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Southeast of Tin Sam, on the western shores of Tung Chung Wan, fine-grained granite country rock is cut bynumerous dykes of feldsparphyric rhyolite, porphyritic microgranite, and basalt. Exposures on the ridge (09931627) to the west comprise slightly weathered, brownish-grey, sparsely megacrystic, fine-grained granite. Theinequigranular groundmass varies from less than 1 mm to over 3 mm, and rounded quartz megacrysts up to 10 mmacross also occur.Lam Chau. The small island of Lam Chau is dominantly composed of pinkish-grey, inequigranular, fine-grainedgranite. A notable feature of exposures on the western tip of the island is the abundance of quartz veins. There arealso zones of brecciation, epidotization and silicification in the granite. These zones have a preferred east-westtrend and are cut by basic dykes (0858 1781). The fine-grained granite is remarkably similar to that seen innorthwest Chek Lap Kok and along the north Lantau coast, but includes pegmatitic patches and zones of biotiteschleiren, as well as irregular aplitic veins.Fan Lau. Megacrystic, fine-grained granite is exposed along the coast from the north shores of Fan Lau Tung Wanand Fan Lau Sai Wan, through Heung Chung Au to Peaked Hill (Kai Yet Kok). Alkali feldspar megacrysts, up to20 mm, quartz megacrysts (20 mm), and biotite crystals are set in a fine-grained groundmass comprising quartz,feldspar, and biotite. 230 m west of the ferry pier at Fan Lau Sai Wan, the fine-grained granite is intruded byquartz syenite.Soko Islands. Megacrystic, fine-grained granite is exposed on the main islands of Siu A Chau and Tai A Chau andon nearby offshore islands. The granite is cut by feldsparphyric rhyolite dykes, trending variably east or northeast,and aplite and basalt dykes, and may be a textural variant of the medium-grained granite. The megacrysticfine-grained granite (Plate 25) is lithologically similar to that exposed at Fan Lau.PetrographySample HK8362 (1101 1967), from Cheung Sha Lan, is a pinkish-white, inequigranular,fine-grained granite with a groundmass typically between 0.5 and 1 mm. A few alkali feldsparcrystals up to 4 mm in size, and rare quartz megacrysts are up to 5 mm. Biotite flakes are lessthan 2 mm across.Fine-grained granite from a borehole east of the kaolin mine on Chek Lap Kok (HK 10511, 11141904) has a grain size of up to 3 mm, but most grains are less than 1 mm. It comprises quartz,sericitised oligoclase and perthitic alkali feldspar with albitic rims. Plagioclase is zoned, withaltered cores, and margins composed of albite. Biotite, fluorite and opaque minerals dominate thegroundmass. The biotite exhibits light brown to olive green pleochroism, and is commonly partlychloritized. Late stage muscovite infills interstices within the groundmass.Age RelationsThe fine-grained granite is generally younger than the other granites of the district. On Chek LapKok, late stage fluids related to pluton emplacement, locally kaolinized the granite and formedaplite dykes and pods of pegmatite. The fine-grained granite on Chek Lap Kok is cut byquartzphyric rhyolite, basalt, and lamprophyre dykes, but not by feldsparphyric rhyolite dykessuggesting at least two ages of felsic dyke.Quartz SyeniteDistribution andLithologyIntrusions of quartz syenite form scattered outcrops in southern parts of the district. The largestoutcrop is between Shek Mun Shan and Luk Keng Shan, and the second largest is between MuiWo and Pui 0. Smaller outcrops and dykes occur at Ma Po Ping Prison near Tong Fuk, FanLau, Sha Lo Wan and Hei Ling Chau.73