Determination of the Effect of Mineralogy and Texture on the Geomechanical Parameters of Metamorphic Rocks =Détermination de l'effet de la minéralogie et de la texture sur les paramètres géomécaniques des roches métamorphiques

摘要

In the last few decades, improvements in mining methods, major increases in global demand for metals, and favorable metal prices has led the industry in mining ore deposits at increasingly greater depths below the surface, i.e. up to a few thousand meters in some cases. The probability of rock mass failure, and more particularly violent and potentially dangerous events such as rockbursts, increases when an underground excavation is carried out in deeper excavation. This increased risk of rock instability is due to several factors, including inherent qualities of rock and external conditions, such as the magnitude of in-situ stresses, dynamic disturbances, excavation sequence, and geological structures. The texture of the rocks plays a very important role in their strength parameter, which is one of the most critical factors in the stability of the underground structures. Primary rock types are generally relatively homogeneous, whereas rocks that were metamorphosed and deformed tend to have heterogeneous characteristics that influence their behavior under major stress. The mineralogy of metamorphic rocks changes according to the degree of metamorphism. Therefore, it is crucial to understand the interactions between petrophysical properties and mechanical properties of metamorphic rocks. This work presents an approach to investigating the different effects of metamorphic rock minerals on the state of the geomechanical parameters of rock by employing different statistical methods.The Westwood gold mine, situated in northwestern Québec, was selected as a case study as mining operations extend from near surface down to about 2,400 m below surface, with potential for mining at greater depth. Rockbursts have been recorded at Westwood at different depths in rocks that show contrasting mineralogical and textural characteristics. In this study, firstly, an entirely new method for determining the mineralogy composition of a large number of samples was developed. For this purpose, thin section study was used to establish the mineralogy of a group of selected samples representative of the principal lithologies present at the mine; other groups of samples were statistically grouped based on similar mineralogical characteristics and assigned to specific lithologies. This method made it possible to classify all the samples according to their mineralogy. Following that, principal component analysis (PCA) was used to determine the metamorphic minerals having the greatest influence on rock mechanics. The samples used in the study, were classified into mafic and felsic groups. Geomechanical tests were conducted in the laboratory. Then, more than 1,300 axial and diametrical point load tests (PLT) were done on the samples. Analyses of the impact of metamorphic minerals on point load index (PLI) were carried out through principal component regression (PCR) calculations. In the study of the effect of mineralogy on mafic and felsic rocks, it was found that quartz has the highest effect in axial and diametrical PLI in mafic rocks. The results show that quartz, epidote, amphibole, and feldspar are the minerals that can increase the axial PLI in felsic rocks, whereas sericite and white mica have a negative effect on felsic rocks axial PLI. Epidote, amphibole and feldspar have the positive effect on axial and diametrical PLI of mafic rock. On the other hand, chlorite and white mica have a negative effect on the axial and diametrical PLI in mafic rocks. In addition, minerals that have a positive effect on the axial test have a less positive effect on the diametrical test. The minerals that have a negative effect on the axial test have a more negative effect on the diametrical tests because of the effect of schistosity (strong planar anisotropy due to a preferential alignment of metamorphic minerals) on diametrical PLT.The effect of metamorphic minerals in volcanic rocks on the uniaxial compressive strength (UCS) and tensile strength where high-qualit