Star – Orion South Diamond Project — 2011 Feasibility Study

The 2011 feasibility study reports a proposed diamond processing plant design for the Star and Orion South kimberlites at Fort à la Corne, Saskatchewan, based on historical bulk sample plant operations and extensive laboratory testwork.

Report context

The Star – Orion South Diamond Project feasibility study (FS) was prepared for Shore Gold Inc. The recovery methods section (Section 17.0) documents the process plant design developed in collaboration with Metso Minerals, based on data from bulk sampling programs conducted between 2004 and 2009 and metallurgical testwork carried out at multiple laboratories.

Processing route

Comminution

The proposed process plant uses fully autogenous grinding (AG) mills, selected because the FalC Kimberlites are categorised as “soft” and amenable to AG milling. Run-of-mine kimberlite is first crushed to -400 mm by a mobile mineral sizer in the pit and conveyed to a conical stockpile holding 45,000 tonnes of live feed. Two apron feeder streams feed material to two 10.97 m diameter by 7.97 m length AG mills, each with 8,000 kW installed power and variable speed drives. Mill discharge passes through a 45 mm trommel screen; -45 mm material reports to spiral classifiers while +45 mm material is recycled via flexowells. The spiral classifiers break up clay balls, wash off loose clays, remove contaminants, float off -250 micron material, and transfer +1 mm material onto sizing screens. The -1 mm material is sent to the processed kimberlite containment facility (PKCF).

Dense medium separation

The DMS section processes two size fractions: -8 +1 mm and -45 +8 mm. The -8 +1 mm fraction is treated through three modules of 450 mm gravity fed cyclones, each module comprising three DMS cyclones, two magnetic separators for ferrosilicon recovery and recycling, a demagnetising coil, a densifier and a nuclear densitometer. The -45 +8 mm fraction is treated through two modules of 800 mm gravity fed cyclones, each module consisting of one DMS cyclone, two magnetic separators, a demagnetising coil, a densifier and a nuclear densitometer. DMS sinks are washed and conveyed to the recovery section feed bin. DMS floats are washed and conveyed to coarse processed kimberlite piles.

Recovery section

The recovery section is designed to treat 30 t/h of DMS concentrate. Feed material is screened into five size fractions: -2 +1 mm, -4 +2 mm, -8 +4 mm, -18 +8 mm and -45 +18 mm. The diamond recovery technologies include wet and dry high intensity magnetic separators (WHIMS and HIMS), X-ray machines (broad band and single particle sorters), grease belts, and laser Raman single particle sorters for the -2 +1 mm fraction. The recovery section uses three different processing routes based on size fraction. Hand sorters conduct the final sort, size diamonds using DTC sieves, weigh each size fraction, and pack diamonds for transport in secure Docklock canisters.

Processed kimberlite containment

The -1 mm tailings are separated into -0.25 mm and -1 +0.25 mm fractions in the spiral classifiers. The -0.25 mm material is pumped directly to the PKCF. The -1 +0.25 mm material is pumped to hydrocyclones on the PKCF berms for dewatering and use as construction material for berms. In winter, hydrocyclones are bypassed and all -1 mm material is discharged into the PKCF.

Bulk sample plant

A bulk sample plant (BSP) attached to the main plant will be used for auditing mining benches, auditing process plant efficiency, and processing exploration bulk samples. The BSP contains a 4.9 m x 2.1 m AG mill, a 420 mm pump fed DMS cyclone, and recovery equipment including a double pass flow sort X-ray machine, grease table, infrared dryer, WHIMS, HIMS, laser Raman sorter, and glove box.

Key reported parameters

Technical qualifications

The report does not provide actual plant performance data as the plant is a proposed design. All recovery efficiency figures are design targets rather than demonstrated performance. Historical BSP data assumes 98% recovery efficiency consistent with bulk sample plants of this design used in other operations. The plant design criteria document drafted by Shore after discussions with AMEC, Metso, OreProX and Metal Dog Minerals (Petersen, 2007) collated information from metallurgical tests and BSP experience. Further simulations in the detailed design phase are noted as required to improve grind efficiency. The report states that no recrushing of DMS floats or recovery plant rejects is planned in the current design. The thickening unit section notes that such a unit is only necessary if water supply cannot meet plant requirements, which is not the case for this project.

Source: Star – Orion South Diamond Project , 2011 Feasibility Study, Section 17.0 Recovery Methods.