Zircon U-Pb dating and Hf isotopic compositions of intrusions in the Erdaohe silver-lead-zinc deposit, Inner Mongolia and the metallogenic process of the deposit

Abstract

二道河银铅锌矿为大兴安岭中段最新发现的一处大型矽卡岩型矿床。银铅锌矿的形成与矿区多期岩体密切相关，矿体主要赋存于矽卡岩、大理岩及细粒花岗闪长岩内。本文对矿区主要岩体及石榴子石矽卡岩开展了锆石LA-ICP-MS U-Pb年代学、Hf同位素研究和石榴子石电子探针分析，获得了绿帘石化细粒花岗闪长岩、绿帘石化细粒闪长岩、花岗斑岩的²⁰⁶Pb/²³⁸U加权平均年龄分别为506±4.3Ma、213±2.8Ma和128±1.1Ma。二道河矿区石榴石矽卡岩与绿帘石矽卡岩常呈相互穿插关系，闪锌矿、方铅矿等矿石矿物具有重结晶特征，矽卡岩矿物石榴子石电子探针分析结果显示在矿区至少存在两期不同性质的流体活动，表明二道河银铅锌矿至少经历了两期以上的矿化事件。获得的三类岩体的锆石ε_Hf（t）值分别为0.9~6.9、8.3~15.1和7.9~14.1，对应的二阶段模式年龄（t_DM2）分别为1.6~1.1Ga、0.8~0.3Ga和0.8~0.3Ga，表明这些花岗岩类均来源于新生地壳部分熔融，它们的成因可能分别与额尔古纳地块和兴安地块的拼合、蒙古-鄂霍茨克洋闭合及古太平洋板块俯冲有关。这些构造体系的叠加与演化对二道河银铅锌矿床的形成和富集具有非常重要的作用。;The Erdaohe silver-lead-zinc deposit is a newly discovered large skarn deposit in central Great Xing’an Range, and its formation is closely related to multi-stage intrusions. The ore bodies in the deposit mainly occur in skarns, marble, and fine-grained granodiorites. In this study, we conducted LA-ICP-MS zircon U-Pb dating, Hf isotopic analysis, and the electron microprobe analysis (EPMA) of garnets for the major intrusions and garnet granites in the deposit. Zircon grains from the epidotized fine-grained granodiorites, epidotized fine-grained diorites, and granite porphyry yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 506±4.3Ma, 213±2.8Ma, and 128±1.1Ma, respectively. The garnet skarns and epidote skarns in the Erdaohe deposit are frequently interspersed with each other, and the ore minerals such as sphalerite and galena in the deposit are characterized by recrystallization. Moreover, the EPMA results of garnets in the skarns show there were at least two stages of fluid activities with different natures. All these indicate that the Erdaohe deposit has undergone at least two stages of mineralization events. Zircons from three types of intrusions obtained yielded ε_Hf(t) values of 0.9~6.9, 8.3~15.1, and 7.9~14.1, respectively, with t_DM2 values of 1.6~1.1Ga, 0.8~0.3Ga, and 0.8~0.3Ga, respectively. This indicates that all these granitoids are originated from the partial melting of the juvenile crust, and their formation may be related to the combination of the Erguna and Xing’an blocks, the closure of the Mongol-Okhotsk Ocean, and the subduction of the Paleo-Pacific Plate, respectively. The superimposition and evolution of tectonic systems play a crucial role in the formation and enrichment of the Erdaohe silver-lead-zinc deposit.