Chemical variation of biotite and hornblende in some Malaysian and Sumatran granitoids

Author : Hutchison, C.S.
Publication : Bulletin of the Geological Society of Malaysia
Page : 101-120
Volume Number : 24
Year : 1989

Bulletin of the Geological Society of Malaysia, Volume 24, Oct.1989, pp. 101 – 120

Chemical variation of Biotite and Hornblende in some Malaysian and Sumatran Granitoids


Professor of Applied Geology

University of Malaya, 59100 Kuala Lumpur, Malaysia


Abstract: Electron probe microanalyses of biotite and hornblende are presented for a variety of granitoids from Peninsular Malaysia and Sumatra. Most biotites from the Main Range have Fe/(Fe+Mn+Mg) mole ratios greater. than 0.62, with exceptions at Sg.Sok and the Cameron Highlands, which have I-type characteristics.

The Eastern Belt granitoids commonly contain hornblende and biotite. The biotite shows a wide range of Fe/(Fe+Mn+Mg), with higher values from the known tin mineralized areas of Jemaluang and Kuantan. Hornblendes and co-existing biotites generally exhibit equilibrium partitioning of Fe/Mg proving a magmatic origin for both. The total aluminium in the amphiboles prove an epizonal environment of emplacement for the Eastern Belt granitoids and an even higher sub-volcanic environment for the SE province.

The known occurrences of amphibole in the Main Range are few (Sg. Sok in Kedah and Bk. Berapit in Perak). They are of actinolitic hornblende and exhibit a non-equilibrium partitioning of Fe/Mg with the biotite. They are probably of hydrothermal origin.

An unusually green coexisting biotite and hornblende in the Gunung Benom area of the Central Belt appears to represent a deeper level of emplacement than the Main Range or Eastern Belt. The biotite-hornblende assemblage is not in equilibrium and the biotite is unusually enriched in magnesium.