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METALS
GOLD Gold is widely dispersed through the earth's crust and is found in two types of deposits : lode deposits, which are found in solid rock and are mined using conventional mining techniques, and placer deposits which are gravelly deposits found in stream beds and are the products of eroding lode deposits. Since gold is found uncombined in nature, early goldsmiths would collect small nuggets of gold from stream beds etc., and then weld them together by hammering.
The metal deposit must be identified. In the case of the first metals color was the most important factor as it allowed the metal to be recognized in surrounding rock, stones, gravel and dirt (gangue) and separated. Clearly, after recognition, separation is next problem followed by concentration. These three steps are very important and the economics of these steps usually define whether it is viable to produce the metal from a set deposit.Gold is widely dispersed throughout the earths crust (0.005 ppm) at a very small level, therefore, it is very important to find naturally occurring concentrations. The scarcity of gold and its value, due to mankinds fascination with its color, have lead to gold being the one of the more important metals in daily life.
SILVER
Although silver was found freely in nature, its occurrence was rare. Silver is the most chemically active of the noble metals, is harder than gold but softer than copper.It is normally stable in pure air and water but tarnishes when exposed to ozone, hydrogen sulfide or sulfur. Due to its softness, pure silver was used for ornaments, jewelry and as a measure of wealth. In a manner similar to gold, native silver can easily be formed
PLATINUM
It was the first metal to be discovered and sourced from the "New World". Early use of platinum was banned because it was used as a blank for coins which were subsequently gold coated, proving that the early metallurgists understood not only density but also economics. Although, platinum was known to the western world, it was not until the 1800's that platinum became widely used.
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