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minimum age of c. 145 Ma (see earlier). Therefore, the medium-grained granite is likely to have aminimum age of c. 145-147 Ma.Fine- to Medium-grained GraniteDistribution and EthologyFine- to medium-grained granite has been mapped in several areas of Lantau Island, Ma Wanand Chek Lap Kok and is regarded as a textural variant of the medium-grained granite. It istypically equigranular and pale pink with equal proportions of plagioclase, alkali feldspar andquartz and scattered flakes of biotite.DetailsMa Wan. Fine- to medium-grained granite is best exposed on the southeast coast of Ma Wan, around Nam Wan(2470 2288), where it is chilled against an inlier of tuffs, with intrusive contacts dipping gently to the northwest.At the northern edge of the inlier (2366 2392) the contact has a complex structure, suggesting foundering of apolygonally-jointed raft of tuff into the roof of a pluton. Further south, bands of fine-grained granite, within thefine- to medium-grained granite, indicate a flat-lying orientation to the complex (2470 2381, 2450 2372).Tang Lung Chau. On Tang Lung Chau, the fine- to medium-grained granite forms small outcrops in the west andnorth of the island. Contacts with fine-grained granite are obscured by feldsparphyric rhyolite dykes.Sam Chuen. Fine- to medium-grained granite is exposed between Sam Chuen and Tai Chuen, and is found inoffshore boreholes at Kap Shui Mun. The granite is non-poiphyritic and underlies a subhorizontal sheet offine-grained granite. Both granites are cut extensively by feldsparphyric and quartzphyric rhyolite dykes.Silver Mine Bay. Megacrystic fine- to medium-grained granite, with some aplite dykes, is exposed as slivers andnarrow belts between the dykes in the Mui Wo area, near Mui Wo Kau Tsuen and Hung Shui. Pink to whitefeldspar phenocrysts, which are up to 30 mm, are set in a granular matrix of biotite (1-3 mm), quartz (1-8 mm) andfeldspar (1-5 mm). Aplite dykes, cutting the granite vary from 0.2 to 0.5 m wide.Sha Lo Wan. Exposures of megacrystic, fine- to medium-grained granite adjacent to the pier (0814 1711) at ShaLo Wan contain feldspar inegacrysts up to 10 mm and prominent biotite crystals up to 3 mm. The rock is grey orrarely pinkish-grey, and has a groundmass with grainsize between 1 and 2 mm. Numerous quartz veins cut thegranite in coastal exposures to the east, and in one locality (0841 17.09) this is accompanied by siliciflcation andbrecciation of the granite. There is also a 0.3 m wide fault breccia and finely fractured granite exposed 25 m to theeast.Chek Lap Kok (prior to development). Inequigranular, fine- to medium-grained granite, intruded byfeldsparphyric and quartzphyric rhyolite dykes, forms much of the eastern part of the island. It is typically lightgrey, but may be pinkish in some coastal exposures. Feldspar megacrysts up to 10 mm long are common, and maybe up to 45 mm. Glomerophyric aggregates of quartz (up to 10 mm) and biotite (up to 7 mm) are also present, setin a fine- to medium-grained groundmass.PetrographyIn thin section, a sample of inequigranular fine- to medium-grained granite from south Chek LapKok (HK9236, 1131 1798) contains microperthitic alkali feldspar crystals from 2 to 4 mm.Plagioclase crystals (1 to 4 mrn) have incipient sericitization and zoned extinction. Quartz, whichis usually strained, is 1 to 2 mm, and rarely up to 4 mm. Subhedral biotite (1-2 mm) is eitherpleochroic, varying from dark to light brown with streaks of green chlorite, or is completelychloritized. The texture is inequigranular, but not obviously megacrystic, with most crystals 1 to4 mm across,Megacrystic fine- to medium-grained granite from a borehole south of Ha Law Wan (HK10518,11309 17165) contains a few quartz crystals up to 10 mm, but most are around 2 mm (Plate 24).The groundmass (0,6 to 2 mm) is mostly composed of quartz, zoned and sericitized oligoclasc,and perthitic alkali feldspar, Biotite is typically chloritized with some epidotization,, but when69