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By S. C. Essack

"Tenova Pyromet has designed a slag flow control valve that throttles the flow of slag in order to control the tapping rate. In addition, the valve has proved to be a reliable tool for closing the furnace during normal operation as well as emergency conditions. The valve makes use of a water-cooled copper element that is hydraulically operated and attached directly to the slag tap-hole. The equipment is compact, simple to maintain, and cost-effective to purchase and install. It can be retrofitted to most existing slag tapholes with minimal modifications.During the development phase, finite element method (FEM) and computational fluid dynamics (CFD) software was extensively used to model predicted operating conditions and to optimize the design. By using CFD, it was possible to understand the flow patterns inside the copper and to optimize these to improve overall performance.The slag valve was installed and commissioned in 2011/2012 on a 12 MW furnace as part of a new mineral wool plant in the USA. It has performed well since its installation despite operating under conditions in excess of the original design criteria. During the first 6 months of operation it quickly became the preferred method of closing the furnace, although the design intent was for occasional use during emergency shutdown conditions only. Since replacing the mudgun as the main method of closing the tap-hole, a few minor changes have been made to the installation in order to cope with the increased heat load and much higher frequency of use."

Jan 1, 2014

By R. Loots

High temperature creep resistant alloys are used in power plants as steam pipes and headers where they have to withstand super heated steam temperatures of up to 600ºC for the lifetime of the plant. Frequently certain portions of pipes may be subjected to excessive temperatures and consequently suffer from creep damage. Damaged portions then have to be replaced by welding new steel to the service exposed steel. Such welds will have to be subjected to a post weld heat treatment (PWHT) to relieve residual stress. During such a PWHT it is then possible for the steel to crack in the heat affected zone (HAZ) by what is known as Reheat Cracking (RHC), also known as stress relief cracking. For the present purpose the RHC susceptibility of service exposed steel was compared with that of new steel by reproducing the temperature cycle to which the HAZ will be subjected during welding in a weld simulator. This was followed by PWHT where the influence of residual stress was studied by applying a constant stress to such a weld-simulated specimen in a creep testing machine. A sharp spiral was machined along the length of the cylindrical specimen to simulate the presence of a possible weld defect. In this way it is possible to subject all portions of the simulated HAZ to the same stress intensity. For the purpose of the investigation 1/2Cr-1/2Mo-1/4V steel known to be susceptible to RHC was chosen. During testing a constant tensile stress was maintained while the temperature was increased to follow the thermal cycle prescribed for PWHT. It was found that the new steel in all instances failed by RHC along the grain boundaries in the high temperature heat affected zone. In the case of the service exposed steel the creep strength of parent metal was lower than that of new steel as a result of exposure to a steam temperature of 540°C for about 15 years. Consequently, all of the failures during testing occurred in a ductile manner by necking outside the HAZ rather than by RHC. When service exposed steel is welded to new material, it is expected that the creep strain associated with stress relaxation will mostly be concentrated in the parent steel outside the HAZ. Accordingly, it should probably not be necessary to make any extra allowance for reheat cracking during repair of steam pipes manufactured from 1/2Cr-1/2Mo-1/4V steel other than that applicable for welding new steel.

Jan 1, 2004

By D. Odendaal, S. Bharat, R. D. Cromarty

The aim of this investigation was to determine the effect of high-temperature heat treatment on the electrical resistivity of charcoal. Samples of two different wood types (eucalyptus and black wattle) were pyrolised in a retort at a temperature of 700°C and the resulting charcoals heat-treated in an induction furnace at temperatures from 800°C to 1800°C and residence times from 60 to 120 minutes. After cooling, the resistivities of the samples were measured at room temperature using the four-point probe technique. It was found that as the heat treatment temperature increased the electrical resistivity of the charcoal decreased, approaching an asymptotic value at higher temperatures. Longer residence times decreased the resistivity, but this effect was not pronounced.

Oct 3, 2023

By M. Z. Emad, M. U. Khan, A. ur Rehman

The use of stemming plugs in surface blasting is gaining popularity because of the environmental, technical, and economic advantages. Although previous studies have established the operational effectiveness of different types of stemming plugs, evaluations of the economic and ergonomic impacts are lacking, thereby hindering their application in many mining operations. Consequently, a significant proportion of mining operations end up performing less efficient blasts. We evaluated the effectiveness of three types of stemming plugs by conducting multiple full-scale production blasts. The results show that stemming plugs reduce the need for secondary blasting and increase blast performance. An economicanalysis showed that the incorporation of stemming plugs can reduce blasting costs significantly.

Jul 1, 2021

By L. A. Cornish, R. Süss, M. Sephton, N. B. Maledi, J. H. Potgieter, L. Chown

The gas turbine industry is faced with a challenge to improve the performance of engines, while simultaneously adhering to stringent environmental legislation. One way of addressing the problem is by further increasing the recipient working temperatures. Unfortunately, the use of nickel based superalloys (NBSAs) in the gas turbine industry has reached its limitations. Although coatings can be used for small increases, and air cooling is also incorporated by design, attention is towards developing stronger metallurgical materials having higher melting points, with acceptable creep and corrosion resistance. A series of ternary and quaternary Platinum-based superalloys were developed. Platinum was selected because of its higher melting points compared to nickel, similar fcc structure and better corrosion properties. Mechanical characterisation studies of Platinum-based superalloys alloys, which included oxidation, creep and hardness, demonstrated reasonable results, outperforming an oxide dispersed strengthening (ODS) Fe-based superalloy (PM2000) and a nickel based superalloy (MAR-M200). During any materials development where high temperatures are concerned, high strength is the primary property of interest. However, during the development of gas turbines, component life and reliability, which are influenced by temperature, need to be taken into consideration, and therefore creep as well as corrosion (both temperature dependant properties), are important. These properties become significant with increasing temperatures. With increasing demand for higher temperatures, it is becoming increasingly important to include hot corrosion properties of the alloy during the material selection process. A short description on hot corrosion and its degradation mechanisms are given in this paper. Coatings are currently dominating as the best practical solution to address temperature increases. This paper looks at benefits and shortcomings of coatings over Pt-based superalloys as candidates for applications under extreme conditions. Key words: Hot corrosion, Pt-based superalloys, Ni-based superalloys, Coatings

Jan 1, 2006

By F. Wang, P. Rosario, A. Vazirizadeh

Advances in data science, machine learning, and artificial intelligence are transforming mining and mineral processing, and making them more algorithm intensive. The paradigm is shifting from one of detection and control to one of prediction and optimisation. To build up reliable prediction and optimisation models these steps should be passed: collect, aggregate, cleanse, and process large amounts of complex, structured, and unstructured data as a first stage. Next, the right tools must be used to extract meaningful features from the operational data for the build-up of a prediction model. A grinding circuit is one of the challenging areas in terms of determining its overall efficiency and the prediction of product quality. In a processing plant, some of the KPIs are typically unmeasurable or infrequently measured for real-time application, e.g. ore grindability and grind size. However, these variables are required to calculate the grinding circuit efficiency and to model the operation performance. In this paper, advanced analytic tools have been used to extract one selected KPI (cyclone overall P80 or final grind size) and its relationship with measured variables for an industrial dataset. The results illustrate that the performance of the grinding circuit can be predicted for real-time monitoring by means of measured data. Keywords: Grinding circuit, data-driven, machine learning, process modelling, hybrid modelling

Jan 1, 2020

By S. J. Swart

This paper discusses the principles and application of risk assessment and management as the basis for environmental management within the mining industry. Unlike in other industries, mines are required to obtain closure certificates in terms of section12 of the Minerals Act, which should ultimately release them from further environmental responsibilities. It is emphasized that the concept of environmental risk assessment and management, when applied correctly will mean that the mine will be identifying and managing environmental issues beyond those set by current legal requirements and management strategies. The focus shifts from conventional minimum legal compliance management to management of real environmental risks. The advantage of this approach is that the perceived ?shifting of legal and management goal posts? due to changing environmental laws or management principles, will not influence or dictate the mine?s short or long-term management objectives or actions, mine closure funds can be more accurately determined and mine closure should become a relatively simple procedure. The risk assessment approach has been applied to the planning of mine closure at Iscor?s Durban Navigation Collieries (Durnacol) in Kwa-Zulu Natal and certain key risk issues such as the long-term risk of water pollution from coal discard dumps have already progressed to fully quantitative risk assessment. This paper will discuss the process, which has been followed to date, with particular emphasis on the most recent phase, namely quantitative risk assessment and management of pollution from coal discard dumps. It is believed that the approach that is being pioneered at Durnacol and which overcomes some of the more obvious deficiencies of both the EMPR and the traditional IEM process will ultimately serve as the model for all responsible mines in South Africa. It is also believed that this approach will enable the authorities to issue closure certificates with the confidence that there will be no unforeseen surprises in the years after closure.

Jan 1, 1998

By A. K. Raji, E. F. Orumwense, M. O. Ojumu

This research paper introduces a novel passive method for ocean mining using an electricpowered robotic subsea dredging crawler designed to operate in various subsea conditions, including unstructured and rough terrain. The electric-powered robotic subsea dredging crawler is equipped with two driving tracks and features a complex assembly of tank tread chain link, tank tread idler wheels, tank tread sprockets, bronze bushings, motor hub, motor mount, and a 12-volt direct current motor. To evaluate the performance of the electric-powered robotic subsea dredging crawler, it was compared with existing ocean hydraulic exploration crawlers, such as MK3 ROST, in terms of drive performance on an inclined ramp with five angles of inclination (0°, 15°, 20°, 25°, 30°). The experiment aimed to determine the maximum velocity, torque, and efficiency of the crawler at different angles of inclination. The collected data were analysed and plotted using Python, and the effect of the electric-powered robotic subsea dredging crawler’s weight on its driving performance was also considered. The results of this study demonstrate a quadratic relationship between driving performance and inclination angle, which can be used to optimise the electric-powered robotic subsea dredging crawler’s performance for future ocean mining robot drive applications.

Oct 2, 2025

By J. M. Stewart

Although the incidence of heat stroke in South African gold mines is small, work continues on its reduction. This paper proposes limits of heat stress that are applicable to South African underground conditions, with the warning that they should not be extrapolated to other situations without careful consideration having first been given to their limitations. These limits of heat stress take physical and physiological considerations into account, and they correspond to there being a 10-6 risk of an essentially nude man developing a rectal temperature in excess of 40°C. It is recommended that further work should be undertaken on the development of equations for the calculation of the heat transfer from clothed men, the derivation of equations that quantify the physiological conductance and sweat rate response of humans, and on establishing the frequency distributions that describe variations in rectal temperature response between individuals in different types of environment.

Jan 1, 1981

By E. V. Lilford

Valuators of mineral properties are faced with a range of valuation methodologies, the most important of which are grouped under the headings of the market approach, the cost approach and the income approach. The way in which value is defined and the detail of the different valuation methodologies is examined here. This paper aims at documenting the variety of valuation procedures and applying each method to a variety of gold projects and comparing the outcomes. Any decision to apply a valuation technique will depend principally on the stage to which the project has been developed. The valuation approach to a greenfield project will be substantially different from that applied to a well-drilled, extensively explored mineral property. Furthermore, a valuation exercise may produce different outcomes for the same gold project depending on which method is applied. In order to investigate the variability in valuation methods and to explore the outcomes of different approaches, a series of five gold projects was analysed. The projects differ in regard to levels of capital application, infrastructural setting, depth below surface, in situ grade, and the stage of development, and were valued using the different methods. The most critical aspect of any valuation is the capacity of the valuer to identify the salient issues and ensure that they are incorporated into the valuation. The danger of simply applying ?black box? solutions to valuation problems without a full understanding of the parameters and the areas of uncertainty is emphasized. The importance of the valuator?s experience, insights into best practice and the ability to recognize and submit to the requirements of compliance within the minerals industry is among the most important characteristics of a valuer.

Jan 1, 2005

By S. Soren, K. Deo Mehta, G. Jha

The paper aims to find a sustainable sintering process through cleaner means, in order to achieve the desired outputs with zero environmental impact. At present, sintering has no control over its environmental impacts. These impacts occur when fossil fuels such as coal and coke are used in metallurgical sintering. These fossil fuels are undoubtedly effective in their assigned reducing task, but simultaneously emit about 220 kg of GHGs (greenhouse gases) per tonne of sinter produced. The current attempt has focused on reducing these emission levels by switching from coke to a renewable fuel source such as biomass. Biomass is a cleaner fuel source with a significantly lower emission footprint compared to coke. In the experimental campaign, sawdust and wood-charcoal were used in substitution for coke. Experiments were designed in a progressing substitution to obtain the maximum substitution ability without compromising the sinter properties. Sawdust as raw biomass source optimally substituted 10% of coke. The substitution levels were remarkably higher (30%) for wood charcoal due to its low moisture and high calorific values. A fuel blend with 30% biomass and remaining coke succeeded in producing a sinter with acceptable quality indices. Sinters prepared with or without biomass contribution shared an identical phase transformation and microstructures. In order to to maintain consistency in the process, every effort was made to maintain all operational and process parameters identically, except for the fuelling framework. Keywords: Sintering, sustainable, biomass, GHGs, fuel substitution

Jan 1, 2020

"Chairman: Professor E. P. PFLEIDER Rapporteur: Mr P. R. JANISCHPapers:Optimum design of an open pit by D. A. PhillipsAn open pit design system for stratiform ore bodies by L. A. J. Pronk van Hoogeveen, J. R. Cutland and M. WeirAn open pit design model by R. H. Robinson and N. B. PrennThe Chairman in opening the session highlighted the current situation in the United States of America where some 85 to 90 per cent of all mining (except for coal) is done by open pit methods, and where some 40 per cent of the coal is mined by open pit. The South African industry is, of course, dominated by the deeper level underground gold mines; however, with the aid of an extensive open-pit technology developed in other countries, South African companies arc continuing to explore possibilities of open-pit exploitation of base mineral, coal and diamond deposits. Several successful ventures are already in operation at Phalabora, Optimum Colliery, Kimberley and elsewhere, and South Africa is undoubtedly benefitting in this regard by drawing on the experience of others.The papers of this session were therefore particularly pertinent, particularly when viewed in conjunction with those presented at an earlier South African conference devoted specifically to open pit mining.Two themes dominated the discussion which followed presentation of the three papers at this session. The first related to the practicability of using the reported techniques as a tool for management, and their acceptability as such to mine management. This was, of course, not peculiar to this particular session, but rather the major point of debate over the entire conference.The second theme concerned the reliability of the initial drill hole data on which any open-pit design must necessarily be based. This gave added emphasis to the problem of practicability, for no management is likely to accept an elaborate pit design unless confidence can be placed in the ore reserve assessment.In noting these two features of the discussion, it should be remembered that all the three papers dealt largely with design and pre-planning; there was an unfortunate lack of papers or discussion on the subject of controlling the day-to-day mining of open pits, and this is an area where the potential impact which can be made by the computer is even greater.In introducing his paper, Mr D. A. Phillips pointed out that it was concerned only with optimization, and that it therefore assumed, firstly, an adequate subdivision of the orebody into ore blocks characterized by grade, rock type, structure, etc., and, secondly, an acceptable forecast of costs and mineral prices in order to generate a suitable profit matrix. However, programs dealing with these problems for both massive, disseminated and stratiform ore bodies are available to Roan Consolidated Mines. The method of optimization which he had described had been used on a region split into 28 000 blocks, for which the program used three hours of C.P.U. time on an IBM 360/40 computer. The computer design had provided a three per cent improve¬ment on a normal design of the same area."

Jan 1, 2014

By T. J. Otto, G. C. Lindeque

Productivity is improved by increasing the ratio of output to input. In an operating open-pit mine, improving the productivity of heavy mining equipment (HME) enables the unit cost of production to be reduced. To optimize HME productivity, the Kolomela open-pit iron ore mine transitioned to an enhanced short-term mine planning (STMP) process that supports the application of a manufacturing-type operating model. At the core of the enhanced STMP process is a focus on integration across the open-pit mining value chain. The interdependencies between mining activities are highlighted and emphasized, thus ensuring that mining activities are synchronized. The improvements related to HME productivity were monitored from 2019 to 2020. The utilization of mining area in the Leeuwfontein pit improved from 71% to 90%, and the blasting frequency reduced by 14% while the average blast size increased by 17%. The distance travelled during shovel relocations between mining phases reduced by 16%, and the lost time associated with drills relocating reduced by 53%. These productivity improvements resulted in an 11% increase in the loading rate of the main waste shovel at Kolomela from 0.9 Mt/month in 2019 to 1.0 Mt/month in 2020. The enhanced STMP process can be adapted to other open-pit mining operations.

Nov 1, 2021

By S. A. Hosseini, O. Asghari

"Recoverable mineral resources assessment has become a standard geostatistical application in the mining industry, with various geostatistical techniques currently available. This investigation aimed to improve the prediction at the Sungun deposit and to obtain mineral resource models capable of handling (i) the change of support from drill-hole composites to selective mining units (SMUs), (ii) the multivariate nature of the ore control selection criteria that involves both copper and molybdenum grades; and (iii) the local uncertainty on the true (unknown) grades. The solution presented in this paper is to use direct block-support sequential cosimulation in order to construct a set of alternative outcomes of the copper and molybdenum grades on block support over the deposit, with no need for storing point-support values, hence with a considerable gain in memory management and CPU time. The grade realizations so obtained are then processed to calculate the uncertainty in the mineral resources that can be recovered above given cut-off grades, both globally and on a blockby- block basis. IntroductionGeostatistical methods are widely used by mining companies to determine a resource model of the tonnage and head grade of a potential orebody, which is one of the first and most critical inputs underpinning any mining project. The prediction of the grade, tonnage, and recoverable metal for a particular mining plan and the corresponding financial forecast constitute the main technical risks in mineral resource evaluation. The conventional approach to this problem is to predict the mineral grade for constant volumes relevant to the mining plan and to base the recoverable mineral resource calculations on those predictions. Alternatively, one can directly predict the local variability in the mining block grades based on a spatial distribution model (David 1988; Rossi and Deutsch 2014). Multiple realizations can also be constructed by conditional simulation, providing a more complete representation of block grade uncertainty, as well as the uncertainty over multiple blocks. Simulation methods allow quantification of the uncertainty of the mineral resource prediction risks in downstream studies such as mine design, mine planning, or operational optimization studies; the risk assessment is achieved after applying transfer functions to the conditional simulation models (Dimitrakopoulos 2012; Rossi and Deutsch 2014)."

Jan 1, 2017

By L. M. Tavares, H. A. Petit, P. P. Cavalcanti

Iron ore pellets experience degradation during handling due low energy impacts and stresses. These impacts lead to volume or surface breakage of the pellets, creating fine particles that accumulate along the process. Some of the particles are in contact with the air and are dragged as dust into the workplace or into the atmosphere. The aerodynamic size of the particles allows them to be potentially inhaled by the workers or to be carried to nearby communities. Dust emission becomes critical at specific locations, such as transfer chutes and stockpiles. This work models the dust generation that occurs in an iron ore pellet stockyard using a methodology that combines experiments to quantify the degradation of the pellets to mathematical modelling of the dust emission mechanisms in the stockyard. First, laboratory tests were used to characterise the amount of mass and the particle size distribution of the dust generated by degradation under controlled conditions. Second, the flow over a stockpile of an iron ore pellet company was simulated with the aid of computational fluid dynamics (CFD) simulations. Third, semiempirical equations linked the data generated by simulations and laboratory tests to estimate the dust emission in the stockyard. Finally, results were validated with measured field data, obtained with a novel online measurement tool. Results suggest that the approach is able to predict dust emission with sufficient accuracy and can be used for further implementation in the management of operations and decision making in order to reduce the environmental impact of the process. Keywords: Iron ore pellets, abrasion, dust emission, mathematical modelling

Jan 1, 2020

By M. S. Shishvan, J. R. van Duijvenbode

The results of dig limit delineation in open pit mining are never truly optimized due to gaps in the underlying data, such as insufficient sampling. Aside from the data uncertainty, there is also an influence on the final dig limit by either humans or by the heuristic character of an optimization method like simulated annealing. Several dig limit optimizers have been published, which can replace the manual dig-limits designing process. However, these dig limit designs are generally not adapted to account for this heuristic character. In this paper we present a stochastic analysis tool that can be used with the results of heuristic dig-limit optimization to increase confidence in the obtained results. First, an enhanced simulated annealing algorithm for dig limit optimization is presented. Then, this algorithm is tested on ten different blasts at the Marigold mine, Nevada, USA, as a case study. Finally, the results are analysed with a destination-based ensemble probability map and an analysis conducted of the final solution data distribution. The generated dig-limit designs of the algorithm include high revenue areas that are excluded in comparable manual designs and show improved objective and revenue values. The analysis tool provides block destination probabilities and box plots with the distribution of opportunity value for the dig limit. Furthermore, with the analysis tool, it is possible to make well-informed design decisions in areas of uncertainty.

Dec 13, 2022

An efficient and portable mathematical model has been developed for simulating heat transfer in six-in-line slag-resistance-heating electric furnaces for smelting sulphide ores to produce base metals and platinum group metals. This model is a steady-state one relating furnace conditions and performances to various control and input parameters. Some transient effects occurring in electric furnaces are neglected for computation efficiency. This article describes the model development and modelling results. The present model is capable of predicting: (i) temperatures at various locations in a six-in-line furnace, such as slag bath, matte bath, solid charge, freeboard space, freeze lining, cooling water, and air gaps between solid material components, etc. (ii) freeze lining thickness, (iii)smelting rate, and (iv) heat loss rate, etc. A typical feature of the model is that it is easily portable to different application platforms and sufficiently efficient with execution times less than a few seconds. Therefore, it is possible to apply the model for online prediction and control of heat transfer and freeze lining thickness in industrial electric furnaces.

Jan 1, 2011

By E. S. Peters, M. J. van Rensburg, M. Le Roux, Q. P. Campbell

"The demand for energy has continued to rise worldwide in line with population growth. The majority of South Africa’s electricity is supplied by coal-fired power stations. The amount of fine coal (-2 mm) generated at coal processing plants has increased, due mainly to mechanized mining methods. Fine coal retains more water, which lowers its heating value.Drying the coal is costly and it is difficult to achieve the required moisture content. Consequently, coal fines are often discarded. An estimated 8% of the total energy value of mined coal is lost1.Fluidized bed technology is often used to dry coal thermally, but this method is expensive and has an adverse environmental impact. The objective of this study was to investigate the removal of moisture from fine coal (<2 mm) in a fluidized bed operated with dry fluidizing air at moderate temperatures as the drying agent. The effects of different air temperatures and relative humidity levels were investigated in a controlled environment. The study further investigated the influence of coal particle size on moisture removal.The drying rate was found to increase with increasing temperature. The relative humidity of the drying air had a more pronounced effect on the drying rate, even at temperatures as low as 25°C.. It became more challenging to remove moisture as the particle size decreased. The gain in calorific value was greater than the energy required to dry the coal samples, showing that a fluidized bed using moderately warm dry air is an energy-efficient drying technology. The energy efficiency of the fluidized bed compared favourably with other thermal drying methods.Paper written on project work carried out in partial fulfilment of Degree in Chemical Engineering(NWU) - Pursuing Masters in Coal Beneficiation"

Jan 1, 2015

By A. Nuric, S. Nuric, L. Kricak, M. Negovanovic, S. Mitrovic

"SynopsisRotary drilling with rolling tricone bits is the most widely used method for drilling large-diameter blast-holes in large surface mining operations. This drilling method is applicable to a wide range of soft to hard rock materials. This paper presents a fuzzy model for predicting the penetration rate of tricone rotary blast-hole drilling. The model is based on data obtained during the drilling of blastholes in rocks with various uniaxial compressive strengths in the Veliki Krivelj open pit mine, Bor, Serbia. The model was developed using the fuzzy logic toolbox of MATLAB with the Mamdani inference system. The fuzzy model was tested with 23% of the total dataset. The results obtained show the high reliability of predicting the penetration rates. Although there are possible limitations in applying the model to other open pit mines because of differences in rock properties, the prediction methodology applied in this paper can be used in many other predictions of the penetration rates.IntroductionAccording to Tamrock, rotary blast-hole drill operations depend on four important elements:•,Torque in the drill string drive sufficient to turn the bit in any strata encountered•,A high bit loading capability (pulldown force) sufficient for optimum penetration•,An air volume sufficient to remove chips generated during the drilling and to provide cool air to the drill bit bearings•,The selection of the proper type of bit for the material being drilled (Tamrock, 1984).The effects of rock mass parameters on the choice of the type of tricone bits were investigated by Kricak (1997)."

Jan 1, 2015

By D. vas As, Constance M. Vleggaar, P. D. Toens

A facility at the National Nuclear Research Centre, Pelindaba, for the calibration of gamma survey meters used in uranium-prospecting operations by P. D. TOENS, D.Sc. (Fellow), D. van ASt, M.Sc. (Visitor), and CONSTANCE M. VLEGGAAR, B.Se. (Visitor) Ground radiometric surveys in uranium prospecting have in the past suffered from two serious shortcomings. Owing to varying instrument sensitivity and the often arbitrary height at which readings are taken, it has been impossible to compare results obtained in different surveys and, moreover, to relate such readings to actual U30s concentrations. A set of calibration sources designed to overcome these problems has recently been constructed on the site of the National Nuclear Research Centre, Pelindaba. A discussion of the standards applied and the instrument calibration procedure is presented.