Vectors to ore in replacive volcanogenic massive sulphide deposits of the northern Iberian Pyrite Belt: Major and trace element mineral chemistry

As part of a broader characterization and study of vectors to ore in VMS systems of the Iberian Pyrite Belt (IPB, Spain), we have investigated in detail mineral chemistry vectors in a representative replacive deposit hosted in felsic volcanic rocks. At the Aguas Tenidas deposit (northern IPB) the hydrothermal system affected rocks of an originally homogeneous composition extending hundreds of metres beyond its footprint. The major and trace element chemistry of white micas, chlorite and carbonates have been analysed by electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to characterize geochemical vectors across the extent of the hydrothermal system at Aguas Tenidas. White micas are dominated by muscovite in both regionally altered lithologies and within the hydrothermal system, with coexisting paragonite occurring in a halo beyond the first disseminated pyrite surrounding the stockwork and in the proximal hanging wall. Systematic variations have been observed in FeO/(FeO + MgO) and Na2O/(Na2O + K2O) across the alteration zone. Chlorite is predominantly clinochlore in composition, with chamosite restricted to the centre of the hydrothermal system. In regionally altered lithologied it is characterized by a constantly low Al and Al-IV at variable Fe/(Fe + Mg); in rocks influenced by the hydrothermal system it presents higher Al-IV and total Al, and a progressive increase in Al, Al-IV and Fe/(Fe + Mg) towards its core. Regional carbonates consist of calcite, with additional dolomite forming in proximal rocks. Iron content in dolomite increases towards the centre of the hydrothermal system, with ankeritic compositions becoming dominant. Systematic variations in Ba, Cs, Li, Pb, Rb, Sn, Sr, T1 and Zn have been observed in white micas consistent with a proximal-distal transition (vector). Trends in chlorite have been less well characterized due to analytical limitations, although variations have been observed in the contents of As, Co, Li and Zn. A schematic model has been proposed which accounts for the observed mineralogical and mineral chemistry trends across the hydrothermal footprint of the Aguas Tenidas VMS deposit. Major element signatures in white micas and chlorite are interpreted as having been controlled by the upwards and outwards flow of hot reducing Fe-rich hydrothermal fluids producing a coupled increase in temperature and fluid Fe/(Fe + Mg), and a decrease in fO(2), with increasing fluid/rock ratios towards the centre of the stockwork. The data presented herein are not only applicable to VMS exploration in the IPB, but on a broader scale improve our general understanding of vectors to ore in VMS deposits in general.

Automated summary

This study investigates the mineral chemistry vectors in a replacive deposit in volcanic rocks to understand the influence of hydrothermal systems on ore formation. The variations in element compositions of white micas and chlorite indicate the flow of hydrothermal fluids and the formation of iron-rich minerals. The findings contribute to the understanding of ore vectors in volcanic massive sulfide (VMS) deposits.