1 - HKU Libraries

More documents

Recommendations

Info

Exposures of the eastern outcrop of quartz syenite are very poor, and the strongest evidence for outcrop form comesfrom the occurrence of a topographic low, rich vegetation and reddish-brown, saprolitic soil on the ridge west ofTung Chung Wan (097 157). To the east, towards Tung Chung, scattered exposures have been noted, and quartzsyenite has been recorded close to medium-grained granite at the base of the slope (1846 1539).On the rocky coast north of San Shek Wan (0714 1611), there is a 3 m-wide, porphyritic, quartz syenite dyke withabundant feldspar megacrysts, up to 6 mm across. The dyke trends eastnortheast, and has a finer-grained, sheared,or trachytic margin against foliated sedimentary rocks to the north.Hei Ling Chan. Quartz syenite crops out as dykes and small bodies on southern Hei Ling Chau, along the eastcoast of Hei Ling Chau, and on both east and west Sunshine Island (Chau Kung To). The largest bodies are on thesouthern ends of both islands, where they are up to 700 m long, and less than 200 m wide.On southern Hei Ling Chau, the quartz syenite trends northeast with an inferred contact against fine-grainedgranite. The contact is obscured by boulders, and no age relationships can be determined. However, on the southerntip of Hei Ling Chau (2266 1147), presumably close to the southern margin of the dyke-like intrusion,medium-grained granite and aplite are cut by fine-grained quartz syenite with a trachytoid texture.On the southwestern tip of Sunshine Island (2306 1325), the quartz syenite has a chilled margin about 50 mm wideagainst feldsparphyric rhyolite. There is a rapid decrease in the feldspar phenocryst content closer to the contact,whereas the older rhyolite appears unchanged at the contact.Small dykes of quartz syenite are common along the east coast of Hei Ling Chau. Some have slightly chilledmargins against the granite country rock. One dyke (2256 1239) is cut by a flow-banded quartzphyric rhyolite dyke,10m wide and trending northeast.Quartz syenite was only seen exposed on the southwest tip of the island, but its presence is inferred from theabundant, dominant corestones which have toppled onto the beach near the northwest tip of the island (237 138).There, the feldsparphyric rhyolite adjacent to the syenite has been strongly deformed. Feldspar megacrysts arestreaked and contorted in a zone over 1 m wide. This is believed to be the result of the younger syenite deformingthe hot, plastic dyke rocks.Abundant boulders of porphyritic quartz syenite disguise the generally deeply weathered outcrop in the southwest."However, in one tumbled block (233 132), the contact between quartz syenite and feldsparphyric rhyolite can beseen. The rhyolite appears to be partially assimilated, or absorbed, by the syenite, and hence is the older rock. Thenorthern margin of the quartz syenite is exposed in a deeply weathered coastal section. It has a chilled margin,about 50 mm wide, in which there is a rapid decrease in the number of feldspar phenocrysts. The older rhyolite hasa distinct margin. Boulders of rhyolite on the point to the south (230 132) suggest that the quartz syenite has acomplex,, dyke-like form, incorporating slivers of older rock.PetrographyThin sections of quartz syenite from across the district are texturally and mineralogically similar.For example HK8117 (1765 1368) from the South Lantau Road contains subhedrai alkalifeldspar phenocrysts 2 to 10 mm long, in a groundmass of alkali feldspar, plagioclase, quartz,mafic and opaque minerals. The groundmass, typically 0.1 to 0.5 mm, forms roughly half therock. Alkali feldspars comprise 62% of the mineral content, mostly sericitized plagioclase only15%, and quartz 15 to 25% (e.g. HK10035, 0170 0804). Quartz rarely occurs as phenocrysts orxenocrysts. Mafic minerals include biotite, usually chloritized (c.5% of the rock), and euhedralhornblende (
Plate 25 - Thin Section of Porphyritic, Granophyric, Fine-grained Granite (HK9900) (08555 02850),fromTaiA Chau ; XPLPlate 26 - Thin Section of Porphyritic Quartz Syenite (HK8348) (22425 11450), from Hei Ling Chau;XPL
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 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: About 1 km east of Nam Shan, exposu
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
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.
Page 138 and 139:
Figure 20 - Areas of Acoustic Turbi
Page 140 and 141:
West Lamma Channel These may be att
Page 142 and 143:
Figure 23 - Depth-Averaged, Maximum
Page 144 and 145:
The formation is Holocene in age. T
Page 146 and 147:
Boreholes (A5/1, A5/2, B2/1, ESC17
Page 148 and 149:
Plate 51 - Deep Weathering Profile
Page 151 and 152:
Chapter 10Economic GeologyIntroduct
Page 153 and 154:
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
Page 163 and 164:
Appendix 2 (continued)Sample HK9913
Page 165 and 166:
Appendix 2 (continued)Sample HK1054
Page 167 and 168:
Appendix 4aSelective normalized pal
Page 169 and 170:
,Appendix 5 -Radiocarbon and Other
Page 171 and 172:
construction materials 151contact m
Page 173 and 174:
molybdenite 149Mong Tung Hang 151Mo
Page 175 and 176:
talus 107,115Tarn Tsui Wan 71,87Tan
Page 177:
LB 555.125 G34 LGeology of Lantaii
show all

1 - HKU Libraries

Create successful ePaper yourself

Delete template?

Save as template?