Journal of Mining and Environement
Volume:6 Issue: 1, Winter 2015

Post-mineralization activities may cause difficulties in the process of ore modeling in porphyry deposits. Sungun, NW Iran, is one of the porphyry copper deposits, in which dyke intrusions have made ore modeling more complicated than expected. Among different kinds of dykes, two types were chosen and the consequent geostatistical analyses were applied on. In this study, simple directional variograms were used for extracting relevant information from dyke systems on which the Sequential Indicator Simulations were applied consequently. One hundred realizations were produced on the simulation grid considering the anisotropy characteristics and E-type map has been provided averaging all realizations. Moreover, a binary state between dyke and non-dyke environments was produced putting threshold on the E-type grid node values to discriminate the ore from barren dykes. Hole-effect models were fitted to the empirical variograms perpendicular to the dyke strike. Dimensional information was elicited from these models and the results were compared with the previously carried out geological investigations, and finally a good numerical match was found between these two sources of information.

Taknar deposit is located about 28 km to the north-west of Bardaskan in the Khorasan-e-Razavi province, which is situated in the north-eastern part of Iran. This deposit is unique, formed within the Taknar formation in the Ordovician time. As a result, it is of much interest to many researchers working in this field. By choosing the lithogeochemical study performed to recognize new exploration targets which a new stage in the field. After pre-processing the lithogeochemical data obtained, the distribution maps were obtained for the element anomalies and alteration indices. The ratios of additive composite haloes were used to study the erosion levels in the Taknar area. In order to produce the favorability map, eight information layers were integrated using the simple overlay method, and four new exploration targets were obtained.

In this study, a hybrid intelligent model has been designed to predict groundwater inflow to a mine pit during its advance. Novel hybrid method coupling artificial neural network (ANN) with genetic algorithm (GA) called ANN-GA, was utilised. Ratios of pit depth to aquifer thickness, pit bottom radius to its top radius, inverse of pit advance time and the hydraulic head (HH) in the observation wells to the distance of observation wells from the centre of pit were used as inputs to the network. An ANN-GA with 4-5-3-1 arrangement was found capable to predict the groundwater inflow to mine pit. The accuracy and reliability of model was verified by field data. Predicted results were very close to the field data. The correlation coefficient (R) value was 0.998 for training set, and in testing stage it was 0.99.

Detection of subsurface structures by means of gravity method can be used to determine mass distribution and density contrast of rock units. This distribution could be detected by different geophysical methods, especially gravity method. However, gravity techniques have some drawbacks and can''t be always successful in distinguishing subsurface structures. Performance of the gravity technique could be further improved by simultaneous combination and introducing additional information from other geophysical data. This study used existing relation between seismic and gravity methods to better clarify subsurface structures. This relationship relates mass distribution of the medium to velocity of wave propagation in that media. This method was applied on an area that consists of three mud volcanoes. After completion of the primary model by forward modeling, mass distribution and analysis of seismic velocity were provided on a 2-D profile. Bouguer anomaly map of gravity data of the area was obtained and negative anomalies were identified. These negative anomalies could be related to the existence of mud volcanoes. A 2-D seismic line was also acquired over the greatest mud volcano, as additional information for direct modeling. The Gardner equation was used for further velocity estimation by density values. This velocity model also compared with seismic velocity analysis for evaluation. The final results indicated that density modeling and the use of seismic velocity model increases the resolution of subsurface structures imaging. Separation of subsurface layers was implemented correctly in the velocity model resulting from gravity data and subsurface discontinuities of the area that become more obvious by this technique.

A good knowledge of the parameters causing casing damage is critically important due to vital role of casing during the life of a well. Cement sheath, which fills in the gap between the casing and wellbore wall, has a profound effect on the resistance of the casing against applied loads. Most of the empirical equations proposed to estimate the collapse resistance of casing ignore the effects of the cement sheath on collapse resistance and rather assume uniform loading on the casing. This paper aims to use numerical modeling to show how a bad cementing job may lead to casing damage. Two separate cases were simulated where the differences between good and bad cementation on casing resistance were studied. In both cases, the same values of stresses were applied at the outer boundary of the models. The results revealed that a good cementing job can provide a perfect sheath against the tangential stress induced by far-field stresses and reduce the chance of casing to be damaged.

Coastal Fars gravimetry project in Fars province was carried out to find the buried salt domes and to determine characteristics of faults in this area. The Lavarestan structure was covered by 4203 gravimetry stations in a regular grid of 1000*250 m. Depth structural model of this anticline made in previous studies was based on geological evidences and structural geology measurements. In order to have a complete coverage of Lavarestan anticline, 4 profiles with appropriate intervals were selected on gravity data for further processing and interpretation. 2D inverse modeling was performed on these profiles using Encome Modelvision and Encome PA software. Geometrical and physical parameters of each layer were changed step by step and forward gravity calculations were repeated until we reached a desirable fitting between observed and calculated gravity anomaly. The results of 2D gravity modeling were focused on Lower Paleozoic and Kazerun (cap rock) top horizon, also the underground contour map was extracted from seismic data after interpretation. The results show appropriate correlation between the underground contour map of 2D gravity modeling and interpretation of seismic data.

Optimization of the exploitation operation is one of the most important issues facing the mining engineers. Since several technical and economic parameters depend on the cut-off grade, optimization of this parameter is of particular importance. The aim of this optimization is to maximize the net present value (NPV). Since the objective function of this problem is non-linear, three methods can be used to solve it: analytical, numerical, and meta-heuristic. In this study, the Golden Section Search (GSS) method and the Imperialist Competitive Algorithm (ICA) are used to optimize the cut-off grade in mine No. 1 of the Golgohar iron mine. Then the results obtained are compared. Consecuently, the optimum cut-off grades using both methods are calculated between 40.5% to 47.5%. The NPVs obtained using the GSS method and ICA were 18487 and 18142 billion Rials, respectively. Thus the value for GSS was higher. The annual number of iterations in the GSS method was equal to 18, and that for ICA was less than 18. Also computing and programming the process of golden section search method were easier than those for ICA. Therefore, the GSS method studied in this work is of a higher priority.

In this work, the mechanism for fracture of brittle substances such as rocks under a uniform normal tension is considered. The oriented straight micro-cracks are mostly created in all the polycrystalline materials resulting from the stress concentrations. The present work focuses on the interactions of the pre-existing micro-cracks, which can grow and propagate within a rock-like specimen. The micro-crack initiation and propagation in rock-like specimens is investigated using the Fortran Code TDDCRACK2D, which is a 2D displacement discontinuity method (DDM) for crack analysis, a boundary element computer code based on the linear elastic fracture mechanics (LEFM) theory. In the present work, a higher order DDM is used to implement special crack tip elements for estimation of the stress intensity factors (SIFs) and crack initiation angles for the wing-crack problems initiated at different angles from the original micro-crack tips in an infinite specimen under a uniform tension.

The cracked Brazilian disc (CBD) specimen is widely used in order to determine mode-I/II and mixed-mode fracture toughness of a rock medium. In this study, the stress intensity factor (SIF) on the crack-tip in this specimen is calculated for various geometrical crack conditions using the extended-finite element method (X-FEM). This method is based upon the finite element method (FEM). In this method, the crack is modeled independently from the mesh. The results obtained show that the dimensionless SIFs for the pure modes I and II increase with increase in the crack length but the angle in which pure mode-II occurs decreases. For the mixed-mode loading, with increase in the crack angle, NI value decreases, while NII value increases to a maximum value and then decreases. The results obtained from the crack propagation examinations show that the crack angle has an important effect on the crack initiation angle. The crack initiation angle increases with increase in the crack angle. When the crack angle is zero, then the crack is propagated along its initial direction, whereas in the mixed-mode cases, the crack deviates from the initial direction, and propagates in a direction (approximately) parallel to the direction of maximum compressive load.

In this work, hydrochloric acid is used to remove iron impurities in the bauxite ore contained in the diasporite mineral located in the Sari region. The bauxite ore was calcined at different temperatures and times, and then dissolved in a hydrochloric acid solution. After determining the optimum calcination conditions in 1 h at 900 °C, the response surface methodology (RSM) with four factors in five levels was employed in order to evaluate the effects of calcination temperature, calcination time, acid concentration, and leaching time on the iron leaching efficiency. A quadratic model is proposed using this methodology to correlate the leaching variables. The test results indicate that the model is consistent with the experimental data, and that the most important varriables involved are the acid concentration, leaching time, and squared term of calcination temperature (A2). The maximum iron recovery was 94.97%, and the Fe grade in the solids remained was 2.35% at the calcination temperature of 900 °C, a calcination time of 1 hour, and a leaching time of 2 h in hydrochloric acid (6 mM).