The distribution of rare earth elements in tropical granitic soil

a case study from Malaysia

Hamzah Mohamad, Abdul Ghani Rafek

    Research output: Contribution to journalArticle

    4 Citations (Scopus)

    Abstract

    A total of 93 samples of rock, altered soil representing various weathering grades from an ideal granite weathering profile exposed at a road cut along the Kuala Lumpur-Karak highway, Peninsular Malaysia, were studied. The fresh, unaltered parent rock is petrographically distinguished into two types: (1) coarse grained porphyritic biotite-muscovite granite, and (2) medium grained biotite-muscovite granite. The rock has undergone some degree of brittle deformation. A weathering index map based on the procedures suggested by Ibrahim Komoo et al. Warta Geologi 17(3), 105-109 (1991) shows the spatial distribution of unaltered to slightly altered rocks (index 2-4), weathered rocks (5-8) and residual soil (9 and 10) for the profile under study. For each sample, 11 major elements were determined using X-ray fluorescence technique (XRF) and nine rare earth elements, La, Ce, Nd, Sm, Eu, Tb, Dy, Yb and Lu, by the instrumental neutron activation analysis (INAA). All REEs decrease with increasing weathering grade, suggesting a depletion of the REEs due to weathering. The depletion rate is variable, the fastest being Sm and La. A Masuda-Coryell diagram for the three groups of samples, that is (1) fresh to slightly weathered rocks, (2) moderately to highly weathered rocks, and (3) residual soils, shows three curves with a similar pattern of negative Eu anomalies. The concentration of elements is in the order 1>2>3, suggesting strongly that the REEs diminish gradually in the course of the weathering. A rock-soil interface has been recognised to exist at weathering index 4. It is believed that at this interface, most REEs leave their primary carriers which undergo rapid breakdown, most probably plagioclase, biotite and hornblende and possibly ilmenite and apatite, into weathering solution, together with Fe2+, Ca2+, K+, Mn2+ and Mg2+. Anomalously low concentration of REEs in index 4 material supports this idea. The leached-out REEs are temporarily incorporated into newly formed secondary minerals (secondary carriers) before gradually leaving the system from index 6 onwards.

    Original languageEnglish
    Pages (from-to)617-625
    Number of pages9
    JournalJournal of Southeast Asian Earth Sciences
    Volume8
    Issue number1-4
    DOIs
    Publication statusPublished - 1993

    Fingerprint

    tropical soil
    rare earth element
    weathering
    rock
    biotite
    residual soil
    granite
    muscovite
    road
    weathering profile
    brittle deformation
    distribution
    secondary mineral
    neutron activation analysis
    ilmenite
    X-ray fluorescence
    hornblende
    apatite
    plagioclase
    soil

    ASJC Scopus subject areas

    • Earth and Planetary Sciences (miscellaneous)
    • Earth and Planetary Sciences(all)
    • Environmental Science(all)

    Cite this

    The distribution of rare earth elements in tropical granitic soil : a case study from Malaysia. / Mohamad, Hamzah; Ghani Rafek, Abdul.

    In: Journal of Southeast Asian Earth Sciences, Vol. 8, No. 1-4, 1993, p. 617-625.

    Research output: Contribution to journalArticle

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    N2 - A total of 93 samples of rock, altered soil representing various weathering grades from an ideal granite weathering profile exposed at a road cut along the Kuala Lumpur-Karak highway, Peninsular Malaysia, were studied. The fresh, unaltered parent rock is petrographically distinguished into two types: (1) coarse grained porphyritic biotite-muscovite granite, and (2) medium grained biotite-muscovite granite. The rock has undergone some degree of brittle deformation. A weathering index map based on the procedures suggested by Ibrahim Komoo et al. Warta Geologi 17(3), 105-109 (1991) shows the spatial distribution of unaltered to slightly altered rocks (index 2-4), weathered rocks (5-8) and residual soil (9 and 10) for the profile under study. For each sample, 11 major elements were determined using X-ray fluorescence technique (XRF) and nine rare earth elements, La, Ce, Nd, Sm, Eu, Tb, Dy, Yb and Lu, by the instrumental neutron activation analysis (INAA). All REEs decrease with increasing weathering grade, suggesting a depletion of the REEs due to weathering. The depletion rate is variable, the fastest being Sm and La. A Masuda-Coryell diagram for the three groups of samples, that is (1) fresh to slightly weathered rocks, (2) moderately to highly weathered rocks, and (3) residual soils, shows three curves with a similar pattern of negative Eu anomalies. The concentration of elements is in the order 1>2>3, suggesting strongly that the REEs diminish gradually in the course of the weathering. A rock-soil interface has been recognised to exist at weathering index 4. It is believed that at this interface, most REEs leave their primary carriers which undergo rapid breakdown, most probably plagioclase, biotite and hornblende and possibly ilmenite and apatite, into weathering solution, together with Fe2+, Ca2+, K+, Mn2+ and Mg2+. Anomalously low concentration of REEs in index 4 material supports this idea. The leached-out REEs are temporarily incorporated into newly formed secondary minerals (secondary carriers) before gradually leaving the system from index 6 onwards.

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