小兴安岭鹿鸣大型钼矿LA-ICP-MS锆石U-Pb和辉钼矿Re-Os年龄及其地质意义

鹿鸣钼矿是小兴安岭地区于近年发现的大型斑岩型钼矿床。为探讨研究区成岩成矿关系及其地质意义,在对矿化特征分析的基础上，采用LA-ICP-MS锆石U-Pb技术对鹿鸣地区含矿二长花岗岩测年，获得成岩年龄为 (187.1±1.2) Ma (n=15, MSWD=0.70) 。通过辉钼矿样品Re-Os同位素分析，获得等值线年龄为(177.4±3.5) Ma (n=11, MSWD=0.71) ，加权平均年龄为(178.08±0.79) Ma (n=11,MSWD=0.46)。两种方法获得的年龄大致相近，表明它们形成于同一成岩成矿系统。鹿鸣钼矿成岩成矿年龄，与乌奴格吐山铜钼矿、兰家沟钼矿和杨家杖子钼矿等矿床辉钼矿Re-Os同位素年龄相近，表明包括小兴安岭地区在内的我国东北地区广泛存在早侏罗世岩浆-成矿作用。微量元素和同位素指纹显示，鹿鸣钼矿形成于地壳挤压向拉伸转换的构造环境，成矿物质为壳幔混合来源。

LA-ICP-MS Zircon U-Pb and Molybdenite Re-Os Dating for the Luming Large-Scale Molybdenum Deposit in Xiao Hinggan Mountains and Its Geological Implication

The Luming Molybdenum deposit is one of newly discovered large porphyry deposits in Xiao Hinggan Mountains metallogenic belt. The deposit occurs in the monzonitic granite. In the monzonitic granite, SiO₂ contents are 71.98％ and 77.17％, K₂O+Na₂O  8.06％ and 9.07％, K/Na ratios 1.14 and 7.25 and A/CNK ratios are 0.95 and 1.05, with high silica and alkali rich. It’s abundant amount of HFSE. The average of FeO^T is 2.0%，Ga×104/Al is 2.75，Zr content are 76.2×10^-6 and 134×10^-6，which showed the characteristics of A-type granite. The granite from Luming area has content of δEu(0.36~0.56), and ratios of element couples (K/Rb, K/Cs, Rb/Cs, Rb/Li, Li×10³/Mg, Rb/Sr) are similar to those of syntexis-type granitoids in South China, showing the characteristics of crustal mantle magma mixing. In the trace element spider diagram, there are a negative anomaly of Ba, Y and positive anomaly of Rb, Th, Ce, Sm. To determine the age of Luming monzonitic granite, the LA-ICP-MS zircon U-Pb dating is applied and gives a diagenesis age of (187.1±1.2) Ma. The Re-Os contents of molybdenite from Luming Mo deposit are determined by ICP-MS. The results show the Re-Os isochron age of (177.4±3.5) Ma and weighted mean age of (178.08±0.79) Ma, which indicate that the mineralization is later than the diagenesis. Trace element and isotopic tracing show that both diagenesis and mineralization of the Luming Mo deposit were related to changes of tectonic environment from compression to extension. Ore-forming materials were derived from upper mantle and lower crust.