A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Geophysics . / Rockbursts continue to be one of the more high profile and problematic worker hazards in the South African gold mining industry. Recent advances in the technology of seismic monitoring systems and seismic data analysis and interpretation methods hold considerable promise towards improving the success rate of rockburst control measures. This study tests different methods for the evaluation of the response of geological structures to mining induced stress changes. A small part of Western Holdings Gold Mine in the Welkom goldfield -- the Postma Area -- offers a challenge because of its geological complexity, accessibility and high incidence of seismicity. The sensitivity of the local network to ground motions in this area of interest and the expected spatial location accuracy is established and deemed adequate for a detailed investigation of seismic activity. The local mining geometry, geology and methods of mining are discussed. The fractured state of the rock mass observed in situ, close to the stope faces, is in agreement with the results of numerical elastic modelling and the high stresses inferred seismically. Almost immediately after the incidence of a large event (ML 3.7) which occurred close to one end of a dyke, an increased rate of seismic activity became apparent at another part of the same dyke, some 250 m to the east. A change in the state of seismic stress, before and after the large event, points to a transfer of stress along this geological discontinuity. A quantitative analysis of recorded seismicity indicates spatial and temporal variations in the state of stress and strain throughout the rock mass surrounding Mining excavations. The elastic stress modelling performed routinely by rock mechanics engineers in the deep gold mines is, by itself, incapable of catering for the rheological nature of the rock mass, but taken together with independent seismic evaluations of a fault orthogonal to a highly stressed dyke it is shown that both methods are mutually complementary and can enhance the assessment of the seismic instability of the structures. A back-analysis is conducted on ten large seismic events (ML 2.5) to identify precursors. These show that the timely recognition of high gradients in physical seismic parameters pertaining to strain rate and stress in time and space immediately prior to major seismic events is a real and practical possibility, as such constituting an early warning mechanism. The fore-warning of a large event is best served by an analysis of seismicity over the short term (weeks or days) through time-history variations and/or contouring of various seismic parameters, although long-term seismic responses (months or weeks) characterise specific patterns and trends which are useful in the forecast. / AC 2018

Thesis (M.Econ. (Economics & Economic History)) - Rhodes University, 2009.

Thesis (Engineer of Mines)--University of Alaska. Thesis summarizes survey of geology, geography, access, gold analysis and type classification, and economic potential of development on the Seward Peninsula Mining Region, Bendeleben Quadrangle. / Alaska "Territorial Department of Mines reports" or "TDM reports" are a collection of reports, notes and maps written by Dept. employees working out of several field offices throughout the territory. Series titles and numbers within the collection were retrospectively assigned with the exception of the few written after statehood (1959). Preliminary leaf is a letter from the author dated "April 29, 1941." Plate I "Outline map of Seward Peninsula showing location of Taylor Region," 1:150,000, sheet unfolds to 22 x 30 cm.; plate II, "Topographic map of Taylor vicinity," 1:12,000, sheet unfolds to 39 x 41 cm.; plate III "Detail sketch Placer deposits in vicinity of Taylor, Seward Peninsula, Alaska," 1:4800, sheet unfolds to 34 x 68 cm.; plate IV Topography - Geology drainage of a part of the Upper Kougarok River," 1 inch = 1.6 miles, sheet unfolds to 68 x 59 cm.; plate V "Cross section sketch - Structure along lines A-B, C-D, E-F," scale varies, sheet unfolds to 38 x60 cm.; plate VI "Contour sketch map surface and bedrock," 1:9600, sheet unfolds to 39 x 41 cm.; and plate VII "Sections along lines shown on Plate II - Kougarok River Bench Placers," scale varies, sheet unfolds to 59 x 45 cm. Includes bibliographical references (leaf [29]). Also available in electronic format via Internet.

Thesis (MS)--University of Montana, 2009. / Contents viewed on January 15, 2010. Title from author supplied metadata.

No description available.

No description available.

No description available.

Includes bibliographical references (p. 241-252) and index. / xxiii, 263 p. ill., maps 23 cm

Graduation date: 1994

Rocks of the South Island of New Zealand are locally enriched in metalloids, namely arsenic (As), antimony (Sb) and boron (B). Elevated levels of As and Sb can be found in sulphide minerals mostly in association with mesothermal gold deposits, whereas B enrichment occurs in marine influenced coal deposits. The mobility of these metalloids is important because they can be toxic at relatively low levels (e.g. for humans >0.01 mg/L of As). Their mobilisation occurs naturally from background weathering of the bedrock. However, mining and processing of coal and gold deposits, New Zealand's most economically important commodities, can significantly increase metalloid mobility. In particular, historic mines and associated industrial sites are known to generate elevated metalloid levels because of the lack of site remediation upon closure. This work defines and quantifies geological, mining, post-mining and regional processes with respect to metalloid, especially As, mobility. At the studied historic gold mines, the Blackwater and Bullendale mines, Sb levels in mineralised rocks were generally negligible (<14 ppm) compared to As (up to 10,000 ppm). Thus, Sb concentrations in solids and in water were too low to yield any meaningful information on Sb mobility. In contrast, dissolved As concentrations downstream from mine sites were found to be very high (up to 59 mg/L) (background = 10⁻� mg/L). In addition, very high As concentrations were found in residues (up to 40 wt%) and site substrate (up to 30 wt%) at the Blackwater processing sites (background < 0.05 wt%). Here, roasting of the gold ore converted the orginal As mineral, arsenopyrite, into the mineral arsenolite (As[III] trioxide polymorph) and volatilised the sulphur. The resultant sulphur-defficient chemical system is driven by arsenolite dissolution and differs significantly from mine sites where arsenopyrite is the main As source. Arsenolite is significantly more soluble than arsenopyrite. In the surficial environment, arsenolite dissolution is limited by kinetics only, which are slow enough to preserve exposed arsenolite over decades in a temperate, wet climate. This process results in surface waters with up to ca. 50 mg/L dissolved As. In reducing conditions, dissolved As concentrations are also controlled by the solubility of arsenolite producing As concentrations up to 330 mg/L. Field based cathodic stripping voltammetry showed that the As[III]/As[V] redox couple, in particular the oxidation of As[III], has a major control on system pH and Eh. Site acidification is mainly caused by the oxidation of As[III], resulting in a close link between As[V] concentrations and pH. Similarly, a strong correlation between calculated (Nernstian) and measured (electrode) Eh was found in the surface environment, suggesting that the overall Eh of the system is, indeed, defined by the As[III]/As[V] redox couple. Once the metalloid is mobilised from its original source, its mobility is controlled by at least one of the following attenuation processes: (a) precipitation of secondary metalloid minerals, (b) co-precipitation with - or adsorption to - iron oxyhydroxide (HFO), or (c) dilution with background waters. The precipitation of secondary minerals is most favoured in the case of As due to the relatively low solubility of iron arsenates, especially at low pH (~0.1 mg/L). Observations suggest that scorodite can be the precursor phase to more stable iron arsenates, such as kankite, zykaite, bukovskyite or pharmacosiderite and their stability is mainly controlled by pH, sulphur concentrations and moisture prevalence. Empirical evidence indicates that the sulphur-containing minerals zykaite and bukovskyite have a similar pH dependence to scorodite with solubilities slightly lower than scorodite and kankite. If dissolved As concentrations decline, iron arsenates potentially become unstable. Their dissolution maintains a pH between 2.5 and 3.5. This acidification process is pivotal with respect to As mobility, especially in the absence of other acidification processes, because iron arsenates are several orders of magnitude more soluble in circum-neutral pH regimes (~100 mg/L). From this, it becomes apparent that external pH modifications, for example as part of a remediation scheme, can significantly increase iron arsenate solubility and resultant As mobility. In contrast to As, the precipitation of secondary Sb and B minerals is limited by their high solubilities, which are several orders of magnitude higher than for iron arsenates. Thus, secondary Sb and B minerals are restricted to evaporative waters, from which they can easily re-mobilised during rain events. Metalloid adsorption to HFO is mainly controlled or limited by the extent of HFO formation, which in turn is governed by the availability of Fe and prevailing Eh-pH conditions. Thus, mineralisation styles and associated geochemical gradients, in particular pyrite abundance, can control the amount of HFO and consequent metalloid attenuation, and these can vary even within the same goldfleld. Furthermore, it was found that there is a mineralogical gradation between ferrihydrite with varying amounts of adsorbed As, amorphous iron arsenates and crystalline iron arsenates, suggesting that the maturity of mine waste is an important factor in As mineralogy. Once dissolved metalloids enter the hydrosphere, dilution is the main control on metalloid attenuation, which is especially pronounced at the inflow of tributaries. Dilution is, therefore, closely related to the size and frequency of these tributaries, which in turn are controlled by the regional topography and climate. Dilution is a considerably less effective attenuation mechanism and anomalous metalloid concentrations from mining related sites can persist for over 10 km downstream. The complex and often inter-dependent controls on metalloid mobility mean that management decisions should carefully consider the specific site geochemistry to minimize economic, health and environmental risks that can not be afforded. On a regional scale, background metalloid flux determines the downstream impact of an anomalous metalloid source upstream. For example, the Bullendale mine is located in a mountainous region, where rapidly eroding slopes expose fresh rock and limit the extent of soil cover and chemical weathering. Consequently, the background As flux is relatively low and As point sources, such as the Bullendale mine, present a significant contribution to the downstream As flux. In contrast, the bedrock at the Blackwater mine has undergone deep chemical weathering, resulting in an increased background mobilisation of As. Thus, the Prohibition mill site discharge, for example, contributes only about 10% to the downstream As flux. This information is relevant to site management decisions because the amount of natural background metalloid mobilisation determines whether site remediation will influence downstream metalloid chemistry on a regional scale.