Beach placers

These deposits are formed in the natural process of weathering, transportation, and concentration at the site of heavy minerals originating from some primary source rock. Commercially, beach placers are the most important along with alluvial streams aeolian deposits are insignificant. 

Brazil Beach placers, carbonatite and alkaline rocks 20 73... 

The U.S. Geological Survey was scheduled to publish a revised study of U.S. thorium resources in August 1979. Partial results of this study, which cover most of these resources but do not include the beach placers of Florida, Georgia, and the Carolinas, were presented orally by Staatz [S5] of the U.S. Geological Survey in 1978. Table 6.14 lists the types of deposit, the principal districts in which potentially economic thorium-bearing deposits have been found, the principal thorium minerals, and estimates of thorium reserves and resources. Thorium from the vein deposits, the first type, could be produced for less than 30/lb. Thorium is the principal salable product in these deposits. Thorium could be coproduced with other elements from disseminated deposits, massive carbonatites, and placers the amount of thorium that might be produced from them, and its cost, depends on the marketability of the other minerals that occur with the thorium. 

Placers represent the third most important REE ore variety that has or is being mined and occur in widely dispersed unconsolidated Neogene and Quaternary beach sands, the most important being Ti-mineral-rich beach sands on the coasts of both western and eastern Australia. REE are by-products of these deposits and the main REE ore minerals are monazite xenotime. Xenotime is of special interest because unlike most other REE ore minerals that are highly LREE eiuiched, xenotime is enriched in the HREE (Figure 4). 

Zircon, ZrSi04, is a common but sparse accessory mineral in alkaline igneous rocks and some pegmatites. It is fairly resistant to weathering and metamorphic processes and can be concentrated in placer or beach sand deposits. Zircons accept a spectrum of lanthanide distributions as is evident from the two shown in fig. 21.32. 

The use of monazite and xenotime is generally linked to the demand of other economically recoverable elements, e.g., titanium (sphene, rutile, ilmenite), tin (cassiterite), niobium (euxenite), zirconium (zircon) in placer alluvial, fluvial, eluvial, and beach deposits. Rarely has monazite or xenotime occurred in great enough concentration to make it economically recoverable as a primary ore mineral. Nevertheless, there is a considerable worldwide reserve of these minerals which could be processed in the future under more favorable economic conditions. 

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