LA ICP-MS study of fluid inclusions in quartz from the Yuzhna Petrovitsa deposit, Madan ore field, Bulgaria

摘要

Major and trace elements contents of individual fluid inclusions in quartz from the Yuzhna Petrovitsa hydrothermal Pb-Zn deposit were analyzed microthermometrically and by LA ICP-MS in order to better characterize the ore-forming fluids and their evolution. We found different trends in T_h vs. depth for fluid inclusions associated with various stages of mineralization, which quantitatively match predictions from published hydrothermal fluid flow simulations. The data indicate that the early quartz-pyrite association formed when the hydrothermal system was still heating up. The somewhat later quartz-galena-sphalerite main ore stage was deposited during the thermal peak under hot hydrostatic head conditions with a temperature-depth distribution representing the fluid's boiling curve, and post-sulphide quartz formed after the thermal peak. Galena and sphalerite precipitated from a slightly acid fluid with a Pb content of about 7-8 ppm and a Zn content of about 33 ppm at the present-day +668 m level, which represents a paleodepth of about -1200 m. Precipitation within the vein structure was mainly the result of cooling from about 310 ℃ to 285 ℃ over the investigated 400 m vertical interval. Ore fluid concentrations of lead and zinc can be used to estimate a minimum time-integrated amount of fluid in the order of 10~2 km~3 that was necessary to form the Madan ore field, which agrees well with typical values for present day hydrothermal systems.