期刊
ORE GEOLOGY REVIEWS
卷 150, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.oregeorev.2022.105177
关键词
Mineralizing fluid; Mo provenance; REE re-enrichment; Calcite; Eastern Qinling
资金
- National Key Research and Development Program of China [2021YFC2901704]
- National Natural Science Foundation of China [41930430, 91962103]
- Key Research Program of the Institute of Geology and Geophysics, CAS [IGGCAS-201901]
- Opening Project of the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization [2021H2280]
This study provides insights into the origin and enrichment of REE resources in the Huangshui'an carbonatite, suggesting that Mo enrichment is caused by contamination and assimilation of wallrocks, and post-carbonatite fluids play a significant role in REE re-enrichment.
The Huangshui'an carbonatite (-210 Ma) in the Qinling orogenic belt (central China) is known for its unique enrichment of heavy rare earth elements (HREEs) and molybdenum (Mo). However, the origin of Mo in car-bonatite veins and the contribution of post-carbonatite fluids to REE enrichment remain enigmatic. In this study, new data of U-Pb dating on zircon and bastnaesite, trace elements and Sr-Nd isotopic compositions of calcite and apatite are obtained to clarify both puzzles. Xenocrystic zircon U-Pb age dating for multiple carbonatite samples yields a concordia age of 2317.0 +/- 7.2 Ma (MSWD = 1.2) and a 207Pb/206Pb weighted average age of 2305.2 +/- 4.5 Ma (MSWD = 1.0), which are consistent with the age of the Taihua Group granitic gneisses and demonstrate that Mo enrichment in the carbonatite veins is caused by the contamination and assimilation of the wallrocks of the Mo-rich Taihua Group during the carbonatite magma ascending. Hand specimens and microtextural relationships show that magmatic calcite (FREE: 180-1511 ppm) were extensively metasomatized by the late fluids, accompanied by abundant hydrothermal calcite, bastnaesite and allanite. Compared with magmatic calcite, hydrothermal calcite is significantly depleted in LREEs, Ba, Sr, Mn, Na and Mg, and shows elevated fractionation between LREE and HREE, which probably reflects the crystallization of cogenetic REE-bearing minerals and phases of barite-celestine series. Regardless of the different REE concen-trations, similarities in elemental patterns and Y/Ho ratio of both calcites indicate that hydrothermal alteration remobilized REEs from magmatic calcite. The U-Pb dating of bastnaesite (127.5 +/- 2.6 Ma) from the hydro-thermal veins yields the same age as the early Cretaceous granitic intrusions and related molybdenum deposits (126-130 Ma) around the Huangshui'an deposit. The Sr-Nd isotopic values of the hydrothermal apatite [(87Sr/86Sr)i: 0.70607-0.70717; epsilon Nd (t): -23.6 --14.3]are between the range of those reported for the Qinling carbonatites [(87Sr/86Sr)i: 0.70373-0.70624; epsilon Nd (t):-14.7 --3.0]and the early Cretaceous granites [(87Sr/86Sr)i: 0.70700-0.71090; epsilon Nd (t):-28.7 --9.0].These results suggest that the fluids involved in REE remobilization are exogenous and may be related to the late Mesozoic granitic intrusions in the Qinling orogenic belt, and that the metasomatism of the early carbonatite veins by the post-carbonatite hydrothermal fluids fa-cilitates the re-enrichment of REEs with economic resources.
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