Koha online

Price: RM 50.00

Abstract.

The map area, which includes the Larut tin fields, was important for its role as the major Malayan tin producer before the discovery of the Kinta tin fields. Today, it has lost its place and glamour as the major producer, but for the period 1964 - 1968, still maintained a much diminished, but steady, record by accounting for about 4% of Perak state's production of tin ore.

The oldest rocks occurs to the southest, consisting of the Salak Baharu beds, Kati beds and the Pondok marbles: these occur as units and are unfossiliferous, so that their exact age is still not certain, but they are here assigned a late Palaeozoic age on the grounds of proximity of occurence, structural similarities and, in part, lithological similarity and contiguity. To the west is the Semanggul formation, comprising conglomerate and rhythmitebeds: the sequence has a typical flysch aspect, and lameli-branchs found in the shales indicate a Mid Triassic age. An isolated body of recrystallized limestone situated in Batu Kurau is considered to be part of the Semanggul formation based on evidence obtained from photogeology, bedrock lithology below the Taiping alluvium and dissimilarities to the Pondok marbles.

The Palaeozoic and Triassic sediments are intruded by porphyritic biotite granite which caused the development of a narrow thermally metamorphosed zone in the country rock. Shearing, which is most prominent along northwest direction in the granite, has resulted in the development of zones of flaser granite, mylonites and other cataclasites. The variations in the texture and mineralogical composition of the granite are attributed to processes of contamination by numerous xenoliths at the time of emplacement and later hydrothermal alteration by pneumatolytic fluids.

Tourmalinization and greisenization, effected by late-phase pegmatite, quartz and aplite veins, have quite extensive, particularly in the contact areas of the granite. Tin mineralization reaches peak development in the Maxwell's Hill area where cassiterite has been recorded in both pegmatite and the altered granite. Weathering and erosion of this tin-bearing granite have accounted for a large part of the alluvial tin ore in the coastal plain. With the possible exception of the dome-shaped body of hornblende-biotite granite northwest of Kuala Kangsar (the Pongging Granite), all the granite in this area is believed to be Triassic.

Younger rocks included the Tertiary coal beds which are found in the Enggor area: these have been exploited in the past for coal. Most of the coastal plain and major river valleys are covered by very thick layers of alluvium. Recent deposits of rhyolitic ash overlie Pleistocene gravel in the valley of the Perak River: these are believed to have originated from volcanic eruptions in Sumatra.