Page 43 - Handbook of Gold Exploration and Evaluation

24 Handbook of gold exploration and evaluation

1.7 Sketches of detrital gold grains, Olipai River, Papua New Guinea: (a) crude
crystal group; (b) layered gold flakes; (c) crude crystal group; (d) rolled up gold
flake; (e) distinctly crystallised crystal group; (f) discoidal gold flake with
outward projecting crystals; (g) discoidal gold flake with outward projecting
crystals.

associated with gold precipitating bacteria and that the gold may have been
biologically as well as chemically mobilised.

Origin of nuggets
The origin of gold nuggets has probably been debated since man first explored
for the metal. Possible explanations have ranged from the supernatural to
physical and chemical accretion, or simply to a primary origin. Arguments that
gold nuggets may be formed by chemical accretion include the apparent occur-
rence of larger gold particles in the regolith than in underlying vein systems.
Geochemical proof of the deposition of gold on suitable reductants and the
occurrence of gold dendrites in zones of secondary enrichment is well known.
The main arguments today seem to be based upon questions of scale.
In 1853, Hopkins (in Smyth, 1869) supported the aggregation concept: `large
masses of gold have been found near the roots of large trees and strong grass,
often in very singular forms and evidently indicating the influence of roots in the