Bench Levels Research Articles

THE APPLICATION OF A STOCKPILE STOCHASTIC MODEL INTO LONG-TERM OPEN PIT MINE PRODUCTION SCHEDULING TO IMPROVE THE FEED GRADE FOR THE PROCESSING PLANT

This paper presents a chance-constrained integer programming approach based on the linear method to solve the longterm open pit mine production scheduling problem. Specifically, a single stockpile has been addressed for storing excess low-grade material based on the availability of processing capacity and for possible future processing. The proposed scheduling model maximizes the project NPV while respecting a series of physical and economic constraints. Differently from common practice, where deterministic models are used to calculate the average grade for material in the stockpiles, in this work a stochastic approach was performed, starting from the time of planning before the stockpile realization. By performing a probability analysis on two case studies (on iron and gold deposits), it was proven that the stockpile attributes can be treated as normally distributed random variables. Afterwards, the stochastic programming model was formulated in an open pit gold mine in order to determine the optimum amount of ore dispatched from different bench levels in the open pit and at the same time a low-grade stockpile to the mill. The chance-constrained programming was finally applied to obtain the equivalent deterministic solution of the primary model. The obtained results have shown a better feed grade for the processing plant with a higher NPV and probability of grade blending constraint satisfaction, with respect to using the traditional stockpile deterministic model.

Application of stochastic programming for iron ore quality control

Stockpiling and blending play a major role in maintaining the quantity and quality of the raw materials fed into processing plants, especially the cement, iron ore and steel making, and coal-fired power generation industries that usually require a much uniformed feed. Due to the variable nature of such materials, they even come from the same source and the produced ores or concentrates are seldom homogeneous enough to be directly fed to the processing plant ore furnaces. Processing plants in iron ore mines need uniform feed properties in terms of each variable (in this work, iron phosphorous ratio and Fe content in magnetite phase) grade of ore, and therefore, homogenization of iron ore from different benches of an open pit or ore dumps has become an essential part of modern mine scheduling. When ore dumps are considered as an ore source, the final grade of the material leaving the dump to the blending bed cannot be easily determined. This difficulty contributes to mixing the materials of different grades in a dump. In this work, the ore dump elements were treated as normally distributed random variables. Then a stochastic programming model was formulated in an iron ore mine in order to determine the optimum amount of ore dispatched from different bench levels in open pit and also four ore dumps to a windrow-type blending bed in order to provide a mixed material of homogenous composition. The chance-constrained programming technique was used to obtain the equivalent deterministic non-linear programming problem of the primary model. The resulting non-linear model was then solved using LINGO. The results obtained showed a better feed grade for the processing plant with a higher probability of grade blending constraint satisfaction.

Inter-ramp and bench design of open-pit mines: the Portage pit case study

Using a case study, this paper presents an integrated methodology for assessing structural slope stability at the inter-ramp and bench levels. Robust algorithms have been developed and implemented to compute, at inter-ramp and bench levels, slope orientations and slope stability using input data compatible with a commercially available mine-design software tool database structure. Multi-criteria stability analyses were performed based on various design criteria. Susceptibility maps were produced enabling the identification of zones of concern in the designed pit. The obtained results suggest that inter-ramp angles do not present instability concerns over the entire pit surface. At bench levels, potential instability zones were identified within two structural domains totalling 6% of the total pit surface.

Inter-ramp and bench design of open-pit mines : the Portage pit case study

Using a case study, this paper presents an integrated methodology for assessing structural slope stability at the in- ter-ramp and bench levels. Robust algorithms have been developed and implemented to compute, at inter-ramp and bench levels, slope orientations and slope stability using input data compatible with a commercially available mine-design software tool database structure. Multi-criteria stability analyses were performed based on various design criteria. Susceptibility maps were produced enabling the identification of zones of concern in the designed pit. The obtained results suggest that inter- ramp angles do not present instability concerns over the entire pit surface. At bench levels, potential instability zones were identified within two structural domains totalling 6% of the total pit surface.

Geometric Parameters as Key Factors for the 3D-modeling of Fluvial Deposits

GIS is an established and appropriate tool for the management and evaluation of geodata which is being increasingly used for the three-dimensional modeling of strata. An advanced technique for the GIS-based 3D-modeling is developed here in order to integrate genetic aspects of deposition into the modeling process. The ArcView® software (ESRI, Inc., Redlands, California) and the extensions 3D-Analyst and Spatial Analyst have been used for the data management and layer rendering. The tools VirGIL and GSI-3D (Insight Corp., Germany) have been applied for the purpose of visualization of the layers in 3D. The main topic of the work is the generation of geometrically consistent models of fluvial terrace bodies, which represent monogenetic fills of Pleistocene palaeovalleys. One peculiarity of the investigated Illerglacier foreland, southern Germany, is the occurrence of highly eroded terrace remnants. The preserved deposits are tied to several accumulation levels, but the usual way of morphostratigraphic interpretation is limited and results in lots of different stratigraphies and palaeogeographic ideas presented in literature. The sediment fill of meltwater valleys, which can be identified in the Illerglacier area is reconstructed based upon intense field mapping. The terrace accumulations are defined by the base and surface layers, which are thought to be isochronous. Some 1,400 data points were used to model these layers in 3D. The geometry of the sediment deposits is defined using basic parameters, e.g. the gradient and the thickness of the terrace, which are used as bench levels for the modeling process. The quality of the calculated maps and cross-sections far surpasses that of those derived in the classic way without a genetic concept and without using the 3D-modeling technique. The results derived from the terrace models are relevant for the stratigraphy and palaeogeography of the investigated region of the Alpine foreland. The advanced modeling technique can be used for the detail analyses of terrace sequences of other regions.

Three-dimensional distribution analysis of phosphorus content of limestone through a combination of geostatistics and artificial neural network

One of the factors that determines the suitability of limestone for industrial use and its commercial value is phosphorus (P) content, i.e., the weight percentage of phosphorus contained in small quantities of limestone. Because P content changes locally, geostatistical techniques including semivariogram, ordinary kriging, and conditional indicator sequential simulation were used in this study to identify the spatial correlation of P content and to estimate its three-dimensional distribution in an open-pit mine. The P content data at 43,000 points of five different bench levels were analyzed. It was found that the horizontal semivariograms produced by using the data at the same bench level show anisotropic behavior and are represented by the sum of two spherical models with different ranges and sills. The twelve vertical semivariograms were also constructed from P content in boring cores. After these semivariograms were classified into four types, a multilayered neural network was applied to clarify the horizontal distribution of each one. One of the twelve semivariograms was assigned to an arbitrary grid point in the study area by the criterion that its type is the same as the one estimated at the point and the borehole site producing the semivariogram is the nearest to the point. With this technique, ordinary kriging combined with the semivariogram of borehole data provided a proper estimation of P content in the depth direction.

The characteristics and rates of the various slope degradation processes in the Barton Clay Cliffs of Hampshire

Summary Research is in progress to determine the nature and pattern of the degradation processes in an actively eroding stretch of the Barton Clay cliffs in the Naish Farm area of Highcliffe, Hampshire. In response to loss of beach material the rate of recession has accelerated and is currently averaging 1.9 m/year, resulting in steepening of the overall cliff angle from an average of 13° in 1947 to a maximum recorded average of 19° in 1976. The presence of three preferred bedding plane shear surfaces at various elevations within the cliff produce a benched type of cliff profile, comparable with that seen in the Gault and Lias Clay controlled cliffs of Fairy Dell, Dorset but in contrast with the published descriptions of London Clay cliffs. The degradation processes include scarp slumping, spalling (including toppling and soil falls), bench sliding (involving movement of colluvium over a preferred bedding plane), debris sliding (including movement of screes over clay scarps), mud sliding (i.e., the traditional lobate ‘mudflows’), mud runs (true flows), stream (or gully) erosion and man-related processes. Regular surveying and monitoring using a variety of techniques and having to surmount difficult field conditions, has begun to elucidate the characteristics, rates and inter-relationships of these processes. A flow chart representing the systematic transfer of soil from the in situ state via various colluvial modes (including the three bench levels) en route to the sea and an accompanying colluvial soil budget for the year July 1981 to July 1982 has been drawn up. It is shown that bench sliding is by far the most significant process in terms of volume of colluvium moved through the under-cliff, accounting for 930f the total volume of colluvium contained in the area. Mud and debris sliding, although important processes, are of relatively minor significance.

The degradation of the Barton Clay Cliffs of Hampshire

Summary The Barton Clay crops out along a 4·8 km stretch of the Hampshire coast and together with its capping of Plateau Gravels forms a cliff profile averaging around 30 to 37 m high. The original classic work on the geology of the Barton Clay had suggested a total thickness of only 34·5 m; more recent work involving boring and levelling on the cliff face has shown the formation to be 46·4 m thick. Active degradation of the outcrop creates a markedly stepped profile, relatively flat bench levels being separated from one another by steeper scarp slopes. The benches are underlain by up to 6 m of slipped debris or bench rubble. The scarps are formed by exposures of the solid Barton Clay and Plateau Gravel in the case of the top scarp. The interface between the bench rubble and Barton Clay is formed by a shear surface, an underground continuation of the scarp surfaces, which has been polished and grooved as a result of the seaward movement of the bench rubble. These shear surfaces are developed along particular, identifiable stratigraphic horizons within the Barton Clay and tend to develop along these horizons irrespective of the height of the latter within the cliff profile. Variations in the morphology occur laterally along the outcrop and can be related to the erosional history and partly to the geology. Five individual processes of degradation are particularly active on the undercliffs; these comprise bench sliding which is sliding of the bench rubble over the shear surfaces, collapse of the scarp slopes or scarp slumping, wearing down of the scarp slope by weathering or scarp spalling, and erosion by mud-flows and running water. Both mud-flows and streams when well developed cut through bench rubble and into the scarp slope and locally destroy the stepped profile. The current activity of these processes is due to marine erosion of the toe, the net result of the processes being a progressive retreat of the cliff top averaging over one metre per year in some places.

Statistical tests for common bankfull frequency in rivers

Two statistical tests are described for investigating the claim that rivers exceed bankfull level with a common frequency. The first test is necessary to demonstrate that vertically adjacent bench level categories at a site are separate in terms of expected recurrence intervals. The second test examines the homogeneity of bankfull frequencies from site to site for each bench level category. The tests were used to examine data from nine stream gaging sites in New South Wales, Australia. It was shown that three distinct bench levels could be identified in the field. The bankfull frequencies associated with the present flood‐ plain level were shown to form a homogeneous population of bankfull frequencies.

Sea water intrusion into a fresh water forebay due to wave action

Sea water intrusion adversely affects the water quality of the Salinas River Lagoon near Castroville, California. Bench levels indicated that the forebay is above mean sea level; however, additional investigations showed that wave action maintains a water level beneath the beach which is above mean sea level and the forebay. Wave action produces a net landward gradient resulting in underflow from the sea into the forebay. The quantity of sea water added to the lagoon was calculated from salt balance and from gradient-transmissibility relationships. The amount of sea water underflow calculated by these two independent methods was 24.5 and 25.1 acre-feet, respectively. Tides, wave action, and density differences between fresh and salt water should be considered in the interpretation of hydraulic relationships between coastal lagoons and the sea.