Madrid, 10 (Europe Press)
The results of the research, which focused on the potential of underground brines and were tested in a Bolivian volcano, are published in Geophysical Research Letters.
The global transition to a zero-carbon energy system will exponentially increase the demand for rare or finite earth minerals. These are essential for manufacturing a wide range of green technologies, such as electric vehicle batteries, wind turbine magnets, and copper electric cables. This raises the urgent need to identify new sustainable sources of these elements.
A potentially rich source of these minerals could be geothermal brines: highly concentrated brines that can accumulate in the Earth’s crust. However, their location can be difficult, since they tend to accumulate at a depth of kilometers. Accurate positioning of these deposits is important to minimize the risk and environmental impact associated with drilling for these mineral-rich brines.
In this new study, which was led by Oxford University’s Department of Geosciences, researchers developed a new method that has been shown to be able to map the location and composition of ground fluids. For the first time, two different geological measurements have been combined: tomography of seismic attenuation and seismic anisotropy.
Lead researcher Dr Thomas Hudson, from Oxford University’s Department of Earth Sciences, explained in a statement: “Seismic attenuation measures the loss of energy from a seismic wave as it propagates through a medium. Seismic anisotropy, on the other hand, measures how fast earthquakes waves vary depending on the direction in which they propagate. Imaging shows Attenuation CT scans of where the fluids are (something similar to a CT scan in a hospital) and whether the rock is partially saturated (has gas) or fully saturated (no gas). It tells us how fluids are moving and accumulating along fault lines.”
An inactive volcano in Bolivia
The researchers tested this combined method at Uturuncu, a dormant volcano in the Bolivian Andes that last erupted 250,000 years ago.
Dr Hudson stated: “The Uturuncu was an ideal system to test our method of mapping liquids and gases, as it sits atop the Altiplano-Puna magma body, the largest active magma body on Earth. It drives a ‘hot metallic’ source – rich fluids rising from the depths of the Uturuncu toward the surface.” Uturuncu is located on the edge of the Atacama Desert, so the surrounding crust is particularly dry, which enhances imaging of any fluid-rich crust.”
Seismic attenuation and anisotropy measurements were taken from a data catalog of 1,356 earthquakes, taken between April 2010 and October 2012 by a network of 33 seismometers near Uturuncu. Together, the two techniques produced a rough map indicating whether the underlying crust was partially or completely saturated with fluid, with a resolution of about one kilometer.
In the words of Dr Hudson: “The combination of these technologies has produced a high-resolution map that identifies what liquids can be found and where they are in that system. Specifically, we can determine where brines – concentrated salt solutions – are located and whether they contain carbon dioxide (i.e. “foamy”) or not (i.e. “still.”).If carbon dioxide bubbles through, that tells us the system is still active, presumably still accumulating minerals, whereas if the brines are calm, then it can handle The system is defined as stable, that is, it does not continue to actively accumulate minerals.
The results are very interesting because these brines are rich in essential minerals for the transition to green energy. We hope that our new method will lay the groundwork for reducing the risks of the mineral exploration process, which could lead to making brine extraction commercially viable.”