Studying magnetic anomalies
José Pichel Andrés/DICYT A team of geologists at the Universidad de Salamanca (Spain) is working on non-studied magnetic anomalies in the Iberian Peninsula. Anomalies may occur when certain ferromagnetic rocks interfere with Earth’s magnetic field. In basic research, these phenomena are useful to understand geological structures.
“The Earth has a magnetic field affecting certain iron minerals such as magnetite and pyrrhotite. These minerals are magnetized, so if you measure the total magnetic field nearby, the result is the addition of the Earth’s magnetic field and that provided by these minerals,” DiCYT was told by researcher Puy Ayarza.
In Castile and León, Castile-La Mancha, Portugal and Galicia there are magnetic anomalies and the Department of Geology at the Universidad de Salamanca aims to understand them better thanks to a new research project that will last for a year. The phenomenon has been linked to deep rocks in these areas. Consequently, “we want to determine what kind of rock is causing it, how old is it, how anomalies are produced and how magnetization was provoked”, the researchers explain.
Magnetic anomalies are located in large areas and are portrayed on maps: from Lugo to Sanabria (Zamora), along the Sistema Central (a system of mountain ranges) and from Salamanca to Portugal. These anomalies are known but have not been analyzed. For instance, “we detect an anomaly thanks to a curve, but we are unable to determine its cause”, José Ramón Martínez Catalán explains.
Geologists usually find clues on the surface to know what’s underneath, that is, rocks outcropping are useful to guess what’s below them. Nevertheless, “there is not a clear representation of these anomalies on the surface”, that may depend on the type of rock or the type of structure at the crust.
To conduct these studies, they use instruments called magnetometers able to measure the magnetic field. In general terms, measures are taken from a light aircraft or from a helicopter in order to cover large areas in a single flight and to measure other parameters at the same time. In Galicia, the research team has also conducted studies on foot to obtain more accurate data.
“Magnetic maps very well inform about faults, ground fractures, so if a mineral has been identified, geological structure provides information on deposits. Anomalies are useful to find faults but are harmless to everything else, just as gravity”, the scientists state.
Regarding the applications of this study, it is important to understand that “a large majority of anomalies are associated with economically interesting areas containing uranium, tin and tungsten. Unraveling the cause of anomalies, we can find an explanation on the origin on this mineralization” as we were told by Juan Gómez, another member of the team. Many mining companies are interested in these issues, but they do not fully understand models (key elements to contextualize geological information).
New data provided by this type of research is being added into maps of the IGME (a Spanish geological and mining institute). When building infrastructure, it is important to know as much information as possible on land; in fact, this research team has been hired by companies building the AVE (high-speed rail) in Galicia. The budget used to drill a rock may be quintupled depending on the material, so geological information has a giant economic value; every study makes a small contribution.