Rock monazite

Monazite (CeP04 in which the Ce site also contains much La, Nd, and other REE elements) is another accessory mineral in igneous and metamorphic rocks. Monazite may take in significant amount of Th (several weight percent) and U (of the order of one weight percent), but not much Pb. Assuming that all Pb in old... 

Rock monazite, obtainable from South Africa, contains a few per cent of the mineral apatite (calcium phosphate) together with a little iron phosphate impurity. The apatite in particular does not respond to the sodium hydroxide breakdown procedure to the same extent as thorium and rare earth phosphates. Consequently, the oxide product after washing still contains a quantity of phosphate about equal to the weight of thorium present. This is too high for passing to the final solvent purification stage and it is therefore necessary to eliminate apatite before the alkali breakdown stage. Removal is accomplished by a pretreatment process " in which... 

Uranium, not as rare as once thought, is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. 

Whereas certain rocks of igneous origin formed by melting and recrystallization can include minerals enriched in the lanthanides (4), cerium is usually present as a trace element rather than as an essential component. Only a few minerals in which cerium is an essential stmcture-defining component occur in economically significant deposits. Two minerals supply the world s cerium, bastnasite [68909-13-7] LnFCO., and monazite [1306-41 -8] (Ln,Th)PO. ... 

There are over 100 minerals known to contain lanthanides but the only two of commercial importance are monazite, a mixed La, Th, Ln phosphate, and bastnaesite, an La, Ln fluorocarbonate (M C03F). Monazite is widely but sparsely distributed in many rocks but, because of its high density and inertness, it is concentrated by weathering into sands on beaches and river beds, often in the presence of other... 

TLC has very important applications in the isolation and determination of REEs in rocks, ores, and monazite sand. 

Thorium is a radioactive metal that occurs naturally in several minerals and rocks usually associated with uranium. However, it is approximately three times more abundant in nature than uranium. On average, soil contains 6 to 10 ppm of thorium. Thorium is most commonly found in the rare-earth thorium-phosphate mineral, monazite, which contains 8% 10% thorium. Current production of thorium is, therefore, linked to the production of monazite, which varies between 5500 and 6500 tonnes per year, with approximately 300 to 600 tonnes of thorium recovered (NEA/IAEA, 2006a). 

Thorium is widely but rather sparsely distributed its only commercial sources are monazite (together with the rare earths) and uranothorite (a mixed Th, U silicate). Uranium is surprisingly common and more abundant than mercury, silver or cadmium in the earth s crust. It is widely distributed and it is found scattered in the faults of old igneous rocks. Concentration by leaching followed by re-precipitation has produced a number of oxide minerals of which the most important are uranite (also called pitchblende) U308 and carnotite, K UC HVO -SF O. 

Several minerals have been identified in polished thin sections of various rock types including massive sulphide, gossan, intermediate crystal-lapilli tuff, and felsic ash tuff (Fig. 2). These minerals include apatite, monazite, zircon, allanite, titanite, xenotime, magnetite, cassiterite, cobaltite-gersdorffite, rutile, ilmenite, goethite, sphalerite, galena, arsenopyrite, chalcopyrite, pyrite, and pyrrhotite. These minerals range in size from 20 pm to 250 pm and represent potential Indicator minerals. 

The Silver Bell Mine area consists of dipping units that are composed of dacite porphyry, alaskite and monazite. The rock ages span the Paleozoic, Mesozoic and Cenozoic periods. The Paleozoic wall rocks consist of quartzite, siltstone and altered limestone. The carbonate rocks are exposed along the contact between the host rock and intrusions, and host the... 

Rock samples collected from archived core, mine workings and outcrop were pulverized, homogenized, then analyzed using four-acid dissolution (SGS Lab, Toronto) to determine the near-total lithogeochemical composition (cassiterite, rutile, monazite, zircon, sphene, gahnite, chromite and barite are partially dissolved). Gold analyses were done by Fire Assay with Atomic Absorption finish on 30g samples and have a detection limit of 5 ppb. 

PI and P5 represent the age of the granite, and agree with previous dating (Rimsaite 1982). P3 represents the age of the pegmatite. P2 and P4 overlap and represent an event that reset monazite in both the granite and pegmatite, and corresponds to the age that Fowler Doig (1983) obtained by whole-rock Rb-Sr methods. 

Samarium occurs in nature widely distributed but in trace quantities, always associated with other rare earth metals. The two most important minerals are (i) monazite, which is an orthophosphate of thorium and the rare earths and (ii) bastanasite, which is a rare earth fluocarbonate. The samarium content of these ores is about 2%, as oxide. It also is found in precambri-an granite rocks, shales, and certain minerals, such as xenotime and basalt. Its abundance in the earth s crust is estimated to be 7.05 mg/kg. 

Uranium occurs in nature in many rocks, minerals and sediments. The principal uranium minerals are pitchblende, carnotite, uranitite, tobernite, uranophane, autunite, and davidite. Uranium also is found in very small quantities in monazite sand, phosphate rock, and lignite. Although uranium is present in very smaU quantites, these sources also are used for commercial recovery of the metal. 

The element was discovered in 1794 by the Swedish chemist Gadolin. He named it after the small town Ytterby in Sweden where the mineral containing yttria was found. Mosander in 1843 determined that the yttria consisted of three oxides yttria, erbia, and terbia. Yttrium occurs in all rare earths. It is recovered commercially from monazite sand, which contains about 3% yttrium. It also is found in bastnasite in smaller amounts of about 0.2%. Abundance of yttrium in earth s crust is estimated to be 33 mg/kg. The metal has been detected in moon rocks. 

A monazite crystal in a metamorphic rock is about 100 pm across. It is estimated that the peak metamorphic temperature was 700°C and monazite formed near peak metamorphism. The metamorphic event lasted for about 20 Myr. Find the diffusion distance and evaluate whether the monazite grain lost a significant amount of Pb. That is, evaluate whether monazite grain can be used to determine the age of peak metamorphism. 

The diffusion coefficient of Pb in monazite depends on temperature as D = exp(-0.06-71,200/7) m /s (Cherniak et al., 2004). You found a 100-/rm-diameter monazite crystal in a metamorphic rock. Assume that the monazite crystal formed at peak metamorphic temperature. 

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