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    <title>UTas ePrints - Alunite in the Pascua-Lama High-Sulfidation Deposit: Constraints on Alteration and Ore Deposition Using Stable Isotope Geochemistry</title>
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    <meta content="Deyell, C.L." name="eprints.creators_name" />
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Constraints on Alteration and Ore Deposition Using Stable Isotope Geochemistry" name="eprints.title" />
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<meta content="The Pascua-Lama high-sulfidation system, located in the El Indio-Pascua belt of Chile and Argentina, contains
over 16 million ounces (Moz) Au and 585 Moz Ag. The deposit is hosted primarily in granite rocks of Triassic age
with mineralization occurring in several discrete Miocene-age phreatomagmatic breccias and related fracture networks.
The largest of these areas is Brecha Central, which is dominated by a mineralizing assemblage of alunitepyrite-
enargite and precious metals. Several stages of hydrothermal alteration related to mineralization are recognized,
including all types of alunite-bearing advanced argillic assemblages (magmatic-hydrothermal,
steam-heated, magmatic steam, and supergene). The occurrence of alunite throughout the paragenesis of this epithermal
system is unusual and detailed radiometric, mineralogical, and stable isotope studies provide constraints
on the timing and nature of alteration and mineralization of the alunite-pyrite-enargite assemblage in the deposit.
Early (preore) alteration occurred prior to ca. 9 Ma and consists of intense silicic and advanced argillic assemblages
with peripheral argillic and widespread propylitic zones. Alunite of this stage occurs as fine intergrowths
of alunite-quartz ± kaolinite, dickite, and pyrophyllite that selectively replaced feldspars in the host rock.
Stable isotope systematics suggest a magmatic-hydrothermal origin with a dominantly magmatic fluid source.
Alunite is coeval with the main stage of Au-Ag-Cu mineralization (alunite-pyrite-enargite assemblage ore), which
has been dated at approximately 8.8 Ma. Ore-stage alunite has an isotopic signature similar to preore alunite,
and Δ34Salun-py data indicate depositional temperatures of 245° to 305°C. The δD and δ18O data exclude significant
involvement of meteoric water during mineralization and indicate that the assemblage formed from H2Sdominated
magmatic fluids. Thick steam-heated alteration zones are preserved at the highest elevations in the
deposit and probably formed from oxidation of H2S during boiling of the magmatic ore fluids. Coarsely crystalline
magmatic steam alunite (8.4 Ma) is restricted to the near-surface portion of Brecha Central. Postmineral
alunite ± jarosite were previously interpreted to be supergene crosscutting veins and overgrowths, although stable
isotope data suggest a mixed magmatic-meteoric origin for this late-stage alteration. Only late jarosite veinlets
(8.0 Ma) associated with fine-grained pseudocubic alunite have a supergene isotopic signature.
The predominance of magmatic fluids recorded throughout the paragenesis of the Pascua system is atypical
for high-sulfidation deposits, which typically involve significant meteoric water in near-surface and peripheral
alteration and, in some systems, even ore deposition. At Pascua, the strong magmatic signature of both alteration
and main-stage (alunite-pyrite-enargite assemblage) ore is attributed to limited availability of meteoric
fluids. This is in agreement with published data for the El Indio-Pascua belt, indicating an event of uplift and
subsequent pediment incision, as well as a transition from semiarid to arid climatic conditions, during the formation
of the deposit in the mid to late Miocene.
" name="eprints.abstract" />
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<meta content="Arribas, A., Jr, 1995, Characteristics of high sulfidation epithermal deposits,
and their relation to magmatic fluids: Mineralogical Association of Canada
Short Course Series, v. 23, p. 419–454.
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696–692.
Bethke, P.M., Rye, R.O., Stoffregen, R.E., and Vikre, P., in press, Evolution
of the Summitville magmatic-hydrothermal acid-sulfate system: Chemical
Geology.
Bissig, T., Lee, J.K.W., Clark, A.H., and Heather, K.B., 2001, The Cenozoic history
of magmatic activity and hydrothermal alteration in the Central Andean
flat-slab region: New 40Ar-39Ar constraints from the El Indio-Pascua Au (-Ag,
Cu) belt, 29°20'–30°30' S: International Geology Review, v. 41, p. 312–340.
Bissig, T., Clark, A.H. and Lee, J.K.W., 2002a, Cerro de Vidrio rhyolite dome:
Evidence for late Pliocene volcanism in the central Andean flat-slab region,
Lama-Veladero district, 29°20' S, San Juan province, Argentina: Journal of
South American Earth Sciences, v. 15, p. 571–576.
Bissig, T., Clark, A. H., Lee, J.K.W., and Hodgson, C.J., 2002b, Miocene
landscape evolution and geomorphologic controls on epithermal processes
in the El Indio-Pascua Au-Ag-Cu belt, Chile and Argentina: ECONOMIC
GEOLOGY, v. 97, p. 971–996.
Chouinard, A., 2003, Alteration, mineralization and geochemistry of the
high-sulphidation Au-Ag-Cu Pascua deposit: Unpublished Ph.D. thesis,
Montreal, Canada, McGill University, 269 p.
Cooke, D.R., and Simmons, S.F., 2000, Characteristics and genesis of epithermal
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Cunningham, C.G., Rye, R.O., Steven, T.A., and Mehnert, H.H., 1984, Origins
and exploration signficance of replacement and vein-type alunite deposits
in the Marysvale volcanic field, west-central Utah: ECONOMIC GEOLOGY,
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Dalrymple, G.B., Alexander, E.C., Jr., Lanphere, M.A., and Kraker, G.P.,
1981, Irradiation of samples for 40Ar/39Ar dating using the Geological Survey
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Deyell, C.L., 2001, Alunite and high sulfidation Au-Ag-Cu mineralization in
the El Indio-Pascua belt, Chile-Argentina: Unpublished Ph.D. thesis, Vancouver,
Canada, University of British Columbia, 300 p.
Deyell, C.L., Rye, R.O., Landis, G.P., and Bissig, T., in press, Alunite in an
evolving magmatic-hydrothermal system: The Tambo high-sulfidation deposit,
El Indio district, Chile: Chemical Geology.
Ebert, S.W., and Rye, R.O., 1997, Secondary precious metal enrichment by
steam-heated fluids in the Crowfoot–Lewis hotspring gold-silver deposit
and relation to paleoclimate: ECONOMIC GEOLOGY, v. 92, p. 578–600.
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intrusion-centered hydrothermal system: Far Southeast-Lepanto porphyry
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deposit types in the El Indio district, Chile: Society of Economic
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del Franja El Indio, Cordillera de Coquimbo: Santiago, Chile, Servicio National
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——1999, Late Paleozoic to Early Jurassic tectonic development of the high
Andean Principal Cordillera, El Indio region, Chile (29–30° S): Journal of
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Maricunga belt, northern Chile: ECONOMIC GEOLOGY, v. 96, p. 1445–1472.
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sulfates and sulfides in hydrothermal systems: Geochimica et Cosmochimica
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——in press, A review of the stable isotope geochemistry of sulfate minerals
in selected igneous environments and related hydrothermal systems:
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Rye, R.O., and Alpers, C.N., 1997, The stable isotope geochemistry of
jarosite: U.S. Geological Survey Open-File Report 97-88, 28 p.
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Stoffregen, R.E., Rye, R.O., and Wasserman, M.D., 1994. Experimental
studies of alunite: I. 18O-16O and D-H fractionation factors between alunite
and water at 250-450°C: Geochimica et Cosmochimica Acta, v. 58, p.
903–916.
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for separation and total stable isotope analysis of alunite: U.S. Geological
Survey Open-File Report 92-9, 20 p." name="eprints.referencetext" />
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<meta content="The Pascua-Lama high-sulfidation system, located in the El Indio-Pascua belt of Chile and Argentina, contains
over 16 million ounces (Moz) Au and 585 Moz Ag. The deposit is hosted primarily in granite rocks of Triassic age
with mineralization occurring in several discrete Miocene-age phreatomagmatic breccias and related fracture networks.
The largest of these areas is Brecha Central, which is dominated by a mineralizing assemblage of alunitepyrite-
enargite and precious metals. Several stages of hydrothermal alteration related to mineralization are recognized,
including all types of alunite-bearing advanced argillic assemblages (magmatic-hydrothermal,
steam-heated, magmatic steam, and supergene). The occurrence of alunite throughout the paragenesis of this epithermal
system is unusual and detailed radiometric, mineralogical, and stable isotope studies provide constraints
on the timing and nature of alteration and mineralization of the alunite-pyrite-enargite assemblage in the deposit.
Early (preore) alteration occurred prior to ca. 9 Ma and consists of intense silicic and advanced argillic assemblages
with peripheral argillic and widespread propylitic zones. Alunite of this stage occurs as fine intergrowths
of alunite-quartz ± kaolinite, dickite, and pyrophyllite that selectively replaced feldspars in the host rock.
Stable isotope systematics suggest a magmatic-hydrothermal origin with a dominantly magmatic fluid source.
Alunite is coeval with the main stage of Au-Ag-Cu mineralization (alunite-pyrite-enargite assemblage ore), which
has been dated at approximately 8.8 Ma. Ore-stage alunite has an isotopic signature similar to preore alunite,
and Δ34Salun-py data indicate depositional temperatures of 245° to 305°C. The δD and δ18O data exclude significant
involvement of meteoric water during mineralization and indicate that the assemblage formed from H2Sdominated
magmatic fluids. Thick steam-heated alteration zones are preserved at the highest elevations in the
deposit and probably formed from oxidation of H2S during boiling of the magmatic ore fluids. Coarsely crystalline
magmatic steam alunite (8.4 Ma) is restricted to the near-surface portion of Brecha Central. Postmineral
alunite ± jarosite were previously interpreted to be supergene crosscutting veins and overgrowths, although stable
isotope data suggest a mixed magmatic-meteoric origin for this late-stage alteration. Only late jarosite veinlets
(8.0 Ma) associated with fine-grained pseudocubic alunite have a supergene isotopic signature.
The predominance of magmatic fluids recorded throughout the paragenesis of the Pascua system is atypical
for high-sulfidation deposits, which typically involve significant meteoric water in near-surface and peripheral
alteration and, in some systems, even ore deposition. At Pascua, the strong magmatic signature of both alteration
and main-stage (alunite-pyrite-enargite assemblage) ore is attributed to limited availability of meteoric
fluids. This is in agreement with published data for the El Indio-Pascua belt, indicating an event of uplift and
subsequent pediment incision, as well as a transition from semiarid to arid climatic conditions, during the formation
of the deposit in the mid to late Miocene.
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    <h1 class="ep_tm_pagetitle">Alunite in the Pascua-Lama High-Sulfidation Deposit: Constraints on Alteration and Ore Deposition Using Stable Isotope Geochemistry</h1>
    <p style="margin-bottom: 1em" class="not_ep_block"><span class="person_name">Deyell, C.L.</span> and <span class="person_name">Leonardson, R.</span> and <span class="person_name">Rye, R.O.</span> and <span class="person_name">Thompson, J.F.H.</span> and <span class="person_name">Bissig, T.</span> and <span class="person_name">Cooke, D.R.</span> (2005) <xhtml:em>Alunite in the Pascua-Lama High-Sulfidation Deposit: Constraints on Alteration and Ore Deposition Using Stable Isotope Geochemistry.</xhtml:em> Economic Geology, 100 (1). pp. 131-148. 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/2011/1/Deyell%2C_Leondardson_et_al_ECON_GEOL_2005.pdf"><img alt="[img]" src="http://eprints.utas.edu.au/style/images/fileicons/application_pdf.png" border="0" class="ep_doc_icon" /></a></td><td valign="top"><a href="http://eprints.utas.edu.au/2011/1/Deyell%2C_Leondardson_et_al_ECON_GEOL_2005.pdf"><span class="ep_document_citation">PDF</span></a> - Full text restricted - Requires a PDF viewer<br />1119Kb</td><td><form method="get" accept-charset="utf-8" action="http://eprints.utas.edu.au/cgi/request_doc"><input value="2564" name="docid" accept-charset="utf-8" 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/10.2113/100.1.0131">http://dx.doi.org/10.2113/100.1.0131</a></p><div class="not_ep_block"><h2>Abstract</h2><p style="padding-bottom: 16px; text-align: left; margin: 1em auto 0em auto">The Pascua-Lama high-sulfidation system, located in the El Indio-Pascua belt of Chile and Argentina, contains&#13;
over 16 million ounces (Moz) Au and 585 Moz Ag. The deposit is hosted primarily in granite rocks of Triassic age&#13;
with mineralization occurring in several discrete Miocene-age phreatomagmatic breccias and related fracture networks.&#13;
The largest of these areas is Brecha Central, which is dominated by a mineralizing assemblage of alunitepyrite-&#13;
enargite and precious metals. Several stages of hydrothermal alteration related to mineralization are recognized,&#13;
including all types of alunite-bearing advanced argillic assemblages (magmatic-hydrothermal,&#13;
steam-heated, magmatic steam, and supergene). The occurrence of alunite throughout the paragenesis of this epithermal&#13;
system is unusual and detailed radiometric, mineralogical, and stable isotope studies provide constraints&#13;
on the timing and nature of alteration and mineralization of the alunite-pyrite-enargite assemblage in the deposit.&#13;
Early (preore) alteration occurred prior to ca. 9 Ma and consists of intense silicic and advanced argillic assemblages&#13;
with peripheral argillic and widespread propylitic zones. Alunite of this stage occurs as fine intergrowths&#13;
of alunite-quartz ± kaolinite, dickite, and pyrophyllite that selectively replaced feldspars in the host rock.&#13;
Stable isotope systematics suggest a magmatic-hydrothermal origin with a dominantly magmatic fluid source.&#13;
Alunite is coeval with the main stage of Au-Ag-Cu mineralization (alunite-pyrite-enargite assemblage ore), which&#13;
has been dated at approximately 8.8 Ma. Ore-stage alunite has an isotopic signature similar to preore alunite,&#13;
and Δ34Salun-py data indicate depositional temperatures of 245° to 305°C. The δD and δ18O data exclude significant&#13;
involvement of meteoric water during mineralization and indicate that the assemblage formed from H2Sdominated&#13;
magmatic fluids. Thick steam-heated alteration zones are preserved at the highest elevations in the&#13;
deposit and probably formed from oxidation of H2S during boiling of the magmatic ore fluids. Coarsely crystalline&#13;
magmatic steam alunite (8.4 Ma) is restricted to the near-surface portion of Brecha Central. Postmineral&#13;
alunite ± jarosite were previously interpreted to be supergene crosscutting veins and overgrowths, although stable&#13;
isotope data suggest a mixed magmatic-meteoric origin for this late-stage alteration. Only late jarosite veinlets&#13;
(8.0 Ma) associated with fine-grained pseudocubic alunite have a supergene isotopic signature.&#13;
The predominance of magmatic fluids recorded throughout the paragenesis of the Pascua system is atypical&#13;
for high-sulfidation deposits, which typically involve significant meteoric water in near-surface and peripheral&#13;
alteration and, in some systems, even ore deposition. At Pascua, the strong magmatic signature of both alteration&#13;
and main-stage (alunite-pyrite-enargite assemblage) ore is attributed to limited availability of meteoric&#13;
fluids. This is in agreement with published data for the El Indio-Pascua belt, indicating an event of uplift and&#13;
subsequent pediment incision, as well as a transition from semiarid to arid climatic conditions, during the formation&#13;
of the deposit in the mid to late Miocene.&#13;
</p></div><table style="margin-bottom: 1em" border="0" cellpadding="3" class="not_ep_block"><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">advanced argillic thermodynamic modelling copper gold</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/260300.html">260000 Earth Sciences &gt; 260300 Geochemistry</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">2011</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">04 Oct 2007 15:06</td></tr><tr><th valign="top" class="ep_row">Last Modified:</th><td valign="top" class="ep_row">23 Jan 2008 14:57</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=2011;">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&amp;eprintid=2011">item control page</a></p>
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