Broken Hill - Southern Operations
The reserve for the Southern Operations at Broken Hill is based on assays from diamond drill holes and geological mapping interpreted on cross sections spaced 19.8 m apart. The current measured, indicated and inferred resource at a cut-off grade of 7% Zn + Pb stands at 29.0Mt at 9.0% Zn, 5.3% Pb and 59 g/t Ag. The resource is based on a three dimensional model of the geology and the mine openings. The reserve is derived from the measured and indicated resource by intersecting actual three dimensional stope design shapes with the resource model. The proved plus probable reserve at 31 March 1999 stands at 17.9Mt at 7.5% Zn, 4.0% Pb and 41 g/t Ag. During the period from 30 June 1998 to 31 March 1999, high resolution modelling of historical cut and fill mining allowed detailed design and mining evaluation of all individual pillar stopes to be undertaken for the first time. This was carried out in conjunction with a Mine Optimisation Study by Australian Mining Consultants. These studies identified 5.1Mt of material in the reserve that had no reasonable expectation of being mined. During the reporting period 1.9Mt of reserve material was mined, 5.1Mt was deleted and 1.2Mt of new material added.
(Compiled by C Lutherborrow, Chief Geologist and D Edwards - Superintendent Projects Pasminco Broken Hill Mine)
Broken Hill - Potosi
The resource for the Potosi Open Cut Mine is based on assays from drilling and geological mapping interpreted on cross sections 10m apart. The reserve is calculated by intersecting the resource model with a three dimensional model of the in situ volume of the final open pit design and applying a mining dilution factor. The Potosi reserve at 31 March 1999 stands at 0.1Mt at 8.5% Zn, 3.4% Pb and 12 g/t Ag. During the reporting period there were no additions to the reserve and mining depleted the reserve by 0.2Mt.
(Compiled by C Lutherborrow, Chief Geologist and D Edwards - Superintendent Projects Pasminco Broken Hill Mine)
Elura
The Elura Mine reserve is based on assays from diamond drill holes and from underground mapping interpreted on cross sections at 10m and 20m spacing. The current measured plus indicated resource stands at 22.8Mt at 8.3% Zn, 5.2% Pb and 62 g/t Ag The resource is based on a three dimensional geological model of the orebody.
The proved plus probable reserve at 31 March 1999 stands at 14.9Mt @ 8.2% Zn, 5.0% Pb and 55 g/t Ag.
A review of the stoping strategy below 6 level to 9 level and completion of stope designs for this area has resulted in the significant increase in the proved reserve from 2.2Mt in 1998 to 13.6Mt in 1999. Mining depleted the reserve by 0.8Mt, 0.3Mt was removed for geotechnical reasons and a further 1.0Mt was lost as a result of the stoping strategy review.
Below 9 level the probable reserve is calculated by applying mining factors to the measured plus indicated resource.
(Compiled by P Leevers, Geology Superintendent and P Fairfield - Senior Mining Engineer Pasminco Elura Mine)
Rosebery
Ore reserves at the Rosebery Mine have been based on assays from diamond drilling conducted on sections spaced from 10m to 40m along strike and 10m to 50m up and down dip and on geological mapping. The current measured, indicated and inferred resource stands at 11.6Mt at 13.4% Zn, 5.0% Pb, 0.3% Cu, 150 g/t Ag and 2.4 g/t Au. The resource is based on a three dimensional model of the orebody and the distribution of remnant pillars.
The proved plus probable reserve at 31 March stands at 3.1Mt at 10.6% Zn, 3.9% Pb, 0.45% Cu, 123 g/t Ag and 2.4 g/t Au. During the nine month period since the last reserve statement, the reserve tonnage has fallen 10% but has been offset by an increase in grade as a consequence of raising the cut-off grade for resource estimation by 30%. This increase in the cut-off grade followed the recommendations of the Rosebery Life of Mine Study and together with an ongoing re-assessment of remnant ore reserves in previously mined areas, were the major contributing factors in the fall in reserves and the increase in metal grades.
Continued success in the exploration program was insufficient to fully offset the losses due to mining depletion and the effects of the increased cut-off grade. During the reporting period, 0.45Mt of the reserve were mined, 0.5Mt were deleted and 0.62Mt were added. The deep exploration drilling program has been deferred and diamond drilling in the coming year will focus on upgrading the status of the inferred resources to allow additional reserve estimation.
Century
More than 500 diamond, reverse circulation and percussion holes have been drilled at an average drilling density of 70 m 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 Mt at 11.6% zinc, 1.7% lead and 43 grams per tonne silver, calculated from a measured (69.3Mt) indicated (32.9Mt) and inferred (2.9Mt) resource of 105.1 Mt at 12.1% zinc, 1.7% lead and 46 grams oer 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 m and a vertical extent from surface of 1,000 m. 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 41grams per tonne silver.
(compiled by J H Duke, Principal Geologist, Metals)
Tennessee - Gordonsville and Clinch Valley
The reserves at the Gordonsville and Clinch Valley Mines in Tennessee USA are based on economic grade ore that is exposed by underground development and by underground drilling. In addition, economic grade ore is included that is delineated by surface drilling and can be developed from existing mine workings. The proved plus probable reserves as at 30 April 1999 stand at 22.7Mt of 3.2% Zn.
The inferred resource is based on surface drill intersections that occur in a primary ore horizon but are currently uncommenced due to the distance from existing mine workings. Unlike the other Pasminco mines, the indicated resource total does not include the proved and probable reserve tonnages. The reserve is 17.1Mt at 3.2% Zn.
Work is in hand to ensure that the reserves and resources quoted will be compliant with the JORC standards.
(Compiled by Wallace Mitchell - Geological Consultant)
Ernest Henry
Pasminco Limited has a 49% interest in the Ernest Henry Mine in Queensland (MIM Ltd 51%).
The following statement is the first major recalculation of the Ernest Henry Mine reserves and resources since the initial feasibility study was completed in 1995. The published resource then was 166Mt which has been depleted by 16.3Mt through mining operations. A successful drilling program in 1998 and a reappraisal of existing data have delineated an additional 5Mt of resources and reserves.
The resource at Ernest Henry Mine is based on ordinary kriging of blocks with dimensions 20m x 20m x 16m. Supergene mineralisation is based on ordinary kriging on a geologically constrained block model at 0.5% Cu cut-off. Primary mineralisation utilises a 0.4% Cu cut-off. The resource as at 30 June 1999 is 155Mt at 1.1% Cu and 0.52 g/t Au. The reserve is 113Mt at 1.1% Cu and 0.54 g/t Au.
(Compiled by R A Crookes, Technical Services Manager Ernest Henry Mine)
*Report of the Joint Committee of the Australasian Institute of Mining and Metallurgy, Australian Institute of Geoscientists and Minerals Council of Australia (JORC)
Click here to download PDF files of:
- Operations at a Glance (173 Kb)
(excerpt from Annual Report 1999)
- Production 5-Year Summary (20 Kb)
(excerpt from Annual Report 1999)
- Performance 10-Year Summary (17 Kb)
(excerpt from Annual Report 1999)
or
- Pasminco Annual Report 1999 (4 Mb)
(full report including the above excerpts)
Due to the size of the file, it may take some time to download depending on your internet connection.
Click here to download Adobe Acrobat PDF Reader
Return to Home