Investigation of physical deterioration of Malayer granitic rocks using a new weathering coefficient (Kr4)

Abstract

The main aim of this research is to find the most appropriate weathering indices among geomechanical, chemical and petrographical indices to characterize Malayer granitic rocks. In the study area, physical weathering and hydrothermal alteration are predominant degradation phenomena. Therefore, it is necessary to distinguish between the effect of these two phenomena and chemical weathering on mineralogy as well as on geomechanical rock properties. The most important evidences of hydrothermal alteration are the selective sericitization of plagioclase and the occurrence of prehnite. Also, statistical analyses, including simple and multiple linear regressions, were applied to identify those indices that are most influenced on the progression of weathering. Based on the simple regression analysis, petrographical and chemical indices do not show any good trend by increasing weathering degrees (R 2 < 34). Although, There are some exceptions in petrographical and chemical indices such as microfracture index (MI: R 2 = 0.68), unsound minerals (UM: R 2 = 0.67), micropetrographic index (Ip: R 2 = 0.59), and Loss on ignition (LOI: R 2 = 0.75) which are sensitive to cold climate and subtle geochemical changes due to hydrothermal alterations. Also, all geomechanical parameters are good quantitative indicators for describing the degree of weathering (R 2 > 0.72). Finally, a new quantitative weathering index (Kr4) has been developed regarding quick absorption index, P-wave velocity (Vp), point load index (Is) and total porosity (n). All the mentioned parameters can be quickly and inexpensively determined by portable laboratory instruments. This new index (Kr4) has strongly correlated with weathering degrees (R 2 = 0.96). Based on some results, it seems that Kr4 could be more suitable and credible to numerically evaluate the physical weathering accompanied by hydrothermal alteration processes of the studied rocks.