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Non-metalliferous MineralsFissure veins of quartz are common throughout the granitic rocks, particularly on Chek Lap Kokand in northeast Lantau Island. They typically strike northnorthwest or eastnortheast, althoughother trends, including more northerly, and northeasterly veins, also occur. There have beennumerous small workings of quartz veins, for some of which mining licences were granted. Thethree most important areas of these workings are at Mong Tung Hang near Penny's Bay, and onnorthern Chek Lap Kok and Sha Chau.Mining at Mong Tung Hang (223 206) took place between 1969 and 1974 along anorthnorthwest-trending vein, up to 6 m wide. However, quantities of quartz mined must havebeen relatively small. Vestiges of the workings are still visible.Quartz vein mining on Chek Lap Kok (Langford, 1990) was concentrated in small,easterly-trending trenches south of Cheung Sha Lan (111 195). The extensive workings werelicenced between 1959 and 1963, but may have had a longer history of mining. The area mayhave been a source of quartz crystal for spectacle lenses produced in Guangzhou in the nineteenthcentury (P. Bruce, oral communication, June 1990). Quartz veins were also mined in northeastChek Lap Kok, at Miu Wan (1213 1986), from where kaolin was also extracted (see below). Themine operated from the early 1950s until the early 1970s.A large quartz vein, trending northeastwards across the centre of Sha Chau (067 230), andassociated with brecciated and mylonitized granite, was mined briefly under licence after 1969.Kaolin has been worked in two areas: northeast Tsing Yi and on north Chek Lap Kok. Themining on northeast Tsing Yi, at Shek Wan (272 238), was in an altered quartzphyric rhyolitedyke. It started in 1976, and continued, albeit illegally, between 1981 and 1983. Kaolin (and veinquartz) was mined in granite at Miu Wan (1213 1986) in northeast Chek Lap Kok. A secondmine on the island operated between 1981 and 1988. It produced only small amounts of kaolin,and concentrated on production of the washed sand by-product. Production figures for kaolin andquartz are available for both mines (Langford, 1990).Graphitic siltstone beds, up to several metres thick, occur throughout the Lok Ma ChauFormation, but the graphite is generally subeconomic. However, on West Brother island (Tai MoTo) high grade graphite ore (1456 2117) was mined (Ruxton, 1957; Woods & Langford, 1991).The soft, dark grey, graphite-bearing sedimentary rocks, now largely obliterated following thelevelling of the island, were generally highly erosive and poorly exposed. The graphite which wasmined probably came from the axial zone of the northeast-plunging syncline which forms theisland. The rock has lustrous foliation surfaces, and was probably thermally metamorphosed.Mining started in late 1952, and production was around 3 500 tons a year in the early 1960s. TheNg Fuk Black Lead Mining Co. Ltd ceased production in 1971, and the licence expired in 1973.Mining, which was entirely underground, extended to 90 m below sea level, yet did not reach thebottom of the succession, which may be over 300 m thick. Some of the workings have nowcollapsed. Other notable occurrences of graphitic siltstone include: a 2 m thick unit, exposed onthe headland west of San Chau, a 3 m-thick, tightly-folded graphitic bed north of Sham Wat Wan(0626 1526), and on Reef Island.Construction MaterialsFreestone quarrying was carried out along the granitic coastline of Lantau Island, and thesurrounding islands, up to the 1950s. Islands such as Chek Lap Kok provided large amounts ofbuilding stone prior to the Second World War, and there is ample evidence of cutting and151