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Gold Mining Method

Gold is a chemical element in the periodic table that has the symbol Au (Latin: 'aurum') and atomic number 79. A transition metal (trivalent and univalent) soft, shiny, yellow, heavy, "malleable", and "ductile". Gold does not react with other chemicals but is attacked by chlorine, fluorine and aqua regia. This metal is widely available in gold nuggets or dust on the rocks and in alluvial deposits and one of the coinage metals. Its ISO code is XAU. Gold melted into liquid form at a temperature of about 1000 degrees Celsius.

In industry, the gold obtained by isolating it from the rock gold ore (extraction). Gold ore categorized into four (4) categories:
  • Thin ore where its content of 0.5 ppm
  • Ore average (typical) easily excavated, a typical value of gold ore in an open tunnel excavation which contains 1 -5 ppm
  • Underground ore / hardrock containing 3 ppm
  • Ore visible eye (visible) with a minimum content of 30 ppm
According to Greenwood et al (1989), gold ore rocks that deserves to be exploited as a gold mining industry, gold content of approximately 25 g / ton (25 ppm).

Gold Mining Method


Gold mining method is strongly influenced by the characteristics of gold deposits. Based on the process of formation, deposition of gold categorized into two types, namely:

Deposition Primary / Primary deposits

In general, gold was discovered in the form of metal (native) contained in the cracks of rocks and quartz in the form of minerals formed by magmatism or the concentration at the surface. Some precipitate formed due to contact metasomatisme process and hydrothermal activity, which form the main body of ore with silica. Primary gold deposits to have a distribution in the form of veins / vein in igneous rocks, rich in iron and is associated with quartz veins.

Deposition plaser / Secondary deposits

Gold is also found in the form of alluvial gold formed by the weathering of the rocks containing gold (gold-bearing rocks, Lucas, 1985). Oxidation process and the influence of water circulation that occurs in the primary gold deposits at or near the surface of the lead to the disintegration of gold ore primary constituent.

The process causes also separated and dispersed gold. Regardless, disseminated gold from ore bonding primer can be deposited back in the cavities or pores of rocks, cracks in the ore body and its surroundings, forming a collection of gold grains with a rough surface texture. As a result of this process, the grains of gold in the secondary gold deposits tend to be larger than the grains of the primary deposits (Boyle, 1979).

Where the concentration of mechanically through a process of erosion, transport and sedimentation of the results of the disintegration of gold deposits pimer produce gold deposits put / alluvial (placer deposit).

Primary gold deposits mineable open pit mine (open pit) and underground mines (underground minning). While secondary gold deposits are generally mined by open pit.

Primary deposits

The primary deposits are deposits that formed simultaneously with the formation of rocks. One common type of primary deposits made on a small scale mining is a vein-type ore (veins), which is generally done by underground mining techniques, especially methods gophering / coyoting (in Indonesia called rat hole).

Mining to underground mining system (underground), by making a hole horizontal openings of tunnels (tunnel) and vertical openings in the form of pitting (shaft) as the access into the mine. Mining is done by using simple tools (like a chisel, hammer, shovel, crowbar) and carried out selectively to choose gold ore containing both low-grade and high-yield.

Against rocks are found, do rock crushing or grinding process, then performed cyanidation or amalgamation, while for secondary mining type generally can be directly performed cyanidation or amalgamation because it is in the form of fine granules.
  • Some characteristics of vein-type ore (veins) that affect mining techniques include:
  • Mineral or metal components are not evenly spread over the body veins.
  • Ore mineral crystals can be rough.
  • Most veins have a narrow width so susceptible to fouling (dilution).
  • Most veins associated with faults, fracture filling, and shear zones (strain), so in this condition allows the dilution effect of the rock.
  • Differences assay (levels) between veins and rock side is generally sharp, associated with contact with the rock side, the impregnation of the rock, as well as the pattern of veins that branching.
  • Fluctuations in the thickness of the veins are difficult to predict, and has a limited range, and has a very erratic levels (random / irregular) and difficult to predict.
  • Most veins are relatively hard and brittle.
By paying attention to these characteristics, mining methods commonly applied are underground mines (underground) with Gophering method, which is a non-systematic way of mining, no need to hold preparations for mining (development works) and the direction of the excavation just follow the direction of flight of the ore deposits. Therefore, the size of the hole (stope) is also not necessarily, depending on the size of the ore deposits in the place and generally without buffering good.

How to mining generally without adequate buffer and excavation generally performed without mechanical devices.

Mining is done in a simple, no development works, and immediately dug ore deposits comply with the direction and shape of natural. When the ore deposits are not homogeneous, sometimes had to be abandoned irregular pillar of poor parts.

The process is done in mining Underground scale artisanal mining methods:

Development into the mine pit.

Inlet is made very simple with a diameter generally can only access one person only.

Construction of access to the ore body.

Access to the ore body is made according to the location of the target orebody. There are two ways to get to the ore body based on the location of deposits, namely:
a. Using drift (inlet horizontal, shoot), if the location of the ore body is relatively parallel to the main entrance.
b. Using shaft (vertical inlet), if the location of the ore body relative under the main entrance.
As well as the inlet to the mine, access to the ore body is made simple, with just enough work location to use just one person with a diameter of about 1 - 1.5 m. The entrance hole is made without buffering or just with a simple buffer for the expected area prone to collapse.

Excavation of gold ore

Gold ore excavation carried out by following the direction of continuity of ore. Tools used for purposes such as rock excavation excavator manual.

Transporting gold ore from the mine to the outside of the mine to be done manually. Transport path using the main entrance. Especially for access using shafts, transport assisted by a pulley system.

Underground mining methods are well done with the following provisions:
The entrance to the gold ore veins must be made more than one piece, and can be made flat / horizontal, tilted / inclined or perpendicular / vertical as needed.
The size of the driveway can be tailored to the needs, recommended diameter> 100 cm.

Location driveway is at a stable area (slope <30 °) and it should not make its way into the steep slopes. Hole openings should be kept in a stable condition / not collapse, if necessary can be installed a buffering system that should be able to guarantee the stability of the hole openings (for inlet with a slope> 60 ° is recommended to always put buffer).

Wood suggested buffer used first class wood. Diameter wood used buffer recommended no less than 7 cm. The distance between the buffer should not be more than 0.75 x diameter of the aperture (depending on grade wood used buffer and rock strength are supported).

Air circulation should be ensured so as to guarantee a minimum requirement of 2 m3 / min, if necessary, can use the blower / compressor to supply the needs of oxygen into the hole

Around the inlet made trenches to prevent water from entering, and trenching directed toward settling ponds with precipitation done gradually, if necessary, can use a submersible water pump to get rid of stagnant water from the hole.

Secondary deposits

Secondary gold deposits, better known as the alluvial gold deposits of gold were deposited along with the material sediment carried by the stream or ocean waves is a common characteristic of easily found and mined by the people, because of the ease of extraction.

Alluvial gold deposits are characterized by sediment deposition conditions are separated with a gold metal content in the form of granules, can be mined and processed by physical gold separation, using simple equipment.

Alluvial gold deposits with distribution on the surface or near surface is easily recognizable, with characteristic is off, and gold has been in the form of metal (native), sufficiently processed by physical separation.

In general, alluvial gold mining is done based on the principles of:
Gold grain is separated so that ore excavation proceeds directly experience processing.
Based on the location of occurrences, in general mining activities carried out in aqueous work environment like rivers and swamps, so that by itself would utilize existing water in the surrounding areas.

Characteristics of alluvial gold deposits will determine the systems and equipment in mining operations. Based on the characteristics of the gold deposition, open pit mining methods commonly applied using equipment such as:

Panning (panning)

Mining by way of panning done by artisanal mining in the river or near the river. This method is mostly done by individual miners using panning tray to separate the gold from concentrates or grains of mineral impurities.

Mine spray (hydraulicking)

At spray mine used syringes (monitor) and pump for memberaikan rocks and mud subsequently poured or pumped spray results to installation concentration (sluicebox / sluice). This method is mostly done on a small scale mining including artisanal mining where the available water resources are sufficient, generally located in or near the river.

Some of the conditions that make alluvial gold deposits can be mined using spray mining methods include:
  •     Conditions / material type allows decomposed by water spray
  •     The availability of adequate water
  •     Availability of space for placement or separation of ore washing results

Dredging

Dredging is done when the mining technique Placer sediment lies below the surface of the water, for example in offshore, river, lake or valley provided a lot of water. At this mine is mostly done on a small scale mining including artisanal mining using a dredger (dredge) or with a dragline in combination with the above processing pontoon (floating washing plants).
According to Turner, 1975, dredges can be classified as follows:

Mechanics
- Bucket line.
- Bucket - wheel suction.
- Dripper.

Hydraulic
- Suction.
- Cutter head.

The tools used in mining dredgers by his digging tool is divided into three, namely:
  •     Multi bucket dredge, dredges that his digging tool in the form of a series of bowl (bucket)
  •     Cutter suction dredge, his trencher cutter form that resembles a crown.
  •     Bucket wheel dredge, excavator equipped with a rotating bucket (bucket wheel)
Although this method has largely been replaced by modern methods, dredging is carried out by small-scale miners using suction dredgers. It is a small machine that floats on the water and are usually operated by several people. A series of suction dredging consists of a suction pump machine, concentrator box, and compressor are supported by pontoons. On the suction hose is controlled by miners working under water (divers). The divers use a compressor to meet the need of oxygen.

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