地质学报2026，Vol.100Issue(3)：920-937,18.DOI:10.19762/j.cnki.dizhixuebao.2025373
四川冕宁牦牛坪稀土矿床成岩成矿年代学及其找矿意义
Metallogenic geochronology and prospecting significance of the Maoniuping rare earth deposit in Mianning,Sichuan
摘要
Abstract
The Maoniuping deposit in Mianning,Sichuan,is one of the most significant rare earth element(REE)deposits,situated within the Mianning-Dechang Himalayan REE metallogenic belt in southwestern China.Its REE mineralization is closely associated with syenite-carbonatite complexes;however,uncertainties persist regarding the mineralization age and the petrogenetic evolution of these complexes.To clarify the magmatic evolution and mineralization mechanisms,this study carried out zircon U-Pb geochronology and whole-rock major and trace element analyses on alkali-feldspar granite porphyry and syenite from the deposit.The results yielded zircon ages of 25.4±0.3 Ma(MSWD=0.8,n=12)for the alkali-feldspar granite porphyry and 26.1±0.4 Ma(MSWD=1.4,n=16)for the syenite,suggesting that they were emplaced contemporaneously during the Himalayan orogeny.Geochemical analyses reveal that the alkali-feldspar granite porphyry is characterized by high SiOz(71.67％～73.67％);low MgO,CaO,and P2O5;no significant-negative Eu anomalies;and relative depletion in Ba,Sr,Ti,Nb,and Ta.Its REE distribution pattern mirrors that of the syenite.The results confirm both silicate and carbonate magmatic evolution pathways within the mining area.The 10000× Ga/Al ratio(2.6～3.5)and Zr+Nb+Ce+Y contents(179×10-6～960 × 10-6)classify the alkali-feldspar granite porphyry as an A1-type granite formed during intraplate extension within a collisional orogenic belt,marking the regional transition of tectonic stress from compression to lithospheric extension.LA-ICP-MS U-Pb dating of bastnäsite from ore veins yields ages concentrated between 32.7 and 27.6 Ma,which slightly predate the emplacement ages of the alkali-feldspar granite porphyry and syenite.This temporal relationship indicates that the mineralization is associated with early magmatic activity prior to the emplacement of the alkaline complex,suggesting that ore formation is a phased product of prolonged magmatic evolution.The late-stage alkali-feldspar granite porphyry,characterized by high silica,low volatiles,and rapid crystallization,did not undergo significant mineralization but serves as an indicator for the terminal phase of regional large-scale REE mineralization.This study broadens the known rock types within the deposit's complexes and deepens the understanding of mantle-derived alkaline magmatic evolution and mineralization patterns in collisional orogenic settings,offering insights for regional REE exploration.关键词
碱长花岗斑岩/正长岩/氟碳铈矿/U-Pb年代学/岩浆演化Key words
alkali-feldspar granite porphyry/syenite/bastnäsite/U-Pb geochronology/magmatic evolution引用本文复制引用
金雅楠,王登红,王伟,何斌,赵芝,刘善宝,赵瑞潍,于扬,于沨..四川冕宁牦牛坪稀土矿床成岩成矿年代学及其找矿意义[J].地质学报,2026,100(3):920-937,18.基金项目
本文为中国稀土集团有限公司科技项目"四川省牦牛坪、大陆槽稀土矿成矿规律与找矿预测"(编号HE2310)资助的成果. （编号HE2310）
