The aim of this thesis has been to analyse and prioritise the geological factors which are prone to risk within British Coal Opencast's site tonnage estimation procedures. Geological variables such as coal seam thickness, specific gravity, washout and old workings deductions have been carefully analysed, using scanning and vectorising software techniques on examples of "ground-truth" recorded from surveyed plans from many worked sites. Techniques such as sensitivity modelling have determined which of the parameters are important in the estimation procedure. Sensitivity modelling has been linked with risk analysis to provide a means to critically review coal tonnage estimation. Statistical, risk analysis and Operational Research methodologies have been developed using commercial and custom written software to analyse and understand the necessary sampling strategies needed to estimate contract tonnages. The reduction of error in a tonnage estimate must be proportional to the increased understanding of the underlying geological variability with increasing sample numbers. A method is demonstrated whereby the optimum number of samples are suggested. However samples which exceed the optimum number do not necessarily increase the accuracy of the estimate proportionately to the extra sampling effort. The rate of this information gain has been modelled using a simulated exploration exercise and the results point towards variability reduction being inversely proportional the square root of the sample numbers. Knowledge gained from the inter-relationship between geological and sampling variability has been recorded, enabling future British Opencast Sites to be drilled and estimated with minimal contract risk. The resulting "Performance Assessment" methodology could be applied to a wider range of mineral exploration activities other than coal applications.

Guyana is one of the major bauxite-producing countries in the world and the majority of the ore is at present mined in the MacKenzie- Ituni region near the Demerara River by the Demerara Bauxite Company. The bauxite deposits underlie considerable thicknesses of Tertiary sands, clays and lignites of the Berbice (White Sand) Formation and appear to be associated with the sub-topographic basement highs. Many geologists consider the bauxites to have been formed by in situ residual weathering of the basement rocks, while others consider they are derived by weathering of sedimentary clays and sandy clays. Guyana appears to have both types of deposit. The primary object of the study was to investigate the nature of the genetic relationship between the bauxite deposits of the MacKenzie-Ituni area and the basement rocks beneath them. The approach was essentially geochemical, although some mineralogical studies were also made. The distributions of selected elements within six complete bauxite to bedrock profiles were investigated. Elemental distribution on an areal scale in two orebodies was also studied to ascertain whether elemental trends in the bauxites could be related to bedrock variations. The majority of the analyses were carried out on an ARL29000 direct-reading optical emission spectrometer and the methods developed for this and other projects are contained in the Appendix. It is concluded that the deposits are derived from superjacent bedrock although the relationship between bauxite and bedrock is obscure. The controlling factor in the location of bauxite deposits in this area is considered to be the intensity of weathering that has taken place, and this in turn depends on a variety of factors.

It is known from the geology that the pillow lava sequence overlying the Troodos igneous complex of Cyprus ought to contain many concealed sulphide orebodies. It has been shown in the past that the only geophysical technique capable of locating such deposits is the induced polarization method. However problems still remain in the implementation of surveys and in discriminating between different IP sources. In-situ measurements using a short spacing Wenner array were carried out over mineralization and barren rocks. The decay curves, after normalization to the value at 0.063 seconds after current cut-off, were all fitted, by a least squares method, to a three component exponential function. The exponential factors showed no discrimination between metallic and membrane IP, but indicated a longer decay for large magnitude chargeability. An estimate of the energy spectral density under each decay curve produced the same result, but did discriminate between Lower Pillow Lavas and mineralization for large chargeability values. IP surveys over two known, but contrasting sulphide deposits showed that the dipole-dipole array is the most applicable when only one traverse per line is carried out. However when combined profiling is undertaken the pole-dipole array is the most suitable due to its asymmetrical nature. Mixed plotting of the data has also been found to be a useful aid to interpretation. Inductive coupling was not a serious problem, but some of the decay curves were dominated by noise for the larger array separations. Criteria were developed for assessing data quality. Computer modelling using the finite-element method has demonstrated its applicability for interpretation and empirical relations have been developed which assist in the selection of survey parameters. The changes produced in the pseudosections by altering various geological parameters have been investigated with simplified models of the Cypriot environment. The resistivity data was found not to correlate with the IP data, but there was an indication of a resistivity decrease with depth.

In the mise-a-la-masse method, conducting bodies are energised using current electrodes in mineralized outcrops or borehole intersections, and the resulting potential distribution mapped and used to indicate qualitatively the form of the conductor. In this thesis a quantitative three dimensional integral equation technique implemented on the Vax 8600 computer at Leicester University is used to develop interpretation schemes and carry out detailed modelling of mineralization in two field areas. The interpretation technique was evaluated by comparing theoretical data derived for bodies of simple shape - spheres, discs and slabs. It is shown that for a thin slab or disk, the potential gradient in a borehole at the intersection of the ore hosting the current electrode is inversely proportional to the area of the upper side of the body. This is also shown to be true for a spherical body, but only if the borehole in which measurements are taken intersects the centre of the sphere. The mise-a-la-masse method was employed at two field sites where borehole and other geophysical data were available. At Gairloch, NW Scotland the data allowed a three-dimensional model of the complex structure of the mineralization to be developed. In San Telmo, in the Spanish Pyrite Belt, an estimate of the size of a large mineralized lens was made by the use of the interpretation scheme and later by modelling. This result was used in planning further boreholes by the company in charge of the site. Downhole resistivity and IP were carried out together with a comprehensive suite of geophysical surveys over the outcropping mineralization at Gairloch. These are evaluated and contribute to the final interpretation of the area. The results from parametric model studies show that the use of the method can provide fast, in-field determination of the approximate size of an intersected conducting body with only one available drillhole. The implementation of the numerical method for modelling the data has also allowed more detailed interpretation of deep conductors.

The Koga feldspathoidal syenite complex is a part of the alkaline igneous province of Northwest Pakistan lying between Loe Shilman and Tarbela. It consists of sodalite - cancrinite rich pegmatites, foyaites, feldspathoidal syenites, pulaskitic and garnet bearing feldspathoidal syenites, alkali syenite, lamprophyres, carbonatites and fenites. The Koga complex rocks have SiO2 concentrations from 55 - 62 % with Agpaitic Index (Na2O + K2O)/(Al2O3 mol. prop) for feldspathoidal syenites range from 0.98 to 1.12 indicating both miaskitic and agpaitic character, showing considerable variation in the concentration and distribution of major oxides. Na2O > K2O except in one rock (alkali syenite). The mafics occur as aggregates, almost without amphibole except in one sample. There are two distinct trends of silica undersaturation. The foyaites and foyaitic feldspathoidal syenites display both a phonolitic trend (eventual decrease in silica with differentiation) and a trachytic trend towards oversaturation of silica. The Koga feldspathoidal syenite rocks are depleted in TiO2, MgO, CaO, Sr, Ba and heavy rare earth elements. Ba and Sr show a strong geochemical coherence. K/Rb ratios are different in different groups ranging from 274 to 758 and are higher than the main trend of igneous suites. Rocks are rich in light rare earths and depleted in heavy rare earths with Ce negative anomaly. The composition of the nepheline is mostly restricted to the Morozewicz - Buerger convergence field in the system Ne - Ks - Qz, which is a characteristic of subsolvus nepheline syenites. The recrystallization process at lower temperatures might have given rise to subsolvus types from a single high temperature feldspar hypersolvus assemblage. The composition of all the groups of the Koga feldspathoidal syenites suggest a pressure > 1 and < 5 Kb, except sodalite rich foyaites. The geochemical and mineralogical evidence suggests a magmatic progression from Babaji soda granite &rarr; Babaji nordmarkite &rarr; alkali syenite &rarr; garnet bearing feldspathoidal syenite &rarr; foyaitic feldspathoidal syenite &rarr; feldspathoidal syenite &rarr; foyaitic feldspathoidal syenite &rarr; feldspathoidal foyaites, miaskitic &rarr; feldspathoidal foyaites, agpaitic &rarr; sodalite - cancrinite rich foyaites and finally sodalite rich foyaites. The processing of the raw material is more effective on -250 +125 ? size fraction and total alkalis increase relative to the starting material and F2O3 contents decrease to 0.13%. Following chemical analyses of sieved and magnetically separated fractions of a number of representative rocks, it is clear that the Koga feldspathoidal syenite could be benificiated to make commercially accepted material.

A taphonomic investigation of Late Miocene mammal bones and teeth and a taxonomic study of the abundant and diverse giraffid material from Kerassia, Greece, were undertaken. The material was collected from seven different sites near Kerassia, where at least two fossiliferous horizons occur. Microbial action caused extensive destruction in almost all the examined specimens of bone and teeth tissues from both horizons. Despite this, and contrary to the established ideas, bioeroded tissues survived to become fossils, preserving their histological and bioerosion features. The diameters of the microtunnels (150-600 nm) in the destructive foci indicate that the invading microorganisms were bacteria. Recrystallization of the apatite crystallites in the foci of damaged tissues occurred immediately after the end of bacterial activity, restraining later diagenetic recrystallization. This process is responsible for differences in the chemistry of the three structural areas of the bioeroded tissues, the undamaged areas, the foci and the rims of the foci. X-ray diffraction mineralogical analyses showed that fossil bone and dentine consist of carbonate fluorapatite and enamel consists of carbonate hydroxyapatite. The crystallinity of the fossil tissues is not age dependent but rather reflects the type of the hard tissue and the conditions of the local burial environment. To date, five different species of giraffes have been determined in Kerassia. Four species were found in the lower horizon, Palaeotragus rouenii, Palaeotragus sp., Samotherium major and Helladotherium duvernoyi and four species were found in the upper horizon Palaeotragus rouenii, Samotherium major, Helladotherium duvernoyi and Bohlinia attica. Finally, this study shows that a seasonal Mediterranean type, relatively temperate to warm and moist climate, can be inferred for the MN12 (Middle Turolian) of the Kerassia region.

A core from sediments of Loch Sionascaig, north-west Scotland was originally analysed to determine the changes in the late-glacial and post-glacial diatom assemblages. These indicate a trend from diatoms of alkaline assemblages in the late- and early post-glacial to those of acid and unproductive waters. This is apparently a response to changes in soils and vegetation upon the catchment area of the lake. Three diatom assemblage zones have been demonstrated within the late-glacial and zone 2 contains an unusually high proportion of planktonic Cyclotella spp. Three other late-glacial profiles were analysed, from L. Cam and L. Borralan in the same neighbourhood, and L. Tarff in the L. Ness area, to discover 1) whether this zonation applied generally, 2) whether taxa were characteristic of certain parts of the profiles, and 3) if other profiles include a similar planktonic phase. The sites varied in size and morphometry but the three zones could always be distinguished although assemblages differed slightly; none included a high percentage of Cyclotella in zone 2. Closer interval analysis has resulted in recognition of several subzones including one that can be correlated with the Bolling-Allerod stade. Esnvironmental interpretation is based on comparison with modem diatom assemblages and most taxa present in the late-glacial now occur in alkaline, nutrient-rich lakes. The lack of diatom plankton in the late-glacial suggests a similarity with some alpine lakes where diatoms are predominantly benthic. This similarity may have been initially due to severe climate and low nutrient supply. Continuation of this type of assemblages throughout the interstadial and into the early post-glacial suggests that the environment depends on the type of soils, vegetation and the amount of inwash of material into the lakes, rather than on climate.

No description available.

The multi-centred carbonatitic complex of Homa Mountain consists of a central cone sheet complex intruded into a domed area of country rock, surrounded by further arcuate zones of intrusive activity. The earlier events included intrusion of a body of ijolite, as a series of discontinuous bodies probably connected at depth. Later events include at least five stages of carbonatite intrusion and also numerous carbonatitic breccias. Syenitic rocks formed by concentration of late stage material at the margins of the ijolite which deuterically altered the ijolite and metasomatised the country rock to fenite contemporaneously. Minerals formed at such contacts are low temperature, potash-rich, orthoclase and aegirine with apatite the chief minor constituent. A second style of fenitization is recognized involving net veining of more widespread areas of country rock away from ijolite contacts. This reaches its climax in arcuate zones of shearing and brecciation within the central high ground. Where there is evidence of partial melting of such fenites to iron oxide-bearing trachytes. Coarse feldspathic rocks also carrying iron oxides are present near ijolites and early carbonatites. The feldspar in these is very similar to that in the fenites. Metasomatism at Homa is believed to involve introduction of large amounts of juvenile potash only, much of the soda being derived by redistribution of that already present in the country rock. A period of erosion during which superficial, lacustrine and possibly pyroclastic deposits were laid down then occurred and the mountain reduced to near its present topography. Following this erosional interval small scale vents of breccia and melilite-bearing material were intruded. The melilitites show all stages of replacement by carbonate. The above later stages of activity occurred during Late Pliocene or Pleistocene time. They were accompanied by some phonolitic activity within the complex and more in the area to the east along an extension of the southern boundary fault of the Nyanza Rift.

Abrasives are used in various forms to produce fine finishes on metal surfaces. Previously, grinding and abrasive processes have been studied in isolation; the present work however has shown that grinding can be usefully interpreted in abrasive wear terms. Wear experiments using small grinding wheels on a pin and ring machine have been able to reproduce many of the effects observed not only in grinding but also in such specialised processes as super-finishing. Abrasive wear theory has been re-examined, especially the parameters making up the K factor, and then applied to the grinding process. In order to test theoretical predictions a grinding dynamomoter was constructed to measure forces in surface grinding. Idealised indentors having simple geometrical shapes, similar to those assumed in abrasive wear theory, were tracked across smooth metal surfaces. Measurements of the seratches produced were then compared with theory. Scratch tests on a range of heat-treated steels using both idealised indentors and abrasive grits showed that pile-up at the edge of scratches is a highly significant factor in determining wear rate in abrasion and cutting forces in grinding. Finally a wide range of techniques for examining abrasives has been studied, the most notable of which involved the use of a scanning electron microscope.