OZ Minerals updates Martabe ore reserves
Tuesday, December 23 2008 - 03:12 AM WIB
1 MARTABE ORE RESERVES STATEMENT -30 JUNE 2008
1.1 Introduction
The Martabe October 2008 Ore Reserves are derived from the gold and silver Mineral Resources at the Martabe project located on Sumatra in Indonesia, operated by PT Agincourt Resources.
In late 2007 the Ore Reserve Estimate was determined as part of the Martabe Project Bankable Feasibility Study (BFS). Following additional drilling in early 2008, the Mineral Resources and Ore Reserves were revised in June 2008. The Ore Reserve Estimate was prepared by Nigel Spicer of Coffey Mining Pty Ltd. The consultancy and engineering groups who contributed information to the BFS are summarised in Table 2.
The Resource model upon which the Ore Reserve is based uses the geological database as at 25 February 2008. The geological interpretation was based on data from 257 Diamond Drill holes (41,792m). No Reverse Circulation drilling was carried out
Ordinary Kriging was used to estimate grades within the geological / metallurgical domains interpreted in the Resource block model.
The BFS considers the mining of the Purnama deposit only. Other potentially mineable Resources in nearby deposits have not been considered at this stage.
1.2 Results
The Ore Reserve is reported within the Purnama final open pit design prepared in June 2008. Table 2 summarises the Pumama Ore Reserves.
Table 2. Purnama Ore Reserve Statement, June 2008
| Classification | Tonnes (Mt) | Au (g/t) | Ag (g/t) | Au (Moz) | Ag (koz) |
| Proved | 3.9 | 2.7 | 41.8 | 0.336 | 5.288 |
| Probable | 31.8 | 1.8 | 23.9 | 1.883 | 24.419 |
| Total | 35.7 | 1.9 | 25.9 | 2.219 | 29.707 |
Compared to the 2007 Ore Reserve estimate, in-fill drilling has upgraded the Mineral Resource classification in parts of near surface Resources and allowed 3.9 Mt of Ore Reserves to be classified as Proved. Apart from this, there are no material changes to the Ore Reserves from 2007 to 2008.
1.3 Compliance with JORC Code Assessment Criteria
This Ore Reserve statement has been compiled in accordance with the guidelines defined in the Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (The JORC Code, 2004 Edition).
All information in this Statement which relates to the Martabe Ore Reserves is based on, and accurately reflects information compiled under the supervision of Nigel Spicer who is a member of the Australasian Institute of Mining and Metallurgy. Nigel Spicer is an employee of Coffey Mining Pty Ltd.
Nigel Spicer has the necessary experience relevant to the style of mineralisation, the type of deposit and the activity undertaken to qualify as a ?Competent Person? under the Code for Reporting of Mineral Resources and Ore Reserves (JORC Code) ? 2004 Edition, and has given his consent for the inclusion of the material in the form and context in which it appears.
The company, consultancy and engineering groups who have contributed information to the BFS, that are relevant to the Ore Reserve Estimate are summarised in Table 3.
Table 3. Contributors to the Martabe Bankable Feasibility Study
| Resources | The competent persons for the mineral resource estimate is Ingvar Kirchner of Coffey Mining Pty Ltd and Graham Petersen of PT Agincourt Resources |
| Geotechnical | Golder Associates Pty Ltd. GHD Pty Ltd |
| Mining | Coffey Mining Pty Ltd |
| Metallurgy | Intermet Engineering Pty Ltd |
| Infrastructure | Intermet Engineering Pty Ltd. Coffey Mining Pty Ltd |
| Operating Cost | Intermet Engineering Pty Ltd. Coffey Mining Pty Ltd. PT Agincourt Resources |
| Environmental | PT Agincourt Resources. PT Environmental Resources Management Indonesia |
| Metal Prices | OZ Minerals |
1.4 Key Points relating to the June 2008 Martabe Gold Ore Reserves Statement
1.4.1 Metal Prices
The Ore Reserve Estimates uses a gold price of US$700 per ounce and a silver price of US$11 per ounce.
1.4.2 Classification
The Ore Reserve Estimate is based on the Mineral Resource Estimate classified as Measured and Indicated after consideration of all mining, metallurgical, social, environmental and financial aspects of the operations. The Proved Ore Reserve has been derived from the Measured Mineral Resource and the Probable Ore Reserve has been derived from the Indicated Mineral Resource.
1.4.3 Mineral Resources Estimate
The Competent Persons for the Purnama gold and silver Mineral Resource estimate are Ingvar Kirchner of Coffey Mining Pty Ltd and Graham Petersen of PT Agincourt Resources.
The Resource model is based on the drillholes completed as at 25 February 2008. The initial geological interpretations were done by PT Agincourt Resources geologists. The lithological and alteration interpretations were revised for use as estimation domains by Coffey Mining. The domains serve as a constraint for block modelling and grade estimation. Two-metre downhole composites were generated from 257 diamond drillholes having predominantly PQ3 and HQ3 diameter core. Geostatistical analyses, variography and block modelling were undertaken by Coffey Mining. Estimation of gold and silver grades into the model utilised Ordinary Kriging methods.
Bulk densities are based on data from measurements of core using sealed core and immersion methods. Bulk densities were applied to the block model using average values based on lithology, with values ranging from 2.2g/cc to 2.6g/cc.
The Resource Estimate has been classified based on data density, data quality, confidence in the geological interpretation and confidence in the estimation.
1.4.4 Cut-off Grade
The cut-off grade used for the Ore Reserve Estimate is the non-mining break-even grade taking into account mining recovery and dilution, metallurgical recovery, site costs, and royalties. Because the Resources are comprised of ore types with varying metallurgical recoveries the cut-off grade is expressed in equivalent plant recovered dollars per tonne. On this basis, the cut-off grade used for the Ore Reserve Estimate is USS13.46/t.
1.4.5 Mining Factors and Assumptions
The Ore Reserve Estimate is based on conventional open pit mining operations using drilling and blasting, and small excavators loading all wheel drive articulated trucks. The mining and recovery parameters reflect industry practices. The average assumed dilution is 10% and the assumed mining recovery is 95%.
1.4.6 Metallurgical Factors and Assumptions
The Ore Reserve Estimate use metallurgical recoveries that vary according to the four metallurgical ore types identified during the BFS. The average metallurgical gold recoveries for the four ore types vary between 55% and 80%. The average silver recovery for all the ore types is 52%. (end of excerpt)