摘要
宜里钼矿为大兴安岭北段新发现的具大型钼找矿潜力的中型钼矿床,赋矿围岩为晚古生代花岗岩和卧都河组地层,矿区深部发现有晚期花岗斑岩脉,其成矿可与"体中体"模式对比。矿区内晚期花岗岩(黑云母花岗岩和花岗斑岩)岩石地球化学表明,岩石具有高SiO2、富K2O+Na2O和相对高的Al2O3,低MgO、TFeO、CaO的特征,K2O/Na2O=0.76～1.27,A/CNK=1.02～1.23;微量元素富集Rb、U、K、Pb等LILE,相对亏损Nb、Ta、Ti、P和LREE等HFSE,(La/Yb)N=11.09～22.41,重稀土明显亏损,无或弱Eu异常(δEu=0.63～0.92),且具低Ni、Cr含量和Mg#,高Sr/Y比值,显示出埃达克质岩石地球化学亲和性。LA-MC-ICP-MS锆石U-Pb同位素精细年代学测试结果显示,矿区内晚期花岗岩的侵位年龄集中在132.43±0.61～134.46±0.58Ma,属早白垩世。辉钼矿Re-Os同位素定年显示,成矿年龄为131.8±1.5Ma,较岩体侵位年龄晚2.7～0.6Ma。结合熔融实验和区域资料,矿区埃达克岩为挤压向伸展转换的构造体制下加厚下地壳部分熔融的产物,而钼成矿作用的触发机制主要是埃达克质岩浆出熔后,残余的加厚下地壳的拆沉作用,推测矿区深部存在与成矿直接相关的花岗质岩体。大兴安岭北段存在有4期钼成矿事件,分别为加里东早期(510～470Ma)、华力西晚期(300～290Ma)、印支晚期—燕山早期(205～175Ma)、燕山中期早阶段晚侏罗世(150～145Ma)和晚阶段早白垩世(143～129Ma)。其中,印支晚期—燕山早期(大兴安岭北段西坡)和燕山中期(大兴安岭北段东坡)为成矿高峰期。宜里钼矿即为大兴安岭北段成矿高峰期燕山中期晚阶段的产物。
Yili porphyry Mo deposit,located in Oroqen of Inner Mongolia,is a newly discovered medium-scale ore deposit in recent years in the northern Great Khing＇an Ranges.The host rocks are Late Paleozoic granites and Woduhe River Formation.Late granitic porphyry dikes have been found in deep by drilling.The metallogenic model of the Yili Mo deposit is similar to the body within body＇ model.The granites emplaced in late stage are characterized by high SiO3,alkalis comprises K3O and Na3O,Al3O3,and low MgO,TFeO,CaO.TheK2O/Na3O=0.76～1.27,A/CNK=1.02～1.23.With respect to trace elements of these granites,enrichment of Rb,U,K,Pb,relative depletion of Nb,Ta,Ti,P and LREE,（La/Yb）N =11.09～22.41,depletion of HREE and slightly negative Eu anomalies （δEu =0.63～0.92） are the major characteristics.These granites show geochemical affinity of adakite also with low Ni,Cr content and Mg#,high Sr/Y.This study carried out the LA-MC-ICP-MS U-Pb isotopic dating for zircons from late granites （biotite granites and granitic porphyry） and molybdenite Re-Os isotopic dating from ore body and obtained their corresponding age data are 132.43 ± 0.61 ～ 134.46 ± 0.58 Ma and 131.8 ± 1.5 Ma,respectively,are belongs to early Cretaceous.The rock-forming age is earlier than the ore-forming age 2.7 ～0.6 Ma.Combined with results of melting experiment and regional data,these granites were produced by partial melting of thickened lower crust,while trigger mechanism of Mo mineralization is the delamination of thickened lower crust after melting.A concealed granitic intrusion,directly related to mineralization,may emplace in deep of mine.Statistics precise chronology data of molybdenites and granitic rock-forming indicate that there occurred 4 periods of Mo-mineralization during Phanerozoic in Northern Great Khing＇an Ranges.These periods of Mo-mineralization are early Caledonian （510 ～470 Ma）,late Variscan （300 ～ 290 Ma）,late Indosinian-early Yanshanian （205 ～ 175 Ma）,early stage of middle Yanshanian （late Jurassic,150～145 Ma） and late stages of middle Yanshanian （early Cretaceous,143～129 Ma）.The Mo mineralization of late Indosinian-early Yanshanian and middle Yanshanian are the major metallogenitic periods.Yili Mo deposit is one of the products of late stages of middle Yanshanian Mo-mineralization in the peak of metallogenitic period in the northern Great Khing＇an Ranges.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2014年第3期361-379,共19页
Acta Geologica Sinica
基金
中国地质大调查项目(编号1212010633901
1212011220369)
北京建龙国基投资有限公司宜里钼矿科研项目(编号E1101)资助成果
