摘要:
内蒙古太平川Cu-Mo矿床位于得尔布干成矿带北段额尔古纳地区,为新近发现的斑岩型矿床。矿区内发育环带状热液蚀变,由内向外主要为硅化-绢云母化和泥化。热液蚀变围绕花岗闪长斑岩分布,Cu-Mo矿化主要受控于硅化-绢云母化蚀变,主要分布在花岗闪长斑岩中。本文获得成矿斑岩岩浆锆石U-Pb谐和年龄为202±5.7Ma,指示该矿床可能形成于晚三叠世。同时在样品中也发现继承锆石(784Ma),表明该地区可能存在晚元古基底。成矿斑岩的元素地球化学数据表明,主量元素SiO2 (65.86%~68.84%)>56%、Al2O3 (15.18%~16.28%)>15%、MgO (0.84%~1.06%)2O/K2O>1; 微量元素亏损重稀土,Sr (471×10-6~513×10-6)>400×10-6、Y (15.0×10-6~17.9 ×10-6)-6、Yb (1.27×10-6~1.81×10-6)-6,表明该花岗闪长斑岩具有明显的埃达克质岩石的地球化学特征。同时成矿斑岩具有相对高的SiO2、Yb含量和Th/Nb、Ce/Nb比值,而相对低的Al2O3、TiO2、MgO、Sr、Th含量和Th/Ce比值,这些特征与源于俯冲板片的埃达克岩相似。然而成矿斑岩(87Sr/86Sr)i (0.70943~0.71019)较大,εNd(t)为-3.4~-3.9,我们推测额尔古纳地块在岩浆上升过程中贡献了部分物质。结合区域构造演化,我们认为该矿区成矿斑岩岩浆形成于俯冲洋壳的部分熔融,矿床形成背景为早中生代蒙古-鄂霍茨克洋向额尔古纳地块俯冲的陆缘弧环境。
Abstract:
Recently discovered Taipingchuan porphyry Cu-Mo deposit is located in the north of Derbugan metallogenic belt, Ergun city of Inner Mongolia. Concentric rings of hydrothermal alteration and Cu-Mo mineralization occurred surrounding the granodiorite porphyry. Two hydrothermal alteration zones from the host porphyry to wall rocks have been recognized in Taipingchuan mine: A silicified-sericite zone and an argillic alteration zone. The Cu-Mo mineralization is clearly controlled by the silicified-sericite alteration. By using the zircon U-Pb dating methods a precise age data of the host porphyry is obtained. The dating data show that the age of host porphyry is 202±5.7Ma. The inherited zircon (784Ma) has also been found in the host porphyry, which indicates that a Proterozoic block was probably located in the study area. Geochemically, the host porphyry of Wunugetushan possesses some geochemical characteristics of adakite (i.e., high SiO2, Al2O3, Na2O and Sr contents, as well as La/Yb ratios, low MgO, Y and HREE contents). Some geochemical characteristics of the host porphyry, including relatively high SiO2, Yb contents and Th/Nb, Ce/Nb ratios and relatively low Al2O3, TiO2, MgO, Sr, Th contents and Th/Ce ratio indicate that the porphyry derived from partial melting of the subducted slab. The Sr-Nd isotopic composition of the porphyry displays an initial (87Sr/86Sr)i ratio of 0.70943 to 0.71019, a negative εNd(t) values of -3.4 to -3.9. The Sr-Nd isotopic data indicates that Proterozoic block had some contribution to the magma sources of the host porphyry. Combining the regional geology, we infer that the subduction of Mongol-Okhotsk ocean slab under the Ergun block led to the host porphyry forming, and Taipingchuan Cu-Mo deposit was related to a continental arc environment.
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