GPR for mapping fractures and as a guide for the extraction of ornamental granite from a quarry: A case study from southern Brazil

This paper presents the results of an application of Ground Penetrating Radar (GPR) method for localizing fractures, unloading or exfoliation joints, massive blocks, and identifying the top of fresh granite. The reason for this work was to orient the mining operation in a way to optimize the extraction costs of large blocks of ornamental granite from a quarry in Capão Bonito region of São Paulo State, southern Brazil. Five GPR profiles using antennae of 25, 50, and 100 MHz were made, as well as six velocity soundings. The work was done in three distinct locations in the quarry: on the land surface above the quarry, along a road crossing the quarry, and in front or below the active quarry face.The results led to the definition of planes of structural discontinuity extending to 25 m depth, including inclined fractures and low-angle unloading joints; as well as the localization of massive blocks surrounded by weathered material. The inclined fractures and unloading joints appear as strong reflectors (high energy), and constitute excellent basal planes for the cutting and removal of standard-sized blocks. The location of these planes is important in the exploration process, as designing the quarrying to take advantage of these structural breaks can minimize the use of explosives and greatly facilitate the extraction of commercial-sized blocks. In addition, it was possible to delineate the regions of the quarry, where high-quality homogeneous granite was located, by the absence of strong internal radar reflectors.Knowledge of the spatial distribution of the joints and structural discontinuities, and mapping the localities of high-quality granite were fundamental for the mining engineer. This information served as the basis, and as a guide for planning the advance of the quarry front to minimize the extraction costs, resulting in significant economies for the company.