Broken Hill - Southern operations
The reserve for the Southern operations at Broken Hill is based on assays from diamond drill holes and mapping data interpreted on cross-sections spaced 19.8 metres apart. The resource is based on a three-dimensional model of the geology and mapping of the mine openings. The reserve has been calculated by intersecting actual three-dimensional stope design shapes with the resource model, and is derived from a measured (31.7 million tonnes), indicated (6.4 million tonnes) and inferred (2.6 million tonnes) resource at 30 June 1998 of 40.7 million tonnes at 9.3% zinc, 5.5% lead and 59 grams per tonne silver, at a cut-off grade of 7% lead plus zinc.

During 1997/8, diamond drilling added 1.9 million tonnes to the reserve. Mining depleted it by 2.5 million tonnes and a further 2.6 million tonnes were deleted as having no reasonable expectation of being mined. The reserve at 30 June 1998 is estimated to be 23.7 million tonnes at 8.1% zinc, 5.2% lead and 51 grams per tonne silver.

(Compiled by C Lutherborrow, Chief Geologist, Pasminco Broken Hill Mine)

Broken Hill - Potosi
The reserve for the Potosi open-cut mine is based on assays from drilling and mapping data interpreted on cross sections 10 metres apart. This information is used to create a three-dimensional block model of the resource. The depth of the production surface in the Potosi open-cut operation during 1997/8 approached the limit of the ore defined by closely spaced grade control drilling. This required additional drilling of the lower section of the resource followed by a re-optimisation of the final pit design. The exercise decreased reserves by 0.3 million tonnes, while the grade increased from 11.6 % to 12.5% lead and zinc.

Mining at Potosi during 1997/98 depleted the reserve by 0.2 million tonnes. At 30 June 1998, the reserve is estimated to stand at 0.3 million tonnes at 9.7% zinc, 2.8% lead and 30 grams per tonne silver.

(Compiled by C Lutherborrow, Chief Geologist, Pasminco Broken Hill Mine)

Century
More than 500 diamond, reverse circulation and percussion holes have been drilled at an average drilling density of 70 metres to delineate the resource and to explore for additional resources.

The reported reserves were developed from mine planning studies completed in April 1997. In the course of these studies, the economic factors impacting upon the exploitation of the identified mineral resource were evaluated. The physical disposition of the mineralisation has been assessed and mining loss and dilution parameters applied.

A variable cut-off grade has been applied in compiling the ore reserves. The cut-off grade is based upon the zinc equivalence (ZnEq) relationship, which includes value for lead and silver, and varies from 8.0% ZnEq reducing to 4.0% ZnEq over the planned life of the open-pit mining operations. The equivalence relationship is based upon analysis of the metallurgical performance of the ore and assumptions of metal prices expected to be achieved for the project. The variable cut-off grade has been developed with the objective of maximising the net present value of the mine operation.

The reserve as at 30 June 1998 was 98.5 million tonnes at 11.6% zinc, 1.7% lead and 43 grams per tonne silver, calculated from a measured (69.3 million tonnes) and inferred (2.9 million tonnes) resource of 105.1 million tonnes at 12.1 zinc, 1.7 % lead and 46 grams per tonne silver.

(Compiled by R A Adam, Mining & Resource Technology Pty Ltd)

Dugald River
The Dugald River resource was estimated using a block modelling technique with a cut-off of 10% zinc plus lead, a minimum block thickness of 5 metres and a vertical extent from surface of 1,000 metres. At 30 June 1998,the indicated (48 million tonnes) and inferred (2 million tonnes) resource is estimated to be 50 million tonnes at 12.1% zinc, 1.9% lead and 41 grams per tonne silver.

(Compiled by J H Duke, Principal Geologist, Metals)

Elura
The reserves at the Elura mine are based on assays from diamond drill holes and samples from underground mapping and have been interpreted on vertical cross-sections at 10 and 20 metre spacings. The reserve is derived from a measured (22.5 million tonnes) and indicated (0.7 million tonnes) resource of 23.2 million tonnes at 8.1% zinc, 5.0% lead and 59 grams per tonne silver.

A total of 4.9 million tonnes written out of the Elura reserve during 1998/9 was partly offset by 1.1 million tonnes moving from resource to reserve in the lower levels. Mine production in 1997/8 reduced ore reserves by 1.1 million tonnes.

During 1997/8, major problems occurred in the recovery of zinc to zinc concentrates from ore mined from the centre pillar between the two lenses that make up the main ore body. As a result, mining of the 4/5 block was curtailed before planned tonnes had been extracted, as production from stopes with satisfactory metallurgical performance was favoured. A total of
1.4 million tonnes was written out of reserves as a result of metallurgical information now known about the area.

(Compiled by P Levers, Geology Superintendent, Pasminco Elura Mine)

Rosebery
Reserves at the Rosebery mine are based on diamond drilling conducted on sections spaced from 10-40 metres along strike, together with information gained from underground ore exposures in some lenses. They are derived from a measured (2.3 million tonnes), indicated (1.5 million tonnes) and inferred (7.9 million tonnes) resource at 30 June 1998 of 11.7 million tonnes at 12.3% zinc, 4.3% lead, 0.35% copper, 139 grams per tonne silver and 2.2 grams per tonne gold.

During 1997/8, successful surface and underground exploration programs increased the measured, indicated and inferred resource by 14% compared with end June 1997. Additions were delineated in the south (T lens), central (V lens) and northern mine areas (B, P, K and W lenses).

The reserve base decreased 7% compared with last year. Moderate increases were defined in B and C lenses with incremental rises in P, K and T lenses, but were offset by mining depletion and conversion of reserves into the inaccessible category, principally in B and J lenses. The reserve at 30 June 1998 is estimated to be 3.4 million tonnes at 9.5% zinc, 3.3%
lead, 0.41% copper, 112 grams per tonne silver and 2.0 grams per tonne gold.

During 1998/9, the focus of drilling will be to continue exploring for new resources in the mine area, together with upgrading the large amount of inferred resource tied up in K and P lenses.

(Compiled by M Berry, Chief Geologist, Pasminco Rosebery Mine)

*Report of the Joint Committee of the Australasian Institute of Mining and Metallurgy,
Australian Institute of Geoscientists and Minerals Council of Australia (JORC)

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