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

X-ray diffraction, optical and electronic microscopy (scanning and transmitted), electron microprobe and Fourier transform infra red spectroscopy has been used to study phyllosilicates in the Palai-Islica Au-Cu epithermal, volcanichosted deposit, in order to link phyllosilicate mineralogy and mineral chemistry to ore genesis. Thus, different phyllosilicate assemblages characterize two types of mineralization, and related hydrothermal alteration. Chlorite and mica appear in polymetallic quartz veins with sulfides, and in the related chloritic and sericitic hydrothermal alteration. These minerals have notable textural and chemical differences (i.e. Fe/(Fe+Mg), Si and Al in chlorite and illitic and phengitic components in mica) amongst veins and altered rocks, revealing different genetic conditions. These chemical features also distinguish propylitic and regional, non ore-1 related, low-temperature alteration. Hot hydrothermal fluids of near-neutral pH are responsible for vein mineralization and alteration. Illite, interstratified illite-smectite, kaolinite and pyrophyllite are characteristic, with a distribution pattern by zones, for the intermediate argillic and advanced argillic alteration around areas of silicification. In the latter, native gold appears associated to interstratified illitesmectite, suggesting a relatively low temperature formation. Hot, low-pH fluids are responsible for this mineralization and alteration assemblage. The present study contributes to epithermal models showing the coexistence of two different alteration styles in the same hydrothermal system.

The Palai-Islica deposit (Almería, SE Spain) is an Au-Cu epithermal deposit hosted in Neogene calc-alkaline andesites and dacites from the Cabo de Gata-Cartagena volcanic belt in the Betic Cordillera. Major element compositions of apatite from Palai-Islica orebody and related hydrothermally altered and unaltered volcanic rock from the region hosting the deposit were obtained to clarify the processes involved in their formation. Apatite in the host volcanic rocks is rich in chlorapatite and hydroxylapatite components (50–57% and 24–36%) and poor in fluorapatite components (12–21%), indicating assimilation processes of cortical Cl-rich material in the magmatic evolution. Apatite in the orebody sometimes has corrosion textures and is mostly fluorapatite (94–100%). Apatite from the hydrothermally altered host rock of the orebody systematically bears signs of corrosion and has variable and intermediate fluorapatite (19–100%), chlorapatite (1–50%), and hydroxylapatite (0–47%) components. The style of zonation and the composition are related to the proximity to the orebody. These features can be interpreted as the result of hydrothermal modification of high Cl, OH-rich volcanic apatites into F-rich apatites. The enrichment of F is related to the intensity of hydrothermal alteration and could therefore constitute a geochemical index of alteration and of mineralization processes.