Origin and evolution of mineralizing fluids and exploration of the Cerro Quema Au-Cu deposit (Azuero Peninsula, Panama) from a fluid inclusion and stable isotope perspective

Corral, Isaac, Cardellach, Esteve, Corbella, Mercè, Canals, Àngels, Griera, Albert, Gómez-Gras, David, and Johnson, Craig A. (2016) Origin and evolution of mineralizing fluids and exploration of the Cerro Quema Au-Cu deposit (Azuero Peninsula, Panama) from a fluid inclusion and stable isotope perspective. Ore Geology Reviews, 80. pp. 947-960.

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Abstract

Cerro Quema is a high sulfidation epithermal Au-Cu deposit with a measured, indicated and inferred resource of 35.98 Mt. @ 0.77 g/t Au containing 893,600 oz. Au (including 183,930 oz. Au equiv. of Cu ore). It is characterized by a large hydrothermal alteration zone which is interpreted to represent the lithocap of a porphyry system. The innermost zone of the lithocap is constituted by vuggy quartz with advanced argillic alteration locally developed on its margin, enclosed by a well-developed zone of argillic alteration, grading to an external halo of propylitic alteration. The mineralization occurs in the form of disseminations and microveinlets of pyrite, chalcopyrite, enargite, tennantite, and trace sphalerite, crosscut by quartz, barite, pyrite, chalcopyrite, sphalerite and galena veins.

Microthermometric analyses of two phase (L + V) secondary fluid inclusions in igneous quartz phenocrysts in vuggy quartz and advanced argillically altered samples indicate low temperature (140–216 °C) and low salinity (0.5–4.8 wt% NaCl eq.) fluids, with hotter and more saline fluids identified in the east half of the deposit (Cerro Quema area).

Stable isotope analyses (S, O, H) were performed on mineralization and alteration minerals, including pyrite, chalcopyrite, enargite, alunite, barite, kaolinite, dickite and vuggy quartz. The range of δ34S of sulfides is from − 4.8 to − 12.7‰, whereas δ34S of sulfates range from 14.1 to 17.4‰. The estimated δ34SΣS of the hydrothermal fluid is − 0.5‰. Within the advanced argillic altered zone the δ34S values of sulfides and sulfates are interpreted to reflect isotopic equilibrium at temperatures of ~ 240 °C. The δ18O values of vuggy quartz range from 9.0 to 17.5‰, and the δ18O values estimated for the vuggy quartz-forming fluid range from − 2.3 to 3.0‰, indicating that it precipitated from mixing of magmatic fluids with surficial fluids. The δ18O of kaolinite ranges from 12.7 to 18.1‰ and δD from − 103.3 to − 35.2‰, whereas the δ18O of dickite varies between 12.7 and 16.3‰ and δD from − 44 to − 30. Based on δ18O and δD, two types of kaolinite/dickite can be distinguished, a supergene type and a hypogene type. Combined, the analytical data indicate that the Cerro Quema deposit formed from magmatic-hydrothermal fluids derived from a porphyry copper-like intrusion located at depth likely towards the east of the deposit. The combination of stable isotope geochemistry and fluid inclusion analysis may provide useful exploration vectors for porphyry copper targets in the high sulfidation/lithocap environment.

Item ID: 45657
Item Type: Article (Research - C1)
ISSN: 1872-7360
Keywords: Cerro Quema, fluid inclusions, stable isotopes, alunite-pyrite, exploration
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Funders: Ministerio de Ciencia e Innovación, Spain (MICINN), SEG Foundation, SEG Canada Foundation
Projects and Grants: CGL2007- 62690/BTE, 2010 and 2011 Hugh E. McKinstry student research grants
Date Deposited: 12 Sep 2016 21:58
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040201 Exploration Geochemistry @ 20%
04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 40%
04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 40%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840102 Copper Ore Exploration @ 50%
84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840105 Precious (Noble) Metal Ore Exploration @ 50%
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