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abundant very fine-grained lithic fragments. The rock also displays some secondary alteration tocalcite and sericite.Volcanic EnvironmentThe Sunset Peak Member is a localized, welded pyroclastic flow that formed during a late,relatively quiescent stage in the development of the volcanic pile. The member includes eutaxitesdeposited from ash flows, but is dominated by tuffs, with cognate lithic fragments, which wereerupted from small vents, or fissures. The volcanic pile is complex and has a varied stratigraphy.Mount Davis FormationThe Mount Davis Formation, which forms part of the Repulse Bay Volcanic Group (Table 3), isdefined for the first time in this memoir. It comprises the coarse ash crystal tuff of western HongKong Island formerly ascribed to the Tai Mo Shan Formation (Strange & Shaw, 1986). The typelocality is Mount Davis, on Hong Kong Island, immediately east of the Lantau district. Theformation, which includes eutaxitic tuffs and epiclastic beds, overlies the Ap Lei ChauFormation. There is no stratigraphic overlap between the Mount Davis and Lantau formations.On Sheet 10 (Silver Mine Bay), it was implied that the Lantau Formation is younger than theMount Davis Formation. Subsequently, however, Rb-Sr age-dating of the Ap Lei Chau andLantau formations by Darbyshire (1990, 1993) has suggested that the Mount Davis Formationmay be younger than the Lantau Formation. Thermally metamorphosed rocks of the MountDavis Formation are exposed, in the district, on Green Island (Strange & Shaw, 1986) and onKau Yi Chau to the west.DetailsKau Yi Chau. Lapilli-ash crystal tuff, with elongate, dark, lithic lapilli, is exposed along the east coast of theisland. The lapilli and mafic crystals define a prominent lineation. There may also be small, sharp-edgedporphyritic lapilli. Blocks of eutaxite on the beach are probably derived from a higher, but unexposed stratigraphiclevel within the formation. The eutaxite is black, with abundant crystals of quartz and feldspar up to 5 mm. Thefiamme are up to 300 mm by 50 mm, and the rock resembles eutaxite partings in the Tai Mo Shan Formation. Thetuffs are cut by quartzphyric and feldsparphyric rhyolite dykes. At the northern end of the beach (2620 1624), thereis an easterly-trending contact between lapilli-ash crystal tuff to the south, and a chilled, largely aphardtic dyke tothe north.58
Plate 16- Block and Lapilli-bearing TuffFormation, Lin Fa Shan(1436 1305) in the Sunset Peak Member, within the LantauPlate 17 - Careous Weathering in Lapilli-bearing Tuffwithin the Lantau Formation, Lin Fa Shan(1520 1395) from the Sunset Peak Member,
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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: Sunset Peak MemberThe Sunset Peak M
Page 63 and 64: Chapter 5Major IntrusionsClassifica
Page 65 and 66: in grain size from 0.4 to 1.5 mm, a
Page 67 and 68: 20 - Megacrystic Medium-grained Gra
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
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Detailstal O. Alluvial deposits for
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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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