Spirals are the simplest and lowest-cost equipment in the gravity family covered on gravity recovery of gold from tailings, and that simplicity, no power beyond feed pumping, no moving parts in the separator itself, is exactly their appeal on higher-tonnage, lower-unit-value tailings work. Their origins are in the mineral sands and coal industries, where the same helical-flow principle has separated heavy minerals from bulk feed for decades before the design was adapted to gold recovery specifically.
How does a spiral concentrator physically separate particles?
A spiral concentrator separates particles by letting slurry flow down a helical trough under gravity, where the combination of centripetal force from the curved path and the natural stratification of a flowing film pushes denser particles toward the inner edge of the channel while lighter gangue is carried toward the outer edge. Adjustable splitters positioned along the trough divert the two streams into separate launders once they've separated. No electricity or moving machinery drives the separation itself; the only power input is whatever pumps the feed to the top of the spiral.
The stratification driving that separation is the same secondary flow phenomenon exploited by a simple sluice box, but the helical geometry compounds it over a much longer effective flow path within a compact footprint. Wash water added at intervals along the trough, in some designs, helps re-suspend fine gangue that would otherwise report with the concentrate stream, further sharpening the cut. Getting that wash water rate right is itself an operating variable: too little leaves gangue reporting with the concentrate and lowers grade, too much can wash fine gold out of the concentrate stream along with the gangue.
Spiral trough geometry itself varies across a small number of standard configurations. Single-start spirals run one helical channel and suit lower-tonnage applications, while double- and triple-start spirals run multiple parallel channels wound around the same central column, multiplying throughput per unit of floor space without a proportional increase in footprint. Pitch, the vertical distance the trough descends per full turn, and trough profile both affect the cut point a given spiral achieves, which is why spiral manufacturers offer several standard profiles rather than a single universal design.
What is the difference between rougher, cleaner, and scavenger spirals?
Rougher spirals take the full classified feed stream and make a first, relatively coarse cut, producing a middlings stream that still carries a meaningful amount of misplaced gangue alongside the gold. Cleaner spirals then reprocess that rougher concentrate to upgrade it further, producing a smaller, higher-grade concentrate suitable for final gravity gold recovery or smelting. Scavenger spirals, run on the rougher stage's tailings rather than its concentrate, catch any gold that escaped the first pass before that material is committed to the tailings stream or the next processing stage. A three-stage rougher-cleaner-scavenger bank is standard practice on higher-tonnage circuits precisely because a single pass rarely achieves both high recovery and high concentrate grade simultaneously.
Recirculating the middlings stream, the intermediate-grade material neither clearly concentrate nor clearly tailings, back through an earlier stage is another common refinement, giving borderline particles a second opportunity to report correctly rather than being forced into a binary concentrate-or-tailings decision on a single pass.
Where do spirals fit relative to centrifugal concentrators?
Spirals sit at a coarser cut point than centrifugal concentrators like a Knelson or Falcon unit, and they trade fine-gold recovery capability for a much lower capital cost and a higher throughput per unit of plant footprint. A spiral bank can process considerably more tonnes per hour per dollar of capital than an equivalent centrifugal installation, but it will not recover the fine fraction a centrifugal unit is built to catch. That tradeoff is set out attribute by attribute on centrifugal vs conventional gravity separation.
The absence of any powered mechanism in the spiral itself also means operating cost per tonne is dominated by pumping and labor rather than electricity draw, which is a meaningfully different cost structure from a centrifugal circuit's continuous power demand. For a project weighing total operating cost over a multi-year retreatment program, that difference in ongoing cost can matter as much as the difference in upfront capital, particularly at sites where grid power is expensive or intermittent.
What tailings characteristics suit a spiral circuit?
Spirals suit coarser, higher-tonnage tailings applications where the value per tonne doesn't justify centrifugal capital, or where a project is processing enough material that even a modest recovery improvement on the coarse fraction adds up. They are a poor fit for a dump where testwork shows most of the recoverable gold sits in the fine fraction, since that gold would simply pass through a spiral bank unrecovered.
The particle size distribution and liberation testwork described elsewhere on this site is the deciding factor here, not a general assumption about what spirals are good for. A dump with a genuinely coarse, well-liberated gold population can be well served by a spiral-only gravity stage at a fraction of the capital cost of a centrifugal circuit, while a dump dominated by sub-75-micron gold would waste that capital saving on equipment that cannot recover the gold actually present.
What are the operating limitations?
Spirals are sensitive to feed density fluctuation in a way centrifugal units, which actively fluidize their bed, are not; an inconsistent feed disrupts the stratified film the separation depends on. Consistent, well-conditioned feed from upstream trommels and scrubbers is therefore just as important to spiral performance as it is to any other gravity equipment, arguably more so given the lack of active correction once the slurry is on the spiral.
Splitter position is the other significant operating variable, and it needs periodic adjustment as feed characteristics drift over the life of a project. A splitter set too far toward the concentrate side captures gold well but drags excess gangue along with it, lowering concentrate grade and burdening downstream cleaning stages. A splitter set too far toward the tailings side protects concentrate grade at the cost of losing recoverable gold to the tailings stream. Because a legacy tailings dump is rarely perfectly homogeneous throughout its volume, splitter settings tuned for one section of the dump may need re-tuning as retreatment moves into a different section with a different particle size profile.
Why are spirals particularly relevant to Ghana's tailings volumes?
Ghana's legacy tailings dumps are frequently large by volume even where grades are modest, a combination that favors exactly the low-unit-cost, high-throughput profile spirals are built for. A project retreating hundreds of thousands or millions of tonnes of historic material benefits disproportionately from equipment that keeps the cost per tonne processed low, since even a modest recovery uplift compounds across that volume into a meaningful total ounce count. This is why spiral banks appear so often as the first gravity stage in Ghanaian tailings retreatment flowsheets, ahead of any centrifugal polishing stage rather than in place of one.
That flowsheet logic also reflects a practical staging consideration for investors and operators evaluating a retreatment project. A spiral-first gravity stage requires a smaller initial capital commitment than a full centrifugal circuit, which lets a project begin generating revenue from bulk coarse gold recovery while a subsequent phase adds centrifugal or fine-gold capacity once early production has demonstrated the dump's actual recoverable grade and confirmed the economics of further investment.
Why a project would choose spirals over centrifugal units at all
The decision usually comes down to the same tonnage-and-capital logic already established for fixed versus modular plant design on gold processing plants for tailings: a large, long-life, lower-grade dump can favor the lower unit cost of spirals over the higher recovery ceiling of centrifugal equipment.
How spirals fit into a hybrid circuit
Spirals are rarely a project's only gravity stage; more often they handle bulk coarse recovery while a centrifugal unit or a cleaning table targets the finer fraction spirals can't reach.
Maintenance and wear on a spiral bank
Spirals have no moving parts in the separator itself, which keeps mechanical maintenance minimal compared with centrifugal equipment, but the trough surface is still exposed to continuous abrasive slurry flow and gradually wears, particularly at the inner edge where dense particles concentrate. Polyurethane-lined troughs are the common answer to this wear, extending service life well beyond an unlined surface, and lining condition is worth including in the same routine inspection schedule applied to other gravity equipment.
How spiral banks scale with plant capacity
Because an individual spiral has a fixed, relatively modest throughput ceiling, plant-scale capacity is built by installing spirals in parallel banks rather than by making a single unit larger. Adding capacity later, as a retreatment project's production ramps up or as more of a dump is brought into the mine plan, is therefore usually a matter of installing additional parallel spiral columns rather than replacing existing equipment, which is a meaningfully simpler expansion path than upgrading a centrifugal circuit's capacity.