Epithermal gold deposits in West Java, Indonesia: geology, age and crustal source

Abstract

Epithermal gold mineralization of the adularia-sericite type in West Java is hosted by strike-slip faults cutting Miocene to Pliocene volcanic and plutonic formations. Mineralization consists of two styles of discordant gold-bearing quartz veins: crustiform banding veins of the “Pongkor” type, with electrum, some minor sulphides and manganese oxides, and breccia veins of the “Cirotan” type with rhodochrosite, rhodonite, electrum, abundant polymetallic sulphides and some cassiterite and wolframite. Except for the Pongkor ore deposit, whose age is Miocene (8.5 Ma), K/Ar dating of adularia gave a Pliocene-Pleistocene (2.1-1.5 Ma) age for both styles of epithermal gold deposits. Most are hosted by volcanic and intrusive rocks related to extensive Pliocene magmatism that we dated in the centre of the Bayah Dome as forming between 5.7 and 2.0 Ma. Lead-isotopic compositions of Miocene volcanic rocks show mantle affinities, whereas the lead of Pliocene volcanic rocks and Miocene-Pliocene gold deposits is highly radiogenic and clearly crustal ( 207 Pb/ 204Pb = 15.66 to 15.72). This indicates that this lead and possibly associated metals have their source in an underlying Precambian crust, which must extend at depth from West Java to the Tin Islands. Mineralogical data, especially the presence of magmatic-related minerals, sulphur isotopes with δ 34S clustered around 0‰, and lead isotopic results, all suggest that the metal content and probably most of these ore-forming fluids of epithermal gold deposits originated from a crustal magmatism through a reworking of the underlying Precambrian crust.