Geochemical Behavior of Trace- and Rare-Earth Elements in the Hydrothermal Alteration Facies of the Cijulang Area, West Java, Indonesia

Myo Min Tun,I Wayan Warmada,Koichiro Watanabe,Kotaro Yonezu,Arifudin Idrus,Agung Harijoko

doi:10.4236/ojg.2019.95019

Abstract

This study examines the behavior of trace- and rare-earth elements (REE) in different hydrothermal alteration facies (silicic, advanced argillic and argillic) of Cijulang high-sulfidation epithermal gold deposit, West Java, Indonesia. The results of the study indicate that remarkable differences in the behavior of trace elements and REE are observed in the studied alteration facies. All REE in the silicic facies are strongly depleted. In advanced argillic facies, Heavy rare-earth elements (HREE) are strongly depleted whereas light rare earth elements (LREE) are quite enriched. REE concentrations in the argillic facies show little or no variation with respect to fresh rock counterparts. A strong depletion of REE in the silicic facies is likely to be favored by the highly acidic nature of the hydrothermal fluids, the abundance of complexing ions such as Cl ˉ, F ˉ, and in the hydrothermal solutions and the absence of the secondary minerals that can fix the REE in their crystal structures. An apparent immobility of LREE in advanced argillic facies is possibly due to the presence of alunite. The immobility of REE in the argillic facies suggests the higher pH of the fluids, the lower water/rock ratios and the presence of the phyllosilicates minerals. -

Highlights

In the past, rare-earth elements (REE) and high-field strength elements have been accepted as rather immobile elements, unaffected by hydrothermal alteration process and metamorphism
This study examines the behavior of trace- and rare-earth elements (REE) in different hydrothermal alteration facies of Cijulang high-sulfidation epithermal gold deposit, West Java, Indonesia
Comparisons were made between precursor rocks and each alteration facies in order to understand the possible fractionation processes where REE could have been encountered during hydrothermal alteration (Figures 6(a)-(d)). (La/Yb)cn ratio was calculated in order to observe the enrichment of light rare earth elements (LREE) over Heavy rare-earth elements (HREE)

Summary

Introduction

REE and high-field strength elements have been accepted as rather immobile elements, unaffected by hydrothermal alteration process and metamorphism. The detailed descriptions of REE mobility in the hydrothermal fluids and hydrothermally-altered rocks of some mineralized systems have been discussed elsewhere ([1]-[16]). The mobility of REE in the hydrothermal fluids is significantly controlled by low pH, high water/rock ratios and the ability of complexing ions such as CO32− , F−, Cl−, PO34− and SO24− ([1] [7] [17]). They are preferentially complexed by Cl− and SO24− in acid conditions [18] [19]. HREE are favorably concentrated in later products of hydrothermal systems as they form more stable complexes with some ligands and exist in solution longer than LREE ([20] [21])

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Conclusion