内蒙古得尔布干成矿带铅锌银矿两期叠加成矿的矿物学证据--以乌尔根矿为例

Mineralogical evidences of the two-stage superimposed Pb-Zn-Ag mineralization in the Derbugan metallogenic belt,Inner Mongolia--A case study of the Ulgen deposit

内蒙古额尔古纳市乌尔根铅锌银矿是得尔布干成矿带上具有代表性的浅成中低温热液型铅锌银矿之一。显微镜下观察、电子探针分析结果等矿物学证据证明,该矿床存在2期成矿作用。其中早期火山热液形成的金属硫化物普遍受应力作用的改造,并广泛被晚期形成的矿物交代,典型矿物是不含乳滴状黄铜矿的闪锌矿,具有高含量Fe、Mn和低含量Cu的特征;晚期次火山(隐爆角砾岩)热液形成的金属硫化物占大多数,常交代早期形成的矿物并与其交生在一起,典型矿物是含固溶体乳滴黄铜矿的闪锌矿,并且具有中等含量Fe、Mn和高含量Cu的特征。在次火山热液期的晚阶段残余热液还形成了较为纯净的呈棕黄色-无色透明的纯净闪锌矿,具有高含量Zn,低含量Fe、Mn、Cu的特征。结合前人测定的研究区火山岩和矿石矿物定年结果以及火山岩主量元素组成数据,推测早期火山热液成矿与中基性塔木兰沟组火山岩关系密切,而晚期次火山(隐爆角砾岩)热液属于满克头鄂博组的(中)酸性岩浆热液的产物。隐爆角砾岩热液富含Cu元素且为成矿提供了主要物质来源,是研究区寻找除铅锌之外其他矿种的重要线索。

The Ulgan Pb-Zn-Ag deposit in Eerguna City of Inner Mongolia is one of the representative meso-epithermal type Pb-Zn-Ag deposits in the Derbugan metallogenic belt.The mineralogical evidences obtained microscope observation and electron probe analyses,show that there are two stages of mineralization in this deposit.The early-stage metallic sulfides formed by the early volcanic hydrothermal fluid are generally transformed by stress,and are widely replaced or metasomatized by late-stage hydrothermal minerals.The typical early-stage ore mineral is chalcopyrite-free sphalerite which has high contents of Fe,Mn and low content of Cu.However,the late-stage metallic sulfides formed by the late-stage subvolcanic(cryptoexplosive breccia)hydrothermal fluid are dominant ones which partly replaced or commonly coexisted with early-stage hydrothermal minerals.The typical late-stage ore mineral is sphalerite containing chalcopyrite of solid solution.It is characterized with medium contents of Fe,Mn and high content of Cu.At the end of the late subvolcanic hydrothermal stage,a kind of pure transparent sphalerite with colors varying from brownish yellow to colorless was formed by the residual hydrothermal fluid.It is characterized with high content of Zn and low contents of Fe,Mn and Cu.Combined with the dating results of volcanic rocks and minerals and analytical data of major elements of volcanic rocks in the study area by previous researchers,it is speculated that the early-stage mineralization could be closely related to the volcanic hydrothermal fluid derived from the magma of intermediate basic volcanic rocks in the Tamulangou Formation,while the late-stage mineralization could be related to the subvolcanic hydrothermal fluid,which could be rich in Cu and other ore-forming materials,derived from the magma of(intermediate)acidic cryptoexplosive breccia in the Manketouebo Formation.Thus,the cryptoexplosive breccia is an important clue for finding other kinds of minerals besides lead and zinc in the study area.