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The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the California Gold Rush. Types of placer deposits include alluvium, eluvium, beach placers, aeolian placers and paleo-placers. [2]
Placer mining is frequently used for precious metal deposits (particularly gold) and gemstones, both of which are often found in alluvial deposits—deposits of sand and gravel in modern or ancient stream beds, or occasionally glacial deposits. The metal or gemstones, having been moved by stream flow from an original source such as a vein, are ...
This list of fossil sites is a worldwide list of localities known well for the presence of fossils.Some entries in this list are notable for a single, unique find, while others are notable for the large number of fossils found there.
The most important known placer deposit of niobium and tantalum in the United States is located in Bear Valley. [14] From 1953 until 1959, dredges there produced $12.5 million ($131 million today [15]) in niobium, tantalum, and uranium. Other minerals mined in the forest include antimony and molybdenum. [14]
For example; the medium-sized Coburn mineral sands deposit, Western Australia, is 230 million tonnes at 1.1% heavy minerals, and is 13 km long. The Tormin mine, on the Western Cape of South Africa's coastline, provides a unique ocean beach feature, which exposes the resource to wave and tidal conditions that result in a natural jigging effect.
The Rhynie chert contains exceptionally preserved plant, fungus, lichen and animal material [1] preserved in place by an overlying volcanic deposit. The bulk of the Devonian fossil bed consists of primitive plants (which had water-conducting cells and sporangia , but no true leaves ), along with arthropods , lichens, algae and fungi.
Placer mining is a method of extracting gold from alluvial deposits such as sand, gravel, and sediment. [43] [44] These are known as placer deposits which are typically found in riverbeds, stream beds, and floodplains. [45] These deposits typically contain minerals that are resistant to weathering and eroision like gold, platinum, diamonds, and ...
These concretions frequently preserve both hard and soft tissues of animal and plant materials, as well as many soft-bodied organisms that do not normally fossilize. The quality, quantity and diversity of fossils in the area, known since the mid-nineteenth century, make the Mazon Creek lagerstätte important to paleontologists attempting to ...