Ularring Hematite Project — 2012 Pre-Feasibility Study

The Ularring Hematite Project Option 2 processing route is designed to beneficiate Run of Mine ore by crushing, scrubbing, gravity separation, magnetic separation and grinding to produce a +60% Fe product at approximately 60% mass yield.

Report context

This pre-feasibility study for the Ularring Hematite Project was prepared for Macarthur Minerals Limited and reports on the processing test work and design completed for what is termed Option 2. The report is dated 2012 and the test work program was undertaken on samples provided for the deposit. Two processing options were investigated (Option 1 and Option 2), with Option 2 selected as the base case. Option 2 includes grinding to -2.5mm and a regrind circuit, whereas Option 1 included jigs and excluded the regrind circuit. The test work at Nagrom focussed on the Option 1 flowsheet and results were extrapolated to suit Option 2.

Processing route

Crushing and Grinding

Run of Mine ore with 95% passing 100mm is pre-sized through a sizer to -25mm. The feed is passed over a static grizzly with a nominal aperture of 100mm. The grizzly oversize can be broken up with an optional rock breaker. The sizer product is conveyed to the primary scrubber, where feed is adjusted to around 50% solids by volume. Scrubber discharge is wet screened on a double deck primary screen. The oversize (-25+8mm) is conveyed to a cone crusher (HP 5), the mids (-8+2.5mm) are conveyed to a High Pressure Grinding Roll (HPGR), and the undersize (-2.5mm) is pumped to the gravity circuit.

The HPGR subjects the ore to two grinding stages in one, reducing product to 3mm in the first pass and 1mm in the second pass, with a reduction ratio ranging between 3:1 and 2:1. Material is screened after a single pass through the HPGR and screen deck oversize is re-fed back to the HPGR. The HPGR consists of two counter-rotating rolls, one fixed and one floating, with grinding forces applied by four hydraulic rams. Total grinding force can range from 750 kPa to 20,000 kPa and pressures in the gap can range from 50 MPa to 250 MPa. The cone crusher and HPGR are housed in the same building and served by a single overhead crane. The plant feed of 500 tph average can be satisfied by a single cone crusher and HPGR.

The ROM sizer option could be replaced with a jaw crusher. A jaw crusher can handle a -750mm top size product and can produce -45mm product, but capacities are relatively low at around 160 tph per machine and multiple machines would be required. Another option is to use a HPGR and remove the cone crusher entirely, as the HPGR is capable of processing -30mm top size particle. The report notes that HPGR suppliers have advised the HPGR will perform more efficiently on an un-truncated feed (-30mm) and should process the whole ore stream.

Coarse Cyclone and Allflux Classifier

The -2.5mm product from the crushing and grinding section is pumped to a coarse cyclone cluster. The coarse cyclones remove the -30 micron fraction to overflow, reducing mass flow to the Allflux units. Approximately 30% of the mass is rejected at this point to overflow. The cluster consists of 6 cyclones, typically 420mm diameter, fed at 35 to 45% solids.

The Allflux unit is a double stage teetered bed separator using up flow water to separate a coarse iron product from the feed material. It has three outputs: coarse underflow (CUF) as concentrate product sized -2.5+0.5mm; middlings underflow (MUF) fed to spiral units sized -0.5+0.1mm; and fine overflow (FOF) sized <0.1mm fed to the magnetic circuit. The up flow flux and bed level can be adjusted independently as the main control variables.

Spiral Gravity Separation

Spirals are configured into three stages: roughers, middlings and cleaners. The Allflux MUF is fed into a constant density tank and pumped to the rougher spirals feed distributor. Rougher spirals produce a concentrate added to cleaner feed, a tails that is discharged, and a middlings pumped to the middlings spiral. Middlings spiral tails are added to rougher tails for disposal and middlings concentrate is added to rougher concentrate to be dressed on the cleaner spirals to produce a final concentrate. Cleaner tails are recycled to the mids spiral and cleaner mids are recycled to the cleaner spiral feed. Approximately 10% of tailings are expected to be rejected from the spirals circuit. The final concentrate, around 20% by mass, is added to the concentrate cyclone/dewatering screen feed.

Magnetic Separation

The feed for the magnetic separators is the underflow from the fine cyclones, which receive the Allflux FOF and the regrind mill product. A fine cyclone cluster ahead of the Low Intensity Magnetic Separators (LIMS) thickens the feed. The LIMS remove low magnetic susceptible material at around 1500 gauss and protect the high intensity magnetic separators (Slons) from choking. Mass pull from the LIMS ranges from 1% to 11%. The non-magnetics are fed to the Slon unit.

The Slon unit operates in the range of >1500 gauss up to typically 3000-4500 gauss and produces around 30% mass yield. The Slon concentrate appears to have a high goethite concentration. The report proposes including attritioners to break up the goethite, liberate silica and improve grade, followed by a cleaner WHIMS/Slon or Up-current Classifier. The non-magnetics from the Slon report to the scavenger spiral circuit.

Concentrate Handling

Concentrate from the coarse gravity circuit is fed to dewatering screen circuit, while regrind/magnetic separation circuits concentrates are pumped to a concentrate thickener. Flocculant is used to settle the concentrate. The thickened concentrate is fed to a disc filter to produce a final product cake of less than 10% moisture. The report notes that a disc filter has been assumed, although a belt filter can be used, and the choice of ceramic pressure filters and belt filters will be reviewed subject to further test work.

Tails Disposal

Fine plant tailings flow into the thickener feed launder with flocculant added. Thickened tailings are fed to tails disc filters. The disc filter product is combined with coarse tails from the dewatering screen and conveyed to a stackable tails stockpile. Coarse tails are dewatered via a cyclone/dewatering screen combination. The report states this will reduce the overall water requirement to between 20-40 m³/h and that a tailings storage facility will not be required. The report notes that thickening rates, filtration rates and stackable tails options will have to be confirmed by the supplier and by further test work.

Water Circuit

Water is recovered from thickeners and excess water drained from product stockpiles for recycle. The water balance shows the plant requires 30 m³/h of water assuming product dewatering circuits produce material with less than 10% moisture. Process water make-up required is 40 m³/h factor. Process water is supplied from the thickener overflow and raw water ponds pumped from a remote location.

Key reported parameters

Technical qualifications

This report presents pre-feasibility level process design based on the test work program undertaken for the Ularring Hematite Project Option 2. The test work at Nagrom focussed on the Option 1 flowsheet and results were extrapolated to suit Option 2. The JKSimMet model focused on using size distributions to calculate the splits which could cause differences shown in the mass balance.

The process uses 39 m³/h of make-up water. The report notes that thickening rates, filtration rates and stackable tails options will have to be confirmed by the supplier and by further test work. The choice of ceramic pressure filters and belt filters will be reviewed subject to further test work. Suitability of the HPGR and trade-off with the mill should be confirmed in the next phase by further trade-offs.

The following areas require additional test work and investigation: bulk sample testing on both low grade and high grade ore; test work on low grade ores and ore variability test work from low grade regions to verify initial test work findings; trade-offs to maximise different options as described in the study. Specific test work is also required for: the sizer manufacturer to provide necessary process guarantees; clay content assessment for scrubber removal; Reflux classifier, HG 10C spirals, and drying options; magnetising block, MIMS, and magnetic flocculation options; and the use of saline water and borehole/RO water purification.

The report states that Option 1 was not optimised and different mass recoveries at the Allflux, spirals and Slon, plus more conservative estimates were used for Option 1. Energy efficiency of HPGR is ore-specific; in general the harder the ore, the greater the energy savings are likely to be. The jaw crusher option would require multiple machines to process the same duty.

Source: Ularring Hematite Project , 2012 Pre-Feasibility Study, Macarthur Minerals Limited, Report No: R260.2012, Sections 17.1-17.8.