Rb-Sr Isotope ages and fluid inclusion characteristics of Pb-Zn deposit and their prospecting significance in Panshi-Panxin region, eastern Guizhou Province

The Pb-Zn deposit in Panshi-Panxin area, located on the Western margin of Xuefeng Mountain and the junction of Yangtze block and Jiangnan orogenic belt, is relatively a typical one in Songtao area, East Guizhou.The Rb-Sr isochronal dating on sphalerite of main metallogenic period yields an age of 486±3 Ma(MSWD=1.2) and (⁸⁷Sr/⁸⁶Sr)_i=0.70918±0.00002.The results of petrography, microthermometer and composition analysis on fluid inclusion in calcite show that the liquid-rich liquid-vapor-type fluid inclusions are the primary ones with a homogenization temperature of 277.23℃, and vapor phases are dominated by CO₂ and H₂O, with minor CH₄ present in individual fluid inclusion, and the ionic compositions are dominated by Na⁺, Ca²⁺, Mg²⁺, Cl^- and minor K⁺and SO₄^2-.The comprehensive studies show that the Pb-Zn deposit of this area was formed in the Late Cambrian to Early Ordovician, later than the country rock of Cambrian Second Series Qingxudong Formation, and indicate a genesis of epigenetic deposit.The(⁸⁷Sr/⁸⁶Sr)_i of sphalerite is higher than the wall rock, similar to the ⁸⁷Sr/⁸⁶Sr ratio of Early Cambrian seawater.Based on the analysis of the ore-bearing potential of the regional strata, it is speculated that the metallogenic material is derived from the Cambrian Niutitang Formation black shale series.The ore-forming fluid is of medium and low temperature hot brine origin and may be mixed with other hydrothermal sources.It is more likely that Pb and Zn migrated in the ore-forming fluid in the form of chloride.