Tectonics and Geology of Porphyry Cu-Au Deposits along the Eastern Sunda Magmatic Arc, Indonesia

Abstract

The discovery of the world class copper-gold deposit at Tumpangpitu, East Java (1.9 Gt @ 0.45% Cu, 0.45 g/t Au), has reinforced the eastern Sunda Arc as a significant metallogenic belt, highly prospective for the discovery of major porphyry deposits. The arc hosts three premier porphyry copper-gold deposits at Batu Hijau, Elang, and Tumpangpitu (>300 t Au and >5 Mt Cu). These giant porphyry deposits are confined to the eastern segment of the eastern Sunda Arc (eastern Java to Sumbawa), constructed on island arc crust where the Roo Rise is being subducted. By contrast, major epithermal (low-sulfidation dominant) deposits associated with poorly-endowed porphyry prospects occur along the western segment of the arc (western Java), developed on thick continental crust on the southern margin of Sundaland associated with subduction of typically thin Indian oceanic crust.Porphyry copper-gold deposits of the eastern-Sunda Arc are spatially associated with small, nested, dioritic to tonalitic intrusive complexes with low-K calc-alkaline to weakly alkaline signatures.Hypogene alteration and mineralization developed during three main temporally and spatially overlapping events, termed early, transitional and late. The hypogene copper-gold mineralized zone of the giant deposits forms a bell-shaped body of 0.3% Cu shell greater than 1 km in both diameter and vertical extent, that is centered on multi-phase, elongate, pencil-like tonalite intrusions, 200 m to 1,200 m in diameter and >2 km vertical extent. Large (>20 km 2 ) lithocaps associated with high-sulfidation epithermal systems and post-porphyry mineralization diatreme breccias characterize productive porphyry districts at Batu Hijau, Elang and Tumpangpitu. The known porphyry deposits with metal content exceeding 300 t Au and > 5 Mt Cu all formed less than 5 Ma, suggesting an important change in the metallogeny of the arc at this time. These giant porphyry deposits formed relatively rapidly, typically over a period of 30 to 860 k.y. during the Pliocene-Pleistocene between 5 and 2.5 Ma.Porphyry deposits along the eastern Sunda Arc display similar characteristic geological features to porphyry deposits elsewhere. Significant differences include low-K systems, dominance of hydrothermal biotite over K-feldspar, early intense actinolite alteration associated with ore, widespread shreddy chlorite after secondary biotite, narrow quartz-sericite-pyrite alteration zones, lack of development of C veins, large overlying lithocaps and abundant chalcocite-bornite-covellite veinlets associated with late overprinting epithermal systems. Hydrothermal oligoclase is also more abundant than K-feldspar in the central biotite-magnetite zones.

Open-system behaviour of magmatic fluid phase and transport of copper in arc magmas at Krakatau and Batur volcanoes, Indonesia

“…The study of silicate and sulfide melt inclusions in samples from Mt Krakatau (Maryono 2015). Structural features from Dahren et al (2012) and Nishimura and Harjono (1992).…”

Indikasi Mineralisasi Tipe Porfiri di Daerah Sumbersari, Kompleks Pengunungan Kulon Progo, Purworejo, Indonesia

“…Sabuk Sunda bagian timur merupakan sabuk tektonik dengan keterdapatan mineralisasi yang sangat baik dan berkelas dunia [1]. Saat ini telah ditemukan beberapa deposit besar tipe porfiri seperti Batu Hijau dan Elang [2], Brambang [3], Tumpang Pitu [4], serta ditemukannya deposit baru seperti Hu'u [5] dan Selogiri [6].…”

“…Deposit itu berasosiasi dengan sabuk tektonik dan magmatisme berumur Miosen sampai Pleistosen dan berhubungan dengan magmatisme Pegunungan Selatan. [1,7].…”

“…(a) (b) Gambar 1. (a) Sebaran mineralisasi pada sabuk Sunda bagian timur [1,7]; dan (b) lokasi penelitian.…”

Potential for Porphyry Copper Deposits in Northern Tōhoku (or the Exploration Potential for Base and Precious Metal Deposits in Japan 2020)

“…However, the discovery in 1988 of the giant Grasberg porphyry Cu–Au deposit adjacent to the Ertsberg Cu–Au skarn in the western part of the island of New Guinea and the successful grassroots campaign by Newmont Corp. in Sumbawa, with the discovery of the Dodo‐Elang and Batu Hijau porphyry Cu–Au deposits in 1987 and 1991, respectively, demonstrated that this negative view was indeed premature. Incidentally, with the discoveries of a giant porphyry Cu–Au deposit at Tujuh Bukit in Java in 2007 (Rohrlach, ; Maryono et al, ) and recently at Hu'u in eastern Sumbawa (Maryono et al, ), the East Sunda‐Banda arc is, today, arguably one of the more densely mineralized porphyry copper belts worldwide.…”