Fluid evolution and Re enrichment in the Maronia Cu-Mo±Au porphyry, NE Greece. Insights from mineral microanalysis and fluid inclusions constraints

Maronia is an exceptional Re-rich Cu-Mo +/- Au porphyry systems in Thrace, NE Greece. Here, we present a micro-analytical, S isotope, and fluid inclusion approach in order to reveal the hydrothermal prerequisites required for the extreme Re enrichment which are poorly constrained up to date. Based on petrography, trace element chemistry of hydrothermal quartz (e.g., Al/Ti, Ge/Ti), and fluid inclusion microthermometry of consecutive vein generations, we establish the spatial and temporal fluid evolution. The fluid inclusions give evidence for systematic fluid cooling and continuous phase separation which is the main ore-forming process during the porphyry stages. The later epithermal stage formed by vapor condensation into meteoric water. This is consistent with salinity-sensitive (Co/As, As/Sb), temperature-sensitive (Se/Tl) and fluid source-sensitive (Se/Ge) pyrite trace element ratios. delta S-34 values in pyrite vary in response to SO2 disproportionation, phase separation, host rock buffering and fluid fO(2). Early extremely Re-rich molybdenite (6631 +/- 4308 ppm) is related to higher temperatures and fO(2) compared to later molybdenite generations with lower Re (1746 +/- 1184 ppm) contents. We conclude, that fluid cooling below 400 - 350 degrees C and decreasing fO(2) are the main control on the Re precipitation efficiency in the potassic alteration on the deposit-scale.