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Silver Mine Bay. On the headland southeast of Silver Mine Bay, a 15m-wide basalt dyke cuts feldspaiphyricrhyolite dykes. The basalt dyke is exposed on the beach and probably lies in the east- to northeast-trendingdepression behind the beach. The slightly weathered exposures comprise hard, greenish-brown, equigranularbasalt, with a grain size of less than 0.5 mm.At Man Kok Tsui, at the eastern end of Silver Mine Bay, a wide basalt dyke intrudes feldspaiphyric rhyolite. Thebasalt is hard and bluish-grey when fresh, and weathers to form well-developed corestones in a brown, clayeymatrix (Plate 33). The dyke, which trends northeast, is up to 10 m wide.Peaked Hill (Kai Yet Kok). On the northern shores of Peaked Hill, a thin, foliated basalt dyke cuts an irregular,impersistent, quartzphyric rhyolite dyke. Both dykes cut the medium-grained granite. The basalt trends southeastand is about O.lm wide.Soko Islands. West of Siu A Chau Wan (0851 0457), there is a 5 m wide, northerly-trending basalt dyke cuttingcoarse-grained granite . The dyke is grey when fresh, and has a sharp, non-foliated margin to the west, and afractured margin to the east. Petrographically, the rock (HK9562) is dominated by laths of sericitized plagioclase,but also contains augite, biotite, chlorite and opaque minerals. The grain size is generally 0.1 to 0.5 mm, althoughthere are some mafic phenocrysts up to 2 mm across and some secondary pyrite crystals. The even-texturedgroundmass also contains xenocrysts of quartz, up to 6 mm long.A 5 m-wide basalt dyke, trending approximately northwards, is exposed on the north coast of Ma Chau (07570375), a small island southwest of Siu A Chau. The dyke, dipping 80° to the west, comprises fresh, dark greycorestones set in a deeply weathered matrix. The grain size of the basalt is mostly less than 0.2 mm, and it displaysa good ophitic texture in thin section (HK10018).Chi Ma Wan. Basalt dykes have been noted at a few localities on the Chi Ma Wan peninsula. Most are in the eastof the area, where the basalt dykes cut both rhyolite dykes and granite. At Ha So Pai (1984 0968), a 0.6 m-wide,eastnortheast-trending basalt dyke intrudes equigranular, medium-grained granite. The dyke is parallel to afeldsparphyric rhyolite dyke to the north. A thin sliver of medium-grained granite, 0.3 to 1 m wide, occurs betweenthe two dykes.Near the easternmost tip of the peninsula (1998 1009), an 8 m-wide, dark, greenish-grey basalt, or microgabbrodyke cuts a quartzphyric rhyolite dyke and medium-grained granite. The basalt dyke lies both along the contactbetween these two older rocks, and cuts across them. The grain size of the basalt ranges from 0.1 to 1 mm, andfeldspar laths and augite crystals form a well-developed sub-ophitic texture (HK8351, Plate 34). The rock alsocontains quartz amygdales, or xenocrysts,Cheung Chau. A few easterly-trending basalt dykes, cutting medium-grained granite, crop out on the eastern coastof Cheung Chau, and a bluish-grey, aphanitic to very fine-grained basalt dyke, about 1.7m wide, is exposed on thesouth coast near Chi Ma Hang (2211 0758). North of Coral Beach (Tung Wan Tsai), there are two, dark grey basaltdykes. The smaller of the two (2165 0909) is only 1.5 m wide, whereas the larger, exposed 110 m to the north, isabout 10 m wide. Both dykes have a grain size of 0.05 to 0.1 mm, with plagioclase feldspar laths up to 0.3 mmlong. Although there is some augite, the dominant mafic minerals in these slightly altered basalts are chlorite,epidote and opaque minerals.Chek Lap Kok (prior to development). There are many small basalt dykes which cut granite, and rhyolite dykeson the northeastern end of the peninsula. A spheroidally weathered basalt dyke, 2.5m wide and trendingsouthsoutheast (1156 1827)> clearly cuts both megacrystic, fine-grained granite, and a flow-banded, quartzphyricrhyolite dyke that intrudes the granite. About 100 m to the north, a swarm of basalt dykes also intrudes the granite(1151 1738), as well as an easterly-trending feldsparphyric rhyolite dyke. These basalts are dark greenish-grey,cariously weathered, mafic-rich, contain altered feldspar megacrysts, and are 0.5-1.5 m wide. Similar basalt andlamprophyre dykes, about 0.5m wide, crop out on the north coast of Fui Yiu Wan. They trend variably east toeastsoutheast (Plate 35, 1203 1964). The lamprophyre follows the dominant joint trend in the area. Two thin basaltdykes, about 0.3 m wide, and deeply weathered and foliated, cut fine-grained granite west of Fu Tei Wan. They arethemselves cut by a small, sinistral fault (1083 1814), with an offset of about 0.3 m (Plate 40). The dykes are alsocut by an aplite dyke in the granite.PetrographyThe basaltic dykes are typically very fine-grained and altered, but one sample (HK10684, 11521810) (Plate 36) has a slightly coarser-grained groundmass with a grainsize of 0.3 to 0.5 mm.This microgabbro has a well-defined sub-ophitic texture of sericitized plagioclase and pyroxene,and includes phenocrysts of sericitized plagioclase up to 2 mm long.89