Las jarositas de Sierra Almagrera (Almeria): Mineralogia y genesis

Resumo

The jarosites and alunites of S. Almagrera are the two most charasteristic minerals founded in the weathering of the sulfides and wall-rocks. They have not been known at the present. In this paper, both minerals are studied from the chemical and genetic points of view, in order to stablish the relation with the mineralizations and wall-rocks. From the results, some mineralogical formulae have been stablished with the folloqing mean value: (H3 O0.80 Na0.10 K0.10) (Fe0.80 Al 0.20)3 (S04)2 (OH)6 appearing also plumbo and natrojarosite. The main genetic mechanism are enough complicated, two different reactions are proposed: 1. - 3S04 Fe+ aq. + 7 H2O -> H3OFe3 (SO4)2 (OH)6 + 5H+ + SO4 with inclusion of Na, K and Al. 2. - 3Fe(OH)3 amorf. + 4H+ + 2SO4 -> H3OFe3 (SO4)2 (OH)6 + 2H2O with more high percentages of Na, K and Al that the previous reaction. The first reaction should correspond to the direct precipitation of the jarosite from the ions in solution, probably in the zones with pH more low. The second one is the result of the reaction of iron hidroxides (limonites) with the elements in solution, at pH conditions more basic