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Kelapa Kampit, Nam Salu, Yen Salu |
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Indonesia |
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Sn Zn Pb
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Kelapa Kampit - Nam Salu stratabound tin deposit is on Belitung Island in Indonesia.
(#Location - Nam Salu: 2° 42' 19"S, 108° 4' 24"E).
Belitung Island is roughly square in shape with dimensions of around 50 x 50 km. The north western quarter of the island is occupied by a Late Triassic granitic body, while quartz-monzonite occupies a strip along the south coast. Other smaller granodiorite, quartz-monzonite and granite bodies from 1 x 1 km to 10 x 2 km in size occur sporadically around the island. The remainder largely comprises an undifferentiated sequence of Permian sediments with a very small area of spilitic pillow lavas on the north coast adjacent to the main granite, and a 9 x 2 km gabbroic body to the east of Kelapa Kampit on the north eastern coast. Other lesser gabbros are found to the south. The sedimentary sequence strikes east-west and usually dips sub-vertically with few observable fold closures.
The Permian sequence is composed predominantly of quartz sandstones to quartzites with lesser inter-bedded siltstones and claystones. The sediments represent shallow water shelf deposits, exhibiting cross-bedding and scour and fill structures with minor slumping and possible ripple marks. It is reasonably massively bedded with few laminations. In places, sandstones and claystones are inter-bedded on a 1 to 2 m thick basis.
Within the Kelapa Kampit mine sequence, stratabound tin mineralisation has been recognised at eleven stratigraphic positions (although some may be fault repetitions) within a sequence of sandstone, claystone and cherts. The strike direction within the mine area is generally ESE-WNW with a variable dip to the south averaging 70°. The mineralised package is distributed over a length of around 3 km. However, individual ore grade lodes only occupy portions of this length, in general being 100 to 500 m in length. A few are longer, with the most extensive being the Yen Salu, which is known for more than 2 km. The sequence is cut by a series of NE-SW faults which carry mineralisation locally, but are of lesser economic importance. These faults also terminate many of the mineralised zones.
In general the mineralised units are only thin (less than 1, to a few metres wide), although the Nam Salu horizon is a 35 m thick unit of stilpnomelane-chlorite-(biotite)-phyllite which is exposed over a 3 km interval. This horizon is characterised by semi-continuous 0.2 to 15 mm scale banding defined by varying iron content as magnetite, pyrrhotite, pyrite, ilmenite and siderite, averaging around 8% by volume. Other horizons have a similar mineralogy, with variations in the proportion of the various sulphides and magnetite. Some are also rich in base metals such as galena and sphalerite with local intersections of up to 10% Zn and 3% Pb over 2 to 10 m.
In the Kelapa Kampit pit a restricted 100 x 100 x 35 m shoot of 1 to 2% tin has been mined within the Nam Salu horizon, the mineralisation being symmetrically distributed on either side of an oblique fault cutting the horizon. Tin is present as fine grained 2 to 200 micron cassiterite randomly distributed in the phyllosilicate matrix and in a number of post dissemination stages of fine veinlets with sulphides.
This mineralisation represent examples of the four styles of mineralisation that had been recognised at Kelapa Kampit when visited in 1978, namely:
• Fault lodes - which are only of minor economic importance and comprise patchy pyrite and pyrrhotite with similarly patchy cassiterite mineralisation. Most of the cross-cutting faults have mineralisation of this type. These lodes are up to 50 cm thick and usually carry associated puggy chloritic material. Cassiterite in these lodes has a grain size of around 1 mm. Where some of the faults cross the stratabound lodes, pipe like patches up to 10 to 20 m in diameter are found, carrying high grade tin associated with disseminated sulphide zones.
• High sulphide - magnetite lodes that are always stratabound and occur as banded pyrite and pyrrhotite with lesser arsenopyrite and chalcopyrite within a chloritic gangue. In other places they grade into layered magnetite-white clay-sulphide beds. The most extensive of these lodes is the Yen Salu, which is known for a strike length of 2 km. Others are developed over lengths of from 200 to 500 m and widths of 0.3 to 0.9 m and occasionally, over limited lengths, up to 3 or 4 m. The Loudon Lode is one such horizon. Examples of this lode shown in plans carried between 1.4 and 3.7% Sn (with local highs of 5 to 6% Sn) over thicknesses of 0.4 to 0.9 m (with local thickenings from 1.2 to 1.3 m). Within these lodes the cassiterite is ~150 µm. The tin mineralisation is usually best developed in the pyrrhotite rich sections of the lode. These inter-finger with magnetite zones, both laterally and vertically.
• Nam Salu Tin Lode, the only deposit of this type is known in 1978. It is the thickest tin lode encountered at Kelapa Kampit, although it has a limited lateral extent. The maximum dimensions are 200 x 50 x 35 m. This lode dips at ~70°N, but is locally vertical to overturned. The main Nam Salu tin lode pinches out rapidly on its extremities into a poorly mineralised horizon. It corresponds to the junction of a major fault structure and the Nam Salu horizon. The Nam Salu tin ore zone differs from the other stratabound lodes in that it is thicker, lower grade and has a lesser sulphide and magnetite content. To 1978, 19 600 tonnes of ore have been extracted from this pod averaging 1.5% Sn. The cassiterite at Nam Salu is of the order of 150 µm in grain size.
• Nam Salu Pb-Zn Lode, the only one horizon of this type known in 1978. It is reflected at the surface by geochemical anomalies supported by ground magnetics for 7.4 km and has been confirmed by trenching and drilling for up to 5 km. Work to 1978 had indicated that the lode varied in thickness from 1 to 23 m, with an uncertain continuity along strike. Drilling indicated thicker sections are laterally on either side of the main Nam Salu tin body. The mineralisation apparently occurs as banded sphalerite and galena intercalated with chloritic claystones, cherts and quartz sandstone. The average width of the lodes was 3.78 m with an average grade of 7.34% Zn and 2.87% Pb. The most significant intersection in 1978 had been 23 m @ 11.6% Zn, 4.63% Pb and 84 g/t Ag. The highest grade intersection was 5 m of 24.3% Zn and 7.16% Pb. This lode apparently contains no tin.
Historically the Kelapa Kampit hard rock mines have produced more than 25 000 tonnes of tin since 1906 to 1990.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1990.
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.
Nam Salu
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Schwartz M O, Surjono 1990 - The strata-bound Tin deposit Nam Salu, Kelapa Kampit, Indonesia: in Econ. Geol. v85 pp 76-98
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