![]() ![]() Exceptions for the LREE-enriched nature in carbonatites are hydrothermal xenotime-(Y)-rich veins associated with carbonatite at Lofdal in Namibia ( Wall et al., 2008), and Yen Phu, a small, and highly weathered carbonatite prospect in northern Vietnam, which is composed of goethite-rich ore containing xenotime-(Y), monazite-(Ce), samarskite-(Y), and fergusonite-(Y) above an intrusive xenotime-bearing dolomite-carbonatite body ( Watanabe, 2014). These deposits are enriched in light REEs because of the genetic condition of the carbonatite magmas (low degree of partial melting of garnet-bearing amphibole lherzolite at depth > 70 km), although the deposits with apatite ores are relatively enriched in HREEs ( Table 11). Some representative deposits (Bayan Obo, Mountain Pass, Mount Weld) possess large reserves (> 1 Mt REO) and relatively high-grade ores (> 4 wt.%) that can fully cover the world REE demand, which is 100–200 kt a year. ![]() The question as to whether these magmas exist has hence shifted to answering the question of how they form.Īlthough carbonatite is magmatic in origin, most of the high-grade ores of this type are formed by subsequent hydrothermal activities ( Smith et al., 2015 Wall et al., 2008 Williams-Jones et al., 2012 Xie et al., 2009). Only slightly later, experimental work (e.g., starting with Wyllie, 1965, as well as Wyllie, 1978) showed that small degree partial melts of carbonate-bearing peridotite are carbonatitic in character. The discovery of extrusive carbonatite lavas at Oldoinyo Lengai in 1960 (reported by Dawson, 1962) proved without a doubt that carbonatite magmas exist. (1962) provided some of the first strong geochemical evidence that carbonatites that came from the mantle were not recycled limestones. Further evidence for the existence of magmatic carbonatites came particularly from detailed studies of alkaline complexes in Northern Europe, for example at Afrikanda, Kola ( Kupletsky, 1938) Alnö, Sweden ( von Eckermann, 1948) and again at the Fen complex ( Saether, 1957). The term carbonatite was introduced by Brøgger in 1921 in his studies of the Fen complex in Norway ( Brøgger, 1921), but the concept of a rock formed from carbonate-dominant magma was not generally accepted at that time. O’Brien, in Mineral Deposits of Finland, 2015 IntroductionĬarbonatite is a unique igneous rock type, in that it formed predominantly of carbonate minerals (of which it must contain >50 modal % by definition) along with lesser silicates, phosphate minerals, and oxides. ![]()
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