Fingerprinting REE mineralization and hydrothermal remobilization history of the carbonatite-alkaline complexes, Central China: Constraints from in situ elemental and isotopic analyses of phosphate minerals

Abstract

Carbonatites and related alkaline rocks host most REE resources. Phosphate minerals, e.g., apatite and monazite, commonly occur as the main REE-host in carbonatites and have been used for tracing magmatic and mineralization processes. Many carbonatite intrusions undergo metamorphic and/or metasomatic modification after emplacement; however, the effects of such secondary events are controversial. In this study, the Miaoya and Shaxiongdong carbonatite-alkaline complexes, in the South Qinling Belt of Central China, are selected to unravel their magmatic and hydrothermal remobilization histories. Both the complexes are accompanied by Nb-REE mineralization and contain apatite and monazite-(Ce) as the major REE carriers. Apatite grains from the two complexes commonly show typical replacement textures related to fluid metasomatism, due to coupled dissolution-reprecipitation. The altered apatite domains, which contain abundant monazite-(Ce) inclusions or are locally surrounded by fine-grained monazite-(Ce), have average REE concentrations lower than primary apatite. These monazite-(Ce) inclusions and fine-grained monazite-(Ce) grains are proposed to have formed by the leaching REE from primary apatite grains during fluid metasomatism. A second type of monazite-(Ce), not spatially associated with apatite, shows porous textures and zoning under BSE imaging. Spot analyses of these monazite-(Ce) grains have variable U-Th-Pb ages of 210-410 Ma and show a peak age of 230 Ma, which is significantly younger than the emplacement age (440-430 Ma) but are This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Untitled

“…The relative enrichment of HREE+Y in sample SAA4 and the abundant crystallization of monazite could have been caused by fluid-induced metasomatism, where apatite reacted with the fluid such that the LREEs were preferentially leached, together with P. The original apatite underwent recrystallization, and the LREEs and P in solution precipitated as monazite near or at the apatite. This phenomenon has been reported from experimental petrology and natural systems (Harlov and Förster 2003;Harlov et al 2005;Antignano and Manning 2008;Ma et al 2021;Su et al 2021). Experimental works (Harlov et al 2002;Harlov and Förster 2003;Harlov et al 2005) show that monazite can form from an interaction of a hydrous metasomatic fluid with fluorapatite.…”

“…Apatite trace element concentrations and element ratios have previously been used to identify their host rocks (Belousova et al 2002) 2000;Belousova et al 2001;Belousova et al 2002;Brassinnes et al 2005;Hsieh et al 2008;Tollari et al 2008;Chu et al 2009;Xu et al 2010;Bonyadi et al 2011;Tang et al 2012;Chen and Simonetti;Mao et al 2016;Pan et al 2016;Broom-Fendley et al 2017;Chakhmouradian et al 2017;Deng et al 2017;Doroshkevich et al 2017;Mukherjee et al 2017;Jiang et al 2018;Andersson et al 2019;Du et al 2019;Duan et al;Hu et al 2019;Palma et al 2019;Qu et al 2019;Ren et al 2019;Wang et al 2019;Yu et al 2019;Zafar et al 2019;Zhang et al 2019;Jia et al 2020;Mercer et al 2020;Zhang et al 2020;Broom-Fendley et al 2021;Lu et al 2021;Su et al 2021; this study. The database is available online in Electronic Appendix B.…”

Magmatic and hydrothermal controls on diverse Nb mineralization associated with carbonatite-alkaline complexes in the southern Qinling orogenic belt, Central China

“…Summary of geochronological data showing multi-stage magmatic, hydrothermal or mineralization events in the region. Geochronological data are collected from Li et al (1989), Xu et al (2008Xu et al ( , 2014Xu et al ( , 2015, Zhu et al (2016), Ying et al (2017Ying et al ( , 2020, Chen et al (2018), Zhang et al (2019a), Su et al (2019Su et al ( , 2021, Wu et al (2021), and this study.…”

“…Typical examples include the REE-Nb deposits associated with the Miaoya and Shaxiongdong carbonatite-syenite complexes (Xu et al 2008(Xu et al , 2010Ying et al 2017;Chen et al 2018;Ma et al 2021;Wu et al 2021) and Nb-rich trachytes (e.g., Zhuxi) that cover an outcrop of approximately 100 km 2 (Nie et al 2019;Wang et al 2021;Yan et al 2021). Despite previous works on the petrogenesis of these complexes (Xu et al 2008(Xu et al , 2010(Xu et al , 2014(Xu et al , 2015Zhu et al 2016;Ying et al 2017;Chen et al 2018;Su et al 2019Su et al , 2022Yan et al 2021) and the origin of REE mineralization (Cimen et al 2018;Nie et al 2019;Zhang et al 2019aZhang et al , 2019bYing et al 2020;Ma et al 2021;Su et al 2021), the styles of Nb mineralization have not yet been well characterized, hindering an understanding of the Nb mineralization process. In this contribution, we investigated the Nb mineralization style and process, and the controlling 6 / 47 factors, exemplified by the Miaoya and Shaxiongdong REE-Nb deposits in the Qinling belt, through a combined mineralogical and in-situ chemical-isotopic investigation.…”

“…6). Such a decoupling of REE and Nb is possibly ascribed to the immiscibility of the conjugated carbonatitic and syenitic melts(Su et al 2021(Su et al , 2022, as the REE and Nb generally tend to favor partitions into carbonatite and silicate melts, respectively(Wyllie et al 1996;Suk 2012).…”