The porphyry copper system and the precious metal-gold potential
- Authors: Gendall, Ian Richard
- Date: 1994
- Subjects: Copper ores , Porphyry , Gold ores -- Geology , Prospecting
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4992 , http://hdl.handle.net/10962/d1005604 , Copper ores , Porphyry , Gold ores -- Geology , Prospecting
- Description: It has been established that porphyry copper/copper-gold deposits have formed from I Ma to 2 Ga ago. Generally, they are related to the Mesozoic-Cenozoic interval with few reported occurrences from the Palaeozoic or Precambrian. A reason cited is the erosion of these deposits which are often related to convergent plate margins and orogenic belts. Observations of the alteration and mineralisation within and around porphyry copper/copper-gold systems have been included in numerous idealised models. These alteration and mineralisation patterns are dependent on the phases of intrusion, the tectonic setting and rock type, depth of emplacement and relationship to coeval volcanics, physiochemical conditions operative within and surrounding the intrusive and many other mechanical and geochemical conditions. Island arc and cratonic arc/margin deposits are generally considered to be richer in gold than their molybdenum-rich, intra-cratonic counterparts. Metal zonation may occur around these copper/copper-gold deposits, e.g. copper in the core moving out to silver, lead, zinc and gold. This zonation is not always present and gold may occur in the core, intermediate or distal zones. Examples of gold-rich porphyry deposits from British Columbia, Chile and the SW Pacific Island regions suggest gold is closely associated with the potassic-rich zones. Generally these gold-rich zones have greater than 2% magnetite and a high oxygen fugacity is considered to be an important control for gold deposition. High Cl contents within the magma are necessary for gold mobility within the host intrusive centres. Beyond this zone HS₂ becomes an important transporting ligand. Exploration for porphyry copper-gold deposits includes an integrated geological, geophysical and geochemical approach. Petrographic work through to Landsat imagery may be used to determine the chemical conditions of the system, ore association, favourable structural zones and alteration patterns, in order to focus exploration activities.
- Full Text:
- Date Issued: 1994
A review of the deposition of iron-formation and genesis of the related iron ore deposits as a guide to exploration for Precambrian iron ore deposits in southern Africa
- Authors: Gapara, Cornwell Sine
- Date: 1993
- Subjects: Geology, Stratigraphic -- Precambrian , Iron ores -- Geology -- South Africa , Iron ranges
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4998 , http://hdl.handle.net/10962/d1005610 , Geology, Stratigraphic -- Precambrian , Iron ores -- Geology -- South Africa , Iron ranges
- Description: Iron-formations are ferruginous sedimentary rocks which have their source from fumarolic activity associated with submarine volcanism, with deposition of iron as oxides, hydroxides, and hydrous oxide-silicate minerals in shallow and/or deep marine sedimentary systems. The Precambrian ironformations of southern Africa have a wide age range, but are more prominently developed before 1.SGa. These iron formations occur in greenstone belts of the Kaapvaal and Zimbabwean cratons, in the Limpopo mobile belt, in cratonic basins and in the Damara mobile belt. The Archaean-Proterozoic sedimentary basins and greenstone belts host iron ore deposits in iron-formation. Iron formations have a lengthy geological history. Most were subjected to intense, and on occasions repeated, tectonic and metamorphic episodes which also included metasomatic processes at times to produce supergene/hypogene high grade iron ores. Iron-formations may be enriched by diagenetic, and metamorphic processes to produce concentrating-grade ironformations. Uplift, weathering and denudation, have influenced the mineral association and composition of the ores, within which magnetite, haematite and goethite constitute the major ore minerals. The iron resources of the southern Africa region include the Sishen deposits, hosting to about 1200 Mt of high grade direct shipping ore, at >63% Fe. Deposits of Zimbabwe have more than 33 000 Mt of beneficiable iron-formation. The evaluation of an iron ore prospect involves many factors which must be individually assessed in order to arrive at an estimate of the probable profitability of the deposit. Many of these are geological and are inherent in the deposit itself. Other factors are inherent aspects of the environment in which the ore is formed. Although the geological character of the ore does not change, technological advances in the processing techniques may have a great effect on the cost of putting the ore into marketable form. Geochemical, geophysical and remote sensing methods would be used for regional exploration. Chip sampling and drilling are useful for detailed exploration. Purely geological exploration techniques are applicable on a prospect scale in the exploration of iron ore deposits. Regional exploration targeting should choose late Archaean greenstone belts containing oxide facies iron-formation or Early Proterozoic basins located at craton margins as they are both known to host high-grade haematite orebodies formed by supergene/hypogene enrichment. Most types of iron ore deposits in southern Africa are described and classified. An attempt is made to emphasize the major controls on mineralisation, in the hope that these may be applicable to exploration both in the southern African region and within analogous settings around the world.
- Full Text:
- Date Issued: 1993
Granitic series and their economic geology
- Authors: Kerber, Paulo Augusto
- Date: 1993
- Subjects: Granite , Geology, Economic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4969 , http://hdl.handle.net/10962/d1005581 , Granite , Geology, Economic
- Description: The granitic rocks are subdivided into four series: tholeiitic, alkaline, calc-alkaline and mobilizates. These series can be formed from melting of mantle material (M-type granites) or from crustal rocks. There are granitic rocks formed from the mixing of these two magmas types. The rocks formed from crustal anatexis are subdivided into those formed from igneous rocks (I-type granites) and those formed from meta-sedimentary rocks (S-type granites). The former has similar characteristics to the mantle-derived granitoids. The mineral deposits related to igneous or mantle derived magma usually are Cu-Au, CUI Cu-Mo, Mo porphyries and have high oxygen fugacity and magnetic susceptibility (magnetite series). The Sn-W deposits usually are related to magma derived from meta-sedimentary or igneous rocks derived magma with low oxygen fugacity and magnetic susceptibility (ilmenite series). According to the tectonic setting, the granitoids rocks are classified as: Andino type, West Pacific type, Hercyno type, Caledonian type and Anorogenic (A-type granites).
- Full Text:
- Date Issued: 1993
Lateritisation and secondary gold distribution with particular reference to Western Australia
- Authors: Coxon, Brian Duncan
- Date: 1993
- Subjects: Laterite -- Australia , Gold ores -- Geology -- Australia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4974 , http://hdl.handle.net/10962/d1005586 , Laterite -- Australia , Gold ores -- Geology -- Australia
- Description: Lateritisation is associated with tropical climates and geomorphic conditions of peneplanation where hydromorphic processes of weathering predominate. Laterites are products of relative (residual) and absolute(chemical) accumulation after leaching of mobile constituents. Their major element chemistry is controlled by the aluminous character of bedrock and drainage. Bauxitisation is characterised by residual gibbsite neoformation and lateritisation, by both residual accumulation and hydromorphic precipitation of goethite controlled by the redox front at the water table. The laterite forms part of a weathering profile that is underlain by saprock, saprolite, the mottled zone and overlain by a soil horizon. The secondary gold in laterites has its source invariably with mineralised bedrock. The distribution of secondary gold is controlled by mechanical eluviation and hydromorphic processes governed by organic, thiosulphate and chloride complexing. The precipitation of secondary gold is controlled by pH conditions, stability of the complexing agent and ferrolysis. Gold-bearing laterites are Cainozoic in age and are best developed on stable Archean and Proterozoic cratons that have suffered epeirogenesis since lateritisation. Mechanical eluviation increases in influence at the expense of hydromorphic processes as a positive function of topographic slope and degradation rate. Gradients greater than 10⁰ are not conducive for lateritisation, with latosols forming instead. High vertical degradation rates may lead to the development of stone lines. In the Western Australian case, post-laterite aridification has controlled the redistribution of secondary gold at levels marked by stabilisation of the receding palaeowater table. Mineable reserves of lateritic ore are located at Boddington, Westonia and Gibson toward the south-west of the Yilgarn Block. A significant controlling variable appears to be the concentration of chloride in the regolith. Based on the Boddington model, the laterite concentrates the following elements from bedrock gold lodes: i) Mo, Sb, W, Hg, Bi and Au as mobile constituents. ii) As and Pb as immobile constituents. Geochemical sampling of ferruginous lag after bedrock and laterite has provided dispersed anomalies that are easily identifiable. "Chalcophile corridors" up to 150 km in length are defined broadly by As and Sb but contain more discrete anomalies of Bi, Mo, Ag, Sn, W, Se or Au, in the Yilgarn Block. The nature of the weathered bedrock, the tabular distribution of secondary gold ore deposition and the infrastructural environment lends the lateritic regolith to low cost, open-cut mining. The western Australian lateritic-gold model perhaps can be adapted and modified for use elsewhere in the world.
- Full Text:
- Date Issued: 1993
The geology of the Welkom Goldfield with special reference to the "A", "B" and Beatrix Reefs
- Authors: Dwyer, Gordon Bransby
- Date: 1993
- Subjects: Gold mines and mining -- South Africa -- Free State , Gold ores -- Geology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4963 , http://hdl.handle.net/10962/d1005575 , Gold mines and mining -- South Africa -- Free State , Gold ores -- Geology -- South Africa
- Description: The first Witwatersrand gold deposits in the Orange Free State were discovered under younger cover rocks in the 1930's with the aid of drilling and geophysics. The Welkom gold deposits are found in the sedimentary rock sequences of the Central Rand Group, which represent unconformity bounded genetic packages. The structural configuration of the goldfield is one of a north to south trending synform that is split near it's axis by the De Bron and Homestead faults. The "B" Reef is a highly variable, erratically mineralised reef that lies on an unconformity at the base of the Spes Bona Formation. The "A" Reef Zone consists of several placers 1 including the "Reworked BPM" 1 the Witpan, the Uitsig, the Hanging Wall Grits and the Upper "A" Reef. The Beatrix Reef lies at the base of the Eldorado Formation on an unconformity surface overlying the Virginia Formation in the southern part of the Welkom Goldfield. The origin of gold in the Witwatersrand basin can be classified into the modified placer theory, the syngenetic theory and the epigenetic theory. From the distribution of basin edge unconformities it can be deduced that the Welkom fan depository was tectonically active on the western, southern and eastern margins during sedimentation. Palaeocurrent studies indicate that sediment was transported predominantly from the south and west. It is thought that the "B", "A" and Beatrix Reefs were all deposited in a braided stream environment. A multidisciplinary approach to ore evaluation of Witwatersrand deposits is considered to be the best method, where sedimentology, geostatistics and structural geology are used.
- Full Text:
- Date Issued: 1993
The influence of geological, genetic and economic factors on the ore reserve estimation of Kwaggashoek east iron ore deposit
- Authors: Latorre-Muzzio, Gina
- Date: 1993
- Subjects: Iron ores -- Geology -- South Africa , Geology -- South Africa -- Transvaal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4972 , http://hdl.handle.net/10962/d1005584 , Iron ores -- Geology -- South Africa , Geology -- South Africa -- Transvaal
- Description: Tectonics plays an important role in the genesis and subsequent mlnlng development of the Kwaggashoek East ore body. Lithological key units control the effectiveness of the ore forming processes, affecting the in situ ore reserve, The Kwaggashoek East deposit is the product of primary and secondary processes. A genetic model focussed on the source, migration and deposition of iron suggests a possible original source of iron as the product of very dilute hydrothermal input into deep ocean waters, with subsequent migration through structural conduits. Supergene processes account for the upgrading of the ore and the phosphorus redistribution. A good correlation between samples in a preliminary geostatistical study reflects the effectiveness of this process in the high grade ore zone. A broad overview of the economic issues which affect the commercialization of iron, indicates a balanced supply-demand situation for the five next years. The reserve estimation procedure requires accurate scientific terminology and appropriate methodology. Documentation is essential and should be detailed enough to allow for future reassessment. The results of three estimation methods in Kwaggashoek East differ by less than 5%. The accuracy of the final results depends more on geological interpretation and assumptions than on the method applied. Although optimization of grade and tonnage in the Kwaggashoek East deposit seems to be met with the actual cut-off grade used in the Thabazimbi mine district, the grade-quality concept introduced in this thesis indicates a decrease in the estimated reserves for the deposit
- Full Text:
- Date Issued: 1993
The nature of olivine-rich cumulate rocks of the lower critical and lower zones of the northwestern Bushveld Complex
- Authors: Haikney, Susan Ann
- Date: 1993
- Subjects: Geochemistry -- South Africa , Igneous rocks -- South Africa , Olivine -- South Africa , Bushveld Complex (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4980 , http://hdl.handle.net/10962/d1005592 , Geochemistry -- South Africa , Igneous rocks -- South Africa , Olivine -- South Africa , Bushveld Complex (South Africa)
- Description: Boreholes NG1 and NG2 were drilled on the farm Nooitgedacht 406 KQ to intersect the lower Critical and lower Zones of the western Bushveld Complex. The aim of this study is to describe the textural features and chemical characteristics of the olivine-bearing rocks in the intersections, as determined by petrographic studies, XRF analysis and microprobe analysis. The olivine-bearing rocks are dunites, harzburgites and olivine pyroxenites. They comprise olivine and orthopyroxene, with minor chromite, clinopyroxene and plagioclase, and their textures vary between adcumulate, mesocumulate and poikilitic. The sequence intersected can be broadly correlated with that in the eastern Bushveld Complex. Of the whole-rock inter-element ratios, the MMF (MgO)/[MgO+FeO])ratio is the clearest indicator of cyclicity. The olivine-rich rocks are more primitive than the associated rocks, and seem to become more primitive with height in most intervals. The plagioclase in the olivine-bearing rocks is unusually sodic in corrposition, having a maximum Na₂0 content of 8.12%. A comparison of olivine and plagioclase compositions with those in other intrusions has revealed that the only other major intrusion with sodic plagioclase is the Kiglapait intrusion of Canada. In the Kiglapait intrusion the sodic plagioclase occurs in conjunction with fayalitic olivine as opposed to the forsteritic variety of this study. Chemical variations in the rocks sampled indicate that periodic replenishment of the magma from which the rocks crystallised must have occurred. In some of the olivine-bearing intervals where little fractionation is evident, replenishment seems to have been continuous. In other intervals fractionation appears to have continued uninterrupted for significant periods, prior to rejuvenation by fresh influxes of magma.
- Full Text:
- Date Issued: 1993
A microstructural kinematic study of selected shear zones in the Hartbees River Thrust Belt, northeastern Namaqua Tectonic Province
- Authors: Jackson, Christopher
- Date: 1992
- Subjects: Metamorphic rocks -- South Africa -- Northern Cape , Mylonite -- South Africa -- Northern Cape , Geology -- South Africa -- Northern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4976 , http://hdl.handle.net/10962/d1005588 , Metamorphic rocks -- South Africa -- Northern Cape , Mylonite -- South Africa -- Northern Cape , Geology -- South Africa -- Northern Cape
- Description: The Hartbees River Thrust Belt (HRTS) is a 40-60 km wide, southwest-vergent zone of complex structure, lithostratigraphy and high-grade metamorphism in the northeastern part of the mid-Proterozoic Namaqua Tectonic Province. The HRTS comprises the boundary zone separating the Bushmanland and Gordonia Subprovinces of the Namaqua Province. A knowledge of the movement histories of major ductile shear zones within the HRTS is fundamental to understanding the tectonic development of the belt, and Namaqua tectogenesis as a whole. In spite of this, no detailed microstructural kinematic studies have been attempted and the movement histories and age relationships of these shear zones have not been described in detail. This thesis represents a detailed microstructural kinematic study of a representative suite of orientated samples of mylonitic rocks, collected from five ductile shear zones within the HRTS. These shear zones include the Neusspruit Lineament, the Kakamas shear zone (KSZ), the Hugosput shear system (HSS), the Rozynenbosch-Ganzenmond shear zone (RGSZ) and the Graafwater shear system (GSS). Accepted modern methods of microstructural kinematic analysis were applied to samples of mylonite from these shear zones, in order to determine the precise orientation of the kinematic vectors, and the sense and relative ages of movements on each of the shear zones. Shear sense criteria, including composite SoC planar fabrics and shear band foliations, asymmetrical porphyroclast systems, mica-fish, oblique grain-shape and subgrain fabrics, asymmetrical microfolds, and the displacement of fractured rigid grains, together with a well-developed mylonite elongation lineation, conclusively indicate that SSW-directed thrusting occurred along the HSS, RGSZ, GSS and possibly along the Neusspruit Lineament, while normal, top-to-NE movements occurred on the Neusspruit Lineament, KSZ and HSS. Rare transposition criteria, and textural and paragenetic contrasts between syn-kinematic fabrics, strongly suggest that the phase of normal, top-to-NE movement seen in the northeastern HRTS shear zones is younger than the more widespread top-to-SW thrusting event. On the basis of mesoscopic structural criteria, SSW-directed thrusting is correlated with the D₂ deformation event in the HRTS. The mylonite zones have been refolded by ENE-SSW trending F₃ crossfolds, whose demonstrated coaxial relationship to the mylonite elongation lineation precluded reorientation of primary kinematic vectors. In the southwestern HRTS, primary thrust vectors have been reoriented by right-lateral, strike-slip shearing adjacent to the Pofadder Lineament during D₄. Simple shear dispersion of mylonite lineations related to normal movement, suggests that they too have been modified by D₄ shearing, and this constrains the timing of extensional movements to post-D₂ and pre- or syn-D₄. Syn-kinematic mineral assemblages, rheological criteria and the annealing states of the mylonites, provide insight into the thermotectonic evolution of the shear zones. A model is proposed in which the movement histories of shear zones within the HRTS are explained in terms of a typical orogenic cycle, involving crustal thickening by thrusting during a compressional orogenic phase, followed by collapse of the thickened crust during an extensional taphrogenic phase.
- Full Text:
- Date Issued: 1992
Exploration for stratabound copper, lead and zinc deposits in the Damara-Katanga orogen, central-southern Africa
- Authors: Latorre, J J
- Date: 1992
- Subjects: Mining geology -- Research -- Africa , Copper ores -- Africa , Lead ores -- Africa , Zinc ores -- Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4946 , http://hdl.handle.net/10962/d1005558
- Description: The Damara-Katanga orogen in central-southern Africa represents an area of 1.73xl0⁶ sq. km. The region is considered one of the wealthiest metallogenic provinces in the world. Successful exploration for stratabound base-metal deposits has taken place at this particular area since the introduction of more organised methodology in the early 1920s. The genesis, location and distribution of the ore deposits are related to their tectonic settings. Geodynamic evolution of the orogen, which initially formed part of a complex Pan-African rift system, comprises the following stages rifting; downwarping, including spreading on the western portion; syn-orogeny and late-orogeny. Two major tectonic events in the history of the region have been identified: the Katangan (900-750 Ma) and the Damaran episodes (750-500 Ma). Timing of mineralisation of ore deposits has been related to the evolutionary stages of the orogen. Genetic models of the most productive deposits are briefly discussed in this dissertation. The sedimentological, geochemical, paleogeographic and structural features can be employed as geological guidelines for integrated exploration programmes. Discoveries of major deposits and prospects in the orogen are also summarised, focussing on the exploration methods employed. The cost-effective use of the exploration techniques includes the classical copper-lead-zinc soil sampling for residual soils such as those in the Copperbelt area. Airborne magnetics and electromagnetics and follow-up ground geophysics have proved successful in areas where the cover is transported in the search for shallow ore deposits such as the Matchless massive sulphides. Remote sensing, geochemical and geophysical techniques have been tried in covered areas of western Botswana. The lack of geological control makes this interpretation difficult. A detailed geological mapping and the use of geochemical and geophysical techniques has been used to delineate carbonate-hosted base-metal deposits at the Otavi Land. The more expensive traditional methods necessary for the delineation of orebodies, such as pitting, trenching and drilling, are also discussed. Using a sequential approach, a possible exploration strategy is suggested, outlining the cost-effective use of remote sensing, geochemical and geophysical techniques. Standardisation in basic geological information is required for future successful explorations in the Damara-Katanga orogen, as well as attractive mining policies. In the event of their implementation, exploration perspectives are promising, specifically in terms of ore potential.
- Full Text:
- Date Issued: 1992
Facies mapping of the Vaal Reef placer as an aid to remnant pillar extraction and stope width optimisation
- Authors: O'Donovan, Anthony Gareth
- Date: 1992
- Subjects: Facies (Geology) -- South Africa -- Vaal Reef placer
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4947 , http://hdl.handle.net/10962/d1005559 , Facies (Geology) -- South Africa -- Vaal Reef placer
- Description: The Vaal Reef placer is situated on the unconformable junction of the Strathmore and Stilfontein formations of the Johannesburg Subgroup. Within the South Division of the Vaal Reefs Exploration and Mining company lease, the Vaal Reef Placer is shown to be composed of several different units. Each unit exhibits its own specific characteristics and trend direction which can be used to establish distinct "Reef packages". These packages can be mapped in such a way as to provide a preliminary lithofacies map for the Vaal Reef Placer. The delineation of such geologically homogenous zones, and the development of a suitable depositional model, can be utilised in several ways. The characteristics of a particular zone are shown to influence the control of stoping width, evaluation of remnant pillars and the geostatistical methodology of evaluating current and future ore reserve blocks.
- Full Text:
- Date Issued: 1992
Genetic models for epithermal gold deposits and applications to exploration
- Authors: Veselinović, Milica
- Date: 1992
- Subjects: Gold ores -- Geology , Hydrothermal deposits
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4950 , http://hdl.handle.net/10962/d1005562 , Gold ores -- Geology , Hydrothermal deposits
- Description: Epithermal gold deposits are the product of large-scale hydrothermal systems in tectonically active regions. They form at shallow crustal levels where the physico-chemical conditions change abruptly. Two major groups of epithermal gold deposits can be distinguished based on their genetic connection with: A) Copper-molybdenum porphyry systems and B) Geothermal systems related to volcanic centres and calderas. Epithermal gold deposits connected with geothermal systems encompass three major types: adularia-sericite, acid-sulphate and disseminated replacement (the Carlin-type). Their essential ingredients are: high heat source which leads to convection of groundwater in the upper crust; source of hydrothermal fluid, metals and reduced sulphur; and high-permeability structures which allow fluid convection and metal deposition. Mixing of these ingredients leads to the formation of epithermal gold deposits throughout crustal history, without any restriction on age. The ores were deposited from near-neutral (adularia-sericite type and some of the Carlin-type) to acidic (acid-sulphate type and porphyry-related epithermal gold deposits), low-salinity, high C0₂ and high H₂S fluids, which were predominantly meteoritic in origin. The transport capability of deep fluids in epithermal hydrothermal systems may be shown to be dependent largely on their H₂S content and, through a series of fluid mineral equilibria, on temperature and on C0₂ content. The most common mechanisms of ore deposition are boiling (phase separation), mixing of fluids of different temperatures and salinities, reaction between them and wall rocks, dilution and cooling. An understanding of genetic models for epithermal gold deposits provides the basis for the selection of favourable areas for regional to prospect-scale exploration.
- Full Text:
- Date Issued: 1992
Geological controls for coal exploration and mining
- Authors: Noppé , Mark Adrian
- Date: 1992
- Subjects: Coal -- Geology , Coal mines and mining
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4954 , http://hdl.handle.net/10962/d1005566 , Coal -- Geology , Coal mines and mining
- Description: The identification and interpretation of geological features is essential for the planning and ultimate success of any mining venture. Examples of geological features significant for mining are presented, and their identification during exploration discussed. In particular, the importance of coal qualities, seam thickness and seam elevation are emphasised in relation to longwall mining. Geostatistical analysis provides a powerful tool for improving the prediction and decision-making capabilities of both exploration and mine geologists. The availability of geostatistics, and the benefits resulting from its application, are demonstrated using actual data for calorific value, seam thickness and seam elevation. Contamination of run-of-mine coal is a common problem on highly-mechanised collieries. The problem generally arises from over-cutting of the designated mining horizon. A practical system for monitoring and controlling contamination on a mechanised bord-and-pillar and longwall colliery is presented. The results and benefits of applying such a system are cited for an actual longwall colliery. Numerical geological predictions are not always reported in terms of the reliability of such estimates. Many of these values can be reported in terms of confidence limits, particularly for routine grade control purposes. The methods and benefits of such reporting are described and illustrated by way of examples for calorific value and contamination levels.
- Full Text:
- Date Issued: 1992
Guidelines to the evaluation of selectively mined, open pit gold deposits during the exploration stage of mine creation
- Authors: Pelly, Frederick Douglas Peter
- Date: 1992
- Subjects: Mining geology , Gold ores -- Geology , Gold mines and mining -- Economic aspects
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4970 , http://hdl.handle.net/10962/d1005582 , Mining geology , Gold ores -- Geology , Gold mines and mining -- Economic aspects
- Description: This dissertation studies the evaluation of selectively mined, open pit gold deposits during the exploration stage of the mine's life. Since 1970 a large number of selectively mined, open pit gold mines have come into operation. The most common deposits include epithermal vein, mesothermal lode and laterite gold deposits. In general the deposits are characterized by small tonnages (1-20 million tonnes), relatively high grades (2-10 grams per tonne gold), submicroscopic to coarse gold, inexpensive mining, and both free milling and refractory ores.The key components that require evaluating during the exploration period are the deposit's geology, ore reserves, pit design, ore metallurgy and environmental impact. Feasibility studies are the main vehicle by which to report and guide the exploration programme. During the exploration period a company may undertake an initial (geological feasibility), second (preliminary mine feasibility) and third (final feasibility) delineation programme in order to gather sufficient data to justify a mine development decision. The responsibility of evaluating the mineral prospect lies primarily with the exploration geologist and mining engineer. Broad experience, a professional attitude, a thorough understanding of mining economics, and a high level of geological, engineering and technical skills are traits required by the evaluators. In order for mining companies to make sound investment decisions the geographical, geological, mining, metallurgical, environmental, marketing, political and financial aspects affecting the economic potential of the venture must be integrated so that the likely costs, risks and returns of the investment alternative are quantified. Ultimately, it is the economic analysis of these three items that determine whether the mineral prospect is developed into a mine I delineated further I retained until economic circumstances improve, or abandoned. To assess the costs, risks and returns, extensive use of the risk analysis is advocated throughout the exploration period . When combined with intelligent judgement of the intangible risk elements, the probabilistic distribution of discounted cash flows are invaluable in making sound investment decisions. However, the economic analysis is only as good as the information on which it is founded. Accurate and representative field data is the most important prerequisite to successfully evaluating and developing a new mine.
- Full Text:
- Date Issued: 1992
Nickel sulphide mineralization associated with Archean komatiites
- Authors: Lane, Monica Leonie
- Date: 1992
- Subjects: Nickel sulfide , Geology, Stratigraphic -- Archaean
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4982 , http://hdl.handle.net/10962/d1005594 , Nickel sulfide , Geology, Stratigraphic -- Archaean
- Description: The distribution of Archean Nickel sulphide deposits reflects tectonic controls operating during the evolution of the granitoid greenstone terrains. Important deposits of komatiitic-affinity are concentrated within, and adjacent to, younger (∼2.7 Ga), rift-related greenstone belts (e.g. Canada, Western Australia and Zimababwe). Two important classes of Archean Nickel sulphide deposits exist, formerly known as "Dunitic" and "Peridotitic", these are now referred to as Group I and Group II deposits, based on their characteristic structure and composition. Mineralization varies from massive and matrix to disseminated, and is nearly always concentrated at the base of the host unit. Primary ores have a relatively simple mineralogy, dominated by pyrrhotite-pentlandite-pyrite, and to a lesser degree millerite. Metamorphic grades tend to range from prehnite-pumpellyite facies through to lower and upper amphibolite facies. Genesis of Group I and II deposits is explained by the eruption of komatiites into rift-phase greenstone belts, as channelized flows, which assimilated variable amounts of footwall rocks during emplacement. Sulphide saturation was dependent on the mode of emplacement and, the amount of sulphidic sediments that became assimilated prior to crystallization. This possibly accounts for variations in ore tenor. The Six Mile Deposit (SMD) in Western Australia, is an adcumulate body of the Group IIB-type, exhibiting disseminated mineralization. The ore has been "upgraded" due to hydration and serpentinization. A profound weathering sequence exists, which was subsequently utilized during initial exploration. Exploration techniques has been focused on Western Australia, as it is here that the most innovative ideas have emerged.
- Full Text:
- Date Issued: 1992
Pegmatite-hosted mineral deposits of central and southern Africa : regional geological settings and preliminary exploration target considerations
- Authors: Senzani, Freeman Elther David
- Date: 1992
- Subjects: Pegmatites -- Africa, Southern , Mineralogy -- Africa, Southern , Pegmatites -- Africa, Central , Mineralogy -- Africa, Central
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5011 , http://hdl.handle.net/10962/d1006087
- Description: Review of literature shows that rocks of all ages from the Archaean to the early Phanerozoic host pegmatite-based mineralisation in the central and southern region of the African continent. The greatest concentrations occur in the Archaean and late Proterozoic orogenic belts, while early to middle Proterozoic granites do not, in general, host mineralisation. Pan-African mineralisation is present, but is not widespread. Some deposits previously considered to be of Pan-African have been shown to be of Proterozoic age. In common with occurrences of other regions, the deposits are closely associated with small, late- to post-tectonic granites. Therefore, preliminary assessment of the potential of granites as sources of pegmatite mineralisation should utilise satellite data or aerial photographs. The granites also tend to be alkaline and peraluminous. Thus, in the next stage, chemical analysis for selected major and trace elements should be conducted directly on granites if they occur as small plutons. For large granitic batholiths or terranes, preliminary stream-sediment surveys may be necessary to reduce the size of the target area. Subsequently, pegmatite zonation around suitable granites should be assessed as it allows attention to be focussed on areas likely to host the specific type of mineralisation being explored for.
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- Date Issued: 1992
Small-scale gold mining in southern Africa
- Authors: Joubert, Barend Daniel
- Date: 1992
- Subjects: Gold mines and mining -- South Africa , Abandoned mines , Abandoned mines -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5002 , http://hdl.handle.net/10962/d1005615 , Gold mines and mining -- South Africa , Abandoned mines , Abandoned mines -- South Africa
- Description: The general characteristics of gold deposits are reviewed, and a classification of gold deposits based on mineability is proposed. Evaluation, mlnlng and beneficiation methods are briefly discussed. It is concluded that the most viable targets for small-scale companies comprise deposits that require the least pre-production time and expense. Great potential exists for the small-scale reclamation of gold from tailings dumps and abandoned mines in Southern Africa. There is also potential for developing new smallscale gold mines in the Archaean greenstone terranes of the Zimbabwean and Kaapvaal cratons.
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- Date Issued: 1992
The development and distribution of heavy mineral concentrations in alluvial systems
- Authors: Lynn, Michael David
- Date: 1992
- Subjects: Heavy minerals -- Research , Alluvial plains -- Research , Geomorphology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4937 , http://hdl.handle.net/10962/d1005549 , Heavy minerals -- Research , Alluvial plains -- Research , Geomorphology -- South Africa
- Description: The objective of this review is to summarise the characteristics, significance and evolution of heavy minerals and their accumulations, and to identify the key controls on the development and distribution of heavy mineral concentrations in alluvial systems. These controls can be broadly classified as tectonic setting, geomorphic setting and grain-scale concentrating processes, each of which is discussed. Based on this review, exploration models are developed which are designed to indicate favourable localities for the accumulation of heavy minerals, and trends likely to be exhibited within these accumulations. The models are structured from the broadest scale of target selection, down to the local scale of sample site selection. The major conclusion of this work is that an understanding of process geomorphology is required to develop genetic models of placer development, including a detailed evaluation of climatic fluctuations throughout the Caenozoic. Palaeoplacers such as the Witwatersrand goldfield, are inferred to have formed under similar circumstances of tectonic setting as genetically comparable Caenozoic placers such as those of Otago, New Zealand. The means of preservation of such major basins is however poorly understood.
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- Date Issued: 1992
The exploration for and possible genesis of, some Archaean granite/gneiss-hosted gold deposits in the Pietersburg granite-greenstone terrane
- Authors: Linklater, Michael Anthony Leonard Flanders
- Date: 1992
- Subjects: Gold ores -- Geology -- South Africa , Gneiss , Granite
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4945 , http://hdl.handle.net/10962/d1005557 , Gold ores -- Geology -- South Africa , Gneiss , Granite
- Description: Abstract The gold mineralization event within Archaean granite-greenstone terranes occurred during the late Archaean, and followed the intrusion of syn- to late-tectonic granitic plutons into previously deformed greenstone belts. An Archaean granite/gneiss-hosted gold deposit, in terms of this project, is classified as having a gold-assay cutoff of 1g/metric ton over widths of at least several metres, or higher grades over narrower widths and/or verbal descriptions that indicate such values. Fluid inclusion studies and isotopic data identify two possible origins for the auriferous fluids; namely magmatic and metamorphic. The exploration target according to the magmatic model, is a late-Archaean, hydrothermally altered, mineralized and fractured granitic intrusion preferably with a granodioritic or quartz-dioritic composition. The exploration target according to the metamorphic replacement model is a granitic stock that has intruded a zone of crustal weakness such as a shear zone, active during the late Archaean. Alternatively, the granitic intrusion should be affected by regionally extensive late-Archaean shearing. It should be hydrothermally altered, deformed and mineralized. Five areas within the Pietersburg granite-greenstone terrane were selected for the 'Regional Area Selection' phase of exploration for Archaean granite/gneiss-hosted gold deposits; namely Roodepoort, Waterval, Ramagoep, Moletsie and Matlala. Roodepoort contains a known granodiorite-hosted gold deposit; the Knight's Pluton, and served as an orientation survey for this project. The use and interpretation of LANDSAT images formed an integral part of exploration techniques; to assess their usefulness in the exploration of Archaean granite/gneiss-hosted gold deposits. Area selection criteria for granite/gneiss-hosted gold mineralization at Roodepoort are the major ENE-trending shear zone, the NNW-trending lineament and hydrothermal alteration, shearing, quartz-stockworks and sulphide mineralization within the Knight's Pluton. The origin of the gold within the Knight's Pluton is uncertain; both magmatic and metamorphic models are possibilities. Ongoing exploration is in progress at Roodepoort. The only area selection criterion for granite/gneiss-hosted gold mineralization at Waterval is the sericitized, subcropping granites located within trenches. Gold mineralization is insignificant. No area selection criteria for Archaean granite/gneiss-hosted gold mineralization were located at Ramagoep, Matlala and Moletsie. No further exploration is recommended for all these areas. The MES image interpretations were successful in identifying lineaments, granitic outcrops, greenstones, vegetation and soil cover. The Clay-iron images adequately differentiated betweeen iron-rich and clay-bearing areas. However, not all clay-bearing areas were associated with hydrothermal alteratian; field checks were necessary to discriminate between weathered granites and hydrothermally altered granites. The Wallis images served to locally enhance the contrasts of the MES and Clay-iron images.
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- Date Issued: 1992
The geology and evaluation of the "A"-reef at No.3 shaft, Western Holdings Mine, Welkom goldfield
- Authors: Blamey, Nigel John Frederick
- Date: 1992
- Subjects: Gold mines and mining -- South Africa -- Free State , Gold ores -- Geology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4957 , http://hdl.handle.net/10962/d1005569 , Gold mines and mining -- South Africa -- Free State , Gold ores -- Geology -- South Africa
- Description: The "A" -Reef occurs within the Aandenk Formation of the Central Rand Group, Witwatersrand Supergroup, in the Welkom Goldfield. It comprises the Witpan and Uitsig Reefs which are both oligomictic conglomerates, and are exploited for their gold content by Anglo American Corporation. The main Witpan channel complex is orientated in a NW-SE direction and occurs close to No.3 Shaft of Western Holdings Mine where it is currently being mined. The Witpan Reef varies in thickness from 7-220cm, with lateral facies changes controlling the thickness. Within the reef, gold is associated with degradation surfaces, carbonaceous material, increase in pebble sphericity, and channel edges. Two channel edges have yielded the best gold values on No.3 Shaft although the potential for further payable gold lies in the recognition of sieve conditions. The potential also exists for extensions of the "carbon"-bearing Uitsig channel currently being mined on President Steyn Mine. The palaeo-environment proposed for formation of the Witpan Reef is a braidplain that was partly reworked by a brief transgression. Ore evaluation using geostatistics was considered a valid technique as the dataset is sufficiently well structured. Semi-variograms in the channel and across-channel directions differ markedly. It was found that variograms of gold in cmg/t lacked sufficient structure for modelling, however, log semi-variogram modelling followed by simple log-kriging and back-transformation, proved to be the most successful method. Owing to the morphology and distribution of gold within the reef, a geologically based geostatistical valuation method is proposed. The potential for further exploration of "A" -Reef depends on a substantially higher gold price. In this event, exploration of Uitsig Reef to the southwest of the current mining area is recommended as well as a new exploration strategy for Witpan Reef.
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- Date Issued: 1992
The geology and geochemistry of the north-western portion of the Usushwana Complex, South-Eastern Transvaal
- Authors: Riganti, Angela
- Date: 1992
- Subjects: Geology -- South Africa -- Transvaal , Geochemistry -- South Africa -- Transvaal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4958 , http://hdl.handle.net/10962/d1005570 , Geology -- South Africa -- Transvaal , Geochemistry -- South Africa -- Transvaal
- Description: The 2.9 Ga old Usushwana Complex in the Piet Retief-Amsterdam area (south-eastern Transvaal) represents an exposed segment of a layered intrusion. It has the form of a dyke-like body elongated in a northwesterly direction, and extends to an estimated depth of 3000 -5500 m. Lithologically, the Complex consists of a cumulate succession of mafic rocks capped by granitoids and has intruded along the contact between the basement and the supracrustal sequences of the Kaapvaal Craton. Differentiation of an already contaminated gabbroic magma resulted in an ordered stratigraphic sequence comprising progressively more evolved lithotypes, with at least two imperfect cyclic units developed over a stratigraphic thickness of about 700 metres (Hlelo River Section). Meso- to orthocumulate textured gabbros and quartz gabbros grade upwards into magnetite- and apatite-bearing quartz gabbros, interlayered with discontinuous magnetitite horizons. The gabbros in turn grade into hornblende-rich, granophyric granodiorites. The differentiation process is regarded as having been considerably enhanced by the assimilation of acidic material, derived by partial melting of the felsic country rocks at the roof of the magma chamber. Recrystallisation of these rocks gave rise to the microgranites that locally overlie the granodiorites. Mineralogical, textural and geochemical features indicate a relatively advanced fractionation stage, suggesting that the exposed sequence of the Usushwana Complex in the study area represents the upper portion of the intrusion. No significant mineralised occurrences were identified. However, on the basis of similarities between the Usushwana Complex and other mafic layered intrusions which host significant ore deposits, it is suggested that economic concentrations of base metal(Cu-Ni) sulphides, PGE and chromitites are likely to be developed at lower stratigraphic levels.
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- Date Issued: 1992