Discovery and determination of the first igneous carbonatite in western Yunnan Province,SW China
Igneous carbonatite(also known as carbonatite)is a mantle-derived,carbonate-rich,and silica-poor igneous rock rarely exposed on the surface.Carbonatite serves as a"probe"rock for studying mantle properties and evolution,and it hosts abundant critical metal mineral resources such as rare earth elements(REEs)and niobium.Therefore,the research on it has important scientific and economic value.In this study,a large-scale carbonatite rock mass was discovered for the first time in the Baoshan area of Yunnan.The exposed area of rock mass is about 60000m2,exposed within the Longling-Luxi fold belt between the Baoshan block and the Tengchong block.These carbonatites are primarily composed of carbonate minerals such as calcite and dolomite,and they also contain significant amounts of apatite,magnetite,biotite,pyroxene,monazite,and baddeleyite.Based on petrography,mineralogy,and whole-rock chemical composition,carbonatite can be classified into calciocarbonatite,magnesiocarbonatite,and ferruginous calciocarbonatite.The different lithologies show significant variations in CaO(29.57％～51.66％),Fe2O3T(0.72％～21.15％),and MgO(1.76％～16.90％).Trace element characteristics reveal that the carbonatites are generally enriched in large-ion lithophile elements(LILEs)such as Sr(3431 × 10-6～9753 ×10-6),Ba(197 × 10-6～2428 × 10-6),Pb(14.4 × 10-6～425 ×10-6),and∑REE(841 × 10-6～2341 × 10-6).Still,they are relatively depleted in high field strength elements(HFSEs)like Nb(1.09 × 10-6～12.48 × 10-6),Ta(0.12 × 10-6～4.74 × 10-6)and Hf(0.07 × 10-6～7.85 × 10-6).The REE distribution pattern is right-leaning,with(La/Yb)N ratios ranging from 58 to 104,showing enrichment in light rare earth elements(LREEs)and a weak negative Eu anomaly(δEu=0.68～0.74).The major rock-forming minerals in the carbonatites,such as calcite,dolomite,and apatite,also exhibit geochemical characteristics similar to those of the whole rock.The 813 CV-PDB values of the carbonatite minerals(-7.45％o to-3.54％o)mostly fall within the range of"primary igneous carbonatites",but the δ18 O V-SMOW values(10.79‰～20.06％o)are relatively high,likely due to post-magmatic hydrothermal alteration.The whole-rock,mineral chemistry,and C-O isotope characteristics are consistent with most carbonatites worldwide,confirming that the Potou carbonatite rock mass is a typical igneous carbonatite.LA-ICPMS dating of baddeleyite in the carbonatite yielded a U-Pb isochron age of 160.7±2.0Ma(MSWD=1.8)and a weighted mean 206Pb/238U age of 159.7±1.8Ma(MSWD=2.4),indicating that it formed in the Middle Jurassic as a result of magmatic activity following Triassic collisional orogeny.The determination of the Potou carbonatite will help reveal the mantle characteristics of the region,and its potential for critical metal mineralization warrants further investigation.
PotouCarbonatiteWhole-rock geochemistryC-O isotopesBaddeleyite U-Pb ageBaoshan,Yunnan Province
万方数据
维普
