| An unparalleled large barium metallogenic belt in the world is located in Dabashan area, Southern Qinling Mountains. There are various kinds of barium minerals in this large barium metallogenic belt. The results of electron miscoprobe analyses and previous researches showed that the main occurrence of barium were barite, witherite, barytocalcite, norsethite, celsian, hanjiangite, ankangite, hyalophane, rosceolite and so on; the major composition of sulfide was pyrite; in addition, there were some other sulfides, such as millerite, sphalerite, sulvanite, digenite, bornite, chalcopytite. Besides, there were some vanadium and titanium oxide.The C of witherite mainly came from organic matter, and the value of δ13C was 10.9‰~21.0‰, according with the results of thermochemical sulfate reduction(TSR). The values of salinity calculating from 87Sr/86 Sr were higher than those calculated from fluid inclusion, indicating that some water would be created in the process of witherite formation, which may lead to dilution of mixing water. The results of the formation of witherite temperature were between 118~303.7 ℃, which was advantageous to the TSR. In addition, the sulfide species in Ba metallpgenic belt were mainly pyrite, matching with the results of TSR. Based on the features of C, O, Sr isotope and the homogenization temperature, going on with the S isotope of sulfide and barite in the metallogenic belt of witherite, the main conclusions of this research were as follows: the formation of witherite have significant relationship with TSR.The geochemical features of ore-bearing rocks and barium ores showed that: cherts mainly formed in anoxic enviroment of deep sea-bathyal, and they were charactered with the mixture of hydrothermal water and biochemistry; Th/U value of barium ores and ore-bearing rocks were situated between 0~2, and δU>1, which indicated that barium ore and ore-bearing rocks were formed in anoxic environment. The Mo content of barium ores and ore-bearing rocks had a postive relation with U, V, Cr, suggesting that the deformation environment of barium ores and ore-bearing rocks were consistent with the sea water. Ore-bearing rocks had high(U+V)/(U+V+ Mo) values and Mo contents, suggesting that ore-bearing rocks were formed in a more strongly anoxic environment, even in the condition containing H2S; the metallogenic belt of barite had higher(U+V)/(U+V+Mo) values and lower Mo content, indicating that the metallogenic belt of barite had more V, U, and poor Mo, suggested that the depositional environment of the metallogenic belt of barite were suboxic-anoxic conditions in absence of free H2S; the metallogenic belt of witherite had higher(U+V)/(U+V+Mo) values and Mo content, suggesting that it was formed in an extremely anoxic conditions; because of higher Mo content of ore-bearing rocks, the ore-bearing rocks had a more anoxic conditions than barium ores. |
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