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Plate 13 - Thin Section of Spherulitic Texture in Porphyritic Lava (HK 9222) (0809 1459), within theLantau Formation, from Nei Lak Shan; XPLPlate 14 - Thin Section of Banded Rhyolite lava (HK 9223) (0735 1467), within the Lantau Formation,from near Sham Shek Tsuen; XPL
appears fragmental, and contains mudstone partings. This suggests autobrecciation at the base of a lava flow, andincorporation of rip-up clasts during emplacement. Banding in lava on the Tai O Road (06021163), near KungShan, dips 54° southeast, and on the Kung Shan Road (0692 1035) near Shek Pik dam, it dips from 17° northwestto 18° southwestLantau Peak (Fung Wong Shan). Well-banded lavas dip 73 to 78° south on a knoll (0947 1150) about 850 msouth of Lantau Peak . They also crop out on the ridge (1254 1148) extending to the west, with steep dips to thenorth and south. Corestones on a ridge north of Tong Fuk display well-developed planar banding in porphyriticrhyolite lava. The bands vary from 1 to 5 cm in thickness, and form thin, upstanding ribs on weathered surfaces. Atthis locality the banding dips 35° north, whereas to the north and south along the ridge-line, the dip can be as steepas 74°. Banded lavas are exposed in cut slopes along the road leading to Ma Po Ping Prison. At one locality (10461016) the banding dips 43° southeast in highly weathered porphyritic lava.Sunset Peak (Tai Tung Shan). Banding in corestones of lava on the lower southeastern flanks of Sunset Peak dips57° to the southeast. The prominent eastnortheast-trending features traversing the hillside probably reflect beddingin the underlying sequence of banded lava, lava and sedimentary rocks. To the southeast of Lin Fa Shan (158 136),steeply dipping banding in corestones and boulders strikes east. 2 km along the ridge (119 146) which trendsnorthwest from Sunset Peak, the banding dips steeply to the eastnortheast. On a small hill top (1487 1508) about900 m north of Lin Fa Shan, weathered surfaces of lava boulders display banding up to 0.1 m thick. Roadsideexposures (1161 1386) of weathered lava on the Tung Chung Road, near the Country Park ManagementCentre, display well-developed planar banding which dips 37° east. Banded lava, dipping 40 to 50° northeast, isalso exposed between 100 and 400 m west of the Tung Chung Road at Pak Kung Au.Por Kai Shan. Banded lava and lava are exposed on the summit of For Kai Shan, and on the ridges to the southand west. On the south side of the hill (1394 1626), the light grey lava is autobrecciated and grades into atuffaceous breccia. The relationship between the banded and brecciated lavas is uncertain because of the steep, butvariable dip of the strata and the rarity of exposed contacts. However, the breccias are probably autobreccias,formed at the tops, bases and fronts of successive, banded lava flows. On Por Kai Shan (1398 1633), the weatheredporphyritic lava has pronounced, steeply inclined banding which dips at 60 to 90°, and generally strikes northwest.Banding, which dips approximately 50 to 60° to the north, is also well developed on a ridge (147 163) 700 m eastof Por Kai Shan. About 1 km south (140 154) of Por Kai Shan, lava displays fine banding, about 5 mm thick,which dips about 60° south, and banding is also well developed at several localities between 400 and 800 m east ofPok To Yan, where it and varies from roughly horizontal, to a dip of 53° to the north.PetrographyTypical porphyritic rhyolite lava from Nei Lak Shan (HK9292, 0908, 1339) is light grey with apronounced banding, and contains prominent quartz phenocrysts up to 7 mm across. In thinsection, the partially recrystallized vitric matrix displays a wavy flow-fabric (Plate 12). Theperthitic alkali feldspar phenocrysts, which are generally up to 5 mm across, but range up to25 mm in length, are commonly shattered. The quartz phenocrysts are mostly subhedral andembayed, but can be either broken or euhedral. The lavas can also contain a few well-developedglomeroporphyritic or bipyramidal quartz crystals around 1 to 2 mm across. Grey corestones ofporphyritic rhyolite lava from Nei Lak Shan (0809 1459) show a pronounced spherulitic texturein thin section (Plate 13, HK9222). The spherulites are both compound and simple, and range upto 3 mm across. They are composed of a recrystallized quartz-sericite microcrystalline aggregate,and contrast with the more sericitized matrix of devitrified and recrystallized glass. Plagioclase iscommonly glomeroporphyritic, and in hand specimen can be up to 7 mm in length. Quartzcrystals, ranging from subhedral to euhedral in form, can be up to 3 mm. There is a relativelyminor alkali feldspar phenocryst content, and the rock composition may tend towards rhyodacite.Grey to light grey corestones of brecciated, flow-banded rhyolite lava crop out near Sham ShekTsuen. In thin section (Plate 14, HK9223, 0735 1467)), banding ranges from 1 mm to less thanO.lmm thick, and is characterized by slight grain size changes in the microcrystallinequartz-sericite matrix, and localized concentration of opaque mineral grains. The magneticsusceptibility of the rock is very high (1.2 x 10" 3 cgs units), indicating that magnetite is thedominant opaque mineral, There are very few phenocrysts in the matrix, although there are a feweuhedral oligoclase crystals up to 0.5 mm long.49
Page 2 and 3: UNIVERSITY OF HONG KONGLIBRARIES
Page 4 and 5: © Government of Hong KongPublished
Page 7 and 8: 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: Plate 11 - Pyroclastic Breccia (086
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 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
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the majority of rocks in the distri
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Chapter 9Superficial GeologyIntrodu
Page 112 and 113:
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
Page 151 and 152:
Chapter 10Economic GeologyIntroduct
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Non-metalliferous MineralsFissure v
Page 155 and 156:
REFERENCESAddison, R. (1986). Geolo
Page 157 and 158:
James, J.W.C. (1993). The offshore
Page 159 and 160:
Sewell, R.J., Strange, PJ., Langfor
Page 161 and 162:
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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