江西彭山锡多金属矿集区尖峰坡锡矿床LA-MC-ICP-MS锡石U-Pb测年及其地质意义

江西彭山锡多金属矿集区位于江西省德安县,处于钦杭成矿带东段靠扬子板块一侧,是扬子板块东南缘地区一个重要的锡多金属矿集区。目前该地区尚缺乏精确可靠的成矿年代学资料。本文应用LA-MC-ICP-MS微区原位U-Pb同位素测年技术,对矿集区内尖峰坡矿床中锡石样品进行了研究,获得尖峰坡锡矿的206Pb/207Pb-238U/207Pb等时线年龄129.7±2.5Ma(N=31,MSWD=5.5),207Pb/206Pb-238U/206Pb谐和年龄为128.3±2.5Ma(N=31,MSWD=7.6),表明尖峰坡矿区锡成矿作用主要发生在早白垩世,与已报道的彭山地区燕山期花岗岩的成岩年龄相一致。紧密的时间以及空间关系显示燕山晚期岩浆-热液活动对形成彭山锡多金属矿集区的大规模成矿作用至关重要。对华南地区锡钨区域成矿年代学对比表明,扬子板块东南缘的锡钨成矿带均形成于早白垩世(146~124Ma),这与其北侧的长江中下游成矿带九瑞-鄂东南铜多金属矿集区的成岩成矿时代相同,而明显不同于南岭地区晚侏罗世(160~150Ma)以及滇东南-桂西北地区晚白垩世(98~76Ma)的锡钨成矿作用,说明扬子板块东南缘具有与南岭以及滇东南-桂西北地区不同的锡钨成矿背景,而应与长江中下游地区的构造岩浆作用事件统一来开展深入研究。

LA-MC-ICP-MS U-Pb dating of cassiterite from the Jianfengpo Sn deposit in the Pengshan Sn-polymetallic ore field, Jiangxi Province and its geological significance

The Pengshan Sn-polymetallic orefield in De'an County, Jiangxi Province lies in the east part of Qinzhou-Hangzhou metallogenic belt which belongs to Yangtze Block. There have no report on the precise dating for the tin-polymetallic mineralization in this district before. Here we report for the first time in-situ U-Pb data on cassiterite obtained by LA-MC-ICP-MS from the Jiangfengpo tin deposit. In this study, we obtain a ²⁰⁶Pb/²⁰⁷Pb-²³⁸U/²⁰⁷Pb isochron age of 129.7±2.5Ma (N=31,MSWD=5.5) and a ²⁰⁷Pb/²⁰⁶Pb-²³⁸U/²⁰⁶Pb concordia age of 128.3±2.5Ma (N=31, MSWD=7.6) for the cassiterite samples. These ages indicate that the Sn-mineralization took place during Early Cretaceous, which are corresponding to the Later Yanshanian magmatic event in the Pengshan area. The close temporal and spatial link between the pluton's emplacement and tin mineralization suggest that the Later Yanshanian magmatic hydrothermal events were the key factor for the formation of the Sn polymetallic deposits in the Pengshan area. The regional geochronological data show that Sn-W mineralization took place during Early Cretaceous (146~124Ma) in the southeastern margin of the Yangtze Block (SMYB), which are similar to the Cu-polymetallic mineralization ages of the Jiurui-E'dongnan ore districts on the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB) but different to the Sn-W mineralization ages of the Later Jurassic (160~150Ma) in Nanling area and the Later Cretaceous (98~76Ma) in the southeastern Yuannan and northwestern Guangxi area in South China. The available data suggested that the Sn-W mineralization in the SMYB, which was under different tectonic setting from that in Nanling and southeastern Yuannan and northwestern Guangxi area, may be influenced by the tectono- magmatism of the MLYRMB.