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

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 degrees 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 delta S-34 of sulfides is from -4.8 to -12.7 parts per thousand, whereas delta(3)4S of sulfates range from 14.1 to 17.4 parts per thousand. The estimated delta S-34(Sigma S) of the hydrothermal fluid is -0.5 parts per thousand. Within the advanced argillic altered zone the delta S-34 values of sulfides and sulfates are interpreted to reflect isotopic equilibrium at temperatures of similar to 240 degrees C. The delta O-18 values of vuggy quartz range from 9.0 to 17.5 parts per thousand, and the delta O-18 values estimated for the vuggy quartz-forming fluid range from -2.3 to 3.0 parts per thousand, indicating that it precipitated from mixing of magmatic fluids with surficial fluids. The delta O-18 of kaolinite ranges from 12.7 to 18.1 parts per thousand and delta D from -103.3 to -35.2 parts per thousand, whereas the delta O-18 of dickite varies between 12.7 and 16.3 parts per thousand and delta D from -44 to -30. Based on delta O-18 and delta D, 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. (C) 2016 Elsevier B.V. All rights reserved.