Petrological studies of fourteen core samples of Bore Holes D-9A, D-10, and D-14 of Kanjamalai Magnetite deposits, Salem, Govt. of Tamil Nadu

Abstract

Fourteen core samples of the three bore holes D-9A (8-samples), D-10 (3 samples), and D-14(3 samples) of the Kanjamalai Magnetite ore deposits, near Salem, were received from the Govt. of Tamil Nadu. Comprehensive petrological studies were undertaken to find out (a) grain size (b) Magnetite-Hematite proportion (c) liberation of magnetite and hematite at 0.3mm (-35+48 mesh) size and (d) comparative grade of the various samples. The investigation has been initiated by M/S. M.N.Dastur & Co. Pvt. Ltd., Calcutta, and the consulting Engineers for the Kanjamalai mining Project were to assess the behavior of the various types of ore encountered in these deposits to ascertain the processing requirements. Samples of Bore Hole D9-A generally showed that the oxidation of the magnetite decreased with vertical depth and was practically absent in the deepest sample was devoid of the hematite. The general texture was gneissic with the siliceous gangue minerals being coarse-grained. Metallics were comparatively fine-grained finer than 0.3mm (-35+48mesh) would be necessary for the complete liberation of the metallics. Special attention must be paid to the recovery of hematite during the processing of the ore, which, otherwise, would be lost in the tailings if only magnetic separation is adopted. Samples of Bore Hole D-10 were completely devoid of hematite, which indicated a stable structural environment in this part of the deposit. The texture was gneissic to sub gneissic, granulated. It was coarse to medium-grained. Magnetite was relatively fine-grained when compared to siliceous gangue. As such, a grind size finer than (-35+48mesh) size would be necessary for the complete recovery of the magnetite during the magnetite treatment of the ore. Samples of Bore Hole D-14 showed the general effect of oxidation at the higher levels and the complete absence of this phenomenon at depth. The texture was granulated to sub-gneissic with grain size varying from medium to fine-grained. Although the siliceous minerals were comparatively coarse-grained, because of the general fine-grained nature of the metallics i.e., magnetite and hematite, a grained finer than 0.3mm (-35+48mesh) size would be necessary for their complete recovery during the concentration processes. The general grades of the various bore holes were more or less uniform as indicated by the Fe content of the various samples examined. For the Bore Hole No. D9-A, the Fe% ranged from 30.0%, although the presence of a leaner zone with Fe varying from 14% to 24% at 29’ to 39’ depth was noticed. For bore hole D-10 the Fe% ranged from 17.75 to 37.65 averaging 27.8%, while in the case of bore hole D-14, the % Fe ranged from 27.54 to 43.67 with an average of 32.0%.