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).
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- Date Issued: 1993
The alluvial diamond deposits of the lower Vaal river between Barkly West and the Vaal-Harts confluence in the Northern Cape province, South Africa
- Authors: Matheys, Fabrice Gilbert
- Date: 1991
- Subjects: Diamond deposits -- South Africa , Geology, Economic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4933 , http://hdl.handle.net/10962/d1005545 , Diamond deposits -- South Africa , Geology, Economic
- Description: The alluvial diamond deposits along the Vaal River, between Barkly West and the Vaal-Harts confluence, have been worked for more than one century by thousands of private diggers. The diamonds are recovered from two sedimentary units of Cenozoic age, the Older Gravels and the Younger Gravels. These rest on a basement of Ventersdorp Supergroup andesites and Karoo Sequence sediments, which have been intruded by Cretaceous kimberlites. The gravels are, in turn, overlain by the Riverton Formation and the Hutton Sand. On a large scale, tectonic setting, geomorphology and palaeoclimate have played a major role in the formation of diamondiferous placers in the area under investigation. A study of the sedimentology of the Younger Gravels was carried out with the aim of acquiring an understanding of the processes responsible for the economic concentration of high quality diamonds. An investigation of facies assemblages, clast composition, clast size, palaeocurrent directions external geometry, particle morphology and led to the conclusion that the Younger Gravels were deposited in a proximal braided stream environment during high discharge. A small-scale experiment was carried out to test the efficiency of different sedimentological trap sites in concentrating kimberlite indicator minerals. The results show that the concentration of indicator minerals is dependent on the size fraction chosen, bed roughness and gravel calibre. The examination of surface features on pyrope, picroilmenite and chrome diopside from kimberlite led to the conclusion that most of these minerals are locally derived. Diamond grade variations within the Younger Gravels are influenced by a combination of factors, including bed roughness, channel width and sorting process from the source. Alluvial diamond exploration programmes must take into account the tectonic setting, the palaeoclimate, the level of erosion, the stability of the drainage system in the area as well as the presence of local trap sites in the river profile. It is concluded that the diamonds are the product of a long and complex process of erosion, reworking and concentration and are derived from Cretaceous kimberlites in the area.
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- Date Issued: 1991
The concept of grade in mineral deposits
- Authors: Esterhuizen, Anton G
- Date: 1983 , 2013-04-04
- Subjects: Mines and mineral resources , Ore deposits , Mineralogy , Geology, Economic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5020 , http://hdl.handle.net/10962/d1006331 , Mines and mineral resources , Ore deposits , Mineralogy , Geology, Economic
- Description: The grade of a mineral deposit is determined by the effectiveness of a geological ore forming process, which is the result of the interaction between an ore forming mechanism and the environment in which it operates. Properties of a mineral deposit controlled by ore forming processes include the distribution, density and nature of ore minerals and gangue, and the metal content and impurities of the ore minerals. More efficient ore forming processes tend to develop in the larger mineralizing systems giving rise to richer deposits. As the geological environment within which a mineral deposit evolves becomes more complex a greater number of variables interact to determine the grade of the deposit. This is reflected in the greater variability of the grade distribution, resulting in greater difficulties in obtaining reliable estimates of the recoverable grade, and increased difficulties in the processing of ores. In response to economic fluctuations the working grade of heterogeneous orebodies, that form in geologically complex environments, can often be altered to ensure the continued viability of a mining venture. In contrast the evenly mineralized orebodies that tend to develop in geologically simple environments do not have this flexibility. All the important decisions in the mining industry, such as feasibility studies, choice of ~ining and processing methods, selection and planning, are made on the basis of, or are related to, grade estimates. If the geological controls of grade are fully understood, then it is possible to optimize the selection of the various mining alternatives, leading to the efficient exploitation of ore deposits.
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- Date Issued: 1983
Geological factors affecting the grade and tonnage of sandstone uranium deposits
- Authors: Holliman, K A
- Date: 1981 , 2013-03-19
- Subjects: Uranium ores , Sandstone , Geology, Economic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5009 , http://hdl.handle.net/10962/d1005914 , Uranium ores , Sandstone , Geology, Economic
- Description: The largest known reserves of uranium are found in sandstone deposits, in the form of roll-front, peneconcordant and stacked types. Drilling on spacings of between 50 m and 5 m centres is the current method of attempting to delineate such ore bodies but because of the apparent random distribution of the mineralization there is a large degree of uncertainty in these predictions. Even on drilling grids of 3,5 m centres the uncertainty in predicting the distribution of stringer ore in roll front mineralization is still 100 per cent. (Sandefur & Grant 1980). Because of escalating costs it is becoming increasingly less economically feasible to delineate bodies of this nature in this manner and much more reliance will have to be placed on the geologist's interpretation of ore distribution when calculating ore reserves. The grade and tonnage of a sandstone uranium deposit can only be calculated with some degree of confidence if the processes forming the ore body are fully understood. The aim of this review is to examine the factors governing the formation and geometry of a sandstone body, the mobility and fixation of uranium and to establish criteria which will enable a more confident prediction to be made of the distribution of sand bodies and the distribution of the mineralization within them
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- Date Issued: 1981
Geological factors in the evaluation of vein deposits
- Authors: Neuhoff, Larry E.
- Date: 1980 , 2013-04-02
- Subjects: Veins (Geology) , Hydrothermal deposits , Mineralogy , Geology, Economic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5029 , http://hdl.handle.net/10962/d1006911 , Veins (Geology) , Hydrothermal deposits , Mineralogy , Geology, Economic
- Description: From introduction: Vein-type mineralization, particularly gold, copper, tin and tungsten has provided a source of metal to man for over 2000 years. These deposits are usually small but in some cases are of very high grade. Prior to 1940 veins were extremely important sources of metals because of their relatively high-grades. However, with improved mining, smelting and concentrating methods, much lower grade material became economic, hence these smaller deposits could no longer hold their dominance. Recently the energy crisis and escalating costs of capital for large projects has made smaller deposits attractive once more (Temblay and Descarreaux, 1978) . At the present time gold, tin and tungsten command high prices on world markets. It is for these reasons that a study of the evaluation techniques pertaining to these deposits has been undertaken. In this review the geological factors which influence the evaluation are stressed. In particular, emphasis is placed on the emplacement of vein deposits, and the subsequent chemical and structural modifications of these deposits. The latter part of the review concentrates on the limitations of the sampling and ore reserve techniques that can be applied to the evaluation of mineralized veins. In the conclusion those techniques that are most applicable are stressed, and an evaluation model is outlined.
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- Date Issued: 1980