云开地区云浮硫铁矿新元古代成矿背景及其显生宙构造剥露研究

Neoproterozoic amalgamation of the Yangtze and Cathaysia blocks is one of the key Precambrian research issues of South China. Most of the previous studies focused on the Neoproterozoic rock assemblage instead of mineral systems, and especially the Neoproterozoic deposits in the Yunkai Domain are rarely mentioned. The giant Yunfu pyrite deposit (Guangdong Province) is hosted in the Neoproterozoic Daganshan Formation. As the largest pyrite deposit in China, its metallogenic dynamics is likely important for understanding the Neoproterozoic tectonic framework of South China. Its ore-forming ages and tectonics have long been debated, and the mechanism for huge accumulation of pyrite but lack of Pb-Zn-Cu sulfides at Yunfu remains unclear. Focusing on the above-mentioned scientific issues, this project will carry out systematic structural analyses to discover the thrust-nappe structures in the Yunfu mining area and Yunkai Domain, and also select the zircon grains hosted in the ores and wallrocks at Yunfu for U-Pb and fission track dating, and then analyze the fission track ages of the apatite grains, thermobarometer of fluid inclusions and mineral chemistry. This contribution can constrain the ore-forming ages, tectonics and exhumation history, and also discover the key factors of the huge accumulation of pyrite and depletion of Pb-Zn-Cu sulfides at Yunfu. These will provide key evidence for the tectonic framework of Precambrian research and Phanerozoic reworking of the Yunkai Domain, and guide the regional deep-crustal exploration of similar mineral systems.

扬子和华夏新元古代汇聚作用的动力学过程是华南前寒武纪研究的热点，但现有成果多集中于相关的岩石组合，而对相关成矿系统的研究相对薄弱。云开是扬子和华夏地块新元古代汇聚的重要场所，其新元古代地层中产出有我国最大的单一硫铁矿床，即云浮硫铁矿。长期以来，关于该矿床精确成矿时代和成矿构造背景尚存争议，其“黄铁矿巨量富集而铅锌铜硫化物相对缺乏”的深层机理仍不清晰，是否是由于显生宙构造剥露所致有待进一步研究。本项目拟在细致矿床地质研究基础上，对厘定的不同高程容矿火山灰层和矿化层进行锆石U-Pb定年以限定其精确成矿时代；通过区域构造解析、裂变径迹、流体包裹体及矿物温压计及锆石原位Hf-O同位素等技术手段限定云浮硫铁矿新元古代成矿动力学背景，并恢复其成矿后的构造剥露史以预测可能“缺失”的铅锌铜硫化物富集带，从而为云浮矿区深部及外围勘查提供科学支撑。

新元古代扬子地块和华夏地块的汇聚作用奠定了华南大陆的基本格架，是华南前寒武纪地质研究的核心问题之一，但现有研究多集中于相关的岩石（组合），对相关成矿系统关注较少，尤其对显生宙改造/再造强烈的云开地区新元古代成矿系统的解剖研究极为薄弱。.广东云浮硫铁矿是产于云开地区新元古代地层中的同生热水沉积矿床，也是我国最大的单一硫铁矿床。长期以来，关于云浮硫铁矿的成矿时代和成矿构造背景存有争议，其成矿后的抬升剥露历史尚无人开展过专门研究。此次研究在前人研究基础上，利用黄铁矿Re-Os测年、碎屑锆石U-Pb定年、流体包裹体和Lu-Hf同位素分析等对其精确成矿时代和成矿后抬升剥露历史展开研究。其中，黄铁矿Re-Os测年获得的条带状黄铁矿的成矿年龄Py1为303.4±6.9 Ma。对不同类型黄铁矿及围岩的碎屑锆石进行U-Pb定年，得到的最新的锆石年龄约为430 Ma，表明成矿作用不晚于430 Ma。在划分成矿期（喷流沉积期、热液改造期）的基础上对流体包裹体进行温度、盐度的测定，测温结果显示石英中包裹体均一温度介于219.8~396.7℃，均值为336.6℃，主要集中于280~300℃和360~380℃两个区间；盐度介于3.9~17.2 wt.% Nacl equiv，主要集中于8~16wt.% NaCl equiv，均值为12.0 wt.% NaCl equiv，石英中包裹体中低温低盐度的特征与前人研究结果基本一致，反映了云浮硫铁矿至少存在两期成矿。碎屑锆石年龄与εHf(t) 值之间的正趋势表明，云开地区经历了太古宙陆核形成、元古宙陆缘弧后盆地以及古生代被动大陆边缘沉积发育的构造演化环境。综合以上研究可以得出，云浮硫铁矿为晚石炭世云开地区被动大陆边缘的局部坳陷盆地内形成的喷流沉积块状硫化物矿床（SEDEX）。