金沙江中段含锰铁矿化点的发现及其找矿前景

西金乌兰-金沙江缝合带东侧原雄松群为一套变基性火山-碎屑岩系,是否属于前寒武系一直存在争议。野外调研期间发现铁矿化线索,初步认为铁矿化与原雄松群变基性火山作用关系密切,并受到印支期二长花岗岩的改造叠加,具有较大成矿潜力。矿石多呈块状、蜂窝状、角砾状,少数呈气泡状、瘤状、绳状。矿石矿物主要为含锰磁铁矿,少量赤铁矿、褐铁矿、孔雀石及氧化残留黄铁矿。捡块样分析, TFe多在50%以上,属于含锰富铁矿。通过LA-ICP-MS锆石微区原位U-Pb同位素测年,赋矿变玄武岩的岩浆喷发时代为(228.3±2.1)Ma,表明该地段雄松群的时代为中三叠世,成矿时代也为中三叠世。含矿变基性火山岩为具E-MORB地球化学特征的拉斑玄武岩系列,指示成矿构造环境可能为小洋盆。铁矿化点与地面高磁异常基本吻合。在金沙江中段甚至更大的范围内,与中三叠世变基性火山岩系(原划雄松群)配套的高磁异常区,是寻找火山岩型含锰磁铁矿的重要方向,可能伴生铜-多金属矿化。

The discovery of the manganese-bearing iron mineralization spots in the central segment of the Jinsha River and the prospecting potential

Located in eastern Xijinwulan-Jinshajiang suture zone and composed of the rock series of metamorphic basic volcanic rocks-clastic rocks, the original Xiongsong Group has been an object of long-term controversy as to whether it belongs to Precambria or not. Some iron mineralization spots were found during the investigation,and it is thus believed that iron mineralization was closely related to the volcanism with the simultaneous superimposition of the Indosinian monzogranite, implying an excellent metallogenic condition and prospecting potential. Iron ores mainly show massive, beehive and brecciated forms, with subordinate bubble, tumor and rope forms. Ore minerals are mainly manganese-bearing magnetite and subordinately hematite, limonite, malachite and relict pyrite of oxidation. The content of TFe from the sample can be over 50%, implying richness of Fe. High resolution LA-ICP-MS zircon U-Pb in situ dating yielded the age of 228.3±2.1 Ma for meta-basic basalt as the host rock of the ore deposit, which shows that the eruption age of Xiongsong Group related closely to mineralization is Middle Triassic. The chemical characteristics of the ore-bearing meta-basic volcanic rocks are similar to those of E-MORB, suggesting the tholeiite series and implying the tectonic setting of a small ocean basin. Meanwhile, the iron ore spots are well consistent with the ground high aeromagnetic anomalies. This may constitute an important clue for finding volcanic type manganese-bearing iron deposits in the middle Jinsha River region and its adjacent areas.