Unconventional non-magmatic sulfur source for the Mazarrón Zn–Pb–Cu–Ag–Fe epithermal deposit (SE Spain)

Abstract

The present study shows the existence of textural, mineralogical, microthermometric and isotopic data that evidences processes such as thermochemical sulfate reduction (TSR) that are not typical features of volcanic-hosted epithermal deposits formed at shallow submarine and/or subaerial environments.Geological evidence and mineralogical, fluid inclusion temperature and geochemistry data suggest that the Mazarrón Zn-Pb-Cu-Ag-Fe deposit is a volcanic-hosted epithermal deposit. It is hosted by dacites ACCEPTED MANUSCRIPT2 with different alteration halos: K-Ar dating of illite from the argillic alteration gives an age of 9.7 ± 1.2Ma, which suggests that mineralization took place very close to the volcanism. The fluid inclusion study in the ore veins shows epithermal temperatures (between 190 and 260ºC), but moderate salinities, between 12 and 18 wt. % NaCl eq, compatible with mixing between surface waters and polygenic deep hydrothermal fluids. Evolution of the hydrothermal activity shows the existence of three stage of mineralization: in the first and last stages, with Fe-sulfides as main phases, mineralization was mainly formed by interaction between basinal fluids that leached Triassic sulfates (+ surface waters), and Cbearing reduced deep waters. During interaction of both fluids, the sulfur was subjected to extreme and geologically unusual fractionation under TSR conditions, with ranging from -2.9 to +28.4‰ δ 34 S, reaching exceptional values up to +53‰ δ 34 S. The intermediate stage is mainly formed by sphaleritegalena-chalcopyrite-fahlore bearing sulfides; this event is compatible with the influx of a magmatic fluid discharge. Finally, this study suggests that Mazarrón could be classified as an intermediate sulfidation deposit. KEYWORDS Unconventional epithermal volcanic-hosted SE SpainStable and radiogenic isotopes Thermochemical sulfate reduction

Geochemical Characterization of Magnetite and Geological Setting of the Iron Oxide ± Iron Silicate ± Iron Carbonate Rich Pb–Zn Sulfides from the La Unión and Mazarrón Stratabound Deposits (SE Spain)

“…The case was different at La Unión where the Pb–Zn–(Fe) ores were mined in modern times and therefore there is abundant and sound information. Nevertheless, as shown by the study of Esteban‐Arispe et al (), magnetite in Mazarrón is also present in the stockwork and veins (Fig. ), although in this case is not accompanied by iron silicates such as greenalite, which seems to be a mineralogical feature restricted to the manto‐type mineralization.…”

“…The Mazarrón Pb–(Ag)–Zn–(Fe) mining district (inactive) (López‐García et al, ; Oyarzun et al, ; Esteban‐Arispe et al, ) is located close to the town of Mazarrón (Figs b). The site was mined, although intermittently, since Roman time, being first mined for lead and later for the alum (aluminium sulfate: alunite) during the 15th–16th Centuries, then for the alum wastes, and finally for lead, silver and zinc during the 19th and 20th Centuries (until the early 1960s).…”

“…The ore field hosts Pb–(Ag) –Zn– (Fe) epithermal deposits of the vein and stockwork type, and manto‐type deposits at depth replacing marbles from the Nevado Filábride Complex (Figs a, b). Hydrothermal activity was triggered by the emplacement of dacitic domes of Tortonian age (9.7 ± 1.2 Ma; Esteban‐Arispe et al, ). The main deposits concentrate at San Cristóbal–Perules (adjacent to the town of Mazarrón), and the mining sites are characterized by the presence of dacitic domes (Fig.…”

“…The unusual and remarkable presence of magnetite, iron silicates and iron carbonates together with Pb–Zn sulfides in Mazarrón and La Unión allows definition of an iron oxide + iron silicate + iron carbonate + Pb–Zn sulfides mineral paragenesis (IOSC–LZS for short). Although the presence of these minerals was well known at La Unión (e.g., Pavillon, ; Oen et al, ; Manteca & Ovejero, ), nothing had been published on this matter about Mazarrón until 2015, when a paper on sulfur isotopes (Esteban‐Arispe et al, ) (Fig. ) brought up some information regarding one of the mineral parageneses of the ore field.…”

“…(A) Schematic sections and mineral parageneses from San Cristóbal (Mazarrón) and Emilia II (La Unión) also depicting potential (district‐scale) exploration targets; SC, sulfides + carbonates; IOSC–LZS, iron oxide, iron silicate, iron carbonate – lead and zinc sulfides. (B) Magma emplacement phenomena and hydrothermal transport of metals including the main isotopic signatures of rocks, lead, and sulfur; 1 Scaillet (); 2 Crespo et al (); 3 Arribas and Tosdal (); 4 Benito et al (); 5 Friedrich et al (); 6 Esteban‐Arispe et al (). (C) Schematic and combined stratigraphic column (depicting ore deposits) for the La Unión and Mazarrón ore fields (not to scale).…”