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Types of Gold Placers
Formation of Placers: The formation of placers is, therefore, a combination of both mechanical and chemical processes working in consort over long periods of time.
The mechanical agencies that assist in the transport and winnowing of gold into placers are gravity, the running water of streams and rivers, the agitation of waves along the shores of lakes, seas and oceans, the wind, and glaciers. Gravity is a force that operates in the formation of all types of placers; it is the principal agent that concentrates gold in eluvial placers.
The other agents give rise respectively to the following types of placers:
- Stream and river (alluvial) placers,
- Deltaic placers,
- Beach placers,
- Aeolian placers.
There are few authenticated aeolian gold placers of any size, and we shall not cons ider them further except to note that near the outcrops of some of the primary deposits in Australia the wind had blown away the finer detritus exposing coarser material in which gold was enriched in places. Auriferous sand dunes have been recorded in the Silver Peak quadrangle, Nevada. These apparently contain only traces of gold and silver. Placers due entirely to glaciation are uncommon.
The minerals concentrated in placers include two types:
- Those with low to medium specific gravity (the light minerals)
- Those with a medium to high specific gravity (the heavy minerals).
All of these minerals have three features in common:
- · Great physical resistance to mechanical abrasion and comminution.
- · Great chemical resistance to solution in superficial waters
- · General Equidimensional character in their form
