Placer Gold Deposits
Source: Gold Investing News, Leia Michele Toovey (5/3/11)
"Alluvial, eluvial, fluvial, marine-sediment and residual deposits, oh my!"
Gold Investing News, Leia Michele Toovey
Lode gold is the most significant source of gold in the world; however, with the gold price skyrocketing, other deposits have become attractive exploration targets. According to the Alaska Geological Survey, in the 1990s, the extraction of placer gold deposits became an economically feasible means to mine gold if gold is over $245/oz. Placer gold mining can be a profitable business for both individual prospectors and miners; these deposits contain gold that's been eroded, transported and deposited to a location other than where the metal was found originally.
Today, the likelihood of finding a huge nugget in a stream isn't as high as it once was. However, there are bountiful opportunities to find gold in other (larger) placer deposit types, the most common of which are alluvial
Alluvial deposits include any deposit formed by water, a subset of which, fluvial, are deposits formed by a river and are often found in bench or terrace deposits, which are formed through floodplains created overtime due to the receding of the river's water levels.
Marine sediment gold deposits could be classified in the alluvial/fluvial category; however, they deserve a specific mention. Gold that is transported by rivers that is not deposited on either the floodplain or streambed often is deposited where the river meets the ocean. When a river meets an ocean, it deposits all the material collected, and carried through their journey across the continent.
Residual gold deposits are shallow mineral deposits forming directly from weathering and chemical disintegration of a gold-bearing quality vein near the surface. Residual deposits tend to be rich, but localized in occurrence. Eluvial gold deposits are not formed through hydraulic processes; instead, they owe their origin to gravity and wind. Eluvial deposits are commonly found in between the lode erosion and drainage system.