Bukit Besi - Sri Bangun, Batu Tiga, Burnt Hill
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The Bukit Besi tin and iron deposit is located within the East Coast Malaysia Tin Belt in Terengganu State, 25 km west of Dungun on the east coast of Peninsula Malaysia (#Location: 4° 46' 46"N, 103° 9' 59"E).
The historic mine comprises three open pits from which iron and tin ores were extracted, namely Sri Bangun and Batu Tiga, the main Burnt Hill-Bukit Besi iron ore pit.
The Bukit Besi area was first prospected by the Japanese in 1916, who recommended the area as an iron prospect. Detailed follow-up exploration and proving commenced in 1923, resulting in the setting up of a mining venture by the Nippon Mining Company in 1932.
During the period from 1932 to the outbreak of the Second World War, approximately 1 Mt of iron ore per year were extracted manually by coolies. Mining continued during the war, but, due to shipping shortages, was stockpiled at the coast. At the end of the war, the mine and stockpile were confiscated by the allies. The stockpile was bought by Messrs. Stanley-Smith and Galvin, who sold it to Japan and with the proceeds set up a modern mechanised operation at Bukit Besi under the name of Eastern Mining and Metals Company (EMMCO). EMMCO removed some 36.5 Mt of saleable 63% Fe over the period until the early 1970s when competition from Australia and Brazil forced their closure. The open pit was the largest on the South-East Asian mainland.
During the early 1960s, it was found that some of the ore had high tin impurities which invoked penalties from the smelter. Investigations revealed that these impurities were coming from the Sri Bangun and Batu Tiga pits. Further investigations showed that tin was commercially extractable from these pits and by 1962 a tin plant was in operation and tin mining had commenced. In 1971-72, a Chinese syndicate purchased the mine and carried on with the tin mining until early 1977.
EMMCO also removed about 1 Mt of approximately 1.5% Sn from the two areas. Some 300 000 tonnes came from the main Batu Tiga pit while a further 50 to 60 000 were extracted from a smaller pit some 300 m to the east. This would leave a production of around 650 000 tonnes from Sri Bangun. EMMCO's records have been destroyed since 1971.
These mines were visited in January, 1978, and observations from the visit and discussions with geologists working on the deposit are included below.
See the separate East Coast Malaysia Tin Belt record.
The Bukit Besi iron-tin mineralisation is hosted by a Lower Carboniferous basal quartzite and overlying shale sequence which has inter-bedded calc-silicate and marble wedges that embrace lenses of magnetite, magnetite-pyrrhotite and pyrite-troilite-pyrrhotite. The sequence is cut by Permian granites which have partially ingested portions of the mineralised horizon. The geology of the three main areas at Bukit Besi is as follows:
• Sri Bangun - The geology at Sri Bangun is more straight forward than that at Batu Tiga. The mineralised sequence is underlain by a quartzite unit which forms a prominent ridge, as is also the case at Burnt Hill-Bukit Besi and Batu Tiga (described below).
In outcrop, this quartzite is a fine-grained pale yellow feldspathic quartz sandstone to quartzite. It contains around 10% feldspar which is apparently perthite, with minor sericite and pyroxene (Thomas 1977). The grain size distribution of the rock is very even, averaging 0.5 to 1 mm. When fresh, it is a pale grey. Bedding is obvious locally with 1 mm to 1 cm thick laminae. The rock usually has a shattered appearance.
Towards the top of the unit shale interbeds become more frequent. These grade into the 'mine shale' which will be described below. Above these, 5 to 10 m thick lensoid slivers of 'mine shale' there is a series of calc-silicates. These are usually pale grey to green with an obvious banding, comprising 1 to 10 mm colour variations from dark green to pale grey-green, with some thin pink-tinged layers. The rock is cut by a fine network of 0.5 to 1 mm thick white veinlets distributed in three directions with a separation of around 1 to 2 cms. In some places the calc-silicates are very siliceous, especially towards their base where they approach a fine grey quartzite in appearance.
In outcrop the calc-silicates are blocky in appearance with a prominent coarse jointing developed in three mutually perpendicular directions. They shatter with a conchoidal fracture. There is very little, if any, marble obvious within the calc-silicates at Sri Bangun in contrast to the Burnt Hill-Bukit Besi area. These calc-silicates embrace much of the ore mineralisation.
Overlying the calc-silicates is a sequence of black, very soft carbonaceous, and in part chloritic shales, the 'mine shales'. This rock type is very characteristic and weathers to a motley red to purple and yellow mass of soggy clay. These shales are up to 200 m or more in thickness and to the south enclose another 70 m+ thick pod of calc-silicates similar to those described above. These calc-silicates also host ore mineralisation. Much of the outcrop of the shales is covered by slumps from the collapsing open pit. Two islands of sulphides poking through the slumps in the north-eastern sections of the open pit may be within the shales and not the calc-silicates.
To the east, the shales appear to pass into a 'disturbed' zone of intercalated shales and quartzites. The outcrop in this area is poor and it is uncertain whether it is along strike from the 'mine shales' or is part of the foot wall quartzites.
To the south, the sequence is cut by a coarse to medium biotite granite. There is a hornfelsed aureole from 1 to 2 m thick on the margin of the granite in the mine area. This granite apparently passes shallowly below the bottom of the open pit, cutting the sequence at a high angle.
• Batu Tiga - Although the sequence at Batu Tiga is similar to that at Sri Bangun, there are a number of variations. The basal unit is a quartzite as at Sri Bangun. However, in the eastern part of the Batu Tiga area the quartzites appear to inter-finger with siltstones to shales, that host the stanniferous iron bearing rocks in the area. These rocks did not appear to be as decomposed or as carbonaceous as the 'mine shale' seen elsewhere. Here, it is a decomposed white siltstone to shale with well preserved fine laminations. These are calcareous in part.
This shale hosts a number of mineralised lenses and encloses beds of heavily altered quartz and quartz-feldspar porphyry which appears to be of volcanic origin. The porphyries are composed of sub-rounded quartz phenocrysts from 2 to 4 mm across, set in a pale green to white highly sericitic matrix. In some places 2 x 3 mm white feldspar laths are still obvious. The porphyry is usually very soft and hence exposure is suppressed. Mapped lenses are from 5 to 30 m thick and 10 to 100 m in length. These are confined to the central and eastern part of the Batu Tiga area. The shales and siltstones in this area in general strike roughly E-W and dip to the north. However, to the north of the ore lenses in this area they dip to the south, although the underlying quartzite does not appear to the north. The host shales are at least 100 m thick in this area.
On the western margin of the Batu Tiga area the main sulphide lens is exposed in the main pit. The nature of the base of the sequence is uncertain in this area, as there is some evidence for a north-south trending fault some 20 m to the east of the massive sulphides. Below the massive sulphides minor outcrops of the inter-bedded shale and calc-silicates are evident. These are highly decomposed and sparse, being masked by slumped material from the walls of the collapsing pit. The main sulphide unit, which has a cumulative width of some 20 m, is cut by a fine to medium grained green lamprophyre dyke which is about 35 m in width. This dyke strikes parallel to the sulphide lens and, at the surface, is sandwiched by the sulphides. However, it is clearly cross-cutting the sequence vertically. The sulphide zone is overlain by 20 m of the 'mine shale'.
Here the 'mine shale' is a fine, black, finely laminated (lamination less than 1 mm thick), partly slumped carbonaceous and chloritic shale with finely disseminated (5%) pyrite throughout. Towards the base of the shale, large fragments of disoriented shale blocks up to 10 cm across are found set within lighter shale bands of the order of 25 cm in thickness. Some fossils are obvious with the shale. This is in turn overlain by a 10 m thick unit of inter-bedded black and white shale. The individual beds are from 1 to 3 cm thick and comprise black, carbonaceous and a white to pale grey shale. This is overlain by 4 to 5 m of heavily bleached siltstone which appears siliceous and contains nodules up to 10 cm in diameter of secondary limonite.
Above this is a 20 m thick unit of laminated dirty, silty shale with 1 to 2 cm thick ferruginous bands, followed by a 1 m thick ferruginous shale and 2 to 3 m of grey quartz sandstone to quartzite. These are overlain by a red ferruginous shale which is from 3 to 4 m thick and a 1 m thick decomposed purple to yellow shale of the 'mine shale' type. These are capped by the hanging wall quartzite, a grey, slightly ferruginous laminated (1 mm) quartzite. It is the only hanging wall quartzite known within the area. This sequence dips to the west at 50 to 60°.
There are much less calc-silicates and only traces of marble (in the calc-silicate unit) within the Batu Tiga area.
• Burnt Hill-Bukit Besi. The sequence in these pits was not traversed but appears to comprise a basal quartzite overlain by calc-silicates with iron sulphides and oxides. These are overlain in turn by the 'mine shale' and a greater thickness of inter-bedded marble and calc-silicates which host the main iron orebody. These are followed by a variable thickness of shale which is cut by the granite to the south. The thickness of carbonates and calc silicates is far greater than that observed at either Batu Tiga or Sri Bangun. Between Burnt Hill and Sri Bangun the sequence appears to be inter-bedded quartzite and siltstone to shale with minor limonite. Most of the intervening sequence between Bukit Besi and Batu Tiga has been covered by tailings.
The Sri Bangun and Batu Tiga pits both yielded tin mineralisation in association with iron sulphides and oxides. In contrast, the Burnt Hill and Bukit Besi magnetite-haematite-minor pyrrhotite ore was almost completely barren of tin.
Much of the production from Batu Tiga and Sri Bangun was from magnetite and limonitic gossan. Consequently, the average grade of 1.5% Sn may have been enhanced by oxidation and leaching of sulphides. As the pits got deeper and more sulphides were encountered, the tin recoveries fell.
At Sri Bangun, most of the sulphide/oxide ore has been mined out and only slivers on faces and fingers protruding downwards from the main bed remain.
• Sri Bangun. The lowest lens at Sri Bangun is some 20 m wide and comprises massive to semi-massive sulphides with rapid facies variations along strike. To the south it comprises poorly bedded intercalated magnetite and pyrrhotite and substantial pyrite within a gangue of coarse muscovite. Only a thin sliver of the unit remains in this area as the skin on a bench face. Further north, it reappears as a very well banded sulphide, largely composed of finely banded pyrite. This pyrite has cores of troilite1 remaining. Most of the sulphide was probably originally troilite which alters to pyrite near the surface. Cores of troilite are found within freshly broken boulders and within the pyritic units. The pyrite has a cindery or spongy texture due to the volume difference between troilite and pyrite.
This sulphide unit has intercalated white siliceous sericite bands from 1 mm to 2 cm thick between pyrite bands of similar thickness. Occasional thin magnetite bands from 2 or 3 up to 10 cm thick are found within the sulphides. To the north, these sulphides pass very abruptly, within a distance of 20 m, into a 20 m thick band of massive 20 to 30% pyrrhotite with a highly siliceous gangue overlying only a 2 m thickness of the pyrite seen 20 m to the south. There may be some fault complications in this area. This lowermost sulphide unit lies completely within the calc-silicates.
Some 20 m to the east, within the shales, just above the calc-silicates, well banded magnetite is found intercalated with the shale. Individual bands of shale and magnetite are of the order of 1 cm thick. The magnetite carries from 2 to 3% finely dispersed pyrite. Occasional thin lenses of pyrrhotite occur within the magnetite rich lens.
Within the upper calc-silicate unit to the east, banded troilite and pyrite is encountered similar to that described above. These sulphides often have intercalated 1 to 2 cm thick bands of soft black mud. In the north eastern portion of the pit, the outcropping sulphides grade into a slumped zone where large disoriented blocks of massive sulphide from a few centimetres to 50 cm across are found within slumped shales with interbeds of sandstone and 'grits'. These grits are composed of mudstone fragments concentrated within scour and fill structures a few centimetres to 20 cm wide. This outcrop is extensive and may represent a higher energy channel which has cut the semi-consolidated ore bed.
To the south, large blocks of banded limonite, pyritic shale and magnetite-haematite are found within the granite. There is a concentration of pyrite within fractures cutting the granite near these blocks. These sulphide blocks have dimensions of up to 100 x 20 m.
Ore mineralisation was apparently largely within the sulphide beds in the Sri Bangun pit. Cassiterite is always very fine and almost never seen with the naked eye.
• Batu Tiga. The main sulphide unit at Batu Tiga comprises massive banded pyrite with beds of 80% pyrite from 1 to 10 and up to 50 cm thick intercalated with 30 to 40 cm thick semi-massive pyrite. The semi massive pyrite comprises 20 to 30% pyrite within black shale to mudstone. Both massive and semi massive sulphides are well laminated with laminae from 1 to 10 mm thick. The mudstone to shale gangue is chloritic in part.
On the southern margin of the pit, sections of the upper part of the sulphide lens have been broken up and occur as blocks from 1 cm in diameter to 75 x 25 cm set in laminated, slumped and irregularly banded shale, siltstone, sandstone and grits (made up of shale fragments). These sediments also exhibit scour and fill structures. Towards the central part of the pit the sulphides appear to have been slumped, and are cut by very finely banded siltstone to mudstone seams (or dykes), from 1 to 10 cm thick, with some displacement having taken place across the 'mudstone dykes'.
This infers that, following partial consolidation of the sulphide bed, movement occurred which cracked the sulphides allowing further soft mud to flow into the cracks resulting in the mudstone dykes. On the far southern face of the pit, a very hard siliceous banded 75% pyrrhotite lens occurs in the lower sections of the sulphide body. The main sulphide lens is some 250 m long and has been mined over about a 50 m vertical interval. Within this, a rod shaped body about 25 m in diameter and 100 m long, plunging at 60° to the north, contained ore based on a 1% Sn cutoff.
Within the current pit outline significant grades of Sn are confined largely to sections of the massive footwall pyrrhotite lens on the southern wall of the open cut. This pyrrhotite lens may continue to the north but would be at present covered by slumped material within the floor of the collapsing pit.
Three hundred metres to the east another lens was mined. This comprised a massive ironstone lateritised gossan up to 15 m thick. A number of other gossans and ferruginous shale outcrops are found in the central and eastern parts of the Batu Tiga area.
There is very little troilite at Batu Tiga although arsenopyrite apparently is present. Cassiterite is very fine and almost never seen with the naked eye.
Neither or the ore lenses at Batu Tiga has been closed off and hence have excellent potential for the development of significant orebodies.
• Burnt Hill-Bukit Besi. Within these pits the main minerals were magnetite and haematite with secondary martite and goethite. The lower lenses apparently had significant pyrrhotite, with troilite at Burnt Hill. The upper lens appears to have been the main iron producer. This carries less than 12% sulphide. No tin was encountered within these ores.
• Other Mineralisation. About 1 km to the north-east of the main pit, just above the quartzite contact, a 'high tin area' was recorded. This lies between Bukit Besi and Batu Tiga and is now totally concealed by tailings.
To the south of Sri Bangun a gravel pump is operating over the granite. The cassiterite obtained is coarse and pale and as such, is substantially different from that of Sri Bangun. It is probably eluvial and derived from the granite.
Apart from the good grades obtained at Batu Tiga, it is found as a general rule of thumb that the more massive pyrrhotite is poor in tin.
In 2013, the Brittania Mining website claimed that Bukit Besi had a remaining 'reserve' of 50 Mt @ 70% Fe.
The most recent source geological information used to prepare this summary was dated: 1978.
This description is a summary from published sources, the chief of which are listed below.
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