Rare earth elements (REEs, ‘lanthanides’) constitute a vital commodity for technological applications. Although these elements occur at trace levels in many minerals, they can comprise major constituents of low abundance phosphate, carbonate, silicate and oxide minerals, some of which form during granite weathering. REE-phosphate phases can be a source of phosphorus for essential biomolecules and certain REEs are required by some bacterial enzymes involved in the oxidation of methanol, an important compound in the global biogeochemical carbon cycle. The mechanisms that promote the dissolution of lanthanide phosphate minerals are largely unknown, but probably vary with the lanthanide phosphate mineralogy of weathered rock and soil. Here, we studied weathering of five I-type, three S-type and one A-type granite to determine the extent of weathering of primary REE- and/or P-bearing minerals apatite, allanite and monazite, and the formation of secondary REE/P-bearing minerals. We found evidence for greater mobilisation of REE and P in weathered I-type and A-type granites than in S-types, reflecting the higher solubility of apatite and allanite relative to monazite. Although monazite persisted in highly weathered S-type granites, some alteration was detected. Secondary REE/P-bearing minerals were not detected in two S-type profiles, while spherical secondary REE/P-bearing mineral aggregates were abundant throughout the third S-type profile. Secondary euhedral REE/P-bearing crystals were abundant even in the slightly weathered I-type and A-type granite material, yet they were not detected in the highly weathered material, indicating that these minerals had dissolved. Our findings indicate that mineralogy constrains substantially, but does not control completely, lanthanide availability as a function of degree of weathering. These results have implications for predicting REE and phosphate bioavailability in soils derived from granitic rock types and suggest that highly weathered I-type granites may provide inocula for bioleaching experiments.

稀土元素（REE，“镧系元素”）是技术应用的重要商品。尽管这些元素在许多矿物中以微量存在，但它们可能包含低丰度的磷酸盐，碳酸盐，硅酸盐和氧化物矿物的主要成分，其中一些矿物是在花岗岩风化过程中形成的。REE-磷酸盐相可能是必需生物分子的磷源，某些参与甲醇氧化的细菌酶需要某些REE，甲醇是全球生物地球化学碳循环中的重要化合物。促进磷酸镧系元素矿物溶解的机制在很大程度上尚不清楚，但可能随风化的岩石和土壤中的磷酸镧系元素矿物学而变化。在这里，我们研究了五种I型的风化 三种S型和一种A型花岗岩，以确定主要的REE和/或P矿物磷灰石，尿石和独居石的风化程度，以及次要的REE / P矿物的形成。我们发现有证据表明，风化的I型和A型花岗岩中REE和P的迁移比S型更大，这反映了磷灰石和尿囊石相对于独居石的溶解度更高。尽管独居石在高风化的S型花岗岩中仍然存在，但发现了一些蚀变。在两个S型剖面中未检测到次生REE / P矿物，而在整个第三S型剖面中球形次生REE / P矿物聚集体很丰富。即使在略微风化的I型和A型花岗岩材料中，次生的具有REE / P的全金属稀土晶体也很丰富，但是在高度风化的材料中却没有检测到它们，表明这些矿物质已经溶解。我们的发现表明，矿物学作为风化程度的函数对镧系元素的可用性有很大的限制，但并不能完全控制镧系元素的可用性。这些结果对于预测源自花岗岩岩石类型的土壤中的REE和磷酸盐生物利用度具有重要意义，并暗示高度风化的I型花岗岩可能为生物浸出实验提供接种依据。