The crushing and screening stage in the industry is mainly composed of three-stage and a closed-circuit process. Gold ores need to go through coarse, medium, and fine crushing processes to be minimized into smaller pieces. The screening equipment is used to sieving the smaller gold ores into the proper size for the next steps.
The grinding operation usually adopts one or two ball mills with types of lattice and overflow. The second stage grinding operation forms a closed circuit with a spiral classifier or a hydro cyclone to ensure the grinding fineness.
Since traditional ball milling equipment appears some shortcomings such as fast wear and large energy consumption, many manufacturers adopt new wear-resisting rubber lining boards, sliding bearing to improve a mill operation efficiency and prolong a machine's service life.
The beneficiation stage is a crucial part of gold extraction during the whole gold ore processing plant. Placer gold mine and rock gold mine are most widely processed to extract gold concentration.
The gold slurry process of the carbon slurry method (CIP and CIL) is to put activated carbon into cyanide ore slurry, adsorb dissolved gold on activated carbon, and finally to extract gold from activated carbon.
Equipment required for carbon slurry gold mining process: Leaching mixing tank, activated carbon screen, Two-layer (three-layer) washing and thickening machine, fast desorption electrolysis system with high-efficiency and low-consumption, high-frequency dewatering screen.
It means that by ion exchange resin, gold also can be extracted from ore pulp. Like carbon, the process makes gold absorbed onto solid spherical polystyrene resin beads instead of activated carbon grains.
According to different physical and chemical properties of different types of gold ores, flotation separation utilizes various reagents to make the gold attached to the bubbles then scraping these gold particles from blades to get the concentrate.
A jigger is one of the main pieces of equipment in the gravity separation process. The jigging process mixes gold ore particles of different specific gravity together, then stratifying these particles. The minerals with small specific gravity will be on the upper layer while the minerals with large specific gravity will be on the lower layer.
A shaking table is used to process gold ores in the horizontal medium flow. The motor drives the surface of the shaker to perform the longitudinal reciprocating motion, as well as the differential motion of the washing stream and the surface of the bed. Gold ore particles are stratified perpendicular to the surface of the bed, then being separated parallel to the surface of the bed in reciprocating motion which allows gold ores with different particle sizes to be discharged from different parts to achieve separation.
It adopts lope water flow to achieve separation. With the effect of the combined force of water flow, mineral gravity, the friction created by the bottom of the tank, and ore particles, the gold ore particles will settle in different areas of the tank. The ore particles with small specific gravity will flow away with the water, while ore particles with larger specific gravity would stay.
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Resources Modular Gold Plants (MGP) are complete turnkeymodular goldplants designed for the 500 to 2000 ton per day producer. Permitting requirements and land disturbance are minimized as a result of the inherent environmentally friendly processing technology and compact footprint of the Modular Gold Plants.
Gold extraction technology found in the modular gold plant includes enhanced gravity recovery as well as sulfide associated gold recovery via flotation. The gravity circuit has been designed to maximize recovery using concentrators in series to produce a high grade gravity concentrate. The flotation circuit includes rougher recovery, scavenging and a cleaner stage for production of a high grade flotation concentrate. Gold recoveries equal to that of chemical leaching processes are achieved by the Modular Gold Plant.
The Modular Gold Plant features central climate control, insulated sound dampening walls, high security construction and heavy duty exterior and interior walls and floors structurally engineered to withstand harsh environmental weather conditions. Standardized mechanical simplicity and ease of access to all components is at the core of the design of all Modular Gold Plants.
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The history of gold recovery is as old as mineral processing itself. Gold is well suited to gravity treatment and early plants used jigs, strakes, shaking tables and amalgam drums. The mineralogy of gold ores with respect to nature and occurrence, particularly liberation, dictates the applicability of gravity processing.
Johnson drums were phased out (Central Norseman), and the Knelson concentrator became the industry standard. This has been significantly improved over time and automated to be self-emptying. The DSM screen aperture ahead of the Knelson and the feed split is important in maximising gravity gold recovery.
The Knelson concentrator treated a portion of the cyclone underflow (20%) stream, however at Bronzewing a vibrating screen was used to treat the cyclone underflow prior to feeding the Knelsons. During the 1980s there was a compelling technical argument concerning higher recovery, faster cash flow, lower operating cost considerations and CAPEX. Some companies used spirals (Ok Tedi, Granites) and gravity traps before the Knelson as a common design feature.
Operationally it was learnt that the cleaning cycle frequency time was important, as was keeping the Knelson bowl holes clean because the flow rate of water was more critical rather than the water pressure.
Two examples of high gravity gold recovery process plants were Callie (approximately 60%) and Bronzewing (70 to 80%) of the gold recovered to a gravity concentrate. These are exceptional high gravity gold recoveries. It is believed a Kelsey Jig was specified for the Wallaby project, one of the few gold applications.
Gravity gold has many advantages which should be seriously considered in any flowsheet. The introduction of centrifugal concentrators such as the Knelson, Falcon and Kelsey Jig have revolutionised gravity gold recovery. Gold flowsheets usually have gravity as the primary step followed by other downstream processes such as carbon in pulp (CIP).
The processing of concentrates was first carried out using strakes and amalgam drums, this was discontinued in the 1970s due to occupational health and safety issues and environmental issues with mercury. Mercury was phased out after payouts of compensation to employees and it is now only used as a laboratory tool. Operators who suffered the effects of mercury poisoning failed to recover their health.
Gemini tables were common (Figure 1). However, many operators returned to half size Wilfley tables, although some operators use gold wheels. The removal of tramp iron continues to be a problem at some operations.
Piloting has rarely been used for Greenfield projects. Generally companies go from bench scale to full scale but piloting has been used where upgrading or retrofitting was considered for an existing operation.
Mineralogy determines the amenability to gravity processing particularly the particle size, degree of liberation, density differential, particle shape, composition and hydrophobicity. Characterising the feed is the first basic step in determining the most applicable separating equipment and developing the optimum flowsheet.
Polished sections are useful, but old technology is being replaced by Qemscan. Sink Float analyses is useful because the major problem with gold is to locate sufficient particles and be confident these particles represent gold occurrence.
The Scanning Electron Microscope and gold analyses combined with diagnostic leaching are useful in understanding the nature and occurrence of the gold present. Metallic gold is common and the size can vary from colloidal gold through to nugget gold and as alloys with other metals or within sulphides. (See Figure 3)
In the case of gravity recovered gold, faster cash flow, higher overall recovery and lower cost per ounce are all significant advantages. Gravity gold recovery is environmentally friendly as no reagents are required. Other benefits include reducing the CIP feed grade, recovering coarse gold that would otherwise be slow to leach, improving CIP leach kinetics, reducing carbon loadings, reducing gold in circuit lock up and reducing cyanide consumption. The trend over the last twenty years has been to maximise gravity gold recovery for the above reasons.
Proper sample selection and planned laboratory testwork form the basis of process selection based on gravity recoverable gold (GRG). Interpretation of test results and translating to an operable flowsheet is critical. Testplans should include gravity testwork on samples selected spatially throughout the ore body to confirm the range of recoveries encountered (see Figure 4). Composites are good at hiding variability. The samples need designated coordinates so the recovery can be assigned to a location in the block model and be used in the mine schedule. This data will be used in conjunction with the variability data and support the recovery predictions used for a particular ore body. Data stored electronically can be used to evaluate various scenarios based on comminution and ore recovery. Testwork should target samples widely dispersed throughout the oxide, transition and primary zones. Samples need to be obtained with greater definition such as laterite, coffee rock, pisolites, saprolite etc. The impact of recovery with depth would be useful to understand if this can be tested in the primary core. Applying geometallurgical modelling techniques can directly reduce the risks associated with meeting production targets. Geometallurgy has the potential to act on both the consequences and likelihood axes to decrease risk. Areas of key focus include: 1. Concentration of deleterious elements 2. Hardness 3. Grindability 4. Mineral species and mineral grade 5. Mineral liberation 6. Metallurgical recovery
There are a number of critical factors that need to be in place if a geometallurgical approach is to be successful. The first and foremost factor is to breakdown some of the traditional barriers between various professional disciplines. The geologists, engineers and metallurgists involved in a project must truly want to work together with a shared goal and jointly recognise the value they can each contribute to the project. This approach requires geologists, engineers and metallurgists to develop significant understanding of the mining and ore treatment flowcharts. Technical professionals must become multi-lingual, (capable of speaking and understanding geological, metallurgical and business language and concepts).
The typical GRG testwork methodology proposed by the late Andre Laplante is to grind a 25 to 100 kg sample through three successively finer sizes (P80 850um to 75um) and between each step passing the tailings reground sample through the Knelson concentrator to recover gold liberated (Laplante, A R, 2000). (See Figure 5). A single P80 75 micron GRG can also be undertaken but this is not as accurate and does not provide any liberation data.
It must be also noted that there is a key flaw in all Knelson gravity recovery tests. The higher mass recovery in a bench-scale test does not reflect typical plant operation. A batch centrifugal concentrator pulls only a fraction of this amount. Therefore, the actual mass recovery and consequently gold and silver recovery is likely to be significantly lower in the plant than these results indicate. This is not the case with the GRG testwork. Intensive leaching of the concentrates is typically carried out and unless there are specific issues, very high gold recoveries are usually obtained. (See Table 1)
Interpreting gravity recovery results requires a person skilled in the art and able to relate the results to plant practice. Consultation with the vendors is also very useful to ensure the correct conclusions are being drawn.
Gravity circuits use large volumes of water and usually require good quality water. This is a problem in Australia due the scarcity and poor quality of water at many locations. The gold industry needed to find solutions to treating resources in hyper saline water that cause buffering problems achieving satisfactory pH levels (Paddington) which may result in high HCN gas levels above the tanks. This high 200,000-ppm TDS water also affects the ability to dissolve cyanide and achieve satisfactory oxygen levels in the pulp. Plants with good quality water suffered with sulphide reducing bacteria (SRBs), which caused severe corrosion within tanks and necessitated the tanks being lined with epoxy glass linings.
Mass balances around the grinding circuit can be carried out using Excel spreadsheets or LIMN flowsheet software. The use of gravity concentrators introduces water which can be a process limitation or require the addition of a thickener for the cyclone overflow stream. Where tailings filtration is used the water balance can be critical. Vendors have responded with centrifugal concentrators that use less water.
The poor quality water necessitated reverse osmosis plants be used for centrifugal concentrator fluidizing water and stripping water. Some plants also used vacuum distillation units utilising waste heat from power plants to produce potable water from saline sources (Bounty & Paddington).
The Wilfley shaking table (Figure 6) was used almost universally for cleanup of gravity concentrates prior to smelting. Shaking tables are gravity concentration devices that consist of a riffled flat surface, inclined slightly from the horizontal, shaken with a differential movement in the direction of the axis of tilt and washed at right angles to the direction of motion by a stream of water. Feed enters through a distribution box along part of the upper edge and spreads out over the table as a result of the shaking action and the wash water. Product discharge occurs along the opposite edge and end. These are high maintenance units and achieve high grade at the expense of recovery. The presence of galena and iron sands can complicate achieving clean separations. These shaking tables were superseded to some extent by Gemini tables in the 1980s through to the 1990s.
The introduction of the Intensive Leach Reactor (ILR) compared particularly to tabling where gravity was proven to offer very low recoveries; often well below 70% and much lower than expected by the minesites operating these devices (See Figure 7). This outcome was true for both installations running IPJs and Knelson Concentrators producing concentrates. The research indicated that tabling was clearly a "below optimum" process. As a result, the concept of finding a production version of a laboratory bottle roll was born in the form of the ILR (Figure 7) where all of the gold in the concentrate was leached. The first ILR prototype was built in 1997 for a trial at Mt McClure Gold Mine, operated by Australian Resources (See Figure 7). At some sites the retrofitting of the ILR replacing tabling resulted in gravity gold recovery increases of between 20% to 50%.
The introduction of centrifugal concentrators was the single largest positive change in gravity flowsheets. The use of 50 and up to 200 g forces resulted in higher recovery of gold at the finer sizes. This was followed by the change from a bleed of the mill discharge to a bleed of the cyclone underflow. At the same time the machines became larger with a greater percentage of feed able to be processed. There was also change from batch manually emptied machines to auto dump machines allowing the concentrate to flow by gravity through to a hopper in the goldroom. At the same time the Falcon concentrator arrived on the market with a higher g force. The latest trend has been to treat cyclone feed rather than cyclone underflow because of higher gold recovery. Consideration in the design must include restricting access and minimising the possibility of theft. High re-circulating loads of gold should be avoided as flat flakes can be produced in the grinding process and these are not amenable to recovery in a centrifugal concentrator. Gold does not occur in nature as flakes.
This was the first centrifugal concentrator (50 gs) developed in Canada. The spinning motion of high-speed centrifugal force against fluidisation water causes separation of the gold particles; it can operate in a batch or semi batch sequence. The main components consist of a riffled concentrating cone, drive motor, water chamber and fluidisation water unit. These are universally used for gravity gold recovery in grinding circuits with a capacity of 300 to 1,000 t/h. Water use is a major consideration. (See Figure 9).
These were developed after the Knelson and the main difference is the 200 gs developed by the spinning bowl. These are universally used for gravity gold recovery in grinding circuits with a capacity of 300 to 1,000 t/h. Water use is a major consideration. (See Figure 10).
The Kelsey Jig is a cylindrical spinning jig that uses ragging and pulsation of the bed to effect concentration of heavy mineral into the jig. The ragging is supported by a laser cut screen. The Kelsey Jig has been used for gold recovery but is more commonly applied to mineral sands, tin and tantalum. (See Figure 11).
Separation occurs based on relative density as well as particle shape and size. High sg particles are drawn into the concentrate hutch during the suction stroke. The screen is pulsed vertically by a hydraulically driven shaft. Length of stroke and speed can be varied as well as screen aperture and ragging dimensions. Both concentrate and tailings are discharged under pressure. Used specifically for very coarse gold even ahead of the grinding circuit.
Essentially a large bottle roll with high cyanide concentration and an oxidant to accelerate leach kinetics. The unit is modular and includes a pump and solid liquid separation cone. It is used for processing gravity gold concentrates. It is preferred over tabling, which leads to higher overall gravity gold recovery. AR and ILR comparison is common. (See Figure 7).
The actual "working surface" of the concentrator is made up of a series of leads (pronounced "leeds") running lengthwise in reverse in a critical tight spiral pattern along the inner barrel. The leads have a 45 degree angle on one side and a 90 degree angle on the other, and are larger in height and width at the rear of the barrel than at the front. During operation, the decreasing height and width of the leads create the classifying effect as the ore passes through the barrel. A set of angled spray heads continuously wash back" the lighter gangue material while the gold and heavy concentrate continue moving forward, falling out of the grooves and into the concentrate holding bin. This is a continuous process allowing the gold concentrate to be recovered. For larger volume processing, multiple Spirals can be installed in "series" with the ore being feed automatically from one Spiral to the next. (see Figure 13 )
These devices are effectively shaking tables wrapped around to form a cylinder. The cylinder revolves subjecting particles to large forces at the same time the shaking enhances the separation. Typically the feed size range 1mm - 1m. There use is not widespread. (See Figure 14)
The Parker Centre Gravity model developed through the AMIRA P420 project has developed a model for predicting gravity gold recovery, but this is only available to sponsors. The model is more suitable for optimizing gravity gold recovery with Brownfield projects. The model requires a three stage GRG test, plant cyclone data and will predict optimum gravity gold recovery. A single stage GRG at P80 75 can also be used for predicting gravity recovery for a Greenfields project but is not as accurate. The Parker Centre has a significant reference data base to draw upon.
It is interesting to note that some conservatism is taken into account when sizing the equipment based on an average circulating load figure typically 250% but allowing for circulating loads up to 400%. The trash screen sizing is typically 3.35 mm using a DSM which cuts at half the aperture however larger plants have resorted to vibrating screens using poly decks. The final cut size depends on the assay by gold distribution and consultation with the vendor on top sizes able to be processed by their machine. (SeeTable 3).
This is rarely undertaken for Greenfields gold project circuits, but has occurred for chrome, metallic copper or in additional specific applications where there was uncertainty. Piloting is common for Brownfields projects or where retrofitting of equipment is being considered. For gold, the limit is batch testing using a Knelson or Falcon concentrator. Gekko may undertake testing using the In Line Pressure Jig (IPJ) where very coarse gold is present.
For a gold project treating 1.2 Mtpa modern Knelson or Falcon concentrator gravity circuit installed in a Greenfields site including pipe work, trash screens, pumps, hoppers, security cages, steelwork, civil and electrics can easily cost an additional $A1M and for larger plants the figure is higher. As a guide ILRs or Acacia reactors can cost in 2010 $A dollars between approximately $600,000 to $900,000 installed in a Greenfield site. The modular transportable nature of these packages keeps the installed cost low. There are plants where the additional CAPEX cannot be justified based on the gravity gold recovery alone. The economic justification current cut point for most projects is 20% gravity gold recovery.
The OPEX for centrifugal concentrators has been calculated at between $0.08 to $0.12/tonne of new feed. The operating costs are very low being essentially power, water, spares and regular maintenance. The OPEX costs are very low and rarely a consideration against installing gravity equipment.
Predicting gold recovery can be difficult to determine based on a metallurgical test drill core sample composite with regards to representivity. GRG based on non-representative samples is the major issue. Mt McClure miscalculated and needed to install a gravity circuit immediately while other plants with a gravity circuit didnt use them (Resolute, Southern Cross). Supergene enrichment and the transition to very high grades can be indicative of the need for a gravity circuit. The presence of nugget gold at Bronzewing, and Granites Gold made it extremely difficult to predict likely gravity gold recovery using small test samples.
The presence of sulphides (galena) and tramp iron can cause problems when cleaning up gravity concentrates for tabling but is not an issue for the ILR. In a number of cases, GRG has over estimated the gravity gold recovery by some 30% because of the way the testwork was undertaken or interpreted.
Another issue is allowing too little of the re-circulating load to be bled to the primary recovery circuit, or the primary unit failing to perform because feed is too coarse or too dense or producing flakes.
Centrifugal concentrators have revolutionised gravity gold recovery. The transition from batch concentrators to auto dump and continuous discharge concentrators has increased effective gravity gold recovery.
Retrofitting of batch concentrators has occurred at a number of sites and older equipment such as Johnson Drums and continuous strakes and amalgam drums are relegated to museum items. The introduction of larger units is a trend that currently sees no limitation. At the same time more of the feed is being processed compared to a small bleed of the re-circulating load. Targeting gravity gold has become a priority with flowsheet development using Knelson or Falcon concentrators. Even recovering gold from copper concentrates has been utilised at Copper Mines of Tasmania. Intensive leaching of concentrates has taken over from tabling resulting in significantly higher gold recovery and more security with regards to potential theft. Using resin rather than electrowinning is being tried in gold rooms as an alternative to electro winning.
The installation of internal scalping screens in the IPJ allows steel to bypass the jigging bed in the circulating load of a milling circuit. At the same time automation of the IPJ to improve operability. Multiple and modular systems are also now available. The Python Processing Plant in modular form suitable for underground ore processing gravity only plants are being proposed and used. At the same time continuous ILRs are available including customized oxygen spargers and multiple units capable of processing much larger tonnages of ore.
The Mina Serto deposit was discovered by a regional exploration Field Geologist working for WMC Resources (WMC) in 1997. WMC decided not to proceed with development of the project because of its small size. The Serto gold mine is part of the Gois Velho gold project, located on mostly-cleared grazing land in the State of Gois, approximately 380 kilometres west of the Brazilian capital of Brasilia. Today the Mina Serto gold mine in the State of Gois in Brazil is one of the lowest cost gold mines in the world following its successful commissioning and official opening in March 2003. The location of the mine is shown in Figure 15.
Gravity gold recovery was mandatory for the oxide ore with 42.9% of the gold recoverable into a gravity concentrate of 0.76 mass percent using a Knelson concentrator. The microscopic examination of the gravity concentrate revealed abundant free gold up to 500um in size and down to 0.5um. This was highly desirable that the gravity gold recovery was maximised as coarse gold entering the leach could result in high tailings. The sulphide ore achieved 53.5% recovery of gold to a concentrate representing 3.9 mass percent using a Knelson concentrator. A Gemini table was used for concentrate clean up before smelting.
The Casposo process plant, as designated by Troy Resources N.L., is situated in North-Western Argentina in the San Juan Province. The current project reserves total 2.1 Mt at 5.06 g/t gold and 137 g/t silver. (See Figure 17).
The Gravity Concentrator processes the screen undersize. This concentrator retains a gravity concentrate and produces a gravity tail. The gravity tail is returned to the comminution circuit via the SAG Mill Discharge Hopper for further liberation. When the gravity concentrate becomes sufficiently enriched, it is transferred to the Intensive Leach Reactor, or ILR, for leaching under intensive conditions. The ILR is a specialist precious metals leach unit that uses an alkaline cyanide solution to leach gold and metallic silver from the high-grade gravity concentrates in batches. The concentrates are collected in the Concentrate Feed Tank. When sufficient concentrate has been collected, the batch is transferred to a horizontal rotating drum together with barren solution and hydrogen peroxide. Cyanide solution, caustic solution and lead nitrate solution are added to the reactor via a solution tank and recirculated using the Discharge Hopper pump until the leaching reactions have completed. The pregnant solution is then pumped to the Clarification area to remove any solids and recovery the gold and silver. The tailings are pumped to the SAG Mill Discharge Hopper for further liberation.
Gold mineralogy particularly particle size determines amenability to gravity gold recovery. There are large financial drivers to maximize gravity gold recovery. Sample selection and representivity are risks that need to be managed in assessing gravity gold recovery. The predictability of using GRG laboratory methods has improved outcomes, thus reducing the previous high risks. The application of the AMIRA P420 gravity model will also help in this regard.
The introduction of centrifugal concentrators and intensive leaching has revolutionized the industry and equipment enhancements are ongoing. These are low operating cost devices proving more efficient on finer particles than any other equipment previously available. The historical and technical importance of the ILR technology has not been duly recognised by the industry compared to the disadvantages of the previous tabling practices.
The management of water balance issues can impact on the flowsheet and choice of equipment. The water quality for fluidizing also introduces limitations requiring the use of raw water not process water. The trend to process a larger mass of recirculating load and the use of auto dump centrifugal concentrators gravitating concentrates direct to goldrooms is now common. From an engineering and operability perspective modern gravity circuits are far superior to what was the basis of design even ten years ago.
Historically we have observed Brownfields projects lifting gravity gold recovery from 17% to 50% by employing the previously mentioned techniques. There has also been a trend towards processing cyclone feed rather than cyclone underflow because of enhanced gold recovery results. Piloting of gravity circuits is not required unless the gold is particularly nuggetty or refractory gold is present. The size of centrifugal concentrators shows a consistent trend of larger machines and intensive leaching machines are moving towards continuous process units rather than batch units and fully automated.
TORONTO, April 20, 2021 (GLOBE NEWSWIRE) -- Probe Metals Inc. (TSX-V: PRB) (OTCQB: PROBF) (Probe or the Company) is pleased to announce positive results of the 2020 metallurgical test work program on its Val-dOr East Project. The program consisted of mineralogy, physical property characterization, gravity, cyanidation and flotation tests. The main objective of the program was to assess gold recoveries by deposit and/or gold trend and to support the selection and design of the flowsheet for the Preliminary Economic Assessment (PEA). The results indicate that all deposits and gold trends are behaving similarly and that they can be treated in a single processing facility. They also indicate that gravity recoverable gold is high in all deposits (above 50% up to 72%) and that the overall gold recovery (gravity + leaching of gravity tails) is above 95% in all cases with the exception of Highway at 91%, which represents only 3% of the 2019 resource estimate. It was demonstrated that the leach gold recoveries can be correlated to head grade and a net gold recovery equation for use in the PEA was established which includes typical plant losses. In addition, the program has demonstrated that all deposits/gold trends are responding very well to other pre-concentration methods like flotation, continuous gravity separation and ore sorting which provides additional opportunities to enhance project value.
David Palmer, President and CEO of Probe, states: The metallurgical test work demonstrates once again how the Val-dOr East project performs beyond expectations and confirms that it is an excellent candidate for development. We have already shown the areas ability to host ounces and now we are building confidence in the development potential of those ounces. We have hit a number of key milestones as we advance the project towards the PEA, which includes strong geotechnical results demonstrating good rock stability; favourable environmental characteristics of host rocks; and now confirmation that all of the mineralized materials not only have high gravity and overall recoveries, but all can be processed together in one mill. These characteristics will provide initial cost savings during construction as well as adding further value downstream during a production scenario.
Yves Dessureault, COO of Probe, states: These results are a very important milestone for the Val-dOr East project. We have gone from a concept of multiple deposits feeding a central mill to actually demonstrating it with the metallurgical test work results. All deposits have the same type of response in Gravity and Leaching. The Gravity Recoverable Gold is coarse to very coarse and we have been able to model most of the resource with a single grade-recovery curve/equation, with potential for future enhancements. Lower strip ratios, less costly waste rock storage, more efficient milling and reduced infrastructure costs are just a few of the benefits we are seeing in the development work, and all should contribute to a more robust bottom line for the project. In my experience, it would be difficult to find a mineral resource that was easier to process than what we have at Val-dOr East.
The goal of the 2020 metallurgical test work program was to improve upon the historical recoveries and establish recoveries on the deposits where no information was available. An additional objective was to build the metallurgical knowledge base to support the design of the PEA and the selection of the process plant flowsheet. The program consisted of mineralogy, physical property characterization, gravity amenability tests (GAT), gravity recoverable gold tests (GRG), cyanidation with grind size assessment and flotation.
Eight composites were created, either from drill core intervals or from products generated in the 2018 ore sorting test program. Composite were created from drill core intervals for New Beliveau, Courvan, Monique, Highway and North-Zone (a total of five composites). All composites assembled from drill core intervals were spatially selected to be representative of both the type of mineralization and the average head grade of the resource. In addition, three New Beliveau composites were created from ore sorting products. A complete summary is provided below:
The mineralogical and chemical analyses performed on the eight composites suggest the presence of coarse gold in every composite sample. The analyses of deleterious elements, such as Arsenic, Tellurium and Antimony were near to or under the detection limit for all samples. All samples were mainly composed of quartz, micas, feldspars and carbonates with varying proportions. Pyrite was the main sulfide mineral detected and accounted for 1.6 to 3.8% by weight of all samples. Pyrite was always very well liberated.
For the 2020 metallurgical program, only New Beliveau samples went through a detailed comminution test work program. Work included Bond Crusher Work Index (CWI), Bond Rod Mill Work Index (RWI), Bond Ball Mill Work Index (BWI), Bond Abrasion Index (AI) and finally SAG mill comminution test (SMC).
The composites were considered to be hard to very hard for CWI (between 16.9 and 20.0 kWh/t) and the SMC tests (A x b between 29.3 to 37.2), both are measurements of resistance to impact breakage. Samples tested showed medium hardness for the RWI and BWI with average values of 12.9 kWh/t and 11.6 kWh/t respectively, and non-abrasive with an average Abrasion Index (AI) of 0.131g.
The Company has continued its work on pre-concentration alternatives to the standard free milling flowsheet. In addition to the ore sorting test work done in 2018 (see Press Release of May 20th, 2020 for test results), flotation and continuous gravity separation were tested as part of the 2020 metallurgical test work program.
Gravity Amenability Tests (GAT) were completed on all composites. The GAT test is a standard test to assess the potential of using continuous gravity separation technology for the separation of heavier minerals from the gangue material. The results show that all deposits are highly amenable to gravity separation with a gold recovery ranging from 57% to 73% for whole ore material and approximately 92% for ore sorting concentrate with an 8% mass yield. These recoveries increase to between 87% to 98% when the mass yield is increased to approximately 18%.
Preliminary flotation test work was performed on a New Beliveau composite. The sample was first subjected to gravity concentration (the GRG test described in next section) and the gravity tails was then floated to recover sulfides and gold. With a coarse grind of 80% passing (P80) = 125 m, 99.1% of the gold reported to the flotation concentrate with mass yields of between 6 to 8%.
Four whole-ore composites (New Beliveau, Highway, Courvan and Monique) and one ore sorting concentrate composite (New Beliveau OSC) were tested with the Gravity Recoverable Gold (GRG) protocol to determine their amenability to gravity concentration. The results are showing that the GRG is coarse to very coarse, and are also indicating very good gold recoveries. At a grind size of approximately 45-50% passing 75m (equivalent 80% passing 226 m), gold recoveries were respectively 50.7%, 54.2%, 69.4%, 71.9% for the New Beliveau, Highway, Monique and Courvan whole ore composites, and was 55.2% for the New Beliveau ore sorting concentrate composite.
The GRG value does not directly predict or correlate gold recovery results from a closed-circuit milling operation. It is indicative of gravity gold amenability and in this scenario all samples would benefit from the inclusion of a gravity circuit.
Leach test work was performed on the composites GRG tailings. A first series of bottle roll tests was executed to assess the impact of grind size. The results are shown in the following figure and based on these results, the target grind of 80% passing 80 m was selected.
The leach and gold dissolution kinetics were then studied by Corem using their proprietary methodology. This methodology facilitates and expedites the finding of the optimal leaching conditions. A first batch of tests were done with cyanide only and then a second series was done with the addition of lead nitrate. As an example, the attached figure shows the changes in the kinetic index over ranges of cyanide concentration for six composites. The methodology shows that the optimum cyanide concentration is around 700 ppm NaCN, above which no further gain can be observed.
The test work has demonstrated that a PEA flowsheet based on grinding to a target of 80% passing 80 microns followed by gravity and then leach of the gravity tails would give very good performance. The combined gold recoveries obtained in the metallurgical test work program are shown in the table below (Note: The gravity separation concentrate has been assumed in the calculations to be 100% recoverable through intensive leach and tailings recirculation).
Leach results above are based on 48 hours and a slurry density of 40% solids. Sodium cyanide consumption was between 0.41 and 0.73 kg/t while lime consumption varied from 0.60 to 2.57 kg/t. Recoveries represent maximum metal extractions and do not include typical plant losses or scale up of gravity recoverable gold for plant operating conditions.
For the PEA, further analysis was performed to assess the differences between deposits, the impact of grind and head grade. It can be concluded that all deposits are behaving similarly and can be grouped together, with some adjustments for the Highway deposit, which is a small percentage of the overall resource.
Due to the coarse to very coarse nature of the GRG, the process design criteria will be based on treating 90% of the grinding mill recirculating load through the gravity circuit, with modeling indicating an average of 55% gravity gold recovery under those conditions. This result aligns well with the 50% gravity recovery achieved by Cambior when they mined the Beliveau deposit from 1989 to 1993. The PEA will conservatively assume 50% gravity recovery.
In addition, the leach test results were analyzed and reviewed to establish leach gold recoveries. It was identified that the New Beliveau, North Zone, Courvan and Monique deposits have similar responses and that their leach gold recoveries can be correlated to head grade. The following relationship has been established from the test results:
When the gravity and the leach gold recoveries are combined, and then reduced with the typical plant losses or impact of scale up of gravity recoverable gold for plant operating conditions (typically about 0.8%), the following net recoveries are obtained:
Following the PEA, a new metallurgical program will be defined to further investigate the selected process route(s) and improve upon the current knowledge base developed through the 2020 metallurgical program and potentially further improve reagent costs and gold recoveries.
Qualified PersonsThe scientific and technical content of this press release has been reviewed, prepared and approved by Mr. Yves Dessureault, P.Eng., COO and was reviewed and approved by Tommaso Roberto Raponi, P.Eng. each of whom is a "Qualified Person" as defined by National Instrument 43-101 - Standards of Disclosure for Mineral Projects ("NI 43-101"). Mr. Raponi is a consultant of Ausenco Engineering Canada Inc. (Ausenco) and is considered to be independent of Probe for purposes of section 1.5 of NI 43-101.
About Corem:Corem is a center of expertise and innovation in mineral processing with the largest concentration of resources dedicated to R&D in this field in Canada. Corem is a not-profit organization that works closely with its members, its clients and its partners to improve competitivenessand to reduce environmental impact through the industrialization of innovative solutions. Corem has extensive equipment and infrastructure, including a pilot plant and laboratories for mineralogy, mineralogy and hydrometallurgy, that allow for innovation. For more information, please visit: corem.qc.ca
About Ausenco:Ausenco is a global diversified engineering, construction and project management company providing consulting, project delivery and asset management solutions to the resources, energy and infrastructure sectors. Ausencos experience in gold projects ranges from conceptual, pre-feasibility and feasibility studies for new project developments to project execution with EPCM and EPC delivery. Ausenco is currently engaged on a number of global projects with similar characteristics and opportunities to the Val-dOr East Project.
About Probe Metals:Probe Metals Inc. is a leading Canadian gold exploration company focused on the acquisition, exploration and development of highly prospective gold properties. The Company is committed to discovering and developing high-quality gold projects, including its key asset the Val-dOr East Gold Project, Quebec. The Company is well-funded and controls a strategic land package of approximately 1,000-square-kilometres of exploration ground within some of the most prolific gold belts in Quebec. The Company was formed as a result of the sale of Probe Mines Limited to Goldcorp in March 2015. Newmont currently owns approximately 11.6% of the Company.
Neither TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release. This News Release includes certain "forward-looking statements" which are not comprised of historical facts. Forward-looking statements include estimates and statements that describe the Companys future plans, objectives or goals, including words to the effect that the Company or management expects a stated condition or result to occur. Forward-looking statements may be identified by such terms as believes, anticipates, expects, estimates, may, could, would, will, or plan. Since forward-looking statements are based on assumptions and address future events and conditions, by their very nature they involve inherent risks and uncertainties. Although these statements are based on information currently available to the Company, the Company provides no assurance that actual results will meet managements expectations. Risks, uncertainties and other factors involved with forward-looking information could cause actual events, results, performance, prospects and opportunities to differ materially from those expressed or implied by such forward-looking information. Forward looking information in this news release includes, but is not limited to, the Companys objectives, goals or future plans, statements, exploration results, potential mineralization, the estimation of mineral resources, exploration and mine development plans, timing of the commencement of operations and estimates of market conditions. Factors that could cause actual results to differ materially from such forward-looking information include, but are not limited to failure to identify mineral resources, failure to convert estimated mineral resources to reserves, the inability to complete a feasibility study which recommends a production decision, the preliminary nature of metallurgical test results, delays in obtaining or failures to obtain required governmental, environmental or other project approvals, political risks, inability to fulfill the duty to accommodate First Nations and other indigenous peoples, uncertainties relating to the availability and costs of financing needed in the future, changes in equity markets, inflation, changes in exchange rates, fluctuations in commodity prices, delays in the development of projects, capital and operating costs varying significantly from estimates and the other risks involved in the mineral exploration and development industry, an inability to predict and counteract the effects of COVID-19 on the business of the Company, including but not limited to the effects of COVID-19 on the price of commodities, capital market conditions, restriction on labour and international travel and supply chains, and those risks set out in the Companys public documents filed on SEDAR. Although the Company believes that the assumptions and factors used in preparing the forward-looking information in this news release are reasonable, undue reliance should not be placed on such information, which only applies as of the date of this news release, and no assurance can be given that such events will occur in the disclosed time frames or at all. The Company disclaims any intention or obligation to update or revise any forward-looking information, whether as a result of new information, future events or otherwise, other than as required by law.
The Hollinger Open Pit is a part of Porcupine Gold Mines, is situated in the gold-mining City of Timmins, in northern Ontario, Canada. The Porcupine Camp, located above a sequence of Archean basaltic volcanic rocks, led to the establishment of Timmins. The Hollinger-McIntyre is a giant deposit, located in the Porcupine Mining Camp of northeastern Ontario. The Hollinger-McIntyre deposit is hosted by mafic volcanic rocks of the central and upper Tisdale assemblages that are intruded by porphyritic intrusions. Mafic volcanic rocks in the deposit have generally been divided into three units: the Northern, Central and Vipond Formations.The Hollinger Mine historically was developed on gold bearing veins which are structurally controlled by lithologic contacts and deformation zones associated with altered Central and Vipond Formation volcanics. These units strike N55E and 70 SE, and are folded into an anticline. The Northern formation occurs in the core of Central Tisdale Anticline. The Central Formation hosts most of the major veins systems in the Hollinger and McIntyre mines. It is comprised of a heterogeneous sequence and the basal units in the Central Formation are the most important ore hosts in the deposit. The Vipond Formation is the youngest volcanic package in the deposit area. The lavas have been intruded by a group of porphyry stocks, the largest of which is the Pearl Lake Porphyry. The porphyries are generally conformable to the folds within enclosed rocks and plunge at 45 to 50 degrees E. The porphyry deposits occur in areas of bedrock depressions beneath the lakes, suggesting that they are softer and more prone to erosion than the mafic volcanic rock units that they intrude into.The core of the Hollinger-McIntyre deposits is an elliptical area of high strain developed along the south limb of the Central Tisdale anticline which surrounds the Pearl Lake porphyry and is approximately 450 to 600 m wide by more than 3 km in length. The elliptical fold of Central Tisdale anticline contains a series of subsidiary folds including the Northern anticline, Hollinger syncline and the Hollinger anticline. The elliptical nature of this structure in plan is due to the non-cylindrical, doubly plunging properties that closes the structure to both the east and west.
There is sufficient grade at specific gold price-points to mine a 150m deep pit, with the rock being processed at the nearby Dome Mine mill. The voids (sub-vertical stopes, shafts, and connecting drifts/drives) are sometimes spaced nearly 20-50m apart extending several hundred metres deep in a 2km square area beneath the City. The pit design was constrained by a regional highway (and the Citys water tower) along the northern wall, with homes and businesses on all other sides of the Property.The Hollinger is being mined using three 6m and two 9m cuts making up 18m high benches in mostly FAIR to GOOD ground. All blasting is done with blast-mats to reduce fly-rock and noise. Because the mine is in-town, damage needs to be minimised. Earlier, blast trials were conducted to determine the depth of blast-damage induced by varying sizes of confined blasts. These trials indicated that a three-row trim shot onto a pre-sheared final wall would not induce excessive damage. To reduce the damage further, the pre-shear drill-hole spacing is adjusted for ground conditions within the immediate vicinity of voids.This strategy sufficiently decreases the back-wall damage to less than 4m. The multi-use of probe holes to presupport the rock mass before blasting is part of the production cycle. Grouting cables into the final slopes, above and alongside voids, before blasting reduces the amount of final wall crown and wall rehabilitation required. This pattern has 8m cable-bolts on 4m spacing, drilled at -45 and -05 from the pre-shear line. On the North Wall, the dominant fabric (72/155) is the main control on the bench face angle. This highly foliated rock mass tends to delaminate when blasted. To reduce the bench-crest attrition from delamination, pre-support is applied using 6m cables on a 6m spacing, drilled at -45 into the crest from the pre-shear line.For each of the larger multi-bench voids encountered, individualised support designs are being implemented.
Gravity separationACACIA reactorSmeltingAgitated tank (VAT) leachingConcentrate leachCarbon in pulp (CIP)Carbon adsorption-desorption-recovery (ADR)ElutionSolvent Extraction & ElectrowinningCyanide (reagent)
Ore from Hollinger is processed at the existing Dome mill.Gold is recovered using a combination of gravity concentration and cyanidation techniques. The circuit consists of primary, secondary and tertiary crushing, rod/ball mill grinding, gravity concentration, cyanide leaching, carbon-in-pulp gold recovery, stripping, electro winning and refining.Gravity gold is recovered by the use of five Knelson CD-30 Concentrators fed from the cyclone underflow. A Consep CS6000 Acacia Reactor is used to intensively leach the Knelson concentrate. The Acacia loaded solution has a dedicated electrowinning circuit. Gravity recovery accounts for up to 45% of the recovered gold, depending on ore type.The cyclone overflows reports to a 155' thickener where the slurry density is increased to 55-60% solids. The thickener underflow feeds six leach tanks in series, which provide about 32 hours residence time.Lime is added to the mill discharge pump boxes, thick ........
It is highly configurable and available in a range of model sizes that will suit any hard rock or alluvial mining operation. With capacity range from laboratory scale up to 1000 tonnes of solids per hour, it combines centrifugally enhanced gravitational forces with a fluidised bed process to provide exceptional recovery of precious metals such as gold, silver and platinum group metals.
This unit includes a one-piece upper frame and tailings launder assembly along with a robust lower frame designed to improve access and simplify maintenance. A free-standing, remote mounted piping is also provided for installation flexibility.
Our concentrators leading-edge cone technology has been built on 40 years of innovation and is designed to capture the maximum amount of gold per cycle. Knelson is the only enhanced gravity concentrator with a fully fluidised bed allowing for upgrading throughout the entire cone surface.
The product is designed to be easily accessible, with fewer parts and an automated greasing system. Unit internals are rubber lined to process abrasive material with ease and minimise wear. The design is built from high-quality materials. Stainless steel parts have been used to upgrade the latest design, offering you better value and longer service life.
Unlike competitors, Knelson concentrators can operate on feed densities of up to 75% solids, meaning that it can be installed in multiple different locations within the process, making the system more versatile.
Our Knelson Semi-Continuous Gravity Concentrator is leaps and bounds ahead of competitors when it comes to equipment features and design. With precise equipment enhancements, the unit not only provides the highest possible gold recovery than anything else on the market, but it has been intentionally built to have fewer moving parts, making it an efficient machine thats easier to maintain.
Similar products on the market face vibration problems if the feed is not diluted before entering the machine. However, you will never face this problem with Knelson concentrators. Refined unit design has allowed the units center of gravity to be lowered and the machine load to be hung rather than supported from below, eliminating overall vibration.
FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.
Offering significant cost benefits and a low environmental footprint; Gekko process designers customise self-contained high recovery plants for minimal start-up capital, using high-quality components and in-house expertise.
These flexible modular plants are engineered to deliver super-efficient, environmentally friendly recoveries, by cleverly combining Gekkos gravitypre-concentration, flotation andintensive leachtechnologies.
Ores that can beconcentrated by gravityor a combination ofgravityand flotation processes are ideal for modular systems.Pre-concentrationsignificantly reduces energy requirements and lowers the carbon footprint of plant operations.
Gekkos modular systems are used worldwide forfree gold,complex gold, exploration, alluvial or hard rock, anddiamondapplications. Where appropriate, Gekko source and include processing equipment from other suppliers if required.
Typically, modular plants are designed and built by Gekko for a given mine operation with specific requirements. Gekkos innovative core technologies and in-house process design expertise will produce an agile, effective modular plant. Contact a Gekko engineer today.
TheInLine Pressure Jig (IPJ)recovers a coarse mineral concentrate. As the desired mineral gets concentrated to approximately 5% of the total mass, the standard practice of cyanide leaching 100% of the ore is eliminated.
This 5% ore is treated with cyanide in Gekkos proprietary high-performanceInLine Leach Reactor (ILR)for superiorgold recovery. The ILR reduces the consumption and environmental impact of whole ore cyanidation.Get in Touch with Mechanic