Year:2009 | Volume:43 | Issue:3 (121)|Papers Count:11

Natural hazards are among destructive agents that annually take thousands of lives and impose devastating damages in Iran. Spotting such a high risk areas can help reducing the amount of their probable risk. A 1:500000 liquefaction and landslide hazard zonation map developed for the southern shoreline of the Caspian Sea. This geotechnical hazard map divides the study area to 15 hazard classes (five and three hazard classes for liquefaction and landslide respectively). Removing negative factors affects the landslide hazard map, using effect analysis and reevaluating the accuracy of hazard map, increased the map accuracy by 93.5%. Based on the compiled geotechnical hazard map, about 30% of the study area is prone to low sliding and high liquefaction hazards.

Simulation of grinding circuits has being performed from 30 years ago and is also to be more complete and powerful approach with improvement of mathematical models which simulate various processing units/machines. The modeling and simulation of various mineral processing circuits are presently performed. In order to simulate the present grinding circuits of Esfordi Phosphate processing plant, at first the breakage and selection functions of its ball mill’s feed sample were determined. According to obtained results, maximum value of selection function (selectivity of particles to be broken), was measured which was equal to 0.011886 min.-1 for 600 microns size fraction (d80 of ball mill feed at primary design). Then by using NGOTC software and measured residency times of particles in ball mill (average residency time in ball mill) which was 2.07 minutes (maximum time was 20 minutes), the selection function of ore was calculated in industrial scale, and accordingly the effect of using balls with various diameters were estimated. The results of selection function indicated that its maximum value reaches to 2.5238 min.-1, when balls with 25mm diameters to be used in ball mill. Finally by using BMCS software (ball mill circuit simulator), primary design data, and results obtained from various experiments, the circuit simulation was carried out. This procedure yielded optimized values of some required parameters such as size distribution and solid percent of ball mill product, and then the results were compared with current circuit values. However the estimated results and their vicinity to current ones proved the fact of estimation accuracy.

The lead and zinc sample from Goosh-e-Fill mine with 2.4%Pb, 8.0%Zn and 10.0% Fe, was used in different flotation experiments to recover lead and zinc minerals. The valuable minerals in prepared sample were oxidized and the results showed that the lead minerals floated at pH= 9.5 and 11.5, probably it can be due to existence of two or more types of lead minerals. The best result was achieved for the particle finer than 100 micron. In zinc minerals flotation, the results of various collectors consumption showed that the zinc recovery was low and the major part of zinc was not recovered. In the best condition, with ARMAC-T as collector, the zinc recovery was 27% by grade of 22% Zn. Therefore flotation isn’t suitable process for zinc recovery but the lead recovery reached to 70% with more than 40% Pb grade.

Due to the importance of material classification issue in grinding circuits, the ‎performance of primary and secondary hydrocyclones in grinding circuit of Esfordi ‎phosphate plant was investigated by sampling within 7 days from feed, overflow, and ‎underflow‎ of these hydrocyclones. At first, the d80 of above streams samples were calculated by ‎the screening analysis. The results showed ‎that the average values of d80 of feed, overflow and underflow‎ of primary hydrocyclone were ‎respectively 238.7, 236.5 and 100.9 microns, and 100.9 and 94.1 microns for the feed and ‎underflow‎ of secondary hydrocyclone. For the primary hydrocyclone, with plotting ‎distribution curves, its cut-points, the actual and corrected cut-points were calculated which were 35 and 45 microns, ‎respectively, whereas they were equal to 100 microns according to the design documents. However based on the undesirable performance of ‎primary hydrocyclone, it was tried to investigate on its performance using simulation ‎software. The results indicated 80 microns cut-point and 192.30 kpa of pressure drop in ‎particle classification. In addition, the amount of circulating load obtained 931.84% (in ‎primary mill design, this amount was equal to 150%), and high feed rate to hydrocyclone was one the major reasons for this high circulating load. ‎To solve this problem, it was considered one more hydrocyclone could be added to this circuit in the form of parallel and series, and results were studied using BMCS software. The results of this criterion of ‎adding a parallel hydrocyclone, showed 86 microns of cut-point with 62.91 kpa of pressure ‎drop which were suitable for the circuit.‎

Accurate estimation of hydrocarbon volume in a reservoir is important due to future development and investment on that reservoir. Estimation of Oil and Gas reservoirs continues from exploration to end of reservoir time life and is usual upstream engineer’s involvements. In this study we tried to make reservoir properties models (porosity and water saturation) and estimate reservoir volume hydrocarbon based on artificial neural network tools, petrophysical and geophysical data. So with gridding the reserve, separate it to same volume cells. Based on porosity and lithology variation in wells, constructed petrophysical zonation in each well and by correlation these zones in wells reservoir has been zoned. Porosity, water saturation and 3D seismic data have been averaged in cells and assigned one value for each cell. At final a three layer perceptron neural network  by back propagation error algorithm has been designed and trained by using cells which had petrophysical data, then these parameters have been estimated in other cells and original hydrocarbon in place calculated and compared with results from Mont Carlo method.

Geological facies interpretation is essential for reservoir studying. The method of classification and identification seismic traces is a powerful approach for geological facies classification and distinction. Use of neural networks as classifiers is increasing in different sciences like seismic. They are computer efficient and ideal for patterns identification. They can simply learn new algorithms and handle the nonlinearity of seismic data. They are often reliable with noisy data or atypical environments.  In this paper, an approach is presented based on competitive neural network for classification and identification of the reservoir facies that uses seismic trace shape. The competitive networks can be applied on discrete facies. Its unsupervised methods are independent on the wells data and other auxiliary information. Its supervised methods are independent on the wells location. This approach can be performed in two ways. In first way, the seismic facies are classified based on entirely on the characteristics of the seismic responses, without requiring the use of any well information. It is implemented by a single layer competitive unsupervised neural network, called Kohonen self organized neural network. In the second way, automatic identification and labeling of the facies is performed by the use of seismic responses and wells data. It is implemented by a two layer competitive supervised neural network, called Learning Vector Quantizer (LVQ) neural network. The results of both analyses on artificial seismic section and actual seismic section of the sixth zone of Asmary formation in Shadegan oilfield showed reservoir facies distribution and predicted heterogeneity of their characteristics.

The successfulness of a mining project requires a precise definition of the subsurface deposit situation. Deposit characterization is potentially a critical part of any mine design process including reserve estimation and production planning. Over the past two decades, several sophisticated modeling techniques have been developed in the mining and mineral industries. In the available commercial systems, various methodologies have been implemented. The process of deposit characterization and modeling consist of determination of the spatial variation of certain geological and mining parameters such as deposit extensions, ore grade and density. This process includes several steps, construction of database, generation of topography, modeling the geometry of the deposit, grade analysis, blocks modeling and reserve estimation. The modeling and visualization process and software application are technically and practically a challenging issue. In this regard, two main groups of challenges can be realized. The first is related to the algorithms used in the modeling and the second is concerned to the user engineering judgments in evaluating of geometry and limits of the deposit. These challenges are related to complexity of ore deposit geometry, unknown spatial limit of ore body, non sufficient number of samples and using of interpolation techniques. In this research, variations of the different parameters of second group that affect the results of modeling are examined. Certain parameters such as those related to block model and wireframe construction are specific to the modeling method and software implementation. Some of the other parameters for example search distance and minimum numbers of samples for estimation are common in the majority of modeling techniques. In the first step, a base model of the Songun copper deposit is constructed using Datamine software and then variations of the effective modeling parameters are studied, i.e 22 parameters which can be grouped in 5 categories: search samples, variogram, grade estimation, geometry and general data. Thereafter applying sensitivity analysis, the parameters were classified according to the degree of influence in the modeling results (ore tonnage, metal content and mean grade). On the basis of obtained results it was found that the variables including search distance and minimum number of samples for estimation are the most critical variables. On the other hand, the number of maximum sample and the random variance parameters were determined as the least effective in this regard. This research provides possibility of differentiating sensitive parameters and perception of behavior of various parameters in modeling process.

In the past, rock slope stability analysis were performed either graphically or using a hand-held calculator, but nowadays there are variety of slope stability analysis which can be used according to the field condition and potential failure mode. In 2-D analysis, effect of convex and concave walls are neglected, however concave slopes are believed to be more stable than straight walls due to the lateral restraint provided by material on either sides of a potential failure in a concave slope. In open pit mines with general tendency to increase the wall angle, this point is really important. In this study slope stability of western wall of Sarcheshmeh mine in its extension plan is analyzed using 3-D distinct element method (3DEC). For stability analysis, west wall is divided into three structural regions according to the rock type. Rock and joint strength properties are determined from previous and new laboratory tests. Also in Andesite (dominant rock of the west wall) geometrical properties of joint sets are determined. Consequently Slide5.0 software is used to identify rock mass stability and effect of disturbance factor, underground water, horizontal seismic acceleration and rock type on wall stability. In the next step, the mine geometry is modeled in 3DEC and wall stability is investigated in different locations. Results obtained from 3DEC prove failure of several benches at the toe. Also results show drainage may improve stability in some zones but there would still be smaller failures in the toe.

Sarcheshmeh copper mine, with the final reserves of 828 million tons of sulfur ore and average grade of 0.74%, is known to be the largest open pit of Iran and most probably the second largest copper mine in the world. This mine is located in the seismotectonic zone of Central-Iran, and 23 Km away from the 150 Km long Rafsanjan active fault.In this study the vulnerability of the west wall of the mine, which is more susceptible to sliding, is determined.  First, the seismic hazard probability was calculated by defining seismic sources and determination of seismicity parameters. Then the most effective source in seismic hazard is determined by seismic hazard deaggregation. The Newmark displacement of the west wall is calculated by the critical acceleration and Arias intensity. Finally, the mine vulnerability and seismic risk for this site, along with the probable earthquakes, is calculated. The seismic risk of this site is estimated to be 0.07 of the overall value of the mine.

The Study area located in southwest Dodehak village in 20km North of Delijan city, Central province, and Eocene volcano-sedimentary rocks in this area which appears to have significant potential in terms of Pozzolanic materials. To evaluate the ability of the Eocene tuffs in this area to supply for industrial cement production, some chemical analysis and physical tests and petrography studies have been carried out on collected samples. The results of petrography and powder x-ray indicated that samples have a minor percentage of glass phase and considerable amount of zeolite-group minerals. The chemical compositions of all samples in terms of pozzolanic composition were consistent with the ISIRI 3433 and ASTM C618 standards. compressive strength were tested for different caring time, 3, 7 and 28 days, and results were higher than required criterion recommended in National Iranian Standard no. 3432 and ASTM-C595-89 as well. Meantime, other physical properties, such as density, autoclave expansion, fineness etc., were measured according to related standards and they also conforms with these standards. In general, this study indicated that  zeolitic phases is the main effective factor on pozzolanic properties and Eocene tuffs of this area have a good ability as natural pozzolans because of existence about 20 % zeolitic phases.