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Geology and Mineral Chemistry of Gold Mineralization in Mirge‐Naqshineh Occurrence (Saqez, NW Iran): Implications for Transportation and Precipitation of Gold
Author(s) -
ASGHARI Golale,
ALIPOUR Samad,
AZIZI Hossein,
MIRNEJAD Hassan
Publication year - 2018
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.13502
Subject(s) - pyrite , arsenopyrite , geology , geochemistry , quartz , mineralization (soil science) , mineralogy , hydrothermal circulation , metamorphic rock , galena , fluid inclusions , chalcopyrite , metallurgy , copper , sphalerite , materials science , paleontology , seismology , soil science , soil water
The Mirge‐Naqshineh gold district is situated at northwest of Iran with a NW‐trending brittle‐ductile shear zone. It is hosted by Precambrian meta‐sedimentary and meta‐volcanic units traversed by mineralized quartz veins. In terms of cross‐cutting relationships and sulfide content three types of quartz veins are identified in the region. Among those, parallel to bedding quartz vein (type I) is the main host for gold mineralization. Gold is found in three different forms: 1) submicrometer‐size inclusions of gold in arsenian pyrite, 2) as electrum and 3) in the crystal lattice of sulfides (pyrite, galena and chalcopyrite). Six types of pyrite (Py1‐Py6) were identified in this ore reserve. Py3 coexists with arsenopyrite and contains the greatest As‐Au concentrations. There is a negative correlation between the As and S contents in Py2 and Py3, implying the substitution of sulfur by arsenic. Pyrites and mineralized quartz veins were formed via metamorphic‐hydrothermal fluid and reflect the gold‐transportation as Au(HS) − 2 under reducing and acidic conditions. The gold precipitation mainly controlled by crystallization of arsenian pyrite during fluid/rock interactions and variation of f O 2 . The volcanic host rock has played an important role in gold concentration, as Py3 in this rock contains inclusion of gold particles, but gold is within the lattice of pyrite in phyllite or other units.