Yuba Mining and Machine
Fine Gold Recovery
High-Recovery Gravity Concentration for Fine and Flour Gold
Fine gold creates one of the most difficult recovery challenges in both placer and hard-rock mining.
As gold particles become smaller, they settle more slowly, remain suspended in process water longer, and are more easily carried away with lighter sand and tailings. Gold that is readily visible in a pan may be comparatively easy to recover, while very fine or flour gold can pass through conventional sluices and other passive gravity systems before it has enough time to separate.
Yuba Mining and Machine’s recovery equipment is specifically designed to address this problem.
Our systems combine the Low-G Horizontal Centrifuge for high-capacity primary recovery with the Reverse Multi-Helix Spiral for secondary concentration, cleaning, and final upgrading. Together, these machines provide one of the highest-performing gravity recovery systems available for fine free gold at commercial production scale.
Fine gold does not discourage us. It was the type of problem our equipment was developed to solve.
Why Fine Gold Is Difficult to Recover
Gold is much denser than most surrounding material, but density alone does not guarantee recovery.
When gold particles become extremely small, their behavior is increasingly influenced by water movement, slurry conditions, particle shape, and the surrounding mineral matrix.
Common fine-gold recovery challenges include:
Proper Gold Liberation
Gold that remains locked inside larger rock particles cannot be recovered effectively by gravity concentration.
The ore must be crushed and milled until the gold is liberated from the surrounding host rock. The required grind size varies from one deposit to another. Some ores release gold at a relatively coarse size, while others must be reduced to 100, 200, or even finer mesh before meaningful recovery is possible.
Milling too coarsely may leave recoverable gold locked in the rock. Milling unnecessarily fine can increase power consumption, reduce throughput, and make gravity recovery more difficult.
Material testing is therefore important when determining the correct grind size and recovery circuit.
Slow Settling
Coarse gold settles quickly because its weight allows it to resist moving water and lighter material.
Fine gold settles much more slowly. In a fast-moving or turbulent process stream, small particles may remain suspended and move through the recovery circuit with the tailings.
Limited Retention Time
Traditional sluices depend on gold settling into riffles or matting as material flows across the recovery surface.
Fine gold may not have enough time to settle before leaving the sluice, particularly when production rates, water velocity, or feed volume are high.
Flat and Flaky Gold
Fine gold is not always spherical or compact. Thin, flat particles can behave differently from heavier rounded particles of the same mass.
Flat gold may remain suspended, move across recovery surfaces, or be pushed back into the process stream more easily than coarse gold.
Improper Classification
Fine-gold recovery becomes more difficult when the feed contains a broad range of particle sizes.
Large particles disturb the separation environment, while excessive slimes can alter slurry behavior and keep fine gold suspended. Consistent classification allows the concentrator to operate under more controlled conditions.
Gold Locked in Other Material
No gravity concentrator can recover gold that has not been liberated.
In hard-rock applications, fine gold may still be enclosed in quartz, sulfides, or other host minerals. In placer material, it may be trapped inside clay or attached to compacted material.
The ore must first be properly milled, scrubbed, or otherwise prepared before the gold can be physically separated.
Competing Heavy Minerals
Magnetite, black sand, sulfides, and other dense minerals are also captured by gravity equipment.
A high volume of these minerals can create a large concentrate and make it more difficult to isolate the gold. The recovery circuit must be selected and adjusted according to the entire mineral composition, not just the expected gold size.
Fine Gold Recovery with the Low-G Horizontal Centrifuge
The Low-G Horizontal Centrifuge is designed as a primary concentrator for fine free gold in both alluvial and milled hard-rock applications.
Unlike passive gravity equipment, the Low-G Centrifuge uses centrifugal force to drive gold and other heavy particles outward into internal concentrate chambers. This provides a stronger separation force than gravity settling alone and allows the machine to recover fine gold under commercial production conditions.
During operation, water and classified material are continuously fed into the centrifuge while the concentrate is collected internally.
The chambers initially form a soft bed of lighter material. As additional slurry enters the centrifuge, gold and other heavy particles displace the lighter particles already inside the chambers. This creates an ongoing upgrading action during production.
At the end of the operating period, the centrifuge speed is reduced and the accumulated concentrate is flushed into a receiving container or hopper.
Why the Low-G Centrifuge Works for Fine Gold
The Low-G Centrifuge is well suited for fine-gold recovery because it provides:
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True centrifugal separation
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High primary concentration ratios
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Large concentrate-holding capacity
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Controlled batch concentrate collection
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Commercial production capacity
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Operation with clean or turbid process water
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Integration into new or existing processing circuits
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Parallel installation options for higher throughput
Its design allows it to capture fine gold that may be difficult to retain using conventional sluices or other passive recovery equipment.
The Low-G Centrifuge does not depend on the gold naturally settling fast enough in normal gravity. Instead, centrifugal force actively drives the dense particles into the internal chambers.
Fine Gold Recovery with the Reverse Multi-Helix Spiral
Primary recovery is only the first step.
The concentrate produced by a centrifuge, sluice, jig, or other recovery machine usually contains gold mixed with black sand, magnetite, sulfides, and lighter gangue. This material must be cleaned and progressively concentrated before a high-grade final product can be produced.
The Reverse Multi-Helix Spiral is designed for this secondary and final concentration work.
Its internal working surface contains a series of reverse-running spiral leads. As material moves through the barrel, gold and heavy minerals settle into the spiral grooves and are conveyed toward the concentrate discharge, while lighter material moves toward the tailings end.
Integrated spray water continuously washes lighter material away from the advancing heavy concentrate.
The separation can be adjusted to produce either a broader recovery cut or a tighter, higher-grade product.
All Reverse Multi-Helix Spiral models are capable of processing a wide range of concentrates and properly prepared feed materials, including:
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Centrifuge concentrate
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Sluice concentrate
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Jig concentrate
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Spiral concentrate
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Fine-milled hard-rock material
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Black-sand and heavy-mineral concentrate
The appropriate spiral is selected primarily based on the required processing capacity and how tightly the cut needed.
24-Inch Spiral Rougher
The 24-inch Spiral Rougher is designed for higher-throughput applications and broader initial separation. It is commonly used to process larger volumes of material, remove a substantial portion of unwanted lighter material, and produce an upgraded concentrate for additional cleaning.
Multiple Roughers may be installed in parallel when greater production capacity is required.
16-Inch Spiral Cleaner
The 16-inch Spiral Cleaner provides a tighter separation than the Rougher while maintaining practical production capacity. It is commonly used to further reduce concentrate volume and remove additional unwanted material while retaining the gold and valuable heavy-mineral fraction.
In many applications, the Cleaner performs most of the concentrate-reduction work.
16-Inch Spiral Finisher
The 16-inch Spiral Finisher is designed to make the tightest separation of the three models. It is typically used during the final cleanup stage to produce clean free gold, a smelt-grade product, or a very high-grade mineral concentrate.
Typical Spiral Circuit
A typical staged spiral circuit may be arranged as:
Fine-Milled, Classified, or Concentrated Material
↪ 24-inch Spiral Rougher
↪ 16-inch Spiral Cleaner
↪ 16-inch Spiral Finisher
The exact configuration can be adjusted based on the feed rate, material characteristics, desired concentrate grade, and recovery objectives. Spirals may also be installed in parallel or arranged in other custom configurations to meet the requirements of a particular operation.
Choosing the Right Fine Gold Circuit
The best fine-gold recovery process depends on more than particle size alone.
Important factors include:
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Whether the gold is liberated
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Gold particle shape
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Feed size distribution
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Clay and slime content
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Magnetite and black-sand content
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Sulfide content
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Slurry density
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Water quality
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Required throughput
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Desired final concentrate grade
Low to Moderate Heavy-Mineral Content
When the material contains fine free gold with relatively low amounts of magnetite and other competing heavies, we generally recommend:
Classified Material
↪ Low-G Horizontal Centrifuge
↪ 16-inch Spiral Cleaner
↪ 16-inch Spiral Finisher
The centrifuge provides high-capacity primary recovery, while the spirals clean and finish the concentrate.
High Black-Sand or Heavy-Mineral Content
When the material contains a high volume of magnetite, dense sulfides, or other heavy minerals, a larger spiral circuit may be more practical.
In these applications, the circuit may use:
Classified Material
↪ 24-inch Spiral Rougher
The spirals continuously reject lighter material while progressively concentrating the heavier material.
Do Not Assume Your Gold Is Too Fine
Many operators believe that their gold is too fine to recover because they cannot see it in a pan or because it has already passed through a sluice or conventional recovery system.
That does not necessarily mean the gold is unrecoverable.
The result may be caused by:
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Insufficient liberation
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Poor classification
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Excessive water velocity
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Inadequate retention time
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Incorrect equipment settings
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High black-sand loading
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Improper concentrate cleaning
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A recovery circuit not designed for fine particles
The best way to determine what can be recovered is to test the actual material.
Bring Us Your Material
If you believe your gold may be too fine for conventional recovery, bring us a representative sample.
Yuba Mining and Machine can run material through our demonstration equipment to evaluate:
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Whether free gold is present
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Whether the gold has been adequately liberated
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How the material responds to centrifugal concentration
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How much black sand or heavy mineral is present
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Whether spiral cleaning improves the concentrate
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Which equipment arrangement is most appropriate
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What portion of the material can be physically recovered
We would rather demonstrate the recovery process with your material than make assumptions based only on an assay report or estimated gold size.
Fine gold does not deter us. It is exactly the type of material our Low-G Horizontal Centrifuge and Reverse Multi-Helix Spiral systems are designed to evaluate and recover.