地壳结构与属性对冈底斯东北缘多金属成矿带成矿作用的控制机制研究

It is well known that the regional metallogenic type could be controlled by the architecture and geochemical properties of the crust. The northeastern Gangdese polymetallic metallogenic belt located in southern Tibetan is one result of the Indian-Asian continental collision, and it has a great potential of ore mineralization. Ore deposits in this metallogenic belt can be subdivided into three sub-belt, which Pb-Zn-Ag deposit is located in the core of the central Lhasa subterrane, and Fe and Mo deposits are located on the southern margin of the subterrane. Preliminary studies have suggested that the zonation of these ore deposits might be result of the heterogeneity of the Lhasa crustal architecture and geochemical properties. However, in present stage, the mechanism of crustal architecture and properties control on the metallic mineralization of these metallogenic belt have not been well constrained. Therefore, we intend to study on petrology, geochemistry, isotopic geochemistry, zircon U-Pb geochronology and zircon Hf-O isotope to constraints on the temporal and spatial of regional igneous rocks in the metallogenic belt, and thus to constraints on the magmatic processes and features of the source regions of these magmas. Finally, we intend to analysis the mechanisms of crustal architecture and geochemical properties influence on the mineralization of the northeastern Gangdese polymetallic metallogenic belt under a continent-continent collision environment.

地壳的结构与地球化学属性对区域金属成矿类型的控制早已被人们所熟知。位于青藏高原南部的冈底斯东北缘多金属成矿带是印-亚板块陆陆碰撞的产物，且极具成矿潜力。成矿带内主要的三类金属矿床具有明显的分带性，其中Pb-Zn-Ag矿床位于中拉萨地体核部，而Fe和Mo矿床则位于地体的南缘。初步研究表明，这种分带性可能与中拉萨地体地壳结构和地球化学属性的不均一性有关。然而，就目前的研究程度而言，地体地壳结构和属性如何控制成矿带内各金属元素聚集成矿并未得到有效限定。因此，项目拟通过对区域岩浆岩和矿区成矿岩体的岩石学、元素和同位素地球化学，以及锆石U-Pb年代学和锆石Hf-O同位素研究，约束冈底斯北缘岩浆岩活动的时空序列，分析岩浆作用过程和岩浆源区性质。在此基础上，详细研究和对比区内各类金属矿床形成机制，并最终系统剖析陆-陆碰撞环境下，地壳结构和地球化学属性对成矿金属元素的迁移、分异、富集和聚集的控制机制。

青藏高原拉萨地体内的冈底斯多金属成矿带是印-亚板块陆陆碰撞的产物，且极具成矿潜力。成矿带以岩浆热液型矿床为主，并在区域上呈现出明显的分带特征。拉萨地体南部以Cu-Mo矿化为特征，中部以Pb-Zn-Ag和W矿化为特征，而两者中间的成矿作用则以Cu-Fe-Pb-Zn-Ag多金属成矿为特征。然而，对这些金属矿床在区域上为何具有分带性的关键控制要素尚缺乏系统限定。众所周知，岩浆热液矿床的金属、流体、挥发分，以及维持热液系统的能量均来源自岩浆系统，因而对成矿岩浆系统的解剖是解决矿床成因的关键所在。因此，本项目通过区域岩浆岩和矿区成矿岩体的岩石学、元素和同位素地球化学，锆石U-Pb和锆石Hf同位素，以及Cu同位素的研究，发现冈底斯多金属成矿带内矿化金属在区域上的分带性主要是受拉萨地体地壳结构和属性差异的控制。冈底斯成矿带南部以新生地壳为特征，新生下地壳的形成与岛弧岩浆的底垫密切相关，并以富Cu元素和富水矿物（角闪石）为特征；这些物质富集为斑岩Cu-Mo矿床广泛发育于拉萨地体南部提供了重要的物质基础。拉萨地体中部以古老地壳物质为特征，因而地壳内缺乏Cu元素，但富集Pb-Zn-Ag和W等成矿元素；古老地壳熔出的壳源花岗岩有利于Pb-Zn-Ag和W成矿，不利于Cu-Mo成矿，故在中拉萨地体的岩浆热液矿床以Pb-Zn-Ag和W矿化为特征。介于中拉萨和南拉萨地体之间的地壳兼具新生和古老地壳属性，因而区内岩浆源区的Cu和Pb-Zn-Pg含量也介于两种端元地壳之间，故在南拉萨和中拉萨地体之间的矿床多以Cu-Fe-Pb-Zn-Ag多金属矿化为特征。