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Zimbabwe
The Mukuyu-1 exploration well being drilled in Zimbabwe by Australian firm Invictus Energy in partnership with the government is being called "a game changer" for the country by President Emmerson Mnangagwa. The well is in license SG 4571, which covers 250,000 acres located in the most prospective portion of the Cabora Bassa Basin in northern Zimbabwe. The license is currently in the second exploration period which runs to June 2024. Invictus entered into an agreement with the Zimbabwe government in March 2022 to increase the license area sevenfold to 1.77 million acres. Previously explored by Mobil Oil, the project contains the largest undrilled structure in onshore Africa.
Industry:
- Energy > Oil & Gas > Upstream (0.66)
- Government > Regional Government > Africa Government > Zimbabwe Government (0.30)
The Journal of Petroleum Technology, the Society of Petroleum Engineers' flagship magazine, presents authoritative briefs and features on technology advancements in exploration and production, oil and gas industry issues, and news about SPE and its members.
Severe instability in an underground hard-rock bord and pillar mine situated on the Great Dyke in Zimbabwe necessitated a thorough revision of the existing design. Local geotechnical conditions characterized by undulating, subhorizontal and intersecting shear structures, variable in thickness and relative location within the hangingwall, orebody (pillars), and footwall, were only partially understood prior to the instability event. As a result, a change in the behaviour of the respective horizons was encountered, with an unfavourable outcome. A revision of the pillar design therefore became necessary. The revised design took a holistic approach, beginning with a re-evaluation of the local rock mass characteristics, a revision of the empirical design, and application of both linear elastic and nonlinear numerical analysis to test and optimize the final outcome. The resulting design is considered to be robust, with the provision of continual evaluation and monitoring of geotechnical conditions concurrent with production activities to test and validate the design. This paper presents a high-level overview of the investigative process that was undertaken to provide the operation with revised, stable pillar design criteria. INTRODUCTION Production at a bord and pillar mine situated on the Great Dyke of Zimbabwe recently suffered a serious setback when geotechnical conditions within the hangingwall, orebody, and footwall gave rise to widespread instability. Unfavourable rock mass behaviour included footwall heave, falls of ground (FoG), and bulking and spalling of pillars. The presence of a shear structure, subhorizontal and undulating in attitude, variable in thickness and continuity, was identified as a primary cause for the deterioration in rock mass conditions. Investigations into the contributing factors that gave rise to the situation were carried out, based on which it was concluded that the design and associated mining practices evidently needed to be revised. A new, robust, workable model was required that would allow the resumption of mining with confidence while at the same time trying to avoid a knee-jerk response of excessive conservativism.
Country:
- Africa > Zimbabwe (0.45)
- Africa > South Africa (0.28)
- North America > United States (0.28)
Industry:
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.69)
SPE Disciplines:
Shallow hard-rock bord-and-pillar mine designs are typically characterized by solid pillar systems and stable span designs. These spans are optimized to maintain stability, which permits safe and economic extraction of the orebody. Reef-parallel structures are known to affect the strength of pillars. In areas where such structures exist, careful considerations need to be given to rock mass properties with respect to pillar design, bord span and type, and support design, depending on the placement of the structure. Part of Unki mine has a reef-parallel structure referred to as the Footwall Fault (FwF), which is located either within or below the mining cut. In addition to the FwF, mining in the upper sections of the mine encountered poor ground conditions, characterized by low-angle joints trending N-S and truncated by E-W high-angle faults, joints, and dykes. These features resulted in frequent falls of ground, which were attributed to incorrect span design, inadequate support design, pillar fracturing, and sidewall failures. This paper presents the bord span review and the corresponding support optimization process, as well as the resultant improvements and benefits to the mining process as applied to this top section of the mine. The results presented here have led to successful mining through the challenging ground conditions. The same conditions had earlier resulted in the closure of one of the uppermost sections of the mine. Crucial to this research is the inclusion of rock mass properties in the bord span re-design, modifications to the design formulae to suit the downrated conditions, and probabilistic numerical modelling for support design. INTRODUCTION Mining in the upper portions of the Unki East shaft has been faced with ground stability challenges, leading to decommissioning of one of the half-levels (1 South). These upper half-levels contain a reefparallel structure referred to as the Footwall Fault (FwF) which is located either within or below the mining cut. Reef-parallel structures are known to affect pillar strength and have been cited as a major contributor to mine collapses. Bimha mine in Zimbabwe and Everest mine in South Africa are typical examples. A combination of the splay faults from the FwF, N-S low-angle joints intercalated by E-W high angle faults, dykes, and sympathetic joints resulted in frequent large falls of ground, which were ascribed to inadequacy of the span and support designs for the prevailing poor ground conditions, which were not envisaged at the mine design phase. Work presented in this paper has been carried out to mitigate the impact of this combination of geological structures and avoid prematurely decommissioning half-levels. The work was conducted when 1 North had intersected poor ground, entailing a high possibility of half-level decommissioning.
Country:
- Africa > Zimbabwe (0.71)
- Africa > South Africa (0.48)
Industry:
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.88)
Abstract: Good support design is of paramount importance in a bid to mitigate rockfalls. Most platinum mines using room and pillar method have failed to reach the target milestones of zero harm due to the presence of geological discontinuities. Geological discontinuities along the Great dyke of Zimbabwe comprise of shear zones, sympathetic joints together with dykes. The prevailing geological structures have led to a decrease in productivity and challenges of support failure. Virtuous mining practices together with good support design will lead to an improved productivity, less operating costs and improved safety. The need to improve the key performance indicators led to the compulsion for this research to be conducted based on support design and mining practices in bad ground conditions. Geological data and geotechnical data were obtained from a Zimbabwean platinum mine. It was clinched that the presence of shear zones deteriorated the rock mass which have led to the unpredictable unravelling of the rocks. The current support systems as well as the mining practices were analyzed and benchmarked. Empirical support designs together with numerical modelling were used to design optimum support system. Support design encompasses regional support of pillars and local support of roofbolts. Various rock mass classification methods were used to get the quality of the rock. From the analysis of the current support systems used, it was noted that the current support systems together with mining practices need to be adjusted for sustainable operations. Furthermore, the current mining practices need to be revised since the use of ANFO explosive results in excessive bad hangings, stoping overbreak and increased costs. The bords currently mined gave a shorter stand-up time which again compromises safety. Pillars need to be redesigned together with the implementation of a new roofbolt system to improve both productivity and safety. Optimum pillar design which gave the prime extraction ratio without compromising safety was proposed. Introduction Upright support design and sound mining practices warrants economic and sustainable mining operations. This research makes a crucial review of the current support systems used in bad ground conditions at a Zimbabwean platinum mine. The area of research is sited on the Great Dyke of Zimbabwe and is infested by faults and sympathetic joints. Platinum Group Elements (PGEs) are the primary metals exploited and base metals are also recovered. The orebody is shallow having a maximum depth of 250m. The Zimbabwean Great Dyke is the second leading reserve of PGEs following the South African Bushveld complex (Oberthür et al [7]). The comprehensive section of the Great Dyke is virtually a bowl shaped which encompasses strata that are dipping towards the axis. The Dyke encompasses for about 550km having a maximum width of 11km (Prendergast [8]). The Mineralized Sulphide Zone (MSZ) contains the minerals of interest and the economic thickness averages 2m. The host rock of minerals is pyroxenite which is sandwiched by bronzitite and websterite. The average dip of the reef is 11 degrees. Figure 1 shows the cross sectional view of the strata.
Artificial Intelligence, benchmarking, classification, current support system, discontinuity, excavation, ground condition, intensity, machine learning, metals & mining, mining practice, overbreak, performance indicator, pillar, probability, productivity, rock mass, roofbolt system, safety, safety factor, strategic planning and management, strength, support design, support failure, support system, Upstream Oil & Gas
Country:
- Africa > Zimbabwe (0.81)
- North America > United States > Texas (0.28)
SPE Disciplines:
Technology:
Abstract Any bord and pillar platinum mine thrives on effective design of bords and pillars. Pillars have to be large enough to ensure safety and small enough to ensure economic and sustainable exploitation of the mineral resource. Consideration of span of the bords of the working area is also crucial to safe and economic design of the mining layout. This research makes a critical review of the current design approach so as to understand the contributors to pillar failure in a section of an underground platinum bord and pillar mine. The research focuses on the areas that have been plagued by bad ground and seeks to determine the suitability of the current design in such conditions with an objective to redesign the section so as to curb the consequences of pillar failure in the operation. At the core of this research is the detailed geotechnical data of the area that was studied. Making use of Rock Mass Classification (RMC) and other rock engineering techniques, the review indicates that the adopted design is not suitable for the ground conditions evaluated, thus confirming the problem’s origin. The safety factor analysis shows that the ground conditions in the area of study would pose a greater risk due to failure of pillars. The conditions, predominantly the closer joint spacing made the rock mass deteriorate in strength and quality thus the pillar size needed to be increased so as to maintain the required strength. This shows that the pillars in the study area are at a higher risk of failure hence motivating for the redesign process. This paper details the proposed redesign which, if implemented, is expected to see a reduced extraction ratio but will enhance stability and facilitate optimum mining operations. 1. INTRODUCTION Accurate pillar design and stability analysis are crucial to safe mining in a bord and pillar layout. This paper makes a critical review of the current bords and pillar design and layout at a platinum mine in Zimbabwe which has been affected by ground failure. The mine is located on the Great Dyke of Zimbabwe and exploits an orebody which is not deeper than 500m below surface for Platinum Group Elements (PGEs). While PGEs are the main minerals of interest and extraction at the mine, copper, nickel and gold are also recovered from the operation. The mine is located in a block delineated by two faults in a fairly stable region. Regionally, the geology at the mine is similar and consistent with the rest of the Great Dyke. Locally, the orebody lies at the bottom of the main sequence of sulphide bearing rocks and is about 1.2m above a footwall fault (FWF) that occurs consistently throughout the mining environment. The fault infill material is known to negatively affect the metallurgical process through which the ore is taken to recover PGEs. Due to the clayey nature of its infill material, the fault presents a high risk on regional support (pillars) especially where it coincides with the footwall of mining excavations and can be subjected to water flows.
bord, calculation, data collected, dimension, excavation, formula, fos, geotechnical data, ground condition, hangingwall, hydraulic radius, knowledge management, metals & mining, mining cut, pillar, pillar design, pillar strength, redesign, Reservoir Characterization, reservoir geomechanics, span, stability, structural geology, unsupported span, Upstream Oil & Gas
Country:
- North America > United States (0.46)
- Africa > Zimbabwe (0.44)
SPE Disciplines:
- Management > Professionalism, Training, and Education > Communities of practice (0.50)
- Data Science & Engineering Analytics > Information Management and Systems > Knowledge management (0.50)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.46)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.46)
ABSTRACT: The success of open stope mining depends largely upon the ideal stope dimensions. If the stopes are made too large, this may cause severe problems such as dilution and increased rehabilitation costs, caving of hangingwall as reported in Zimbabwe's Gath's mine; and chimney caving occurring on Zambian Copperbelt mines. These occurrences can seriously jeopardize mine profitability and public safety. There are several methods currently available for stope optimization. The question that remains is - "which geometric layout provides the greatest recovery from the orebody assuring maximum geomechanical security and stability"? The paper discusses this question. RESUME: Le succes de mines a ciel ouvert en gradien depend fortanant des dimensions ideales des gradius. De trop larges gradius penvent etic respnsable de graves probleimes telle que l'erosion du mon suspendu entrainant de fortes depenses de rehabilisation, comme cela a etc le cas a la mine due GATH on Zimbabwe on encore de l'effeordiement des cheminees dans les mines du Copperbelt en Zambie. Tout cela remet en question la rentabilite et la rsecurite de la mine. Ilya flusiurs methodes d'optimilisation des gradient l'expose suivant e'tudie queles sort les organisations giometriques garantissant le plus grand rendement de minerai tout en assurant une securite geomechanique, maximode. ZUSAMMENFASSUNG: Der Erfolg beim offenen Kammerabbauverfabren hangt im wesentlichen vom richtigen Wahl der Kammerdimension. Sind die Kammern zu grop dimensioniert, so mup dem zufulge mit hahe Verdunnung/Verunreinmigung, hohe Wiederherstellosten, Bruchdes Hangenden (wie etwa z.B. Garith Grube in Simbabwe) und "Schornsteinantiger" Bruche (wie in "Kupfergurtel" des sanbisehen Bergbaugebiet) gerechnet werden. Diese Geschchen sind haufig mit hohen Wiederherstellkasten gebunden und beeintrachtigen die Sicherheit und Wirtschaftichbeit eimes Grubens. Dennoch gibt es in der Literatur einige Optimierungsverfahren zur Dimensionierung von Kammern aber bleibt nock unbeant-worted die Frage mach weiche geometrichen Vorrichtung gearbeiten werden soll lum moglichst der hochste Ausbeutefaktor und geo-mechanische Sicherheit und Stabilitait zu erziclen? Diese Articel befarst sich mit dieser Fragesterllung. 1. INTRODUCTION Stope and pillar mining is probably the oldest underground mining method having been developed by flint miners in Europe some 6,000 to 8,000 years ago (Temple 1972). This shows that ancient underground miners had learned the fundamental rules of stope and pillars mining to (1) leave sufficiently large ore pillars for roof support and (2) to limit the width of openings to minimize the possibility of roof falls. However, since the turn of the century, investigators have been trying to evaluate ore pillar strength by relating it to representative samples of ore tested in the laboratory and in the field. 2. STOPE DESIGN INPUT DATA The stope and pillar design is intimately tied to the geomechanical aspects. In a typical design practice the data base must, at least, include the general geology, intact rock properties, structural geological data, rock mass classification and in-situ stresses (i.e. loading conditions). Methods of determining the above data are available in several literatures. Generally, a great deal of input data are already available in the mine. However, the three main geomechanics database include the in situ stress analysis, field data base and laboratory testing. 2.1 In-Situ Stress A comprehensive description of fundamental of state analysis is documented in standard texts. The formation of stoping in an orebody causes stress distributions and an increase in pillar loading. Mining interest is usually concentrated on the peak-load bearing capacity of a pillar, when the rupture in the body of the pillar mass occurs. 2.2 Field Instrumentation Standard rock mass classification techniques should be applied to determine the strength and deformability of the fractured rock. For this purpose Barton's the NGI'Q' system and Bieniawski the RMR system should be used.
classification, dilution, dimension, exponent, layout, metals & mining, optimization, Orebody, pillar, pillar strength, re-thinking, Reservoir Characterization, reservoir geomechanics, safety, stability, Stability Graph, stope, stope dimension, strength, underground mining method, Upstream Oil & Gas
Industry:
- Materials > Metals & Mining (0.55)
- Energy > Oil & Gas > Upstream (0.54)
SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
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