Mineralogical and textural influence on physico-mechanical properties of selected granitoids from Besham Syntaxis, Northern Pakistan

Abstract

The Dubair-Shang granitoids are the major intrusive bodies in Besham group and are exposed along the Karakoram Highway in Besham and lower Kohistan districts. A variety of these granitoid rocks have been investigated in terms of their petrographic features and physicomechanical properties. The studied rocks are classified into four different textural varieties including Dubair mylonitized (DM), Dubair coarse grained (DCG), Shang coarse grained (SCG) and Shang foliated (SF) granitoids based on field observations and petrographic features. Petrographically quartz, potash feldspar, plagioclase and biotite are the essential minerals present in all varieties in varying amount. Beside these hornblende, chlorite, epidote, ore mineral(s) and sphene are also present in the accessory amount. As a part of the present investigation some of the mechanical and physical properties including uniaxial compressive strength (UCS), uniaxial tensile strength (UTS), specific gravity, water absorption, total porosity, and Los Angeles abrasion were also determined. The combined approach of petrographic features with the physicomechanical investigation revealed that the textural characteristics and mineralogy have a significant influence on the physico-mechanical properties of the studied rocks. It is determined that modal percentage of minerals, degree of alteration, recrystallization, grain size and shape, types of grain boundary contacts have significant effect on characteristics of these granitoids. Based on strength tests studied rocks fall in category of moderately strong to strong. The values of specific gravity, porosity, water absorption and Los Angeles are within the range permissible for their use as constructional materials except SF. Based on physico-mechanical properties and petrographic examination Dubair-Shang granitoids could be used as aggregate for the construction of road, railway tracks, embankment, and canals. Theses rocks could also be used as sills, lentils, and roofing but should not be used for load bearing masonry like bridges, tunnels, buildings, dams