Optimizing geochemical sampling sizes and quantifying uncertainties for environmental risk assessment using Anglogold-Ashanti Gold Mines as a case study
- Authors: Chihobvu, Elizabeth
- Date: 2010-04
- Subjects: Environmental risk assessment , Geochemical prospecting
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/24443 , vital:62796
- Description: Generally, and particularly in South Africa, limited work done on the development of methodologies for sample sizing and quantifying uncertainties in geochemical sampling and analyses. As a result, little trust is placed on the long-term predictions of geochemical modelling for Environmental Risk Assessment (E.R.A). In addition, this leads to the slow approval of mining authorisations, water use licenses and mine closure plans. This dissertation addresses this deficiency in geochemical sampling and analyses specifically for ERA and proposes two methodologies (i) for quantifying uncertainties in geochemical sampling and analysis as a function of sample size and analyses and (ii) for determining the optimum sample size to ensure data quality. The statistical analysis approach was adopted as the best method for sample size determination. The approach is based on the premise that the size of the study sample is critical to producing meaningful results. The size of the required samples depends on a number of factors including purpose of the study, available budget, variability of the population being sampled, acceptable errors and confidence level. The methodology for estimating uncertainty is a fusion of existing methodologies for quantifying measurement uncertainty. The methodology takes a holistic view of the measurement process to include all processes involved in obtaining measurement results as possible uncertainty components. Like the statistical analysis approach, the methodology employs basic statistical principles in estimating the size of uncertainty, associated with a given measurement result. The approach identifies each component of uncertainty; estimates the size of each component and sums the contribution of each component in order to approximate the overall uncertainty value, associated with a given measurement result. The two methods were applied to Acid-Base Accounting (ABA) data derived from geochemical assessment for ERA of the West Wits and Vaal River (Ashanti Gold mines) tailings dams undertaken by Pulles and Howard de Lange Inc. on behalf of AngloGold Ltd. The study was aimed at assessing and evaluating the potential of tailings dams in the two mining areas to impact on water quality and implications of this in terms of mine closure and rehabilitation. Findings from this study show that the number of samples needed is influenced by the purpose of the study, size of the target area, nature and type of material, budget, acceptable error and the confidence level required, among other factors. Acceptable error has an exponential relationship with sample size hence one can minimize error by increasing sample size. While a low value of acceptable error value and high confidence are always desirable, a tradeoff among these competing factors must be found, given the usually limited funds and time. The findings also demonstrated that uncertainties in geochemical sampling and analysis are unavoidable. They arise from the fact that only a small portion of the population rather than a census is used to derive conclusions about certain characteristics of the target population. This is further augmented by other influential quantities that affect the accuracy of the estimates. Effects such as poor sampling design, inadequate sample size, sample heterogeneity and other factors highly affect data quality and representivity hence measurement uncertainty. Among these factors, those associated with sampling, mainly heterogeneity was found to be the strongest contributing factor toward overall uncertainty. This implies an increased proportion of expenditure should be channelled toward sampling to minimise uncertainty. Uncertainties can be reduced by adopting good sampling practices and increasing sample size, among other methods. It is recommended that more information be made available for proper uncertainty analysis. , Thesis (MSc) -- Faculty of Science and Agriculture, 2010
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- Date Issued: 2010-04
Geochemical exploration in calcrete terrains
- Authors: Krug, Mark Alan
- Date: 1995 , 2013-10-02
- Subjects: Duricrusts , Silcrete , Geochemical prospecting
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5026 , http://hdl.handle.net/10962/d1006891 , Duricrusts , Silcrete , Geochemical prospecting
- Description: This work takes a look at some of the literature on calcretes and especially the problem of geochemical exploration in calcrete terrains. The conclusion that will be reached is that exploration in calcrete terrains is not futile and that provided the explorationist is aware of the types of calcrete and their genetic implications calcrete can be used as a sampling medium and anomalies can be detected through calcrete (p.1.) , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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- Date Issued: 1995
Geochemical exploration in arid and semi-arid environments
- Authors: Van Berkel, Ferdinand
- Date: 1983 , 2013-04-02
- Subjects: Geochemical prospecting , Arid regions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4920 , http://hdl.handle.net/10962/d1004389 , Geochemical prospecting , Arid regions
- Description: Anomalous element distributions within the regolith result from chemical adjustments of the earth's surface to prevailing climatic conditions. Because of the lack of moisture in the arid environment, chemical equilibrium related to paleoclimates is largely maintained. Mechanical or clastic dispersion dominates arid weathering and hence the exploration approach is largely dictated by the degree of preservation of the paleoregolith. Arid environment geochemists thus have to contend with surface materials ranging from laterite and calcrete in areas where the imprint of aridity is minimal, to more conventional sample media such as bedrock, stream sediment and lithic soils in actively dissecting areas. Extraction techniques are designed specifically to isolate clastic dispersion trains. Thick mantles of aeolian and water-borne overburden characterise desert lowlands and are a challenge to the exploration geochemist. Techniques showing the most promise in these areas include groundwater geochemistry, vapour geochemistry, surface microlayer geochemistry, geobotany and biogeochemistry which attempt to isolate gaseous and weak hydromorphic, ore-related trace-element dispersions. Termite mound sampling yields convincing results and appears to be an under-utilised geochemical approach. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
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- Date Issued: 1983
The factors affecting the interpretation of geochemical surveys in mineral exploration
- Authors: Fletcher, B A
- Date: 1982
- Subjects: Geochemistry , Geochemistry -- Environmental aspects , Mining geology , Minerals , Ore deposits , Geochemical prospecting
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5014 , http://hdl.handle.net/10962/d1006142
- Description: [From introduction] Exploration geochemistry is an indirect method of detecting mineral deposits by measuring the abundance and distribution of ore elements and elements closely associated with ore in natural materials at or near the earth's surface. The method relies on the assumption that a mineral deposit is reflected by unusual element abundances or distribution patterns (geochemical halos), and that these indications of mineralization can be detected by geochemical surveys involving the collection and analysis of natural materials. The interpretation of geochemical surveys in mineral exploration involves: 1) The use of geological and statistical inference, based on a knowledge of the normal behaviour and distribution of indicator elements in the exploration area, to recognize apparent geochemical anomalies in field and analytical data and to predict the type of geochemical halo reflected by the anomalies. 11) The use of geological inference, based on a knowledge of the characteristics of geochemical halos and their relationship to mineral deposits, to predict the presence and probable location of an ore body. The interpretation process is, however, complicated by the absence of a simple universal formula that relates the abundance and distribution of elements in natural materials to the presence or absence of a mineral deposit. The interpretation of a geochemical survey must, thus, be based on an empirical approach which avaluates each survey as an individual problem. The objective of this dissertation is to illustrate the factors affecting the "nuts and bolts" approach to the interpretation of geochemical surveys in mineral exploration. The discussion is aimed at providing field geologists responsible -for the planning and execution of geochemical surveys with some basic guidelines for interpreting the surveys. I hope that the contents of this dissertation will help field geologists to "look in the last place first".
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- Date Issued: 1982