What is the connection (if any) between jarosite and subsoil biological activity near Spain's Río Tinto?
From what I've read so far, it appears jarosite may not be a prerequisite for the formation of certain life forms, instead that it is produced by certain organisms.


  Río Tinto (Huelva, southwestern Spain) is an extreme environment with a remarkably constant acidic pH and a high concentration of heavy metals, conditions generated by the metabolic activity of chemolithotrophic microorganisms thriving in the rich complex sulfides of the Iberian Pyrite Belt (IPB). Fungal strains isolated from the Tinto basin were characterized morphologically and phylogenetically. The strain identified as Purpureocillium lilacinum specifically induced the formation of a yellow-ocher precipitate, identified as hydronium-jarosite, an iron sulfate mineral which appears in abundance on the banks of Río Tinto. The biomineral was characterized by X-ray diffraction (XRD) and its formation was observed with high-resolution transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled to energy-dispersive X-ray spectroscopy (EDX) microanalysis. Jarosite began to nucleate on the fungal cell wall, associated to the EPS, due to a local increase in the Fe(3+) /Fe(2+) ratio which generated supersaturation. Its formation has been also observed in non-viable cells, although with much less efficiency. The occurrence of P. lilacinum in an ecosystem with high concentrations of ferric iron and sulfates such as Río Tinto suggests that it could participate in the process of jarosite precipitation, helping to shape and control the geochemical properties of this environment.


Another reference, states that


  But there is something else about jarosite that makes it interesting. One of the steps in its formation involves combining pyrite (ferrous sulfide) with oxygen. This oxidation reaction can be performed by certain "rock-eating" microorganisms.
  
  ... And yet, there remains the tantalizing possibility that martian jarosite owes its existence to the martian version of rock-eating microbes. If so, remnants of these organisms may be locked in the mineral.
  
  ... This is because jarosite on Earth is known to let all sorts of foreign elements incorporate into its crystal structure.


including, 


  amino acids, the basic components of proteins


Fate of Lipid Biosignatures in a Mars-Analogue Sulfur Stream

Formation of Rubidium Jarosite During the Microbiological Oxidation of Ferrous Iron at Room Temperature