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Discovery of Contact Metamorphism‐Related Baddeleyite from the Bayan Obo Deposit, Northern North China Craton
Author(s) -
ZHANG Shuanhong,
ZHAO Yue
Publication year - 2017
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.13129
Subject(s) - beijing , china , paleomagnetism , chinese academy of sciences , geology , geomechanics , metamorphism , craton , tectonics , mining engineering , library science , seismology , archaeology , geochemistry , geography , paleontology , geotechnical engineering , computer science
Baddeleyite (ZrO2) occurs primarily as an accessory mineral in igneous rocks with low silica activity and has been widely used to determine crystallization ages of maficultramafic rocks and alkaline rocks including carbonatites and kimberlites. The Bayan Obo deposit on the northern margin of the North China Craton (NCC) is the world’s largest REE deposit. Many previous studies show that the main component of ore-hosting dolomite marble is magmatic in origin and the REE-Nb mineralization is closely related to the carbonatites in the Bayan Obo deposit. This study attempted to separate baddeleyite from the REENb-rich carbonatites in the Bayan Obo deposit to determine their crystallization ages in order to better understand the timing, genesis and tectonic setting of this deposit. Our samples were collected from two open pits for REE-Nb mining exploitation near Boluotu in the easternmost part of the Bayan Obo deposit. The sample sites are 2–6 m to 650 m from the intrusive contacts between Bayan Obo REE-Nb-rich carbonatites and Permian granitoids with zircon U-Pb ages of ca. 280–260 Ma. The REE-Nb-rich carbonatite samples consist mainly of dolomite (80 vol.%–66 vol.%), calcite (8 vol.%–5 vol.%), magnetite (8 vol.%–6 vol.%), humite (7 vol.%–<1 vol.% ), bastnäsite (5 vol.% –<1 vol.% ), monazite (6 vol.%–1 vol.%), fluorite (3 vol.%–<1 vol.%), pyrite (4 vol.%–0) and hematite (1 vol.%–0); other minerals include diopside, ankerite, fergusonite-Ce, cordylite, apatite, pyrochlore, aeschynite, galena, zircon and baddeleyite (Fig. 1). Some humite has been identified as mineral inclusions in baddeleyite (Fig. 1).