Petrography, geochemistry and physico-mechanical properties of dolerite from Oghi (Mansehra), Khyber Pakhtunkhwa, Pakistan
Ismaeel, M; Anjum, MN; Ahmed, W; Hussain, A; Sajid, M
Dolerite dykes having excellent exposures around Maira Chanser and Jodan Khatta areas of District Masehra are studied in terms of their suitability for aggregates and dimension stone using a combination of petrographic, geotechnical and geochemical characteristics. Petrographically, these rocks, known as black granites in commercial market, are fine to medium-grained having ophitic to sub-ophitic texture. Plagioclase and clinopyroxene occurs as the major mineral phases, whereas opaques, quartz, biotite, amphibole, olivine, apatite, chlorite, orthopyroxene and epidote constitute minor to accessory phases. Geochemically, these dolerites show sub-alkalic, metaluminous, tholeiitic to alkalic basalt character and fall in gabbroic category. These rocks have relatively high TiO2 contents and are ferroan in nature. The geotechnical properties such as 2 unconfined compressive strength (32702psi-34965psi), unconfined tensile strength (485psi-535psi), specific gravity (3.109 and 3.169), water absorption (0.14%-0.61%), loss Angeles abrasion (17.34%-2 2 17.36%), soundness (13.86-14.31), and flexural test values (30.065 N/mm2-30.066 N/mm2) show their suitability for construction work as aggregate for concrete and light foundation loads as well as indoor and outdoor dimension stones. The strength properties of all the studied samples have inverse ratio with the plagioclase content which is more probably due to perfect cleavage pattern of the plagioclase. The samples from Jodan Khatta show a relatively small grain size and fractured nature and demonstrate slightly weak mechanical properties as compared to Maira Chanser dolerite. Similarly, the Jodan Khatta samples show more alteration along their grain boundaries which have also affected their grain to grain relationship and thus have lower down their strength values. Moreover, their relatively fine-grained nature has also contributed to higher extent of alteration. The study confirms that mineralogical and textural variations have an important control on mechanical properties of the studied rocks. © 2019, National Centre of Excellence in Geology. All rights reserved.