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Details J .Pak Kok. On the east side of the headland (056 082), finely bedded tuffite and tuffaceous siltstone are dominant.Sey*°athito a light greenish-grey and can contain abundant quartz crystals up to 1 mm across. Bedding which?Sefmed by abrupt variations in the abundance of quartz grams, dips 57° to the southeast. Furfter south theSffite is stratigraphically overlain by quart/ crystal ash-bearing tuffs, and underlain to the north, by tuffitesSandstones and siftstones. On the coast west of Pak Kok, the member compnses grey to dark grey, laminatedmudstones and siltstones. It is underlain by banded porphyritic lavas, but the overlying sequence has not beenpreserved.Kan Lins Chung Poorly bedded, pebbly tuffaceous sandstone, which is exposed along the footpath (0358 0750) toFan Lau, dips gently to the southeast. Overlying strata include lithic lapffli-bearing tuff and porphyritic lava, but theupper contact of the member can not be distinguished.At Kau Ling Chung (041 071), laminated siltstone and tuffaceous sandstone are overlain by rhyolite lava. Thesequence is well bedded, dipping 21° to the southeast, and the common laminae are less than 1 mm thick. Thesiltstone displays small-scale sedimentary structures, inqluding syn-depositional microfaults, flattened sand ballsand graded beds A narrow (
Sunset Peak MemberThe Sunset Peak Member is defined for the first time in this memoir. It coincides in part withagglomerate outcrops mapped by Allen & Stephens (1971) on both Sunset Peak (Tai Tung Shan)and Lantau Peak (Fung Wong Shan). The member is almost entirely pyroclastic and dominantlycomprises tuff-breccia and lithic lapilli-bearing tuff, but also includes eutaxitic tuff. A notablecharacteristic is the flattening of clasts, which imparts a planar fabric.The member only crops out in restricted areas on the highest peaks in east Lantau Island. Its typelocality is the summit (1336 1305) of Sunset Peak, where it is about 50 m thick. There is asmaller outcrop on a lower peak to the east, and substantial exposures occur on, and around, LinFa Shan, where the member is less than 70 m thick. An isolated outcrop around the summit ofLantau Peak is less than 100 metres thick.DetailsSunset Peak (Tai Tung Shan). Lapilli-bearing tuff and tuff-breccia form much of the summit of Sunset Peak, thetype locality of the member. On the summit (1318 1317), the tuff is poorly banded and includes quartz crystals upto 8 mm, and a few pebble-like lithic lapilli set in a fine ash matrix. Although exposures are mostly exhumedcorestones, the banding is generally sub-horizontal. Tuff-breccias near the summit (Plate 16, 1336 1305) are lightgrey when fresh, and contain clasts of vitric tuff or lava, up to 1 m across, although most clasts are less than 60 mmacross. There are also rare volcanic lava bombs, and the matrix consists of crystal-bearing vitric tuff. A eutaxiticvitric tuff occurs locally (1345 1306), and is dark grey, with flat, streaky pumice lapilli which are visible onweathered surfaces. Its dominantly vitric matrix contains a few quartz and feldspar crystals up to 2 mm across. Atthe base of the member, there are tuffaceous siltstones and mudstones, but their contact with the underlyingsuccession of mainly lava and tuff is not exposed.East of Sunset Peak, there are exposures (1446 1389) of lithic lapilli-bearing crystal tuff or tuff-breccia., similar tothose on both Sunset Peak and Lin Fa Shan. The pock-marked surface of the light, brownish-grey bouldersindicates the presence of abundant, rounded lithic clasts. In tuffs (1432 1332) to the west, rounded lapilli of vitrictuff, or lava are up to 30 mm across. The matrix is comprised mainly of coarse ash crystals, and there is anindeterminate layering defined by clast orientation.Lin Fa Shan. On the summit (1502 1514), light grey, lapilli-ash crystal tuff with a fine ash matrix includes lithiclapilli which weather preferentially, leaving elongate hollows (Plate 17) up to 50 mm long. Fabric in the corestonesappears to dip to the east at 40°. Elsewhere on the summit, fabric is poorly developed, but the rock containsangular tuff blocks, up to 300 mm across, which weather preferentially. The slopes to the south are dominated bydisplaced boulders of elongate lapilli- and block-bearing tuff. The member is underlain by tuffaceous sandstone.Although the contact is not exposed, it may be locally unconformable. The succession is preserved in a synclinalcore, whose northerly-trending axial plane passes through the summit.Lantau Peak (Fung Wong Shan). South of the summit of Lantau Peak (0975 1217), the member comprises ablock- and lapilli-bearing vitric tuff. The blocks, which are up to 250 mm across, are set in a dominantly vitricmatrix which contains ash crystals. On the eastern ridge of the peak, the block-bearing tuff, or tuff-breccia,contains sub-rounded blocks up to 200 mm across, and on the northwestern ridge (0960 1244), the blocks define asub-planar surface. In the crystal-bearing vitric matrix, there is also a streaky eutaxitic fabric which dips 45° to thenorthwest. The member overlies porphyritic rhyolite lava and pebbly tuffite, and is capped on the summit by poorlybanded, porphyritic rhyolite lava.PetrographyThe typical block-, and lapilli-bearing tuff has a welded matrix (HK7886, 1500 1418) thatincorporates subhedral to broken crystals. Small quartz crystal aggregates suggest eitherrheomorphism of the vitric matrix, or a pyroclastic origin from a lava-dominated vent. Thematrix of vitric tuff from Sunset Peak (HK8432, 1337 1328) is vitroclastic and containsabundant, small, strained shards, and some well-defined, broken bubble-shaped shards. There aresmall, subhedral to euhedral quartz and feldspar crystals, which are generally less than 2 mmacross. The feldspar is partially replaced by chlorite and calcite. Typical tuff-breccia from thetype locality on Sunset Peak (HK 8435, 1336 1305) is light grey, with clasts up to 1 m across,set in a crystal-rich vitric matrix. Most of the pyroclasts are broken, and in thin section there are57
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UNIVERSITY OF HONG KONGLIBRARIES
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© 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 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: dipping northwest at 46°, is prese
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
Page 107 and 108: the majority of rocks in the distri
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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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