Petrographic, physical–mechanical and fracture modeling of granites: an integrated approach to evaluating the stone reserves and mineral deposits of Ment Granite (western Meseta, Central Massif of Morocco)

Abstract

Promising information provided here concerns the stone's potentiality for building purposes and the evaluation of mineral deposits associated with granites, through integrated fieldwork, petrographic, and physico-mechanical studies of Meseta Ment granite massif from Morocco. Hence, the detailed field description and mapping of the joint sets and related structural context of diverse mineralized veins are conducted. The joint sets have mainly NE-SW and NW–SE to NNW-SSE geographic trending, with their average aperture of 2 cm, the average length (Jl) generally exceeds 4 m, the average joint spacing (Js) of about 0.65–1.58 m, and about 0.97–7.12 joints/m³ for the volumetric number of joints (Jv). Accounting for these joint sets parameters, a multiple regression model was used to propose a new granite fracture index (GFI). The correlation between petro-mineralogical and physico-mechanical characteristics shows that the studied coarse-grained rocks (e.g., porphyritic granite) have a uniaxial compression strength (UCS) value of about 93.8 MPa, attributed to the following features: megacrystalline texture, network of intragranular microfractures (80%), significant modal concentration of feldspar (36%), low quartz content (27%) and high porosity (1.65%). Conversely, the other studied medium-grained granitic types, monzogranites with high UCS (123 MPa) and leucogranites with UCS (119 MPa), exhibit opposite properties. These results give evidence that some parts of this granite can provide several voluminous blocks, reaching 1 × 2.5 × 3.5 m³ with remarkable quality. The mineral deposit veins (quartz, tourmaline, baryte) were controlled by the circulation of the mineralized fluids, through the interplay of the joints with active faults during the late-Variscan tectonic phase.