Tracking the origin of metasomatic and ore-forming fluids in IOCG deposits through apatite geochemistry (Nautanen North deposit, Norrbotten, Sweden)

International audienceThe relative contribution of magmatic and non-magmatic fluids to the metasomatic and ore-forming processes in iron-oxide copper‑gold (IOCG) deposits is still widely debated. In this study, the petrography, detailed composition and Usbnd Pb ages of various apatite occurrences from the Nautanen North IOCG deposit, Norrbotten, Sweden, were determined to decipher the evolution of fluid sources in the area. The hydrothermal apatite grains grow over muscovite, intergrow with magnetite, amphibole, K-feldspar, chalcopyrite and sericite, and are replaced by epidote, allanite and/or chlorite along the grain margins. Irregular patterns of the apatite grains were revealed by cathodoluminescence imaging. Fluorine in all apatite occurrences is the dominant halogen (1.62-3.58 wt%), chlorine is depleted (up to 0.34 wt%), while bromine and iodine are found in traces (0.7-72 ppm and 0.15-4.2 ppm respectively). The δ37Cl value of the apatite grains ranges between -0.8 and 3.4‰. Uranium-Pb data yield ages between 1.63 and 1.55 Ga (with one exception at 1.49 Ga showing large age errors). Textural evidences show that the apatite grains have been precipitated during the potassic alteration of the D2 event (1.81-1.78 Ga), which is considered a regional, IOCG-related, high-temperature event. Cathodoluminescence textures reveal that all the apatite occurrences have been chemically modified by the late-stage metasomatic and ore-forming fluids during the nucleation of epidote ± allanite ± chlorite. The Br/I and δ37Cl values of the apatite grains can be considered representative of the associated fluid values and show a trend between two end-members, which indicates the contribution and progressive mixing of two different fluids during late-stage ore-related hydrothermal circulation. The ore-forming fluids were mainly issued from exsolved magmatic fluids from S-type bodies, as revealed by the strong affinity of the Br/I ratio of the ore zone with the pegmatite-related apatite. The other end-member associated with the apatite occurrences that co-exist with metasomatic assemblages, is consistent with fluids linked to evaporite dissolution. Apatite dating is interpreted to reflect resetting ages

Mineralogical Constraints on the Potassic and Sodic-Calcic Hydrothermal Alteration and Vein-Type Mineralization of the Maronia Porphyry Cu-Mo ± Re ± Au Deposit in NE Greece

The Maronia Cu-Mo ± Re ± Au deposit is spatially related to a microgranite porphyry that intruded an Oligocene monzonite along the Mesozoic Circum-Rhodope belt in Thrace, NE Greece. The magmatic rocks and associated metallic mineralization show plastic and cataclastic features at the south-eastern margin of the deposit that implies emplacement at the ductile-brittle transition, adjacent to a shear zone at the footwall of the Maronia detachment fault. The conversion from ductile to brittle deformation caused a rapid upward magmatic fluid flow and increased the volume of water that interacted with the host rocks through high permeable zones, which produced extensive zones of potassic and sodic-calcic alteration. Potassic alteration is characterized by secondary biotite + K-feldspar (orthoclase) + magnetite + rutile + quartz ± apatite and commonly contains sulfides (pyrite, chalcopyrite, pyrrhotite). Sodic-calcic alteration consists of actinolite + sodic-calcic plagioclase (albite/oligoclase/andesine) + titanite + magnetite + chlorite + quartz ± calcite ± epidote-allanite. The high-oxidation state of the magmas and the hydrothermal fluid circulation were responsible for the metal and sulfur enrichments of the aqueous fluid phase, an increase in O2 gas content, the breakdown of the magmatic silicates and the production of the extensive potassic and sodic-calcic alterations. Brittle deformation also promoted the rapid upward fluid flow and caused interactions with the surrounding host rocks along the high temperature M-, EB-, A- and B-type veins.This article is published as Melfos, V.; Voudouris, P.; Melfou, M.; Sánchez, M.G.; Papadopoulou, L.; Filippidis, A.; Spry, P.G.; Schaarschmidt, A.; Klemd, R.; Haase, K.M.; Tarantola, A.; Mavrogonatos, C. Mineralogical Constraints on the Potassic and Sodic-Calcic Hydrothermal Alteration and Vein-Type Mineralization of the Maronia Porphyry Cu-Mo ± Re ± Au Deposit in NE Greece. Minerals 2020, 10, 182. doi:10.3390/min10020182.</p

Mineralogical Constraints on the Potassic and Sodic-Calcic Hydrothermal Alteration and Vein-Type Mineralization of the Maronia Porphyry Cu-Mo ± Re ± Au Deposit in NE Greece

International audienceThe Maronia Cu-Mo ± Re ± Au deposit is spatially related to a microgranite porphyry that intruded an Oligocene monzonite along the Mesozoic Circum-Rhodope belt in Thrace, NE Greece. The magmatic rocks and associated metallic mineralization show plastic and cataclastic features at the southeastern margin of the deposit that implies emplacement at the ductile-brittle transition, adjacent to a shear zone at the footwall of the Maronia detachment fault. The conversion from ductile to brittle deformation caused a rapid upward magmatic fluid flow and increased the volume of water that interacted with the host rocks through high permeable zones, which produced extensive zones of potassic and sodic-calcic alteration. Potassic alteration is characterized by secondary biotite + K-feldspar (orthoclase) + magnetite + rutile + quartz ± apatite and commonly contains sulfides (pyrite, chalcopyrite, pyrrhotite). Sodic-calcic alteration consists of actinolite + sodic-calcic plagioclase (albite/oligoclase/andesine) + titanite + magnetite + chlorite + quartz ± calcite ± epidote-allanite. The high-oxidation state of the magmas and the hydrothermal fluid circulation were responsible for the metal and sulfur enrichments of the aqueous fluid phase, an increase in O 2 gas content, the breakdown of the magmatic silicates and the production of the extensive potassic and sodic-calcic alterations. Brittle deformation also promoted the rapid upward fluid flow and caused interactions with the surrounding host rocks along the high temperature M-, EB-, A-and B-type veins