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Minerals 2016, 6(2), 46; https://doi.org/10.3390/min6020046

Chromite Composition and Accessory Minerals in Chromitites from Sulawesi, Indonesia: Their Genetic Significance

1
Department of Applied Geosciences and Geophysics, University of Leoben, Peter Tunner Str. 5, A-8700 Leoben, Austria
2
Department of Geological Engineering, Gadjah Mada University, Jl. Grafika 2, Bulaksumur, 55281 Yogyakarta, Indonesia
*
Author to whom correspondence should be addressed.
Academic Editor: Raymond M. Coveney
Received: 16 March 2016 / Revised: 12 May 2016 / Accepted: 16 May 2016 / Published: 20 May 2016
(This article belongs to the Special Issue Advanced Research on Accessory Minerals)
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Abstract

Several chromite deposits located in the in the South and Southeast Arms of Sulawesi, Indonesia, have been investigated by electron microprobe. According to the variation of the Cr# = Cr/(Cr + Fe3+), the chromite composition varies from Cr-rich to Al-rich. Small platinum-group minerals (PGM), 1–10 μm in size, occur in the chromitites. The most abundant PGM is laurite, which has been found included in fresh chromite or in contact with chlorite along cracks in the chromite. Laurite forms polygonal crystals, and it occurs as a single phase or in association with amphibole, chlorite, Co-pentlandite and apatite. Small blebs of irarsite (less than 2 μm across) have been found associated with grains of awaruite and Co-pentlandite in the chlorite gangue of the chromitites. Grains of olivine, occurring in the silicate matrix or included in fresh chromite, have been analyzed. They show a composition typical of mantle-hosted olivine. The bimodal composition and the slight enrichment in TiO2 observed in some chromitites suggest a vertical zonation due to the fractionation of a single batch magma with an initial boninitic composition during its ascent, in a supra-subduction zone. This observation implies the accumulation of Cr-rich chromitites at deep mantle levels and the formation of the Al-rich chromitites close or above the Moho-transition zone. All of the laurites are considered to be magmatic in origin, i.e., entrapped as solid phases during the crystallization of chromite at temperature of around 1200 °C and a sulfur fugacity below the sulfur saturation. Irarsite possibly represents a low temperature, less than 400 °C, exsolution product. View Full-Text
Keywords: chromitites; platinum-group minerals; olivine; ophiolite; Sulawesi; Indonesia chromitites; platinum-group minerals; olivine; ophiolite; Sulawesi; Indonesia
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Zaccarini, F.; Idrus, A.; Garuti, G. Chromite Composition and Accessory Minerals in Chromitites from Sulawesi, Indonesia: Their Genetic Significance. Minerals 2016, 6, 46.

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