This dry gold separator uses a bellows to blow air upward through a riffled screen. Fine sand and dust can be carried away while dense gold collects at the riffles. Explore the air pulses and compare solid and fluid specific gravities. The concentration criterion describes density contrast, not the fraction of gold recovered.
Gold Separator Interactive Calculator
Compare heavy-mineral, light-mineral and fluid specific gravities using the standard gravity-concentration criterion.
Equation Used
- Heavy and light component specific gravities both exceed the fluid specific gravity.
- Concentration criterion is used only as a preliminary density-contrast index.
- The 2.5 value is a heuristic comparison threshold, not a universal acceptance limit.
- The screen slope, riffle spacing, air flow and particle paths are illustrative rather than calculated.
- No particle size, shape, liberation, viscosity, flow, residence-time, recovery or grade model.
Concentration criterion is an amenability heuristic, not a separator-performance model. The animation shows a bellows-fed dry riffle screen. Its air and feed markers are schematic and do not predict trajectories, recovery, grade or losses.
Bellows and riffled screen
Hiscox item 1245 describes a dry separator whose bellows supplies an air blast beneath a riffled screen. Material enters from the hopper. Air passing upward through the screen carries fine sand and dust away from gold at the riffles. The illustrated crank drive shows how repeated bellows compression produces pulses; its dimensions and the feed paths are illustrative. The calculator starts with fluid SG 0.0012 as an air-density example. Air density varies with temperature and pressure; enter the value appropriate to your comparison.
Preliminary density comparison
The concentration criterion can screen whether a heavy and light mineral pair has favorable density contrast in a selected fluid. Equipment selection and performance still require particle-size and liberation data plus tests on an identified sluice, jig, table, spiral or other separator.
Concentration criterion
CC=(SGheavy−SGfluid)/(SGlight−SGfluid). It compares the two solids' excess density above the separating fluid. A larger value generally indicates an easier density separation under otherwise comparable conditions.
The displayed 2.5/CC value is only a transparent comparison with a common heuristic threshold. It is not risk, probability, recovery or efficiency.
Example: comparing gold and quartz densities
Use heavy-mineral SG 19.3, light-mineral SG 2.65 and fluid SG 1. These represent an illustrative gold–quartz–water comparison.
- Heavy-mineral excess over fluid: 19.3 − 1 = 18.3.
- Light-mineral excess over fluid: 2.65 − 1 = 1.65.
- Concentration criterion: 18.3 / 1.65 = 11.09.
- Solid-density ratio: 19.3 / 2.65 = 7.28.
- Comparison with 2.5: 2.5 / 11.09 = 0.2254.
The density contrast is favorable under the usual preliminary interpretation of this index. It does not establish feed rate, screen slope, settling velocity or recovery. Fine, flat or unliberated gold can behave differently from the idealized density comparison; test the actual feed and equipment.
What density contrast leaves out
Concentration criterion is a preliminary amenability index. Actual separation depends strongly on particle size distribution, shape, liberation, feed composition, viscosity, air or water flow, screen or trough slope, riffle form and spacing, residence time and operating practice. Those factors are not inputs here.
Technical references
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), page 306, item 1245: dry gold separator. The EPA references below describe wet placer separation for comparison.
Frequently asked questions
Does CC above 2.5 guarantee gold recovery?
No. It indicates favorable density contrast under a screening convention. Particle size, shape, liberation and operating conditions still control separation.
What does 2.5 / CC mean?
It compares the calculated concentration criterion with a reference value of 2.5. A result below one means CC exceeds that reference; it is not a loss fraction, probability or recovery percentage.
Why does Heavy Delta have SG units?
It is the heavy-mineral specific gravity minus fluid specific gravity. Specific gravity is a dimensionless density ratio; this difference is not a settling velocity or force.
Can Heavy SG be lower than Light SG?
The sliders allow it, but then their names no longer describe the entered materials. A concentration criterion below one indicates that the component entered as heavy has less excess density than the component entered as light.
Why do particle paths not change when I adjust density?
The moving markers illustrate feed direction and pulses of air through the screen. No particle-trajectory or capture calculation drives them.
Can this predict concentrate grade?
No. Feed composition, liberation and equipment performance are not inputs.
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