Tomography and ground penetrating radar used to characterise mud from metal mining

Added to other techniques in the arsenal of Geochemistry and mineralogy like chemical analysis and X-rays, and with the added advantage of them being cheap, fast and non-destructive methods, a great precision is achieved.

This statement has been described in the research work titled “Aplicación conjunta de técnicas geofísicas, mineralógicas y geoquímicas para la caracterización geoambiental de balsas de lodos mineros” (Combined application of geophysic, mineralogical, and geochemical techniques for the geoambiental characterisation of mining mud ponds) and is directed by the geology professor Tomás Martín Crespo from the Rey Juan Carlos University (URJC).

The south of Spain alone has over 80 metal mines, some still active and some already inactive. The abandoned storage ponds are made up of grain sized materials, ranging from medium to fine, that contain sulphides of low economical importance and a small proportion of waste metal that failed to be extracted. They represent an environmental issue, being a source of acidic mine drainage and heavy metals. It is crucial that all the storage ponds are evaluated and characterised prior to the natural restoration work of the mining fields.

The researchers at the URJC have focused on two particular mining fields (Monte Romero and Río Tinto) both in the Spanish province of Huelva, where the new geophysical techniques have provided excellent results. The electrical resistivity tomography worked particularly well, not only determining the precise geometry of the storage pool thanks to the high electrical resistivity contrast among the tailings and the bottom of the pool but also determining the different deposited layers and their heterogeneity. It even succeeded in differentiating the flows of groundwater inside the pool by the low resistivity of water.

The ground penetrating radar is very helpful in determining the characteristics and geometry of the sides and surface of the pool, detecting changes in humidity, but being more limited than the tomography because of the high attenuation effect that the tailings and the water in the pool have.