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

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 δ 34 S of sulfides is from − 4.8 to − 12.7‰, whereas δ 34 S of sulfates range from 14.1 to 17.4‰. The estimated δ 34 S ΣS of the hydrothermal fluid is − 0.5‰. Within the advanced argillic altered zone the δ 34 S values of sulfides and sulfates are interpreted to reflect isotopic equilibrium at temperatures of~240°C. The δ 18 O values of vuggy quartz range from 9.0 to 17.5‰, and the δ 18 O 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 δ 18 O of kaolinite ranges from 12.7 to 18.1‰ and δD from − 103.3 to − 35.2‰, whereas the δ 18 O of dickite varies between 12.7 and 16.3‰ and δD from − 44 to − 30. Based on δ 18 O 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.

Intermediate sulfidation type base metal mineralization at Aliabad-Khanchy, Tarom-Hashtjin metallogenic belt, NW Iran

“…The lack of hydrogen isotope values, as well as lack of knowledge of the isotopic composition of meteoric fluids in THMB at the time of mineralization, prevents definitive identification of fluid sources (e.g., Mehrabi et al, 2016). Studies of fluid-mineral isotopic equilibrium in geothermal systems have shown that quartz is very resistant to isotopic exchange and preserves its original isotopic signature (Clayton et al, 1968;Taylor, 1968;Blattner, 1975;Clayton and Steiner, 1975;Fifarek and Rye, 2005;Corral et al, 2017). If the hydrothermal fluids had uniform oxygen isotopic composition, the increase in δ 18 O would reflect decreasing temperatures of mineral precipitation, which is in agreement with the decrease in the homogenization temperatures obtained from fluid inclusions.…”

“…Cooling, mixing, boiling and water-rock reaction are the main factors that can promote the precipitation of precious and base metals from an ore fluid in the epithermal environment (e.g., Giggenbach and Stewart, 1982;Heald et al, 1987;Hayba, 1997;Hedenquist et al, 2000;Federico et al, 2002;Zhai et al, 2009;Corral et al, 2017). Boiling is considered to be the main factor leading to deposition of precious metals in many epithermal deposits (e.g., Izawa et al, 1990;Simon et al, 1999;Faure et al, 2002;John et al, 2003), whereas the dilution and/or cooling resulting from fluid mixing are key mechanisms for base metal precipitation (e.g., Spycher and Reed, 1989;Yilmaz et al, 2007Yilmaz et al, , 2010Kouhestani et al, 2015Kouhestani et al, , 2017.…”

Trace-metal content of the Cerro Quema Au-Cu deposit (Azuero Peninsula, Panama): Implications for exploration

“…Hydrothermal alteration at Cerro Quema follows an eastward trend that is parallel to secondary faults related to the Río Joaquín Fault Zone. It is defined by several concentric alteration halos that are mainly restricted to dacite domes of the Río Quema Formation, which have higher porosity and permeability than other rock types of the volcano-sedimentary sequence (Corral et al, 2017). According to Corral et al (2011Corral et al ( , 2016, four distinct alteration zones can be identified at Cerro Quema: several vuggy quartz centers (up to ~600 m in length) and local advanced argillic alteration zones (up to ~250 m in length) are observed within the central core of the deposit, enclosed by an argillic alteration zone (up to ~1900 m in length).…”

“…The propylitic alteration zone contains chlorite, epidote, calcite, rutile, pyrite, chalcopyrite, and minor hematite and mag-netite. Stable isotope (S, O, H) geochemistry and fluid inclusion studies revealed that hydrothermal alteration at Cerro Quema was produced by magmatic-hydrothermal fluids that were variably mixed with meteoric fluids (Corral et al, 2017).…”

“…Additional orebodies have been discovered to the east of Cerro Quema; however, their resources have not yet been assessed. Although several studies have been performed on the geology of the deposit (Leach, 1992;Horlacher and Lehmann, 1993;Torrey and Keenan, 1994;Nelson, 1995;Corral et al, 2011), on its origin and evolution (Corral et al, 2016(Corral et al, , 2017, and on the metallogenic potential of the Azuero Peninsula (Del Giudice and Recchi, 1969;Ferenčić, 1970;Kesler et al, 1977;Corral et al, 2016), there is still a gap in the knowledge of the trace metal composition of the Cerro Quema Au-Cu ore. Lithocaps associated with high-sulfidation epithermal deposits can have large extensions of advanced argillic altered rocks (> 20 km 2 ). However, typically only a small portion of the lithocap is mineralized, and due to the lack of directional indicators, exploration in this environment can be difficult (Sillitoe, 1995;Corbett and Leach 1998;Chang et al, 2011).…”