The Rio Tinto (Red River), Spain and its resemblance with Martian Soil Surface - A particular interest for Astrobiologist

The Rio Tinto (red river) is a river in southwestern Spain that begins in Andalusia's Sierra Morena Mountains. It flows south-southwest until it reaches the Gulf of Cadiz in Huelva. Copper, silver, gold, and other minerals have been mined along the riverbank since ancient times. Iberians and Tartessians began mining the site around 3,000 BCE, followed by the Phoenicians, Greeks, Romans, Visigoths, and Moors. The mines were rediscovered in 1556 after a period of abandonment, and the Spanish government resumed operations in 1724.

Figure 1 Flowing channel of Rio Tinto in Spain.

Ro Tinto is known for being very acidic (pH 2) as a result of the mining and its deep reddish tint is owing to iron dissolved in the water. Because of the high quantities of heavy metals in the river, acid mine drainage from the mines causes serious environmental problems. The Rio Tinto Company was founded in 1873 to operate the mines, and by the end of the twentieth century, it had grown to become one of the world's greatest mining firms, albeit it no longer owns the Rio Tinto mines, which are currently held by EMED Mining Ltd. The image was taken on July 16, 2007, and it spans a 43.5 x 43.5 km region. It was taken from 37.7 degrees north latitude and 6.6 degrees west longitude.

Figure 2 ASTER image of Rio Tinto, Space Image Credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan.

While the acid has rendered the Rio Tinto unfriendly to most forms of life, it has made it more hospitable to sulfide-consuming bacteria and other extremophiles that help to accelerate the acidification process. These organisms produce ferric iron, a rust-colored material that gives the river its red tint. The combined effects of chemical weathering of rocks and bacterial activity in the water have lowered the river's typical pH to 2, which is about the same as vinegar.

Figure 3 Flowing water shows the concentration of sulphur and iron, take makes its color tint.

Mining in the area for thousands of years has likely accelerated natural acidity processes by increasing the amount of exposed sulphide ore. People have been mining in the area periodically for 5,000 years, and archaeologists consider it a major location during the Copper and Bronze Ages. Mining in the area continues today: the contemporary mine (shown below) resumed copper production in 2016 after being briefly shut in 2001.

Figure 4 The Rio Tinto, which is exceptionally red and acidic, is home to tiny life that could aid in the quest for life on Mars. On February 2, 2020, the Operational Land Imager (OLI) on Landsat 8 captured this image of one colourful part of the river.

Hydrothermal activity on the seafloor deposited the ore body during the Carboniferous period (300–350 Ma). The Tartessans and Iberians began mining in the Rio Tinto area about 3000 BC and were followed by the Phoenicians, Greeks, Romans, Visigoths, and Moors. Approximately 5,000 years of ore extraction and chemical refining have taken place in the Rio Tinto region, principally for copper, silver, and gold, but also for iron, manganese, and other minerals. The region's terrain has been drastically altered by this long-running mining activity.

Figure 5 (A) Mapping of Corta Atalaya's major hydrothermal alteration (Rio Tinto). (B) and (C) Thin sections of portions of the San Miguel stockwork showing significant hydrothermal alteration (chloritization and silicification). (C: cross polarised light, 100; B: plane light, 100).

The Rio Tinto and its environs are of particular interest to astrobiologists since the region's soils are comparable to those found on Mars. The iron- and potassium-rich sulphate mineral jarosite is particularly prevalent along the river and on Mars. Because the jarosite and other minerals found in this section of Spain often retain bacterial activity signatures, astrobiologists believe that researching how extremophiles survive in and around the Rio Tinto could provide insight into how to look for signs of life on Mars.

Figure 6 Rio Tinto and its cyanobacteria assist NASA in preparing for the exploration of Mars.

Figure 7 The Tinto River's subsurface. PNAS (Public Library of Science) (CAB) These cyanobacteria can perform oxygenic photosynthesis and are among the planet's oldest microbes. Following the discovery, the NASA Ames Research Center and the California Academy of Sciences have continued their investigations in order to prepare for the Mars mission and conduct sample collecting experiments.