british geological d programme the limestone resources … · ahononou quarry, tongatapu. note the...

BRITISH GEOLOGICAL SURVEY

TECHNICAL REPORT WC/93/23

Overseas Geology Series

ODA/BGS R & D PROGRAMME PROJECT NO 91/4

THE LIMESTONE RESOURCES OF TONGATAPU AND VAVA’U, KINGDOM OF TONGA

BY

D J HARRISON

This report was prepared for the Overseas Development Administration

Cover Illustration: Coralline Limestone, Pili Quarry, Tonga (November 1991)

Geographical Index: SW Pacific, Kingdom of Tonga, Tongatapu, Vava’u

Subject Index: Limestones, Mineral Resources, Aggregates, Quarrying, Environment

Bibliographic Reference Harrison D J 1993. The Limestone Resources of Tongatapu and Vava’u, Kingdom of Tonga. British Geological Survey Technical Report WC/93/23

NERC Copyright 1993

Keyworth, Nottingham - British Geological Survey

CONTENTS

EXECUTIVE SUMMARY

INTRODUCTION

GENERAL GEOLOGY OF THE LIMESTONES

LIMESTONE QUARRYING IN TONGA

Production of Limestone Quarry Production Methods

LIMESTONE RESOURCES

Resource Assessment Data Aggregate Properties Chemical Properties

QUARRY PLANNING

Limestone Quarrying and the Environment Planning Controls on Quarrying Operations in Developed Countries Recommended Planning Guidelines for Quarrying in Tonga

CONCLUSIONS

RECOMMENDATIONS

BIBLIOGRAPHY

APPENDIX

1. Description of Quarries 2. Petrographic Descriptions 3. Aggregate Testing Procedures

1

3

6

6 10

13

13 15 18

22

22 23 23

26

27

29

31 34 37

FIGURES

1 Location Map 2 3

Distribution of quarries on tongatapu Distribution of quarries on Vava’u

TABLES

1 2 3 4 5 6 7 8 9 10

Limestone production in the Kingdom of Tonga (1988-1991) Structural layers in road construction Test procedures for limestone aggregates Typical specification requirements for roadstone aggregates Physical properties of limestone aggregates from Vava’u and Tongatapu Mechanical properties of limestone aggregates from Vava’u and Tongatapu Classification of coralline limestone aggregates in the Kingdom of Tonga Classification of limestones by calcium carbonate content (Harrison, 1992) Chemical analyses of quarried limestones from Vava’u, Kingdom of Tonga Chemical analyses of quarried limestone from Tongatapu, Kingdom of Tonga

PLATES

1

2 3 4

5 6

7

8 9 10

Neiafu, Vava’u from the air, showing Vaipua Landing Quarry and the recently constructed causeway. The proposed site (Mata’ihoi) for a new quarry is situated at the waters edge in the northwest of the photograph. The steep limestone cliffs on the northern coast of Vava’u. Crushed limestone chippings, Ahononou Quarry, Tongatapu. Concrete blocks made from Fiji cement, local beach sand and quarry ’fines’, Neiafu, Vava’u. Topsoil contaminating quarried limestones, Fualu, Tongatapu. Ahononou Quarry, Tongatapu. Note the piles of large blocks of hard coral/algal limestone which remain unprocessed. Crusher and screens at Pili Quarry, Tongatapu. Note large pile of fines (by the figure) produced during processing. Screen at Vaipua Landing Quarry, Vava’u. Rubbly, coral/algal limestones. South Malapo Quarry, Tongatapu. Vughy, porous, rubbly limestones. South Malapo Quarry, Tongatapu.

2 4 7

10 10 14 14 16 17 17 20 20 21

8 8 9

9 11

11

12 12 19 19

INTRODUCTION

Many low-lying coralline islands in the southwest Pacific have few indigenous sources of building and civil engineering materials. In 1990 a project was formulated to address the problems of aggregates supply using the Kingdom of Tonga as a model for the region. The study, ’Evaluation of Aggregate Potential on Coralline Islands in the Southwest Pacific’, Project No. 91/4, commenced in 1991. It was funded by the Overseas Development Administration (ODA) under the ODABritish Geological Survey (BGS) Research and Development Programme, as a contribution to the British Government’s programme of technical assistance to developing countries.

The original proposal envisaged five main objectives;

1. 2. 3.

4.

5.

To map and report on the limestone resources of the main Tongan islands. To assess present coralline sand resources and identify alternative sand sources. To set up a land and nearshore database for archiving requisite data to serve the production of geological and land-use maps. To provide advice and assistance to local geologists to upgrade their approach to bulk minerals and assessment. To raise the profile of bulk mineral studies in the field of geological aid projects.

A preliminary visit to Tonga and Fiji was undertaken during November 1991 (Tappin and Harrison, 1991) with the aim of gathering all available data to reappraise the Project objectives. During this visit, discussions were held at the South Pacific Applied Geoscience Commission (SOPAC) office in Fiji and at offices of the relevant Government Departments in Tonga. Some preliminary field inspections of the beaches and quarries on Tongatapu, Ha’apai and Vava’u were also undertaken at this stage.

The reconnaissance visit resulted in some modification of the original project objectives to take account of recent developments in research into aggregate resources in Tonga. Two new reports, one on limestone resources (by the New Zealand Department of Scientific and Industrial Research, DSIR) and another on offshore sand resources (by SOPAC), modified the need for a major BGS contribution in these fields. However, although the DSIR report provided a general account of the limestone resources in Tonga, it lacked any quantitative investigation of the physical, mechanical and chemical properties of the limestones and any systematic evaluation of aggregates production in Tonga. The aims of the project were therefore reappraised and it was decided that efforts should focus on three main areas: beach sand assessment; limestone aggregate evaluation; and minerals planning guidance. The training of local personnel in aggregate assessment remained an important aspect of the Project.

This report presents the results of those parts of the Project concerned with the evaluation of limestone resources and the limestone quarrying industry in Tonga. It summarises the field investigations carried out in Tonga in October 1992 and laboratory-based studies undertaken at BGS Keyworth between November 1992 and February 1993. It should be read in

British Geological Survey Coastal Geology Group

1 The limestone resources of Tongatapu and Vava’u

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176" M U BASIN 174OW

laos

1 9 O

2$

21°

Figure 1 Location Map

conjunction with the separate report (Tappin, 1993, in preparation) detailing the survey of beach sand resources on the main Tongan islands.

The principal aims of the field visit were to collect samples of limestones from quarries and exposures on Vava’u and Tongatapu, to collect information on limestone production statistics and to make a general assessment of the environmental effects of quarrying limestone in Tonga. The geology and lithological variability of the limestones at each site were also studied and quarry production methods noted.

The laboratory programme was designed to evaluate fully the physical and mechanical properties of the limestones and to assess their anticipated in-service performance as aggregates. Test results were complemented by petrographic descriptions and detailed chemical analyses. The programme will provide data of direct use to the civil engineering industry for provision of material for construction. Emphasis was given to the identification of high quality aggregate resources as it is these premium materials which are required in road surfacing, airport runways and in many concrete structures.

In order for the Tongan Government to optimise development of the limestone resource with appropriate regard to the environmental effects of quarrying, BGS also undertook to make an analysis of the quarrying industry with the aim of providing guidance for aggregates provision in Tonga. Recommendations are based on mineral planning regulations in operation in the developed world but are set in the context of the local Tongan economy and environment.

Although the work considers only the limestone resources of the main islands of Tonga it is intended that the procedures, results, conclusions and recommendations will be applicable to other small limestone islands in the southwest Pacific.

GENERAL GEOLOGY OF THE LIMESTONES

The Kingdom of Tonga comprises a double chain of 160 islands (Figure 1) located on the crest of the Tonga Ridge, an active fore-arc, parallel to and west of the Tonga Trench at the Pacific Plate boundary. The eastern chain of islands comprise mainly limestones whereas the islands of the western chain are volcanic.

The centres of population are in the eastern limestone islands, the largest of which are Tongatapu, the Vava’u Group and the Ha’apai Group. The limestones are up to 250 m thick and are mainly of Quaternary age. They overlie Tertiary volcaniclastic rocks (Roy, 1990). There are no extrusive igneous rocks near surface except for minor exposures on ’Eua (an island south east of Tongatapu). The limestones are thickly covered by soils which are derived from the weathering of volcanic ash. The soil blanket is generally between 1 m and 10 m thick, depending on topography, but averages around 3 m in thickness.



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Tongatapu is made up of up to 250 m of Pliocene and Pleistocene limestones overlying Pliocene and older volcaniclastics (Cunningham and Anscombe, 1985), but late Pleistocene and Holocene limestones are the only rocks exposed at surface. These limestones rise at their highest point to some 65 m - 70 m above sea level at the southern end of the island where they form a narrow, crescent-shaped ridge (mostly over 20 m above sea level) and extending to the northeast and northwest along the windward coast. This ridge is interpreted as the oldest palaeoreef on Tongatapu (Pemn and Mansergh, 1989). To the north of the ridge the ground is low lying and relief is subdued, apart from occasional steep-sided hills 10 m - 25 m high formed by palaeo patch reefs. The patch reefs developed on the sheltered northwest (lagoonal) side of the palaeoreef (Figure 2).

The palaeoreef limestones are relatively massive, cream coloured biomicrites and biosparites. There are many in-situ corals and algal-bound masses and, although there are usually numerous open vughs and cavities, the limestones are often well cemented. In some deposits there is much secondary growth of calcite (spar) cement. Patches of less dense, friable, detrital limestones occur within the palaeoreef deposits but are not widespread.

The patch reef limestones in the lagoonal areas also contain coravalgal limestones but these are less massive, less well-cemented and generally comprise relatively porous, low density, rubbly, detrital limestones. The deposits are of variable consistency with irregular areas of hard, coral/algal bound limestones surrounded by a matrix of partially consolidated reef detritus.

The lagoonal deposits are generally not exposed as they are usually concealed beneath the thick soil. They are, however, anticipated to be generally composed of soft, porous, friable and rubbly limestones with some algal bound limestones.

The Vava’u group comprises many islands. The main island of Vava’u is downtilted to the south (Taylor, 1978). There are steep cliffs up to 210 m high (Plate 2) at the northern end of the island. To the south of the main island cluster numerous small islands and sand cays of lower relief. The main island of Vava’u (Figure 3) shows a variety of landforms which are unique in Tonga. Major features include isolated hills, linear ridges and rims, gently sloping plateau surfaces and cliffed and scalloped shorelines. This unique morphology may be due to marine erosion on an emerging limestone terrain (Roy, 1990).

Two limestones units are recognised in the Vava’u Group. An upper unit of Quaternary coralline limestones rests on bedded limestones which are thought to be of Pliocene age (Katz, 1976). These older limestones are exposed in the lowest parts of Tefisi Quarry where they are described as well bedded, soft, fine grained, detrital tuffaceous limestones (biomicrosparites) with tuff interbeds (see Appendices 1 and 2). The coralline limestones developed on the Pliocene base as a series of reefs of hard, dense, coral/algal bound limestone with flanking beds of detrital, loosely cemented reef rubble.



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LIMESTONE QUARRYING IN TONGA

Production of Limestone

The coralline limestones forming the main islands of Tonga are the only available source of coarse aggregate materials and are widely quarried on Tongatapu and Vava’u and to a minor degree on Eua and Ha’apai. At the time of the survey there were seven working (or recently worked) quarries on Tongatapu and a further seven disused or abandoned quarries. On Vava’u there were currently two working quarries and three disused or abandoned workings. Many of the quarries are small (<1 hectare), but others such as Vaipua Landing Quarry on Vava’u and Pili Quarry on Tongatapu are extensive excavations (> 2.5 hectares). Almost all quarries are worked as a single bench of shallow (4 m to 7 m) height, but some quarries are much deeper (eg. Vaipua Landing, Tapuhia, South Malapo) with 10 m to 35 m high faces. Many are worked down to the watertable.

Production statistics gathered from the Ministry of Works are listed in Table 1 and show a total production of around 450,000 cu. metres (or about 1 million tonnes) for the four year period, 1988-1991. Demand for coarse aggregate is fairly consistent at around 60,000 to 70,000 cu metres per year apart from the occasional short term demands of large construction contracts such as the foreshore protection scheme in Nuku’alofa, the construction of a new terminal and runway works at Fua’amotu airport, the resurfacing of Vava’u airport runway and major road improvement projects, which are confined mainly to Tongatapu. The recent Chinese hotel development at Fua’amotu airport uses imported aggregates in its construction.

All the limestone quarried in Tonga is used for constructional purposes, for roadstone (Plate 3)’ concreting aggregate (as chippings and limestone ’dust’) (Plate 4) and as rip-rap (large blocks) in foreshore construction and port development. There are generally three types of limestone aggregates used in road construction in Tonga; material used in the sub-base and road base layers is rough crushed and not screened, material used in the base course layer is screened limestone chips and in those roads which are sealed then bitumen-coated chippings are used as surface dressings (Table 2). There is an increasing demand for surface dressings on Tongatapu due to current and projected road improvement programmes. Only Ahononou Quarry currently produces sealing chip aggregate as the limestone there is said to be stronger and less porous than stone from other sites.



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Table 1 Limestone production in the Kingdom of Tonga (1988-1991)

Production ( m3) 1988 1989 1990

Government Quarries 59,225 42,237 36,574

Private Quarries 76,027 13,087

TOTAL >59,225 245,664 65,661

-

1991

54,583

1 5,006

69,589

Notes: Total for 1988 does not include production from private quarries Total for 1989 includes 127,400 cu metres for construction of Nuku’alofa foreshore Total for 1990 includes 16,000 cu metres for Fua’amotu airport construction

Wearing course

Table 2 Structural layers in road construction

Road surface 10-40 mm

II Basecourse I 40-75 m ll II Roadbase I 100-200 mm II I1 Subbase I (varies in thickness) 11

Bedrock

Quarry Production Methods

The soft nature of most of the coralline limestones allows ease of excavation and in most quarries the stone is extracted by bulldozer (mechanical shovel or ripper). Blasting techniques are only used on the harder limestones as typified by those at Ahononou Quarry.

Prior to extraction the cover of weathered ash soil is usually scraped from the bedrock surface and stockpiled for sale as topsoil, general constructional fill or for site rehabilitation work. In many cases it was noted that the stripping of surface soils was either not undertaken (Plate 5) or not done efficiently leading to significant contamination of the limestone feed to the quarry plant and resulting in ’dirty’ aggregate products.

The differential cementation of the coralline limestone with its consequent highly variable consistency, results in the production of large blocks (Plate 6) of the better quality (harder, less porous) limestone in a matrix of softer, crushed limestone during quarrying. These blocks are normally rejected as the equipment (drop-ball or pneumatic impact h a m e r ) is not available to reduce the blocks to a size suitable to feed the quarry crusher. Thus the blocks



Report WC/93/23

tend to remain as a waste product and are often too large to move with on-site equipment. The result is inefficient and messy site development and there are several disused quarries with large piles of abandoned limestone blocks. The blocks are capable of producing the higher quality aggregates if the necessary plant were available. It should be noted that in the past year the piles of large blocks from certain quarries (eg Ahononou) have been reduced by demand for rip-rap for wharf construction in Nuku’alofa.

Processing of the quarried limestone to aggregate products is achieved by a variety of plant and operating conditions ranging from sites (eg Fualu Quarry) where minimal processing is carried out, apart from crudely crushing by bulldozer tracks (sub-base grade material), to sites (eg Ahononou, Vaipua Landing quarries) where the stone is separated, crushed, screened and classified to various product specifications (Plates 7 and 8). The plant may be either fixed (eg Ahononou, Tapuhia, Vaipua Landing quarries) or mobile equipment may be used (eg Holonga Quarry). Quarry crushers are mainly of the jaw crusher type, but a gyratory cone secondary crusher has also been used at Ahononou quarry. The grading of the aggregate products vanes between quarries but nominal 34 inch (20 mm), ?4 inch (12.5 mm), % inch (10 mm) and ’fines’ (limestone dust) are typical products. All screening is done without water with the result that the quarry products are ’dirty’ and contain large amounts of ’fines’ (limestone dust and soil). This has a deleterious effect on the in-service performance of the limestone chippings (eg it results in a large uptake of bitumen in pre-coated roadstone aggregates and when used in concrete, it may reduce the strength and durability of the concrete, as well as tending to discolour the concrete product). The large amounts of fines produced during processing is largely the result of the soft nature of the limestone, but the cleanliness of the aggregates could be greatly improved by introducing wet screening and washing facilities and by better soil stripping and handling within the quarry.

LIMESTONE RESOURCES

Resource Assessment Data

The factors governing the suitability of a material for use as aggregate are its physical and mechanical properties. The former are a measure of the intrinsic physical characteristics of the material (eg density, porosity), while the latter are a measure of the physical response of the material to external stimuli such as compressive, impact or shear stresses. Strength and durability are of prime importance in assessment for aggregate use (in concrete or as roadstone), together with other properties such as specific gravity and water absorption. Several standard index tests (British Standards, ASTM Standards etc) have been devised to measure these properties and are used to evaluate the likely in-service performance of aggregates. Details of the objectives and procedures used in each of the index tests used in this study (AIV, LAAV etc) are given in Appendix 3 but are also outlined in Table 3. Some specification requirements for roadstone aggregates relating to British and American Standards are given in Table 4.



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Table 3 Test procedures for limestone aggregates

Physical Tests:

Flakiness index measures degree of flaky particles

I Relative density specific gravity

Water absorption

Table 4 Typical specification requirements for roadstone aggregates

measures porosity and capacity to absorb water

Mechanical Tests:

Aggregate impact value

Aggregate crushing value

Los Angeles abrasion value

11 Flakiness index I I <35 II

measures resistance to granulation under impact stresses

measures resistance to crushing under a gradually applied load

measures resistance to attrition by impact and abrasion forces

Particle density

Water absorption

Los Angeles abrasion value I generally I <40

generally >2.65

<2%

The investigation of the aggregate properties of the coralline limestones of Vava’u and Tongatapu, Kingdom of Tonga is based primarily on a field survey carried out by BGS in 1992 involving studies of limestone lithofacies and the selection of samples for laboratory testing. All testing was carried out in the BGS Aggregate Testing facility at Keyworth. Supplementary data were made available by the Ministry of Works, Government of Tonga and particularly by G.G. Candler, formerly Laboratory Manager at the Ministry of Works.

Aggregate impact value

Aggregate crushing value

Aggregate property data were obtained from samples taken from working or recently disused quarries although several natural exposures were also investigated. Samples were either taken as quarry face lump samples or chipping from quarry stockpiles. Care was taken to sample unweathered or only partially weathered limestone.

generally <25

generally -e30



Report WC/93/23

Samples were also taken from the same quarry exposures for chemical analysis. Although all the limestone quarried is utilised in the constructional industry where the chemical properties of the stone are not generally important in determining end-use, it was desirable to indicate the general chemical quality of the limestones, particularly as their general lithologies suggest a high grade of purity. High purity limestones or lime (CaO) are used in a wide range of manufacturing industries including glass, sugar refining, iron and steel and chemicals. Ground limestone is used as fillers and pigments in papers, plastics, paints and rubbers. Lime is also used in the construction industry for the manufacture of mortar, plaster and limewash and is also valuable in road construction through the process of soil stabilization and as an additive to bituminous road surfacings (Dave, 1981). It is possible that, in the future, Tonga may wish to develop some of these industrial uses of limestone.

The chemical analyses were carried out by X-ray fluorescence spectrometry (XRF). They provide only a guide to the likely chemical quality of the limestones, but when combined with observations of lithology both in the field and laboratory, they provide the basis for the reconnaissance evaluation of the potential of the limestone for non-aggregate uses.

Aggregate Properties

Summary aggregate property data obtained from samples of the limestones of Vava’u and Tongatapu, with additional data where available, are shown in Tables 5 and 6. These results indicate wide variations in physical and mechanical properties and show that most limestone aggregates in Tonga fail to meet specifications for concrete and roadstone commonly used elsewhere in the world. Most Tongan limestone aggregates are weak (soft) and abrade easily, are highly porous and contain large amounts of absorbed water and are of low density. Nevertheless the limestones are the only source of coarse aggregates in the Kingdom of Tonga and are widely used for both concreting and roadstone aggregates.

Testing data indicate that the quality of the aggregates is extremely variable and supports the general conclusions of previous studies that the highest quality (the densest, least porous, strongest and most durable) aggregates in current production are extracted from Ahononou Quarry which works palaeoreef limestones on the south coast of Tongatapu. These limestones are creamy white, dense, hard coral/algal biosparites with a recrystallised fabric. The deposit is generally massive with only minor pockets of rubbly, detrital limestone. There are numerous large vughs but the matrix is strongly cemented. Limestones of similar, though more variable, lithology and aggregate properties are present at Farm Quarry near Ahononou and also in Pangaimotu quarry and in the upper benches of Tefisi Quarry on Vava’u. The test data indicate that all these limestones have the potential to produce Group 1 aggregate materials (Table 7) suitable for a wide range of constructional end uses (concrete aggregate, road base and sub-base aggregates), including road surfacing. It should be noted, however that the assessment of the limestones as an aggregate resource is based on a limited field survey and the testing of a few bulk samples. The natural lithological variation present in the limestones will lead to some variability in aggregate properties. Nevertheless it is anticipated that the limestones at these sites yield the highest quality coarse aggregate currently extracted in Tonga.



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Table 5 Physical properties of limestone aggregates from Vava’u and Tongatapu

Location Flakiness Relative Density Water Absorption (%I

Pangaimotu Quarry

Tefisi Quarry (upper bench

Tefisi Quarry (lower bench)

Holonga Quarry

Vaipua Landing Quarry

Mata’ihoi Proposed Quarry

NOTE: Most values given result from testing to BS812, 1990, but values in brackets are from Ministry of Works, Tonga (Candler, 1992) and are derived from Australian test methods for aggregates (Australian Standards: 1141 sections 5 and 6; Bulk Density and Water Absorption).

22 2.35 (2.39) 3.3 (3 -6)

11 2.27 (2.15) 4.4 (7.6)

13 1.90 11.2

33 2.33 (2.30) 3.9 (5.6)

16 1.83 (2.13) 11.8 (8.5)

20 2.21 5.7


Ahononou Quarry

Farm Quarry

Pili Quarry

Longoteme Quarry

Tapuhia Quarry

Fualu Quarry

Cockers Quarry

Mataki’eau Quarry

South Malopo Quarry

16

14 2.44 (2.49) 2.1 (2.6)

17 2.35 3.1

5 2.22 (2.18) 4.9 (5.4)

5 2.10 (2.07) 7.5 (7.8)

18 2.17 5.6

9 2.09 (2.14) 8.0 (7.8)

16 2.32 (2.27) 3.9 (4.9)

8 2.06 (2.04) 9.9 (7.7)

9 2.14 ( 1.84) 8.1 ( 12.9)

The limestone resources of Tongatapu and Vava’u

Report WCl93l23

Table 6 Mechanical properties of limestone aggregates from Vava’u and Tongatapu

Location AIV ACV LAAV

Pangiamotu Quarry

Tefisi Quarry (upper Bench)

26 30 28

31 33 32

Tefisi Quarry (lower bench)

Holonga Quarry

Vaipua Landing Quarry

Mata’ihoi Proposed Quarry

42 49

36 39 39

45 49

35 37

Note: AIV (Aggregate impact value) and ACV (Aggregate crushing value) are British Standard tests to measure the strength of aggregates. LAAV (Los Angeles abrasion value) is an American Standard for testing both strength and durability of aggregates.

Ahononou Quarry

Table 7 Classification of coralline limestone aggregates in the Kingdom of Tonga

27 31 26

Group

1

2

3

Farm Quarry

Pili Quarry

Longoteme Quarry

Tapuhia Quarry

Fualu Quarry

Cockers Quarry

Mataki’eau Quarry

South Malopo Quarry

Possible Uses

31 29

34 37 35

37 40 38

37 40 37

44 45 38

38 39

48 38

42 39

Road surfacing aggregate. Also suitable for most construction purposes.

Description

Base and sub-base (roadstone). Most concreting aggregate.

Typical index test values

Generally only suitable for road sub-base or constructional fill.

Weak with low durability. Highly porous, low density.

AIV and LAAV >40. Rel. Den. <2.1, Water Abs. >8.0%.

Relatively strong and durable. Least porous aggregate.

AIV and LAAV <32. Rel. Den. >2.3, Water Abs. < 4.4%

Moderate strength and durability. Porous a€!wgate-

AIV and LAAV < 40, Re1 Den. > 2.1, Water Abs. ~8.0%.

I

Quarry sources

Ahononou, Farm, Tefisi (upper) Pangaimotu

Holonga, Mat’ihoi, Pili, Longoteme, Tapuhia, Cockers.

Vaipua Landing, Tefisi (lower), Fualu, Mataki’eua, South Malapo.



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The testing data show that a second group (Group 2) of what might be called moderate strength, medium low density, porous aggregates are produced from the limestones quarried at Holonga (Vava’u), Pili, Longoteme, Tapuhia and Cockers on Tongatapu and from the proposed quarry site at Mata’ihoi on Vava’u. The results show a range of densities between 2.10 and 2.33 and water absorption values of 3.9% to 7.5%. Strength values (AIV etc) show less variation, but indicate only moderate strength and are considerably higher (ie they are weaker) than typical specifications for roadstone aggregates elsewhere in the world. These limestones are generally suitable for most constructional purposes on Tonga apart from road sealing grade aggregates. The quarries at Pili, Longoteme, Tapuhia and Cockers on Tongatapu are all situated in patch reef deposits which are typically friable, detrital limestones comprising poorly cemented reef rubble with irregular patches of hard, recrystallised coral/algal micritic limestone. Inspection of these deposits indicates that a wide variation in aggregate properties can be anticipated. The limestone at Holonga and Mata’ihio on Vava’u are similarly a mixture of well cemented, coral/algal, vughy limestones and detrital, rubbly limestones.

It should be noted that at most of these sites where the testing indicates Group 2 aggregate materials then there are numerous large blocks of harder, denser limestone which are not generally utilised. These blocks have the potential to produce stronger, less porous (ie Group 1) aggregates and could be usefully blended with current production or even worked selectively for higher grade output. This also illustrates the capacity of these deposits for producing a wide range of grades of aggregate materials.

Some of the coralline limestone deposits on Tonga are particularly soft, are highly porous and of low density (Plates 9 and 10). These rocks produce Group 3 aggregate materials (Table 7) which are generally suitable only for road sub-base or fill material. The sample test data obtained during this study suggest that the quarries at Vaipua Landing on Vava’u and those at Fualu, Matakieau and South Malapo on Tongatapu tend to produce aggregates of this grade. In addition, the soft, detrital, bioclastic limestones forming the lowest bench of Tefisi Quarry on Vava’u, also fall within this category. These results are based on a limited number of samples, but are supported by the testing of the physical properties of these limestones by Candler (1992). Again, it should be noted that in all these deposits (except the consistently soft, lower beds in Tefisi Quarry) the very variable nature of the limestones is likely to result in a considerable range of aggregate grades. Thus the fragmental patch reef limestones at these sites are likely to produce Group 3 aggregate materials, but areas of limestone which are harder and less porous have the potential to produce a slightly higher grade of aggregate.

Chemical Properties

Analytical data obtained from spot samples of coralline limestones from quarries in Vava’u and Tongatapu are shown in Tables 9 and 10 respectively. These results indicate uniformly high chemical grade. Amounts of silica, iron and other impurities within these limestones are very small and it is anticipated that virtually the whole outcrop area could be classified (Table 8) as very high purity limestone (>98.5% CaCO,).



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The only analysis which indicates significant levels of specific impurities is of a sample taken from the lower beds (Pliocene age) exposed in Tefisi Quarry, Vava’u. These limestones contain tuffaceous material which results in the higher silica, iron and alumina values. Nevertheless, the amounts of impurities are low and the analysis suggests that even these beds fall within the very high purity grade.

High purity

Medium purity

Low purity

Table 8 Classification of limestones by calcium carbonate content (Harrison, 1992)

97.0-98.5 54.3-55.2

93 597.0 52.4-54.3

85.0-93.5 47.6-52.4

11 Category I Percentage CaCO, I Percentage CaO

Pangaimotu Quarry

~~ 11 Very high purity

Tefisi Quarry (upper Tefisi Quarry (lower Holonga Vaipua Landing bench) bench) Quarry Quarry

Ba

c u

Pb

Zn

Table 9 Chemical analyses of quarried limestones from Vava’u, Kingdom of Tonga

2 5 8 9 5

7 9 10 8 8

1 1 1

4 5 6 3 3

II parts uer million


20 The limestone cesources of Tongatapu and Vava’u

Report WCA3/23

Table 10 Chemical analyses of quarried limestones from Tongatapu, Kingdom of Tonga

II parts per mdlion

II Ba I II I

2 Ba

cu

Pb

zn

3 2 3 8 6

6 8 9 8

2 3 2 1

Fualu Quarry Cockers Quarry Mataki’eau Quarry South Malopo Quarrg

8

zn

6

2 3 2 1

I Fualu Quarry

6

Cockers Quarry Mataki’eau Quarry South Malopo Quarrg

TiO,

so3

p*o,

MnO

LOSS

8

0.00 0.00 0.00 0.01

0.1 0.2 0.2 0.2

0.04 0.05 0.05 0.05

0.01 0.01 0.00 0.00

43.15 43.91 43.69 43.92

9

Ba

c u

Pb

zn

8

5 8 13 4

8 9 10 9

1

2 3 5 4

Ba

c u

Pb

zn

5 8 13 4

8 9 10 9

1

2 3 5 4


21 The limestone resources of

Report WC/93/23 Tongatapu and Vava’u

QUARRY PLANNING

Limestone Quarrying and the Environment

The quarrying of limestone in the Kingdom of Tonga is a well established industry resulting in numerous surface workings, particularly on Tongatapu. Most quarries are situated on rising ground or small hills and many have been excavated down to the watertable.

Limestone quarrying, in common with all surface mineral working, has some adverse effects on the environment and the community. The main problems with stone quarries are visual, particularly scars on the landscape and unsightly waste heaps, although traffic, noise and dust all give rise to concern. Other aspects such as groundwater, loss of agricultural land and the need for site restoration, may be equally important environmental considerations.

Landscape effects. The numerous quarries on Tongatapu are mostly small, but they are generally sited on the higher ground and can be considered as visual intrusions. Many of the small hills formed by patch-reefs have either been totally removed or are in the process of being removed by quarrying. The hilly topography of Vava’u has also locally been modified by quarrying and careful siting of quarries is required to avoid breaking ridge profiles and minimising loss of landscape.

In most quarries on Tonga there appears to be little consideration of site layout, direction of working, disposal of ’waste’ rock and temporary storage of soil. Landscaping is not practised and worked-out quarries are not restored.

Traffic. All stone is transported from the quarries by heavy trucks, resulting in increased road traffic, noise, damage to roads and increased dust generation. There appears to be no control or restriction on quarry haulage.

Dust. The soft nature of the limestones facilitates dust generation during quarrying and processing and the areas surrounding quarries and haul roads are usually coated in white dust. The prevailing windy climate results in widespread distribution of the limestone dust. There is little or no control of dust in the quarry or processing plant.

Groundwater. The porous limestone bedrock stores groundwater which is the public water supply of Tonga. Quarrying of the limestone creates potential groundwater problems such as possible derogation (a reduction in water quality or quantity) or loss of aquifer capacity, but the most important water problem is the potential for pollution of the groundwater resource. In many quarries stone has been extracted down to the depth of the watertable, thus exposing the watertable to direct contamination by, for example, an oil spill. The coralline limestones are generally extremely porous and this factor, together with the rapid flow rates of water in limestone aquifers, could result in rapid contamination of groundwater over a large area.



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Planning Controls on Quarrying Operations in Developed Countries

In most developed countries there are planning controls governing most forms of ’development’ of land, including quarrying activities. In Britain, for example, the planning framework is provided by the Town and Country Planning Act, 1971 as amended by the Town and Country Planning (Minerals) Act, 1981 and 1990. Further information on minerals planning is given in the Minerals Planning Guidance Notes issued by the Department of the Environment. These set out Government Policy and provide updated information on the 1981 Minerals Act.

The key feature of the planning system is that most forms of development in Britain require planning permission before development can take place. Most permissions for mineral development have conditions attached which are designed to control their impact on the environment. For example, conditions may be imposed which control access arrangements, set noise limits or limit the depth of working. Other conditions may govern the restoration of the site. If the application is refused, or the conditions are unacceptable, the applicant has the right of appeal to Government.

In order to meet and fully satisfy these planning and environmental guidelines, many mineral operators in Great Britain (and in other developed countries) have developed corporate environmental policies. In addition, it is standard practice for the quarrying trade federations to take the initiative to produce an Environmental Code. Such codes (eg British Aggregate Construction Materials Industries - BACMI - Environmental Code) aim to contain the minimum requirements which quarrying companies should apply, recognising their responsibility to the environment and to the community in which they operate. The pursuit of a sound environmental policy related to mineral extraction can also be guided by the recently published international standard (BS7750) covering environmental management s y s tems .

Relevant literature sources providing advice on minerals and environmental planning are included in the Bibliography.

Recommended Planning Guidelines for Quarrying in Tonga

The minerals planning guidelines outlined above are not necessarily appropriate to the industrial, economic and legislative requirements of the Kingdom of Tonga but they serve as an example of common practice elsewhere in the world. However, if the Government of Tonga wishes to address the environmental effects of limestone quarrying, then it is recommended that consideration should be given to the formulation of a series of quarrying guidelines. These should seek to reduce to a practical minimum any adverse effect on the environment caused by the quarrying and processing of limestone and could be used as the basis for the creation of a series of quarry regulatory conditions and requirements.



Report WO93123

It is recommended that the following topics should be addressed by any guidelines;

1. All new sites and further developments of operational sites should consider their potential for visual intrusion and for modification of landforms. This is particularly relevant on Vava’u due to the hilly, irregular topography, although quarrying on Tongatapu is continuing to remove the few hill features.

2.

3.

4.

5.

All quarries should aim to operate appropriate, but efficient, handling, control and processing systems - this will ensure that a deposit is worked efficiently, minimising waste and maintaining a high, but practical standard of housekeeping.

This may require improvement and upgrading of the extraction, crushing and screening plants as previously detailed by Applied Geology Associates in Pemn and Mansrigh (1989) and referred to elsewhere in this report.

All topsoils (including the uppermost ’weathered’ zone of limestone) should be efficiently stripped before quarrying. The topsoils should be stored in a temporary disposal area on the site before being used for restoration when operations have ceased.

Consideration should be given to the siting of quarries in designated areas. These ’quarry development’ areas would be sited in limestones of appropriate quality and be located suitably close to the demand for the limestone products. The preferred areas should also be environmentally acceptable.

It should be noted that the identification of preferred areas for future limestone extraction, may lead to rationalisation within the industry, such as the closing of numerous small quarries and the development of larger, but fewer quarries. This may also lead to the centralisation of quarry processing facilities and a reduction in the number of truck routes.

The limestone aquifer is particularly vulnerable to pollution, particularly when quarrying ’exposes’ the water table. It is recommended that the quarries should not be utilised as land fill sites unless it can be proved by detailed environmental, hydrogeological and engineering investigations that the groundwater will not be contaminated by any leachate.

It is desirable that land taken for quarrying should be reclaimed at the earliest possible opportunity and should be capable of an acceptable use after working has ceased.

Many abandoned quarries in Tonga are littered with derelict quarrying equipment or with quarry waste materials (often including large piles of ’hard’ limestone blocks). In many cases it is doubtful if satisfactory reclamation could be achieved, because of the scale of the excavation or the cost of restitution. However, it may be



Report WC/93/23

possible to fill some quarry voids using waste materials, up to or above the original ground levels. The only readily available fill materials are quarry wastes or domestic wastes. If waste other than quarry wastes are brought in, their disposal must be carefully controlled due to the risk of pollution to groundwaters (see Recommendation 4, above).

It is recommended that all quarries in Tonga should be developed with a view to their future reinstatement. Thus all quarry waste, including ’fines’, soil and oversize blocks should be stockpiled on site and used to fill the voids left by limestone extraction. If the topsoil is replace on restoration then the land can be returned to productive agriculture.


The limestone resources of Tongatapu and Vava’u

Report WC/93/23

CONCLUSIONS

Limestones are a large and very important natural resource in the Kingdom of Tonga. They are quarried extensively and are used principally as coarse aggregate in concrete and road construction, as rip-rap in coastal protection and harbour developments and as fine aggregate in concrete products.

Demand for coarse aggregate in Tonga is fairly consistent at around 65,000 cubic metres per year although sporadic short term demands for major construction works can boost this figure dramatically. In recent years there have been several major constructional works including Fua’amotu airport and foreshore/harbour works in Nuku’alofa. There is also currently a major scheme of road improvements on Tongatapu, including the sealing of many roads.

In many quarries the production methods are fairly basic, involving nothing more than a bulldozer to extract and crush the limestone before loading into trucks for sale. Several quarries are equipped with crushing and screening facilities, but blasting is generally only utilised at Ahononou Quarry. The quarries are mostly small and are worked as a single shallow bench. A few quarries are more extensive and some are deep voids worked down to the watertable.

The soft nature of the limestones results in the generation of large amounts of fines (typically of very fine grain size) during quarry processing, but the lack of adequate processing systems and the poor control of overburden soils typically results in ’dirty’ aggregates.

Harder areas of limestone are often not processed after extraction as the blocks are either too strong or too large for the available processing plant to deal with. They therefore remain as abandoned quarry waste and in many quarries there are substantial piles of these harder blocks, although they are on occasion used as rip-rap for foreshore protection.

There are wide variations in the aggregate properties of the coralline limestones both within, and between quarries. Most of the limestone aggregates are weak, dirty, porous and of low durability and they would generally fail to meet internationally recognised specifications for aggregates used in concrete and in road building. However, they are the only available source of coarse aggregate in Tonga.

Three groups of aggregate materials have been identified by the survey. The strongest and most durable limestone aggregates are produced from Ahononou Quarry, Tongatapu. This is situated in an area of palaeoreef limestones forming a narrow, crescentic shaped ridge at the southern end of Tongatapu. These limestones are relatively massive and are well cemented. Similar palaeoreef limestones, although of a more rubbly and variable nature, form many of the upstanding ridge features on Vava’u and testing of samples from Pangiamotu Quarry and the upper parts of Tefisi Quarry indicate similar aggregate qualities to Ahononou Quarry. All these limestones have been classified as Group 1 aggregate materials (Table 7), capable of being used as road surfacing aggregates in Tonga as well as being suitable for most constructional purposes.



Report WC/93/23

Two other main groups of limestone aggregate have also been identified. These aggregates are generally weaker and of lower density, lower durability and higher porosity than Ahononou-type materials. They are generally associated with patch reef deposits or with the less well-cemented or more friable, detrital parts of palaeoreef deposits. The results obtained from Holonga, Pili, Longoteme, Tapuhia and Cockers quarries indicate aggregates of high porosity but moderate strength and durability. They are classified as Group 2 aggregates and such materials are generally suited for most constructional uses in Tonga, except road surfacing. A further group (Group 3 aggregates) of test data were given by samples from Vaipua Landing, Fualu, Mataki’eau and South Malapo quarries as well as from samples of the older (Pliocene) limestones exposed in the lower levels of Tefisi quarry on Vava’u. These aggregates are weak with low durability and high porosity. They are generally suited only for use in sub-base layers of roads or for general fill purposes.

The test data also indicate that the coralline limestones of Tonga are consistently of very high chemical quality and, although there is no local and little regional demand for such limestones at present, they are generally suitable for all industries which require high purity limestone as feedstock. The limestones could be calcined to produce lime which has a potential local application in the stabilization of roads.

The extraction of limestone by open pit quarrying inevitably creates environmental problems such as scars on the landscape, the creation of dust and noise, increased volumes of heavy traffic, groundwater loss or pollution and loss of agricultural land. There is a need to minimise these environmental effects and yet continue to develop the valuable stone resources. It is the author’s opinion that these complex land use problems need to be urgently addressed in Tonga. A series of quarrying guidelines are required to cover all aspects of limestone extraction from site selection, through quarry development to site reinstatement. Specific recommendations are given below.

RECOMMENDATIONS

1. It is recommended that quarrying on Tongatapu is concentrated in the palaeoreef limestones which form the ridge of relatively high ground in the south of the island. Ahononou Quarry is situated in these deposits and testing has proven that this site produces the best quality coarse aggregate available in Tonga. Similarly, limestone quarrying on Vava’u should concentrate on the harder palaeoreef limestones as exposed in Pangaimotu Quarry, Tefisi Quarry or in the core of Vaipua Landing Quarry.

2. In order to overcome the problems caused by excessive fines in the crushed limestone (’dirty aggregates’) it is recommended that all topsoils are efficiently removed before quarrying and the aggregates are wet screened.

3. Improved quarry plant (hydraulic chipper or drop-ball) should be introduced to facilitate the processing of the harder blocks of limestone.


27 The limestone resource of Tongatapu and Vava’u

Report WC193l23

4.

5.

6.

Quarries should be reclaimed wherever possible, using quarry waste materials.

It is recommended that consideration is given to the designation of ’quarry development areas’, eg the Ahononou area. These would aim to develop a relatively small number of large quarries in a restricted area. It would be supported by plans to close and reinstate the many small quarries and to modernise and centralise both quarry processing plant and distribution facilities.

It is recommended that the methodology developed during this assessment is applied to aggregate supply problems on other coralline islands elsewhere in the Pacific.


The limestone rewurces of Tongatapu and Vava’u

Report WCA3l23

BIBLIOGRAPHY

American Society for Testing and Materials ASTM C131, Standard test method for resistance to abrasion of small size coarse aggregate by use of the Los Angeles Machine.

Australian Standards. Bulk density and water absorption of fine aggregate. AS 1141.5.

Australian Standards. Bulk density and water absorption of coarse aggregates. AS1 141.6.

BACMI 1992. Environmental Code. British Aggregate Construction Materials Industries, London.

British Standards Institution 1983. Aggregate from Natural Sources for Concrete, BS882.

British Standards Institution 1990. Methods for Sampling and Testing of Mineral Aggregates, Sand and fillers, BS812.

British Standards Institution 1992. Environmental Management Systems, B S7750.

Candler, G.G. 1992. Engineering testing of building materials in Tonga. Ministry of Works, Tonga.

Cunningham, J.K. and Anscombe, K.J. 1985. Geology of 'Eau and other islands, Kingdom of Tonga. In Scholl, D.W. and Vallier, T.L. 1985. Geology and offshore resources of Pacific Island arcs: Tonga region. Circum-Pacific Council for Energy and Mineral Resources Earth Science Series 2, 221-257. Houston.

Dave, N.G. 1981. Technical feasibility studies for the establishment of lime and some lime based industries in Fiji. Ministry of Works, Suva, Fiji.

Harrison, D. J. 1992, Industrial Minerals Laboratory Manual: Limestone. British Geological Survey Technical Report WG/92/29.

Katz, H.R. 1976. Sediment and tectonic history of the Tonga ridge and the problem of the Lau Basin. In Glassby, G.P. and Katz, H.R. (eds), UN. ESCAP, CCOP/SOPAC Technical Bulletin 2.

MPG 6. Guidelines for Aggregates Provision in England and Wales. 1993. Department of the Environment, London.

MPG 7. The reclamation of mineral workings. 1989, Department of the Environment, London.

New Zealand Standards. Methods of test for water and aggregate for concrete. NZS3 1 1 1.

New Zealand Standards. Specification for water and aggregate for concrete. NZS3 12 1.


29 The limestone resources of Tongatapu and Vava'u

Report WC/93/23

New Zealand Standards. Methods of sampling and testing road aggregates. NZS4407.

Perrin, N.D. and Mansergh, G.D. 1989. Construction materials investigation (onshore), Tonga. New Zealand Department of Scientific and Industrial Research. Report EGI 89/054.

Roy, P.S. 1990. The morphology and surface geology of the islands of Tongatapu and Vava’u, Kingdom of Tonga. South Pacific Applied Geoscience Commission (SOPAC) Technical Report 62.

Tappin, D.R. and Harrison, D.J. 1991. Visit to Tonga and Fiji: Evaluation of Aggregate Potential on Coralline Islands in the Kingdom of Tonga. British Geological Survey Technical Report WB/9 1/27R.

Tappin, D.R. 1993. Beach sand resources of Tonga (in preparation). BGS Technical Report.

Taylor, F.W. 1978. Quaternary tectonic and sea level history, Tonga and Fiji, southwest Pacific. PhD Thesis, Cornell University (unpublished).

Town and Country Planning Act, 1971. HMSO. London.

Town and Country Planning (Minerals) Act, 1990. HMSO. London.



Report WC/93/23

APPENDIX

1. DESCRIPTION OF QUARRIES

A. TONGATAPU

Ahononou Quam/. The Ministry of irks regard this quarry as the source of the best quality aggregate on Tongatapu. Blasting techniques are used, but many large blocks are produced. In the past year many blocks have been removed for use as rip-rap in Nuku’alofa. The stone is generally massive, hard algal coral biosparite with a recrystallised fabric.

Cockers Quam/. Stone from this quarry is not being worked but a concrete batching plant is operational using limestone transported from adjacent sites. The quarry is sited on a patch reef deposit and has worked down to the watertable. The limestone is a mixture of porous, friable, micritic rubble and harder coral/algal micrite.

Farm Quarry. This quarry extracts limestones similar to those at Ahononou, although the deposits are more lithologically varied and contain a higher proportion of weaker, rubbly limestones.

Fualu Quarry. This quarry appears to be almost worked out. It forms a substantial excavation and has worked down to the watertable. It is situated in patch reef limestones which are a mixture of fragmental, weak limestones and harder irregular blocks of coral/algal and shelly biomicrite. There is no crushing and screening plant.

Longoteme Quarry. This working quarry is extracting patch reef limestone from one of the few remaining knoll features on Tongatapu. About one third to one half of this feature has been removed by quarrying. The limestones are extremely friable, vughy, porous reef rubble (biomicrites) with some well-cemented coral/algal patches. The stone is extracted by bulldozer which pre-crushes the material under its tracks before processing through the on-site crusher and screens.

Mataki’eau Quarry. This quarry is generally disused but at the time of survey some stone was being extracted. The limestones are mainly soft, porous, rubbly patch reef deposits. There is a substantial stockpile of large, tough coral/algal limestone blocks abandoned on the quarry floor.

Pili Quarry. This is a very large quarry and appears to be nearly worked out. It is situated in a large patch reef deposit which generally consists of vughy, granular, partially consolidated reef rock, with scattered patches of stronger coraValga1 limestone (biosparites). There is a concrete block works on site.

South Malapo Quarry. This quarry appears to be virtually worked out but some peripheral extraction was taking place at the time of survey. The site is a large , deep



Report WC/93/23

(25 m) excavation, partially filled with abandoned large limestone blocks and derelict plant. The limestones are mainly rubbly, detrital, vughy coral/algal micrites and appear to be very weak. Minor amounts of stronger, more highly cemented limestones were noted.

Tapuhia Quam. This largely disused quarry is to be the site of the new Ministry of Works crushing plant in 1993. Limestone will then be transported (from Ahononou Quarry) to this centralised processing facility. At the time of survey the quarry consisted of large, virtually worked out patch-reef deposits, although some minor extraction was taking place at the margins of reef. The quarry descends some 10 to 15 m below ground level. The limestones are very vughy and porous with much detrital reef debris. Some irregular patches of harder, coral/algal reef limestone were recorded.

B. VAVA’U

Holonga Quarry. In 1992 this quarry was re-opened to provide crushed limestone for resurfacing and extending the airport runway which is unsealed. The deposit forms a small hill and is composed of vughy recrystallised coral/algal reef limestone (biosparite) with some zones of friable reef detritus. The harder limestones are not processed and remain as numerous large blocks on the quarry floor. The thick soil cover on the flanks of the hill is removed and used to reinstate the land flanking the runway.

Pangaimotu Quam/. Disused quarry in fractured and brecciated coral/algal reef limestone (micrite and biomicrite). Variable degree of vughy porosity but limestones are well cemented and generally hard and relatively consistent. The quarry is situated on the south side of a ridge and if the quarry is further developed care should be taken not to break the ridge line, as the quarry would then be visible from Neiafu and the Port of Refuge.

Tefisi Quarry. This disused quarry exposes about 10 m of massive, hard algal limestone overlying older bedded, soft, fine grained, tuffaceous detrital limestone. The upper beds are fragmental, well cemented, vughy limestones with palaeokarst surfaces. The lower beds are well bedded, and highly porous. Bedding planes are after marked by thin layers of tuff.

Vaipua Landing Quarry. This large quarry has a working face of over 50 m in height but it is anticipated that the quarry will cease production in the near future. The qumy is situated in a steep ridge of reef limestone and extracts relatively dense coral/algal limestone from the central core of the reef ridge and weaker, rubbly, bedded detrital limestone flanking the reef core. There is a crushing and screening plant onsite. The quarry is reported as being capable of producing good quality aggregate but much of the stone is relatively weak and porous resulting in variable quality aggregate products.



Report WC/93/23

Mata’ihoi Proposed Quarry. This proposed site is close to Vaipua Landing and appears to be generally in similar limestones. It is anticipated that stone properties will be similar to those at Vaipua. There is negligible soil cover.


33 The limestone reaources of Tongatapu and Vava’u

Report WCl93l23

APPENDIX

2. LIMESTONE PETROGRAPHY

This section describes the characteristics of thin sections of limestone samples from quarries and from selected DSIR boreholes on Tongatapu and Vava’u.

Vava’u limestone petrography

1. Pangaimotu Quarry

Biomicrite (wackestone), scattered comminuted bioclastic (coral, algal, bivalve, rare foram etc) debris in micrite and microspar matrix. Common fine arenite, peloidal debris. Poorly sorted. 10% vughy porosity, usually cavities in bioclasts or dissolved out bioclasts.

2. Tefisi Quarry (upper beds)

Biomicrosparite (wackestone), very poorly sorted, abundant very fine arenite peloidal debris and finely comminuted skeletal grains. Scattered rudite and coarse arenite coral and other bioclastic debris. Many large vughs within coarse bioclasts.

Tefisi Quarry (lower beds - Pliocene? limestones)

Biomicrosparite (packstones), very fine arenite comminuted bioclastic debris (foram, bivalve, sponge, algal debris etc) closely packed in rnicrospar/fine spar matrix. Scattered coarser bioclasts, well sorted. Sporadic angularhb-angular tuffaceous fragments. Rare siliceous sponge spicules. Fine porosity (%5).

Tefisi Quarry Borehole CMV 1,3.2 m (lower beds - Pliocene? limestones)

Biomicrosparite (packstone), medium arenite, well sorted. Abundant finely comminuted bioclastic debris (foram, echinoderm, bivalve, algal) in microspar and micrite matrix. Scattered fine tuffaceous grains. Some (c. 10%) fine porosity.

Tefisi Quarry Borehole CMV 1, 8.2 m (lower beds - Pliocene? limestones)

Biomicrosparite (packstone), fine arenite, well sorted. Abundant finely comminuted bioclastic debris (foram, echinoderm, bivalve, algal etc) in microspar matrix. Scattered fine tuffaceous grains. Some (c.5%) fine porosity.

3. Holonga Quarry

Biosparite (packstone), coarse arenite, moderately sorted. Abundant forams and other skeletal (algal, coral, echinoderm, bivalve etc) debris. Some micrite patches.



Report WC/93/23

Approximately 30% porosity due to cavities in skeletal debris and reef structures.

4. Vaipua Landing Quarry

Biosparite (boundstone), abundant coral, algal, foram debris in spar and fine spar matrix. Common encrusting algae. Some micrite patches. Poorly sorted. Rare siliceous spicules and secondary growths of silica around bioclasts. Highly porous (> 50%).

Tongatapu limestone petrography

1.

2.

3.

4.

5.

Pili Quarry

Biosparite (packstone), medium to coarse arenite, moderate sorting. Foram, echinoderm, algal, coral and other skeletal material, comminuted in a mix of fine spar and micrite. Highly porous (c. 35% porosity in thin section).

Ahononou Quarry

Biosparite (packstone), medium to coarse arenite, moderate sorting. Foram, echinoderm, coral algal skeletal debris in coarse spar matrix with patchy micrite. Well packed < 10% porosity. Much secondary growth of calcite (spar) cement.

Longoteme Quarry

Biomicrite (packstone), rudite to fine arenite, poorly sorted. Abundant skeletal debris (coral, algal, echinoderm, foram etc) in micrite matrix with some patchy spar and microspar. Very vughy (> 40% porosity).

Fualu Quarry

Biomicrite (wackestone), medium to coarse arenite, moderate sorting. Common comminuted coral, algal, foram, bivalve and ostracod debris in a micrite matrix with patchy recrystallisation to microspar. Some porosity (10- 15%), mainly within bioclastis.

CMT 2 Borehole 5.4 m Ha’ateiho

Biomicrite (boundstone), coarse rudite, poorly sorted, mainly corayalgal debris in a micrite matrix. Very porous (> 50% porosity), due to cavities in fossils and in reef structures.

CMT 2 Borehole 7.4 m Ha’ateiho

Biomicrite (boundstone), coarse rudite, poorly sorted, mainly coraValga1 debris, rare bivalve and gastropod material in a micrite matrix with much secondary recrystallisation of spar. About 25% vughy porosity (in thin section).



Report WCl93l23

6. CMT 7 Borehole 7.1 m Ha’ateiho

Biomicrite (wackestone), fine arenite to medium rudite, poorly sorted, in micrite and recrystallised spar matrix. Algal, coral, echinoderm, foram debris. Highly porous (> 35%) with large vughs.



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APPENDIX

3. AGGREGATE TESTING PROCEDURES

The procedures used in each of the standard index tests (mainly BS812: 1990) are summarised below. In addition, the objective of each test is outlined and some guidance is given for the interpretation of the test results.

In all cases the testing was carried out on +10 mm - 14 mm sized aggregate.

1. Physical Tests

a) Flakiness Index. This test measures the weight-percentage of particles whose least dimension is less than 0.6 times the mean dimension. The test procedure involves the use of either a standard shape gauge or a specially designed sieve.

In this test a higher numerical value indicates a more flaky aggregate. Flaky aggregates should be avoided as they are relatively weak, but aggregate shape can be improved by selective methods of crushing and screening.

b) Relative Density and Water Absorption. Relative density was calculated on an oven- dried basis using a standard aggregate sample, thus enabling water absorption (expressed as a percentage of the dry weight of the aggregate) to be measured during the same test procedure. Tests values for relative density (specific gravity) are usually unspecified but values of at lest 2.65 are generally desirable. Water absorption is an indirect measure of porosity. Aggregates with a high porosity have a high surface area and therefore have an excessively high water requirement in concrete and a similarly high bitumen uptake in coated roadstones. Classifications of absorption values are imprecise and debatable, but a low absorption value (the smaller the better) might reasonably be considered as less than 2 percent.

2. Mechanical Tests: Strength

a) Aggregate Impact Value (AIV). In this test a standard sample of aggregate is subjected to 15 blows from a hammer, weighting between 13.5 and 14.0 kg, falling through a standard height of 380+5 mm. The sample suffers degradation to a graded assemblage of fines and the percentage of material passing a 2.36 mm sieve, relative to the initial sample weight, gives the AIV. It is a measure of the resistance of an aggregate to granulation under impact stresses. A lower numerical value indicates a more resistant rock.

b) Aggregate Crushing Value (ACV). In this test a sample weighing approximately 2 kg is subjected to a steadily increasing load totalling 400 KN (about 40 tonnes) over a period of 10 minutes. As in the AIV test, the fines passing a 2.36 mm sieve are calculated as a percentage of the initial weight and this is the ACV. Once again, a



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3.

lower value indicates a more resistant rock. The ACV gives a relative measure of the resistance of an aggregate to crushing under a gradually applied load.

Mechanical Tests: Strength and Durability

a) Los Angeles Abrasion Value (LAAV). This test is a well established and internationally recognised test procedure which assesses the resistance of an aggregate to attrition by impact and abrasion forces. It is described in ASTM C131 and European (CEN) Standards. The principle of the test is that a 5000 g sample of aggregate is put into a steel drum with eleven steel balls, and then the drum is turned for 500 revolutions. On removal from the machine, the mass of aggregate retained on a 1.70 mm sieve is determined and this value, relative to the initial sample weight, gives the LAAV. A lower value indicates a more resistant rock.



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