Chappell Mark, Rojas Harold, Andros Charles, Acree Autumn, Masue-Slowey Yoko, Young Christine, Fowler Paige, Lotufo Elizabeth, Rowland Wesley, Wynter Michelle, Salles Marcelo, Gonzalez Leopoldo
Environmental Laboratory, U.S. Army Engineer Research & Development Center, Vicksburg, Mississippi, United States of America.
Dirección General de Minería, República Dominicana.
PLoS One. 2025 Jan 10;20(1):e0315147. doi: 10.1371/journal.pone.0315147. eCollection 2025.
This study investigates the geochemical characteristics of rare earth elements (REEs) in highland karstic bauxite deposits located in the Sierra de Bahoruco, Pedernales Province, Dominican Republic. These deposits, formed through intense weathering of volcanic material, represent a potentially valuable REE resource for the nation. Surface and subsurface soil samples were analyzed using portable X-ray fluorescence (pXRF) and a NixPro 2 color sensor validated with inductively coupled plasma optical emission spectrometry (ICP-OES). We employed compositional data analysis (CoDA) and machine learning models to estimate total REE concentrations, demonstrating that pXRF and the color sensor, when properly calibrated, are effective tools for remote geochemical exploration. The results reveal that REE concentrations increase with depth and elevation, with light REEs (LREEs) dominating the profiles. The correlation of REE concentrations with morphological soil development suggests that higher-altitude areas are enriched in REEs due to progressive weathering processes. The study also shows a strong relationship between REE concentrations and environmental factors such as latitude and elevation. While pXRF provided reliable estimates of total REE concentrations, to our surprise, the NixPro2 color sensor proved similarly accurate. The research emphasizes the practical value of the x-ray and color sensors for remote exploration, provided that a well-explored, robust calibration is performed to account for site-specific variability. These findings contribute to understanding the geochemical distribution of REEs in karstic bauxite deposits and highlight the potential for further exploration in remote, high-altitude regions. Future research should explore using these and other portable sensors, singly or combined, to predict REE speciation, for expediting information related to the environmentally sustainable extractability and potential economic feasibility of resources in expeditionary locations.
本研究调查了位于多米尼加共和国佩德内莱斯省巴霍鲁科山脉的高地岩溶铝土矿矿床中稀土元素（REEs）的地球化学特征。这些矿床是由火山物质的强烈风化形成的，对该国来说是一种潜在的宝贵稀土资源。使用便携式X射线荧光光谱仪（pXRF）和经电感耦合等离子体发射光谱法（ICP - OES）验证的NixPro 2颜色传感器对地表和地下土壤样本进行了分析。我们采用成分数据分析（CoDA）和机器学习模型来估算稀土元素的总浓度，结果表明，经过适当校准后，pXRF和颜色传感器是远程地球化学勘探的有效工具。结果显示，稀土元素浓度随深度和海拔升高而增加，轻稀土元素（LREEs）在分布中占主导地位。稀土元素浓度与土壤形态发育的相关性表明，由于渐进的风化过程，高海拔地区的稀土元素更为富集。该研究还表明，稀土元素浓度与纬度和海拔等环境因素之间存在密切关系。虽然pXRF能够可靠地估算稀土元素的总浓度，但令我们惊讶的是，NixPro2颜色传感器也同样准确。该研究强调了X射线和颜色传感器在远程勘探中的实用价值，前提是要进行充分的、稳健的校准以考虑特定地点的变异性。这些发现有助于理解岩溶铝土矿矿床中稀土元素的地球化学分布，并突出了在偏远高海拔地区进一步勘探的潜力。未来的研究应探索单独或组合使用这些及其他便携式传感器来预测稀土元素的形态，以便更快地获取与偏远地区资源的环境可持续开采性和潜在经济可行性相关的信息。
