滇西南西盟—澜沧地区土壤稀土地球化学异常的发现及找矿意义

REE geochemical anomalies in soils of the Ximeng-Lancang area in southwestern Yunnan and their discovery and their implications for ore prospecting

滇西南西盟—澜沧地区属西南“三江”造山带南段,通过1∶5万土壤地球化学测量工作,发现研究区稀土地球化学异常24个,并主要集中分布在昌宁—孟连深大断裂带上及其附近的石炭系平掌组基性火山岩、石炭—二叠系鱼塘寨组碳酸盐沉积岩地层中。通过对评序靠前的AP00稀土地球化学异常进一步进行1∶1万土壤地球化学测量、1∶1万专项地质测量和少量的轻型山地探矿工程等工作的详细解剖,首次在沉积型碳酸盐岩地层中发现了新型的风化壳型稀土矿,初步估算稀土资源量已达中型规模,取得了较好的找矿突破,拓宽了找矿思路,值得业界借鉴。通过区域地质地球化学背景和AP00稀土异常区资料的综合分析,认为AP00风化壳型稀土矿的形成是经历了4次不同地质作用逐渐富集成矿的过程,是多因复成型稀土矿。根据AP00稀土矿的浸出率较低,重稀土Y元素构造(岩浆)叠加成矿作用明显,推断在深部可能存在以钇为主的重稀土原生矿,预示着寻找重稀土矿具有较大潜力。

The Ximeng-Lancang area in southwestern Yunnan resides in the southern section of the Nujiang-Lancangjiang-Jinshajiang orogenic belt in Southwest China.The 1∶50,000 geochemical soil survey revealed 24 rare-earth-element(REE)geochemical anomalies,which are primarily distributed in the Carboniferous Pingzhang Formation mafic volcanic rocks and the Carboniferous-Permian Yutangzhai Formation sedimentary carbonate rocks within and near the Changning-Menglian deep fault zone.Furthermore,the AP00 REE geochemical anomalies ranking high in the evaluation were analyzed in detail through a 1∶10,000 geochemical soil survey,a 1∶10,000 special geological survey,and light-duty prospecting engineering in mountainous areas.A new type of REE ores in weathering crusts has been first discovered in sedimentary carbonate strata,with preliminarily estimated REE resources reaching a medium scale,suggesting a prospecting breakthrough.This finding shows a new prospecting approach,which can be referenced for similar research.As revealed by a comprehensive analysis of the regional geological and geochemical settings and the data of AP00 REE anomalies,the AP00 REE ores in weathering crusts have undergone a gradual enrichment and mineralization process involving four different geological processes,suggesting polygenetic compound REE ores.Considering the low leaching efficiency of AP00 REE ores and significant structural(magmatic)superimposed mineralization of the heavy REE yttrium,it is inferred that yttrium-dominated primary REE ores might exist in the deep part,implying high potential for heavy-REE ores.