中国地质科学院地质研究所袁学银、杨志明等通过实验证据揭示了碳酸岩中稀土元素的运移和矿化过程。该研究于2024年7月5日发表于国际一流学术期刊《科学进展》杂志上。

据介绍，碳酸盐型稀土矿床的成因一直是研究的热点，但岩浆-热液作用对稀土的运移和成矿的控制作用仍存在争议。

该实验对稀土(氟)碳酸盐矿物在高达850°C和11.6kbar的碱性碳酸盐盐水熔体中的溶解和结晶进行了研究。结果表明，稀土元素可溶于Na₂CO₃盐水熔体中，在650℃以上的温度下，稀土元素的浓度重量超过8%。钙和/或氟化物的加入对稀土元素的迁移影响极小，而二氧化硅的引入使稀土元素的溶解度降低了一半，这是由于在550°C以上形成的铈磷灰石。

冷却后，钠和稀土结合，在富钠盐水熔体中结晶成碳酸钠矿物或碳硅钙石中，即使在氟饱和时也是如此。然而，尽管卤水熔体中含有大量的铁或铝硅酸盐，但氟碳酸盐中的稀土矿化发生在碱性硅酸盐矿物中充分的钠沉淀之后，从而揭示了硅酸盐和碳酸钠如何控制稀土矿化。

附：英文原文

Title: Experimental evidence reveals the mobilization and mineralization processes of rare earth elements in carbonatites

Author: Xueyin Yuan, Zhiming Yang, Robert A. Mayanovic, Zengqian Hou

Issue&Volume: 2024-07-05

Abstract: Whereas the genesis of carbonatitic rare earth element (REE) deposits has long been a focus of study, the controls on mobilization and mineralization of REEs during magmatic-hydrothermal processes still remain open to debate. Here, we present our investigation of the dissolution and crystallization of REE (fluor)carbonate minerals in alkaline carbonate brine-melts up to 850°C and 11.6 kbar. Our results show that REEs are soluble in Na₂CO₃ brine-melts, achieving concentrations exceeding 8 weight % at temperatures above 650°C. The addition of calcium and/or fluoride has minimal impact on REE mobilization, whereas introduction of silica suppresses REE solubilities by half, due to britholite formation above 550°C. Upon cooling, sodium and REEs combine to crystallize in burbankite or carbocernaite in sodium-enriched brine-melts, even at fluoride saturation. However, while the brine-melts contain substantial ferro- or aluminosilicate, REE mineralization in fluorcarbonates occurs after sufficient sodium precipitation in alkaline silicate minerals, hence revealing how silicate and sodium carbonate govern REE mineralization.

DOI: adm9118

Source: https://www.science.org/doi/10.1126/sciadv.adm9118