Garnets occur in more than 30 natural mineral parageneses forming the rocks of magmatic, metamorphoric and metasomatic origin, which suggests their crystallization in a wide range of physicochemical parameters. By the ratio of main components (Ca, Mg, Al, Fe, Cr, Mn), garnets are divided into two major groups: almandine (pyrope, almandine, and spessartite) and andradite (grossular, andradite, and uvarovite). Pyropes are contained mainly in high-temperature peridotites and eclogites from deep xenoliths carried by kimberlite and alkaline-basaltic melts. In high-temperature and mesobaric metamorphic complexes (eclogites, granulites, gneisses, and schist), as well as in metasomatic rocks (skarns) garnets are represented by the varieties of almandine-grossular-pyrope series. When systematizing garnets by chemical compositions and parageneses in which they occur, normally different binary diagrams are used, including the diagrams in CaO–Cr2O3 coordinates [Sobolev, 1964; Sobolev et al., 1973]. <...>

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