CHI Guang-cheng, WU Yue, HU Jian-fei

(Shenyang Institute of Geology and Mineral Resources, Shenyang 110032, China)

Abstract: The determination of which Spinel-group minerals occur in kimberlite from diamond mining at Mengyin, Shandong Province – chromite or spinel – has been highly controversial. In order to determine the species from the spinel-group of minerals that occur at the Mengyin mine, all of which have a complex morphology, spinel-group minerals from the mine were systematically sampled. Micro-chemical compositions of MgO, FeO, TiO₂, Al₂O₃, MnO and Cr₂O₃ were analyzed by electron microprobe on 50 spinel-group minerals. The results showed that: A, B end-members of the spinel-group minerals in kimberlite from the Mengyin diamond mine have complex compositions, and there is no easily defined chromite or spinel mineral species. Based on the chemical formula, the classification of the spinel-group minerals can be divided into seven subspecies: iron magnesium-chrome iron titanium, magnesium iron-chrome iron aluminum titanium, iron magnesium-chrome aluminum iron, magnesium iron-chrome aluminum iron, iron magnesium-chrome iron titanium aluminum, magnesium iron-chrome aluminum, and magnesium iron-aluminum chrome. The major end-member compositions of the spinel-group minerals in the Mengyin kimberlite are MgAl₂O₄, MgCr₂O₄ and FeCr₂O₄. The chemical analysis of the composition of the spinel-group minerals showed that the Mg content is higher (MgO 7.3%–11.8%), and the ratio of Fe to Mg is close to 1∶1, indicating a magnesium-rich chromite.

Key words: Mengyin mine, Shandong Province; kimberlite; spinel-group minerals; chromite; spinel; micro- chemical composition; mineral classification