Speculations Linking Monazite Compositions to Origin: Llallagua Tin Ore Deposit (Bolivia)

Abstract

Monazite [(Ce,Th)PO 4 ] from the Llallagua tin ore deposit in Bolivia is characterized by low radiogenic element contents. Previously reported field evidence and mineral associations suggest the mineral formed via direct precipitation from hydrothermal fluids. Monazite compositions thus may provide insight into characteristics of the fluids from which it formed. Chemical compositions of three Llallagua monazite grains were obtained using Electron Probe Microanalysis (EPMA, n = 64) and laser ablation mass spectrometry (LA-ICP-MS, n = 56). The mineral has higher amounts of U (123 ± 17 ppm) than Th (39 ± 20 ppm) (LA-ICP-MS, ±1σ). Grains have the highest amounts of fluorine ever reported for monazite (0.88 ± 0.10 wt %, EPMA, ±1σ), and F-rich fluids are effective mobilizers of rare earth elements (REEs), Y, and Th. The monazite has high Eu contents and positive Eu anomalies, consistent with formation in a highly-reducing back-arc environment. We speculate that F, Ca, Si and REE may have been supplied via dissolution of pre-existing fluorapatite. Llallagua monazite oscillatory zoning is controlled by an interplay of low (P + Ca + Si + Y) and high atomic number (REE) elements. We suggest monazite compositions provide insight into fluid geochemistry, mineral reactions, and tectonic settings of ore deposits that contain the mineral.

Further Characterization of the RW-1 Monazite: A New Working Reference Material for Oxygen and Neodymium Isotopic Microanalysis

“…It also occurs as a detrital mineral in many clastic sedimentary rocks. Monazite is sensitive to relatively low-grade metamorphism (down to greenschist facies) [2] and hydrothermal fluids [3]. Due to its high U and Th contents, low initial nonradiogenic Pb content, and apparent resistance to metamictization, monazite has been widely acknowledged as a good geochronometer (e.g., [1,4,5]).…”

Analysis of radioactivity in commercially available products aiming to improve health and wellness

“…The powder was assumed to be some form of by-product obtained from mineral processing of rare earth metals, presumably monazite sand, which is known to contain up to 25% of Th ( 11 ) . Thus, the composition of monazite sand was taken to be the average of that given by Catlos and Miller ( 12 ) and Nagy and Draganits ( 13 ) .…”

Rare earth elements and neodymium and strontium isotopic constraints on provenance switch and post-depositional alteration of fossiliferous Ediacaran and lowermost Cambrian strata from Arctic Norway

“…Adding even a small amount of monazite can result in a significant increase of Gd N /Yb N in the sediment (McLennan et al, 1993). Monazite is a phosphate mineral with high LREE content (Deer et al, 1992) and commonly between 0.5 and 4 % Gd 2 O 3 (Lee and Bastron, 1967;Milodowski and Zalasiewicz, 1991;Catlos and Miller, 2017;Lazareva et al, 2018). In case of monazite enrichment, one would expect elevated LREE (especially Ce) and Gd in the absolute element abundances of these samples which is not the case (Table 2).…”