���������������������������������������������� ������������� ��������� ���������� ���������� ��������� ���������������������������� ������������������������������� ����� EONO MONO OEO」OOHCA」 S口出〉EL hhhh�L峙hn。峙�Lh。oL h Lantau Island and North tung Chung Geology of 出.J. Sewell&P.A.Mirk 10-NW-D，Tungat Conditions Oround of Study & ChungNewTown Offshore Part Sheets9-NE-D，10-NW-A， 10-NW-B， 10-NW-C & 1:5 000Sheets9-SE-A， 9-SE-B OOMN MONO EONO Civil Engineering Department Oeotechnical Engineering Office July 2002 shore 。 Government of the Hong Kong Special Administrative Region

First published July 2002

ISSN xxxx-xxxx

Prepared by:

Geotechnical Engineering Office Civil Engineering Department Civil Engineering Building 101 Princess Margaret Road Homantin， Kowloon Hong Kong

Cover: Oblique aerial view of Tung Chung New Town from above Chek Lap Kok taken in June 1998.

This publication is available from:

Chief Geotechnical Engineer/Planning Geotechnical Engineering Office Civil Engineering Department Civil Engineering Building 101 Princess Margaret Road Homantin， Kowloon Hong Kong

2 Foreword

This report and associated 1:5 000-scale maps specifically relate to development areas in the vicinity of Tung Chung New Town and parts of proposed development areas for Northshore Lantau Island.

The report forms part of the published results of a programme of systematic geological mapping of Hong Kong that began in 1982. It complements geological information contained in the Hong Kong Geological Survey Memoir No. 6 - Geology of Lantau District， and in two Hong Kong Geological Survey Sheet Reports (No. 2 - Geology of Chek Lap Kok， and No. 4 - Geology of North Lantau Island and Ma Wan). These reports have greatly enhanced our understanding of the stratigraphy， structure， and geological history of Hong Kong's rocks. At the same time， they have allowed a geological database， necessary for the continuing economic development of the Hong Kong Special Administrative Region， to be established and developed.

The mapping programme was undertaken by the Hong Kong Geological Survey， which is a section of the Planning Division of the Geotechnical Engineering Office， Civil Engineering Department. The section was led by Dr C.J.N. Fletcher and the Division was under the direction of Dr R.P. Martin during the mapping project reported here. The report was subsequently written and compiled by Dr R.J. Sewell and Mr P.A. Kirk， at which time the section was led by Dr S.D.G. Campbell and the Division was under the direction of Mr H.N. Wong.

The 1:5 000-scale onshore geological survey of Tung Chung was conducted by Mr P.A. Kirk， who also managed a consultancy， on behalf of the Territory Development Department， and undertaken by members of the British Geological Survey， to study complex ground conditions at Tung Chung New Town. Some of the information from the consultant's study is incorporated in this report. Much helpful advice and review comments were also given by GEO colleagues， including Mr K.W. Lai and Dr X.C. Li.

The Survey benefitted from the co-operation of many organizations and individuals. In particular， the co- operation of Mott Macdonald (Hong Kong) Ltd， Scott Wilson (Hong Kong) Ltd， the Airport Authority， Electronic and Geophysical Services Ltd， and Cosine Ltd.， is gratefully acknowledged.

This report and the accompanying map sheets will be of interest and value to earth scientists， engineers， planners， developers and educators.

R. K. S. Chan Head of the Geotechnical Engineering Office July 2002

3 4 CONTENTS Page

Title Page 1 Foreword 3 Contents 5 Map and Report Series Notes 9 Chapter 1 Introduction 11 Location and Physiography 11 Previous Work 12 Complex Ground Conditions at Tung Chung 12 The Northshore Lantau Development Feasibility Study 12 Offshore Geophysical and Marine Ground Investigations 14 Purpose and Scope of Study 14 Data Sources 14 Chapter 2 Outline of Geology 1勻 Chapter 3 Palaeozoic Sedimentary Rocks 23 San Tin Group (Carboniferous) 23 Classification and Distribution 23 Lok Ma Chau Formation 23 Yuen Long Formation 23 Tolo Harbour Formation (Permian) 24 Chapter 4 Mesozoic Sedimentary and Volcanic Rocks 25 Tai O Formation 25 Tsuen Wan Volcanic Group 25 Yim Tin Tsai Formation 25 Lantau Volcanic Group 26 Chapter 5 Intrusive Igneous Rocks 28 Classification and Distribution 28 Major Intrusions 28 Granite 28 Lantau Granite 29 Chek Lap Kok Granite 29 Quartz Monzonite 30 Tong Fuk Quartz Monzonite 30 Minor Intrusions 31 Feldsparphyric Rhyolite 31 Porphyritic Microgranite 32 Quartzphyric Rhyolite 32 Aplite 32 Quartz Veins 33 Mafic Dykes 33

5 Chapter 6 Structure 34 Folds 34 Faults 34 Photolineaments 36 Joints 36 Chapter 勻 Metamorphism and Alteration 39 Thermal Metamorphism 39 Hydrothermal Metamorphism 39 Chapter 8 Superficial Deposits and Weathering 40 Classification and Distribution 40 Onshore Superficial Deposits 41 Slope Debris 41 Alluvial Sediments 41 Beach Deposits 42 Intertidal Deposits 42 Offshore Superficial Deposits 42 Tung Chung Formation 42 Chek Lap Kok Formation 43 Sham Wat Formation 45 Hang Hau Formation 45 Weathering 4勻 Chapter 9 Complex Ground Beneath the Tung Chung Reclamation 48 Introduction 48 Tung Chung Study 48 Data Sources 50 Developing the Geological Model 50 Xenoliths 50 Weathering 50 Karst 51 Complex Ground Conditions at Site 3 52 Laminated Deposits 52 Diamict 52 Sand and Gravel 52 Model for Formation of Karst Deposits at Site 3 52 Ground Investigation Techniques 53 Implications of the Revised Geological Model 55 Complex Ground Conditions in Areas Adjacent to Tung Chung 55 Chapter 10 Economic Geology 5勻 Non-metalliferous Minerals 5勻 Metalliferous Minerals 5勻 Construction Materials 58

6 References 59 Index 62 Appendix Lexicon of Terms Used for Drillcore Logging and Surface 64 Mapping at Tung Chung， Lantau Island， Hong Kong by M.R. Gillespie， A.J. Humpage， and R.A. Ellison List of Tables Table 1 Grain-size Description and Classification of Rocks and Superficial 10 Deposits in Hong Kong

2 Summary of the Onshore and Offshore Stratigraphy of the District 18

3 Whole-rock Major- and Trace-element Geochemistry for Representative 20 Rock Types in the Tung Chung District. Major Oxides in wt%， Trace Elements in ppm

List of Figures Figure

1 Location Map of Major Infrastructure Developments Related to Tung Chung 11 New Town and Northshore Lantau Island

2 Traverses Undertaken During 1968， 1988-89 and 1991-92 Field Surveys 13

3 Locations of Boreholes Drilled for Tung Chung New Town and Northshore 15 Lantau Island Infrastructure Developments

4 Locations of Seismic Lines around Northshore Lantau Island 16

5 Simplified Onshore Geology of the District 19

6 Simplified Seabed Sediment Map of the District 22

勻 Generalized Classification and Nomenclature of Selected Major and Minor 28 Intrusive Rocks (after Le Maitre， 1989)

8 Principal Structural Features of Tung Chung and Northshore Lantau Island 35

9 Contoured Pole Plots of Joints Measured for All Rock Types on Tung Chung 3勻 and Northshore Lantau Island (after Woods， 1993). a) Sha Lo Wan to Hau Hok Wan， b) Hau Hok Wan to Tin Sam， c) Tung Chung to Lau Fau Sha， d) Lau Fau Sha to Kei Tau Kok， and e) Kei Tau Kok to Pak Mong

10Schematic Section Showing the Relationship between Superficial40 Deposits and the Different Environments of Deposition

勻 11 Location Map Showing the Distribution of the Tung Chung Formation 44 Determined from Interpretation of Gravity and Borehole Data (Modified after Kirk et al.， 2000)

12 Distribution and Isopachs (in Metres) of the Hang Hau Formation 46

13 Location Map of Part of the Tung Chung East Reclamation Potentially 49 Underlain by Complex Geological Conditions

14 Examples of Different Interpretations of Problematic Materials Encountered in 51 Boreholes Drilled at various locations at Site 3 of the Tung Chung East Reclamation

15 Schematic Representation of the Development of Karst Deposits Beneath 53 Tower 5， Site 3， Tung Chung East Reclamation (after Figure 6 in Fletcher et al.， 2000)

16 Simplified Averaged Rockhead Models (Top of Grade III or Lower) for 54 Offshore Parts of the District Based on 3-D Modelling of the Terrain Corrected Bouguer Anomaly (after EGS 1999a， 1999b)

1勻 Volcanotectonic Map of Hong Kong (c.146 Ma) Showing the Distribution of 56 the Tung Chung and Ma On Shan Marble Subcrops and Major Faults that Were Active During Emplacement of Rocks Belonging to the Lantau Volcanic Group and Kwai Chung Suite (Modified after Kirk， 2000).

List of Plates Plate

1 Steeply-dipping and Deformed， Fine-grained Metasandstone and 24 Carbonaceous Metasiltstone of the Lok Ma Chau Formation Exposed on Tsz Kan Chau (1588 2085)

2 Altered， Silicified， Banded Coarse Ash C rystal Tuff Exposed on Pok To Yan 26 (1350 158勻)

3 Fine- to Medium-grained Lantau Granite from a Borehole South of Ha Law 29 Wan (1131 1勻16)

4 Thin Section of Fine- to Medium-grained Lantau Granite from Pak Sha Tsui， 30 Tung Chung (HK 9236， 1131 1698); XPL

5 Fine-grained Chek Lap Kok Granite from Tin Sam (HK 9252， 0945 1勻09) 30

6 Fine-grained， Porphyritic Tong Fuk Quartz Monzonite from Sha Lo Wan (HK 31 1006勻， 0812 1633)

勻 Thin Section of a Mafic Dyke from Hau Hok Wan (HK 923勻， 1156 1勻2勻) 33

8 Tung Chung Wan from the Northwest Showing Quaternary Superficial Deposits 43 Composed of Intertidal Deposits in the Foreground， and Beach Deposits and Alluvial Deposits in the Background. (Photo taken on 5.12.1989)

8 Map and Report Series Notes

This report describes the geology of central Lantau Island in the vicinity of Tung Chung New Town and the offshore parts of the North Lantau coast between Chek Lap Kok and Yam O. The report should be read in conjunction with the 1:5 000-scale Geological Maps 9-SE-A and 9-SE-B (revised 2002). The 1:20 000- scale Geological Map Sheet 9 (Chek Lap Kok)， and Memoir 6， Geology of Lantau Island， also include relevant information on the geology of the area.

This report forms one of a series that records findings of the Hong Kong Geological Survey. An index of the 1:5 000-scale Geological Maps to which this report relates is shown below.

The symbols for major rock units on the maps have been revised from the first edition maps in order to be consistent， where possible， with the symbols used in the recently published 1:100，000-scale geological map (Sewell et al.， 2000). A prefix is used to indicate the age of the rocks， followed by lower-case letters to indicate: (i) the group， where appropriate， and/or (ii) the formation name. Prominent stratigraphic beds within the Mesozoic volcanic succession are indicated by a lower-case letter (or letters) denoting the dominant lithology.

The symbols for superficial deposits on the maps comprise a prefix to indicate the age of the sediments， followed by superscripted lower-case letters to indicate environment of deposition and upper-case letters to indicate material. Ages of the sediments are interpreted as Pleistocene (Qp)， Holocene (Qh) and Quaternary undivided (Q). The environments of deposition seen in the district are interpreted to be colluvial (Df)， alluvial (a)， beach (b)， intertidal (i)， and marine (m). The materials of colluvium (Df， slope debris) include boulders， cobbles， gravel， sand， and silt. The materials of alluvial， beach， intertidal， and marine environments， are dominantly sand (S) and mud (M).

Onshore superficial deposits are not generally considered mappable if less than 2 m thick. This minimum thickness is also used as a mapping criterion for offshore sediment.

Most place names referred to in the text are shown on Figure 2. Grid references cited for specific localities are based on the Hong Kong 1980 Metric Grid as shown on the 1:5 000-scale Geological Maps. Eight-figure references indicate positions to the nearest 10 m， with Eastings followed by Northings， eg 2200 2230.

All onshore and offshore levels and depths are reduced to Hong Kong Principal Datum (PD)， which is 1.2 m below Mean Sea Level and 0.15 m above Admiralty Chart Datum.

Samples in the SAR-wide rock collection archived by the Hong Kong Geological Survey are prefixed HK followed by the serial number， eg HK 98勻2.

Boreholes are generally referred to by the drilling contractor's number followed by the Geotechnical Information Unit (GIU) accession number， or Works Order number (WO)， for the relevant ground investigation report， eg 5SW32/13464. The GIU is located in the Civil Engineering Library of the Civil Engineering Department and is maintained by the Geotechnical Engineering Office， Civil Engineering Department.

The system used in this report for grain-size description and classification is summarized in Table 1.

9 Table � � Grain Size Description and Classification of Rocks and Superficial Deposits in 0ong Kong

Solid Rocks Grain Superficial Size Deposits Igneous Rocks Metamorphic Rocks mm Sedimentary Pyroclastic Rocks Rocks Acid Acid-Intermediate Intermediate Basic Other Foliated Other Pyroclastic Boulders Brecia, Sedimentary Agglomerate Cobbles 200 Pegmatite Breccia, Very 10 Coarse 60 Conglomerate Coarse Quartz Quartz Gabbro Quartzite, Gravel Medium 20 Lapilli- TuffCoarse Syenite Schist Syenite Monzonite Marble, Fine 6 Medium Granite Granodiorite Hornfels, Fault Coarse 2 gouge, 0.6 Coarse Ash Sand Medium Sandstone Fine Lamprophyre Fault 0.2 Tuff Microgabbro breccia Fine Aplite, Micro- 0.06 Microgranitegranodiorite Very Silt Siltstone Fine Mud Mudstone Fine, Rhyolite Dacite Quartz Trachyte Quartz Andesite Basalt Mylonite, Ash Tuff 0.002 Aphanitic Trachyte Latite Phyllite Clay Claystone Rhyodacite