How to Choose
Gold Mining Equipment

The water runs deep in this part of the process. Here is a specific example of how deep: an EPC contractor's equipment proposal to a mine owner might include Brand A and Brand B with performance differences within 5%, and similar quotes, yet Brand A gets picked in the end. Why? Because Brand A's regional distributor has a long-standing relationship with the contractor's project manager, Brand A's distributor commission is two points higher, and the contractor's procurement department got better commercial terms from A. What the technical comparison report says is that Brand A has a slight edge in a certain parameter. Design institutes work in a similar way when recommending equipment. Their engineers tend to recommend brands they have used before, brands they know how to troubleshoot if something goes wrong. This is not purely interest-driven; there is a professional risk-avoidance factor as well. If the mine owner has no in-house technical team doing an independent evaluation, there is no choice but to be led by these filter layers. This is not to say the contractor and the design institute are necessarily cheating anyone. Most of the time the solutions they recommend work fine. The gap between "works fine" and "optimal," multiplied by ten years of operation, adds up to a lot of money.

The mode of occurrence of gold is the first thing that must be understood. Native gold embedded in quartz veins versus micro-disseminated gold locked inside arsenopyrite corresponds to two entirely different equipment systems. The mode of occurrence determines the process route, and the process route determines the equipment system.

Within a single ore body, the mode of occurrence can be completely different at different depths and in different zones. In the oxide zone, gold is free. Moving into the transition zone, gold starts to become partially encapsulated by sulfides. Entering the primary zone, gold may be completely locked inside arsenopyrite. If samples are only taken from the oxide zone for metallurgical testing, and a set of equipment suitable for oxide ore is purchased, the entire equipment set becomes useless once mining progresses into the primary zone. This happens far more frequently than one might expect. The proper approach is to sample, test, and develop process flowsheets separately for each ore type, and the equipment selection must be compatible with all ore types that will be encountered over the mine's full life, or at a minimum must include provisions for modification and expansion.

The degree of oxidation of the ore. Fully oxidized ore usually responds well to direct cyanide leaching, and equipment investment is manageable. In primary sulfide ore, gold is tightly encapsulated by sulfides, cyanide solution cannot reach the gold, and the sulfide structure must first be destroyed. This corresponds to roasting furnaces, pressure oxidation autoclaves, or bio-oxidation reactors, any of which pushes equipment investment up by an order of magnitude.

Standard CIL diagnostic tests and pre-soak tests can provide quantitative data, yet in many project test reports this data is either missing or vague. If preg-robbing test results are poor, it means the entire process route has to be scrapped and rebuilt, test costs double, and the project timeline gets pushed back. Nobody wants to see that result, so sometimes the test simply "was not done" or its "results were not representative." When reviewing a metallurgical test report, flip to the preg-robbing test page. If that page does not exist, everything that follows can be taken with a discount.

Throughput. Daily processing of 50 tonnes and daily processing of 5,000 tonnes represent entirely different process philosophies. Many projects set throughput at a number the mine owner "hopes to achieve" rather than a number the geological report and mine plan can actually support. Equipment is sized for 3,000 tonnes per day, the mining face can only supply 1,500 tonnes, the mill runs chronically underfed, and the unit processing cost doubles relative to design values. Throughput must be determined in coordination with the mine plan.

Geographic and infrastructure conditions at the mine site. Above 3,000 meters elevation, diesel engine output drops noticeably. In water-scarce areas, closed-loop water recycling must be considered. If road conditions are poor and equipment cannot be transported in, nothing else matters.

The separation principle for alluvial gold has exactly one element: density difference. Gold has a density of about 19.3 g/cm³, common sand and gravel about 2.6 g/cm³.

The decisive variable in alluvial gold equipment selection is the particle size distribution of gold. When gold particles are coarse, above 0.5 mm in diameter, sluices, jigs, and even gold pans can achieve high recovery rates. When fine gold is prevalent, below 0.074 mm, recovery rates on conventional gravity equipment can plummet from 90% to 40% or lower, and centrifugal concentrators become necessary.

Knelson and Falcon are the two benchmark brands in the centrifugal concentrator space. The two have fundamentally different operating principles. Knelson is a fluidized-bed type, relying on injected water to create a fluidized layer for separation, and it is very sensitive to feed density and fluidization water pressure, with a narrow operating window. Falcon is a film-flow type, where the slurry forms a thin film on the rotating wall to achieve separation, and it tolerates feed fluctuations better. For most small to mid-scale alluvial gold projects, Falcon is the more suitable choice. Not because Falcon's separation performance is necessarily superior, but because Falcon's tolerance for feed variation is higher and its operating window is wider, making it less likely to cause major problems when the operating crew has limited experience. Knelson, under optimal operating conditions, has stronger capture ability for fine gold particles. If there is an experienced operator who can keep fluidization water and feed density consistently within the optimal range, Knelson's performance will be excellent. The problem is that "consistently within the optimal range" is a condition that is not easy to maintain at most alluvial gold mining sites. The best approach is to run comparative tests with actual ore samples on both machines. This kind of test is rarely done. When it is done, there is no need to guess.

Trommel scrubbers, through prolonged tumbling and water flushing to break apart mud balls, are more important than any separation device downstream in this type of ore.

The key parameter in trommel scrubber selection is retention time. The problem commonly seen in practice is that trommels are too short and rotate too fast, and material exits the drum before it has been properly scrubbed. It is better to make the trommel longer, slow the rotation, and sacrifice some throughput.

River-channel alluvial deposits suit dredges. Dryland alluvial deposits are better served by mobile processing units. This choice is fairly straightforward and does not need further elaboration.

In hard rock gold, gold is locked inside the rock and must be liberated through crushing and grinding before entering the separation stage. The crushing circuit is fairly standardized: jaw crusher for primary crushing, cone crusher or impact crusher for secondary and tertiary crushing, two-stage or three-stage closed-circuit flowsheets. Selection is based on ore hardness and throughput; match them properly and that is sufficient. The closed-side setting of the cone crusher needs to be calculated in coordination with the downstream grinding system rather than simply set to the manufacturer's recommended value. Getting this optimization right saves a meaningful amount on annual power and grinding media costs.

Grinding accounts for 40% to 60% of total plant power consumption. Over ten years of operation, the electricity bills and steel ball costs in the grinding circuit alone may exceed the purchase price of the entire equipment set. Any parameter deviation in the grinding circuit compounds costs continuously.

Ball mills are the most widely used grinding equipment. For projects exceeding 10,000 tonnes per day, SAB or SABC circuits with semi-autogenous mills plus ball mills are more economical, eliminating the secondary and tertiary crushing stages and greatly simplifying the flowsheet. SAG mills are very sensitive to ore grindability and must be validated through SAG Power Index and SMC testing. For projects below 10,000 tonnes per day, a ball mill with closed-circuit hydrocyclone classification is the safest configuration, carrying the lowest technical risk and the most widely available spare parts.

Determining grinding fineness. The method is staged grinding tests: run separation tests at different finenesses such as 50%, 60%, 70%, 80%, and 90% passing 200 mesh, plot the recovery-versus-fineness curve, and find the inflection point where the curve begins to flatten. The fineness at that inflection point is the technical optimum. Overlay the grinding cost at each fineness and the economic optimum emerges.

After grinding fineness is determined, work backwards to the required installed mill power, then select mill specifications and quantity based on that power. Do not start by looking at what mill models are available on the market and then try to match them to the throughput. Power is the core language of grinding system design. The Bond Work Index test provides the data that bridges ore properties and mill power.

There is a scale-up effect between the Bond Work Index from a laboratory mill and the actual energy consumption of an industrial mill, with scale-up factors ranging from 1.1 to 1.4. The way to address this is pilot testing, running several tonnes to tens of tonnes of ore through a continuous grinding system at pilot scale.

Now steel balls need to be discussed in detail, because their impact on operating costs is severely underappreciated relative to how much they actually matter.

Steel balls are not a standardized commodity. Different suppliers' steel balls vary enormously in hardness, toughness, and diameter consistency. Poor quality balls wear fast and have high breakage rates. Broken ball fragments block the mill discharge grate, reducing efficiency. The same processing plant, switching to a different steel ball supplier, can see a 30% to 40% change in ball consumption per tonne of ore.

Between high-chrome and low-chrome balls, the choice depends on slurry corrosiveness. If slurry pH is low and sulfide ion content is high, low-chrome balls get severely corroded and wear rates spike. In that case, high-chrome balls are more expensive per unit but cheaper in total. If the slurry is alkaline with low corrosiveness, low-chrome balls offer sufficient value for money. Steel ball material selection should be based on wear testing. If a decision must be made without testing: low-chrome forged balls for alkaline slurry, high-chrome forged balls for acidic slurry. That will not be far off.

Ball size distribution also matters. The mill should contain a mix of large, medium, and small ball diameters, and the diameter of freshly added make-up balls should be determined based on feed particle size and target grind fineness. Balls too large will over-crush fine particles and waste energy. Balls too small lack the impact force needed for coarse particles and reduce grinding efficiency. Most processing plants commission with whatever ball make-up scheme the design institute specified initially and never optimize it afterward. Periodically analyzing the particle size distribution of the grinding product and adjusting the make-up ball size ratio based on the results is a low-cost, high-return operational optimization measure.

Steel balls were given this much space because their impact is large but the attention they receive is disproportionately small.

Gravity separation. Suited for ores with a significant proportion of coarse native gold. Core equipment: jigs, shaking tables, spiral chutes, and centrifugal concentrators. Zero chemical reagents, no pollution, extremely low operating costs. Highly dependent on particle size.

Gravity separation as a "mid-circuit interceptor" within the grinding loop is a frequently recommended scheme: installing a centrifugal concentrator in the classifier underflow to recover coarse free gold early, before it gets over-ground into flat flakes that become harder to recover. Whether this scheme is warranted can be determined with a simple heavy liquid separation test. If the free gold content in the ore is inherently low, the centrifugal concentrator will not intercept much gold. This scheme is repeatedly recommended at industry conferences. Many projects installed the equipment without doing the validation. Running this validation costs a few thousand dollars in test fees and a few days of time.

When gold is intimately associated with sulfide minerals like pyrite and arsenopyrite, xanthate-type collectors are added to make the sulfide surfaces hydrophobic, causing them to attach to air bubbles and float, achieving gold enrichment. Flotation does not directly recover gold itself. What it recovers is sulfide mineral concentrate containing gold, typically grading 30 to 100 g/t, which then needs further treatment by concentrate cyanidation or pyrometallurgy.

Flotation equipment selection looks at cell volume and aeration-agitation capacity. Large-volume flotation cells (100 to 300 cubic meters per cell) reduce cell count and simplify the flowsheet. Flotation columns achieve better separation precision than mechanical agitation cells in cleaner circuits and are worth considering in projects requiring high-grade concentrates. Equipment selection to this point is not the hard part.

The hard part is the reagent regime. The same flotation cell, with a different reagent regime, can see recovery rates differ by more than 20 percentage points. Flotation equipment selection must be done in conjunction with reagent testing. Equipment specifications and the optimal flotation conditions established by reagent testing (air flow rate, agitation speed, slurry residence time, slurry density, pH) are bound together.

There is another equipment-level consideration in flotation: whether to use a few large cells or many small cells. Large cells have advantages in smaller footprint, simpler piping, and fewer maintenance points. The problem with large cells is that a single cell going down for maintenance means losing a large proportion of total flotation volume. If there are only three or four rougher cells and one goes offline, flotation volume drops by 25% to 33%, with a noticeable decline in recovery. Small cells offer higher redundancy; losing one has minimal impact. Where throughput allows, configuring a few extra cells with cell volume below the maximum rather than chasing the fewest possible cell count is a more robust approach. This preference diverges somewhat from the textbook trend toward larger cells and fewer units. It comes from an operating reliability perspective.

Cyanide leaching. The workhorse of the global gold mining industry, processing over 80% of the world's gold ore. CIL is the most widely used configuration today. A standard CIL circuit consists of pre-leach thickening, pre-leach agitation tanks, 6 to 8 CIL adsorption tanks in series, loaded carbon elution and electrowinning, and gold sludge smelting. The key design parameters are total slurry residence time in the adsorption tanks (typically 24 to 48 hours) and activated carbon concentration.

Coal-based carbon is cheaper, but its mechanical strength is poor. In the agitated environment of a CIL tank, it breaks into fine particles, and those fine carbon particles pass through the inter-tank carbon screens with the slurry, taking the gold they have already adsorbed with them. This loss is invisible, continuous, and undetectable without a carbon balance calculation. Some plants search the entire flowsheet for the cause of below-target recovery and eventually discover that carbon losses were carrying the gold away. Coconut shell carbon costs 30% to 50% more. Its carbon loss rate may be only one-third that of coal-based carbon. Carbon type selection should be incorporated into the evaluation during the equipment selection phase. Unless project funding is extremely tight and slurry abrasiveness is very low, coconut shell carbon is the safer choice.

Heap leaching. The solution for low-grade, large-tonnage ores. The core equipment is infrastructure: liner systems, drip irrigation networks, pregnant solution ponds and pump stations, ADR plants. Equipment investment is far lower than a CIL circuit. Leach cycles run 60 to 120 days or longer. Recovery rates typically range from 50% to 75%.

The success or failure of heap leaching frequently hinges on ore permeability. When heap permeability is poor, cyanide solution takes "shortcuts" and channels through select pathways, leaving large volumes of ore un-wetted. Ores with high clay content and high fines content are particularly susceptible. The solution is agglomeration, spraying cement or lime slurry onto the ore surface so that fines adhere to coarse particles, forming stable pellets that maintain heap porosity and permeability. Agglomeration equipment (disc pelletizers or drum agglomerators) is the make-or-break equipment in heap leach projects with high clay content. Building a heap leach pad without permeability testing is irresponsible.

Pre-treatment of refractory gold ores. Four routes: roasting, pressure oxidation, bio-oxidation, ultra-fine grinding. This section will state preferences directly.

Roasting is the most technically mature. It emits sulfur dioxide. Environmental approvals are increasingly difficult to obtain, and in countries with strict environmental regulations this route is essentially blocked. Temperature control errors can cause gold particles to sinter and re-encapsulate, actually lowering recovery. The operating window is not wide. For new projects, unless located in a region with lenient environmental oversight and established roasting operating experience, this should not be the first choice.

Ultra-fine grinding. Simple flowsheet, high energy consumption. Suited for specific ore types where gold is primarily encapsulated by a thin sulfide film rather than deeply embedded within the sulfide crystal lattice. Not a universal solution.

Pressure oxidation. Expensive. Expensive in autoclaves, expensive in titanium linings, expensive in associated flash vessels and acid recovery systems. Its strengths are high oxidation efficiency, strong process controllability, lower dependence on operator skill than bio-oxidation, and no sensitivity to climate conditions. Among large refractory gold projects built in the past ten years, the adoption rate of pressure oxidation has been steadily rising. Small projects cannot afford it. Large projects increasingly lean toward it. If a project processes more than 3,000 tonnes per day and the ore is a typical arsenic-sulfide-encapsulated refractory gold ore, pressure oxidation is most likely the safest choice.

These stages are not the core difficulty of equipment selection. Brief coverage.

Thickeners control the plant water balance. In arid regions, water supply may constrain capacity more than power supply. Tailings dewatering equipment is central to dry stacking schemes. The choice between filter presses and ceramic filters must be based on settling and filtration tests.

The INCO process is the most established cyanide destruction method. The AVR process can recover cyanide for reuse, and its economics are compelling where sodium cyanide prices are high.

Online XRF analyzers and online particle size analyzers are good investments in plants processing more than a thousand tonnes per day. Once installed, a matching periodic calibration system must be established, cross-referencing with wet assay data from the laboratory. Otherwise, accuracy drifts and the data becomes unreliable, and operator adjustments based on erroneous data will actually worsen process performance.

Over the past twenty years, China's mining equipment manufacturing industry has made enormous progress. In mainstream equipment categories such as crushers, ball mills, flotation cells, and thickeners, the gap in basic performance parameters between domestic equipment and international brands has narrowed substantially, at prices typically one-third to one-half of imported equipment.

The gaps are concentrated in three areas: the integration and reliability of automation control systems, the metallurgical quality consistency of critical castings and wear parts, and reliability under extreme operating conditions such as high altitude, extreme cold, or highly corrosive slurry where insufficient design margins in some domestic equipment become apparent.

Used equipment can save 30% to 60% on initial investment. Buy core equipment new. Auxiliary equipment can be considered used.

When buying a used ball mill, focus inspection on shell ovality and end-flange flatness. For a used flotation cell, check stator-rotor clearance and tank corrosion. For a used thickener, check rake arm deformation and main shaft bearing condition. Running-state vibration and temperature rise measurements are preferable to static inspection where possible.

The production value lost to a single day of equipment downtime is often greater than the value of the entire spare parts inventory.

Prioritize suppliers with service centers and spare parts warehouses in the same country as the mine, or at least on the same continent. For remote mine site projects, the initial procurement should include a full inventory of at least six months' worth of all wear parts: ball mill liners, flotation cell stator-rotor assemblies, hydrocyclone spigots and vortex finders, slurry pump impellers and frame plate liners, vibrating screen panels, crusher swing jaws and cheek plates.

Standardize all pumps plant-wide to one brand and one series in different sizes. Spare parts interchangeability increases dramatically.

Choosing gold mining equipment is not picking individual items. It is building a complete system where capacities match and parameters connect across every stage. A proper gold mining project must complete three things before equipment selection: ore process mineralogy studies, metallurgical testing (from scoping tests through locked-cycle tests to continuous pilot testing), and a feasibility study. The three are linked sequentially, each one's output feeding the next as input, and the final equipment list is derived from the end of that chain.

Equipment manufacturers' interest is to sell equipment. EPC contractors' interest is to build and hand over as quickly as possible. The mine owner's interests overlap with theirs only partially. In equipment selection, if the mine owner lacks in-house technical judgment or has not hired an independent technical advisor, there is no choice but to passively accept someone else's proposal, and whether that proposal is good or not comes down to luck.