The Gunung Gupit High- and Low-Sulfidation Epithermal Gold Mineralization in Menoreh, Central Java, Indonesia

Gunung Gupit in the Menoreh range, situated in Magelang regency, Central Java, is one of several Neogene volcanoes in Java Island, Indonesia. Hornblende basaltic andesite, hornblende dacitic andesite porphyry, and microdiorite are exposed in a half-circular depression, where hydrothermal alteration and ore mineralization occurred in northern Kulon Progo mountain. The presence of diagnostic minerals such as enargite-luzonite as well as chalcopyrite—pyrite—goethite and hematite, with acidic hydrothermal minerals including alunite, kaolinite, pyrophyllite, dickite, and halloysite, along a NE-trending silicified alteration zone, together with a vuggy-quartz texture, indicating a high-sulfidation epithermal deposit type. The highest grade of ore obtained from in situ channel sampling is 1.37 g/t Au, 595 g/t Ag, and 1.1% Cu. This mineralization system is overprinted by NE- and NW-trending banded quartz-carbonate ± pyrite veins containing 3 g/t Au, a typical LS epithermal deposit type. This deposit type is also supported by a moderate temperature (266–389 °C) and salinity (2.7–8.2 wt% NaCl eq.) of fluid inclusions in sulfide-quartz veins. These findings indicate that the Neogene intermediate magmatism in Java Island could have formed high-sulfidation epithermal-type deposits in Menorehas previously found in Tumpangpitu (East Java) and Cijulang (West Java), etc., which are situated along the West–East trending Sunda-Banda magmatic arc. This implies that, in the future, new LS and HS epithermal prospects might still be discovered along the Neogene magmatic belt.