Experimental study on the formation mechanism of the skarn gold deposits of stratabound metasomatic type

The unaltered and unmineralized rocks of the same stratigraphic horizons, which are sandstone and carbonate rock, limestone and siliceous rock, limestone and pelitic shale, udstone and striped limestone as well as single marl were used as starting materials, and the ore forming hydrothermal solutions of 0 5 M NaCl+0 5 M KF+0 1 M K 2 SO 4 +0 05 M AuCl 3 of pH=4 5, 5 5, 6 5, and 7 5 were made separate simulating preparations as reactive solutions for the experiments.Experimental starting materials and reactive solutions were sealed in silver test tubes, and placed in the reactive cavities of high pressure vessels. Durations of the metasomatic experiments were 96 hours.Experimental results show that in the weak redox environments at 250～650℃ and 200×10 5 ～800×10 5 Pa,skarn mineral and gold mineral associations were both formed and in the experimental of Donggua mountain cleposit(carbontite and sandstone metasomatism)system, three groups skarn mineral associations of tremolite + serpentine + anhydrite + native gold (Ⅰ), wollastonite + andradite grossular + serpentine +anhydrite +electrum (Ⅱ) and scapolite + diopside hedenbergite + andradite grossular + serpentine (Ⅲ) which are separate in accord with the mineral associations of ore and H 2 O bearing skarn, Au bearing skarn and high temperature unmineralized skarn found in the mines are formed and native gold is precipitated at 250～350℃ and little electrum is come out at 350～600℃, while gold is not existed as any independent minerals at more than 600℃.