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Environment – Geology
March 29, 2012 |
Tectonically, Peninsular Malaysia forms part of the Sunda Shield. Its Triassic fold-mountain belt, the spine of the Peninsula, continues from eastern Burma through Thailand, Peninsular Malaysia, the Banka and Billiton Islands, and eastwards into Indonesian Borneo. All the systems, ranging from the Cambrian to the Quaternary, are represented in Peninsular Malaysia. The Triassic and older strata are essentially marine whereas the post- Triassic rocks are characteristically non-marine. Sedimentation was continuous throughout the Palaeozoic and Mesozoic. Because of the instability of the basin major breaks are apparent within and between the Palaeozoic, Mesozoic, and Cainozoic groups of rocks. Granitoids occupy almost half the peninsula, commonly forming topographic highs, notably in the Main Range. The main episode of granitic emplacement coincides with the culminating late Triassic orogenic event during which all the older strata were folded and deformed.
Regional metamorphism is widespread and most of the Palaeozoic and Mesozoic rocks show slight to moderate deformation but the grade has never been higher than green schist facies. The contact metamorphosed rocks generally form narrow aureoles around the igneous bodies. The major mineralisation occurred during the granitic emplacement and commonly associated with faulting. Faulting is common in all rocks. At least three sets of faults have been recognised on a regional scale, the youngest of which is at most post-Early Cretaceous in age.
The Machinchang Formation in the northwest part of the peninsula provides the oldest evidence of sedimentation. It consists of shallow-water, current-bedded deposits in the Langkawi Island. The extent of the basin could have transgressed as far as Malacca, by Ordovician times. By Silurian times thick successions of limestone and graptolitic shales were laid down. Volcanic activities also occurred and mainly acidic tuffs were deposited in Kedah and northern Perak. During the Devonian, sediments continued to be deposited, they occur as a thick succession of limestone in central Perak and as clastics in the northwest. East of the Main Range in the foothill regions of western Pahang and southwestern Kelantan, they consist of graptolitic shales, cherts quartzites and intraformational conglomerates with minor intrusives of ophiolitic rocks. Sediments of the Upper Paleozoic, e.g. the Kenny Hill Formation, Singa Formation, and Kati Formation are unconformable over the Lower Palaeozoic sequences.
Thick formations of Lower Carboniferous limestone in central Pahang and carbonaceous shales with limestone lenses in east Pahang provide the earliest indications of the formation of the basin to the east of the Main Range. Sedimentation here was typically shallow marine and, in Kelantan, was probably continuous till the Early Permian. The Sediments deposited consist of four main facies, viz: (i) argillaceous, (ii) volcanic, (iii) calcareous and (iv) arenaceous. Here, sedimentation with inter- mittent volcanism appears to have continued from Carboniferous through the Permian to the Triassic. The general relationship of the Trias with the Permian is one of unconformity. However, in Kelantan, Lower Triassic beds most probably overlie the uppermost Permian conformably. Lower Triassic limestones are common, but following that, the strata became more arenaceous and argillaceous in character. The Middle and Upper Trias are characteri s e d by a flysch-type-sedimentation . Widespread volcanic activity with the eruption of andesite and other intermediate to acid tuffs and lavas occurred in the axial basin. The Upper Triassic orogeny which was also accompanied by granitic intrusions brought an end to marine sedimentation in the Peninsula.
Post-Triassic sediments are essentially continental in character and are described as molasses. These Upper Jurassic-Lower Cretaceous sediments in the Malay Peninsula overlie the older rocks with marked unconformity. The sedimentary basins occupy a zone on the eastern portion of the peninsula from Gunung Gagau in the north to Gunung Panti in the south. The sediments consisting essentially of sandstone, conglomerate and shales with minor coal seams and volcanics, show fluvial, lalcustrine and deltaic conditions of deposition.
The Tertiary rocks are distributed onshore as isolated lacustrine basins underlying the Quaternary deposits and offshore areas mainly as thick continental areno-argillaceous sequences. The Quaternary deposits which consist mainly of unconsolidated to semiconsolidated gravel, sand, clay and silt occupy the coastal terrains and floors of some of the inland valleys. In the Kinta and Klang Valleys, the alluvium contains valuable concentrations of tin ore.
Petroleum is the most valuable mineral resource. It is found in the Malay Basin, off the coast of Terengganu.
Tin ore is found in many parts of Peninsular Malaysia and is richest in the Kinta, Batang Padang, Batang Berjuntai and Klang Valley. Base metals like copper, lead and zinc are known in Ulu Sokor (Kelantan), Tasik Chini and the Mengapur area (Pahang). Gold is found along the central axial belt from Kelantan (Sungai Pergau, Sungai Galas) to Pahang (Merapoh, Kuala Lipis, Raub), Terengganu (Lubuk Mandi), Negeri Sembilan and Johor (Gunung Ledang).
There is potential of tungsten in Kedah and Terengganu. Iron ore is mined on a very small scale from mines in Pahang, Kedah, Perak and Johor. Very small tonnages of low-grade manganese deposits are found in Sungai Aring and Gual Periok in Kelantan and Machang Setahun in Terengganu.
Rare earth minerals such as monazite, xenotime, rutile, struverite, ilmenite and zircon are recovered as by products of tin-mining. A deposit of two million tonnes of ilrmenite are found near Kampung Ajil, Terengganu. Silica sand is exploited from beaches in Johor and mine tailings in Selangor and Perak. There is potential of high grade beach silica sand deposits in Terengganu. Barite is mined in Pahang, Kelantan and Terengganu.
Bauxite is presently mined only in Penggarang, Johor. There exist potential reserves of 17 million tonnes in the Jabor valley, Terengganu and 50 million tonnes at Bukit Goh, Pahang. Small deposits occur in Tanah Mas (Melaka), Batu Pahat, Endau, Sri Medan and Lenga in Johor. Kaolin is presently exploited in the Bidor area of Perak and the Jemaluang area of Johor. There is very good potential for ball clay within the coastal alluvial flats of the country.
Sabah, situated at the northern tip of Borneo Island, is geologically complex. The oldest rocks are the Early Triassic metamorphic rocks (amphibolites, genisses, meta tuffaceous and meta-volcanics) of the Crystalline Basement, found mainly in eastern Sabah. Large bodies of granite, granodiorite, tonalite, ultramafic and mafic rocks intrude into the metamorphic rocks. The ultramafic bodies are distinctly elongated and commonly aligned east-west along the general metamorphic foliation trend.
During Early Cretaceous time, limestone was deposited in several localities on an emerging basement in eastern Sabah. By Late Cretaceous time, thick clastic and calcareous sediments, chert, limestone and volcanic rocks were deposited over a large part of eastern, central, and southwest Sabah and part of northern Sabah. Deposition was continuous up to Eocene time.
By early Tertiary, an elongated northeast trending marine trough already existed extending from the Kalimantan border into western and northern Sabah, and deposition of thick sequences of sandstone and mudstone occurred uninterrupted into the Upper Miocene when it was terminated by folding and uplift, accompanied by the intrusion of the Kinabahu Batholith.
During this major Late Miocene tectonic event, slump deposits and pyroclastics accumulated in several deep basins in eastern Sabah, followed by the deposition of sandstone and mudstone with minor amounts of limestone and coal in a chain of circular to sub-circular shallow basins. Rapid uplift in Late Miocene time resulted in the formation of conglomerate at Lahad Datu and cessation of deposition in the area, except in the easternmost part-the Dent Peninsula-where Pliocene sediments were deposited in coastal swamps and shallow- marine waters.
From the Late Miocene to Quaternary time, extensive volcanism and associated shallow intrusions along the Semporna Peninsula and a batholith-size granitic intrusion at Gunung Kinabalu occurred. The post- tectonic volcanic rocks that erupted in the Semporna Peninsula are typical of the calc-alkaline Pacific island arc type, being rich in soda-lime feldspar and generally low in potash. The early eruptions are mainly andesite, dacite and basalt. Several volcanic cones are still recognisable, and hot springs-remnants of volcanism- occur at several places in the peninsula.
Quarternary deposits, consisting of coarse gravel, sand, silt, clay, peat and coral accumulated along the coast and are now found in raised terraces and in inland plains in Tenom, Klias, Padas valley, and the Sook- Keningau plains.
Most metallic mineral deposits and occurrences in Sabah occur along a central belt stretching from the northern islands of Banggi and Malawali, through Taritipan, Gunung Kinabalu and the Labuk valley to the upper Segama valley-Darvel Bay area and Semporna Peninsula. The only operating mine, Mamut Copper Mining Sdn. Bhd., is situated along this belt. Industrial minerals consisting mainly of limestone, silica, clay, and constructional stones are mainly found outside this belt. Oil and gas are found offshore of the east and west coasts. Coal is found in Tertiary sedimentary basins in south-central Sabah.
Mineralisation is associated with four main groups of rocks, namely, the Crystalline Basement, the ophiolite suite, the young volcanic and associated hypabyssal rocks, and the granitic intrusions.
Copper sulphides have been found in the pre- Triassic Crystalline Basement schists in the upper Segama area, and silver mineralisation is found associated with schistose and doleritic rocks of the basement. Alluvial gold occurs in several rivers, especially the Segama and Diwata rivers, which drain areas underlain by the basement rocks. The auriferous alluvium in the Segama valley also contains detrital native platinum. The sources of gold are thought to be the acidic intrusives of the Crystalline Basement.
Nickel, chromium, iron, pyrhotite, and copper sulphides are associated with the Cretaceous-Miocene ophiolitic rocks which are found in the upper Segama- Darvel Bay area, the Labuk valley, around Gunung Kinabalu, in Taritipan, and in the northern islands. Platinum group metals occur as inclusions in chromite found associated with the basic igneous rocks of the ophiolite suite. Bauxite is developed from these rocks in places; in Sungai Mansan it is formed from gabbro.
Epithermal gold and lead-zinc-copper mineralisations are found in the Pliocene volcanic rocks and associated hypabyssal rocks in the Semporna Peninsula (Bukit Mantri and Nagos). Porphyry copper deposits at Mamut and Gunung Nungkok are closely associated with Miocene-Pliocene granitic intrusions in the Kinabalu area.
Montmorillonitic clay is found in the Miocene volcano-sedimentary strata in the Sandakan, Dent Peninsula and Tawau areas, and kaolinitic clay in the Plio- Pleistocene formations on the south west coast of Sabah.
Only one metalliferous deposit is being mined at present. Several other promising deposits, such as the Gunung Nungkok Copper Prospect, the Tavai nickeliferous iron deposit, and the Karang Copper Prospect, have been investigated in detail, but were found to be uneconomic to mine at present. Two Cyprus-type massive sulphide deposits in the lower Labuk valley (west Sualog and Kiabau) were discovered during 1983 to 1985. Many coal seams, some of economic thickness, were discovered in the Maliau Basin and surrounding Tertiary sedimentary strata in recent years. Numerous other occurrences of copper, asbestos, chromium, gold, iron, nickel, lead, zinc, silica, and manganese have also been found. Oil and gas are found on the west and east coasts. Oil production started in 1974 from an offshore well on the west coast where all the present producing wells are situated.
In Sarawak, the oldest formations go back only some 300 million years, and so barely one-sixth of the world’s recorded geological history is represented here. These ancient rocks form part of the West Borneo Basement which is the exposed part of the Sunda Shield in Southwest Borneo, and is thus related to continental South-East Asia. The Basement is built up of Palaeozoic and Mesozoic rocks. Most of Sarawak, however, is underlain by younger Tertiary sedimentary rocks especially the region northeast of the Lupar river.
Among the more prominent geomorphorlogical landforms are the many caves developed in limestone formations including the famed Niah Caves and Mulu Caves; and the high waterfalls developed over Tertiary volcanic rocks of the Usun Apau Plateau and Hose Mountains in the interior of the state.
The Mulu Caves developed in the Melinau Limestone of Tertiary age stakes its claim as one of the most spectacular cave systems of the world. Located in the Mulu National Park, some 100 km west of Miri town, it boasts of having the world’s largest cave passage (the Deer Cave). the world’s largest natural rock chamber (the Sarawak Chamber) and the longest cave system in South- East Asia (the Clearwater Cave).
Petroleum and gas are by far the most important mineral resources and production comes from offshore fields in the northern part of the state.
Gold is mined in the Bau area and there is potential for further discoveries in old gold workings in the area, and in the Lundu-Sematan and Marup areas of west Sarawak.
Coal is abundantly found in the state and occurs in four main Tertiary coal basins: the Silantek, the MeritPila, the Mukah-Balingian and the Bintulu coal fields. A total resource of about 730 million tonnes have been identified of which 171 million tonnes are measured reserve, 101 tonnes indicated and 456 tonnes inferred Coal from the Merit-Pila field is presently being mined whereas redevelopment of the underground mine at Silantek is currently being undertaken.
To date (1995), 42 deposits of mainly high quality silica sand with an estimated reserve of about 54 million tonnes have been identified in the state. The deposits are found chiefly in the coastal region of the Kuching (Lundu-Semantan), Samarahan (Roban), Sibu (Lebaan), Bintulu (Bintulu, Suai, Similijau) and Miri (Baram valley) Divisions. Silica sand is presently be mined and processed by two plants located in the Bintulu and Lundu-Semantan areas and up to 1994 about 3.4 million tonnes of processed silice sand have been exported.
Kaolinitic and ball clays suitable for use in the ceramic and related industries are extensively found in the Kuching, Sarikei and Sibu Divisions. To date (1995), 9 deposits of kaolinitic clay with an estimated reserve of about 22 million tonnes and 24 deposits of ball clay with an estimated reserve of about 38 million tonnes have been identified.The major deposits are found in the Balai Ringin-Abok are (19 millions tonnes, kaolinitic clay), Sarikei-Bintangor are (18 millions tonnes, ball clay) and Sibu area (16 millions tonnes, ball clay).
Constructional stones of several rocks types including igneous, sedimentary and metamorphic rocks are quarried for use by the constructional industry. Good quality igneous rocks are found mainly in west Sarawak and moderate to low quality sedimentary/metamorphic rocks such as sandstone, limestone and gravel in central-north Sarawak. Limestone are abundantly found in west Sarawak and large deposits occurs in the Bau, Kuap, Penrissen, Subis, Batu Gading and Melinau aresa – most are suitable for cement manufacture.
Other minerals of minor importance include antimony, mercury, bauxite, iron, copper, manganese, phosphate and dolomite.
Source from Information Malaysia 1997 Yearbook