Gold ore

The most important ores are bismuthinite or bismuth glance and bismite. Peru, Japan, Mexico, Bolivia, and Canada are major bismuth producers. Much of the bismuth produced in the U.S. is obtained as a by-product in refining lead, copper, tin, silver, and gold ores. 

A proposed method which avoids cyanide consists of treating gold ore with gaseous chlorine at elevated (<250° C) temperatures to volatilise gold as chloride Au2Clg [12446-79-6] or AuMCl, (M = Fe [12523-43-2] A1 [73334-09-5], or Ga [73334-08-4]) and recovering it by condensation (23). 

Modem heap leaching practice has also made possible the treatment of extremely lean (ca 1 g/1) gold ores, which had been considered uneconomic... 

Montana. These deposits consist of stibnite and other sulfide minerals containing base metals and silver or gold. Ores of the complex deposits are mined primarily for lead, copper, 2inc, or precious metals antimony is a by-product of the treatment of these ores. 

Arsenic is widely distributed about the earth and has a terrestrial abundance of approximately 5 g/t (4). Over 150 arsenic-bearing minerals are known (1). Table 2 fists the most common minerals. The most important commercial source of arsenic, however, is as a by-product from the treatment of copper, lead, cobalt, and gold ores. The quantity of arsenic usually associated with lead and copper ores may range from a trace to 2 —3%, whereas the gold ores found in Sweden contain 7—11% arsenic. Small quantities of elemental arsenic have been found in a number of localities. 

Includes copper-lead ore, gold ore, gold—sHver ore, lead—zinc ore, molybdenum ore, tungsten ore, zinc ore, fluorspar, flux ores, cleanup, ore shipped direcdy to smelters, and tailings. 

Gold ores can be concentrated by froth flotation, the resulting concentrate being roasted at 600-800°C to oxidize off sulphur and arsenic as their oxides. The product is extracted with cyanide under oxidizing conditions (using either peroxide or air itself) before displacement with powdered zinc. More reactive metals (silver etc.) can be removed by chlorination of molten gold. 

Abe, H. (1981) Chemical compositions of gold ores and Ag/Au values of electrums from the Oya mine. Mining Geology Special Issue, 10, 119-125 (in Japanese with English abst.). 

Urashima, Y, Sato, M. and Sato, E. (1981) The Iwato gold ore deposits, Kagoshima Prefecture, Japan. Mining Geology Special Issue, 10, 1-14 (in Japanese). 

This hematite is not soluble in the cyanide solution. The oxidative pretreatment of gold ores thus reduces the cyanide consumption. Some impurity elements inhibit leaching reactions, examples include elements, carbon, sulfur and arsenic in gold ores are such impurities, but these can be removed by heating in air. 

The use of activated charcoal dates back to ancient times when it was acclaimed as the reductant for precipitating gold from solutions generated by leaching gold ores with chlorine water. The reactions can be shown as ... 

The precipitation of gold occurred on the surface of the reductant charcoal. The charcoal was subsequently burnt and the gold recovered. This process was used successfully for some time until it was withdrawn in favor of using cyanide solution because of the ineffectiveness of chlorine water to dissolve silver, which more often than not co-occurs with gold ores. 

Gold ores grouped as refractory are those in which the gold does not lend itself easily to dissolution in cyanide solutions. There are at least three different types of refractory ores that are encountered ... 

A list of the mines where different processing of gold ores is carried out is shown in Table 5.12. Although the pressure oxidation process appears to be the current leading technology, selection of the optimum route depends on several factors. 

For molybdenite concentrates hydroxy ions must be added to maintain a near neutral pH value. The pH value at which the electroleaching of other metal sulfides is conducted depends upon the amount of hydroxy ions added. For example, when a low grade cinnabar ore is treated, the pH remains almost neutral because of the calcite content of the ore. This is also true of carbonaceous gold ores. 

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