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Investigating the Pathways and P‐T‐X Conditions of Hydrothermal Fluid Flow responsible for Cu‐Au Mineralization in the Ertsberg East Skarn System, Papua, Indonesia
Author(s) -
LEDVINA Matthew D.,
KYLE J. Richard
Publication year - 2014
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12374_38
Subject(s) - skarn , mineralization (soil science) , library science , fluid inclusions , citation , hydrothermal circulation , geology , history , geochemistry , computer science , seismology , soil science , soil water
The Ertsberg East Skarn System (EESS), a 3 Gt orebody at 0.59% Cu and 0.49 ppm Au, is located in the Ertsberg-Grasberg mining district, a 50km region of world class Cu-Au porphyry and skarn deposits in the highlands of Papua, Indonesia (Leys et al., 2012). The region is tectonically complex; subduction of the Australian plate beneath the Pacific plate ca. 12 Ma (Cloos et al., 2005) uplifted and deformed a succession of Upper Cretaceous siliciclastic to Lower Paleogene carbonate strata that serve as host rocks for the skarn orebodies. The transition to a strike-slip margin ca. 4 Ma is associated with ca. 3 Ma magmatism and episodic hydrothermal fluid flow, which resulted in porphyry stockwork and skarn mineralization (Cloos et al., 2005). Whereas the neighboring Grasberg porphyry Cu-Au deposit is believed to have formed by the throttling cupola mechanism, a process where hydrothermal fluids collect at the top of a batholith and periodically are released into the overlying magmatic complex (Cloos & Sapiie, 2013), the origin and transport mechanism for the fluids that formed the EESS are unknown. Several structural and stratigraphic pathways have been proposed as EESS fluid conduits connecting a deep fluid source with the reactive carbonate strata (Gandler, 2006), but controls on the P-T-X conditions of calc-silicate alteration and Cu-Au mineralization are essential to describing skarn formation. Cu-Au mineralization in the EESS is stratigraphically controlled in the exoskarn and also occurs within hydrothermal quartz veins in the endoskarn, hornfels, and exoskarn facies (Gandler, 2006). This relationship suggests that quartz veining and silicification record the evolution of fluids during calcsilicate alteration and Cu-Au mineralization. ESEMCathodoluminescence imaging reveals zonation textures and cross-cutting relationships in vein quartz that results from changes in the P-T-X conditions and growth rates throughout multiple generations of Si-saturated fluid input. When partnered with fluid inclusion analysis and Ti in quartz thermometry, it may be possible to quantify fluctuations in the depositional conditions of Cu-Au skarn formation with time to identify the pathways of mineralizing fluid migration.