PETROGRAPHIC AND PHYSICO-MECHANICAL PROPERTIES OF GRANITOIDS FROM BIBIOR AREA, DISTRICT UPPER DIR, KHYBER PAKHTUNKHWA, PAKISTAN

Abstract

The Bibior area belongs to the western part of Kohistan Batholith in Kohistan Island Arc. Geographically the area is located at the south of the Dir Town, Upper Dir District, NW Pakistan. The rocks exposed in the study area are mainly granites, and amphibolites. The granitic rocks i.e., porphyritic granite, coarse-grained foliated granite, and fine-grained granitearound the Bibior area were study to determine their petrographic characteristics and mechanical properties. Field observations and petrographic examination revealed that the granitic rocks were broadly porphyritic in texture. However, fine-grained equigranular and coarse-grained foliated varieties were also found at places. The petrographic examination showed that the porphyritic granite, foliated granite and fine-grained granite are essentially composed of quartz, plagioclase, and alkali feldspar which also contributed as ground-mass in some of the representative samples. The minor mineral assemblage is biotite, muscovite and hornblende with accessory amount of sericite, chlorite, opaque-ore minerals, zircon, titanite, epidote, apatite, garnet, and hematite. The quartz grains mostly display undulose extinction and are strained. To determine the behavior and durability of the granitic rocks as construction materials, physical and mechanical properties were studied, including water absorption, specific gravity, porosity, unconfined compressive strength (UCS), and unconfined tensile strength (UTS). Three different texture varieties (fine-grained granite, coarse grained foliated and porphyritic granite) were study according to ASTM practices, and the tests revealed that these rocks had average values of water absorption 0.255-0.326%, specific gravity 2.680-2.710 kg/cm3, porosity 0.675-0.87%, UCS 72.3- 129MPa, andUTS 5.74-12.23MPa.The petrographic and physico-mechanical properties relationship through statistical analysis shows that the mineral composition, texture, and lower amount of flaky minerals make rocks stronger. The fine-grained granitic rocks from Bibior area having higher strength values due to their finer grain size compare to coarse-grained foliated and porphyritic varieties.The strength tests show that allvii varieties from the area can be used in construction projectssuch as dimension stone and embankment fill.