Kalimantan, Indonesia

Main commodities: Diamonds Au PGE PGM
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The Cempaka alluvial diamond deposit is located 45 km east of the coastal city of Banjarmasin in south-eastern Kalimantan, Indonesia.

The regional setting comprises exposed late Jurassic and Cretaceous rocks of the NNE trending Meratus Mountains, surrounded by shallow Tertiary sedimentary basins. These Mesozoic sequences include diamondiferous fanglomerates, which have in turn been derived from older sequences of diamondiferous conglomerates in their hinterland, and from possible primary sources thought to be lamproites.

Diamonds have been derived from the weathering and denudation of the Mesozoic diamondiferous fanglomerates of the tectonically emerging Meratus Mountains, and then re-worked through several sedimentary cycles into Tertiary and Quaternary depocentres within low-lying coastal swamps. The resultant multi-phase reworked gravels contain enhanced diamond deposits within concealed palaeochannels beneath these swamps, which partly dry out during the dry season.

The Cempaka mine works two palaeochannels, as follows:

i). The Danau Seran channel, which supported phase I of mining and is the northern tributary of the much larger Cempaka channel. The channel is quoted as containing 25 million cubic metres of gravel of dredgeable gravel at a stripping ratio was 3.4:1 (USGS, 1996). This channel contained a probable mineral reserve of 0.163 million cubic metres @ 0.15 carats per cubic metre, containing 24 500 carats, and an indicated mineral resource of 0.28 million cubic metres @ 0.15 carats per cubic metre, containing 42,000 carats (BDI Mining, 2005).   During 2002, PT Galuh Cempaka sold 4447.03 carats of Cempaka diamonds recovered from the Danau Seran channel during trial mining at an average sale price of US$182.39 per carat. Parcels of diamonds mined from this channel in late 2005 sold included 4276.66 carats of run-of-mine gem diamonds >2 mm, which sold for US$274 per carat. Also included from the same production were 2636.84 carats of <2 mm diamonds selling at US$118 per carat.

ii). The Cempaka channel, which is a 1.6 km wide and 11 km long palaeovalley infilled by diamondiferous gravels. The channel is quoted as containing 236 million cubic metres of gravel of dredgeable gravel (USGS, 1996). It is the target of phase II of mining and contains an inferred mineral resource of 13.5 million cubic metres @ 0.1 carats per cubic metre (BDI Mining, 2002), containing a Canadian NI43-101 compliant resource of >1.4 million carats (Antam, 2005). This resource is from a 6 km length of the channel only.   Phase II operations at Cempaka will target production of 100 000 carats per year. The first diamond recoveries from the Cempaka channel took place during the last quarter of 2005, with the initial 702 carat parcel achieving an independent valuation of US$266 per carat.

The mine also produces byproduct gold and PGE. Approximately 6.5kg of gold and platinum concentrates were also produced during the same period as the output of 2636.84 carats of <2 mm diamonds quoted above.

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

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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