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Placer deposit. Heavy minerals (black) forming placers along ripple marks. In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. [1] The name is from the Spanish word placer, meaning " alluvial sand".
Placer mining. 19th-century miner pouring water into a rocker box which, when rocked back and forth, will help separate gold dust from the alluvium. Placer mining (/ ˈplæsər /) [1] is the mining of stream bed deposits for minerals. [2] This may be done by open-pit mining or by various surface excavating equipment or tunneling equipment.
Kimberlite from the United States. Composition. Forsteritic olivine and carbonate minerals, with trace amounts of magnesian ilmenite, chromium pyrope, almandine-pyrope, chromium diopside, phlogopite, enstatite and titanium-poor chromite. Sometimes contains diamonds. False-color scanning electron microscope image of kimberlite from South Africa.
This includes placer deposits, laterite deposits, and residual or eluvial deposits. Superficial deposits processes of ore formation include; Erosion of non-ore material. Deposition by sedimentary processes, including winnowing, density separation (e.g.; gold placers).
Eluvium. In geology, eluvium or eluvial deposits are geological deposits and soils that are derived by in situ weathering or weathering plus gravitational movement or accumulation. The process of removal of materials from geological or soil horizons is called eluviation or leaching. There is a difference in the usage of this term in geology and ...
Colluvium. Colluvium (also colluvial material or colluvial soil) is a general name for loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, sheetwash, slow continuous downslope creep, or a variable combination of these processes. Colluvium is typically composed of a heterogeneous range of rock ...
An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but are also found in more humid environments subject to intense rainfall and in areas of modern glaciation.
Gold became highly concentrated in California, United States as the result of global forces operating over hundreds of millions of years. Volcanoes, tectonic plates and erosion all combined to concentrate billions of dollars' worth of gold in the mountains of California. During the California Gold Rush, gold-seekers known as "Forty-Niners ...