Plate 4 - Thin Section <strong>of</strong> Fine- to Medium-grained Lantau Granite from Pak Sha Tsui, Tung Chung (HK9236,1131 1698); XPLQuartz MonzoniteSmall intrusions <strong>of</strong> quartz monzonite crop out at the faulted contact between the Lantau Volcanic Group andother rocks south <strong>of</strong> Sha Lo Wan and Hau Hok Wan.Tong Fuk Quartz Monzonite<strong>The</strong> Tong Fuk Quartz Monzonite crops out in a series <strong>of</strong> discontinuous stocks along the faulted contactbetween the Lantau Volcanic Group and other rocks. Major outcrops occur at Sha Lo Wan on the westernside <strong>of</strong> Lantau Island and at Tong Fuk on the eastern side <strong>of</strong> Lantau Island (Plate 6). Smaller outcrops arefound at Fan Lau and Pui O.2i, i . t . i j l . i 1..A..1. i . j i3 l L 1,,,) .1. i .1 i44 l i ii . » i b lPlate 5 - Fine-grained Chek Lap Kok Granite from Tin Sam (HK9252, 0945 1709)30
" .-.": •' - • • *"» JI i I • i , I , I ,3| , I , I , J ,4| , I , I . ,.J._i?L6 - Fine-grained, Porphyritic Tong Fuk Quartz Monzonite from Sha Lo Wan (HK10067, 0812 1633)<strong>The</strong> Tong Fuk Quartz Monzonite is typically fine-grained and porphyritic, with roughly equal abundances<strong>of</strong> alkali feldspar and plagioclase phenocrysts, although alkali feldspar usually predominates. Roundedmafic enclaves composed mostly <strong>of</strong> quartz microdiorite, are common. In the Sha Lo Wan area, the quartzmonzonite locally may vary to porphyritic fine-grained granite, but it is distinguished by the presence <strong>of</strong>scattered alkali feldspar phenocrysts with prominent twinning. In places, the quartz monzonite has beenhighly weathered to a reddish brown soil.In thin section, euhedral to subhedral alkali feldspar phenocrysts (1-7 mm) display well-developed Carlsbadtwins and are weakly zoned. Plagioclase phenocrysts are strongly zoned with sericitized andesine cores andalbite rims. <strong>The</strong> matrix is generally granular and fine- to very fine-grained and comprises quartz and alkalifeldspar, with subordinate plagioclase. <strong>The</strong> mafic minerals consist <strong>of</strong> greenish brown biotite and rare brownamphibole. Biotite is commonly altered to chlorite. Accessory minerals include zircon, fluorite, titanite,apatite, allanite, epidote, and Fe-Ti oxide.A sample <strong>of</strong> quartz monzonite from Tong Fuk has yielded a U-Pb single zircon age <strong>of</strong> 140.4 ± 0.3 Ma.Minor IntrusionsWith the exception <strong>of</strong> mafic dykes, the minor intrusions <strong>of</strong> the district are divided on the basis <strong>of</strong> texture int<strong>of</strong>eldsparphyric rhyolite, porphyritic microgranite, and quartzphyric rhyolite. <strong>The</strong> felsic dykes are present asa dense swarm <strong>of</strong> strongly eastnortheast-westsouthwest-oriented multiple intrusions cutting granitic andvolcanic rocks. <strong>The</strong> dykes were intruded in at least three pulses and show evidence for compositional zoning(Li et ah, 2000). Composite intrusions, featuring a felsic phase injected into a more mafic one, are sometimesobserved. None <strong>of</strong> the dykes in the district have been dated. However, rhyolite dykes to the northeast <strong>of</strong> thedistrict have returned ages <strong>of</strong> 146 Ma which suggests that the age <strong>of</strong> emplacement is synchronous with that<strong>of</strong> the Lantau Volcanic Group.Feldsparphyric RhyoliteFeldsparphyric rhyolite is the general term given to dykes ranging in composition from rhyodacite to highsilicarhyolite which contain abundant feldspar (±quartz) phenocrysts (
- Page 2 and 3: THE UNIVERSITY OF HONG KONGLIBRARIE
- Page 4 and 5: ,11 DEC'£• Government of the Hon
- Page 7: CONTENTSPageTitle Page 1Foreword 3C
- Page 10: 11 Location Map Showing the Distrib
- Page 18 and 19: Seismic reflection line8Onshore are
- Page 20 and 21: Table 2 - Summary of the Onshore an
- Page 23: These faults offset the caldera bou
- Page 27 and 28: Chapter 4Mesozoic Sedimentary and V
- Page 29 and 30: Tuffite. A prominent outcrop of ban
- Page 31: Lantau GraniteThe Lantau Granite is
- Page 35 and 36: Quartz VeinsQuartz veins are ubquit
- Page 37 and 38: LEGENDOoI2PhotolineamentFaultConcea
- Page 39 and 40: No. of Joints measured=82No. of Joi
- Page 41 and 42: Chapter 7Metamorphism and Alteratio
- Page 43 and 44: Offshore superficial deposits withi
- Page 45 and 46: Plate 8 - Tung Chung Wan from the N
- Page 47 and 48: Sham Wat FormationThe formation, kn
- Page 49 and 50: to infill depressions and channels
- Page 52: ased on recommendations contained i
- Page 57 and 58: over a wider area. The survey resul
- Page 59 and 60: Chapter 10Economic GeologyEconomic
- Page 61 and 62: ReferencesAllen, P.M. & Stephens, E
- Page 63 and 64: Li, X.C., Sewell, RJ. & Fletcher, C
- Page 65 and 66: microgranite, 17, 28, 31, 32, 48 Tu
- Page 67 and 68: Marine sedimentDescriptionUnconsoli
- Page 73: Plate Ala- Marble. The generally da
- Page 76 and 77: Plate A9 - Skarn from Site 3 showin
- Page 78 and 79: 1 8Plate Alia - Cavity-fill deposit
- Page 80 and 81: Plate A12b - Pervasively weathered
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RhyoliteDescriptionAcid igneous roc
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Plate A 16a - Pervasively weathered
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1 f < 1 9 2 OPlate A 18b - A Itered
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2 1 2 2Plate A21 - Lamprophyric roc
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Residual soil derived from metasedi
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