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Resources 2017, 6(3), 36;

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

Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, 1 University Sta. C9000, EPS 1.130, Austin, TX 78712, USA
Author to whom correspondence should be addressed.
Received: 3 May 2017 / Revised: 24 July 2017 / Accepted: 25 July 2017 / Published: 29 July 2017
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Monazite [(Ce,Th)PO4] 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 spectrometer (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. View Full-Text
Keywords: monazite; rare earth elements; geochemistry; Bolivia; apatite; Llallagua monazite; rare earth elements; geochemistry; Bolivia; apatite; Llallagua

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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    Description: Excel file of EPMA and LA-ICP-MS analyses of the monazite grains.
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Catlos, E.J.; Miller, N.R. Speculations Linking Monazite Compositions to Origin: Llallagua Tin Ore Deposit (Bolivia). Resources 2017, 6, 36.

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