The mineral resources defined at the Halley's, Hale-Bopp, Shoemaker-Levy, Nindilbillup and Shoemaker-Levy North nickel laterite deposits have developed over Archaean ultramafic rocks through prolonged deep weathering. Sub-horizontal tabular zones containing residual and supergene accumulations of nickel, cobalt, manganese and iron have developed in
association with extensive leaching of principally magnesium.


The majority of nickel mineralisation in the RNO deposits is hosted in the goethite/limonite zone, whilst the upper levels of the saprolite zone is also commonly well mineralised. In all RNO deposits, nickel mineralisation forms as a blanket beneath barren surface units whilst cobalt mineralisation occurs mainly in a narrow zone generally towards the top of the nickelenrichment zone in association with manganese accumulation. It is often centred around the redox boundary in the limonite zone, recognised by an accumulation of manganese enrichment.

Operations at Ravensthorpe involve open pit mining and beneficiation of nickel laterite ore.

All mining activities will take place in the three mining areas, each of which has been split into smaller stages as described in Section 15, and Appendix VII. The current mining activities in Halleys involve a conventional Drill/Blast and Load/Haul operation. There is up to 40% free diggable ore and waste to be mined over the life of mine. All remaining ore and waste requires drilling and blasting.

FQM owns most of the mining equipment, and has contracted Piacentini & Son, a mining contracting company based in south-west Western Australia, to operate and maintain this equipment under a three year, bcm rate based contract which includes drill and blast activities and management of the explosives supply.

FQM commenced mining and crushing operations in May 2011 with daily production rates of 10Kt per day of Saprolite and 17 Kt per day of Limonite. The HY11 pit is currently 40 metres deep and the HY13 and HY14 pits are between 4 and 24 metres deep. The current monthly requirement for material movement is 1.5 million tonnes per month which is within the capability of the mining fleet.

Beneficiation
Nickel and cobalt values are enriched in the fines fractions of both the limonite and Saprolite ores, and the beneficiation process consists of rejecting the principally siliceous coarse fractions using conventional wet ore sizing equipment. Typical mass rejections of 60-70% are achieved at a nominal nickel recovery of 60-65%.

Crushed ore to each Beneficiation circuit is recovered from its respective reclaimer stockpile. Both feeds direct the crushed ore to a drum scrubber, where loose ore agglomerates are broken up and dispersed, and any loosely attached mineralisation is scrubbed from the siliceous gangue. The scrubber product is treated through a combination of screening and hydraulic classification to recover the nickel and cobalt values, which are now concentrated in the -100µ fraction. The +100µ material is discarded to a reject stream which is mechanically transported to a dump.

Limonite beneficiated products are treated through Pressure Acid Leach (PAL) and Saprolite beneficiated products are treated through Atmospheric Leach (AL) after being thickened.

Pressure Acid Leach (PAL)
Thickened beneficiated limonite ore slurry is processed in two parallel Pressure Acid Leaching (PAL) trains to selectively leach the nickel and cobalt values from the ore concentrate. This is achieved at a temperature of 250oC and a pressure of 4,500 kPa using concentrated sulphuric acid at a design acid consumption of 332 kg/t of ore.

Slurry is preheated to a temperature of approximately 190oC before it is pumped into the autoclave. Each PAL train consists of a continuous six-compartment horizontal autoclave, operating at a temperature of 250oC. Steam injection is used for temperature control in the first four compartments; this supplements the autogenous heating of the slurry by sulphuric acid dilution. Acid is added to the first two compartments.

Autoclave discharge from each train is flash cooled in three staged letdown vessels; the third stage flash bottoms report to the AL stage, while the vent steam is ducted to the heater condensers for preheating the incoming ore slurry.

Pre-Leach
The thickened Saprolite slurry from the Saprolite beneficiation plant is leached under atmospheric pressure to solubilise the bulk of the contained nickel and cobalt values. The Pre-Leach step is a high intensity stage in which Saprolite slurry is blended with concentrated sulphuric acid and leached at approximately 95oC. Leach slurry from the Pre-Leach stage, containing significant residual of acid, iron and other impurities in solution, passes to the AL stage.

Atmospheric Leach (AL)
Output streams from the PAL and Pre-Leach stages are combined and allowed to react in a series of stirred tank reactors maintained at a temperature of 95 - 100oC. As acid levels decrease below 30 grams/litre H2SO4, iron commences to precipitate in the form of sodium jarosite (NaFe3(SO4)2(OH)6), simultaneously regenerating acid to maintain a driving force for continued nickel and cobalt leaching.

Effluent slurry from the atmospheric leach stage enters the Induced Jarosite Precipitation (IJP) stage.

Induced Jarosite Precipitation (IJP)
The function of the IJP stage is to precipitate excess ferric iron from solution under hot, mildly acidic conditions. Some precipitation of other impurities, such as aluminium and chromium, also occurs at this stage.

AL effluent is partially neutralised with recycled Secondary Neutralisation Precipitation residue slurries, simultaneously recovering the metal values associated with those streams. The residual acid is then further reduced and controlled to approximately 5 – 10 g/l H2SO4 using ground limestone slurry. Temperature is maintained at >95oC to favour improved solids settling characteristics.

Slurry then proceeds to the Primary Neutralisation (PN) stage.

Primary Neutralisation (PN)
In Primary Neutralisation, further limestone slurry is added in stages to increase the pH to 2.0 – 2.5, which precipitates the bulk of the remaining ferric iron, along with portions of the aluminium, chromium and other impurities. After a residence time of 1.5 hours, the slurry is delivered to the CCD circuit.

Counter-current Decant Washing (CCD)
The CCD separates the leach liquor from barren residues in a series of thickeners with counter-current flow of solids and liquor. Wash liquor consists of acidified Manganese Removal overflow, which is added to the final thickener. Thickener 6 underflow reports to the tailings neutralisation and disposal system, while Thickener 1 overflow proceeds to the
Secondary Neutralisation (SN) stage.

High molecular weight, low charge anionic flocculant is added to each thickener to assist in settling.

Secondary Neutralisation (SN)
The aim of the SN stage is to remove the last of the iron and aluminium from the CCD1 overflow before proceeding to the Mixed Hydroxide Precipitation (MHP) stage. This is achieved by oxidation with air and precipitation using limestone of the ferrous iron as ferric hydroxide, and by hydrolysis of the aluminium ion.

Mixed Hydroxide Precipitation (MHP)
The MHP stage recovers the bulk of the nickel and cobalt from solution as a mixed hydroxide using magnesium oxide (MgO) powder as the precipitant in a train of three reactors. After a residence time of three hours, the solids are collected in a thickener.

The MHP thickener overflow, still containing approximately 5% of the incoming nickel and cobalt, is treated in the Scavenger Precipitation (SP) stage. MHP thickener underflow is forwarded to a belt filter where the solids are washed with clean water to remove any soluble impurities before the solids are repulped and filtered through a pressure filter. The pressure filter product is put into nominally 1t bulk bags and containerised for export as the final product.

Scavenger Precipitation (SP)
The objective of the SP stage is to recover the remaining nickel and cobalt from solution, while still leaving manganese in solution for removal in the Manganese Removal (MnR) stage. This is achieved by staged slaked lime addition through a train of three reactors with the resultant product thickened in a thickener to separate the solids and liquor.

Thickener overflow proceeds to the Manganese Removal (MnR) stage whilst thickener underflow is returned to the SN stage for retreatment.

Manganese Removal (MnR)
The aim of MnR is to precipitate the bulk of the remaining manganese. Precipitation occurs due to a combination of increased pH and mild aeration using slaked lime slurry and air in each of the two tanks. The resultant product is thickened to separate the solids and liquor.

Thickener overflow is mildly acidified and returned to the tail of the CCD as CCD wash liquor whilst the thickener underflow is disposed to residue storage.