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RhyoliteDescriptionAcid igneous rock which is compositionally identical to granite but in which individual crystals in thegroundmass are too fine grained to be distinguished by the unaided eye.Key diagnostic features :(i) Crystals in the groundmass are too fine grained to be distinguished by the unaided eye.(ii) No (or very few) phenocrysts.(iii) siliceous, does not scratch with a steel knife.(iv) Flow banding may be discernible.(v) Fresh rock is dark grey to black. Alteration changes the colour to grey, purple or pink.CommentsRhyolite containing no phenocrysts is relatively rare in the Tung Chung drillcores. It is observed mostcommonly along the 'chilled' margins of feldsparphyric rhyolite bodies.Reference sample no. : No sample.Coarsely feldsparphyric rhyoliteDescriptionRhyolite (see Section 2.19) with abundant phenocrysts of feldspar, mostly 5-25 mm.Key diagnostic features:(i) As rhyolite, but with abundant phenocrysts of feldspar (iquartz), mostly 5-25 mm.CommentsFresh rock has a distinctive appearance : white and grey phenocrysts in a dark grey groundmass (Plate 15a).With slight alteration, the phenocrysts become pinkish and the groundmass alters to greyish-green, or greyishpurple (Plates 15b and 15c). Pervasive weathering turns the groundmass to orange-brown (Plate 16a).Intensely altered coarsely feldsparphyric rhyolite containing pyrite and galena (Plate 16b) occurs in andnear to borehole A-18 in Site 4. A texturally modified variant of coarsely feldsparphyric rhyolite, in which'phenocrysts' of feldspar and quartz have irregular, curved outlines, occurs rarely in Tung Chung drillcores.Reference sample no. : 14, 7, 2, 13, 1980
Plate A 15a - Typical fresh coarsely feldsparphyric rhyolite. Tung Chung, Site 5; Drillcore D-23; Box 7,57.3 m% 3t a 19 2O i? 1P/ate A15b - Typical altered coarsely feldsparphyric rhyolite. Tung Chung, Site 5; Drillcore E-84; Box 3,48.05 mPtoe A15c - Typical altered coarsely feldsparphyric rhyolite. Tung Chung, Site 5; Drillcore E-44; Box 3,33.55 m81
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THE UNIVERSITY OF HONG KONGLIBRARIE
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,11 DEC'£• Government of the Hon
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CONTENTSPageTitle Page 1Foreword 3C
Page 10:
11 Location Map Showing the Distrib
Page 18 and 19:
Seismic reflection line8Onshore are
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Table 2 - Summary of the Onshore an
Page 23:
These faults offset the caldera bou
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Chapter 4Mesozoic Sedimentary and V
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Tuffite. A prominent outcrop of ban
Page 31 and 32: Lantau GraniteThe Lantau Granite is
Page 33 and 34: " .-.": •' - • • *"» JI i I
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
Page 84 and 85: Plate A 16a - Pervasively weathered
Page 86 and 87: 1 f < 1 9 2 OPlate A 18b - A Itered
Page 88 and 89: 2 1 2 2Plate A21 - Lamprophyric roc
Page 90 and 91: Residual soil derived from metasedi
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