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The Geology of Hong Kong (Interactive On-line)
South Lamma Granite - Jkl

The South Lamma Granite (Table 6.3) forms a subcircular, equigranular biotite monzogranite pluton centred on the southern part of Lamma Island (Figure 6.4). The best exposures are found at the type locality on the east side of the island north of Shek Pai Wan where the granite is seen to intrude the Lantau Granite. A body of texturally modified, slightly metamorphosed biotite monzogranite outcropping in the vicinity of Kam Lo Hom may be a related outlier.

South Lamma Granite is typically equigranular and medium grained, although fine-grained equivalents are found adjacent to contacts with older units and as late stage aplite dykes. The granular texture is characterised by euhedral to subhedral oligoclase, subhedral to anhedral perthitic microcline and orthoclase, and subhedral to anhedral slightly strained quartz and minor reddish brown biotite. Perthitic microcline is generally more abundant than orthoclase and may partly be derived from subsolidus recrystallization. Plagioclase often displays weakly sercitized Ca-rich cores and is also slightly strained. Trace muscovite occurs either as a late stage magmatic mineral or replacing biotite. Accessory minerals include fluorite, allanite, zircon, titanite and Fe-oxide.

A U–Pb age of 148.1 ± 0.2 Ma has recently been obtained for the South Lamma Granite (GEO, unpublished data).