Western Kenya hosts a number of Tertiary and Quaternary alkaline volcanic carbonatite centres, such as Rangwa, the North and South Ruri centres, Kuge, Homa Mountain and Legetet which are located along an old Precambrian major shear zone lying within the Nyanza rift, off the main Kenyan (Gregory) rift. The centres consist of agglomerates and breccias with mixed clasts of silicate rocks and carbonatites, interbedded with carbonatitic and nephelinitic tuffs. The volcanic assemblage is transected by high level sheets and dykes of calcite carbonatite and ferrocarbonatite which were probably later feeders for the volcanic eruptions. Carbon, oxygen, and sulphur isotopic compositions were determined for calcite, siderite and barite from the Buru and Kuge carbonatite centres. Wide ranges in the isotopic compositions of the minerals were observed with values for delta13C and delta18O for the Buru calcites ranging from +1.27 to -3.23&permil; (PDB) and +11.25 to +26.21&permil; (SMOW). The delta13 C and delta18O for the Kuge calcites are -3.11 to -8.44&permil; (PDB) and +18.09 to +25.73&permil; (SMOW). The Buru siderites plot in a narrow and restricted range at -3.07 to -4.39&permil; (PDB) and +12.61 to +16.10&permil; (SMOW). Data on the sulphur isotopic composition from the Buru hill carbonatite show a fairly widespread variation in delta34S ranging from +4.50 to +12.40&permil; (CDT), whereas Kuge hill displays a slightly more homogenous isotopic composition with values ranging from +1.10 to +5.10&permil; (CDT). The carbon and oxygen isotopic compositions from the Buru and Kuge carbonatite centres do not retain the primary isotopic signatures expected for magmatic primary carbonatites. Most of the variations in isotopic composition have been attributed to secondary processes involving low temperature (60&deg; to 144&deg;C) hydrothemal alteration and isotopic exchange between the carbonatites and fluids (meteoric water). Higher delta18O values (+21.91 to +26.21&permil;) with a significant increase in delta13Cvalues (-1.48 to +1.27&permil;) shown by the most oxidized samples from the Buru carbonatite may indicate the involvement of supergene exchange with atmospheric CO2 at relatively lower temperatures (< 50&deg;C). The variations in 34S shown by the two centres compared to mantle sulphur could be due to either redox processes and/or isotopic fractionations due to loss of volatiles. The Buru and Kuge carbonatite centres are characterized by enriched rare earth element (REE) values dominated by higher abundances of LREEs with steep chondrite-normalized distribution patterns. The lateritic zone at Buru hill, however, contains the greatest concentrations of REEs, barium, iron and manganese compared to the fresh carbonatite in which calcite and particularly siderite increase in abundance as the influence of supergene processes decrease with depth. The most common rare earth minerals encountered in the Buru and Kuge carbonatite centres are the fluorocarbonates (bastnaesite, synchysite and parisite), and monazite. The lanthanide fluorocarbonate and monazite control the concentration and bulk distribution of the REEs. The replacement textures of the lanthanide fluorocarbonates and monazite indicate that they are secondary in origin and appear to have been introduced by late stage, low temperature hydrothermal processes. The rare earth minerals are commonly accompanied by fluorite, and barite. Stable isotope studies suggest that the low temperature mineralogical changes and REE mineralization observed in western Kenyan carbonatites were controlled initially by hydrothermal activity and later by supergene processes. Higher delta18O and values, especially in the oxidized zones, correspond to higher REE abundances.

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 9, 2008) Includes bibliographical references (p. 131-139).

Thesis (doctoral)--Faculté des sciences de Paris, (197-?). / Includes bibliographical references (leaves [43]-[46]).

The Seabrook Lake carbonatite complex is one of the smallest of nine known carbonatite complexes in central Ontario. The complex, which is one-half square mile in area and pear-shaped in plan, consists of fenitized granite and breccia, mafic breccia, ijolite and related breccia, and carbonatite. The bulbous northern part of the complex consists of a plug-like core of carbonatite surrounded by mafic breccia and carbonatite dykes. The narrow southern part consists of ijolite and related breccia. Enveloping all of these rocks is a fenitized aureole which grades outward to unaltered granite that underlies much of the surrounding area. The carbonatite is composed of calcite with the following minor mineral, in decreasing order of abundance: goethite, microcline, magnesioriebeckite-riebeckite, magnetite-ulvospinel, apatite, hematite, pyrite, albite, biotite, chlorite, pyrochlore, brookite, sphene, ferroan dolomite (ankerite?), aegirine, chalcopyrite, wollastonite and quartz. The chemical constituents are as follows: Major CaO + CO₂ Minor Fe₂O₃, SiO₂, MgO, Nb₂O₅, SrO, BaO, Na₂O, K₂O, MnO, Al₂O₃, P₂O₅, S and H₂O. Trace Cu, Pb, Zn, As, Ce, Y, Li, Cr, Co, Ni, V, In, Zr, and Ti. The complex is believed to have formed by desilication and metasomatism of fractured and brecciated granite by a soda-iron-rich carbonatite magma of unknown origin. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis (Ph.D.), Memorial University of Newfoundland, 2000. / Bibliography: leaves R-1-R-17. Also available online.

Thesis (Ph. D.)--University of Chicago, Dept. of the Geophysical Sciences, August 1999. / Includes bibliographical references. Also available on the Internet.

Mémoire (M.Sc.T.)-- Université du Québec à Chicoutimi, 1988. / Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Sc.T.)--Université du Québec à Chicoutimi, 1990. / "Mémoire présenté à l'Université du Québec à Chicoutimi comme exigence partielle de la maîtrise en sciences de la terre" CaQCU Document électronique également accessible en format PDF. CaQCU

Thèse (D.Ress.Min.) -- Université du Québec à Chicoutimi, programme extensionné à l'Université du Québec à Montréal, 2002. / Bibliogr.: f. 105-109. Document électronique également accessible en format PDF. CaQCU

A mina de fosfato de Cajati localiza-se a 230 km a sudeste da cidade de São Paulo. Nela aflora, de forma alongada segundo a direção N27ºW, um corpo de carbonatito mineralizado a apatita. O corpo mineralizado é subdividido em unidades litológicas a partir de variações nas características físicas (estruturas) e mineralógicas da matriz carbonática, dos principais acessórios e menores constituintes (textura e proporções). Dentro das unidades litilógicas existentes destacam-se a Zona de Xenólitos e Zonas de Diques, regiões caracterizadas por misturas entre magnetita-clinopiroxenitos, rocha encaixante e estéril com relação à mineralização de fosfato, e carbonatito em proporções que podem chegar a quase 100% de clinopiroxenito. Observam-se ainda zonas de reação, no contato entre as rochas descritas, caracterizando um bandamento centimétrico de composição silicática / carbonática com mineralogia peculiar e que na maioria das vezes são mineralizados economicamente a apatita. Considerando as Zonas de Xenólitos e de Diques como de aproveitamento parcial em função da presença do clinopiroxenito estéril e que as relações de distribuição espacial desta fase contaminante é errática sem qualquer controle geológico conhecido de distribuição, buscou-se estabelecer indicadores que permitem a caracterização percentual entre minério e estéril contidos nesta região. Para tanto foram realizados estudos de relação entre a composição química e a mineralogia do minério que permitiram estabelecer tais índices, os quais aplicados aos dados de análises químicas obtidos a partir de testemunhos de sondagem rotativa e de percussão (pó de perfuratriz) associados a parâmetros de lavra permitiram estabelecer níveis de aproveitamento mineral para as rochas existentes nestas unidades litológicas. Os indicadores matemáticos se apoiaram nos teores de sílica que refletem as proporções de silicatos (flogopita, olivina e piroxênio) e estabelecem nítidas fronteiras composicionais entre as três litologias presentes nas zonas de xenólitos, e definiram a Função Xenólitos. As variáveis mineralógicas apóiam as determinações de potencialidades volumétricas dos recursos discretizados no modelo de blocos de longo prazo e o aproveitamento das frentes nos planos de pré-lavra. / The Cajati phosphate mine is located 230 km southeast of São Paulo city. The ore body is composed by carbonatites mineralized with apatite, which are disposed in plant as an ellipse N27ºW oriented. The carbonatite is subdivided in lithologics units defined by variations in the physical aspects (structures) and the mineralogical characteristics of the carbonatic matrix, mainly related with the principal accessories and smaller constituents (texture and proportions). Xenoliths zones and Dikes zones are remarkable among the lithological units, they comprise portions characterized by mixtures of carbonatite and magnetite-clinopiroxenites, the hosting waste rock, in proportions that can reach almost 100% of clinopiroxenite. Some reaction zones are observed in the described rocks contact, characterizing centimetric bands (silicatic / carbonatic composition) with peculiar mineralogy that are frequently mineralized. Considering the Xenoliths zones and Dikes zones only partially profitable in function of the presence of the clinopiroxenite waste and that the spatial distribution of this contaminant rock is erratic without any geological known settings, efforts were applied in the establishment of mineralogical indicators to define the relative proportions of the constituent rocks. Stechiometric relationships between chemical and mineralogical characteristics associated with mining parameters allowed to set up levels of mineral profitability for these lithological units, which were applied in the data obtained by rotative and percussion drilling. Mathematical indicators based on silica grades, which reflect the silicates (phogopite, olivine and pyroxene) proportions, established a clear compositional division between the three litologies present in the xenoliths zones and defined the Xenoliths Function. The mineralogical variables support the profit potentiality definition for the ore resources associated with these assimilation zones, which were applied in the block model and are also used in the mining fronts.