Assessing the Geomechanical Behaviours of Skarn-Related Hydrothermal Veins in Intact Laboratory Tests

Intrablock structures such as hydrothermal veins and stockwork have been observed to control additional or delayed development of ground failures in deep mines and tunnels. Key geomechanical parameters for excavation design are typically measured using unconfined compressive strength (UCS) laboratory tests of intact rock, but it is currently standard practice to test only homogeneous samples and discard or ignore heterogeneous rocks such as those with veins. To improve the accuracy of geotechnical design and the understanding of rockmass behaviours in complex rockmasses, it is therefore critical to measure heterogeneous rocks in the laboratory. This paper presents UCS test results of 29 samples from the Legacy skarn ore deposit in New Brunswick, Canada, including 3 quartz-plagioclase granodiorite units with subsets of matrix (homogeneous) and vein (heterogeneous) types. Strain-based methods were used to calculate elastic properties, peak strength, crack initiation, and crack damage. The vein-type samples were on average softer, weaker, and had lower brittle thresholds than their matrix counterparts. Variability within the vein-type samples is attributed to vein mineralogy and geometry. Significant differences between the matrix-types of the 3 units are explained by their mineral compositions and differential grain size, which is controlled by their different alterations (potassic, sericitic, and sausseritic).