Hofrat en Nahas Cu-Au-U deposit, Sudan: Fluid inclusion evidence for a magmatic origin

摘要

The Hofrat en Nahas Cu-Au-U deposit in western Sudan is hosted by highly sheared mylonites in the NE-trending Central African Shear Zone and occurs as gold-sulfide-quartz-calcite veins associated with granitic dykes in late-stage brittle structures. Four types of primary fluid inclusions in vein quartz include: (1) 2-phase H_2O-NaCl; (2) monophase H_2O-NaCl; (3) 3- to multi-phase H_2O-NaCl with daughter minerals; and (4) monophase gaseous CO_2-rich inclusions, representing heterogeneous entrapment of the inclusions during mineralization. The high salinity (up to 69 wt.% NaCl equivalent) CO_2-rich fluids were possibly derived from exsolution of magma at a minimum temperature of 570℃, and the low to moderate salinity (up to 26 wt.% NaCl equivalent) fluids were mixed with and diluted by external low salinity (<10 wt.% NaCl equivalent) fluids at a maximum temperature of 350℃. It is suggest that the mineralizing fluids at Hofrat en Nahas are magmatic in origin