Determining absolute ages of orogenic faults is critical to understanding the deformation process in the upper crust, but obtaining age remains a problem due to the lack of readily available techniques. Carbonates occur as veins in faults in a range of geological settings, and thus it is a suitable mineral for U-Pb geochronology. Here, we apply the new approach of U-Pb dating on syn-tectonic dolomite veins from the Gelouang gold deposit in the western Qinling Orogen to unravel the absolute timing of the fault formation shedding new light on the regional upper crustal deformation archive. In situ LA-ICP-MS U-Pb dating of dolomite yielding a successful age of 115–112 Ma demonstrates that the dolomite precipitated coeval with tectonic events ascribed to the post-orogenic deformation phase in the Qinling Orogen. This event is possibly correlated with broader intracontinental processes and might be an inevitable response to the extensional deformation of the Qinling Orogen. The presented LA-ICP-MS dolomite U-Pb age successfully represents the age of a specific structure that encompasses the intracontinental process in the Qinling Orogen. Moreover, it demonstrates the utility of the method to decipher a response to complex deformation histories on a regional scale.

大兴安岭南段黄岗梁Fe-Sn矿床是我国北方最大的Fe-Sn多金属矿床,其成矿作用与燕山期花岗质岩浆活动密切相关。本文以矿区内中细粒黑云母二长花岗岩、英云闪长岩(包体)和粗粒黑云母正长花岗岩中的黑云母为研究对象,系统分析了黑云母的主微量元素、挥发分组成及副矿物组合特征,探讨了岩浆的结晶分异程度、氧逸度条件及其对锡成矿能力的制约。结果显示,两类花岗岩中的黑云母为铁叶云母,具有较低的K/Rb比值和较高的Rb、Cs、Nb、Ta、F及Sn含量,结晶自还原性(钛铁矿系列)、富F、高分异的壳源岩浆系统,是锡成矿的关键;而英云闪长岩包体中的黑云母为铁质黑云母,形成于相对较高氧逸度(磁铁矿系列)的壳幔混源岩浆系统,可能为早期铁矿化提供了部分物质与流体基础。从中细粒黑云母二长花岗岩到粗粒黑云母正长花岗岩,岩浆分异程度增强,氧逸度降低,F含量显著升高,为锡的富集与成矿创造了有利条件。与国内外典型锡矿区的黑云母成分对比表明,黄岗梁矿区花岗岩具有良好的锡成矿潜力。本研究为理解Fe-Sn共生机制及区域锡成矿潜力评估提供了重要依据。

Tungsten and tin deposits provide numerous valuable and critical resources to the world, which has led to them attracting the increasing attention of economic geologists