Abstract: Portugal produces a great diversity of ornamental stones. Besides the internationally known white and pink marbles, also light cream limestones are produced, as well as grey, yellow and pink granites, and dark grey slates. A first exercise is presented on the evaluation of the available resources of ornamental stones in the whole Portuguese territory. The results show a total availability of 410 million cubic meters, of which 274 million refer to granite, 76 million to limestone, 51 million to marble, and 9 million to slate.
Abstract: Soapstone is a talc and carbonate containing metamorphic ultramafic rock commonly found in greenschist-amphibolite facies greenstone belts. The regional metamorphism and shear zones as pathways for CO2 containing water fluids are interpreted to have been essential to the formation of soapstone. In spite of the supposed uniform metamorphic conditions favourable to talc-carbonate soapstone, also unaltered serpentinites are usually found in the same location areas and deposits. The objective of this study is to define the bulk chemical response of ultramafic rocks to form soapstone in hydration-carbonation metamorphic processes. Thermodynamic calculations and pseudosection modelling indicate that soapstone is most likely to occur in high silica low magnesium ultramafic sequences, because they turn to talc-carbonate even with very low CO2 content of metamorphic fluids. This is a new approach to classify and locate potential deposit areas in soapstone exploration.
Abstract: “Alpalhão granite”, also called SPI, is used as a high quality ornamental stone for interior and exterior applications. It is fine grained and equigranular, and has disseminated feldspar phenocrysts showing a homogeneous bluish grey colour. The SPI was mapped and scanlines (14) and drill cores (4) were carried out for lithofacies and joints characterization, besides petrographical study. Three of the 5 granite outcrops were studied regarding their potential for ornamental blocks exploitation (Carvalhal, Pinheiral and Ribeira de Sor). The Carvalhal area has generally no potential, due to intense fracturing and frequent heterogeneities except for drill core SCA1 area. The Pinheiral area has been exploited in all its extent, but still assures 368,800m3 estimated resources of good granite at depth. Ribeira de Sor area presents a good potentiality for commercial blocks in the eastern zone and a limited potential in the western area due to subsurface fracturing and chromatic changes.
Abstract: There are several different methodologies for the evaluation of the reserve of a mineral deposit. Traditionally, classic methods of volume computation for mineral deposits have been used to evaluate the reserve according to its commercial quality. Nevertheless, in previous works it has been demonstrated the functionality of the advanced kriging techniques applied to granite batholiths. Comparing fuzzy kriging techniques with universal classical kriging, it was concluded that the fuzzy techniques had good results for planning the selective mining of the ornamental rock deposit. Since geostatistical methods had good results, these techniques are applied to a metallurgical quartz deposit in this work. The objective of the investigation is to develop the most adequate technique for the determination of the different material qualities in this type of deposits, where the chemical composition of the mineral (aluminium oxide and impurity contents) mainly determines the grade. The obtained results show that the compositional kriging technique is more adequate than fuzzy methods for this type of deposits, allowing a sufficiently coherent prediction of the distribution of grades in the deposit. Based on the results, a 3D geostatistical model composed of cubed cells was done as well. The model provides a visual tool, easy to put into practice for the exploitation management. Keeping all this in mind, the selective mining of the reserves would be possible, being that fact necessary to compete in the rising, competitive world market.
Abstract: Exploitation and processing of small stone blocks and tombolons has a major impact on profitability. It is pointed out that the natural stone needs to be rationally used in deposits. Resources of rock mass tend to be greatly increased due to the utilization of different sizes of blocks in deposits or quarries. This approach encourages the application of Lasky's relationship in the deposits of natural stone and quarries. Based on this relationship we can simply say that if the sizes of stone blocks and other stone products decrease arithmetically, then reserves increase geometrically or exponentially. On the presented examples, the utilization of the rock mass was analysed by the application of two different technologies of exploitation. Besides, if the exploitation of stone blocks of different sizes achieves high utilization of the rock mass, then exploitation of aggregates and fillers increases much more. It is necessary to emphasize the existence of the border area based on favourable discontinuity density and spatial discontinuity position. Decision should be made whether to apply I or II variant of the exploitation (making vertical and horizontal cuttings or separation of the blocks along natural discontinuities, or using slanting cuts). The example is shown and analysed as a two-dimensional problem.
Abstract: Fracturing is the most limiting factor in the extraction of large blocks of granite for gang saw processing and should be carefully studied in the exploration stage. This paper presents the results of the fracturing evaluation of the granite from the quarries of Mondim de Basto, located in the north of Portugal. This very weathered granite has a high market demand and its commercial value is controlled by its yellowish brown colour. The fracturing was evaluated based on the mean/median joint spacing, as well as the volumetric joint count. The results stress the difficulty in obtaining large blocks since few places have the appropriate degree of jointing.
Abstract: The current socio-economic situation, characterized by energy problems and environmental concerns, urgently requires an innovative intervention. Such action should be carried out in order to improve competitiveness and the strength of companies in general, and those belonging to the natural stone sector in particular. Production processes provide the largest source of data within a factory and it is therefore necessary to carry out an energy analysis, as it is a prerequisite for informed decision-making. This energy analysis would identify those areas where most energy is consumed. Consequently, an energy analysis was conducted on two of the most representative production processes (slab and tile production). First of all, researchers analysed each stage of the production process using IDEF0 standard notation. Previously, the power consumption was monitored from both electrical and thermal perspective and, using several energy indicators, an energy balance had been carried out. As a result of this analysis, the significance of electricity compared to gas was clearly identified; the analysis also showed that cutting and abrasive processes were more critical from an electrical point of view (in that order). Another important finding was that related to thermal energy: reinforcement processes were those with the greatest significance (and in particular those performed in ovens). Based on the conclusions of the energy analysis, it was possible to establish new research lines: design of cutting disc and multiblade framesaws, microwave curing technology applications, etc. Those research lines would therefore provide the most significant beneficial effects on the environment and energy saving and, hence, companies can overcome the current economic situation.
Abstract: The sawing of granite blocks using multi-blade gangsaws and an abrasive mixture is one of the most complex operations in the transformation of commercial rocks. Many of the technological advances in sawing equipment have been accompanied by a mere handful of studies on the intrinsic properties of the rock that influence the sawing process. To optimize this process, it is vital to consider the rock as a “truly natural product”, keeping in mind that there is no quality control in its genesis. Thus, it is a material that has diversity in its characteristics and needs a technological control that considers, among other variables, the minerals’ relationships and ratios, namely: texture, structure and degree of microcracking and rock alteration. These peculiarities respond differently to the set of requests imposed during sawing, as for instance abrasion resistance and the impact of the blades in the gangsaw machines. This paper presents the study results on the quality of the sawing process developed by researchers at the Geotechnical Engineering Department of the São Carlos School of Engineering - São Paulo University. The surface quality of the finished slabs is the major determinant of the volume of material to be removed in subsequent polishing operations, thus influencing the final cost of the product. This quality was determined by using equipment capable of carrying out direct measurements of the roughness and coefficient of dynamic friction of the slab surface. The measurements carried out on three types of Brazilian siliceous dimension stone slabs showed differences in the sawing speed and industrial process costs. The roughness values obtained, together with the test results for the uniaxial compressive strength, Amsler wear, sawability, coefficient of dynamic friction and petrographic analysis, showed that the rock texture has the most important influence on the production cost of polished slabs.
Abstract: The objective of this work is to present a new laboratory testing methodology suitable for estimate the forces generated during multiple blade gangsawing employed on marble and limestone. This methodology allows analysing the tool behaviour aiming to contribute for developing new products and/or optimize the working conditions for processing different classes of stones. In the present research, 3 different diamond linear blades were tested against 2 types of stones (limestone and marble), studying the effect of two working parameters. The linear blades differ in the characteristics of the segments: size of diamond grit and type of metallic binders used to embed the diamond. The classification equipment used in this work consists in a special bridge cutting machine incorporating a tailored instrumentation / sensing system to control the working conditions while all the necessary cutting outputs are monitored and stored by special software. Taking into account the output parameters measured to evaluate the tool behaviour (vertical and horizontal forces, electric energy consumption, vibrations measured by accelerometers and tool wear); it is possible to classify and select tools with relation to the efficacy of the cut.