Study Of Ore-forming Fluid In Weishancheng Au-Ag Polymetallic Metallogenic Belt, Henan Province

The Poshan Ag-Pb-Zn deposit, Yindongpo Au-Ag deposit and Yindongling Ag-Pb-Zn deposit are three large representational deposits of the Weishancheng Au-Ag polymetallic metallogenic belt, which located in Tongbai Mountains, southern Henan province, China. The occurrences are respectively in the southern wing, the axial collapse and the northern wing of Heqianzhuang anticline and the composite compresso-crushed zone. The ore bodies are stratiform and stratabound within carbonaceous sericite-quartz-schist of the Neoproterozoic Waitoushan Formation and respectively located in its lower, middle and upper part. We compare the ore-forming fluid characteristics in three deposits, and analyses the genesis of the polymetallic ore belt. Main conclusions as following:(1) The fluid inclusions in three deposits can be divided into three types, i.e.: type-I (NaCl-H2O inclusions) and Type-II (CO₂-bearing) fluid inclusions, occasionally type-III (daughter-mineral-bearing multiphase inclusions);(2) The ore fluid system of the Weishancheng polymetallic ore belt is typically mesothermal (200³30°C), K⁺-SO₄^2--dominated (Poshan and Yindongpo deposits) and Na⁺-Cl^--dominated (Yindongling), low salinity (0.18～13.83wt% NaCl.eqv, average <10wt% NaCl.eqv), low-density (0.53～1.11g/cm3) and CO2-rich (4.2～15.8 mol%);(3) The H-O-C isotopic analysis of the fluid inclusions from each deposit indicates that the ore-forming fluid in the early and middle stages are from the metamorphic devolatilization, that"organic water"entered Yingdongling deposit, while mineralizing fluid in Poshan and Yindongpo deposits turned to be K⁺-SO₄^2--dominated. And in the late stage much meteoric water entered the fluid system of Poshan and Yindongpo deposits, but Yindongling deposit almost had no meteoric water enter because of the baffle layer (carbonaceous sericite-quartz-schist) above it;(4) The geochemical studies of C-S isotope geochemistry show that the ore metals were mainly sourced from carbonaceous sericite-quartz-schist, granulitite and carbonatite in the Waitoushan Formation;(5) The Weishancheng metallogenic belt is a typical stratabound orogenic-type metallogenic system in terms of their ore-forming fluid, metal source and geologic characteristics. The ore-forming process took place under the continental collision setting between Yangtze Block and North China Block in Mesozoic. The metamorphic dehydration reaction of plunging down induced the developing of mineralizing fluid in Weishancheng, during the collision transformed from compression to extend, because of the intense water-rock reciprocity, mineralizing substance in the Waitoushan Formation was extracted and transferred to advantaged lodging space and then deposit.