粤北大宝山矿区船肚岩体和大宝山花岗斑岩锆石LA-ICP-MS U-Pb年龄及多阶段成矿分析

粤北大宝山矿床矿区出露船肚和大宝山矿化岩体。本文分析了两个岩体矿物组成特征和锆石LA-ICP-MS U-Pb年龄。船肚岩体为似斑状结构,块状构造,主要由似斑状花岗岩、似斑状二长花岗岩及似斑状花岗闪长岩等组成,和云英岩型及矽卡岩型Mo-W矿化紧密共生。大宝山岩体为斑状结构,块状构造,主要由碱长花岗斑岩、普通花岗斑岩、二长花岗斑岩及花岗闪长斑岩组成,矿物组成和船肚岩体的基本相同,和细脉浸染状Mo-W矿化紧密共生。船肚似斑状二长花岗岩和大宝山二长花岗斑岩锆石LA-ICP-MS U-Pb年龄分别为162.1±1.6 Ma,MSWD=2.72和165.8±2.0 Ma,MSWD=1.38。据船肚和大宝山岩体矿物组成基本相同、岩石结构不同及两者锆石Th/U比值不同和U-Pb年龄存在约4 Ma左右时差,提出大宝山矿区在燕山期发生了两阶段岩浆成矿事件,第一阶段岩浆成矿事件发生在166 Ma左右,形成大宝山斑岩型矿床,第二阶段岩浆成矿的形成时间约为162 Ma左右,形成船肚似斑状二长花岗岩及与岩体紧密共生的矽卡岩型和云英岩型矿化;大宝山斑岩体和船肚似斑状岩体是同一岩浆房两次脉动侵入形成的。

LA-ICP-MS Zircon U-Pb Age of the Chuandu and Dabaoshan Porphyries in the Dabaoshan Ore Filed,Northern Guangdong Province and its Metallogenic Implication

The Chuandu and Dabaoshan porphyries outcrop in the Dabaoshan orefield, northern Guangdong province. The Chuandu intrusion, with a cropping area of 0.7 km2, intruded the Cambrian weakly metamorphosed siltstone and slate and the Devonian sandstone with limestone interlayers. The Chuandu intrusion is associated with skarn-type Mo-W mineralization in its southern contact zone and greisen-type Mo-W mineralization in its northern contact zone, respectively. The Dabaoshan porphyry, with a cropping area of 0.18 km2, intruded the Jurassic sandstone and carbonaceous shale and the Galedonian tufflava. The Dabaoshan intrusion is associated closely with veinlet and disseminate Mo-W mineralization. Field and thin section observations reveal that the Chuandu intrusion is characterized by massive structure and porphyritic-like texture, and consists mainly of porphyritic monzonite granite with small amount of porphyritic granite and porphyritic granodiorite. The Dabaoshan intrusion is characterized by porphyritic texture and composed mainly of mozogranite porphyry. The Chuandu porphyritic monzonite granite and the Dabaoshan monzonite porphyry have LA-ICP-MS zircon U-Pb ages of 162.1±1.6 Ma (MSWD=2.72) and 165.8±2.0 Ma (MSWD=1.38), respectively. The Chuandu porphyritic felsic intrusion and the Dabaoshan porphyry are similar in mineral composition and different in LA-ICP-MS zircon U-Pb ages. Based on that the two adjacent intrusions are different in U-Pb ages, we suggest that the adjacent Chuandu and the Dabaoshan intrusions come from the same magma chamber at different time periods, and consequently, the Dabaoshan ore field underwent two stages of mineralization related to the two phases of Yanshanian felsic magmatic activities.