Economic geology of the carbonate rocks from Mesozoic Alpurai group, Peshawar basin, Pakistan

This study aims at evaluating the utilization of carbonate rocks from the Bampokha (Nikanai Ghar Formation) and Sawaldher (Kashala Formation) areas in different industries. Two varieties from the Nikanai Ghar Formation, known under the trade names as Super-white and Sunny-grey, are selected for petrographic and geochemical analysis to evaluate these as a source of calcite (CaCO3), in chemical industries. Petrographically, both the varieties from Bampokha area, are calcitic marbles that exhibit heteroblastic mosaic texture. Geochemical data coupled with X-ray diffraction and petrographic analysis confirms that the Super-white variety is very high purity marble and hence meets the specifications for different chemical industries such as iron and steel industry, glass manufacturing, flue gas desulphurization, soda ash manufacturing and water purification and effluent treatment. In contrast, the high silica (4.1 wt.%) and low calcite contents (<95 wt.%), render the Sunny-grey unsuitable for chemical industries. The rock from Sawaldher quarry, exhibiting an interlocking mosaic pattern, is calcitic marble. Minor amounts of quartz, muscovite and opaque minerals also occur. Comparing the physico-mechanical properties of the aggregate from Sawaldher marble with time-honoured international standards suggests its suitability in concrete work with ordinary portland cement and asphalt. The concrete mix, designed for Class D2 concrete, has an average 28-days compressive strength value of 518 kg/cm and thus well above the minimum targeted strength of 425 kg/cm for the mentioned class, and hence further endorses that the aggregate can produce strong concretes. This study also suggests the utilization of the studied carbonate resources on industrial scale.