%0 Journal Article
%A Fernández Caliani, J.C.
%A Crespo Feo, María Elena
%A Rodas González, Magdalena
%A Fernández Barrenechea, José María
%A Luque Del Villar, Francisco Javier
%T Formation of nontronite from oxidative dissolution of pyrite disseminated in Precambrian felsic metavolcanics of the southern Iberian Massif (Spain)
%D 2004
%@ 0009-8604
%U https://hdl.handle.net/20.500.14352/50260
%X This paper describes a rare occurrence of nontronite associated with sulfide-bearing felsicmetavolcanics, providing evidence of colloidal deposition in open spaces as result of a low-temperaturewater-rock interaction. Microbotryoidal masses of green nontronite with impurities of kaolinite, illite,barite, amorphous silica and iron oxyhydroxides are found as vein and cavity fillings in deeply kaolinizedrhyolites and rhyolitic tuffs of Precambrian age, at Oliva de Me´rida in SW Spain. Clay mineralcharacterization has been carried out by X-ray diffraction, infrared spectroscopy, thermal analysis,analytical electron microscopy and stable isotope (oxygen and hydrogen) analysis. Nontronite was formedunder low-temperature alteration conditions, from a continuous sequence of reactions and aqueous solutioncompositions, involving two basic processes that acted in concert: oxidative dissolution of pyrite andhydrolysis of K-feldspar. After acidity neutralization, dissolved silica released by incongruent dissolutionof K-feldspar reacted with ferric sulfate derived from pyrite oxidation to form nontronite under oxidizingconditions, in the presence of relatively warm meteoric water.
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