Mobility and fractionation of REEs during deep weathering of geochemically contrasting granites in a tropical setting, Malaysia

Abstract

In this study we describe the mobility and fractionation of REEs in two deep (up to 30 m) tropical weathering profiles developed on two granites from the Kuala Lumpur pluton, Malaysia, sampled at Cheras and Rawang. On the basis of Na2O and K2O both are S-type granites, but Rawang has higher CaO, MgO and FeO than Cheras and lower SiO2. With respect to Al-saturation Rawang is I-type and Cheras is S-type. We compared the two profiles in terms of total REEs, magnitude and changes in Ce and Eu anomalies, REE mobility and LREE/HREE fractionation. Rawang profiles have higher REE contents, display lower mobility for most except the heaviest REEs and show higher LREE/HREE fractionation than those from Cheras. These differences can be linked to differences in primary mineralogy and degree of weathering, the latter controlling the type and volume of secondary minerals. Specifically, bowl-shaped parent-rock-normalised patterns in the Cheras saprolites appear to be a result of apatite dissolution. Moreover, moderate weathering evident in lower Mineralogical Indices of Alteration (MIA) at Cheras has conserved parent rock REE patterns and fractionation factors in the saprolites. By contrast, more intense weathering observed in Rawang profiles has produced abundant kaolinite group minerals that have preferentially retained LREE, which consequently display high LREE/HREE fractionation. This study provides important insights into the factors controlling REE mobility during tropical weathering, and its potential as an indicator of weathering intensity.

REE geochemical characteristics of titanium-rich bauxites: the Permian Kanigorgeh horizon, NW Iran

“…The secondary minerals like phosphates along with oxides and hydroxides of Fe and Mn are important scavengers for REEs (Aubert et al, 2001;Karadağ et al, 2009;Abedini and Calagari, 2013a;Yusoff et al, 2013). In this study, for determination of potential host minerals for REEs in the ores at Kanigorgeh, attempts have been made to calculate Pearson correlation coefficients between REEs and major and minor elements (Table 6).…”

“…La N / Yb N establishes the degree of fractionation of LREEs from HREEs during geochemical processes (Aubert et al, 2001;Yusoff et al, 2013), while the other 2 ratios determine the degree of fractionation between LREEs and MREEs and between MREEs and HREEs (Yusoff et al, 2013). The values of those ratios have ranges of La N /Yb N = 0.44-1.85, La N /Sm N = 0.80-5.15, and Gd N /Yb N = 0.14-3.18 (Table 4), which are indicative of relatively weak fractionations between LREEs and MREEs as well as HREEs during bauxitization.…”

Saprolitologia aplicada à gênese e às implicações ambientais de regolitos do Estado de Pernambuco

“…A micromorfologia de alguns saprolitos estudados exibe sistemas de fraturas com revestimentos e irregularidades superficiais bastante semelhantes a feições comumente descritas na literatura como fontes para a retenção e para o transporte de elementos na subsuperfície de regolitos MCVAY et al, 2004;TAYLOR et al, 2010;BRAUN et al, 2012;YUSOFF;NGWENYA;PARSONS, 2013 BAKER; SIMPSON, 1992;MCVAY et al, 2004;.…”

“…Este processo pode ser observado em horizontes de P1, P2, P4, P5, P7 e P12 (Tabela 4). O expressivo conteúdo de Na e K no complexo de troca e a presença de esmectita implicam no incremento relativo dos valores de ADA em horizontes superficiais e subsuperficiais (BRAUN et al, 2012;YUSOFF;NGWENYA;PARSONS, 2013).…”

“…Pesquisas sobre a dinâmica de colóides na subsuperfície de regolitos respaldam os resultados geoquímicos, mineralógicos e micromorfológicos aqui descritos e levam a inferir que as constituições mineralógicas de revestimentos e preenchimentos nos sistemas de fraturas dos saprolitos também podem contribuir para a retenção de possíveis contaminantes ou poluentes carreados na subsuperfície dos perfis estudados TAYLOR et al, 2010;ANDO et al, 2012;BRAUN et al, 2012;LAPANJE et al, 2012;YUSOFF;NGWENYA;PARSONS, 2013 KABATA-PENDIAS; MUKHERJEE, 2007;MICO et al, 2007).…”