富镉锌矿成矿流体地球化学研究:以贵州都匀牛角塘富镉锌矿为例

Geochemistry of mineralizing fluid of Cd-rich zinc deposit: Taking Niujiaotang Cd-rich zinc deposit, Duyun, Guizhou for example

通过对贵州都匀牛角塘富镉锌矿包裹体的研究，发现有一定数量的有机包裹体。该矿床与密西西比河谷型 (MVT)矿床相似，均属于 Na＋-Ca2＋-K＋-Mg2＋-Cl－体系，同时，两者在成矿流体温度、盐度和密度方面也有一定差别。该矿床成矿流体组分与油田卤水相似，仅 Ca2＋和 Mg2＋含量偏高，这可能与晚阶段的碳酸盐化有关。笔者认为，成矿流体可能与麻江古油藏的油田卤水有关，正是由于油田卤水携带了 Cd和 Zn等成矿物质，在矿区与温度和盐度较低的富含 Ca2＋和 Mg2＋的流体混合，使得 Cd和 Zn等成矿物质沉淀并富集成矿，同时形成方解石和白云石。从成矿早阶段到晚阶段，成矿流体的氧逸度逐渐升高，流体的 pH值（介于 6.40～ 7.30之间）也逐渐升高，说明成矿流体性质为偏碱性弱还原。成矿流体由油田卤水演变而来，其中和 Cl－含量较高，且 Cl-> F－， Na＋ > K＋，说明成矿物质主要以 HS－和 Cl－的络合物和有机络合物形式搬运和迁移。

Some organic inclusions were found in Niujiaotang Cd-rich zinc deposit, Duyun, Guizhou Province. The results show that this deposit is of Na＋＋ Ca2＋-Mg2＋-Cl-system, which is similar to the MVT deposit, but different in temperature, salinity and density of mineralizing fluid. Except high contents of Ca2＋ and Mg2＋ , the compositions of the mineralizing fluid are similar to those of the oil-field brine. This may be related to the later carbonation stage. It is suggested that the mineralizing fluid may be have some relationship with the oil-field brine of Majiang paleo-oil pool. The mixing of oil-field brine containing mineralizing elements, such as Cd and Zn, with the low temperature and salinity fluid enriched in Ca2＋ and Mg2＋ resulted in the deposit, enrichment and mineralization of Cd and Zn, and formed calcite and dolomite in the ore area. From the early mineralizing stage to the later stage, the fO2 and pH of mineralizing fluid rose gradually, showing that the characters of the mineralizing fluid is on the alkalescence side and feeble deoxidize. The mineralizing fluid, which contains high and Cl-and with Cl->F-, Na＋ >K＋ , was derived from oil-field brine, and the mineralizing elements transported and migrated as complexes of HS-and Cl-and organic complex.