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Geotechnical Engineering OfficeCi viI Enginee ring D epartmen tHONG KONG August 1992

@ Government of Hong KongPublished

August 1992

Prepared by:

Geotechnical Engineering Office11fF Civil Engineering Building101 Princess Margaret RoadHomantin, KowloonHong Kong

Cover: Oblique aerial viewof Yuen Long and Tin Shui Waiin 1987

This publication is available from:

Hong Kong Geological SurveyGeotechnical Engineering Office11fF Civil Engineering Building

101 Princess Margaret RoadHomantinKowloonHong Kong

This report specifically relates to the Designated Area, which is the part of the northwest NewTerritories defined by the Hong Kong Geological Survey in 1987 as possibly underlain by marble. Thegeology of the area is depicted on twenty sheets of the 1:5 000 Geological Map Series HGP5A andHGP5B. The 1:20 000 Geological Map Sheets 2 (San Tin), 5 (Tsing Shan) and 6 (Yuen Long), andMemoir No.3, Geology of the Western New Territories, also include information about the geology ofthe area covered by the report.

This report forms part of the published results of a programme of systematic geological mapping thatbegan in 1982. This work has greatly enhanced our understanding of Hong Kong's stratigraphy andstructure, and is establishing the geological database necessary for the continuing economicdevelopment of the Territory. The mapping programme is being undertaken by the Hong KongGeological Survey, which is a section of the Planning Division of the GCO. The section was led byMr P. J. Strange and the Division was under the direction of Dr A. D. Burnett during the mappingproject reported here.

The 1:5 000 scale geological survey of the Designated Area was conducted by Dr D. V. Frost of theBritish Geological Survey under a consultancy agreement between Hong Kong Government and theNatural Environment Research Council, United Kingdom. Dr Frost was assisted by Ms N. J. Darigo,Mr D.K.M. Yuen and Mr A.H.P. Chau of Dames & Moore (Hong Kong), and the project wasundertaken between May 1988 and April 1990. Prior to this, preliminary work in the Designated Areahad been carried out by Mr K. W. Lai and Dr R. L. Langford of the Hong Kong Geological Survey.

The Survey benefitted from the co-operation of many organizations and individuals. The co-operationof Dr L. J. Endicott and staff of Dames & Moore (Hong Kong), Acer Freeman Fox Ltd, Binnie &Partners, Fugro (Hong Kong) Ltd, Maunsell Geotechnical Services Ltd, Ove Amp & Partners (HongKong) Ltd, and Electronic and Geophysical Services Ltd is gratefully acknowledged.

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

A. W. MalonePrincipal Government Geotechnical EngineerApril 1992

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2323232525262627

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Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Title Page

Foreword

Contents

Map and Report Series Notes

Introduction

Location and Physiography

Previous Work

The Designated Area Project

Outline of Geology

Sedimentary and Volcanic Rocks

Palaeozoic Rocks of the San Tin GroupClassification and DistributionY uen Long Formation

Long Ping MemberMa Tin Member

Lok Ma Chau FormationMai Po MemberTai Shek Mo Member

Mesozoic Sedimentary and Volcanic Rocks

Metamorphic and Igneous Rocks

Metamorphic RocksRegional MetamorphismThermal MetamorphismMetasomatism

Intrusive Igneous RocksGranitoid Rocks and Heat Generation

Structure

Granite Plutons

Volcanic Rocks

Folds

Faults and Joints

Superficial Deposits

Classification and Distribution

Clay Residues

Debris Flow Deposits

Alluvium

Marine Deposits

Estuarine Deposits

Karst

Reactivation of Karst Features

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56

56

56

56

Chapter 8 HydrogeologyInuoduction

Groundwater Characteristics

Water Quality

References 59

62

Index 67

Appendix

1

2

3

62

64

64

4

5

6

7

Abbreviated Borehole Logs

Classification of Zircons by Colour and Morphology

Heavy Minerals in Cavity Fill and Associated Sedimentsin the Marble of Yuen Long

Microfossil Determinations of Samples from the Carboniferous San Tin Group

Minerals from Insoluble Residues from Yuen Long Marbles

Heavy Minerals from Sandstones in the Yuen Long Area

Carbon 14 Dating of Quaternary Deposits in the District

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65

66

66

List of TablesTable

10

2

Grain Size Description and Classification of Rocks and Superficial Depositsin Hong Kong

Solid Rocks and Superficial Deposits of the District 19

11

12

3

4

15

2021

24

33

5

6

73435

36

38

8

9

6

Figure

1 Location Map of the Original Designated Area, as at 30 October 1987

2 The Redefined Designated Area in the Northwest New Territories(Scheduled Area No.2)

Location of Boreholes (BGS) Drilled for the Marble Project

Generalised Solid Geology(a) Yuen Long(b) Lok Ma Chau

Generalised Section of the San Tin Group

Ribbon Section Showing the Structural Framework of the Designated Area

Main Structural Features of the District(a) Yuen Long(b) Lok Ma Chau

Marble/Granite Association in a Site Near Tin Shui Wai

Structure of the Long Ping Estate, Yuen Long

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40

1011

1213

14

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43

44

15

45

16

1746

47

1850

19

51

20 52

2122

53

55

23

2457

58

Rose Diagram of Faults of the Yuen Long District

Graph Showing Frequency and Inclination of Joints in theMa Tin Road Borehole

Contours on the Base of the Superficial Deposits

Ribbon Section Showing the Superficial Deposits Typical of the District

Contour Map Showing the Base of the Alluvial Deposits Suggesting aPalaeogeography of Meandering Channels

Contours and Isopachytes of Superficial Deposits Overlying Marble ofSite YLTL 313 on the Yuen Long Industrial Estate

Generalised Thickness of Marine Deposits in the District

Generalised Rockhead Contours of the Carboniferous Strata around Yuen LongBetween Marble and Granodiorite Located at Site YLTL313,Yuen Long Industrial Estate

Karst Features on Part of Site YLTL 313, Wang Lok Street,Yuen Long Industrial Estate

Rockhead Contours and Section Showing a Doline Developed along theFaulted Boundary

Contour Map of the Top Karstic Surface of the Marble at Site YLTL 442adjoining Hop Hoi Street, Yuen Long

Cavity Infill Deposits from a Mazier Sample in BGS 2Large

Area of Soft Silt Formed at the Thrust Boundary Between the Mai Po andMa Tin Members of the San Tin Group. Site YLTL 446, Yuen Long

The Shan Poi River Catchment, Yuen Long

Schematic Model of Groundwater Flow Beneath Yuen Long

List of Plates

Plate

1 13

14

16

3

4 17

5

22

6 22

7

2526

27

8

9

10 27

112812

Yuen Long Looking South from the Industrial Estate

Fish and Duck Ponds Northeast of Fairview Park

Large Block of Karst Marble (inverted Ma Tin Member) Excavated from theRockhead at the LRT Site, Yuen Long

Marble Quarry near Shenzhen Showing Palaeokarst Scarp and Dip Topography.A Small Doline Depression on the Extreme Left is Filled with Superficial Deposits

Highly to Completely Weathered Metasiltstone of the Mai Po Member ShowingLiesgang Rings in Ferruginous Concretions; BGS 17, 52.90-53.90 m

Highly to Completely Weathered Metasiltstone of the Mai Po Member ShowingSecondary Growth of Manganese Dioxide (Pyrolusite); BGS17, 42.90-43.90 m

Marble From the Long Ping Member, Yuen Long Fonnation; BGS2

Marble From the Ma Tin Member, Yuen Long Fonnation; BGS3

Metasiltstone and Metasandstone of the Mai Po Member, Lok Ma Chau Fonnation;BGSll,112.55-117.50 m

Graphite Schist of the Mai Po Member, Lok Ma Chau Fonnation, with ProminentWhite Quartz Veins; BGS27, 51.10-54.75 m

Highly to Completely Weatherd Tuffaceous Siltstone with Clasts of Marble,Tin Shui Wai Member, Tuen Mun Formation; BGS8, 91.80-97.40 m

Interbedded Tuffite and Marble-bearing Breccia, Tin Shui Wai Member,Tuen Mun Fonnation; BGS18, 40.62-44.24 m

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29

48

48

13

14

15

16

Veined and Fractured Marble Closely Overlying Granodiorite; BGS9. 45.25-49.46m

Granodiorite Showing Stained Joints; BGS6. 22.66-26.17 m

Karst Features in Borehole Cores: Solution Feature Showing Feffilginous Staining

Karst Features in Borehole Cores: Solution Widened Joint Showing Fretted Surface

8

.This report describes the geology of part of the western New Territories and should be read inconjunction with the 1:5 000 Geological Maps 2-NE-D, 2-SW-C, 2-SW-D, 2-SE-A, 2-SE-B, 3-NW-C,6-NW-A, 6-NW-B, 6-NW-C and 6-NW-D. The 1:20000 Geological Map Sheets 2 (San Tin), 5 (TsingShan) and 6 (Yuen Long), and Memoir No.3, Geology of the Western New Territories, also includerelevant information on the geology of the Yuen Long area.

.The report forms one of a series that records the findings of the Hong Kong Geological Survey. Anindex of the 1:5 000 Geological Maps to which this report relates is shown below. This reportspecifically relates to the Designated Area (Figure 1), which is an area defined by the Hong KongGeological Survey as an envelope within which the presence of a marble subcrop containing cavitieswas possible. The boundaries of the Designated Area were based upon the geological informationavailable on 30 October 1987, comprising both borehole data from ground investigations as well assurface exposures. On completion of this present survey the envelope of marble subcrop was redefined,and following amendment of the Buildings Ordinance and Regulations is known as Scheduled AreaNo.2 (Figure 2).

~

.+. .' '2-NE-D~

2-SE-B

3-NW-C I

6-NW-A 6-NW-B I

6-NW-C 6-NW-D I

.Onshore superficial deposits are not generally considered mappable if less than 2 m thick.

.Grid references are based on the Hong Kong 1980 Metric Grid as shown on the 1:5 000 GeologicalMaps. Eight-figure references indicate positions to the nearest 10 m, with Eastings followed byNorthings, eg, 26722739. Six-figure references indicate positions to the nearest 100 m.

.Hong Kong Principal Datum (PD) is 1.2 m below Mean Sea Level and 0.15 m above AdmiraltyChart Datum.

.Samples in the Territory-wide rock collection archived by the Hong Kong Geological Survey areprefixed HK followed by the serial number, eg, HK 2263.

.Boreholes are generally referred to by the drilling contractor's number followed by the GeotechnicalInformation Unit (GIU) accession number for the relevant ground investigation report, eg 1201D/03412.Boreholes with the prefix BGS were specifically drilled for the Hong Kong Geological Survey. TheGIU is located in the Civil Engineering Library of the Civil Engineering Department and is maintainedby the Geotechnical Engineering Office.

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

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