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Toka Tindung - Pajajaran, Blambangan, Kopra and Araren

Indonesia

Main commodities: Au Ag
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The Toka Tindung low sulphidation epithermal gold deposit is located on the northern tip of the island of Sulawesi, Indonesia, ~35 km ENE of the regional capital of Manado,   (#Location: 1° 35'N, 125° 40'E).

It is located on the eastern margin of the Southeast Asia Plate, within the Sulawesi-East Mindanao magmatic arc, a well mineralised belt volcanics and high level intrusives of lower Miocene to Quaternary age. The same arc hosts the Mesel gold deposit ~120 km to the SW, and a string of other gold occurrences/deposit on the same east-west to NE-SW trending peninsular of northeastern Sulawesi.

In the Toka Tindung district, the stratigraphy comprises Late Miocene to Pliocene predominantly of andesitic to basaltic flows and volcaniclastics, although felsic volcanic and volcaniclastic rocks and breccias consisting of rhyolite, rhyodacite and dacite with minor andesite are exposed in the northeast of the project area. All of these rocks are overlain by a blanket of Quaternary to Recent tephra and volcanics that is widely distributed throughout the region, derived from the recent volcanic centres to the immediate south of the project area. The area is dominated by ENE, NNE, NW and NNW structural trends, with volcanic sequence being cut by a series of NNW-SSE trending faults that define a 2 x 15 km structural corridor encompassing the Toka Tindung deposits. Satellite imagery and aerial photography suggest the presence of circular fracture sets representing eroded caldera features.

The main gold deposits in the Toka Tindung area are interpreted to lie peripheral to one such circular feature, associated with dilational north-trending fracture sets localised at the intersection of regional ENE and NW trending faults. Toka Tindung is a sheeted vein stockwork deposit, hosted by an andesitic volcaniclastic unit in fault contact with a basaltic flow unit. Mineralisation is capped to the north by a younger volcaniclastic breccia (hydrothermal eruption breccia) to a depth of 40 m.

The main Toka Tindung deposit, comprises two parallel vein stockwork zones of subvertical to moderately dipping sheeted vein systems hosted within silica and adularia altered andesitic volcaniclastic rocks which, above and below the deposit, are composed of weakly mineralised lava flows and volcanic breccias. These two vein systems, the Ako and the Western, have a total strike length of more than 1.7 km and range in width from 20 to 50 m. They comprise structurally complex veins ranging in width from several mm to several metres that host high grade shoots assaying >30 g/t Au enveloped by lower grade (<5 g/t Au) stockwork veining. These vein stockworks mostly trend to the north, although, in the south of the deposit the veins trend sub-parallel to a major NNW trending fault zone.

These veins are sulphide-poor with abundant chalcedonic silica, microcrystalline and fine-grained quartz, adularia and minor calcite. Colloform to crustiform banding and cockade crustiform breccias are the dominant vein textures. Gold occurs as occluded <20 µm anhedral free grains of native gold and electrum interstitial to quartz and adularia crystals, and in microcrystalline quartz and subordinate adularia, although it also coexists with pyrite and the silver sulphide minerals of acanthite or argentite.

The banded and brecciated quartz-adularia veins range in thickness from <1 up to 10 m and are associated with a zone of pervasive quartz-adularia alteration. In excess of 61 veins have been defined within the deposit, typically grading between 3 and 5 g/t, and locally up to 30 g/t Au. Silver grades are generally low, with a Ag:Au ratio of 2:1. Quartz vein stockwork zones are found between the main veins and have a bulk grade ranging between 0.2 to 3 g/t Au. Weathering and oxidation to depths of up to 80 m is localised along the main veins and structures.

The low sulphidation-type epithermal character of the veins is reflected by the alteration assemblages and vein mineralogy. The presence of sinters and hydrothermal eruption breccias in the vicinity imply a shallow hot spring environment related to volcanic and geothermal activity that led to the formation of the deposit.

The satellite deposits at Pajajaran, Blambangan, Kopra and Araren are much simpler ore systems than Toka Tindung. Pajararan (on the northern side of the Araren River) consists of two steeply SW-dipping parallel, 2 to 7 m wide veins that extend along the entire length of the deposit with minor associated NW-SE trending stockworks. The Blambangan vein adjoins the south eastern end of the Pajajaran gold deposit beneath the Araren River and consists of a single curvilinear 1 to 10 m wide vein with minor flanking and splay veins trending north-south. The northern spur vein of Blambangan is termed the Mataram prospect. The Araren deposit consists of two 1 to 7 m wide veins.

Aurora Gold prior to 2001 had announced an in situ Mineral Resource for the immediate Toka Tindung deposit of:
    14 Mt @ 3.2 g/t Au, 8 g/t Ag for 45 t Au.

Reserves and resources at December 31, 2010 were (Archipelago Resources plc, 2011):
    Mineral Inventory - 7.6 Mt @ 3.7 g/t Au, 9 g/t Ag;
    Measured + Indicated + Inferred Resource - 15 Mt @ 3.4 g/t Au, 8 g/t Ag, for 54 t Au

Production was commenced in April 2011.

Reserves and resources at December 31, 2011 were (Archipelago Resources plc, 2012):
    Proved + probable ore reserves - 23.4 Mt @ 1.3 g/t Au, 3.0 g/t Ag;
    Measured + indicated + inferred mineral resource - 55.6 Mt @ 0.91 g/t Au, 1.9 g/t Ag, for 50.7 t Au

The most recent source geological information used to prepare this summary was dated: 2006.    
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:
van Leeuwen, T.M. and Pieters, P.E.,  2011 - Mineral Deposits of Sulawesi: in   The Sulawesi Mineral Resources 2011 Seminar, 28‐29 November 2011, Manado, North Sulawesi, Indonesia, Masyarakat Geologi Ekonomi Indonesia - Indonesian Geologists Association (MGEI‐IAGI), Jakarta    Proceedings, 130p.
Wake B, Silvio N, Lattore A, Iswahyudi A S and Purwanto A,  1996 - Geology of the Toka Tindung epithermal gold deposit, North Sulawesi, Indonesia: in   Porphyry Related Copper and Gold Deposits of the Asia Pacific Region, Conf Proc, Cairns, 12-13 Aug, 1996, AMF, Adelaide    pp 9.1 - 9.8


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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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