摘要
毛登矿区位于内蒙古锡林浩特,是大兴安岭南段典型的锡钼铋多金属矿床。文章选择毛登矿区阿鲁包格山斑状二长花岗岩为研究对象,开展了高精度锆石U-Pb定年和锆石、角闪石、黑云母矿物学研究,以探讨成岩时代、岩浆结晶的物理化学条件及其对成矿的意义。研究显示,斑状二长花岗岩锆石U-Pb年龄(140±0.9)Ma,侵位于早白垩世;锆石w(Ti)为(3.99~10.9)×10^(-6),结晶温度672~805℃(平均734℃),岩浆氧逸度lgf(O_(2))为-19.6~-14.4。角闪石化学成分显示富铁(w(TFeO)为22.38%~26.41%)、富钙(w(CaO)为9.57%~10.36%)、贫镁(w(MgO)为5.67%~8.09%),暗示了岩浆经历了明显的结晶分异演化作用;w(Al_(2)O_(3))为5.13%~6.29%,小于10%,以及Si/(Si+Ti+Al)值(0.86~0.88)大于0.765,表明具壳源角闪石特征;角闪石结晶温度709~753℃,形成压力145~241 MPa,形成深度5.5~9.1 km,寄主岩浆氧逸度lgf(O_(2))为-16.6~-15.4,含水量H_(2)O_(melt)为3.6%~4.4%。黑云母化学成分显示,富铁(w(TFeO)为24.73%~28.53%)、镁(w(MgO)为6.21%~9.02%),I_(Mg)(Mg/(Fe+Mg))值(0.28~0.39)小于0.5,表明具壳源黑云母特征;黑云母结晶温度为650~712℃,寄主岩浆氧逸度lgf(O_(2))为-18.3~-16.5;黑云母I_(Mg)值与华南含锡花岗岩I_(Mg)值区间范围一致,且I_(Fe)值(0.61~0.72)较高,显示岩体与矿区内Sn矿化关系密切。结合前人研究,认为斑状二长花岗岩可能为新生地壳经部分熔融后,在上升过程中经历较明显的结晶分异演化作用而形成;具A型花岗岩特征,成岩环境处于伸展构造背景。岩浆演化处于较低氧逸度,较高温度,较高的水、F和Cl含量的环境,是毛登矿区锡、钼、铋多金属矿化形成的重要条件。
Located in Xilin Hot City of Inner Mongolia,the Maodeng deposit is a typical Sn-Mo-Bi polymetallic deposit in the southern segment of Da Hinggan Mountains.In this paper,the authors present high-precision zircon U-Pb ages as well as chemical compositions of zircon,amphibole and biotite from Alubaogeshan porphyritic monzogranite in the Maodeng deposit,aiming to investigate the petrogenic age,the formation conditions and the petrogenic and metallogenic significance of this rock body.The zircon yielded a weighted mean U-Pb age of(140±0.9)Ma,which indicates that the emplacement of porphyritic monzogranite took place during the Early Cretaceous.Ti content of zircon ranges from 3.99×10^(-6)to 10.9×10^(-6)and crystallization temperature of zircon is 672~805℃with an average of 734℃.The oxygen fugacity lgf(O_(2))of the magma was-19.6~-14.4 when zircon crystallized.Electron microprobe analyzer(EMPA)analysis shows that the amphibole is rich in iron(w(TFeO)=22.38%~26.41%)and calcium(w(CaO)=9.57%~10.36%)but poor in magnesium(w(MgO)=5.67%~8.09%),which indicates that the magma has experienced obvious evolution.The content of Al_(2)O_(3)(5.13%~6.29%)is lower than 10%,whereas the w(Si)/w(Si+Ti+Al)ratio(0.86~0.88)is higher than 0.765,indicating that the amphibole was derived from the crust.The crystallization temperature of amphibole is 709~753℃,with the crystallization pressure of 145~241MPa and the emplacement depth of 5.5~9.1 km.The oxygen fugacity lgf(O_(2))of magma was-16.6~-15.4,and the water content(H_(2)O_(melt))was 3.6%~4.4%when the amphibole crystallized.The biotite is rich in iron(w(TFeO)=24.73%~28.53%)but poor in magnesium(w(MgO)=6.21%~9.02%).The I_(Mg)(Mg/(Fe+Mg))values change from0.28 to 0.39,suggesting that the biotite is crustal.The oxygen fugacity lgf(O_(2))of magma was-18.3~-16.5 and the tempterature was 650~712℃when biotite crystallized.The I_(Mg)value is consistent with that of tin-bearing granite in South China,and the I_(Fe)(Fe/(Fe+Mg))value(0.61~0.72)is relatively high.It is believed that the porphyritic monzogranite is related to the Sn mineralization in the Maodeng deposit.In combination with previous studies,the authors hold that the porphyritic monzogranite was dominantly derived from the partial melting of a juvenile lower crust,followed by strong fractional crystallization during magma ascent.The porphyritic monzogranite belongs to A-type granite,which was formed in an extensional setting.The magma has relatively high H_(2)O,F and Cl content,suggesting that it evolved under the condition of relatively low oxygen fugacity,high temperature and shallow emplacement.Therefore,it is believed that the porphyritic monzogranite played an important role in Sn-Mo-Bi polymetallic mineralization in the Maodeng deposit.
作者
季根源
江思宏
张龙升
李高峰
刘翼飞
易锦俊
张苏江
JI GenYuan;JIANG SiHong;ZHANG LongSheng;LI GaoFeng;LIU YiFei;YI JinJun;ZHANG SuJiang(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,CAGS,Beijing 100037,China;Cores and Samples Center of Natural Resources,Langfang 065201,Hebei,China;Exploration Unit of North China Geological Exploration Bureau,Langfang 065201,Hebei,China;Key Laboratory of Orogen and Crust Evolution,Peking University,Beijing 100871,China)
出处
《矿床地质》
CAS
CSCD
北大核心
2021年第3期449-474,共26页
Mineral Deposits
基金
国家自然科学基金项目(编号:41873051)
科技部深地项目(编号2017YFC0601303)
地质调查项目(编号DD20190411、DD20201113)联合资助。
关键词
地球化学
锆石
角闪石
黑云母
大兴安岭南段
毛登矿床
geochemistry
zircon
amphibole
biotite
southern segment of Da Hinggan Mountains
Maodeng deposit
作者简介
第一作者:季根源,男,1987年生,工程师,博士研究生,矿物学、岩石学、矿床学专业。Email:csujigenyuan@163.com;通讯作者:江思宏,男,1968年生,研究员,博士,博士生导师,主要从事金属矿床成矿规律研究。Email:jiangsihong1@163.com。
