Journal
MINERALS
Volume 9, Issue 8, Pages -Publisher
MDPI
DOI: 10.3390/min9080456
Keywords
columbite; U-Pb dating; Li pegmatite; Kalu'an; Chinese Altay orogen
Funding
- Ministry of Science and Technology of the China [2017YFC0602701]
- Fundamental Research Funds for the Central Universities of China [300102279101, 300102279401]
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The Kalu'an-Azubai pegmatite field, one of the most important rare-metal metallogenic regions in China, contains a large number of pegmatite dikes belonging to spodumene and lepidolite subtypes. Columbite-group minerals (CGMs) collected from three spodumene subtype pegmatites (No. 802, No. 803, and No. 805 pegmatites) were analyzed for major element contents using EPMA (electron probe micro-analyzer) and dated using LA-ICP-MS (laser ablation-inductively coupled plasma mass spectrometer). The crystallization ages of the CGMs from No. 802, No. 803, and No. 805 pegmatites are 209.5 +/- 1.4 Ma (2 sigma), 198.3 +/- 2.0 Ma (2 sigma), and 224.3 +/- 2.9 Ma (2 sigma), respectively. Oscillatory zoning and/or sector zoning along with the associated mineral assemblages suggest that the dated columbite is of magmatic origin. The crystallization ages of the columbite grains thus represent the emplacement ages of the Li pegmatites. Therefore, our dating results indicate that there were three emplacement events of the Li-rich pegmatite-forming melts in a timeframe of similar to 30 Ma. In combination with previous studies, we conclude that the Li pegmatites were formed before the Be-Ta-Nb pegmatites (similar to 194-192 Ma), which precludes the genesis of rare-metal pegmatites via fractional crystallization of a granitic magma in the Kalu'an-Azubai region.
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