Therma, physicochemical and biological weathering processes of organic material and genesis of sulfurated mineralization: The genesis of the La Florida lead zinc deposit (Cantabria, Spain)

The La Florida lead-zinc deposit (Cantabria, Spain), which is hosted by Urg onian carbonates, is located on the border of the Basco-cantabric Lower Cre taceous basin. The stratiform orebody, which is composed of sphalerite, gal ena, and barite in iron-dolostones, occurs in an envelope of dolostone. Org anic matter studies have been carried out on samples from this deposit to u nderstand its genesis and later evolution. The results of this work reveal the immatury of the autochthonous organic matter despite a slight paleother mal anomaly centred on the deposit. Various alteration processes have affec ted the hydrocarbons associated with autochthonous organic matter and (or) allochthonous bitumens, namely geochromatographic fractionation, water-wash ing, and biodegradation. Together with previous geological work, the result s of this study are consistent with epigenetic and (or) diagenetic emplacem ent of the mineralization. The proposed genetic scheme involves hydrotherma l fluids that would have acquired at least some of their characteristics du ring their upward migration through the Mesozoic cover. These solutions pro bably brought in the metals, the sulphates, and the organics all necessary for in situ hydrogen sulphide production and ore genesis. Sulphate reductio n probably proceeded mostly at the expense of allochthonous organics by bac teria introduced by meteoric water infiltrations.