Lithium (Li), as a strategic critical metal, plays a pivotal role in the emerging energy landscape, particularly in the context of Li-ion batteries driving the new energy economy. Recently, Li-rich strata (with Li2O > 0.3 wt%) have been discovered in the Mesoproterozoic Wumishan Formation in Hebei Province, North China, suggesting a prospective Li reservoir. This study investigates these Li-rich strata using geochemical and in-situ micro-analytical techniques to explore the occurrence of Li and the formation mechanism of Li-host minerals, aiming for a comprehensive understanding of the supernormal enrichment of Li. The Li-rich samples are predominantly composed of dolomite and quartz, followed by clay minerals such as illite, interstratified illite–smectite (I/S), and chlorite, with minor amounts of K-feldspar, albite, biotite, calcite, baryte, fluorite and fluorapatite. In-situ analysis and 7Li NMR spectroscopy reveal that Li predominantly occupies the octahedral sites within the structures of authigenic illite and I/S, while its absence in clastic illite, clastic chlorite, unaltered K-feldspar, and dolomite. The presence of veined minerals (e.g., fluorite, baryte, and calcite) and a strong positive correlation between Li and F imply that post-depositional hydrothermal fluids have significantly contributed to the formation of Li-host minerals. The paragenesis of these minerals suggests that Li-bearing illite has formed through the hydrothermal alteration of K-feldspar. These Li-bearing illites subsequently transformed into Li-bearing I/S, consisting of illite-rich I/S and smectite-rich I/S, under continuous hydrothermal alteration. Lithium could have been leached from the surrounding carbonate rock and tuff through water–rock interaction and subsequently enriched by post-depositional hydrothermal fluids in specific regions, leading to mineralization. These findings provide valuable insights for targeting exploration of this promising Li resource.

中文翻译：

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中元古代五密山组富锂地层的水热套印


锂 （Li） 作为一种战略关键金属，在新兴能源格局中发挥着举足轻重的作用，尤其是在锂离子电池推动新能源经济的背景下。最近，在河北省中元古代五密山组发现了富锂地层（Li2O > 0.3 wt%），表明存在潜在的锂储层。本研究利用地球化学和原位微观分析技术对这些富锂地层进行调查，以探究锂的赋存和以锂为主体矿物的形成机制，旨在全面了解锂的超常富集。富锂样品主要由白云石和石英组成，其次是粘土矿物，如伊利石、层状伊利石-蒙脱石 （I/S） 和绿泥石，以及少量的钾长石、钠长石、黑云母、方解石、重晶石、萤石和氟磷灰石。原位分析和 7Li NMR 波谱显示，Li 主要占据自生伊利石和 I/S 结构内的八面体位点，而在碎屑岩伊利石、碎屑绿泥石、未蚀变的 K 长石和白云石中不存在。脉状矿物（例如萤石、重晶石和方解石）的存在以及 Li 和 F 之间的强烈正相关意味着沉积后热液流体对 Li-主体矿物的形成做出了重大贡献。这些矿物的共生作用表明，含锂的伊利石是通过 K-长石的热液蚀变形成的。这些含锂的伊利石随后在持续的热液蚀变下转化为含锂的 I/S，由富含伊利石的 I/S 和富含蒙脱石的 I/S 组成。 锂可能通过水-岩石相互作用从周围的碳酸盐岩和凝灰岩中浸出，随后在特定区域被沉积后热液流体富集，导致矿化。这些发现为靶向勘探这种有前途的 Li 资源提供了有价值的见解。