SOME EVIDENCE FOR CONTEMPORAEOUS FAULTS IN THE DONGSHENGMIAO SULFIDE POLYMETALLIC ORE DISTRCT IN INNER MONGOLIA AND THE GENESIS OF THE ORE DEPOSIT
JiangXiaoqingGeological Publishing House,Beijing)
The Dongshengmiao sulfide deposit located on the northern margin of the North China platform is a Middle Proterozoic deposit,and the mineralization spots lie in a third-grade fault basin within the Langshan-Bayan Obo rift system. Some evidence shows that there exist contemporaneous faults in the ore district which might have served as channelways for hydrothermal soluti- ons in the process of mineralization and controlled the evolution of the basin. There is also evidence for the presence of volcanic activity that took place simultaneously with the ore-forming process,and this volcanic activity might have provided heat for the hydrothermal activity. Some exhalites have been observed in the ore deposit,such as biotitite and chloritite. Isotopic studies indicate(1) Pb came from the depth of the crust;(2)sulfide was derived from seawater and hydrothermal solution;and(3)C and O in dolonite of ore veins were mixtures of hydrothermal solution and sedimen- tary dolomite. B and Ba contents of wall rocks are extremely high,implying the exis-ence of hydrothermal exhalative activities. From the bottom of the orebody upward and from the center to both sides there is indistinct zoning of elements:Cu(FeS)→Pb(FeS)→Zn(feS)→Fe(FeS_2)→Fe(FeCO_3).Studies on inclusions in minerals show that the seawater was less than 340m in depth and the temperature of the hydrothermal solution was 240℃_±. The ore deposit is of exhalative-sedimentarytype.