Buckreef PEA Adds Flotation and a 15 µm Concentrate Regrind to Lift Sulphide Recovery as the Plant Grows to 3,000 t/d

This independent technical report provides an updated mineral resource estimate for the Buckreef Gold Project based on exploration drilling completed through February 2020.

Report context

This independent technical report, effective May 15, 2020, was prepared by Virimai Projects for Tanzanian Gold Corporation (TRX) to update the mineral resource estimates for the Buckreef Gold Project located in the Geita District of north-central Tanzania. The project comprises four gold prospects: Buckreef, Eastern Porphyry, Tembo, and Bingwa, held under Special Mining License SML04/1992 and 12 Prospecting Licenses. The update is based on exploration and drilling data collected by TRX during the period January 2019 to February 2020, totaling 17,650 m of drilling, which brings the total meterage drilled on the project to approximately 125,750 m.

Processing route

Metallurgical testwork history

No detailed metallurgical testwork was completed as part of this mineral resource update study. Assumptions on economic recoveries are based on several previous testwork programs carried out and reported in prior SEDAR filings.

Testwork conducted by MPC and SGS demonstrated that more than 90% of the gold can be recovered by a combination of gravity concentration and leaching of the tails. MMSA testwork established that 93% of the gold from oxide ore can be recovered without gravity concentration by carbon-in-pulp leaching, and that 85% of the gold from sulphide ore can be recovered in a similar manner.

Previous testwork programs

Key results from Geita Gold testwork are documented in the report. Gallery Gold conducted scoping and diagnostic testwork. IAMGOLD completed Phase 2 metallurgical testwork including grinding testwork and process selection testwork. Heap leaching testwork included simulated heap tests by SGS in 2009 and heap leaching amenability testwork by SGS in 2016.

Current testwork program

The purpose of the current testwork was to inform the processing strategy for the prefeasibility study. Samples originated from oxide and sulphide ore materials from the Buckreef deposit. Bond mill indices were determined for both oxide and sulphide ore materials. Pilot milling was conducted using the EDS multi-shaft mill.

Head grade and deportment

Head analysis for gold was completed. Gold deportment in the milled material was examined by size fraction for both ore types. For the oxide ore, gold deportment is higher in the fine fraction. For the sulphide ore, gold is not concentrated in any one size fraction.

Gravity concentration and cyanidation

Gravity concentration testwork was performed using a Falcon L40 concentrator, with grade and recovery curves against mass pull generated for both oxide and sulphide ores. Cyanidation results were reported for both oxide and sulphide ores. Cyanide and lime consumption were summarized.

Design processing route

The processing strategy is described for a proposed plant. The process description and design criteria include: ore receipt and scrubbing, crushing and milling, gravity concentration, thickening plant, carbon-in-leach plant, carbon acid wash and elution, carbon regeneration, and tailings treatment. The design incorporates an EDS mill for the milling circuit.

Overall design criteria

The overall design criteria are specified in Table 17.2 of the report. Design head grades for oxide and sulphide ores are defined. Mass balance information is provided.

Design criteria by area

Design criteria are presented for the scrubber/screen, jaw crusher, EDS mill and classification circuit, gravity concentrators, shaking table, dewatering cyclone, thickener, carbon-in-leach section, tails screening, carbon elution, and tailings detoxification.

Reagents and utilities

Reagent requirements are documented. Utility requirements including power consumption are reported.

Key reported parameters

Technical qualifications

This report is an update of mineral resource estimates only. No detailed metallurgical testwork was completed as part of this current mineral resource update study. The mineral reserves reported are from the June 2018 technical report and have not been updated. A new pit optimisation taking into account the current mineral resources update and current prevailing economic factors is still to be completed. Inferred mineral resources are considered geologically speculative and are not used in project economics, nor are they considered for mining plans. The study is restricted to open pit mining at this stage.

*Source: NATIONAL INSTRUMENT 43-101 Independent Technical Report – Updated Mineral Resource Estimate for the Buckreef Gold Mine Project, Tanzania, East Africa, effective May 15, 2020.*

This report describes the proposed expansion of the Buckreef processing facility from its current configuration to a 3,000 tpd circuit incorporating flotation and fine grinding for sulphide ore treatment.

Report context

This preliminary economic assessment (PEA) for the Buckreef Mine, Report No. 473, was prepared for TRX Gold Corporation. The processing section (Section 17.0) presents recovery methods for the Buckreef Deposit, drawing on expansion modelling by Orway Mineral Consultants (WA) Pty Ltd (“OMC”) summarised in “Buckreef Gold Project Expansion Review, Report No. 7833” dated January 6, 2025.

Processing route

Existing operations (historical operating data)

In April 2020, TRX initiated mining of Buckreef’s oxide mineralization and processing up to 60 tpd via an on-site pilot oxide gravity CIL plant. The plant was expanded in 2022 to 360 tpd, and again in 2023 with the addition of a 1,000 tpd capacity ball mill expected to process both oxide and sulphide mineralization. In July 2024, the Company announced plant expansion to 2,000 tpd, averaging 1,750 tpd of process plant throughput.

The current processing facility consists of two trains of three-stage crushing, four closed circuit ball mills, eleven carbon-in-leach (“CIL”) tanks, and complete elution (less reactivation kiln), electrowinning, and smelting for the production and sale of gold doré.

Proposed expansion design (Phase 1 and Phase 2)

Expansion modelling by OMC confirmed that to improve recovery, an expanded circuit needs to include flotation and fine grinding. A rationalisation of the flowsheet was undertaken to finalise the process plant consolidated flowsheet containing the following unit operations:

• Existing Primary Crushing;
• New Surge Bin with overflow to dead stockpile and reclaim;
• Retire Secondary and Tertiary Crushing, and product screening;
• New SAG Mill;
• Existing 1,000 tpd Ball Mill;
• New Classification;
• New Flotation;
• New Flotation Concentrate Regrind Circuit;
• New Flotation Concentrate Regrind Thickener;
• New Flotation Tails Leach Feed Thickener;
• New Flotation Concentrate Regrind Leach Circuit with potential to add oxygen addition;
• Existing Modified CIL 3 Flotation Tails Circuit;
• New Split AARL Acid Wash and Elution Circuit;
• New Carbon Regeneration Kiln; and
• Existing Tails Storage Facility.

Comminution would be via primary crush, surge bin, overflow to dead stockpile with front-end loader (“FEL”) reclaim, and grinding via SAG and ball mill circuit that would incorporate the existing ball mill No.5. Flotation of a sulphide concentrate and regrinding to P80 15 µm was included. Thickening of both the concentrate regrind stream and flotation tails stream was included to improve leaching performance and reduce cyanide consumption. Two new leach tanks of identical size to the CIL 3 tanks would be added for concentrate regrind leaching, which would then join the flotation tails feed to CIL 3 through the existing tankage. A new split AARL elution circuit with a dedicated acid wash column and subsequent carbon regeneration kiln was adopted to improve carbon activity and reduce soluble gold losses to tails.

Expansion circuit modelling was undertaken for two throughputs: Option (Phase) 1 – 2,000 tpd (current – 1,750 tpd); Option (Phase) 2 – 3,000 tpd (2,960 tpd nominal).

Phase 1 has a production target rate of 1,750 tpd (636,738 tpa) for YR1 and YR2 with capital expenditures for the following major equipment: Flotation Circuit (trash screens, reagent conditioning tank, and five Metso e50 tanks cells (50 m³/cell) and blower system); Flotation Concentrate Regrind Mill (High Intensity Grinding (“HIG”) Metso HIG700); Pumping and Cycloning within Regrind Circuit; Concentrate Leach Feed Thickener (16.5 m diameter); Two additional CIL Tanks to treat Flotation Concentrate; Flotation Tailings Thickener (16.5 m diameter); 4 tpd Elution Circuit; and Associated Screens, Pumps, Reagent System, and upgraded Water System.

During operations in Phase 1, expansion will be underway for an increased production target rate of 3,000 tpd (1,080,000 tpa) for YR3. With a planned grinding target of P80 at 100 – 150 µm, capital expenditures are planned for: SAG mill circuit Surge Bin, Feeders, Conveyors; SAG Mill (7.32 m diameter x 3.75 m Effective Grinding Length, 3,500 kW); Cyclone Cluster with SAG and Ball Mill(s) Circuit; Reverting to Single Toggle Jaw Crusher (750 m x 1,069 m for SAG mill feed prep); and Cyanide Destruction System (to coincide with underground mine construction).

Water management (historical and proposed)

Surface water is scarce in the Project area. The main surface water source is the Nyamazovu River, a small stream which has been used as a fresh water supply for the process plant. The current Buckreef operation has an efficient system in place to conserve and recycle water including process, mine and storm water. Current water requirements are 2,644 m³/day for processing approximately 1,488 tpd (Mills 2, 3, 4 at 440 m³/d each; Mill 5 at 1,320 m³/d; total 2,640 m³/d; Elution columns totalling 6.3 m³/d). Water requirements for the Phase 1 and Phase 2 expansion are approximately 5,200 m³/day.

Key reported parameters

Technical qualifications

The report recommends that cyanide destruction testing be conducted at an external laboratory. Further metallurgical testwork is recommended on comminution, confirmatory flotation, thickening, rheology of flotation tails and concentrate, and concentrate leach test at 40% solids, P80 of 100 – 150 µm with oxygen sparging and kinetic sampling to confirm that the predicted recovery of the proposed circuit is achievable.

Source: TRX Gold Corporation, Buckreef Mine PEA, Report No. 473, Section 17.0 Recovery Methods (pages 243-255)

This section details the proposed processing routes for the Buckreef Project, drawing on the May 2012 PEA, with separate large conventional and small modular plant designs for oxide and sulphide ores.

Report context

The recovery methods described in this section form part of the NI 43-101 Independent Technical Report for the TRX Buckreef Project Preliminary Economic Assessment, dated May 2012. The process plant design and costing for the large conventional plant was undertaken by K'Enyuka and reported in a document entitled "Preliminary Economic Evaluation – Processing" Dec 2011. A high level study of smaller 30,000tmp modular plants was conducted by SMS for Case 3, reported in "Mining Study for a PEA for Buckreef Gold Project, Tanzania" (SMS-058-12, March 2012). The PEA process design concept is modular in configuration, so that the process plant at BRMA can be relocated to the BZMA to increase capacity in the latter area.

Processing route

Ore types and mineralogy

The BRMA and BZMA orebodies consist of an upper, weathered, oxidised zone overlying a variable transition zone and lower, primary, fresh sulphide orebodies with depth. The ores are free milling with direct leach recoveries in the lower 90% range and are amenable to gravity recovery. The fresh sulphide orebody contains pyrite and arsenopyrite. The oxide zone is clay rich saprolitic material, which potentially poses a significant problem in terms of material handling and secondary crushing. The oxide zone is more developed at BZMA.

Large Conventional Processing Plant

Comminution Circuits

A semi-autogenous grinding (SAG) circuit, followed by a ball mill, would minimise the impact of clay rich saprolitic material. However, the rod mill to ball mill index ratios of the various orebodies indicate a likelihood of a build up of critical size material in the SAG mill, indicating the need for a pebble crusher in the circuit. The large tonnage of oxide material at BZMA favours the use of this SAG mill, ball mill and pebble crushing (SABC) circuit, although the pebble crushing might be delayed until harder transition or sulphide ore is treated.

The oxide zone at BRMA is significantly less developed than at BZMA. As the design strategy is to relocate the initial plant to BZMA after BRMA ore is depleted, smaller modular units are preferable. Secondary and tertiary crushers with their associated conveyors and screens would be easier to relocate than a large SAG mill. The secondary and tertiary crushers would feed a ball mill. It may be possible to defer installation of the tertiary crusher if only oxide material is treated in the early stage.

BRMA Plant – Crushing and Screening

The 150,000tpm RoM is tipped onto a static grizzly above the RoM bin, from where ore is extracted via an apron feeder to a vibrating grizzly. Oversize from the grizzly is fed to a jaw crusher. Grizzly undersize, together with jaw crusher product, is fed to the secondary crusher screen. Secondary screen oversize is fed to the secondary crusher via a feed bin. Screen undersize, together with secondary crusher product, is conveyed to the tertiary crusher screen. Tertiary screen oversize is fed to the tertiary crusher via a feed bin and tertiary crusher product joins the feed to the tertiary screen. Tertiary screen undersize is conveyed to the ball mill feed bin.

BZMA Plant Phase 1 – Primary Crushing

The 300,000tpm BZMA RoM ore is tipped onto a static grizzly above the RoM bin, from where ore is extracted via an apron feeder to a vibrating grizzly. Oversize from the grizzly is fed to a jaw crusher. Grizzly undersize, together with jaw crusher product, is fed to the SAG mill.

Milling and Gravity Concentration – BRMA

Crushed ore from the mill feed bin is fed to the ball mill. Mill discharge flows through a vibrating screen into the mill discharge sump and is pumped to the classifying cyclone. A portion of the cyclone underflow is fed via a tramp screen to a centrifugal gravity concentrator. Tramp screen oversize and concentrator tailings are returned to the mill feed, along with the balance of the cyclone underflow. Classifying cyclone overflow feeds via a tramp/woodchip screen to the pre-leach thickener. Flocculant is added to the thickener feed. Thickener overflow discharges into a process water tank.

Milling, Pebble Crushing and Gravity Concentration – BZMA Phase 1

SAG mill discharge flows through a mill discharge vibrating screen into the mill discharge sump and is pumped to the classifying cyclones. Oversize material from the SAG mill discharge screen is either discarded or, if necessary, conveyed to a pebble crusher with product returned to the SAG mill feed. A portion of the cyclone underflow is fed via a tramp screen to a centrifugal gravity concentrator. Tramp screen oversize and concentrator tailings are returned to the ball mill feed, together with the balance of the cyclone underflow. Ball mill discharge passes through a vibrating screen and is returned to the mill discharge sump.

Gravity Circuit

Metallurgical testwork results indicate a recovery advantage to utilising gravity concentration of free gold. Some sulphide associated gold in the gravity concentrate can be subjected to more intensive cyanidation. The gravity circuit would be incorporated into the ball milling circuit with the concentrate processed in a secure area, possibly within the gold room area.

Carbon-in-Leach

Metallurgical testwork indicates limited "preg robbing" effect, hence CIL will be used in preference to leach/carbon-in-pulp (CIP).

Pre-leach, Leach and Recovery Circuits

These circuits are duplicated in each of the BRMA and BZMA plants. Thickener underflow is pumped to a pre-leach tank where final pH adjustment with lime and pre-aeration of the pulp takes place. Slurry flows through a series of leach/adsorption tanks where cyanide is added, gold dissolved and adsorbed onto activated carbon. Activated carbon is retained by inter-stage screens and transferred counter-currently. Loaded carbon from the first CIL tank is transferred to the elution plant. Barren regenerated carbon is added to the tail end of the circuit.

Loaded carbon is screened, washed, and transferred via a holding bin into a column for acid washing to remove calcium build up. Carbon is then transferred to an elution column where gold is removed by a caustic-cyanide soak and washing with hot water. Eluted carbon is transferred to a bin prior to regeneration in a rotary kiln. Regenerated carbon together with fresh make up carbon is screened and returned to the tail end of the CIL circuit.

Gold in the eluate is recovered by plating onto stainless steel wool in electrowinning cells and stripped by high pressure spray. Gold sludge is filtered and dried in a calcine oven and smelted with fluxes to produce gold bullion.

Gravity concentrate from the milling circuit is subjected to intensive cyanidation in a reactor with high concentrations of cyanide and possibly other additives including oxygen. Solid residue is returned to the milling circuit and gold-bearing solution is treated in electrowinning cells.

Tailings from the CIL circuit are screened to recover any carbon which may have escaped and are then processed in a series of tanks to reduce cyanide content prior to pumping to the tailings disposal facility.

Small Modular Processing Plants

As an alternative to the large conventional plants, a small modular plant configuration was interrogated for the PEA. SMS obtained quotations for 30,000tpm modular plants and reviewed capital and operational costs. Each modular plant is a self-contained unit comprising a 30,000tpm crushing/milling, CIL and electrowinning module. The initial plant at BRMA would require five such modules at an individual cost of USD20m each. Site preparation would be approximately USD0.5m per unit and relocation cost to BZMA would be USD1.0m per unit.

The SMS review highlighted several issues. The total capital requirement for the small modular BRMA plant would be USD129.0m and USD125.0m for BZMA. Installed power requirement per 30,000tpm module is 1.9MW, equating to approximately 10MW for the BRMA plant alone. Equipment capital for the five modular plants for BRMA is USD100.0m compared to equipment capital of USD78.7m for the large plant. Non-equipment based costs were not included in the modular plant quotation. The technical and economic review suggests that small capital savings in the modular plant option are off-set by higher power, labour, reagent and maintenance costs.

Alternative Processing

SMS metallurgical consultants suggested alternative process plant components that could improve project economics and efficiencies, to be interrogated in the PFS. These include alternative comminution strategies to reduce power and cost, skid mounted comminution units (jaw crusher/cone crusher), skid mounted Vertical Shaft Impactors or High Pressure Grinding Rolls, and RoM single stage milling.

Heap Leach

Heap leach technology was investigated on the BRMA and BZMA materials. Based on metallurgical testwork, heap leaching is not recommended. Heap leach of milled ore is not feasible and RoM material would require agglomeration using lime and cement. The sulphide component is unlikely to be amenable to heap leach. The oxide component contains significant quantities of clay, creating channelling and coating of particles, rendering them impervious to cyanide leaching.

Key reported parameters

*Values assumed based on available information per the source.

Technical qualifications

The process design and costing for the large conventional plant was undertaken by K'Enyuka and reported in Dec 2011. The small modular plant study was conducted by SMS and reported in March 2012. Process design criteria values marked with an asterisk were assumed based on available information. The PEA is a preliminary assessment and the technical and economic review of the modular plant option suggests further optimisation could be investigated in a PFS. The separate flotation of sulphides has not formed part of the PEA due to the presence of arsenic in both oxide and sulphide ore.

Source: NI 43-101 Independent Technical Report for the TRX Buckreef Project PEA, May 2012, Section 17 Recovery Methods.

This article presents the processing design, ore characterisation parameters, and testwork results for the Buckreef Project as reported in the May 2012 NI 43-101 Independent Technical Report.

Report context

The process plant design and costing for the large conventional plant for the Buckreef Project was undertaken by K'Enyuka and reported in a document entitled "Preliminary Economic Evaluation – Processing" Dec 2011. In addition, a high level study of smaller 30,000tpm modular plants was conducted by SMS for Case 3, the results of which are reported in a document entitled "Mining Study for a PEA for Buckreef Gold Project, Tanzania" (SMS-058-12, March 2012). The report forms part of the NI 43-101 Independent Technical Review for the TRX Buckreef Project PEA dated May 2012.

Processing route

Ore Characterisation

The BRMA and BZMA orebodies consist of an upper, weathered, oxidised zone overlying a variable transition zone and lower, primary, fresh sulphide orebodies with depth. The ores are free milling with direct leach recoveries in the lower 90% range and are amenable to gravity recovery (Section 13). The fresh sulphide orebody contains pyrite and arsenopyrite and some improvement in recovery could be obtained by flotation of the sulphides and subjecting them to fine grinding to liberate the gold. However the incremental recovery would be unlikely to justify the added expense and complexity of the plant.

The oxide zone of the deposits is clay rich saprolitic material, which potentially poses a significant problem in terms of material handling and secondary crushing. The oxide zone is more developed at BZMA and therefore the comminution circuits of the conventional plants are designed to accommodate the higher quantities of clay rich, oxide zone RoM at BZMA.

The presence of arsenic has impact on the environmental management and the possibility of flotation and separate processing and disposal of the concentrated sulphide stream could be considered. However, there is also arsenic in the oxide ore and therefore the separate flotation of the sulphides has not formed part of the PEA.

Large Conventional Processing Plant Design

Comminution Circuits

The oxide zone of the BRMA and BZMA deposits is clay rich saprolitic material and potentially poses a significant problem in terms of material handling and secondary crushing. A semi-autogenous grinding (SAG) circuit, followed by a ball mill, would minimise this impact. However the rod mill to ball mill index ratios of the various ore bodies indicate that there is a likelihood of a build up of critical size material in the SAG mill, which would indicate the need for a pebble crusher in the circuit.

The large tonnage of oxide material in the BZMA favours the use of this SAG mill, ball mill and pebble crushing (SABC) circuit for this material, although the pebble crushing might be delayed until harder transition or sulphide ore is treated.

The oxide zone at BRMA is significantly less developed than at the BZMA and although clay rich oxide zone material it may still represent a handling and crushing problem, this will be of shorter duration. Furthermore, there is potential to blend fresh RoM material with oxide material as there are a number of deposits to be processed in this area.

As the design strategy adopted is to relocate the initial plant to the BZMA after the BRMA ore is depleted, it would be preferable to have smaller modular units. Secondary and tertiary crushers with their associated conveyors and screens would be easier to relocate than a large SAG mill. The secondary and tertiary crushers would feed a ball mill, which would need to be relocated. It may be possible to defer installation of the tertiary crusher if only oxide material is treated in the early stage of the plant.

Gravity Circuit

The metallurgical testwork results indicate that there is a recovery advantage to utilising gravity concentration of free gold and has the advantage that some sulphide associated gold in the gravity concentrate can be subjected to a more intensive cyanidation. The gravity circuit would be incorporated into the ball milling circuit with the concentrate being processed in a secure area, possibly within the gold room area.

Carbon-in-Leach

The metallurgical testwork indicates that there is limited of a "preg robbing" effect and hence CIL will be used in preference to Leach/carbon-in-pulp (CIP).

BRMA Plant Description

The 150,000tpm RoM is tipped onto a static grizzly above the RoM bin, from where the ore will be extracted via an apron feeder to a vibrating grizzly. Oversize from the grizzly is fed to a jaw crusher and grizzly undersize, together with jaw crusher product, is fed to the secondary crusher screen. The secondary screen oversize is fed to the secondary crusher via a feed bin and screen undersize, together with the secondary crusher product, will be conveyed to the tertiary crusher screen. The tertiary screen oversize is fed to the tertiary crusher via a feed bin and the tertiary crusher product joins the feed to the tertiary screen. The tertiary screen undersize is conveyed to the ball mill feed bin.

The crushed ore from the crushing and screening circuit stored in the mill feed bin is fed to the ball mill. The mill discharge flows through a vibrating screen into the mill discharge sump and is pumped to the classifying cyclone. A portion of the cyclone underflow is fed via a tramp screen to a centrifugal gravity concentrator. The tramp screen oversize and concentrator tailings are returned to the mill feed, along with the balance of the cyclone underflow. The classifying cyclone overflow feeds via a tramp/woodchip screen to the pre-leach thickener.

BZMA Plant Phase 1 Description

The 300,000tpm BZMA RoM ore is tipped onto a static grizzly above the RoM bin, from where the ore will be extracted via an apron feeder to a vibrating grizzly. Oversize from the grizzly is fed to a jaw crusher and grizzly undersize, together with the jaw crusher product, is fed to the SAG mill.

The SAG mill discharge flows through a mill discharge vibrating screen into the mill discharge sump and is pumped to the classifying cyclones. The oversize material from the SAG mill discharge screen is either discarded or, if necessary, will be conveyed to a pebble crusher and the product thereof returned to the SAG mill feed. A portion of the cyclone underflow is fed via a tramp screen to a centrifugal gravity concentrator. The tramp screen oversize and concentrator tailings are returned to the ball mill feed, together with the balance of the cyclone underflow. The ball mill discharge passes through a vibrating screen and is returned to the mill discharge sump to feed the classifying cyclones.

Pre-Leach, Leach and Recovery Circuits

These circuits are duplicated in each of the BRMA and BZMA plants. The overflow from the mill circuit classifying cyclones is fed via a tramp/woodchip screen to the pre-leach thickener. Flocculant is added to the thickener feed to aid settling and the thickener overflow is discharged into a process water tank.

The thickener underflow is pumped to a pre-leach tank where a final pH adjustment with lime and pre-aeration of the pulp takes place. The slurry flows through a series of leach/adsorption tanks where cyanide is added, the gold dissolved and adsorbed onto activated carbon. The activated carbon is retained in tanks by means of inter-stage screens and transferred in a counter-current flow by pumping slurry containing the carbon from each tank to the preceding tank. The gold loading increases progressively up the train and the loaded carbon from the first CIL tank will be transferred to the elution plant. Barren regenerated carbon is added to the tail end of the circuit.

The loaded carbon is screened from the slurry stream and washed on a vibratory screen, and transferred via a holding bin into a column for acid washing to remove calcium build up on the carbon. Thereafter, the carbon is transferred to an elution column where gold is removed from the carbon by a caustic-cyanide soak and washing with hot water. The eluted carbon is transferred to a bin prior to regeneration in a rotary kiln, where adsorbed impurities will be removed from the carbon.

The gold in the eluate from the elution process is recovered by plating onto stainless steel wool in the electrowinning cells and then stripped by high pressure spray. Gold sludge from the cells and stripping process is filtered and dried in a calcine oven and smelted with fluxes to produce gold bullion for dispatch to a refinery.

The gravity concentrate from the milling circuit is subjected to intensive cyanidation in a reactor with the addition of high concentrations of cyanide and possibly other additives including oxygen. The solid residue from this process is returned to the milling circuit and the gold bearing solution is treated in the electrowinning cells.

The tailings from CIL circuit are screened to recover any carbon which may have escaped from the CIL circuit and are then processed in a series of tanks to reduce the cyanide content of the tailings prior to pumping to the TDF.

Small Modular Processing Plants

As an alternative to the large conventional plants, a small modular plant configuration was interrogated for the PEA. SMS obtained quotations for 30,000tpm modular plants and reviewed the capital and operational costs in comparison to the large conventional plant design. Each modular plant is a self-contained unit comprising a 30,000tpm crushing/milling, CIL and electrowinning module. The initial plant at BRMA would require five such modules at an individual cost of USD20m each. The site preparation would be approximately USD0.5m per unit and the cost of relocation to BZMA would be USD1.0m per unit.

The SMS review highlighted that the installed power requirement per 30,000tpm module is 1.9MW, which equates to approximately 10MW for the BRMA plant alone. The equipment capital for the five modular plants for BRMA is USD100.0m compared to the equipment capital of USD78.7m (installed equipment cost only) for the large plant.

Alternative Processing and Heap Leach

SMS metallurgical consultants suggested alternative comminution strategies that could improve project economics and efficiencies and which should be interrogated in the PFS, including skid mounted comminution units, Vertical Shaft Impactors or High Pressure Grinding Rolls, and RoM single stage milling.

Based on the metallurgical testwork, heap leaching is not recommended due to the sulphide component of the ore being unlikely to be amenable to heap leach, and the oxide component containing significant quantities of clay which creates channelling and coating of the particles rendering them impervious to cyanide leaching.

Key reported parameters

Processing Plant Availability and Throughput

Source: K'Enyuka 2011

Buckreef Project Ore Characterisation for the Processing Plant Design

Source: K'Enyuka 2011

*Values assumed based on available information

Capital Expenditure of the Buckreef Project Large Conventional Process Plant