Matthews Ridge Manganese Project — 2013 Pre-feasibility Study

This pre-feasibility study report from August 2013 describes the proposed processing plant design for the Matthews Ridge manganese deposit, including design criteria, equipment specifications, and expected concentrate grades.

Report context

The report, Section 17 of a pre-feasibility study for Reunion Gold Corporation, was completed in August 2013. It covers the recovery methods for processing manganese ore from the Matthews Ridge project in Guyana. The processing plant design is based on a continuous and homogenous feed from open pits, with mechanical components oversized to handle fluctuations.

Processing route

Design basis

The processing plant was designed for a daily throughput of 10,000 t/d but, based on targeted concentrate production to match market opportunities, will be operated at 7,500 t/d. The plant operating schedule is 365 days per year.

Run-of-mine ore

Run-of-mine ore is dumped at a feeder stockpile located on the western side of the plant on high ground at elevation 130. The stockpile is designed to accommodate up to 200,000 t of ore. Ore is blended and pushed by a dozer to an excavator, which feeds through a grizzly onto the process plant feed hopper.

Reclaim and primary crushing

Reclaim equipment is located in a concrete tunnel. One apron feeder, 7 m long by 1.5 m wide, reclaims material and feeds the primary roller crusher feed conveyor. A grizzly with 450 mm by 450 mm openings is installed above the apron feeder. The ore is fed into a 510 mm by 1,220 mm primary roller crusher, which reduces particle size to 100 mm at discharge.

Scrubbing and screening circuit

The circuit is designed to segregate product sizes of -19 mm / +6.3 mm, -6.3 mm / +0.85 mm, and -0.85 mm. A scrubber 3.6 m in diameter by 10 m long, with 450 kW power, allows scrubbing and washing of 450 t of ore per hour. Water is added to de-agglomerate lumps and chunks.

After scrubbing, material is discharged onto a double deck vibrating screen, 2.4 m wide by 6.1 m long. A protective deck prevents oversized particles (+75 mm) from falling directly on finer screening media. The upper screen has 20 mm square openings; the bottom deck has 6.5 mm square openings.

Oversized material from the protective deck and top screen (+19 mm) is recirculated to a 915 mm by 915 mm secondary roller crusher, which crushes particles to minus 30 mm before re-introduction to the scrubbing and screening circuit.

The oversize of the lower deck (-19 mm / +6.3 mm) is sent to the lump jigging circuit. The undersize (-6.3 mm) contains both rejects and fine manganese concentrate. A bank of four stack sizers, each with five decks, screens the fine material. The -6.3 mm / +0.85 mm material is sent to fine jigging; minus 0.85 mm is pumped to the rejects thickener.

Jigging circuit

The jigging circuit has two independent circuits: one for lump manganese concentrate (-19 mm / +6.3 mm) and one for fine manganese concentrate (-6.3 mm / +0.85 mm). Each circuit is fed from a 555 t storage bin to maintain steady feed rates.

The lump jigging circuit consists of a 2.5 m wide by 3.0 m long, three-chamber jig, which uses specific gravity differences to collect heavier manganese oxide at the bottom discharge. Dewatering screens recover water from tails and concentrate. The concentrate dewatering screen is a single deck, 1.8 m wide by 4.8 m long vibrating screen; the tails dewatering screen is a single deck, 2.4 m wide by 4.8 m long vibrating screen. Maximum water content in the final product is below 8%.

The fine jigging circuit is similar, with a jig 4.0 m wide by 3.0 m long. The work done by the jigs increases manganese concentration to above 36% for the fine product and 38% for the lump product.

Rejects thickening and pumping

Rejects are sent to a 25 m diameter high-rate thickener to increase density from 14% to 40% solids by weight. Thickened rejects are pumped to the rejects pond; overflow water is collected into process water tanks and returned to the process.

Concentrate storage and loading

Concentrate is conveyed to four storage silos in two lines of two silos. Each silo holds 400 t of concentrate, giving total storage capacity of 800 t per product. Silos are emptied by gravity through rotary valves into haul trucks for daily transport to Port Kaituma concentrate storage and barge loading facilities.

Air and water services

Two screw compressors, with one operational and one backup, provide compressed air for instrumentation and services. Each jig has a dedicated blower for jigging pulsation; two blowers operate with one on standby.

Total water requirements are estimated at 1,500 m³/h. The main water source is the rejects pond, collecting rain and tailings decant water. Water is stored in two tanks, each of 400 m³ volume, next to the thickener. Process water is recovered from thickener overflow; reclaim water is pumped from the rejects pond. Water is also recovered from jig dewatering screens.

Reagents

Flocculant is the only reagent required, with expected consumption of approximately 30 g/t of ore. Two mixing and distribution tanks are installed next to the thickener. Settling tests are required to confirm this value.

Process control

Mill operation is monitored by electronic control and instrumentation using a programmable logic controller (PLC) interface in the mill control room. The system is organized into three levels: field networks and instruments; equipment control and measurements; and process control and supervision via a human-machine interface (HMI).

Motor control centers control full voltage motors; variable frequency drives are used for variable speed motors. Motors are remotely controlled by the PLC via Ethernet communication. Fiber optic cables serve as the plant communications backbone.

Control systems are designed to be fail-safe, preventing damage to equipment and injury to personnel. No equipment will automatically restart after a fault or emergency stop clearance.

Operating modes

Equipment has Manual and Auto modes, both considering safety and process interlocks, with the Local/Remote selector set to Remote. Local mode permits operation without process interlocks but with safety interlocks, used primarily for maintenance.

Grades and recoveries

The wash plant and jigging circuit increase ore grade from 15% Mn at feed to 36-40% Mn. Ore blending on the feeder stockpile is required to homogenize feed grades. Mass pull (concentrate/feed) is estimated at 27.4% (2,055 tpd). Manganese recovery is expected to be about 73%.

Expected average final product specifications are: lump concentrate (-19 mm / +6.3 mm) at 57.5 t/h (1,265 t/d) with 39.1% Mn, 8% moisture, 12% LOI, 4.9% Fe, 21.2% SiO₂, 7.7% Al₂O₃, and 0.050% P. Fine concentrate (-6.3 mm / +0.85 mm) at 35.9 t/h (790 t/d) with 36.4% Mn, 8% moisture, 12% LOI, 5.5% Fe, 25.4% SiO₂, 8.6% Al₂O₃, and 0.049% P.

Testwork limited the lump concentrate to 19 mm; further optimization is required to evaluate increasing the top limit to 50-70 mm.

Key reported parameters

*Note: Values are design criteria from the study unless otherwise stated. Testwork-based values are noted in the text.*

Technical qualifications

The report notes that testwork was performed on samples from across the deposit to determine expected product specifications. The proposed flowsheet does not contain any technological issues, and mechanical components are well established in typical industrial processing plants. Met-Chem Canada Inc. provided technical assistance in process plant engineering, including equipment sizing, material take-offs for civil and structural works, plant layout drawings, and cost estimate.

Settling tests are required to confirm the flocculant consumption value of 30 g/t. Further optimization is required to evaluate increasing the top limit of lump concentrate beyond 19 mm to 50-70 mm.

*Source: Section 17, Recovery Methods, Reunion Gold Corporation Pre-feasibility Study, Matthews Ridge Manganese Project, August 2013.*