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Plate 31 - Thin Section ofMegacrystic Quartzphyric Rhyolite (HK9040)Kok: PPL(1180 1897), from Chek LapPlate 32 - Basalt Dyke in Granite(2079 1938), Penny's Bay (ChokKo Wan)
also cut volcanic rocks of the Tsuen Wan Volcanic Group in the east, but not in the west. Theyhave not been recorded either within lavas and tuffs of the Repulse Bay Volcanic Group ofcentral Lantau Island, or in Carboniferous strata of west Lantau Island. They are generally thin,commonly ranging from 0.1 to 0.5 m in width (Plate 32), and are rarely more than a few metreswide. They may persist along strike, but generally, due to their preferential weathering, thiscannot be confirmed, and exposures are largely restricted to coastal sections. Most are basaltic,or basaltic andesite in composition. However, they are all strongly altered, and this explains theirlow magnetic susceptibility, as the fresher lamprophyres have a high magnetic mineral content.DetailsTsing Yi. Wide basalt dykes occur at only two localities on Tsing Yi. Around Lo Uk (2816 2376), basalt wasintersected in several site investigation boreholes, and a substantial intrusion is inferred to strike northeasterly. Tothe south, in cut-slopes (2767 2282) north of Sai Tso Wan, a dyke about 8 m wide, with a northeasterly strikecross-cuts southeasterly-trending dykes of fine-grained granite and feldsparphyric rhyolite. In both cases, thebasalt dykes vary texturally to fine-grained gabbro in their cores, and it is possible they are parts of the sameextensive intrusion.Elsewhere on Tsing Yi, basalt forms only minor bodies. Thin dykes crop out in shear zones on the cut-slopes (27902241) west of Sai Tso Wan, and intersect quartzphyric rhyolite at Kam Chuk Kok (2700 2304). On the headlandwest of Shek Wan, several thin dykes intrude tuffs and quartzphyric rhyolite, and they are accompanied by a narrowzone of Fe-Cu-Pb mineralization.Ma Wan. On Ma Wan, basalt dykes are relatively numerous, but they are usually narrow, and intruded parallel todykes of feldsparphyric rhyolite. Several occur on the west coast (2390 2300) of the island, north of Lung Ha Wan,where basalt dykes, 0.5-1 m wide, form the margins to rhyolite dykes which are up to 10 m wide. The same groupof basalt and rhyolite dykes appears to be exposed along strike on the opposite coast of the island, at Tai Lung(2460 2327). It could be inferred that the rhyolite dykes are older than the basalt dykes, but at Lung Ha Wan(2390 2294), they contain xenoliths of basalt, although these in turn contain xenocrysts of alkali feldspar. Hence, insome cases, the two magmas could have been generated broadly at the same time.Other minor basalt dykes on Ma Wan, occur around Nam Wan (2435 2270)j where they intrude along the contactzone of the tuffs and the fine-grained granite. Thin dykes also occur in the north of the island, around Tarn ShuiWan (2392 2378) and Pak Wan (2450 2395), where they intrude tuffs of the Yim Tim Tsai Formation.Sha Chan. A completely weathered, sheared basalt dyke is exposed in the middle of Sha Chau (0659 2304),trending parallel to an earlier quartz vein and mylonitized zone in the granite.Sha Lo Wan. A basalt, or microgabbro dyke, over 10 m wide and trending eastnortheast, is exposed (0735 1697)on the coast west of Sha Lo Wan. It is mafic-rich, has an aphanitic margin, and contains abundant hornblende, up to4 mm long, set in a felsic groundmass (HK9309). This basic dyke is cut by a thin aplite dyke. About 90 m to thesouth, an easterly-trending basalt dyke, about 2.4 m wide, cuts the megacrystic, fine-grained granite. It containsneedle-like phenocrysts of amphibole, and quartz amygdales up to 7 mm across, set in a glassy groundmass.A garnet-bearing, dark green, metabasalt dyke crops out parallel to the eastnortheast-trending contact betweenmegacrystic fine-grained granite and Carboniferous sedimentary rocks at San Shek Wan (0712 1613). The dyke,which intrudes granite, is about 1 m wide. It comprises pseudomorphs after feldspar, up to 3 mm long, set in anaphanitic groundmass. The garnet crystals indicate skara-type mineralization, and are up to 3 mm across./Tin Sam. A greenish-grey, eastnortheasterly-trending basalt dyke, 1.5 m wide, cuts weathered, fine- tomedium-grained granite on the ridge (0993 1628) south of San Tau, The basalt is poorly foliated, sub-parallel tothe dyke margins, and also contains pyrite.On the coast (0957 1705) northeast of Tin Sam s there is a northnortheast-trending basalt dyke that cuts fine-grainedgranite. The dyke is 0.6 to 1 m wide, and contains quartz amygdales and small garnet crystals. A small xenolith ofaltered garnetiferous granite was also noted.An eastnortheast-trending basalt dyke cuts fine-grained granite country rock on the east side of Hau Hok Wan(0892 1691). It is 2,4 m wide, and greenish-grey, with black augite phenocrysts, up to 3 mm across, set in a felsicgroundmass. 80 m to the southwest, there is a dark green, aphanitic, basalt dyke, 0.4-1 m wide, which bifurcatestowards the north. It trends northeastwards and is closely jointed.87
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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
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Table 1 — Grain Size Description
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0 1 2 3 4 5 k mCONTOURS AT 100m INT
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properties of the marine deposits b
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Archival DataAll records from the s
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Chapter 2Outline of GeologyThe soli
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The Mesozoic volcanic rocks are div
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Chapter 3Palaeozoic Sedimentary Roc
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Carboniferous metasedimentaiy rocks
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Plate 1 - Fining-Upward Sequence of
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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 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: Plate 29 - Flow-banded Quartzphyric
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
Page 116 and 117: Plate 44 - Boulder Debris on the So
Page 118 and 119: gazetted for recreational purposes.
Page 120 and 121: DetailsTai O. Extensive intertidal
Page 122 and 123: Plate 48 - Sandy Beach at Fan Lau S
Page 124 and 125: Pre-Chek Lap Kok Formation Deposits
Page 126 and 127: formation. The sequence is usually
Page 128 and 129: BOREHOLE NO: ESC 17GRID REFERENCE:
Page 130 and 131: BOREHOLE NO: A5/1GRID REFERENCE: 80
Page 132 and 133: formation, thinly laminated clays o
Page 134 and 135: Quinqueloculina seminulum, which is
Page 136 and 137: 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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