NR  Vol.9 No.2 , February 2018
Mineralogical and Petrographic Characteristics of Indium and REE-Bearing Accessory Phases in the Kymi Granite Stock, Southern Finland

The Wiborg rapakivi batholith (1.64 Ga) in southeastern Finland with documented occurrences of REE, indium and Zn-Cu-Pb sulphide mineralization was studied. Hydrothermal greisen and quartz vein type Fe-Sn and Zn-Cu-Pb are found in the Kymi granite stock as intrusions. They are enriched with indium and rare earth elements, with roquesite (CuInS2) being a major indium- carrier, whereas monazite (Ce), allanite (Ce), bastn&#228;esite (Ce), xenotime-(Y) and thorite are the main REE carriers. Combination of optical and field emission scanning electron microscopy (FE-SEM) and electron probe microanalysis (EPMA) were used to study the indium and REE-bearing mineral assemblages. EPMA of roquesite found in galena had a composition of 26.16% S, 0.02% Fe, 25.06% Cu, 0.03% Zn, 1.06% As, 0.31% Sb and 47.14% In. Substitution reaction Pb2+S2-<->Cu+In3+S2- is the cause of the incorporation of indium in the galena structure. The majority of the LREE are carried by monazite, bastn&#228;esite and allanite, and the HREE by xenotime and zircon. There is a partial solid solution between monazite and xenotime with minor or trace amounts of LREE in xenotime grains (6.0 wt%). LREE (>95 mol% LREE) and less than 5 mol% HREE + Y reflects the enrichment of chondrite-normalized REE of the monazite grains of the Kymi granite stock. The xenotime grains (small and irregular) main composition contains 71 - 76 mol% YPO4, 16 - 27 mol% HREE, and 6 - 8 mol% LREE. It is believed that indium and REE-mineralization presence is due to the combination of magmatic and postmagmatic processes, particularly at later stages by fluid fractionation.

Cite this paper
Al-Ani, T. , Ahtola, T. , Kuusela, J. and Al-Ansari, N. (2018) Mineralogical and Petrographic Characteristics of Indium and REE-Bearing Accessory Phases in the Kymi Granite Stock, Southern Finland. Natural Resources, 9, 23-41. doi: 10.4236/nr.2018.92003.
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