Data on rare earth (including yttrium) mines, deposits, and occurrences were compiled as part of an effort by the USGS and the University of Arizona Center for Mineral Resources to summarize current knowledge on the supply and demand outlook and related topics for this group of elements. Economic competition and environmental concerns are increasingly constraining the mining and processing of rare earths from the Mountain Pass mine in California. For many years, the deposit at Mountain Pass was the world's dominant source of rare earth elements and the United States was essentially self-sufficient. Starting approximately 10 years ago, the U.S. has become increasingly dependent (> 90 percent of separated rare earths) upon imports from China, now the dominant source of rare earths. Knowledge of the known economic and noneconomic sources of rare earths is basic to evaluating the outlook  for rare earth upply and associated issues. <...>

Rare Earth Oxides are used in mature markets (such as catalysts, glassmaking and metallurgy), which account for 59% of the total worldwide consumption of rare earth elements, and in newer, high-growth markets (such as battery alloys, ceramics, and permanent magnets), which account for 41% of the total worldwide consumption of rare earth elements.

This paper describes a soil extraction method developed to investigate the different chemistries of Au in various soils in the Yilgarn Craton. The extraction solution is 1 M sodium bicarbonater0.1 M potassium iodide, saturated with CO2 and adjusted to pH 7.4 with hydrochloric acid. A soil : solution ratio of 1 : 2 Žg : ml. is used. Two different methods were used: Ž1. net iodide-extractable Au, with solutions analysed directly for Au; Ž2. gross iodide-soluble Au, where activated carbon is added to the mixture and the carbon analysed at the end of the extraction, thus providing a measure of all Au dissolved during the extraction Žincluding that readsorbed during the net extraction.. Depending on the extraction conditions, there may be appreciable readsorption of Au, particularly for organic-rich ŽG50%. and Fe-rich lateritic soils Ž)80%.. This readsorption is enhanced by pulverizing to -75 mm. Consequently, for simple extractions longer than 1 day, pulverized soils give lower apparent Au solubility than do unpulverized soils. Unpulverized carbonate-rich soils show high Au solubilities and little Žoften -20%. readsorption, and consequently show high net iodide-solubilities. These readsorption phenomena could affect other methods used in exploration and should be thoroughly investigated before incorrect conclusions are drawn. The readsorption problems are removed by adding activated carbon to the extraction mixtures; the carbon adsorbs Au as it is dissolved from the sample and is subsequently analysed. However, different soil types still show distinctly different Au solubilities, which should be recognized for interpretation of extraction results. Again, this effect should be tested for other extraction techniques. A more intractable problem may be that biological cycling of the Au through plants and other organisms appears to cause high Au solubilities in many soils. This effect may obscure any potential ‘mineralization signature’ that is being tested by selective extractions, and could cause problems for any extraction method, no matter how well designed

Le Crétacé inférieur de l’Estramadura, au Portugal, m’apparaissait, lorsque j’en entrepris l'étude, comme un thème de recherches à la fois séduisant et redoutable. Séduisant, car tout examen systématique avait été abandonné depuis plus de soixante ans, en dépit de la présence de classiques ensembles stratigraphiques, de la richesse des faunes et de la variété des faciès. Redoutable, car il m’amenait à suivre les traces de cet illustre géologue que fut Choffat. Il était bien évident que je ne pouvais mener cette tâche à son terme que grâce à de nombreux et bienveillants appuis. J’en ai largement bénéficié, sinon même abusé. Il m’est donc particulièrement agréable de remercier aujourd’hui tous ceux qui, durant les longues années de travail, m’ont aidé, conseillé et encouragé. <...>