Sungei Lembing - Gakak, Myah, Willinks
Sn Cu W
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The Sungei Lembing group of three tin mines, Gakak, Myah and Willinks, are located 40 km NW of Kuantan in Pahang State, Malaysia (#Location: 3° 54' 38"N, 103° 1' 59"E).
The Sungei Lembing lodes were worked from as early as 1800 by Malays and Chinese, who, by the late nineteenth century, had excavated a series of open pits in the area, each with surface dimensions of up to 300 x 60 m and around 45 m in depth.
In 1888 the Pahang Corporation Limited negotiated a concession from the Sultan of Pahang over an area of some 6500 km2 around Sungei Lembing, and commenced mining in 1892. An associated company had held a previous similarly sized concession from 1882 but this had lapsed by 1888 with no mining having been commenced. In 1898 the Pahang Corporation's concession was replaced with a lease agreement to the same corporation over an area of 907 km2 under the mining laws of the newly formed Federated Malay States. In 1906 the Pahang Corporation closed down and its rights were taken over by the Pahang Consolidated Co. Ltd.
During the Japanese Occupation from 1941 to 1945, there was no production as the mines had been allowed to flood immediately prior to their capture. They were rehabilitated in late 1945 and production was continuous until closure in 1986. Since 1892 the Sungei Lembing mines had yielded some 110 000 tonnes of tin metal, over half the production of the entire east coast of Malaysia. The average grade of ore mined over the last sixty years is stated to have been 1.2% Sn and 0.3% Cu.
These mines were visited in January 1978, including an underground inspection of the Gakak mine, 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 Sungei Lembing tin mineralisation occurs within and on the margins of white quartz veins which cut Lower Carboniferous sediments and Upper Permian to Lower Triassic granitic intrusives.
The Lower Carboniferous sedimentary rocks comprise a monotonous sequence of dark grey to black shale with lesser siltstone and minor beds of hard clear quartzite which are up to 6 m thick. Bedding is obvious in most areas, although rocks with well developed laminations are relatively restricted. The more laminated rocks display compositional variations of from 0.5 to 1 cm and sometimes up to 2 cm, in contrast to the coarse 30 to 100 cm thick beds obvious elsewhere. No marker units have been recognised and the exact structure of the area is not known. In general, the bedding only dips shallowly at around 30°.
In the vicinity of the granite bodies, the shale comprises an amorphous graphitic black shattered rock with only broadly visible bedding. This zone carries a broad network of 1 to 10 mm thick veinlets. These veinlets are lensoid and very variable in both direction and thickness. Some are mineralised. Away from the granite contact the shales appear less disturbed.
Granitic rocks are found in two zones within the Sungei Lembing area. The main intrusive is the medium grained biotitic Sungei Lembing granite which occurs to the west of the main mines. The eastern margin of this granite dips to the east at around 30°. Further south-west, in the Gakak workings, a second granite is encountered. The contact of this body is faulted with respect to the shales and dips at between 30 and 80° NE. It does not persist to the surface and is believed to be limited to the west by the roughly north south trending Timor Fault. This intrusive is predominantly a fine to medium grained grey granite with 2 mm feldspars and lesser 1 mm quartz crystals accompanied by muscovite. It is intruded in part by Sungei Lembing type granite. Within the Gakak Mine, the lodes are developed in a NE-SW direction and dip at from 30 to 90° SE.
Mineralisation is not present throughout the veins, but occurs in the form of shoots within them. The veins always have an accompanying parallel fault which may cut or be cut by the vein. Within the north eastern part of the Gakak Mine, the veins are cut by a series of parallel dykes. These dykes comprise about 5% quartz crystals with a 1 mm grain size set in a fine grained grey feldspathic matrix. In some areas these dykes remobilise sulphides associated with the mineralised veins. As is the case with the veins, the dykes both cut and are cut by the faults.
In the Gakak area, there are three groups of vein system. The first is the NE-SW trending and steeply dipping North Gakak Lode, which is developed over a length of 150 m. Some 150 m directly to the south-east of North Gakak is the parallel Gakak II group of veins comprising four lodes developed over a 150 m width and 450 m strike length. Individual veins are only mineralised over lengths which are of the order of 200 m.
A further 150 m directly to the south is a further lode system comprising two veins which, like the other vein systems, strike NE-SW. These veins are interpreted to represent two faulted segments of the same vein and are developed over a length of 300 m and down dip extent of at least 90 m. Individual veins within the mine average 120 cm in thickness, but range from a few centimetres up to 200 cm wide (see vein description below).
The Myah and Willinks Mines are developed on a series of veins which are interpreted to represent a single system split and offset by the north-south Timor Fault. These lodes strike at from 90 to 120° and dip steeply both to the north and south. Dips are generally >70°, although some as shallow as 30° are known. The Willinks lodes are developed over a length of around 1.4 km and width of some 300 m. The Myah lodes are found over a similar width, and a known down plunge extent of around 1 km.
The mineralised shoots within the veins plunge to the east at around 30°, parallel to the underlying granite contact. The lodes are mineralised over a broad 'down-dip distance' of ~250 m within the 100 to 150 cm thick veins.
Within the Willinks and Myah systems of lodes, there are around 30 individual economic ore shoots known. These range in size from 50 x 50 m to the largest which is 900 x 150 m. While the lodes at Gakak and Myah do not enter the granite, those on the lower western extension of Willinks penetrate the granite for some 200 m.
Known economic mineralisation at Sungei Lembing is intimately associated with quartz veining. At the Gakak Mine it occurs on the margins of veins in chloritic selvages. At Willinks and Myah it is found within the confines of the veins and on their margins.
Tin is present exclusively as pale red-brown cassiterite, sometimes as coarse as 3 mm, but usually from 0.25 to 0.5 mm. It is often accompanied by minor amounts of chalcopyrite, pyrite, arsenopyrite and traces of pyrrhotite, galena and sphalerite. In an example sighted, pyrite was seen to be developed in a 15 cm selvage as 1 mm veinlets and as irregular fine aggregates up to 1 cm wide. The zone contained around 30% pyrite. In general, little sulphide was seen, although it may be more abundant elsewhere in the mine.
A section observed along the Gakak III Extended vein on the No. 11 level was as follows:
• On the north eastern heading, the vein comprised a 40 cm wide interval cut by thin veinlets of white quartz from 0.5 to 10 cm thick and totalling around 35% of the interval, the remainder being chloritic shale. The veinlets were variable in attitude, but the zone had an overall dip of 80° SE. There was a graphitic fault zone on the footwall of the area of veining. Visible cassiterite was seen over a 1 cm width on the hanging wall of the vein.
• Around 3 m to the SW, this zone has developed into a solid 1 m thick white quartz vein.
• A further 30 m along, the vein was around 1.2 m thick, but 10 to 15 m to the SE splits into two stringers, one 2 cm, the other 20 cm thick. These rejoined after ~20 m into a single 80 cm vein. The massive veins carried up to 20% lenses and slivers of grey chloritic and graphitic shale from 20 cm to several metres in length and 1 cm to 20 cm thick. The accompanying fault zone is either in the footwall or hanging wall of the lode, often disrupting the vein where it changes direction.
• About 30 m further to the SE, the vein was being mined at a heading. Here it dipped at 80°, was 1 m thick, and carried 10 to 15% country rock as lenses within white quartz. Graphitic pug was seen developed over a 10 cm width on the footwall, while a 20 cm chloritic zone on the hanging wall carried a 3 to 4 cm wide zone of very strongly disseminated fine grained reddish cassiterite.
As a general rule of thumb, if a vein pinches out, the accompanying fault is followed, with the vein invariably being found to redevelop.
Grades of up to 15% Sn were occasionally encountered over the 1.2 m mining widths, but these apparently only persist for a few metres along the vein. No tourmaline is found in the Sungei Lembing lodes. The 'barren shale' within the mine area carries around 25 ppm Sn while the granite has up to 50 ppm.
During the Second World War, the Japanese located a wolframite lode of limited extent to the south of Willinks, and extracted some tungsten
For the 12 months ending 31/7/77, the total ore hauled was 208 788 tonnes @ a head grade of 0.99% Sn, mill recovery was 75%, and fine tin production of 1399 tonnes. The coarse tailings contain 0.14% SnO2, while the fine tailings have 0.28% SnO2.
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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