Recent Advances in Gold & Silver Extractive Metallurgy

Mining In Many Developing Countries
In the same manner as in many other countries of the world, the countries whch are in devlopment have produced a noticeable increase in the mining activities related to the mining of gold. The average estimate of the active projects worldwide were those of 145 in the year 1988: 67 in the United States, 15 in South America, 32 in Africa, 5 in Asia and 26 in Oceania, representing a total investment of an average of about US$ 9,500 million, the half of this investment is found in South Africa.

The reason of this great interest has been the high price and the sustaining of gold in the decade of the eighties, the optimus future perspectives of the market and the technological advances, both in the prospection as in the extraction.

The great amount of countries involved in this expansion explains the reason why, in the difference of other precious metals as is the case of the platinum, the gold is found amply distributed in different geological surroundings and, what is most importantly known, in recuperable amounts economically. Furthermore, one can say that the gold has been the exception in what has occured in themetallic mining in the past years. In other words, it represented one of the few oportunities of obtaining a high internal rate of return, in contrast with the depressed situation of the rest of the metals.

At the same time, this higher interest has reprecuited logically in the technological development, the one which has experimented important advances, which are resumed in the gold, in a determined auriferous province is the following:

• First, the alluvial deposits are worked.
• Then, the small high law deposits, with fine gold in hard rock.
• Immediately afterwards, the large deposits of low law, with fine gold in hard rock.
• In a parrallel form the residues of the previous operations are re-treated, when one can count with technological betterings or when the prices increase.

The best example of this scheme of development has been found in South Africa, pioneer country in the worldwide production of gold. For example, presently, the gravitational concentration is still being used in South Africa, but normally as a simple unitary operation in the circuit of grinding, to remove the small quantities of thick gold which can be present.

On the other hand, in many Southeast Asian countries and in South America, they are still in the stage of exploitation of alluvial resources or beginning to exploit beds of thick gold in hard rock.

In some countries, due to the special characteristics of our mining, all the stages mentioned are present.

We will furthermore present the main recent advances in the extractive metallurgy of the gold and the silver, especially in the lixiviation and the gravitational concentration.