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Decomposition of organic carbon under anoxic conditions creates a wide range of organic intermediates, e.g., organic acids, that are important determinants of gold mobility. Key microbial processes in the nitrogen cycle can be influenced by gold and vice versa; for example autotrophic denitrifying bacteria can destabilize Au-complexes and may ...
Placer gold deposits form via gravity, with the density of gold causing it to sink into trap sites within the river bed, or where water velocity drops, such as bends in rivers and behind boulders. Often placer deposits are found within sedimentary rocks and can be billions of years old, for instance the Witwatersrand deposits in South Africa .
Gold occurs principally as a native metal, i.e., gold itself.Sometimes it is alloyed to a greater or lesser extent with silver, which is called electrum.Native gold can occur as sizeable nuggets, as fine grains or flakes in alluvial deposits, or as grains or microscopic particles (known as colour) embedded in rock minerals.
Amalgamation of disrupted continental masses to form new supercontinents, known as Wilson cycles, play a key role in the formation of deposits, by initiating major regional change of the geochemical, mineralogical and structural nature of the lithosphere. [6] Orogenic gold deposits were only formed in certain time slices of the Earth's history.
The main source of the minerals comes from the volcanic rocks through which the sea water flows, taking with it the minerals of the volcanic rock. The sea water is heated, convection currents are formed and they ascend carrying the minerals which are discharged at the bottom of the sea or immediately below the surface in the form of black smokers.
Gold cyanidation (also known as the cyanide process or the MacArthur–Forrest process) is a hydrometallurgical technique for extracting gold from low-grade ore through conversion to a water-soluble coordination complex. It is the most commonly used leaching process for gold extraction. [1]
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The riffles are designed to create dead zones in the current to allow gold to drop out of suspension. [46] [47] The box is placed in the stream to channel water flow. Gold-bearing material is placed at the top of the box. The material is carried by the current through the volt where gold and other dense material settles out behind the riffles.