黔中清镇-修文铝土矿带锂的赋存状态及富集机制研究

In our country, lithium deposits are the emerging industry strategic resources. However, the development of lithium industry was faced with a conflict situation, in which “Occupying resources but highly depending on imports”. Recent studies indicate that lithium always anomalous enrichment in bauxite ore-bearing rock series in China. It has the potential of comprehensive utilization as an independent deposit or associated resources. However, the model of occurrence and enrichment mechanism of the lithium in bauxite are not well-constrained. This largely hindered the compressive utilization of lithium in bauxite. In this project, we will mainly focus on the typical sections of lithium-rich bauxites from Qingzhen-Xiuwen district in Central Guizhou Province, by using Tessier’s chemical sequential extraction experiment, correlation analysis of elements and minerals, specialization of environmental implication, and Micro-XRD to find out the enrichment regularity and the model of the occurrence of lithium, to explore the enrichment mechanism and it’s controlling factors (e.g., the relationship between bauxite mineralization and lithium enrichment, and the redox condition as well as the level of paleo-groundwater). This research will not only improving both the understanding of the low temperature geochemical properties of lithium, but also provide important scientific support for comprehensive utilization of lithium in bauxite.

锂矿是我国战略性新兴产业矿产。然而，我国锂产业发展却长期面临着“守着资源却严重依赖进口”的矛盾状况。最新研究表明，我国铝土矿含矿岩系中常见锂的超常富集，具有作为独立矿床或伴生资源综合利用的巨大潜力。然而，铝土矿含矿岩系中锂的赋存状态及富集机制尚不清楚，很大程度上阻碍了该类锂资源的清洁高效综合利用。黔中清镇-修文铝土矿带锂富集现象普遍，是《全国矿产资源规划（2006-2020年）》划定的重要矿产资源重点勘查区。本项目拟选取该区典型富锂铝土矿含矿岩系作为研究对象，采用逐级化学提取、元素及矿物相关性分析、元素及矿物的环境指示专属性分析、微区X射线衍射等手段，以期查明该区铝土矿含矿岩系中锂的赋存状态及富集规律，探究锂的富集机制及控制因素（铝土矿成矿与锂富集间的关系、地下水水位及氧化还原条件等）。该研究不仅可以促进对低温条件下锂地球化学性质的认识，还将为该类锂资源的综合利用提供重要科学依据。

针对黔中清镇-修文地区下石炭统九架炉组锂超常富集的现象，本研究选取典型剖面进行元素和矿物相关性分析、锂元素原位微区分析及锂同位素分析，获得以下认识和成果：（1）厘清了Li的分布富集规律：锂在铝土矿含矿岩系中分布不均，粘土岩锂含量最高，其次为铝土岩，铝土矿最低。富锂粘土岩的分布受控于沉积环境，偏陆相的沉积环境利于锂的超常富集；（2）查明了锂的精细赋存形式：①通过飞行时间二次离子质谱（TOF-SIMS）及原子探针（APT）等原位微区分析方法，查明Li主要以吸附态的形式赋存于蒙脱石的层间。因蒙脱石具有独特的层间阳离子交换层，具有强大的阳离子吸附能力（高达84.8mmol/100g），最多可吸附锂离子5885 ppm；（3）锂同位素示踪揭示锂的超常富集机制：富锂黏土岩剖面锂同位素示踪结果显示 [Li]与δ7Li呈显著正相关关系，表明锂的主要赋存形式为吸附态，根据趋势线推断其锂同位素特征符合结构锂和吸附锂二端元混合模型，进一步估算出蒙脱石吸附锂饱和（5885ppm）后的δ7Li约为 +10‰，低于河水的平均值+23‰，表明锂的超常富集应是成岩期吸附更低δ7Li值的孔隙水/地下水锂离子的结果。本项目的研究成果为“碳酸盐粘土型锂矿”这一新类型锂资源的提出和评价提供了重要的科学依据。