The advent of powerful new tools, the need to better understand the biodiversity, origins of life on Earth and on other planets, and the wide applications of the microbe-mineral interactions, have led to a rapid expansion of interest in subsurface environments. Recently reported results indicate signs of an early wet Mars and rather recent volcanic activity which suggest that Mars’s subsurface can house organic molecules or traces of microbial life, making the search for microbial life on Earth’s subsurface even more compelling. Caves on Earth are windows into the subsurface that harbor an especially interesting variety of mineral-utilizing microorganisms, which may contribute to the formation of unusual microstructures recognized as biosignatures. This proposal aims toward a multi- and inter-disciplinary approach to characterize the enigmatic microorganisms and unusual mineral features within black deposits found in limestone caves and lava tubes. A broad suite of tools from geology, mineralogy, geochemistry, hydrochemistry and molecular microbiology will be used: (i) To morphologically, geochemically and mineralogically characterize black deposits from Ardales Cave (Malaga, Spain) and lava tubes from Canary Islands; (ii) To identify and characterize the microbial communities within black deposits using powerful new molecular tools; (iii) To assess the microbe-mineral interactions associated with these cave deposits, permiting to elucidate on the role of microorganisms in the formation of secondary minerals and understand certain biomineralization and rock-weathering processes; (iv) To recognize biominerals, microbial fabrics or fossil bacteria as biosignatures valuable for astrobiology. Hence, the geomicrobiology of cave black deposits represents a research of great interest, which is likely to yield major advances on the identification of microbial biosignatures plausible to provide evidences on the origin of life on Earth and elsewhere in the Solar System.