International Journal of Mining & Geo-Engineering
Volume:48 Issue: 1, Winter and Spring 2014

The helicopter-borne electromagnetic (HEM) frequency-domain exploration method is an airborne electromagnetic (AEM) technique that is widely used for vast and rough areas for resistivity imaging. The vast amount of digitized data flowing from the HEM method requires an efficient and accurate inversion algorithm. Generally, the inverse modelling of HEM data in the first step requires a precise and efficient technique provided by a forward modelling algorithm. The exact calculation of the sensitivity matrix or Jacobian is also of the utmost importance. As such, the main objective of this study is to design an efficient algorithm for the forward modelling of HEM frequency-domain data for the configuration of horizontal coplanar (HCP) coils using fast Hankel transforms (FHTs). An attempt is also made to use an analytical approach to derive the required equations for the Jacobian matrix. To achieve these goals, an elaborated algorithm for the simultaneous calculation of the forward computation and sensitivity matrix is provided. Finally, using two synthetic models, the accuracy of the calculations of the proposed algorithm is verified. A comparison indicates that the obtained results of forward modelling are highly consistent with those reported in Simon et al. (2009) for a four-layer model. Furthermore, the comparison of the results for the sensitivity matrix for a two-layer model with those obtained from software is being used by the BGR Centre in Germany, showing that the proposed algorithm enjoys a high degree of accuracy in calculating this matrix.

The uniaxial compressive strength (UCS) of intact rocks is an important geotechnical parameter required for designing geotechnical and mining engineering projects. Obtaining accurate estimates of the rock mass UCS parameter throughout a 3D geological model of the deposit is vital for determining optimum rock slope stability, designing new exploratory and blast boreholes, mine planning, optimizing the production schedule and even designing the crusher’s feed size. The main objective of this paper is to select the preferred estimator of the UCS parameter based on accuracy performance using all the available geological-geotechnical data at the Sarcheshmeh copper deposit, located 160 km southwest of Kerman City, in south-eastern Iran. In this paper, an attempt is made to estimate the spatial distribution of the UCS parameter using commonly-used statistical-structural and geostatistical methods. In order to achieve the aim of the current study, the UCS parameter was measured along with other qualitative geological properties, including the rock type, weathering, alteration type and intensity of core samples taken from 647 boreholes. The 3D distribution of the UCS parameter is obtained using different algorithms including statistical-structural (the nearest-neighbour technique), linear (ordinary Kriging) and nonlinear (indicator Kriging) geostatistical methods. After estimating the UCS parameter at block centres using the above-mentioned methods, the performance of each method is compared and validated through 21 set aside borehole data. The assessment of selecting best estimator of UCS parameter is based on scatter plots of the observed versus estimated data plus the root mean square error (RMSE) statistics of the differences between observed and estimated values for 21 set aside borehole data. Finally, due to the special characteristics of the UCS spatial variability, it is concluded that the nearest-neighbour method is the most appropriate method for estimating the UCS parameter in porphyry copper deposits.

Understanding the performance and role of each formation in a petroleum play is crucial for the efficient and precise exploration and exploitation of trapped hydrocarbons in a sedimentary basin. The Lorestan basin is one of the most important hydrocarbon basins of Iran, and it includes various oil-prone potential source rocks and reservoir rocks. Previous geochemical studies of the basin were not accurate and there remain various uncertainties about the potential of the probable source rocks of the basin. In the present research, the geochemical characteristics of four probable source rocks of the Lorestan basin are studied using Rock-Eval pyrolysis and discriminant analysis. In achieving this goal, several discriminant functions are defined to evaluate the discriminant factor for the division of samples into two groups. The function with the highest discriminant factor was selected for the classification of probable source rocks into two groups: weak and strong. Among the studied formations, Garau and Pabdeh had the richest and poorest source rocks of the Lorestan basin, respectively. The comparison of the obtained results with the previous literature shows that the proposed model is more reliable for the recognition of the richness of source rock in the area.

Considering the fact that rocks fail faster under tensile stress, rock tensile strength is of great importance in applications such as blasting, rock fragmentation, slope stability, hydraulic fracturing, caprock integrity, and geothermal energy extraction. There are two direct and indirect methods to measure tensile strength. Since direct methods always encompass difficulties in test setup, indirect methods, specifically the Brazilian test, have often been employed for tensile strength measurement. Tensile failure is technically attributed to crack propagation in rock. Fracture mechanics has significant potential for the determination of crack behaviour as well as propagation pattern. To apply Brazilian tests, cracked disc geometry has been suggested by the International Society for Rock Mechanics ISRM. Accordingly, a comprehensive study is necessary to evaluate stress field and stress intensity factor (SIF) around the crack in the centre of the specimen. In this paper, superposition principle is employed to solve the problem of cracked straight-through Brazilian disc (CSTBD), using two methods of dislocation and complex stress function. Stress field and SIF in the vicinity of the crack tip are then calculated. With the proposed method, the magnitude of critical load for crack initiation in structures can be predicted. This method is valid for any crack of any arbitrary length and angle. In addition, numerical modelling has been carried out for the Brazilian disc. Finally, the analytical solution has been compared with numerical modelling results showing the same outcome for both methods.

Slope stability analysis is a geotechnical engineering problem characterized by many sources of uncertainty. In slope stability computations, some of these sources are encountered, such as geological details missed in the exploration program, estimation of soil properties that are difficult to quantify and many other relevant factors. Therefore, accurate reproduction of the spatial variability in the field could be essential to decrease uncertainty. The Sabzkuh-Choghakhor water conveyance tunnel is currently under construction using the NATM and TBM tunnelling methods in the Zagros Mountains in south-western Iran. In the slope stability assessment of the Sabzkuh tunnel portal, despite adequate geotechnical investigations, field studies have not been performed with appropriate accuracy. A landslide and collapse has occurred in a part of the portal due to tunnel excavation. In this paper, the importance of having a precise and predetermined schedule for selecting site location, monitoring, complexities of the geological model, uncertainty and its effects on the stability of the trench were investigated and the necessity of comprehensive slope management was emphasized.

Adopting a policy and deciding on long-term investment in the mining industry by a government or private sector actors depends strongly on the ability to predict the scarcity of mineral reserves. Change in scarcity of mineral reserves is a function of several technological and non-technological factors. Among them, change in technology is the most significant factor affecting scarcity. This paper aims to investigate the relationship between mineral scarcity changes and technological changes. In this study, the effective factors on mineral scarcity were initially considered, and the main and most commonly proposed approaches in the field of scarcity were briefly analysed. The problems associated with these approaches in explaining the relationship between scarcity and changes in technology are then discussed. These approaches are mainly limited to the past available data, whose direction is the development “from scarcity to technological changes”; therefore, they are inefficient in predicting scarcity due to technological changes. To overcome such limitations, a chain technology method was introduced with an approach moving “from technological changes to scarcity”. In this approach, scarcity is firstly explained based on the objective technological changes, and secondly it is related to some technologies affecting scarcity, such as mineral exploration, exploitation, mineral processing, metal production, consumer goods and recycling of scrap metals. The results obtained from this paper can be effectively used to make decisions regarding investment in the mineral industry.

Many studies have considered the effects of suspension properties on the dewatering process but few have focused on ore properties. Thus, the present work studied the effects of ore properties (density, particle size, mineralogy) on the dewatering process based on lab and pilot experiments. A hydrocyclone was used to prepare the required samples for the experiments. To study the effects of mineralogical properties, the sedimentation behaviour of hydrocyclone feed and underflow samples were compared. It was observed that the free-settling velocity of feed (2 to 6mm/sec) was less than in the underflow sample (2 to 7mm/sec) and the final concentration of underflow sample (0.45 to 0.48t/m3) was more than the feed sample (0.44 to 0.47t/m3). Additionally, to study the effects of particle size and density, the sedimentation behaviour of hydrocyclone overflow and feed samples were compared. The settling velocity and final concentration of overflow sample were obtained at 0.15 to 0.4mm/sec and 0.32t/m3, respectively, which was significantly less than the feed sample. This was due to the amount of clay reduction in the underflow sample and particle size and density reduction in the overflow sample. Following on, the pilot experiments were carried out. It was observed that the bed formation of the feed sample tended to overflow in the sample at low flux (10t/m2/day) and tended to underflow in the sample at high flux (28.5t/m2/day). This meant that the long time at lower flux created an opportunity for fine particles to settle easily, similar to coarser particles and as such, ore properties did not play a decisive role in bed formation, but their effects appeared instead at higher flux. Furthermore, it was observed that the underflow concentration increased by decreasing the flux from 28.5 to 10t/m2/day. These increasing amounts were 0.05t/m3 and 0.12t/m3 in hydrocyclone overflow and underflow samples, respectively, at a height of 2.5 metres. This meant that the compressibility and permeability of the hydrocyclone underflow sample was much better than in the hydrocyclone overflow sample, which was clearly a result of the ore properties (density, particle size, mineralogy).