Laterite gold deposits are formed from pre-existing gold deposits ( including some placer deposits ) during prolonged weathering of the bedrock.
32.
The most economical ways of mining tin are by dredging, placer deposits, which can contain as little as 0.015 % tin.
33.
Other placer deposits on the west bank of the Colorado River were quickly found, including the Picacho and Cargo Muchacho districts.
34.
A steam-powered dragline was used to mine the placer deposits of Peters Creek, below the canyon that cuts through the Peters Hills.
35.
Placer deposits clustered near the village of Hughes and Indian Mountain are the other significant source of placer gold from the district.
36.
In areas where the ground is permanently frozen, such as in Siberia, Alaska, and the Yukon, placer deposits may be mined underground.
37.
The Golddust Camp placer deposits are found in the alluvium of the dry gulches radiating off Copper Flat and the andesite flows.
38.
Cassiterite often accumulates in alluvial channels as placer deposits because it is harder, heavier, and more chemically resistant than the accompanying granite.
39.
If pure platinum is found in placer deposits or other ores, it is isolated from them by various methods of subtracting impurities.
40.
Since gems and heavy metals like gold are considerably more dense than sand, they tend to accumulate at the base of placer deposits.
