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against the granite country rock. Medium-grained granite, very similar to that exposed at Pa Tau Kwu, is present asa small pod on Tang Lung Chau.Penny's Bay (Chok Ko Wan). Along the coast between Sam Pak Wan and Sz Pak Wan (2058 1900) there is asmall outcrop of granite in contact with younger, easterly-trending rhyolite dykes. The granite is porphyritic andmedium grained with pinkish alkali feldspar phenocrysts up to 30 mm long. Aplite dykes which cut this granitealso cut the adjacent rhyolite dykes. Less than 100 m to the west, the granite contains dark xenoliths.At Sz Pak Tsui there are well exposed contacts between granite and rhyolite dykes. The granite is medium grained,and contains aplite dykes and pegmatitic patches. At one locality (Plate 19, 2145 1898), it is coarsely porphyritic,with feldspar megacrysts up to 60 mm across, and a groundmass ranging from medium-, to coarse-grained. Thegranite also contains sub-horizontal, fine-grained granite dykes, and has well-defined intrusive contacts withyounger feldsparphyric rhyolite dykes to the north and south.Siu Ho Wan. Porphyritic medium-grained granite with characteristics similar to that at Sam Pak Wan is exposedalong the coast north of Siu Ho Wan. It occurs as pods between dykes of feldsparphyric rhyolite and is thought tointrude crystal tuff belonging to the Shing Mun Formation (Shek Lung Kung Member) exposed on hills to the east.The contact between the tuff and granite is obscured by the rhyolite dykes.Discovery Bay. Weathered granite, forming a fine gravel quartz sand, is occasionally exposed between rhyolitedykes at the golf course. The granite appears to be medium grained and equigranuiar, at least in part, withprominent, single biotite crystals. However, less weathered exposures show that the main lithology is afine-grained, conspicuously megacrystic granite, which may grade into fine- to medium-grained granite. Singlebiotite flakes characterize the rock, and the groundmass crystals are typically less than 1 mm. Larger feldsparcrystals are up to 10 mm across, with quartz up to 6 mm.The granite exposed in cut slopes east of the Discovery Bay ferry pier is porphyritic and medium grained, witheuhedral white alkali feldspar phenocrysts up to 40 mm long and individual biotite flakes up to 4 mm across.Pinkish porphyritic medium-grained granite is also exposed at the eastern end of the golf course (Plate 20),although the dominant bedrock type is feldsparphyric rhyolite, occurring as numerous dykes cutting the granite.West of the Trappist Haven Monastery, there are exposures of granite and dykes which have been hydrothermallyaltered and silicified. At one locality (1940 1589), the altered medium-grained granite comprises quartz relicts from1 to 8 mm across set in a light brown, slightly weathered, aphanitic matrix. This zone of alteration extends east andwest for no more than 500 m, but has no obvious structural control.Weakly megacrystic, medium-grained granite is the main bedrock lithology around Hai Kam Tsui, Minor zones ofsparsely megacrystic fine-grained granite, grading into fine- to medium-grained granite have been reported inboreholes of the Discovery Bay Phase V development.Silver Mine Bay (Mui Wo). At Tung Wan Tau, north of Silver Mine Bay, there are exposures (1854 1515) in astream bed of slightly weathered poiphyritic medium-grained granite, with large pink alkali feldspar and smallindividual biotite flakes. The granite is cut by thin aplite dykes, and is texturally similar to the granite at Sam PakWan. Exposures on the adjacent hillsides and ridges are limited to highly weathered corestones, although thepresence of coarsely granular quartz-rich soil is a good indication of medium-grained granite bedrock. Thiscontrasts with the fine, clay-rich soil that is a characteristic of the weathered rhyolite dykes. Extending for up to400 m to the northnortheast, there are exposures and debris deposits consisting of altered granite andfeldsparphyric rhyolite. These rocks are light green when fresh, and are composed of quartz and sericite. The quartzrelicts give an indication of the primary texture of the rock. The extent of alteration cannot be accurately mapped,but it is probably coincident with a northeast-trending fault that forms part of the Pui 0-Sha Tau Kok Fault Zone(Lai &Langford, 1991).From Man Kok to Kau Shat Wan, east of Silver Mine Bay, porphyritic medium-grained granite is characterized bypatches of pegmatite. East of Kau Shat Wan (2032 1468), a pegmatite vein typically includes alkali feldsparcrystals up to 1 m long by 0,1 m across. These are sometimes separated by long, thin patches of grey crystallinequartz.On the coast south of Silver Mine Bay, from Shui Teng Wan to Wang Tong, there are xmoliths of medium-grainedgranite in the feldsparphyric rhyolite dykes. At one locality (1838 1222), the xenolith is 1,5 m wide and over 8 mlong, whereas at another (1874 1240), the xenolith is over 15 m long.64
20 - Megacrystic Medium-grained Granite (2059 1 749), Discovery Bay1 ? 13^WW^r^^^;f"^V i xgl '9! ' T|027 - Pegmatite in Medium-grained Granite (2241 1250), Displaying Graphic IntergrowthGranophyric Texture) in Coastal Exposures on Hei Ling Chau
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UNIVERSITY OF HONG KONGLIBRARIES
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© Government of Hong KongPublished
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CONTENTSTitle pagePage1ForewordCont
Page 9 and 10:
Distribution and Lithology 73Detail
Page 11 and 12:
Chapter 10 Economic Geology 149Intr
Page 13 and 14:
(Plates)Plate 22 - Porphyritic Medi
Page 15: Table 1 — Grain Size Description
Page 18 and 19: 0 1 2 3 4 5 k mCONTOURS AT 100m INT
Page 20 and 21: properties of the marine deposits b
Page 22 and 23: Archival DataAll records from the s
Page 24 and 25: Chapter 2Outline of GeologyThe soli
Page 26 and 27: The Mesozoic volcanic rocks are div
Page 29 and 30: Chapter 3Palaeozoic Sedimentary Roc
Page 31 and 32: Carboniferous metasedimentaiy rocks
Page 33 and 34: Plate 1 - Fining-Upward Sequence of
Page 35 and 36: Plate 3 - Well-bedded Sandstones an
Page 37 and 38: Reef Island. The northern end of th
Page 39 and 40: Table 3. Evolution of Nomenclature
Page 41 and 42: are crudely stratified and welded i
Page 43 and 44: Shing Mun FormationThe type localit
Page 45 and 46: Tai Che Tung. Crystal tuff, interpr
Page 47 and 48: Plate 7 • Lapilli-Ash Crystal Tuf
Page 49 and 50: Plate 11 - Pyroclastic Breccia (086
Page 51 and 52: appears fragmental, and contains mu
Page 53 and 54: exposures in the stream bed consist
Page 55 and 56: Lin Fa Shan. The steep eastern flan
Page 57 and 58: dipping northwest at 46°, is prese
Page 59 and 60: Sunset Peak MemberThe Sunset Peak M
Page 61 and 62: Plate 16- Block and Lapilli-bearing
Page 63 and 64: Chapter 5Major IntrusionsClassifica
Page 65: in grain size from 0.4 to 1.5 mm, a
Page 69 and 70: Pui O Wan. Porphyritic medium-grain
Page 71 and 72: minimum age of c. 145 Ma (see earli
Page 73 and 74: The granite on Chek Lap Kok is most
Page 75 and 76: Southeast of Tin Sam, on the wester
Page 77 and 78: About 1 km east of Nam Shan, exposu
Page 79 and 80: Plate 25 - Thin Section of Porphyri
Page 81 and 82: Chapter 6Minor IntrusionsIntroducti
Page 83 and 84: The microgranite grades southwards
Page 85 and 86: the Lantau Formation, however, and
Page 87 and 88: Plate 29 - Flow-banded Quartzphyric
Page 89 and 90: also cut volcanic rocks of the Tsue
Page 91 and 92: Silver Mine Bay. On the headland so
Page 93 and 94: Plate 33 - Core stone Development i
Page 95: Plate 37 - Thin Section ofLamprophy
Page 98 and 99: Pre-Yensfaanlan StructureWithin the
Page 100 and 101: separates areas of different lithol
Page 102 and 103: NeotectonicsFault activity in the r
Page 105 and 106: Chapter 8Metamorphism and Alteratio
Page 107 and 108: the majority of rocks in the distri
Page 109: Chapter 9Superficial GeologyIntrodu
Page 112 and 113: Detailstal O. Alluvial deposits for
Page 114 and 115: trains. The regolith on most steep
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Plate 44 - Boulder Debris on the So
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gazetted for recreational purposes.
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DetailsTai O. Extensive intertidal
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Plate 48 - Sandy Beach at Fan Lau S
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Pre-Chek Lap Kok Formation Deposits
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formation. The sequence is usually
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BOREHOLE NO: ESC 17GRID REFERENCE:
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BOREHOLE NO: A5/1GRID REFERENCE: 80
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formation, thinly laminated clays o
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Quinqueloculina seminulum, which is
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Channel and Transgressive Deposits.
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Figure 20 - Areas of Acoustic Turbi
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West Lamma Channel These may be att
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Figure 23 - Depth-Averaged, Maximum
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The formation is Holocene in age. T
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Boreholes (A5/1, A5/2, B2/1, ESC17
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Plate 51 - Deep Weathering Profile
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Chapter 10Economic GeologyIntroduct
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Non-metalliferous MineralsFissure v
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REFERENCESAddison, R. (1986). Geolo
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James, J.W.C. (1993). The offshore
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Sewell, R.J., Strange, PJ., Langfor
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Appendix 1Microfossils identified f
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Appendix 2 (continued)Sample HK9913
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Appendix 2 (continued)Sample HK1054
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Appendix 4aSelective normalized pal
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,Appendix 5 -Radiocarbon and Other
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construction materials 151contact m
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molybdenite 149Mong Tung Hang 151Mo
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talus 107,115Tarn Tsui Wan 71,87Tan
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LB 555.125 G34 LGeology of Lantaii
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