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Tujuh Bukit - Tumpangpitu, Candrian, Katak, Gunung Manis
Java, Indonesia
Main commodities: Au Cu

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The Tujuh Bukit group of telescoped epithermal - porphyry copper-gold-silver deposits are located in the province of East Java in Indonesia, ~205 km southeast of Surabaya, and 120 km due west of Denpasar in Bali (#Location: 8° 35' 21", 114° 01' 08" E).

The Tujuh Bukit deposits lie within the east-west trending Sunda-Banda magmatic arc, above the north dipping subduction zone at the convergent intersection of the Australian-Indian and the Eurasian plates. The main cluster of deposits and prospects at Tujuh Bukit includes Tumpangpitu, Candrian, Katak and Gunung Manis distributed over an area of ~5 km in diameter.

Tumpangpitu - comprises high sulphidation Cu-Au-Ag epithermal mineralisation that is telescoped onto a large underlying Au-rich porphyry Cu-Au-Mo system. Broadly, the overall mineralised system covers a northwest-southeast elongated area of ~2.4 x 1.4 km, and comprises a deep, magnetic, tonalitic intrusive complex that has been emplaced within an older and more extensive feldspar-hornblende diorite stock. The latter has in turn been intruded into a cover sequence of lithic and crystal-lithic volcanic breccias that are found at shallow levels of the deposit and conformably overlie a succession of sedimentary rocks that partially dip inwards towards the tonalitic intrusive centre. The contact between the tonalitic complex, believed to be the source of porphyry mineralisation, and the older intrusive, volcanic and sedimentary rocks, is characterised by the presence of one or more extensive diatreme breccia bodies and numerous smaller breccia masses. In particular, the upper margin of the tonalitic complex is intensely altered and fluid metasomatised, and is transitional with the intrusive breccia (which has upward entrained interstitial melt). This breccia is in turn transitional at shallower depths with hydrothermal breccias as fluids are interpreted to have progressively exsolved from the decompressed melt.
    The shallow epithermal levels of the system are dominated by intense silica-clay-alunite-pyrite hydrothermal alteration of the andesitic lithic volcanic breccia, diatreme breccia, hydrothermal breccias and diorite over an area of ~4 x 2.5 km. This envelope is cross-cut by several northwest-trending (possibly structurally controlled) zones of hydrothermal breccias that have undergone advanced argillic alteration and form ~2500 x 300 m ridges that parallel the regional structure and the aeromagnetic grain. This resistant, more siliceous, advanced argillic alteration comprises vuggy silica, silica-alunite, silica-alunite-clay, silica-clay-alunite and silica-clay.
    The deeper parts of the deposit are characterised by alteration and veins characteristic of porphyry systems, centred on the apex of a large, deep tonalitic intrusive complex. Porphyry-style Cu-Au-Mo occurs within a shell of magnetite, quartz-magnetite and quartz vein stockwork within and around the periphery of the tonalitic complex, overprinting the outer margins of the tonalite and adjacent intruded wall rocks. The mineralisation is dominantly within areas of phyllic alteration overprinting potassic assemblages, and to a lesser degree within zones of potassic alteration within the tonalite.
    An ovoid, upward flaring diatreme breccia body, with a diameter of ~500 m, occurs within the central-western part of the deposit, and contain clasts of porphyry style mineralisation. It is composed of milled polymict breccia in its upper sections, with roots that penetrate down into the tonalite, where it has characteristics of an intrusion breccia. The diatreme breccia body is overprinted by steeply oriented structural feeders to high sulphidation mineralisation.
    There are five zones of known near surface Au-Ag oxide mineralisation and deeper sulphide copper-gold mineralisation within Tumpangpitu, denoted A to E. In October 2012, a JORC compliant inferred resource for the porphyry sulphide mineralisation was released (Intrepid Mines) at a 0.2% Cu cutoff of: 1.9 Gt @ 0.45 g/t Au 0.45% Cu, 90 ppm Mo. This resource is within an area of 3.4 x 2.8 km and vertical extent of ~1.1 km, and has a high grade core of 1 Gt @ 0.61 g/t Au, 0.61% Cu,
    Not included within the porphyry resource, is the Tumpangpitu oxide Au-Ag zone with a measured + indicated resource of 70 Mt @ 0.71 g/t Au, 21 g/t Ag and an inferred resource of 19 Mt @ 0.75 g/t Au, 21 g/t Ag for 64 t of contained gold (Intrepid Mines, Sept. 2012).
    Drilling several hundred metres to the east of, and angled away from, this resource, has intersected additional porphyry mineralisation (with no overprinting high sulphidation-style) at a higher RL, apparently associated with a separate intrusion and accompanying stockwork vein system. The best intersection has been 689 m @ 1.0% Cu, 0.85 g/t Au, including 244 m @ 1.42% Cu, 1.06 g/t Au and 466 m @ 1.19% Cu 1.05 g/t Au (Intrepid Mines release Feb. 2012).

Katak - is located ~2 km northeast of Tumpangpitu where an 800 x 300 m magnetic diorite intrusion with associated stockwork chalcopyrite-pyrite mineralisation is developed.

Candrian - is a northwest-southeast elongated prospect which covers an area of 2.5 x 1 km, ~2 km east of Tumpangpitu and underlies soils rich in pyrophyllite, dickite and alunite. Drilling has encountered porphyry style gold-copper mineralisation with intersections grading ~0.8 g/t Au, 0.2% Cu, with cores of >1.5 g/t Au and >0.35% Cu.

Gunung Manis - is a low sulphidation epithermal system that lies ~3 km east of Tumpangpitu, 1 km east of Candrian and 2 km southeast of Katak, and is the basis of artisanal mining of visible gold in drainage systems. Mineralisation is associated with an area of argillic alteration within a diorite body that coincide with a magnetic low, and comprises narrow (1 to 10 mm thick) open space sheeted veins and fractures. Chalcedony occurs in many veins, with abundant bladed calcite. Locally quartz-sericite-pyrite veins are observed. Sulphides include pyrite, chalcopyrite, galens and tetrahedrite-tennantite.

Further porphyry style mineralisation is indicated by mapping, sampling and historic gold and copper workings at Salakan, ~ 5 to 6 km to the northwest of Tumpangpitu.

The most recent source geological information used to prepare this decription was dated: 2011.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Harrison, R.L., Maryono, A., Norris, M.S., Rohrlach, B.D., Cooke, D.R., Thompson, J.M., Creaser, R.A. and Thiede, D.S.,  2018 - Geochronology of the Tumpangpitu Porphyry Au-Cu-Mo and High-Sulfidation Epithermal Au-Ag-Cu Deposit: Evidence for Pre- and Postmineralization Diatremes in the Tujuh Bukit District, Southeast Java, Indonesia: in    Econ. Geol.   v.113, pp. 163-192.
Maryono, A., Harrison, R.L., Cooke, D.R., Rompo, I. and Hoschke, T.G.,  2018 - Tectonics and Geology of Porphyry Cu-Au Deposits along the Eastern Sunda Magmatic Arc, Indonesia: in    Econ. Geol.   v.113, pp. 7-38.
Norris M, Rohrlach B and Maryono A,  2011 - The discovery of the Tujuh Bukit porphyry epithermal copper-gold-silver deposits, Eat Java, Indonesia: in   NewGenGold 2011 Conference, Case Histories of Discovery, 22-23 November 2011, Perth Western Australia, Louthean Media, Perth   Proceedings volume, pp. 201-211

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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