Page 40 - Handbook of Gold Exploration and Evaluation

Table 1.9 Simplified model relating placer gold characteristics to environment and best recovery methods (from Giusti, 1986) a

(Increasing distance from source)
ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ!
Eluvial placer Alluvial placer

Gold grain Irregular; primary Irregular, rounded Flaky, jagged surface Flaky, rounded, Rounded,
morphology crystals still preserved; protuberances; some rounded outline; multiple bending; often porous;
lots of inclusions; primary crystals still re-crystallised; re-crystallised; some small ED;
very high CSF preserved, often in plastic deformation; secondary octahedral high±very
cavities or folded medium±small CSF crystals on the surface; high CSF
portions of the metal; high CSF
mainly inclusions of
quartz; high CSF
Rim effect Porous rim is Porous to compact Compact Compact Compact to
frequent porous
Abrasion Moderate Strong Strong Strong Moderate
Chemical Very strong Moderate±minor Minor Minor Minor
weathering
Most-representative ‡35 ÿ35 to ‡120 ÿ120 to ‡200 ÿ200 to ÿ400 ÿ200 to ÿ400
mesh size
Prevalent Cobbles, pebbles Pebbles, sand Sand Sand, silt Silt, sand
sediment type
Environment High energy High±medium energy Medium±low energy Low energy
Suggested recovery Mechanical (panning, Mechanical and Chemical and Chemical and Chemical and
methods sluicing, jigging, chemical (sluicing, mechanical mechanical mechanical
rocking) tabling, flotation)

a
The model assumes (1) monocyclic gold and (2) relatively coarse-grained gold at the source.