柴北缘造山带滩间山金矿田多期侵入岩年代学及其地质意义

柴北缘造山带位于青藏高原北缘，其复杂的地质演化过程造就了区域上多期多阶段的岩浆活动与金铅锌多金属成矿作用。地处柴北缘西段的滩间山大型金矿田，以广泛发育中酸性岩脉（墙）为显著特征，但岩浆活动的时代、构造背景及其与金成矿关系尚不清楚。本文以野外调查与显微观测为基础，对新识别出的青龙沟闪长玢岩、青龙滩细晶闪长岩和金龙沟霏细斑岩，开展了LAICP-MS锆石U-Pb定年，结合已有资料探讨了滩间山金矿田岩浆侵入序列及其构造背景，分析了岩浆活动与金成矿的时空-成因联系。结果表明，滩间山金矿田先后经历早奥陶世（474.6±1.3 Ma）、中泥盆世（383.9±0.8 Ma）、早白垩世（127.4±0.6 Ma）三期构造-岩浆活动。早奥陶世闪长玢岩侵位于大规模金成矿前，是柴北缘洋俯冲阶段的产物；中泥盆世和早白垩世岩浆活动均与碰撞后陆内造山地质过程有关，并呈现出绢云母化-硅化蚀变组合及浸染状黄铁矿和黄铜矿化。研究认为晚古生代-中生代多期岩浆-热液叠加可能是滩间山大型金矿田成矿的关键。

Geochronology and geological significance of multistage intrusive rocks in the Tanjianshan gold field, northern margin of the Qaidam orogenic belt

The northern Qaidam orogenic belt is located in the northern margin of the Qinghai-Tibet Plateau. Its complex geological evolution has resulted in multistage tectono-magmatic events and been associated with gold-lead-zinc-polymetallic metallogeny of the belt. The large Tanjianshan gold field occurs at the western part of the northern Qaidam orogenic belt, and is characterized by widespread intermediate-acid dikes. It is yet unknown about the emplacement age, tectonic setting, and their link to gold mineralization. Based on detailed field investigations and geological observations, this work carried out zircon LA-ICP-MS U-Pb dating on the newly identified Qinglonggou diorite porphyrite, Qinglongtan fine-grained diorite and Jinlonggou felsophyre. The magmatic sequences and tectonic setting of the Tanjianshan gold area were discussed in conjunction with the existing ages. Investigations were also conducted on the spatio-temporal-genetic relationships between magmatic activity and gold mineralization. Results show that the Tanjianshan gold field has experienced three discrete tectonic-magmatic activities in the Early Ordovician (474.6 ± 1.3Ma), the Middle Devonian (383.9 ± 0.8Ma), and the Early Cretaceous (127.4 ± 0.6Ma), respectively. The Early Ordovician diorite porphyrite, which was formed during the northern Qaidam oceanic subduction stage, emplaced prior to extensive gold mineralization. The latter two magmatic episodes, however, were connected to the post-collisional, intracontinental geological process, and the intrusive rocks in these episodes exhibited sericite-quartz alteration as well as disseminated pyrite and chalcopyrite mineralization.It is proposed that multistages tectono-hydrothermal superposition of Late Paleozoic and Mesozoic may be critical for formation of the large Tanjianshan gold field.