| Written by Yeudiel Valdivia

The stages of the mining production process are common in general terms for all projects, but it is important to understand that each mine is unique and therefore, the technology used in each case, as well as the modifications that are introduced at each stage to make the production process more efficient, make each mine a unique and specific project, so no two mines are the same, even if they exploit the same type of mineral in the same mining basin. The way in which minerals are extracted will depend on various geological and economic factors, and this selection of the extraction method gives rise to the types of mines. There are different types of mines in Mexico, each with its own challenges, advantages, and disadvantages.

Mines in Mexico

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MINING AS AN INDUSTRIAL ACTIVITY

Starting from its broadest concept, mining is defined as the industrial activity that allows the extraction and selective obtaining of those solid, liquid or gaseous mineral substances existing in the earth's crust for their transformation into raw materials, minerals and/or energy products that allow covering the supply needs of adequate materials for the development of human societies.

In this sense, the development and exploitation of a mine require the production of a mineral substance, which society demands through markets that establish product specifications and sell these minerals at a profitable price.

The exploitation of mineral resources is primarily conditioned by two factors:

  • Demand
  • The costs of extraction, processing, transport, distribution and marketing

The quality of the mineral is expressed according to the concentration of the element of interest contained, which is expressed as a percentage of that element or metal, this percentage is what is known as the 'grade' of the mineral, so the grade in mining is a measure that describes the degree of concentration of valuable natural resources (minerals) present in an ore.

In the different types of mines in Mexico, the ore grade is used to determine the economic viability of a mining operation. The cost of extracting natural resources from their deposit directly relates to their concentration (grade).

 

MINING TECHNOLOGY

Mining technology is understood as the techniques, knowledge, and technologies applied to the extraction, processing, and utilisation of natural resources of a mineral nature, which meet certain characteristics and are to be used to satisfy human needs. Mining technology covers the following fundamental areas:

  • Prospecting and exploration (Geology)
  • Design and operation of mines (Mining)
  • Mineral processing (Mineralurgy)
  • Environmental protection of the environment in which the operations take place
  • Marketing of products
  • Innovation

Mining technology depends on the type of mine, i.e. how the mineral is extracted.

 

SELECTING THE MINING METHOD

The problem of selecting the mining method becomes the most important aspect of mining, as the method that is most compatible with the unique criteria of each deposit, such as spatial characteristics, geological, hydrogeological and geotechnical conditions, as well as other considerations such as economic, technological and environmental factors, must be selected.

Five broad areas have been identified into which most of the criteria can be grouped:

  • Spatial characteristics of the deposit (size, shape and depth of the mineral deposit).
  • Geological and hydrogeological conditions.
  • Economic considerations (operational costs, financing needs, rehabilitation and restoration costs).
  • Technological factors (availability of skilled labour, machinery capacity and productivity).
  • Environmental considerations.

A mining operation can be carried out on the surface or below the surface, depending on the depth of the deposit and other technical parameters, for which the extractions and, therefore, the types of mines are mainly classified into open-pit mines and underground mines, each with different methods corresponding to particular parameters; underground methods are used when the depth of the deposit is too great to be reached by open-pit mining.

Read more about critical minerals strategy for the energy transition

 

TYPES OF MINES IN MEXICO

Four types of mines are currently recognised in Mexico:

  • Surface or opencast mines
  • Underground mines
  • Boreholes
  • Subsea or dredge mining

SURFACE MINING

This is an excavation carried out from the surface of the ground, creating the necessary hole for access to the ore, and is used for the extraction of metallic and non-metallic minerals from ore bodies located at depths of less than 160 metres.

In general, deposits that can be mined entirely by open-pit methods are close to the surface and have a relatively uniform geology. Such deposits are not economical to extract by underground methods.

Within surface mines, three types of mines are identified:

  • Placer mining. Concentration of heavy minerals from detrital materials:
  • Pans and Chutes
  • Hydraulic mining
  • Dredging
  • Open pit mine. Any type of ore deposit in any type of rock, located on or near the surface of the ground.
    • Single bench
    • Multiple benching
    • Overburden stripping
    • Quarrying
  • Glory Hole. Open pit excavation from which ore is removed by gravity through one or more shafts to underground haulage levels.

Another option is where deposits are initially more cost-effective to extract by open-pit mining and then evolve to underground methods as the depth of the deposit increases.

When the circumstances are right, open-pit methods are more productive, cheaper and safer for workers than underground methods but are often more damaging to the environment and communities.

 

Examples of open pit mines

Peñasquito Mine (Newmont): This mine is located in the northeast of the state of Zacatecas and is one of the largest open-pit mines in Mexico. It is currently the fifth-largest silver mine in the world and the second-largest in Mexico. It produces mainly silver, gold, zinc and lead. The mine has two processing plants that use different methods to extract the metals from the rock.

Buenavista del cobre (Grupo Mexico): Located in Cananea, Sonora. It is the largest copper mine in Mexico and the fifth largest in the world, with a surface area of 5,200 hectares. In 2022, it produced more than 338,000 tonnes of copper, making it one of the most productive mines in the world. This mine employs 4,500 direct and indirect workers.

La Caridad (Grupo Mexico): Located in the mountains of Sonora. It produces mainly copper, gold, refined silver, and molybdenum. It employs 1,500 direct and indirect workers.

 

UNDERGROUND MINES

This is the exploitation of mineral resources below the surface of the ground. For the selection of this method, several factors must be considered, such as the strength of the ore and the caprock; size, shape, depth, dip angle and position of the deposit.

The types of underground mines are as follows:

  • Naturally supported stopes. Excavations in which the loads exerted by the rock on the opening are supported by the walls or pillars hewn from the same rock.
    • Open stopes
    • Halls and pillars
    • Sub-level excavation
    • Load-bearing shaft
    • Open stoops with horizontal braces
  • Artificially supported stopes. A work in which a significant part of the load or weight of the surrounding rock is supported by some artificial support such as props, frames or backfill.
    • Cut and fill
    • Conjugate frames
    • Long faces
    • Short faces
    • Downward slices
  • Sinking stopes. Applicable to massive-type ore deposits with large horizontal developments likely to collapse to follow the subsidence of the ore as it is removed and mined.
    • Sinking of sublevels
    • Block and panel subsidence

 

Some of the most important underground mines in Mexico

Fresnillo (Fresnillo PLC, Peñoles): One of the largest silver producers in the world and one of the largest underground mines in the Americas. It mainly extracts silver but also produces gold, zinc and lead.

Santa Barbara (Grupo Mexico): Located in the state of Chihuahua. It mainly mines gold, silver and copper. In 2022, the mine produced 34600 tonnes of gold, 1.1 million tonnes of silver and 10,000 tonnes of copper. It generates around 1200 direct and indirect jobs.

San Martin (Grupo Mexico): Located in the state of Zacatecas. Produces mainly gold, silver, zinc and lead. The mine was discovered in the 16th century and has been exploited by different companies. Grupo Mexico acquired it in 2006.

Charcas (Grupo Mexico): Located in the state of San Luis Potosi. It has been operated by Grupo Mexico since 2000. It mainly mines silver, copper, zinc and lead. It employs 1100 direct and indirect workers.

 

SPECIAL METHOD MINES

This type of mining employs techniques of dissolution of the values contained in the deposit, no physical penetration of the deposit is required for extraction.

  • Leaching. It works by bringing a solid into contact with a liquid (called a lixiviant) that dissolves the interest component. The resulting solution, rich in the desired solute, is separated from the solid material and processed to recover the pure component.
  • Frasch process. This is an innovative method for extracting sulphur from underground deposits. The method involves drilling a borehole into the sulphur deposit, inserting three concentric pipes, and then pumping hot water through the outer pipe and compressed air through the intermediate pipe. The molten sulphur is extracted through the inner pipe. The liquid sulphur is collected on the surface and solidified for storage and transport.
  • Hot water dissolution. In this method, the solid material containing the component of interest is crushed or ground into small particles to increase the surface area in contact with the water; hot water is added to the solid material, and the solute dissolves in the water, forming a liquid solution. The solute-rich solution is separated from the insoluble solid material by techniques such as filtration, decantation or centrifugation, and the solution is processed to recover the pure solute by techniques such as evaporation, crystallisation, or precipitation.  

 

Example of a mine with special methods

La Perreña Mine (Industrias Peñoles): Also known as Milpillas, it is located in Sonora, Mexico and is Peñoles' only copper mine.

Exploration of this deposit began in the 1980s. At that time, mining concessions were granted to Minera Cuicuilco and later to Peñoles. Various exploration works were carried out, and it was not until 2001 that an aggressive drilling programme was completed. This programme gathered sufficient data to calculate mineable reserves of approximately 35 million tonnes, with an average grade of 1.95% copper, to justify the construction of the unit.

The underground mine is mined using the cut-and-fill method with long-boring and long-drilling. Once crushed, the ore is leached in heaps and then goes through a solvent extraction process; finally, the copper is deposited in electrolytic cells to produce copper cathodes.

See also: Mine Technology

 

FAQ

What are the advantages and disadvantages of an open pit mine?

When the circumstances are right, open pit methods are more productive, cheaper and safer for workers than underground methods. However, they are often more damaging to the environment and communities.

What have been the main challenges of underground mining in Mexico?

Underground mining in Mexico has faced a number of challenges throughout its history, the most important of which have been related to safety, such as accidents caused by cave-ins, flooding, explosions and fires.

What is the Mexican government's position on open-pit mining?

The Mexican government has included a modification to the mining law that aims to prohibit both the granting of concessions and open-pit mineral exploration and exploitation activities. The main argument for this initiative is environmental damage and damage to nearby communities.

 

TAKEAWAY

The different types of mines in Mexico are defined once the method by which the ore will be extracted has been selected, which in turn depends on various factors such as the size, shape and depth of the mineral deposit, geological and hydrogeological conditions, economic aspects such as operating costs, technological factors and environmental considerations.

Open-pit mines have a greater impact on habitat, biodiversity and communities as they involve the removal of large tracts of land and increased air pollution. The Mexican government has introduced initiatives to limit or even eliminate open-pit mining in the country, and investment in new open-pit mining projects has decreased considerably.

On the other hand, underground mines often present greater safety risks to workers associated with cave-ins. Worker safety regulations for other types of mines, such as underground mines, should accompany the Mexican government's initiative to limit the types of open-pit mines.

What's next? Learn more about responsible mining in Latin America


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Author

Yeudiel Valdivia, VP Sales Safe Mining

Yeudiel Valdivia holds a Master’s degree in Engineering (Telecommunications) and a Bachelor of Electrical and Electronic Engineering. He spent most of his professional career in sales and business development for industry segments including mining. Yeudiel is fascinated by the positive impact of technology in people’s life and how people can work safer and under better conditions, he is interested in how technology can transform businesses making them more efficient, agile, and productive and its potential for the economy growth in countries and regions. Yeudiel writes mainly about the digitalization of industries, driven by advancements in technology enabling new business models.

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