at 0.5% error) are reported for porphyritic rocks and hydrothermal alteration from the Rosario and Ujina mineralized
centers. A weighted mean 40Ar/39Ar plateau age of 34.4 plus or minus 0.3 Ma is obtained for igneous biotite in a
monzonite porphyry that hosts copper mineralization at the Rosario deposit. Illite and hypogene alunite from
separate overprinting alteration events yielded 40Ar/39Ar ages of 34.5 plus or minus 0.5 Ma (plateau age) and 32.6 plus or minus 0.3 Ma (plateau age), respectively. An Re-Os age of 33.3 plus or minus 0.2 Ma for molybdenite at Rosario is slightly younger than the 40Ar/39Ar age of illite, but older than the alunite. A weighted mean plateau age of 32.7 plus or minus 1.6 Ma for hypogene alunite from the La Grande Cu-Ag-(Au) vein south of Rosario is indistinguishable from the age of Rosario alunite. At Ujina, the weighted mean 40Ar/39Ar plateau age of igneous biotite for a monzonite intrusion that hosts copper mineralization is 35.2 plus or minus 0.3 Ma. The monzonite is intruded by postmineralization porphyry dikes
of similar composition, from which igneous biotite yielded a 40Ar/39Ar age of 34.7 plus or minus 0.3 Ma.
Igneous biotite in the Rosario Porphyry cooled through its closure temperature during and after the formation
of illite, implying that porphyry-style ore and alteration minerals in the Rosario deposit had formed by 34.3
Ma. The age of alunite at Rosario and La Grande indicate that a second discrete episode of hydrothermal
activity was superimposed, 1.8 plus or minus 0.4 m.y. later, onto the earlier-formed porphyry Cu system. Hydrothermal activity at Ujina is constrained by the 40Ar/39Ar ages of igneous biotite in the premineralization and postmineralization intrusions and occurred during a minimum interval of 0.5 plus or minus 0.4 m.y. The biotite granite at La Profunda, 1.5 km east of Ujina, has a igneous biotite age of 81.2 plus or minus 2.9 Ma, indicating that this intrusion is unrelated to the mineralized Eocene-Oligocene porphyry intrusions at Ujina, Rosario, and Quebrada Blanca. The 40Ar/39Ar data for igneous biotite in the Rosario and Ujina porphyries are cooling ages after multiple hydrothermal events. In most cases, these are minimum hydrothermal ages (i.e., ages of the last high-temperature hydrothermal event to have affected the samples), not magmatic ages. However, the biotite age for the Inca Porphyry is possibly only slightly younger than the intrusion age because biotite has not been affected by
later hydrothermal alteration." name="eprints.abstract" />
<meta content="2004" name="eprints.date" />
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Bisso, C.B., Duran, M., and Gonzales, A.A., 1998, Geology of the Ujina and Rosario copper porphyry deposits Collahuasi district, Chile, in Porter, T.M., ed., Porphyry and hydrothermal copper and gold deposits: A global
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Chesley, J.T., and Ruiz, J., 1997, Preliminary Re-Os dating on molybdenite mineralization from the Bingham Canyon porphyry copper deposit, Utah, in John, D.A., and Ballantyne, G.H., eds., Geology and ore deposits of the
Oquirrh and Wasatch Mountains, Utah: Society of Economic Geologists Guidebook 29, p. 237-244.
Clark, A.H., 1993, Are outsize porphyry copper deposits either anatomically or environmentally distinctive?: Society of Economic Geologists Special Publication 2, p. 213-283.
Clark, A.H., Archibald, D.A., Lee, A.W., Farrar, E., and Hodgson, C.J., 1998, Laser probe 40Ar/39Ar ages of early- and late-stage alteration assemblages, Rosario porphyry copper-molybdenum deposit, Collahuasi district, I Region,
Chile.: ECONOMIC GEOLOGY, v. 93, p. 326-337.
Dalrymple, G.B., Alexander Jr., E.C., Lanphere, M.A., and Kraker, G.P., 1981, Irradiation of samples for 40Ar/39Ar dating using the Geological Survey TRIGA Reactor: U.S. Geological Survey Professional Paper 1176, 55 p.
DeBeer, L.J., and Dick, L.A., 1994, Development of the Collahuasi copper deposits, a world class copper project in the Andes of northern Chile: London Institute for Mining and Metallurgy, Mining Latin America, Santiago,
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Dick, L.A., Chavez, W.X., Gonzales, A., and Bisso, C., 1994, Geologic setting and mineralogy of the Cu-Ag-(As) Rosario vein system, Collahuasi district, Chile: Society of Economic Geologists Newsletter, no. 19, p. 1, 6-11.
Dilles, J.H., and Wright, J.E., 1988, The chronology of early Mesozoic arc magmatism in the Yerington district of western Nevada and its regional implications: Geological Society of America Bulletin, v. 100, p. 644-652.
Gustafson, L.B., Orquera, W., McWilliams, M., Castro, M., Olivarez, O., Rojas, G., Maluenda, J., and Mendez, M., 2001, Multiple centers of mineralization in the Indio Muerto district, El Salvador, Chile: ECONOMIC GEOLOGY,
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Hall, C.M., 1981, The application of K-Ar and 40Ar/39Ar methods to the dating of recent volcanics and the Laschamp event: Unpublished Ph.D. dissertation, Toronto, Canada, University of Toronto, 186 p.
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Hunt, J.P., Bratt, J.A., and Marquardt, J.C., 1983, Quebrada Blanca, Chile: An enriched porphyry copper deposit: Mining Engineering, v. 35, p. 636-644.
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<meta content="The Rosario and Ujina porphyry Cu-Mo deposits, together with porphyry copper mineralization at the nearby Quebrada Blanca deposit, constitute the third-largest concentration of copper mineralization associated with the Domeyko fault system in northern Chile. At Rosario, fault-hosted Cu-Ag-rich massive sulfide veins are associated with pyrophyllite-alunite-quartz altered rocks. The Rosario massive sulfide veins cut biotitealbite-magnetite, K-feldspar and illite-chlorite altered rocks associated with porphyry-style copper-molybdenum mineralization. Similar massive sulfide veins occur in the La Grande area, 1 to 2 km south of Rosario. Copper ore at Ujina is associated with a K-feldspar-biotite-altered quartz monzonite intrusion. The
K-feldspar-biotite assemblage has been overprinted by white mica-chlorite alteration.
New geochronologic data presented in this paper constrain the ages of hydrothermal activity in the Rosario and Ujina deposits. The 40Ar/39Ar biotite, illite, and alunite dates (at 2 sigma error), and a Re-Os molybdenite date (at 0.5% error) are reported for porphyritic rocks and hydrothermal alteration from the Rosario and Ujina mineralized
centers. A weighted mean 40Ar/39Ar plateau age of 34.4 plus or minus 0.3 Ma is obtained for igneous biotite in a
monzonite porphyry that hosts copper mineralization at the Rosario deposit. Illite and hypogene alunite from
separate overprinting alteration events yielded 40Ar/39Ar ages of 34.5 plus or minus 0.5 Ma (plateau age) and 32.6 plus or minus 0.3 Ma (plateau age), respectively. An Re-Os age of 33.3 plus or minus 0.2 Ma for molybdenite at Rosario is slightly younger than the 40Ar/39Ar age of illite, but older than the alunite. A weighted mean plateau age of 32.7 plus or minus 1.6 Ma for hypogene alunite from the La Grande Cu-Ag-(Au) vein south of Rosario is indistinguishable from the age of Rosario alunite. At Ujina, the weighted mean 40Ar/39Ar plateau age of igneous biotite for a monzonite intrusion that hosts copper mineralization is 35.2 plus or minus 0.3 Ma. The monzonite is intruded by postmineralization porphyry dikes
of similar composition, from which igneous biotite yielded a 40Ar/39Ar age of 34.7 plus or minus 0.3 Ma.
Igneous biotite in the Rosario Porphyry cooled through its closure temperature during and after the formation
of illite, implying that porphyry-style ore and alteration minerals in the Rosario deposit had formed by 34.3
Ma. The age of alunite at Rosario and La Grande indicate that a second discrete episode of hydrothermal
activity was superimposed, 1.8 plus or minus 0.4 m.y. later, onto the earlier-formed porphyry Cu system. Hydrothermal activity at Ujina is constrained by the 40Ar/39Ar ages of igneous biotite in the premineralization and postmineralization intrusions and occurred during a minimum interval of 0.5 plus or minus 0.4 m.y. The biotite granite at La Profunda, 1.5 km east of Ujina, has a igneous biotite age of 81.2 plus or minus 2.9 Ma, indicating that this intrusion is unrelated to the mineralized Eocene-Oligocene porphyry intrusions at Ujina, Rosario, and Quebrada Blanca. The 40Ar/39Ar data for igneous biotite in the Rosario and Ujina porphyries are cooling ages after multiple hydrothermal events. In most cases, these are minimum hydrothermal ages (i.e., ages of the last high-temperature hydrothermal event to have affected the samples), not magmatic ages. However, the biotite age for the Inca Porphyry is possibly only slightly younger than the intrusion age because biotite has not been affected by
later hydrothermal alteration." name="DC.description" />
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<h1 class="ep_tm_pagetitle">40Ar/39Ar and Re-Os Geochronology of Porphyry Copper-Molybdenum Deposits and Related Copper-Silver Veins in the Collahuasi District, Northern Chile</h1>
<p style="margin-bottom: 1em" class="not_ep_block"><span class="person_name">Masterman, G.J.</span> and <span class="person_name">Cooke, D.R.</span> and <span class="person_name">Berry, R.F.</span> and <span class="person_name">Clark, A.H.</span> and <span class="person_name">Archibald, D.A.</span> and <span class="person_name">Mathur, R.</span> and <span class="person_name">Walshe, J.L.</span> and <span class="person_name">Duran, M.</span> (2004) <xhtml:em>40Ar/39Ar and Re-Os Geochronology of Porphyry Copper-Molybdenum Deposits and Related Copper-Silver Veins in the Collahuasi District, Northern Chile.</xhtml:em> Economic Geology, 99 (4). pp. 673-690. ISSN 0361-0128</p><p style="margin-bottom: 1em" class="not_ep_block"></p><table style="margin-bottom: 1em" class="not_ep_block"><tr><td valign="top" style="text-align:center"><a href="http://eprints.utas.edu.au/1967/1/Masterman%2C_Cooke%2C_Berry_ECON_GEOL_2004.pdf"><img alt="[img]" src="http://eprints.utas.edu.au/style/images/fileicons/application_pdf.png" class="ep_doc_icon" border="0" /></a></td><td valign="top"><a href="http://eprints.utas.edu.au/1967/1/Masterman%2C_Cooke%2C_Berry_ECON_GEOL_2004.pdf"><span class="ep_document_citation">PDF</span></a> - Full text restricted - Requires a PDF viewer<br />2746Kb</td><td><form method="get" accept-charset="utf-8" action="http://eprints.utas.edu.au/cgi/request_doc"><input accept-charset="utf-8" value="2447" name="docid" type="hidden" /><div class=""><input value="Request a copy" name="_action_null" class="ep_form_action_button" onclick="return EPJS_button_pushed( '_action_null' )" type="submit" /> </div></form></td></tr></table><p style="margin-bottom: 1em" class="not_ep_block">Official URL: <a href="http://dx.doi.org/10.2113/99.4.673">http://dx.doi.org/10.2113/99.4.673</a></p><div class="not_ep_block"><h2>Abstract</h2><p style="padding-bottom: 16px; text-align: left; margin: 1em auto 0em auto">The Rosario and Ujina porphyry Cu-Mo deposits, together with porphyry copper mineralization at the nearby Quebrada Blanca deposit, constitute the third-largest concentration of copper mineralization associated with the Domeyko fault system in northern Chile. At Rosario, fault-hosted Cu-Ag-rich massive sulfide veins are associated with pyrophyllite-alunite-quartz altered rocks. The Rosario massive sulfide veins cut biotitealbite-magnetite, K-feldspar and illite-chlorite altered rocks associated with porphyry-style copper-molybdenum mineralization. Similar massive sulfide veins occur in the La Grande area, 1 to 2 km south of Rosario. Copper ore at Ujina is associated with a K-feldspar-biotite-altered quartz monzonite intrusion. The
K-feldspar-biotite assemblage has been overprinted by white mica-chlorite alteration.
New geochronologic data presented in this paper constrain the ages of hydrothermal activity in the Rosario and Ujina deposits. The 40Ar/39Ar biotite, illite, and alunite dates (at 2 sigma error), and a Re-Os molybdenite date (at 0.5% error) are reported for porphyritic rocks and hydrothermal alteration from the Rosario and Ujina mineralized
centers. A weighted mean 40Ar/39Ar plateau age of 34.4 plus or minus 0.3 Ma is obtained for igneous biotite in a
monzonite porphyry that hosts copper mineralization at the Rosario deposit. Illite and hypogene alunite from
separate overprinting alteration events yielded 40Ar/39Ar ages of 34.5 plus or minus 0.5 Ma (plateau age) and 32.6 plus or minus 0.3 Ma (plateau age), respectively. An Re-Os age of 33.3 plus or minus 0.2 Ma for molybdenite at Rosario is slightly younger than the 40Ar/39Ar age of illite, but older than the alunite. A weighted mean plateau age of 32.7 plus or minus 1.6 Ma for hypogene alunite from the La Grande Cu-Ag-(Au) vein south of Rosario is indistinguishable from the age of Rosario alunite. At Ujina, the weighted mean 40Ar/39Ar plateau age of igneous biotite for a monzonite intrusion that hosts copper mineralization is 35.2 plus or minus 0.3 Ma. The monzonite is intruded by postmineralization porphyry dikes
of similar composition, from which igneous biotite yielded a 40Ar/39Ar age of 34.7 plus or minus 0.3 Ma.
Igneous biotite in the Rosario Porphyry cooled through its closure temperature during and after the formation
of illite, implying that porphyry-style ore and alteration minerals in the Rosario deposit had formed by 34.3
Ma. The age of alunite at Rosario and La Grande indicate that a second discrete episode of hydrothermal
activity was superimposed, 1.8 plus or minus 0.4 m.y. later, onto the earlier-formed porphyry Cu system. Hydrothermal activity at Ujina is constrained by the 40Ar/39Ar ages of igneous biotite in the premineralization and postmineralization intrusions and occurred during a minimum interval of 0.5 plus or minus 0.4 m.y. The biotite granite at La Profunda, 1.5 km east of Ujina, has a igneous biotite age of 81.2 plus or minus 2.9 Ma, indicating that this intrusion is unrelated to the mineralized Eocene-Oligocene porphyry intrusions at Ujina, Rosario, and Quebrada Blanca. The 40Ar/39Ar data for igneous biotite in the Rosario and Ujina porphyries are cooling ages after multiple hydrothermal events. In most cases, these are minimum hydrothermal ages (i.e., ages of the last high-temperature hydrothermal event to have affected the samples), not magmatic ages. However, the biotite age for the Inca Porphyry is possibly only slightly younger than the intrusion age because biotite has not been affected by
later hydrothermal alteration.</p></div><table style="margin-bottom: 1em" cellpadding="3" class="not_ep_block" border="0"><tr><th valign="top" class="ep_row">Item Type:</th><td valign="top" class="ep_row">Article</td></tr><tr><th valign="top" class="ep_row">Keywords:</th><td valign="top" class="ep_row">massive sulfide alteration halo numerical modelling</td></tr><tr><th valign="top" class="ep_row">Subjects:</th><td valign="top" class="ep_row"><a href="http://eprints.utas.edu.au/view/subjects/260109.html">260000 Earth Sciences > 260100 Geology > 260109 Geochronology</a><br /><a href="http://eprints.utas.edu.au/view/subjects/260100.html">260000 Earth Sciences > 260100 Geology</a></td></tr><tr><th valign="top" class="ep_row">Collections:</th><td valign="top" class="ep_row">UNSPECIFIED</td></tr><tr><th valign="top" class="ep_row">ID Code:</th><td valign="top" class="ep_row">1967</td></tr><tr><th valign="top" class="ep_row">Deposited By:</th><td valign="top" class="ep_row"><span class="ep_name_citation"><span class="person_name">Mrs Katrina Keep</span></span></td></tr><tr><th valign="top" class="ep_row">Deposited On:</th><td valign="top" class="ep_row">19 Sep 2007</td></tr><tr><th valign="top" class="ep_row">Last Modified:</th><td valign="top" class="ep_row">29 Jan 2008 20:24</td></tr><tr><th valign="top" class="ep_row">ePrint Statistics:</th><td valign="top" class="ep_row"><a target="ePrintStats" href="/es/index.php?action=show_detail_eprint;id=1967;">View statistics for this ePrint</a></td></tr></table><p align="right">Repository Staff Only: <a href="http://eprints.utas.edu.au/cgi/users/home?screen=EPrint::View&eprintid=1967">item control page</a></p>
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