Mexico’s Ministry of Environment and Natural Resources ( Semarnat ) is working on creating a National Catalog of Mining Units to provide a comprehensive registry that will allow for more accurate monitoring of the country’s mining and metallurgical operations, said Luz Mariana Pérez, director of the Mining and Metallurgical Industry at the Directorate General for the Comprehensive Management of Hazardous Materials and Activities (DGGIMAR).
The new catalog will include information not only on existing tailings dams, but also on other mining deposits, such as dumps and leach pads, which until now have not been systematically documented.
“Today, we are working on a national catalog of mining units in which we will identify not only existing tailings dams but also other mining deposits that are part of the important monitoring required for mining and metallurgical activities,” Pérez explained in his presentation during a workshop for journalists in Mexico City.
The catalog will be based on the Preliminary Approved Inventory of Tailings Dams, launched in 2021 and last updated on March 1, 2024, which currently lists 568 dams. This publicly available inventory details the name of the mining unit, the responsible company, the operating status (active, closing, or abandoned), the type of waste generated, and its geographic location.
According to the official, the next step will be to expand the scope of the registry.
“This inventory has been an interesting tool, but the national catalog will allow for more rigorous monitoring of how mining units are currently operating.”
Pérez emphasized that the work is inter-institutional, with the collaboration of the Ministry of Economy, the State Representation Offices (OREs), and Semarnat itself, since “mining is not the sole responsibility of a single institution, but rather part of a coordinated effort.”
Tailings dams
The official explained that tailings dams are deposits where sludge from mining and metallurgical processes, containing water, minerals, and chemicals, is dumped. However, there are other forms of waste disposal, such as dumps—accumulations of rock with low-grade ore—and leach pads, which use chemical processes to recover metals.
He indicated that in some states, such as Zacatecas, technologies have been implemented to solidify tailings and reduce their viscosity, in order to reduce environmental risks.
Among the main environmental impacts associated with these structures, Pérez mentioned the dispersion of dust that affects air quality, the loss of soil and vegetation cover, and the potential contamination of water bodies. However, he acknowledged that there are good practices within the sector:
“Fortunately, there are also mining units that have sought to prevent this ecological risk. There are also mining companies that do things right.”
Updating the regulatory framework
In parallel, Semarnat is working on reviewing and updating the official Mexican standards (NOM) that regulate mining and metallurgical activities.
Among the most relevant, Pérez mentioned NOM-120, which regulates mining exploration and is currently undergoing systematic review; NOM-141, which refers to the construction, operation, and closure of tailings dams; and NOM-157, on waste management plans, which is already updated and will soon be published in the Official Gazette of the Federation (DOF).
Likewise, NOM-147, which establishes the maximum permissible limits for metals in contaminated soil, is being updated “following international reference methodologies to ensure better environmental protection.”
“Laws tell us what we have to do, regulations tell us how we should do it, and standards are the technical instruments that support compliance with our environmental obligations,” he emphasized.
Pérez emphasized that all these efforts—from the creation of the catalog to the regulatory update—seek to strengthen the transparency and environmental traceability of Mexican mining, from the opening of a mine to its closure and post-closure, avoiding the generation of environmental liabilities.