Monazite is a member phosphate group, and a phosphate of Th and REE. Monazite is a rare mineral and occurs as an accessory mineral in granites, gneisses, aplites, pegmatites and as rolled grains in the sands derived from decomposition of such rocks. Due to the high content of turium and rare earth elements this mineral is the most important and economic mineral in placer deposits. Marvast monazite placer, has been identified through the regional geochemical exploration in Yazd – Sabzevaran zone. Detailed exploration shows that younger gravel fan and recent alluvium contain monazite grains. The grade of monazite in this placer varies from 50-525 g/ton. The reserve of placer is 8866425 t. with a grade of 150 g/ton of monazite. Monazite concentrate samples analyzed by mass spectrometry and microprobe techniques. The results show that Marvast monazite enriched in light rare earth elements (Ce, La, Nd, Pr, Eu, Sm) and the content of REE2O3 is about 55.45%.
In this placer deposit, Monazite accompanied by hematitized pyrite, epidotes, celestite, cerisite, rutile, magnetite, garnets, ilmenite, pyroxenes, amphiboles and sometime with zircon and apatite. Black shales are the host rock of monazite in the Marvast area, interbedded with calcareous sandstone, limestone and conglomerate. Monazite nodules, occurs sporadically in shales. Monazite grains are released by weathering and erosion of these rocks and are concentrated in younger gravel fan and recent alluvium.