Grass Valley Project
The Grass Valley Project is located 15km south of the town of Mokopane and approximately 20km south of Ivanhoe Nickel and Platinum’s PGM‑Ni‑Cu project on the Platreef. Grass Valley is a joint venture with Impala Platinum under terms of which PPD may earn a 75% interest in the Impala properties by completing a Bankable Feasibility Study within a five‑year period. Impala also has a first right of refusal to acquire the concentrates (or other end product) in an off‑take agreement to be negotiated at arm's length.
The Grass Valley Project consists of the farms Volspruit 326 KR and a small portion of Zoetveld 294 KR covering a total area of 1,279 hectares.
The rocks underlying Volspruit comprise cumulates of the Lower Zone of the Bushveld Complex and its immediate floor rocks. The succession is dominated by ultramafic cumulates which range in composition from dunites and harzburgites to ortho-pyroxenites.
In the northern limb the Lower Zone can be subdivided into three major litho-stratigraphic units – in order of increasing height these are: the Volspruit pyroxenite sub-zone; the Drummondlea harzburgite-chromitite sub-zone; and the Moorddrift pyroxenite-harzburgite sub-zone. The zone of PGE and base metal sulphide mineralisation – informally referred to as the Volspruit PGE-Ni Reef – is hosted in orthopyroxene cumulates in the middle portion of the Volspruit sub-zone, usually several tens of metres above a ±100m thick zone of olivine cumulates – the only significant sequence of olivine cumulates in the Volspruit sub-zone. Cumulates hosting the mineralisation are generally fine-grained, compact orthopyroxene and orthopyroxene-chromite cumulates. The sulphides occur as fine pentlandite and chalcopyrite grains intergrown with pyrrhotite that occupy the intercumulus spaces in the pyroxenite. Mineralised intervals are typically in the order of 10 – 50m in width. No change in texture or mineral assemblage is apparent in the mineralised zones. Present evidence points strongly towards an orthomagmatic origin for the mineralisation.
The prefeasibility technical work, overseen by PPD, used teams of consultants in the relevant disciplines. These included The Mineral Corporation, Bateman Africa, Knight Piesold and Prime Resources, together with independent peer review consultants.
Grass Valley Prefeasibility
· Resources: 71 million tonnes
· 1.23g/t PGE + 0.14% Ni + Cu
· Ore mined:28m tonnes
· 1.40g/t PGE + 0.15% Ni + Cu
· Waste mined: 104m tonnes
· Stripping Ratio 3.65:1
· Life of mine: 8 years
· Pit depth 130/160m
· Fleet size: 16 haultrucks
· PPD has expended to date ZAR 7.18M
(A$ 1.29M) on a prefeasibility study.
(Excludes all drilling and assaying costs)
Comparison of Evaluation released to ASX in January 2005 compared to same study with only varying the commodity prices and FX rates updated to market prices as at 1 May 2006.
Evaluation Results
Improvements to Grass Valley Prefeasibility
PPD currently investigating a range of improvements to enhance the Grass Valley Prefeasibility including:
· Improved capital and operating costs
· Increased resources/ additional exploration ground i.e. Longer project life
· Potential hydrometallurgy joint venture with metallurgical specialist company
· Provided PPD has sufficient funds, the programme is to commence further pre and full feasibility studies
· The aim is to generate an economically sound project with high rate of return
Exploration and Expenditure and Drilling Coverage
Project Future Feasibility Study Expenditure: Grass Valley
Drilling, Resources and Orebodies
A total of 249 holes were drilled, generally at spacings of 75 to 100m. Total core length obtained was 25,663 metres, resulting in over 17,000 assay samples. Appropriate controls were employed with the assay laboratories to ensure accuracy and reliability of results.
Two distinct orebodies are present; the Northern orebody, having a strike length of 1.8km, and the Southern orebody, with a strike length of 1.0km
The mineral resource estimate for the project was an Indicated 71 million tonnes at 1.23 g/t 3PGE+Au (Pt: 0.52g/t, Pd: 0.60g/t, Rh: 0.08g/t, Au: 0.03g/t) plus 0.11% Ni and 0.03% Cu.
Mining
The ore is amenable to open pit extraction via sequential mining of two areas in relatively close proximity - the larger ‘North’ orebody followed by the ‘South’ orebody. A mine life of eight years at a milling rate of 3.6 million tonnes per annum was indicated.
Economic comparisons indicated that contract mining (as opposed to operating own equipment) would be appropriate for a relatively short life operation.
Metallurgy and Process
The plant design was based on a conventional mill/float (MF) circuit with a capacity of 3.6m tonnes ore per year or 10,000 tonnes per day.
Recovery rates were based on testwork covering a range of materials drawn from the different areas that would be encountered under mining conditions. The overall average recoveries, for a concentrate grading 50g/t 2PGE+Au, were 71.3% (average weighted by value).
A limited amount of testwork was conducted on hydrometallurgical studies. Whilst preliminary results are promising, with high PGM recoveries, the base metal recoveries are lower. The process is not sufficiently advanced to proceed with any recommendations at this stage, but is an avenue for continued research.
Infrastructure
The total site area as designed would be approximately 20 square kilometres and infrastructure plans included provision of roads, buildings, electricity and water.
Environmental Studies
Environmental studies and investigations included land use and soils, air quality, waste dumps and dams, noise, flora and fauna. No major obstacles to development were encountered in these areas.
Nyl floodplain
The Nyl River (normally dry in the vicinity of the project area) is to the west but the 50 year floodline encroaches on the Northern Pit. Although this is a low frequency event, three main aspects would require attention in any development plans:
• Obtaining appropriate permits
• Ensuring minimal environmental impact to the area
• Dealing with any potential water ingress to the pit to ensure minimal interruption to mine operations
Conclusions
The project has been taken to a level considered appropriate and reliable for a prefeasibility study estimate. All project disciplines have been addressed in parallel and the most important aspects have been subject to peer reviews.
Significant progress was been made towards improving metallurgical recoveries at lower head grades. Further geotechnical and geohydrological work together with a detailed topographical survey would be required in the event of any full feasibility study.