RARE EARTH ELEMENTS PLUS

The source need not be an alkaline igneous rock or a related rare-earth deposit. Depending on the source of the erosion products, certain rare earth elements-bearing minerals, such as monazite and xenotime, can be concentrated along with other heavy minerals. The process of erosion concentrates denser minerals, most notably gold, into deposits known as placers. Weathering of all types of rocks yields sediments that are deposited in a wide variety of environments, such as streams and rivers, shorelines, alluvial fans, and deltas. Scandium is found in most rare earth element deposits and is sometimes classified as a rare earth element.

RARE EARTH ELEMENTS PLUS

REE Periodic Table: The Rare Earth Elements are the 15 lanthanide series elements, plus yttrium. Economic concentrations of REE-bearing minerals occur in some alkaline rocks, skarns and carbonate-replacement deposits associated with alkaline intrusions, veins and dikes cutting alkaline igneous complexes and surrounding rocks, and soils and other weathering products of alkaline rocks. Carbonatites, and especially phoscorites, are relatively uncommon, as there are only 527 known carbonatites in the world (Woolley and Kjarsgaard, 2008). Some of the more unusual alkaline rocks that host, or are related to, REE ores are carbonatite and phoscorite, igneous rocks composed principally of carbonate and phosphate minerals, respectively. Table 2 presents a relatively simple classification that follows analogous categories for deposits related to nonalkaline igneous rocks. Rare Earth Ore ClassificationĬlassification of ores related to alkaline rocks is also controversial. Widespread andesitic and rhyolitic dikes, of Mesozoic or Tertiary age, are not shown.

Only a representative minority of the hundreds of shonkinite, syenite, and carbonatite dikes are shown. Rare earth element geologic map: Generalized geologic map of most of the Mountain Pass rare earth element district, southern California. The mineral deposits associated with these rocks are likewise quite diverse and awkward to classify, in that the distinctive features of these deposits and their rarity can result in classifications that have only one or a few known examples. The result is an astonishing diversity of rock types that are variably enriched in economic elements, including the rare earth elements. When these magmas ascend into the Earth's crust, their chemical composition undergoes further changes in response to variations in pressure, temperature, and composition of surrounding rocks. The resulting alkaline magmas are rare and unusually enriched in elements such as zirconium, niobium, strontium, barium, lithium, and the rare earth elements. The formation of alkaline rocks is complex and not fully understood but can be thought of as a geologic process that extracts and concentrates those elements that do not fit into the structure of the common rock-forming minerals. Alkaline igneous rocks form from cooling of magmas derived by small degrees of partial melting of rocks in the Earth's mantle.

Rare earth elements