Water quality and space constraints have become major concerns regarding the No. 7 waste water dam at Petra Diamonds’ Cullinan mine. The unique location of the dam constrains further development, while unsustainable accumulation of waste water inside the dam increases the risk of potential environmental contamination from seepages and spillages. The dam retains a significant amount of very poor quality water. Its excessively high pH, dissolved salt content, density and extreme turbidity result from the concentration of natural weathering products of the diamond bearing kimberlite ore. The turbidity results from the dispersion of colloidal chlorite, saponite and nontronite clay. Along with the chemistry of the solution, their colloidal shape contributes equally significantly to the non-settlement of these suspended clays. Flocculation of the dispersed clay particles will provide (a) for easy and effective separation of the clay material from the waste water and (b) more convenient options for water treatment (and subsequent redistribution) This study was aimed at contributing to a better understanding of the dynamic interactions in the No 7 Dam system to contribute towards identifying a suitable means/method for chemical flocculation of the clay particles. The individual components of the system (clays, water quality) and influx contributors (kimberlite and its leachate) were systematically characterized by means of X-Ray Diffraction, X-Ray Fluorescence, petrographic microscopy, electron microscopy, electrophoretic mobility and standard water- and soil quality analyses. The baseline quality of the Cullinan kimberlite leachate was obtained based on ASTM D5744 principles. It was found that adjusting the pH-level and ionic strength of the waste water to the critical coagulation point (cK) (as determined by electrophoretic mobility and batch jar experiments) automatically induced coagulation. Higher valence cations were displaced from pH dependent surface charge sites by proton adsorption. The resultant increased ionic strength, in combination with decreased thickness of the ionic double layer, was sufficient for the automatic initiation of high strength disordered face-face and edge-face bonds. During batch Jar tests, flocculation initiated within 4 minutes after the addition of HCl (0.5 M) and total sedimentation completed within 3 hours. The use of commercial flocculants might decrease the sedimentation time. As expected a significant increase in dissolved salt content of the clear supernatant was observed. No re-dispersion of the dried clay occurred. Throughout the study geochemical modeling was performed with PHREEQC software to identify/determine possible effective experimental conditions, minimizing experimental time and expenses. The program was also used to model outcomes of the possible water treatment options, indicated in literature as viable options for similar situations. These options can be tested to extend upon the current research. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The common presence of large volumes of coarse-grained olivine in kimberlite magmas has been proposed to attest to the volume of mantle xenolith material that has been disaggregated during the ascent of the magma. Orthopyroxene should constitute 10-50 vol% of mantle xenoliths in kimberlites, some of which must be disaggregated into the kimberlite, yet it is typically absent. This work tests the stability of orthopyroxene in ascending kimberlite magma by conducting experiments at pressures between 2.0 and 3.5 GPa and temperatures between 1100 and 1300°C. The starting material consisted of natural hypabyssal kimberlite that is close in composition to primary group I kimberlite magma with 5wt% orthopyroxene sourced from a natural peridotite added. At higher temperatures and pressures it is seen that orthopyroxene quantities exceed that of the starting material, but at lower temperatures and pressures it is absent. These results indicate that orthopyroxene is not stable in the magma composition investigated within the shallower part of the sub-continental lithospheric mantle. Based on increased olivine volumes in the experiments where orthopyroxene disappeared, as well as textural relationships between olivine and orthopyroxene, it is found that orthopyroxene dissolution is incongruent along the reaction Mg2Si2O6 (opx) = Mg2SiO4 (ol) + SiO2 (in the liquid). It is concluded that this reaction leads to a maximum addition of 5.5 vol% peritectic olivine to the kimberlite as it ascends through the depths equivalent to a pressure window of 2.0 to 3.5 GPa. / AFRIKAANSE OPSOMMING: The common presence of large volumes of coarse-grained olivine in kimberlite magmas has been proposed to attest to the volume of mantle xenolith material that has been disaggregated during the ascent of the magma. Orthopyroxene should constitute 10-50 vol% of mantle xenoliths in kimberlites, some of which must be disaggregated into the kimberlite, yet it is typically absent. This work tests the stability of orthopyroxene in ascending kimberlite magma by conducting experiments at pressures between 2.0 and 3.5 GPa and temperatures between 1100 and 1300°C. The starting material consisted of natural hypabyssal kimberlite that is close in composition to primary group I kimberlite magma with 5wt% orthopyroxene sourced from a natural peridotite added. At higher temperatures and pressures it is seen that orthopyroxene quantities exceed that of the starting material, but at lower temperatures and pressures it is absent. These results indicate that orthopyroxene is not stable in the magma composition investigated within the shallower part of the sub-continental lithospheric mantle. Based on increased olivine volumes in the experiments where orthopyroxene disappeared, as well as textural relationships between olivine and orthopyroxene, it is found that orthopyroxene dissolution is incongruent along the reaction Mg2Si2O6 (opx) = Mg2SiO4 (ol) + SiO2 (in the liquid). It is concluded that this reaction leads to a maximum addition of 5.5 vol% peritectic olivine to the kimberlite as it ascends through the depths equivalent to a pressure window of 2.0 to 3.5 GPa.

Neste trabalho apresenta-se uma revisão da técnica de magnetometria terrestre, com informações detalhadas a respeito do planejamento, aquisição e processamento dos dados. A técnica foi aplicada em uma área de 0,7 km2 no Planalto Catarinense, na região do Domo de Lages, o qual diferencia-se em relação aos demais domos da Bacia do Paraná pela presença de rochas alcalinas com idade de aproximadamente 75 Ma. Estas rochas, já foram alvo de investigações principalmente mineralógica e petrológica. A investigação magnetométrica de detalhe apresentada neste trabalho teve como objetivo inferir a geometria de um corpo kimberlítico, denominado \"Janjão\". Trabalhos geofísicos, anteriormente realizados nessa região, tiveram baixa resolução e pouca representatividade da área de estudo. Este trabalho permitiu gerar um mapa de campo magnético anômalo que apresentou duas anomalias dipolares. Essas anomalias apresentaram polarização reversa àquelas esperadas para anomalias induzidas na latitude e inclinação do campo da região do levantamento, o que indica forte magnetização remanescente das rochas estudadas. A técnica de Amplitude do Sinal Analítico forneceu informações a respeito dos limites laterais dos corpos magnéticos geradores das anomalias. Foi realizada também uma estimativa da profundidade do topo desses corpos a partir da técnica da Meia Largura e da Deconvolução de Euler 3D. Os resultados obtidos entre as duas técnicas se mostraram compatíveis. As informações obtidas por meio do processamento dos dados magnéticos serviram de base para avaliar o modelo gerado pela Inversão do Vetor de Magnetização. A inversão apresentou um modelo de distribuição de susceptibilidade magnética em subsuperfície e dois corpos magnéticos sub-verticalizados, com vetor de magnetização oposto à direção principal do campo magnético terrestre, associados às posições do corpo kimberlítico. Os valores de susceptibilidade magnética variaram de 8 até 20 X \'10 POT.-3\'(SI). Para a susceptibilidade de 8 X \'10 POT-3\'(SI), os corpos magnéticos referentes às duas anomalias são conectados entre si em profundidades de aproximadamente 180 m. O vetor de magnetização indicou fraca susceptibilidade magnética e magnetização primariamente induzida em regiões onde se estima a presença de rochas sedimentares encaixantes à Diatrema Janjão, cujas características físicas são compatíveis com aquelas sugeridas pelo modelo da inversão. Por fim, com a hipótese de campo magnético reverso no momento da formação da diatrema e com as idades estimadas para essas rochas kimberlíticas, foi possível reduzir a incerteza da idade de formação da Diatrema Janjão. Para trabalhos futuros foram mencionadas a localização de outras 16 ocorrências kimberlíticas na região do domo, também foi proposto, além da magnetometria terrestre, o emprego de gravimetria e técnicas eletromagnéticas que possam auxiliar na identificação e caracterização dessas ocorrências, e assim, contribuir com o conhecimento sobre a Província Kimberlítica de Lages, em Santa Catarina. / This work presents a review of the ground magnetometry technique, with detailed information regarding its planning, acquisition and data processing. The technique was applied in an area of 0.7 km2 in the Planalto Catarinense, in the Dome of Lages. The Dome of Lages differs from the other domes of the Paraná Basin by the presence of alkaline rocks with an age of approximately 75 Ma. These rocks, in the 70s and 80s of the last century, were the subject of investigations mainly mineralogical and petrological. The detailed magnetic survey presented in this work had the goal of inferring the geometry of a kimberlite body, named \"Janjão\"(in homage to its discoverer). Geophysical work, previously performed in this region, had low resolution and low representativity of the study area. This work allowed to generate an anomalous magnetic field map that presented two dipole anomalies. These anomalies presented reverse bias to those expected for induced anomalies in the latitude and inclination of the magnetic field of the survey region, indicating strong remanent magnetization in the rocks studied. The Analytical Signal Amplitude technique provided information about the lateral limits of the magnetic bodies that generate the anomalies. An estimation of the depth of the top of these bodies was also made from the Half-Width technique and the 3D Euler Deconvolution. The results obtained between the two techniques were compatible. The information obtained through the processing of the magnetic data served as a basis to evaluate the model generated by the Inversion of the Magnetization Vector. The inversion presented a model of magnetic susceptibility distribution in subsurface and two sub verticalized magnetic bodies, with magnetization vector opposite the main direction of the geomagnetic field, associated to the positions of the kimberlite body. The values of magnetic susceptibility ranged from 8 to 20 X \'10 POT.-3\'(SI). For the susceptibility of 8 X \'10 POT.-3\'(SI), the magnetic bodies relating to the two anomalies are connected to each other at depths of approximately 180 meters. The magnetization vector indicated weak magnetic susceptibility and magnetization primarily induced in regions where it is estimated the presence of sedimentary rocks nesting to Janjão diatreme, whose physical characteristics are compatible with those suggested by the inversion model. Finally, with the hypothesis of reverse magnetic field at the time of diatreme formation and with the estimated ages for these kimberlite rocks, it was possible to reduce the age uncertainty of the Janjão diatreme formation. For future work, was mentioned the location of 16 other kimberlite occurrences in the dome region and also proposed the use of gravimetry and electromagnetic techniques that may help in the identification and characterization of these occurrences, and thus, contribute to the knowledge about the Lages Kimberly Province in Santa Catarina.

Estudos mineralógicos e petrológicos foram realizados em amostras de xenólitos do manto inclusos em dique de kaersutita lamprófiro de Ubatuba (SP) (Província Ígnea da Serra do Mar) e no Kimberlito Limeira 1 (Monte Carmelo, MG; Província Alcalina do Alto Paranaíba) utilizando petrografia e geoquímica de elementos maiores e traços em minerais por microssonda eletrônica e LA-ICPMS. Os espinélio lherzolitos de Ubatuba, para os quais foram estimadas temperaturas de equilíbrio entre 750 e 950°C, representam um manto fértil, afetado por proporções variáveis, mas sempre moderadas de empobrecimento. Evidências de dois tipos de metassomatismo mantélico foram observadas em amostras distintas. Cristais de clinopiroxênio das amostras com evidências de empobrecimento prévio mais acentuado (maior Mg# de olivina e piroxênios, menor Al e Na em piroxênios, pouco espinélio) mostram enriquecimento caracterizado por alta razão LILE/HFSE, atribuído a fluidos/fundidos provenientes de zonas de subducção. Em amostra de wehrlito pobre em espinélio, por outro lado, observa-se enriquecimento de LILE e HFSE no clinopiroxênio, sugestivo de interação com fluidos/fundidos alcalinos. Os xenólitos do manto do Kimberlito Limeira 1 representam lherzolitos e dunitos, com maior variedade mineralógica e textural, para os quais foram estimadas temperaturas de equilíbrio entre 760 e 820°C. Evidências de metassomatismo modal mantélico são identificadas pela presença frequente de bolsões com concentração de minerais secundários, com notável enriquecimento de LILE e HFSE, em alguns casos com fases exóticas exclusivamente relacionadas a metassomatismo no manto superior. As assinaturas químicas das fases secundárias são semelhantes às presentes na suíte MARID e em peridotitos venulados metassomatizados de xenólitos de kimberlitos da África do Sul. Evidências petrográficas e químicas de descompressão (sugerindo a presença pretérita de granada) foram observadas em uma amostra afetada por enriquecimento com alta razão LILE/HFSE. As diferentes evidências de processos de empobrecimento e metassomatismo observadas entre os dois grupos de xenólitos estudados (Ubatuba e Monte Carmelo), são indicativas da variabilidade lateral do manto superior de fácies espinélio do sudeste brasileiro, refletindo os processos geológicos (tectônicos e magmáticos) distintos vivenciados pelas duas regiões. / Mineralogical and petrological studies were conducted in mantle xenoliths included in a kaersutite lamprophyre dyke from Ubatuba (SP) (Serra do Mar Igneous Province), and in the Limeira 1 Kimberlite (Monte Carmelo, MG; Alto Paranaíba Alkalic Province), using petrography and major and trace element geochemistry in minerals by electron microprobe and LA-ICPMS. The Ubatuba spinel lherzolites, with equilibrium temperatures ranging from 750 to 950°C, represent a fertlie mantle affected by variable but moderate depletion. Evidence of two types of mantle metasomatis were detected in different samples. Clinopyroxene crystals of the samples with evidence of stronger previous depletion (olivine and pyroxenes with higher Mg#, pyroxenes with lower Al and Na, few proportion of spinel) show enrichment with high LILE/HFSE, attributed to fluids/melts derived from subduction zone. On the other hand, a spinelpoor wehrlite shows a clinopyroxene with both LILE and HFSE enrichment, suggestive of interaction with alkaline fluids/melts. The Limeira 1 mantle xenoliths correspond to lherzolites and dunites showing more textural and mineralogical variety and equilibrium temperatures ranging from 760 to 820°C. Modal metasomatism was identified by the presence of abundant pockets with concentration of LILE and HFSE-rich secondary minerals, including in some cases, exotic phases typical of upper mantle metasomatism. The chemical signature of the metasomatic minerals is similar to those found in MARID and in veined metasomatic peridotites from South Africa kimberlite xenoliths. Petrographic and chemical evidences of decompression (suggesting the former presence of garnet) were observed in a sample affected by enrichment with high LILE/HFSE. The different evidences of depletion and enrichment processes observed in the two groups of xenoliths (Ubatuba and Monte Carmelo) indicate a lateral variability of the spinelfacies upper mantle in southeast Brazil, which may reflect the distinct tectonic and magmatic processes that affected these two regions.

O kimberlito Régis localiza-se no município do Carmo do Paranaíba, Minas Gerais. A intrusão possui formato elíptico e área aproximada de 1 km2. Com provável idade cretácea intrude rochas metassedimentares Neoproterozóicas do Grupo Bambuí. O ambiente geotectônico permanece em debate entre Faixa Brasília e Cráton do São Francisco. A presente dissertação contempla a descrição de afloramentos e de dois testemunhos de sondagem, com 250,6 e 316,4 metros. Através da caracterização macroscópica e petrográfica buscou-se subdividir a intrusão em fácies e compreender os mecanismos formadores destes depósitos, além de caracterizar o manto através dos xenólitos. A química mineral foi utilizada para caracterizar os minerais de xenólitos mantélicos e alguns minerais kimberlíticos, com aproveitamento para classificação de rocha. A área mapeada e os dois testemunhos descritos foram subdivididos em 9 unidades faciológicas principais, com base na estrutura, contatos, textura e associação mineral. Duas unidades, descritas em superfície, são correlacionáveis a outras duas descritas nos testemunhos. Estas fácies demonstram uma sucessão sedimentar grano-estrato decrescente interpretadas como produtos de fluxo de detritos e decantação em ambiente subaquoso, possivelmente lacustrino. As outras 5 unidades são distinguidas entre si pela estrutura, textura, tipo e proporção entre cristais, magmaclastos e xenólitos. Estas últimas foram interpretadas como sendo piroclásticas com base nas seguintes feições: (1) xenólitos mantélicos, crustais e de rochas encaixantes com borda de reação; (2) presença de lapili peletal com borda vítrea de resfriamento; (3) presença de magmaclastos amebóideis; (4) acumulações de cristais de olivinas em camadas; entre outras. Os xenólitos mantélicos foram caracterizados petrograficamente como granada-lherzolito e dunitos. A granada é composta predominantemente pela molécula piropo, sua composição química situa-se no campo de peridotito lherzolítico. A olivina é forsterítica, com Fo entre 0,90 e 0,92%. O ortopiroxênio predominante é enstatita. Dentre os clinopiroxênios identificam-se variedades de augita, diopsídio, onfacita e aegirina-augita. A geotermobarometria indica amostragem em condições de equilíbrio com o diamante. As análises químicas de flogopita kimberlítica situam-se no campo do kimberlito tipo I e do lamproíto, e seguem a linha de tendência do kimberlito tipo I. A composição da ilmenita localiza-se no campo de kimberlitos cratônicos. As análises indicaram que o kimberlito Régis apresenta potencial diamantífero, e as fácies caracterizadas podem ser empregadas visando um melhor aproveitamento da lavra. / The Regis Kimberlite surfaces in the Carmo do Paranaíba County, western of the State of Minas Gerais, Brazil. The pipe forms a 1km2 elliptical body. A Cretacic age for the instrusion seems the most probable. It intruded Neoproterozoic metamorphic rocks of Bambuí Group, and if it is located on Sao Francisco Craton or Brasilia Belt remains on doubt. The studies comprise two drills hole, with 250.6 and 316.4 meters, and outcrops descriptions. The kimberlite rocks and their mantle xenoliths samples were investigated through the macroscopic and microscopic characterization. The mantle and kimberlitic minerals have been analysed chemically and were used to support the rocks classification. The surveyed area, including the drilled hole cores, was subdivided into nine facies units. The division was based on structures, contact types, correlated rock texture and mineral association. Two units, with outcrop description, are correlated to two units with drill hole core description. This facies shows a fining-upward sedimentary sequence understood as deposited by debris flow and decantantion on lacustrine environment. In respect to the other five units each one has a specific proportion of crystals, magmaclasts and mantle xenoliths, furthermore a structure and rock fabric. This was explained as formed by pyroclastic flows based on: (1) crustal and mantle xenoliths with reaction rims; (2) pelletal lapilli with glassy rims; (3) ameboid magmaclasts; (4) accumulation of olivine in layers, and others. The mantle xenoliths were characterized through petrographic examination as garnet lherzolite and dunite. The garnet is predominantly pyrope, and plots on the lherzolític field. The olivine is forsteritic, with Fo between 0.90 to 0.92%. The ortopyroxene is predominantly enstatite. Among the clinopyroxene recognizes augite, diopside, omphacite and aegirine-augite. The geothermobarometry reveals sampling on diamond P-T conditions. The kimberlitic phlogopite chemical composition plots on kimberlite type-1 and lamproite field, with the kimberlite type-1 trend. The ilmenite chemical compositions reflect a cratonic environment. The results presented here indicate a diamondiferous potential of the Regis kimberlite. The facies units characterized here may be used to a better mine planning.

Estudos mineralógicos e petrológicos foram realizados em amostras de xenólitos do manto inclusos em dique de kaersutita lamprófiro de Ubatuba (SP) (Província Ígnea da Serra do Mar) e no Kimberlito Limeira 1 (Monte Carmelo, MG; Província Alcalina do Alto Paranaíba) utilizando petrografia e geoquímica de elementos maiores e traços em minerais por microssonda eletrônica e LA-ICPMS. Os espinélio lherzolitos de Ubatuba, para os quais foram estimadas temperaturas de equilíbrio entre 750 e 950°C, representam um manto fértil, afetado por proporções variáveis, mas sempre moderadas de empobrecimento. Evidências de dois tipos de metassomatismo mantélico foram observadas em amostras distintas. Cristais de clinopiroxênio das amostras com evidências de empobrecimento prévio mais acentuado (maior Mg# de olivina e piroxênios, menor Al e Na em piroxênios, pouco espinélio) mostram enriquecimento caracterizado por alta razão LILE/HFSE, atribuído a fluidos/fundidos provenientes de zonas de subducção. Em amostra de wehrlito pobre em espinélio, por outro lado, observa-se enriquecimento de LILE e HFSE no clinopiroxênio, sugestivo de interação com fluidos/fundidos alcalinos. Os xenólitos do manto do Kimberlito Limeira 1 representam lherzolitos e dunitos, com maior variedade mineralógica e textural, para os quais foram estimadas temperaturas de equilíbrio entre 760 e 820°C. Evidências de metassomatismo modal mantélico são identificadas pela presença frequente de bolsões com concentração de minerais secundários, com notável enriquecimento de LILE e HFSE, em alguns casos com fases exóticas exclusivamente relacionadas a metassomatismo no manto superior. As assinaturas químicas das fases secundárias são semelhantes às presentes na suíte MARID e em peridotitos venulados metassomatizados de xenólitos de kimberlitos da África do Sul. Evidências petrográficas e químicas de descompressão (sugerindo a presença pretérita de granada) foram observadas em uma amostra afetada por enriquecimento com alta razão LILE/HFSE. As diferentes evidências de processos de empobrecimento e metassomatismo observadas entre os dois grupos de xenólitos estudados (Ubatuba e Monte Carmelo), são indicativas da variabilidade lateral do manto superior de fácies espinélio do sudeste brasileiro, refletindo os processos geológicos (tectônicos e magmáticos) distintos vivenciados pelas duas regiões. / Mineralogical and petrological studies were conducted in mantle xenoliths included in a kaersutite lamprophyre dyke from Ubatuba (SP) (Serra do Mar Igneous Province), and in the Limeira 1 Kimberlite (Monte Carmelo, MG; Alto Paranaíba Alkalic Province), using petrography and major and trace element geochemistry in minerals by electron microprobe and LA-ICPMS. The Ubatuba spinel lherzolites, with equilibrium temperatures ranging from 750 to 950°C, represent a fertlie mantle affected by variable but moderate depletion. Evidence of two types of mantle metasomatis were detected in different samples. Clinopyroxene crystals of the samples with evidence of stronger previous depletion (olivine and pyroxenes with higher Mg#, pyroxenes with lower Al and Na, few proportion of spinel) show enrichment with high LILE/HFSE, attributed to fluids/melts derived from subduction zone. On the other hand, a spinelpoor wehrlite shows a clinopyroxene with both LILE and HFSE enrichment, suggestive of interaction with alkaline fluids/melts. The Limeira 1 mantle xenoliths correspond to lherzolites and dunites showing more textural and mineralogical variety and equilibrium temperatures ranging from 760 to 820°C. Modal metasomatism was identified by the presence of abundant pockets with concentration of LILE and HFSE-rich secondary minerals, including in some cases, exotic phases typical of upper mantle metasomatism. The chemical signature of the metasomatic minerals is similar to those found in MARID and in veined metasomatic peridotites from South Africa kimberlite xenoliths. Petrographic and chemical evidences of decompression (suggesting the former presence of garnet) were observed in a sample affected by enrichment with high LILE/HFSE. The different evidences of depletion and enrichment processes observed in the two groups of xenoliths (Ubatuba and Monte Carmelo) indicate a lateral variability of the spinelfacies upper mantle in southeast Brazil, which may reflect the distinct tectonic and magmatic processes that affected these two regions.

O kimberlito Régis localiza-se no município do Carmo do Paranaíba, Minas Gerais. A intrusão possui formato elíptico e área aproximada de 1 km2. Com provável idade cretácea intrude rochas metassedimentares Neoproterozóicas do Grupo Bambuí. O ambiente geotectônico permanece em debate entre Faixa Brasília e Cráton do São Francisco. A presente dissertação contempla a descrição de afloramentos e de dois testemunhos de sondagem, com 250,6 e 316,4 metros. Através da caracterização macroscópica e petrográfica buscou-se subdividir a intrusão em fácies e compreender os mecanismos formadores destes depósitos, além de caracterizar o manto através dos xenólitos. A química mineral foi utilizada para caracterizar os minerais de xenólitos mantélicos e alguns minerais kimberlíticos, com aproveitamento para classificação de rocha. A área mapeada e os dois testemunhos descritos foram subdivididos em 9 unidades faciológicas principais, com base na estrutura, contatos, textura e associação mineral. Duas unidades, descritas em superfície, são correlacionáveis a outras duas descritas nos testemunhos. Estas fácies demonstram uma sucessão sedimentar grano-estrato decrescente interpretadas como produtos de fluxo de detritos e decantação em ambiente subaquoso, possivelmente lacustrino. As outras 5 unidades são distinguidas entre si pela estrutura, textura, tipo e proporção entre cristais, magmaclastos e xenólitos. Estas últimas foram interpretadas como sendo piroclásticas com base nas seguintes feições: (1) xenólitos mantélicos, crustais e de rochas encaixantes com borda de reação; (2) presença de lapili peletal com borda vítrea de resfriamento; (3) presença de magmaclastos amebóideis; (4) acumulações de cristais de olivinas em camadas; entre outras. Os xenólitos mantélicos foram caracterizados petrograficamente como granada-lherzolito e dunitos. A granada é composta predominantemente pela molécula piropo, sua composição química situa-se no campo de peridotito lherzolítico. A olivina é forsterítica, com Fo entre 0,90 e 0,92%. O ortopiroxênio predominante é enstatita. Dentre os clinopiroxênios identificam-se variedades de augita, diopsídio, onfacita e aegirina-augita. A geotermobarometria indica amostragem em condições de equilíbrio com o diamante. As análises químicas de flogopita kimberlítica situam-se no campo do kimberlito tipo I e do lamproíto, e seguem a linha de tendência do kimberlito tipo I. A composição da ilmenita localiza-se no campo de kimberlitos cratônicos. As análises indicaram que o kimberlito Régis apresenta potencial diamantífero, e as fácies caracterizadas podem ser empregadas visando um melhor aproveitamento da lavra. / The Regis Kimberlite surfaces in the Carmo do Paranaíba County, western of the State of Minas Gerais, Brazil. The pipe forms a 1km2 elliptical body. A Cretacic age for the instrusion seems the most probable. It intruded Neoproterozoic metamorphic rocks of Bambuí Group, and if it is located on Sao Francisco Craton or Brasilia Belt remains on doubt. The studies comprise two drills hole, with 250.6 and 316.4 meters, and outcrops descriptions. The kimberlite rocks and their mantle xenoliths samples were investigated through the macroscopic and microscopic characterization. The mantle and kimberlitic minerals have been analysed chemically and were used to support the rocks classification. The surveyed area, including the drilled hole cores, was subdivided into nine facies units. The division was based on structures, contact types, correlated rock texture and mineral association. Two units, with outcrop description, are correlated to two units with drill hole core description. This facies shows a fining-upward sedimentary sequence understood as deposited by debris flow and decantantion on lacustrine environment. In respect to the other five units each one has a specific proportion of crystals, magmaclasts and mantle xenoliths, furthermore a structure and rock fabric. This was explained as formed by pyroclastic flows based on: (1) crustal and mantle xenoliths with reaction rims; (2) pelletal lapilli with glassy rims; (3) ameboid magmaclasts; (4) accumulation of olivine in layers, and others. The mantle xenoliths were characterized through petrographic examination as garnet lherzolite and dunite. The garnet is predominantly pyrope, and plots on the lherzolític field. The olivine is forsteritic, with Fo between 0.90 to 0.92%. The ortopyroxene is predominantly enstatite. Among the clinopyroxene recognizes augite, diopside, omphacite and aegirine-augite. The geothermobarometry reveals sampling on diamond P-T conditions. The kimberlitic phlogopite chemical composition plots on kimberlite type-1 and lamproite field, with the kimberlite type-1 trend. The ilmenite chemical compositions reflect a cratonic environment. The results presented here indicate a diamondiferous potential of the Regis kimberlite. The facies units characterized here may be used to a better mine planning.

Kimberlite whole rock geochemistry has been under-appreciated in deciphering Group I kimberlite petrogenesis. Although there is considerable debate on the definition of Group I kimberlite, there is agreement on certain characteristics. These include that Group I kimberlites are ultramafic rocks (MgO >15 wt%), have near primitive mantle nickel (∼ 1400 ppm) and chromium (∼1600 ppm) contents, have close to bulk silicate earth radiogenic isotopic signatures, are volatile rich (predominantly CO2) and have stable isotopic signatures typical of mantle sources. The debate, however, centers on petrogenetic models and parental magmatic compositions of Group I kimberlites. Petrogenetic models include both low degree (<1 %) partial melting of metasomatized asthenospheric mantle (Dalton and Presnall, 1998a; 1998b; Becker and Le Roex, 2006) and, conversely, high degree partial melting (10<20 %) of metasomatized veined asthenospheric mantle (Mitchell, 1995, 2004). Inferred kimberlite parental magma compositions have been suggested to be low silica (<5 wt%) and high CO2 (<44 wt%) melts, as suggested by high-pressure melt experiments conducted on synthetic carbonatized mantle (Dalton & Presnall, 1998a, 1998b), or much higher silica (<30 wt%) and lower CO2 (<12 wt%) melts as suggested by geochemical analysis of aphanitic kimberlite (Price et al., 2000; Kopylova et al., 2007). In an effort to contribute to the resolution of this debate on petrogenic models and parental magma compositions of Group I kimberlites, I have completed a systematic investigation of the whole rock geochemistry and petrology of three kimberlite occurrences in the Foxtrot Kimberlite Field of Northern Quebec. A clear correlation exists between whole rock chemistry, mantle source, and diamond grade of the three Group I kimberlites in the Foxtrot Kimberlite Field. Two phases, olivine and carbonate, dominant theserocks and thus control the kimberlites geochemistry. Electron microprobe analysis of over 800 olivines in the Foxtrot kimberlite indicate that it is predominantly xenocrystic (Mg# (Mg/(Mg+Fe)) of 91.5), largely derived from harzburgite mantle, but the absence of harzburgitic orthopyroxene in the Foxtrot kimberlites suggests that it has been assimilated. Whole rock geochemistry (major and trace elements) of the Foxtrot hypabyssal kimberlite dykes indicate they have chemical characteristics similar to Group I kimberlite from the Slave Province. The olivine content of the Foxtrot kimberlites, and thus their Mg#'s, are positively correlated with diamond abundance indicating that diamond grade is a reflection of the incorporation of harzburgite mantle. These results indicate that Group I kimberlite petrogenesis in the Foxtrot example is best modeled as a mixture of harzburgitic mantle xenocrysts and a carbonate rich fluid, and that the parental magma is silica poor "5 wt %) and CO 2 rich (<40 wt%).

La prédiction des ressources récupérables d'un gisement kimberlitique passe par l'estimation de la loi en taille des diamants commercialisables qu'il contient. Cette estimation repose traditionnellement sur les pierres de plus de 0,5mm, sans tenir compte des petites pierres qui sont de loin les plus abondantes mais sans valeur économique. Le problème soulevé par cette approche est la taille des échantillons: ils doivent être d'autant plus volumineux que les grandes pierres sont rares. Une façon de réduire la taille des échantillons est d'abaisser le seuil de récupération à des pierres non commercialisables. A cette fin, des techniques spécifiques ont été développées (dissolution de la kimberlite à l'acide) pour récupérer toutes les pierres de plus de 75 microns (0,0000018carat). Une procédure itérative a été aussi mise au point pour estimer la loi des pierres commercialisables à partir des petites pierres. La solution proposée repose sur une hypothèse de lognormalité de la taille des pierres, hypothèse pertinente dans la totalité des gisements primaires de diamants étudiés. L'estimation des paramètres lognormaux tient compte du nombre limité des données et de leur biais, dû à la perte inévitable des pierres les plus petites au cours du traitement des échantillons. Elle permet la prise en compte simultanée de différents jeux de données prélevés à différents seuils de récupération correspondant à differents modes d'échantillonnage. Cette procédure met en jeu une représentation graphique comparée des lois expérimentale et simulée, mettant ainsi en évidence la quantité de pierres perdues.

Crystallization temperatures (T) and oxygen fugacities (fO2) of kimberlite magma estimated from oxides included in olivine phenocrysts from eight kimberlite pipes in the central Slave Province, Canada, are compared to the degree and character of resorption observed in diamonds recovered from these kimberlites. The mechanism of diamond oxidation in kimberlite melts and the rate-controlling parameters for this reaction are explored in oxidation experiments. The T and maximum fO2 recorded by olivine - chromite pairs at an assumed pressure of 1 GPa are 970° -- 1070°C and 2.2 - 3.1 log units below the nickel - nickel oxide (NNO) buffer. This mineral assemblage crystallized from a magma with 1 1 to 28 mol% of liquid, 10 mol% of earlier-precipitated olivine phenocrysts and 62 to 79 molc7o of mantle xenocryst olivine. The T - fO2 values vary between kimberlites from Northwest and Southeast clusters within 150°C and one log unit, respectively, and form a trend of decreasing fO2 and increasing crystallization T in the southeast direction. This trend corresponds to substantial differences in the diamond populations. A detail description of morphological forms and surface resorption features for five diamond parcels (> 7000 stones) show an increase in diamond resorption with increase in kimberlite crystallization T and more extensive surface etching in more oxidized kimberlites. The surface etch features on diamonds are determined by the conditions in the kimberlite melt, whereas some of the volume resorption occurs in the mantle and its relationship with the melt conditions is obscure. The diamond grade is higher in kimberlites with lower fO2 confirming the effect of the melt conditions on diamond preservation. Diamond oxidation experiments at 1350°C to 1500°C and 1 GPa produced only surface graphitisation, and no diamond resorption in volatile undersaturated melts. In contrast, volatile oversaturated conditions produce resorption features seen in diamonds recovered from kimberlites, suggesting that the process of diamond resorption is its reaction with the fluid and not with the melt. Both CO2 and H2O oxidize diamonds at a similar rate, but produce very different surface features. Therefore, the surface features of natural diamonds may provide information on the H2O/CO2 ratio in the kimberlitic fluid. The morphologies of diamonds from this study imply high H2O/CO2. The scarcity of surface graphitisation and presence of highly resorbed diamonds in kimberlites suggest presence of free fluid phase in kimberlite magmas for the most of their history. The diamond oxidation is not affected by the physical properties of diamonds.