La longue expérience mexicaine des activités minières : leçons du passé pour gérer l'avenir

Résumé

Mining commercial history in Mexico begins 500 years ago. Actually, Mexico is still one of the biggest mineral producers, ranked into the first ten places in 10 metallic elements, and eight in non-metallic, particularly in silver, occupying the first place, followed by bismuth, lead and cadmium among the metallic; and the non-metallic fluorite, wollastonite and celestite. The country has been categorized by mining enterprises as one of the main destinies for exploration due to its mining and geological infrastructure. Noncommercial mining precedes the Spaniard conquer.

Undoubtedly, ancient mining processes used all available technologies in each epoch to obtain precious and industrial minerals required by humanity through centuries. Today, although mining deposits exploitation has developed enough technology to operate harmonically with the environment, it is not possible to ignore the severe effects inherited from the old processes, especially the use of mercury for amalgamation which, in Mexico, was introduced in 1585 by the Spaniard metallurgist Bartolomé de Medina, practice that transformed gold and silver beneficiation in the patio mills receiving mineral from the mines of Pachuca, Hidalgo.

Amalgamation is a functional process to recover gold and silver from auriferous and silvery ores. Mercury has the capability of forming an amalgam with most of the metals, except iron and platinum. Gold is particularly capable to combine with mercury in order to produce a great variety of components, from AuHg2 to Au8Hg. Main amalgams are: AuHg2, Au2Hg and Au3Hg.

Even though México does not produce mercury since 2009, concentrations due to use after more than 450 years, have obligated to identify zones with high contents of this mineral, many of which are already confined and ready to be recovered by a number of companies.

In México, these anthropogenic disequilibrium lead to a series of standards and organizations at the three levels of government, whose mission is to control the use and disposal of these elements that could be very toxic for the environment, and to prevent any leakage or exposure as well, in order to restore possible extreme damages due to accidental or involuntary contamination.

In 1940, México produces its first Law on Conservation of Soil and Water, nevertheless, it is not until 1970 when intensifies and proceeds to make official the processes. By 1988, it is published in the Federal Official Gazette, the General Law in Ecological Equilibrium and Environment Protection (LEEGEPA) by SEMARNAT, the Environmental and Natural Resources Secretariat, since 2000.

On the other hand, the Mexican Geological Survey has played an important role concerning these actions, as it have generated a great deal of information, integrated an published through GeoInfoMex. The data is basic and fundamental for understanding, comprehension and analysis of the places, location, control and benefit of metallic and non-metallic minerals, especially those referred to geochemical responses of element contents in active sediment stream samples over the entire national territory after an extensive 1:50,000 geological mapping program.

Not less important is the participation of the Mexican Geological Survey in promoting the formation of "Mining Clusters", whose objective is to work as a technologically and synchronically team to generate social benefits, and at the same time, allowing the sustainable exploitation of the mineral resources.