Seventy two chromite specimens have been studied from Hindubagh, Harichand and Fort Sandeman areas of Pakistan. Out of these sixty seven samples were selected from Hindubagh area comprising Nisai, Saplaitorghar, Jungtroghar and North Hindubagh. Three samples from Harichand and two from Fort Sandeman were studied for purposes of comparison.
Chromites with different structures such as orbicular, nodular, banded, disseminated and chain, have been observed and are described briefly. Colour of chromites in thin section varies from brownish yellow to deep cherry red. Brownish yellow chromites have been found to have low Cr/Fe ratio as compared to deep cherry red chromites.
Some chromites showed alteration with opaque alteration products along cracks or along the grain boundaries. Such chromites showed the presence of abnormally high amount of Fe2 O3 as compared to other chromites which are without such alteration. Such chromites gave a number of sizable chromite separation on an isodynamic separator . The variation in chemistry of fractions of a chromite specimen from mine 155 is described. The main inference is that chromite fractions obtained at 0.1 Amp has Fe2 O3 16.28% as compared to the fraction separated at (0.4 Amp.) which has Fe2 O3 10.35%.
An improved scheme for chromite analysis is presented, the accuracy of which has been checked on synthetic standard.
A gradual change in chemical composition of chromites was observed from Nisai (Cr/Fe ratio 2.24-2.99) to Jungtorghar (Cr/Fe 2.52-3.75). A variation in chemistry has been found with in a mine e.g, in mine 7ML Cr/Fe ration varies -----------
Certain physical properties such as, specific gravity and micro-indentation hardness, have been determined on all the specimens, where as cell edge dimensions and Refractive indices were determined on some selected specimens. These physical properties were compared with chemistry and a relationship was found to be present, between specific gravity and chemistry of chromites from Hindubagh in the form of a mathematical expression. This can be used to estimate weight percentage of Cr2 O3 . Al2 O3 and MgO in Hindubagh chromites from known values of weight percentages of FeO, Fe2 O3 and specific gravity. The results obtained showed the error to be within 5% of the contained oxides.
A relationship was also found to exist between cell edge dimension and weights percentages of Cr2 O3 . This relationship helped to derive a method by means of which weight percentages of Cr2 O3, FeO and MgO of Hinudbagh chromites can be determined within about 5% of the contained oxides. The other two physical properties, Micro-indentation hardness and refractive indices showed no definite relationship which could be sued determine the weight percentages of the constituents oxides. However a rough conclusion that can be drawn is that chromites with a higher Al2 O3 weight percentages have higher values of Vickers hardness number and refractive index