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DEPARTMENT OF INFRASTRUCTURE (PLANNING AND BUILDING CONTROL) Proposed Quarry Extension - Stoney Mountain Quarry Report on Poortown Quarry Product Splits
August 2010
DATE ISSUED: 3rd August 2010 JOB NUMBER: CA10324 REPORT NUMBER: 02 DEPARTMENT OF INFRASTRUCTURE (PLANNING AND BUILDING CONTROL) Proposed Quarry Extension - Stoney Mountain Quarry Report on Poortown Quarry Product Splits
August 2010
PREPARED AND APPROVED BY:
D N Hughes Associate Director
This report has been prepared by Wardell Armstrong LLP with all reasonable skill, care and diligence, within the terms of the Contract with the Client. The report is confidential to the Client and Wardell Armstrong LLP accept no responsibility of whatever nature to third parties to whom this report may be made known.
No part of this document may be reproduced without the prior written approval of Wardell Armstrong LLP.
1 Introduction 1-2 2 Assessment of Planning and Building Control Queries 3 A. Is all material extracted and sold from Poortown all high grade psv 3 B. Is information available to demonstrate split between high grade psv and non psv product 4-5 C. Could non psv products be used as a replacement for certain products produced at Stoney Mountain 6 D. Review of the Isle of Man Hard Rock Land Bank 7-8 3 Conclusions 9 4 Recommendations 9
Appendix 1 Schedule of Poortown Product Splits Appendix 2 Analysis of Poortown Product sales (27.03.2006 – 21.10.2009)
1.11 This Report, commissioned by the Director of Planning, is supplemental to the previous Wardell Armstrong Report (Ref. CA10234/01) on the “Assessment of Need” for the proposed extension at Stoney Mountain Quarry.
1.12 One of the key points highlighted in the aforementioned Report is that Poortown Quarry is the sole supplier of high quality PSV stone on the Island which is regarded as being of national importance. This reserve is primarily used to produce aggregates required for road construction.
1.13 Whilst Poortown stone could be considered as an alternative supplier of aggregates for other construction purposes, the use of such high quality stone where lesser stone would be adequate would be wasteful and the Island’s ability to self supply the necessary high psv material for road maintenance and construction would not be sustainable.
1.14 It is considered that the use of the deemed nationally important reserves at Poortown as an alternative/replacement source of supply of aggregate which would otherwise have been supplied from Stoney Mountain should be resisted.
1.15 An assessment of the land bank of hard rock reserves on the Island, incorporating the reserves at Cringle (c. 1.2mt); Billown (c. 0.49mt) and Stoney Mountain (c. 0.1mt) revealed that as of May 2010, there was c. 1.79 million tonnes (mt) of reserves available.
1.16 The land bank estimate excludes the deemed nationally important reserves at Poortown on the basis that these reserves are theoretically ‘ring-fenced’ for high specification use only.
1.17 Presently, there is no formal Government policy that totally excludes the reserves at Poortown as being of national interest.
1.18 The “Independent Review into the Scope and Structure of Government Report” published c. 2006 questioned whether or not it should be a core function of the Government to operate a quarry. The Report considered that the possibility of at least contracting out the Government owned quarries section should be explored. The Report went on to state that Poortown is the only supplier of gabbro on the Island which is an essential stone required for road building and other major engineering works.
1.19 As a point of clarification, the stone at Poortown was originally classified as a gabbro but recent geological investigations reveal that the rock is actually a dolerite. Dolerite is an intrusive rock which is similar in composition to basalt (the lava erupted from volcanoes) and gabbro (which is plutonic being a body that has
crystallized from magma slowly cooling below the surface of the Earth). The differing crystal sizes are due to the different rates of cooling where basalt cools quickly and has a very fine structure, while gabbro cools very slowly, at great depth, and large crystals develop. Dolerite is intermediate and has medium sized crystals.
1.20 Subsequently, in the “Report of the Council Ministers on the Review of the Scope and Structure of the Isle of Man Government” published in January 2010, the Council of Ministers Governance Committee concluded that “...the self sustainability of the Island regarding the supply of gabbro for highways construction demonstrates the national strategic importance of Government’s continuation of the operation by the Department of Transport of Poortown Quarry and would not support private ownership of such a national strategic asset’. Hence, the Committee did not support the Review Report recommendation.
1.21 Officers of Planning and Building Control (P&BC) studied the Wardell Armstrong Assessment of Need Report for Stoney Mountain and raised several queries in relation to Poortown Quarry concerning its reserves and the type of products produced. There was a requirement to further interrogate the use of the reserves at Poortown suggesting that robust geological evidence would be required to argue that all Poortown reserves should be classed as being of national interest.
1.22 P&BC wished to know:
A. Is all the material extracted and sold from Poortown all high grade psv; B. Is information available to demonstrate the split between high grade psv products and non psv product; C. Could non psv products be used as a replacement for certain products produced at Stoney Mountain;
D. Carry out a review of the Island’s hard rock land bank by considering i. The inclusion of all Poortown reserves; ii. The inclusion of Poortown reserves that are non psv; and iii. Excluding all Poortown reserves.
1.23 This report attempts to address these queries.
2.1 The various queries raised by P&BC have been assessed and the findings discussed below.
2.2 The simple answer to this question is no.
2.3 Poortown is the largest basic intrusion on the Isle of Man. The rock is a fine to medium grained dolerite consisting of augite crystals in a dark green matrix of plagioclase and chlorite. The dolerite has been intruded into the adjoining ‘country rock’ which comprises the Creggan Mooar Formation of the Manx Group. Deformation has since generally folded and faulted the intrusive igneous rocks, often producing disconnected lenticular masses of the igneous rock. In general however, the main alignment of the sills is ENE-WSW. Site prospecting established that the Poortown dolerite was intruded into the Manx Group rocks in the form of 3 separate sills. A sill is a sheet like body of igneous rock which conforms to bedding or other structural planes. The dolerite reserves are overlain by an overburden comprising glacial boulder clay of the Snaefell Formation which varies in thickness between zero and 6 metres.
2.4 Where the dolerite lies close to the surface it will have undergone the effects of weathering which will have affected the quality of the rock. It has been established that the rock is poorer in quality close to the surface but improves with depth. There will also be areas of ‘country rock’ present within the quarry’s working limits which is not psv quality but will need to be quarried in order to expose the underlying dolerite.
| Category | Tonnage | Split of Overall Sales | DoT Sales | Private Sales | ||
|---|---|---|---|---|---|---|
| PSV MACADAMS | 113,509 | 42% | 81,556 | 30% | 31,953 | 12% |
| Non PSV products | 99,008 | 36% | 37,889 | 14% | 61,120 | 22% |
| PSV Clean Aggregate | 59,040 | 22% | 47,767 | 18% | 11,273 | 4% |
| 271,557 | 100% | 167,211 | 104,346 |
2.5 Wardell Armstrong has been provided with a breakdown of the sales of each product type from Poortown Quarry during the period between 27.03.2006 to 31.10.2009.
2.6 The range of products are grouped into three categories namely, PSV Macadam’s; PSV Clean Aggregate and Non PSV Products. These products and categories are listed within Appendix 1. The PSV Macadam category includes all sales of coated materials as well as the sized aggregate sold to Billown Quarry where this material is used in the manufacture of coated roadstone at Colas’ asphalt plant at Billown. PSV clean aggregates include sized chippings which are washed and these are used as a surface dressing on roads where the chippings are spread over a layer of hot bitumen. The Non psv products generally comprise Type 1, scalpings and rubble.
2.7 During this period, the total sales from Poortown amounted to 271,557 tonnes.
2.8 Based on the aforementioned product categories, the combined sales tonnage; split proportion of overall sales; DoT and Private Sales are summarised in the table 1 below.
2.9 Based on the above figures, the ratio between PSV and Non PSV products is 62%:38%.
2.10 The 38% proportion of Non PSV product should not be taken as being a true indicator as to the amount of non PSV material at Poortown. This is because the quantity of non PSV product has been bolstered in recent years by the sale of c. 37,600 tonnes of inferior scalpings. During the period of analysis, Poortown Quarry has been extended in an easterly direction into the area known as ‘Rockmount’. The extension of the workings involved the advancement of the upper benches which would have encountered weathered dolerite and occasional pockets of the Manx Formation ‘country rock’ into which the dolerite would have been intruded. The degree of weathering of the dolerite will have affected its physical properties rendering it unsuitable in the manufacture of high psv products. Therefore, the weathered dolerite and ‘country rock’ would in all probability either been used to
produce a non psv product or if unsuitable treated as a waste product and disposed of within the quarry.
2.11 Analysis of the sales splits of psv and non psv products prior to the expansion of the quarry, i.e. pre April 2007 reveals that ratio of PSV/Non PSV was 70%:30%.
2.12 Wardell Armstrong is aware that detailed prospecting works to evaluate the stone reserves at Poortown was undertaken in 2003 by the CSA Group on behalf of the then Department of Transport. The current reserves at Poortown (as of November 2009) are estimated to be of the order of c. 1.2 million tonnes (mt). However, it is unclear if this total reserve relates solely to the reserve of dolerite or the combined reserve of dolerite and ‘country rock’ within the quarry limits. Inspection of the CSA Factual and Interpretative Reports of the prospecting works would help to clarify this point.
2.13 In the absence of these CSA reports, it is assumed that the 1.2 mt reserve relates to the combined reserve of dolerite and ‘country rock’ within the quarry limits. Applying the PSV/Non PSV ratio of 70:30, then the remaining PSV reserves is approximately 0.84mt with the amount of NON PSV material being approximately 0.36mt.
2.14 The average saleable output from Poortown over the past 10 years has been c. 0.072mt per annum. Based on this rate of output, then the life of the 1.2 mt reserve is c. 16.6 years (1.2mt ÷ 0.072mt).
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