The origin and composition of carbonatite-derived carbonate-bearing fluorapatite deposits

Carbonate-bearing fluorapatite rocks occur at over 30 globally distributed carbonatite complexes and represent a substantial potential supply of phosphorus for the fertiliser industry. However, the process(es) involved in forming carbonate-bearing fluorapatite at some carbonatites remain equivocal, with both hydrothermal and weathering mechanisms inferred. In this contribution, we compare the paragenesis and trace element contents of carbonate-bearing fluorapatite rocks from the Kovdor, Sokli, Bukusu, Catalão I and Glenover carbonatites in order to further understand their origin, as well as to comment upon the concentration of elements that may be deleterious to fertiliser production. The paragenesis of apatite from each deposit is broadly equivalent, comprising residual magmatic grains overgrown by several different stages of carbonate-bearing fluorapatite. The first forms epitactic overgrowths on residual magmatic grains, followed by the formation of massive apatite which, in turn, is cross-cut by late euhedral and colloform apatite generations. Compositionally, the paragenetic sequence corresponds to a substantial decrease in the concentration of rare earth elements (REE), Sr, Na and Th, with an increase in U and Cd. The carbonate-bearing fluorapatite exhibits a negative Ce anomaly, attributed to oxic conditions in a surficial environment and, in combination with the textural and compositional commonality, supports a weathering origin for these rocks. Carbonate-bearing fluorapatite has Th contents which are several orders of magnitude lower than magmatic apatite grains, potentially making such apatite a more environmentally attractive feedstock for the fertiliser industry. Uranium and cadmium contents are higher in carbonate-bearing fluorapatite than magmatic carbonatite apatite, but are much lower than most marine phosphorites

Dental fluorosis in Brazil: a systematic review from 1993 to 2004 Fluorose dentária no Brasil: uma revisão sistemática do período 1993/2004

The current article proposes a reflection on several aspect pertaining to dental fluorosis in Brazil, based on a systematic review of epidemiological surveys. The authors assess the prevalence and degrees of severity found in different studies and show that in methodological terms, there is a need for progress in procedures for population-based studies on fluorosis. Despite the different data collection approaches, there is some consensus among the different studies as to the limited severity of fluorosis in Brazil, as well as its association with the independent variables age and socioeconomic status. The authors also highlight the importance of adding subjective aspects to the normative diagnosis as a contribution to public health policy decisions, since the use of exclusively clinical criteria gives dental fluorosis more space than society ascribes to it. There is a lack of empirical evidence to reassess the fluoride content in public water supplies, a method that is known to be necessary to improve dental caries epidemiological indicators.<br>O presente trabalho propõe uma reflexão sobre alguns aspectos relativos à fluorose dentária no Brasil, a partir de uma revisão sistemática de estudos e inquéritos epidemiológicos. A prevalência e os níveis de severidade encontrados nos diferentes estudos são avaliados, verificando-se que, quanto aos aspectos metodológicos, há necessidade de avançar no que diz respeito aos procedimentos para estudo da fluorose em âmbito populacional. Apesar das diferentes abordagens para coleta de dados, há algum consenso, entre os diferentes estudos, quanto à baixa severidade da fluorose no Brasil e a sua associação com as variáveis independentes idade e condição sócio-econômica. Destaca-se também a importância de incluir aspectos subjetivos ao diagnóstico normativo, como uma contribuição às decisões que envolvem o planejamento de políticas públicas de saúde, uma vez que o uso de critérios exclusivamente clínicos oferece à fluorose dentária um espaço maior que aquele que lhe confere a sociedade. Nota-se a ausência de evidência empírica para a reavaliação dos teores de flúor nas águas de abastecimento público, um método reconhecidamente necessário no contexto brasileiro para a melhoria dos indicadores epidemiológicos de cárie