Clay weathering in shales is an important component of the global Li budget because Li is mobilized from Li-rich clay minerals and shale represents about one quarter of the exposed rocks on Earth. We investigate Li isotopes and concentrations to explore implications and mechanisms of Li isotopic fractionation in Shale Hills, a first-order catchment developed entirely on shale in a temperate climate in the Appalachian Mountains, northeastern USA. The Li isotopic compositions (δ⁷Li) of aqueous Li in stream water and groundwater vary between 14.5 and 40.0‰. This range is more than half that observed in rivers globally. The δ⁷Li of aqueous Li increases with increasing Li retention in secondary minerals, which is simulated using a box model that considers pore fluid advection to be the dominant transport process, silicate dissolution to be the source of Li to the pore fluid, and uptake of Li by kaolinite, Fe-oxides, and interlayer sites of clays to be the sinks. The simulations suggest that only those deep groundwaters with δ⁷Li values of ∼15‰ are explainable as steady state values; those fluids with δ⁷Li values > 18‰, especially near-surface waters, can only be explained as time-dependent, transient signals in an evolving system. Lithium is highly retained in the residual solid phase during chemical weathering; however, bulk soils (0.5 ± 1.2‰ (1 SD)) and stream sediments (0.3‰) have similar, or higher, δ⁷Li values compared to average bedrock (−2.0‰). This is attributed to preferential removal of clay particles from soils. Soil clays are isotopically depleted in ⁷Li (δ⁷Li values down to −5.2‰) compared to parental material, and δ⁷Li values correlate with soil Li concentration, soil pH, and availability of exchangeable sites for Li as a function of landscape position (valley floor versus ridge top). The strong depletion of Li and clay minerals in soils compared to bedrock is attributed at least partly to loss of Li through export of fine-grained clay particles in subsurface water flow. This process might be enhanced as the upper weathering zone of this catchment is highly fractured due to former periglacial conditions. The Li isotopic composition of vegetation is similar to soil clay and both are distinct from mobile catchment water (soil pore water, stream and groundwater). Extrapolating from this catchment means that subsurface particle loss from shales could be significant today and in the past, affecting isotopic signatures of soils and water. For example, clay transformations together with removal of clay particles before re-dissolution support weathering conditions that lead to a low aqueous Li flux but to high δ⁷Li values in water.

页岩中的粘土风化是全球锂预算的重要组成部分，因为锂是从富含锂的粘土矿物中调集出来的，而页岩约占地球裸露岩石的四分之一。我们调查了锂的同位素和浓度，以探讨页岩山中锂同位素分馏的意义和机理，页岩山是美国东北部阿巴拉契亚山脉温带气候下完全在页岩上发育的一级流域。锂同位素组成（δ ⁷在流水锂水溶液Li）和地下水14.5 40.0‰之间变化。该范围是全球河流观测范围的一半以上。该δ ⁷Li水溶液中的Li随次生矿物质中Li的保留量的增加而增加，这是使用Box模型进行模拟的，该模型认为孔隙流体对流是主要的输运过程，硅酸盐溶解是Li进入孔隙流体的来源，并且Li被以下物质吸收高岭石，Fe-氧化物和粘土的层间位点成为汇。该模拟表明，只有那些δ深地下水^7个‰可以解释，稳态值的~15李值; 用δ那些流体⁷栗值> 18‰，特别是表面附近的水域，仅可作为与时间相关的，瞬变信号在不断变化的系统进行说明。锂在化学风化过程中高度残留在固相中。但是，散装土壤（0.5±1.2‰（1 SD））和河流沉积物（0.3‰）的δ相似或更高。与平均基岩（-2.0‰）相比，Li值为⁷。这归因于优先从土壤中除去粘土颗粒。土壤粘土同位素贫⁷李（δ ⁷栗值降至-5.2‰）相比亲本材料，并且Δ ⁷Li值与土壤Li浓度，pH值以及Li交换位置的可用性与景观位置（谷底对垄顶）的函数相关。与基岩相比，土壤中锂和粘土矿物的大量消耗至少部分归因于地下水流中出口细粒粘土颗粒导致的锂损失。由于以前的冰川环境，该流域的上部风化带高度破裂，因此可能会增强该过程。植被的Li同位素组成类似于土壤黏土，并且都不同于流动的集水（土壤孔隙水，溪流和地下水）。从该集水区推断，意味着如今和过去，页岩的地下颗粒物流失可能非常严重，从而影响土壤和水的同位素特征。例如，水中的锂含量为⁷ Li。