Rb-Sr Isochron Ages of Sphalerites from the Ganluo Lead-Zinc Ore Concentration Area in Sichuan Province and Their Geological Implications
The Ganluo lead-zinc ore concentration area is located north of the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic belt along the southwestern margin of the Yangtze Massif,which is a major Pb-Zn producing area in Sichuan Province with significant economic value.This work aims to clarify the metallogenic epoch,geotectonic setting,and the Pb-Zn mineralization mechanism,and thus to support the regional mineral exploration.Rb-Sr isotopic dating of sphalerites was conducted on the Chipu and Ergadiji Pb-Zn deposits.The Rb-Sr dating yielded an isochron age of 246±17 Ma(MSWD=2.3),which indicates the Pb-Zn mineralization occurred in the Early Triassic.This age coincides well with the closure epoch of the Paleo-tethys Ocean.Sphalerite(87Sr/86Sr)i values vary from 0.71061 to 0.71393,which are greater than the mantle 87Sr/86Sr value of 0.70355 and that of Emeishan basalt of 0.704979 to 0.706938,but smaller than the 87Sr/86Sr values of basement rock of 0.7243 to 0.7288.The mineralized materials were suggested to be mainly originated from the crust.Combined with previous research,it is indicated that under the background of Paleo-Tethys Ocean closure,the strong orogeny induced the deep circulation of brine fluids in foreland basin and extracted mineralized materials from the basement rocks.Under the thermodynamic condition of Emeishan basalt,the mineralized fluids further migrated and precipitated to form the Chipu and Ergadiji Pb-Zn deposits.The Malaha deep fault,interlayer or fault fractures derived from the orogeny and the carbonate strata are the dominant ore-controlling factors in the Ganluo area.
sphaleriteRb-Sr isochron agemetallogenic epochsource of ore-forming materialsGanluo ore concentration areaSichuan Province
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