蒙古国东部矽卡岩型铁多金属矿床成矿岩体年代学及地球化学

为探讨蒙古-鄂霍茨克洋演化有关的金属成矿问题，对蒙古国东部哈拉特乌拉Fe?Zn矿床花岗闪长斑岩和查希尔Fe?Mo矿床黑云母二长花岗岩开展了锆石U?Pb年代学、岩石地球化学和Hf同位素组成研究.成矿岩体的年龄分别为278 Ma和258 Ma，均富钾、碱，富集轻稀土元素和大离子亲石元素（K、Rb），亏损高场强元素（Nb、Ta、Ti），属高钾钙碱性I型花岗岩. 锆石ε_Hf（t）值分别为6.6~9.8和6.9~11.1，Hf两阶段模式年龄分别为672~877 Ma和568~855 Ma，表明岩体母岩浆源于新元古代亏损地幔形成的新生地壳的部分熔融. 哈拉特乌拉和查希尔矽卡岩型铁多金属矿床成矿岩体应是蒙古-鄂霍茨克洋板块南东向俯冲的产物，间接证明了蒙古-鄂霍茨克洋板块开始向南东俯冲的时间应早于278 Ma. 

Geochronology and Geochemical Features of the Ore-Related Granite in the Skarn Type Fe Polymetallic Deposits in Eastern Mongolia

In order to reveal the relationship between the ore genesis and the evolution of Mongolia?Okhotsk Ocean, we studied the whole rock geochemistry, U?Pb ages and Hf isotopes of the zircons from the ore?related granodiorite porphyry inthe Haraat Uul Fe?Zn deposit and biotite monzogranite in theTsahir Fe?Mo deposit. The ore?related granites were formed at ca. 278 Ma for the Haraat Uul Fe?Zn deposit and ca. 258 Ma for the Tsahir Fe?Mo deposit. The granitic rocks have high contents of K₂O and alkali, enrichments of LREE and LILEs (K, Rb), and depletions of HFSEs (Nb, Ta, Ti), which is indicative of high?K calc?alkaline Ⅰ?type granites. The granodiorite porphyry of the Haraat Uul Fe?Zn deposit has positive ε_Hf(t) range of 6.6~9.8 with two?stage depleted mantle Hf model ages of 672~877 Ma; the biotite monzogranite for the Tsahir Fe?Mo deposit has positive ε_Hf(t) range of 6.9~11.1 with two?stage depleted mantle Hf model ages of 568~855 Ma, indicating that both of the photoliths were probably derived from a Neoproterozoic depleted mantle. Fe polymetallic mineralisation at the Haraat Uul and Tsahir areas was intimately related to the south?eastward subduction of the Mongol?Okhotsk Ocean, indirectly proved that the Mongolian?Okhotsk Ocean plate began to south?eastward subduction before 278 Ma.