Day 5, eluvial, fluvial and alluvial. Part I.

The relationship between  fluvial deposits and hydrothermal process where heat, pressure and time form minerals, processes alluvial, eluvial and river transport are processes and materials formed through the currents of rivers and seas . We can say that the factories are hydrothermal deposits of rocks (along with other similar processes) while fluvial deposits, alluvial and eluvial are transporting these types of rocks or geologic materials already formed. These transports are to be discussed…

Placeres eluvial , alluvial  and fluvial.

Are terms applied to surface deposits that have formed by the accumulation of heavy minerals not easily altered in quantity and economic importance. These mineral veins or lodes existed that were weathered and crumbled on the surface by the action of atmospheric agents, heavy minerals being uprooted, transported and sorted by the action of water currents. The pleasures are classified into two types: eluvial and alluvial deposits and river.

Eluvial

Eluvial is the term applied to the pleasures to be found in the immediate vicinity of the parent rock, so that the free gold found on the slopes above the outcrop of a gold vein is a eluvión. Auriferous reefs or veins, when exposed to erosion are attacked by weathering. These processes determine the formation of weathering and rock eluvión in one degree or another has suffered destructive proceses being unchanged its initial location. Except for their external appearance and physical properties of eluviones not differ from the rocks that originated; eluvión subsequently undergoes a transformation: part disappears other aqueous solutions are drawn in the form of debris away from the places where originally formed. The eluvial pleasures can be considered as the initial phase of the pleasures of beaches and alluvial deposits and river. The eluvial deposits are formed without intervening water flows on the slopes of the mountains fromthe materials rel

eluvial gold

Eluvial Gold, details

eased from weathered outcrop reefs above them. The heavier and resistant minerals accumulate below the outcrop, the lightweight and resistant products of decomposition are dissolved or swept down hillsides rainwater, this site concentration determined in part by production volume, a process that continues to as the level goes down the slope. Eventually the lower mass is eroded and transported material into the channels of the mightiest rivers, where water currents begin to move the material and they allow or cause the river alluvial placers.

alluvial-gold-dust-particles

Alluvial gold dust particles, taken from Motagua River in Guatemala

Alluvial or fluvial deposits

The river placers are the type most important placer deposits, are those that have produced the largest amounts of gold in the history of this metal, account for a considerable part of the total gold production in the world. Tap water is the most effective separator for light and heavy materials. The river water always flows in one direction does not regularly: precipitated by the throats, backs up in places as wide and eddies in the outer parts of the river, the gentle inner portions of rivers are not favorable to the accumulation pleasures, nor headers, due to shortage of material transported. The bright spots are located in the middle reaches of the river where the current flows quickly meanders. The faster the water that is on the outside of the bend and the slowest on the opposite bank.

At the confluence of two rivers where gravel bars are formed, is a favorable place for the deposit of placers, when cross riverbeds steep rocks or layered vertical harder layers tend to project upwards while the softer decreasing, natural depressions form, these segments are excellent for deposition of minerals. If a river flows through a vein ore and minerals extracted from him pleasure, by corrosion, the boom extends downstream of the river from the corresponding vein.

The accumulation of the placeres requires well leveled rivers, where a balance is achieved between the erosion, transport and deposition (Lindgren.1933 in V.Lopez.1981). Lindgren considered moderate slopes close approximately 10 meters per kilometer are likely optimal concentrations. A slight rise, a sudden decrease of the load of the river or a volume increase of the current, causing the rejuvenation of the river and the formation of terraces and gravel bars in the valley, with the repetition of this phenomenon can form more than one series of high and low terraces. The top of the terraces primitive representing the valley floor may consist of landslides or the bedrock covered by the barrage. Commonly the gravels of the terraces, are again dragged laterally toward the river water and subjected to a second concentration. In the absence of lateral drag, the placer gold deposits in banks or terraces.

In areas affected by subsidence regional surcharges have buried river gravels to a depth of several meters; these deposits, reached by dredging or by wells, their exploitation is difficult when there are excessive abundance of groundwater.
The age of the goldfields periods ranging from Precambrian to late Tertiary, are found all over the world, especially where there was igneous activity, showing preference for intermediate     composition intrusions or silica.where-to-find-gold-alluvial-gold

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