Discovery of Ni-smectite-rich saprolite at Loma Ortega, Falcondo mining district (Dominican Republic): geochemistry and mineralogy of an unusual case of “hybrid hydrous Mg silicate – clay silicate” type Ni-laterite
Discovery of Ni-smectite-rich saprolite at Loma Ortega, Falcondo mining district (Dominican Republic): geochemistry and mineralogy of an unusual case of “hybrid hydrous Mg silicate – clay silicate” type Ni-laterite
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在法尔孔多矿区洛马奥尔特加（多米尼加共和国）发现富含镍蒙脱石的腐泥土：“混合水合镁硅酸盐 - 粘土硅酸盐”类型镍红土的不寻常情况的地球化学和矿物学
作者：
E. Tauler;J. Lewis;C. Villanova;T. Aiglsperger;J. Proenza;C. Domènech;Tamara Gallardo;F. Longo;S. Galí
含水镁硅酸盐型镍红土矿床以富镍蛇纹石和柘榴辉石为主，如多米尼加共和国Falcondo地区。最近，在Falcondo地区9个镍红土矿床之一的Loma Ortega，在腐岩带发现了丰富的镍蒙脱石。除了对Loma Ortega剖面的地球化学和矿物学特征（XRF、ICP-MS、XRD）外，还对这些ni -蒙脱石进行了首次详细的研究（μXRD、SEM、EPMA）。与世界各地红土剖面中发现的其他蒙脱石不同，Loma Ortega蒙脱石为三八面体，具有以前从未报道过的高镍含量。这些镍蒙脱石可能是由辉石和橄榄石风化作用形成的，其组成可以用贫铝富橄榄石母岩的矿物学和组成来解释。研究表明，镍红土具有复杂的矿物学特征，在风化剖面中，含水硅酸镁矿和粘土矿可局限于同一层位，具有重要的勘探意义。据此，将洛马奥尔特加镍红土矿床划分为“含水硅酸镁-粘土硅酸镁混合”型较为合适。
Hydrous Mg silicate-type Ni-laterite deposits, like those in the Falcondo district, Dominican Republic, are dominated by Ni-enriched serpentine and garnierite. Recently, abundant Ni-smectite in the saprolite zone have been discovered in Loma Ortega, one of the nine Ni-laterite deposits in Falcondo. A first detailed study on these Ni-smectites has been performed (μXRD, SEM, EPMA), in addition to a geochemical and mineralogical characterisation of the Loma Ortega profile (XRF, ICP-MS, XRD). Unlike other smectite occurrences in laterite profiles worldwide, the Loma Ortega smectites are trioctahedral and exhibit high Ni contents never reported before. These Ni-smectites may be formed from weathering of pyroxene and olivine, and their composition can be explained by the mineralogy and the composition of the Al-depleted, olivine-rich parent ultramafic rock. Our study shows that Ni-laterites are mineralogically complex, and that a hydrous Mg silicate ore and a clay silicate ore can be confined to the same horizon in the weathering profile, which has significant implications from a recovery perspective. In accordance, the classification of “hybrid hydrous Mg silicate – clay silicate” type Ni-laterite deposit for Loma Ortega would be more appropriate.