فصلنامه مهندسی معدن
پیاپی 12 (تابستان 1390)

Grade estimation is one of the important stages for mining assessment. Grade values have asignificant effect on scheduling, designing and management of the mine. Therefore, it is importantto apply a method, which is able to estimate the necessary parameters with a high accuracy. One ofthe direct methods for figuring out the grades is to use exploration wells, which, because of theirhigh costs, usually it is impossible to use them extensively. In this study, a novel method based onfuzzy logic, neural networks and genetic algorithm is presented. This algorithm, by applying geneticalgorithms for optimization of the architecture and the neuro-fuzzy parameters, is able to achievebetter results as compare with other traditional methods for grade estimation. This is because ofusing different artificial intelligent methods. Foe this aim, Darrehzar copper porphyry was selectedas the case study. According to the results obtained our proposed algorithm able to capture theexisting pattern between the inputs and outputs finely and to estimate the grade with a highprecision.

One of the estimate methods in mining is geostatistical methods. The advantage of the statistical method is good mathematical background and also in results acquired through their practical application. But through the geostatistal methods, choosing the most useful method is very important. One of most important thing, that operators usually don’t use it, is the ability of using liner kriging. Therefore the concentrating on non-liner kriging has been seen. One of the powerful methods in non-liner kriging is Co-kriging. According to complicated mathematical theory and untouchable usefully software, this method hasn’t been used. This method based on hermitian polynomial and isofactorial model that use for estimating the black points with the primary data histogram then the value of hermitian polynomial are estimated by this histogram. Finally with liner composited of this value in hermitian polynomial and estimated value in black points the value of parameter is determined. In this paper, using by computer programming in Co-kriging the grade of copper distribution was determined in Sungon mine and produced data was compared with producing data by kriging. According to this study, the soft western-north and eastern-south districts have lower grades and the middle district of mine has higher grade than other parts. Also the normalizing and data inversing by hermitian polynomial has high capability. Using this method improves some problems in kriging such as smoothing and compability in non-liner estimated function

Air curtains are ventilation control devices for temporary or permanent use in underground mining. They can be used to deflect air into the unventilated areas such as dead end regions. Their design and installation are fundamental issues for maintaining a sufficient supply of fresh air and achieving effective air circulation and contaminant removal. At the same time, they should have little impact on the mine ventilation system. This paper presents the results of a two-dimensional CFD model, which examines the effects of air curtain dimension on fluid flow behavior in the mine dead end regions. By using CFD code Fluent, which uses model for fluid flow turbulence modeling, a 2D model of dead end was constructed. The result showed that with no brattice that streamlines proved weak compared to when a brattice was used. Depending on air curtain dimension, the use of an air curtain increases the airflow into the dead end region. Higher air curtain length and width showed a higher velocity near the right wall of the dead end, a minimum air re-circulation and, therefore, a better ventilation mechanism

Separation of molybdenite from copper sulfides concentrate BY thioglycolic acid (TGA) as a depressant of copper and iron sulfides was investigated. The results showed that the consumption amount of TGA was lower (3-3.5 kg per ton of feed) than that of sodium sulfide, which is more than 14 kg per ton of feed. It was found as a very effective depression for copper and iron sulfides. The final grade and recovery of molybdenite reached to 56% and 96%, respectively, while the copper and iron grades were about 0.26% and 0.56% respectively. These values are desirable for molybdenite concentrate and are in the standard range.

Andalosite group minerals are the most suitable materials for refractories, which are mainly applied in furnace lines. Since these materials are currently used predominantly in alominosilicats refractories, then recognition and extraction of andalosite deposits, their processing studies and mullitization are important. In this research, the feasibility of the processing and mullitization of Mishdovan Andalosite ore were investigated. Semi-detail exploratory studies related to the Mishdovan ore have already been done in 2000 with more than 1.6 Mt reserve and 20% Al2O3 content. The primary samples were divided into two fractions based on crushing and thin section studies. In order to increase the Al2O3 content for 150 -355 µm fractions, the gravitational method (vibrating table) and for 75-150 µm fractions, the flotation method were employed. Also the Fe2O3 content was decreased to less than 1% by employing high intensity magnetic separator. Consequently, using of the mentioned techniques, it is possible to produce a concentrate with 56% Al2O3 content, which is suitable for mullitization. The mullitization process was studied at different temperatures (1400 – 1600 °C), periods of time (1- 3.5 hours) and grain sizes. Phase evolution was studied by XRD diffraction. Morphology, distribution and size of the grains were analyzed by means of SEM. The obtained results showed that the complete transformation of Andalosite group minerals to mullite takes place between 1500 – 1550 °C during 2hr for the grain size of 38 microns. At higher temperatures, the mullite grain revealed round and platelet morphology. Presence of the primary Corundum mineral in Andalosite sample caused a considerable decrease of the glass phase in the refractory.

Nowadays, application of rod mill in new comminution circuit designs is almost absolute. Nevertheless, many installed rod mills are still in operation throughout the country and their performance optimization might be of interest to plant engineers. Simulators are specialized tools for circuit design and optimization. Due to the screening effect observed in rod mills, their mathematical modeling is totally different from that of ball mill units. In this study, rod mill was simulated as a new module in BMCS (BMCS-Based Modular Comminution Simulator) environment. Matrix modeling was considered as an established mathematical model of rod mills. Hence, the rod mill module of BMCS was mainly based on this type of rod mill model. The matrix model was constructed using the concept of consecutive stages of breakage. In each stage of breakage, the ore was subjected to selection, breakage and classification processes. The algorithm followed by the rod mill module of BMCS has been presented in this work. The close agreement between the predicted and measured product size distributions proves the validity of the predictions made by rod mill simulation module and the accuracy of model implementation in BMCS.

The hydraulic fracturing is a suitable operational method for stimulating and increasing the productivity of oil and gas wells. In this method, a liquid is pumped to the wellbore until creation and then propagation of a fracture in the wall of wellbore. The aim of this paper is to determine the minimum pressure required for developing a hydraulic fracture from an initial perforation in the wall of well. The evaluation of the minimum pumping pressure is an important task for performing an optimum and successful hydraulic fracture operation. Since the hydraulic fracturing is essentially a process of crack growth in the wellbores and in the reservoir formations, it is preferred to investigate this method using the concepts of rock fracture mechanics. In this paper, the minimum pumping pressure diagrams have been presented for different conditions of a wellbore during the hydraulic fracturing process. In order to obtain the diagrams, several 3D finite element models of the well having an initial semi circular perforation were analyzed under different loading conditions and the influence of affecting parameters such as the in-situ stresses, the depth of initial perforation and the wellbore inclination angle on the minimum pumping pressure were investigated numerically. It is shown that the minimum horizontal in-situ stress is the most affecting parameter on the required pumping pressure at great depths. The pumping pressure increases by increasing the minimum in-situ stress. Meanwhile, inclined wells require smaller pumping pressures in comparison with the vertical wellbores.