安徽安庆铜铁矿床钴的赋存状态、分布与富集规律研究

长江中下游成矿带是我国东部最重要的成矿带之一, 广泛发育矽卡岩型铜铁矿床且伴生Co资源, 而成矿带内的矽卡岩型铜铁矿床中关键金属Co元素的赋存状态、分布以及富集规律研究尚未系统开展。本文以矽卡岩型铜铁矿床——安庆铜矿为研究对象, 通过系统采样、显微观察、扫描电子显微镜、全岩化学分析及矿物原位LA-ICP MS微量成分测试手段, 初步估算矿床中伴生Co的资源量约为8769t, 达到中型规模, 查明了伴生Co的平均含量为166×10^-6, 综合利用潜力较大。查明了铜矿石中Co含量(平均含量为166×10^-6)明显高于铁矿石(平均含量为126×10^-6), 尤其是含铜磁黄铁矿型矿石中Co元素富集程度最高, 且计算得出磁黄铁矿、黄铁矿、磁铁矿和黄铜矿分别赋存矿石Co含量的45.1 %、52.8%、0.5%和1.6%。
此外, 矿床内不同类型矿化蚀变岩中Co含量与磁黄铁矿和黄铁矿总量具有较强的正相关性, Co主要以类质同像的形式赋存于黄铁矿和磁黄铁矿内, 黄铁矿中Co的含量变化范围较大, 早石英硫化物阶段的黄铁矿(Py1)中Co含量为258×10^-6~25920×10^-6, 晚石英硫化物阶段的黄铁矿(Py2)中Co含量为0.3×10^-6~594×10^-6, 磁黄铁矿中Co含量变化范围较小, 主要集中于311×10^-6~1181×10^-6, Co主要富集于早石英硫化物阶段, 晚石英硫化物阶段不富集。含铜磁黄铁矿型矿石中Co元素变化范围大(85×10^-6~430×10^-6)是由于矿石中黄铁矿和磁黄铁矿的含量以及黄铁矿Co含量极不均匀造成的。综合前人研究, 本次工作认为大气降水混入引起的成矿流体冷却和稀释可能是导致安庆铜矿中Co元素沉淀富集在黄铁矿和磁黄铁矿内的主要因素。

Study on the occurrence,distribution and enrichment of cobalt in Anqing copper-iron deposit,Anhui Province

The Middle-Lower Yangtze River Metallogenic Belt is one of the most important ones in eastern China, which is characterized by widespread skarn-type copper-iron deposits with associated cobalt (Co) resources. However, the occurrence, distribution and enrichment patterns of the Co element in skarn-type copper-iron deposits within this metallogenic belt have not been systematically studied. This study focuses on the Anqing copper deposit, a skarn-type copper-iron type one, and carries out a systematic sampling, microscopic observations, scanning electron microscopic and whole-rock chemical analyses, LA-ICP MS trace element and TIMA testing. The preliminary estimation of the associated Co resources in the deposit is approximately 8769 tons, indicating a medium-scale deposit with significant potential for comprehensive utilization. The average Co content of the associated minerals is 166×10-6. It was found that the Co content in copper ores is significantly higher than those in iron ores, especially in copper-bearing pyrrhotite ores, which exhibit the highest Co enrichment. The calculated ore composition shows that the magnetite, pyrite, magnetite and chalcopyrite account for 45.1%, 52.8%, 0.5% and 1.
6% of the total Co content, respectively. Furthermore, there is a strong positive correlation between the Co content in different types of mineralized altered rocks and the total content of pyrrhotite and pyrite. Co is mainly present in pyrite and pyrrhotite as solid solution and exsolution. The Co content in pyrite varies significantly, ranging from 258×10-6 to 25920×10-6 in the early sulfide stage (Py1) and from 0.3×10-6 to 594×10-6 in the late sulfide stage (Py2). The Co content in pyrrhotite shows a smaller range, mainly concentrated in between 311×10-6 and 1181×10-6. Co is primarily enriched in the early quartz sulfide stage, while there is no significant enrichment in the late quartz sulfide stage. The wide range of Co element variation (85×10-6~430×10-6) in copper-bearing magnetite ores is due to the uneven distribution of pyrite and pyrrhotite in the ore, as well as the highly heterogeneous Co content in pyrite. Based on previous studies, this work suggests that the cooling and dilution of ore-forming fluids caused by the infiltration of atmospheric precipitation may be the main factor for the precipitation and enrichment of Co in pyrite and pyrrhotite in the Anqing copper deposit.