Pyrite is a yellowish mineral or it known also as sulfide mineral with chemical formula FeS2, it can manifest at high and low temperatures, pyrite present in igneous rocks, metamorphic and sediment, in society its nickname known as gold delivery or fake gold, because it has gold-like color with metallic luster, and it has high specific gravity. Sometimes the people can be confuse to distinguish between pyrite and gold, both these minerals were formed together, even in some deposits the pyrite contain a gold about 3.7%.
There is a mineral similar to pyrite, its name is marcasite, it has a pale yellow or greenish yellow color and lighter density than pyrite, chemically its crystal was orthorhombic. Actually, between gold and pyrite can be distinguished easily, the gold has smooth layer and elastic while pyrite has yellow-green color, in addition the gold density is higher than pyrite. Although pyrite contains iron and sulfur compounds, pyrite isn't main of iron source, because iron extract iron sulfide (FeS2) is more difficult, the pyrite commonly used for sulfur dioxide and sulfuric acid manufacture, most of the sulfur produced from pyrite as by-product of gold processing. In fact, the pyrite used for prospecting mineral to indicate the gold location, because gold and pyrite formed in the same state in the rock.
In partial deposit, a amount of gold formed as inclusion in the pyrite, but it can also to form as substitute for organic material in organic sediments, decomposition of organic material in the rocks will consume oxygen (O2) and release the sulfur (S), in this condition, the pyrite can't be used as a hint of gold existence.
The gold was present in hydrothermal alteration zone or a zone where the water come from magma (magmatic water) moves up to the earth's surface. The result of volcanic activity causes high-pressure magmatic water that going up to the earth's surface. When magmatic water become as steam (vapor), it reaches to the earth surface, then it contaminated with meteoric water that causes the gold precipitate, because carried away by complex ion solutions, sulphide ion, and chloride ions. The alteration zone potentially contain the gold, it can be identified by looking at pyrite or copper layers in reservoir composed of granite or diorite rocks.
In geochemical methods, the trace elements and gold indicating elements determine of gold presence, for example element silver (Ag) and surrounding rocks and vegetation around the gold location indicates the gold presence, The gold much abundant in Cu, As, or Sb elements.
Amalgamation is a process of gold depositing particles by mercury to form amalgam (Au ± Hg),
Amalgam is a simple process of gold extraction and inexpensive, but this method is a effective process for gold that has high grade and coarse size. This process was physical chemistry process, when amalgam was heated, the gold will decompose into element of mercury and gold bullion. Amalgamation methods was involving mercury, it can only isolate about 50% gold, In addition to being inefficient, this process also produces residues that give negative impact for environment.
The utilization of mercury as extraction agent was ineffective, because the sulfur element in the rock can to form H2S compounds, The H2S solution could be reacts with mercury then form mercury II sulfide layer, chemically the equation can be formulated:
H2S + Hg → HgS + H2
The outer layer of HgS liquid mercury can to prevent gold ores to entry and penetrate mercury, the result is low gold bullion yield, the mercury breakdown and form small droplets of metal then form black layer of mercury II sulphide (Hg2S)
Because, the sulfide compounds soluble during amalgamation process and damage outer layer of gold ore, this due to silver (Ag) of gold ores react with H2S, form Ag2S black layer on the gold ore surface. Determination of silver sulphide compounds will prevent amalgamation process. Both reaction can be formulated as follow :
Ag + H2S → Ag2S + H2
Generally, the sulfur in golden rock bind on primary metal and silver metal compound, then form to metal sulfide compound such as Copper to form CuS, CuFeS2, Cu2S .The combination of sulfur and aluminum can increase temperature in pyrometallurgy process, and can reduce metals, especially metals that has maximum melting temperature about 1200oC.
3Ag2S + 2 Al → 3Ag + Al2S3
3FeS2 + 4 Al → 3Fe + 2Al2S3
The oxidation of aluminum metal to become Al2S3 compounds conduce of increasing temperature then releases latent heat in aluminum metal. At 2000oC temperature, this process can produce gold metal that still contains impurities (metal)
If we have never seen pyrite, we would assume the pyrite is gold, whereas gold and pyrite can be distinguished by color and outer shell, the gold has smooth outer shell and heavier density, inside the pyrite also contains about 3.7% weight of gold. The gold in pyrite can be extracted with mercury and also aluminium.
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