The extreme conditions in the Rio Tinto River in Huelva also appear to be similar to those in deposits on Jupiter's moon, Europa, they said.
Radiation, lack of moisture and extreme temperatures and pressures on the surface of Mars make the development of life difficult, scientists say, so they've been searching the Earth for "friendlier" niches that could encourage life, and one of the candidates is the salt deposits of the Rio Tinto, which are highly acidic and ferrous.
"The salt deposits are good 'hosts' for biological remains and even life itself in extreme circumstances," said researcher Felipe Gomez, coauthor of the study published in the journal Planetary and Space Science.
"The discovery of these protected microniches in one of Mars' analogue on Earth, like Río Tinto, is an important step in evaluating the habitability potential of the Red Planet," the researchers said.
NASA's Mars Global Surveyor probe has detected alluvial fan-shaped salt formations on the Martian surface and scientists believe that they could exist below the frozen oceans on Europa.
"From the astrological point of view, salt deposits are of great importance and should be considered when searching for life on space exploration missions, like the current Curiosity rover mission on Mars," Gomez said.