Regional metallogenic geological background of granite-type Nb-Ta deposits in Southeast China

In order to explore the regional metallogenic geological background of granite-type Nb-Ta deposits in southeast China and to provide geological tectonic basis for the regional mineralization regularity and resource potential evaluation of granite-type Nb-Ta deposits in southeast China, the authors collected and collated data from 15 typical granite type Nb-Ta deposits and, in combination with the deposit characteristics, metallogenic age, metallogenic rock mass and rock geochemical research analysis, concluded that the formation ages of the deposits are concentrated at 124 ~ 185 Ma, suggesting Yanshanian period.Geochemical characteristics show that the concentration of P₂O₅ is different in different ore-forming granites, with both high P and low P, A/CNK equal to 0.97~1.99, mostly greater than 1.1, and peraluminous characteristics; trace elements show enrichment of Rb and Nb, Ta, Th, Zr, Hf and other elements but loss of Sr, Ti, Ba; the content of rare earth elements generally shows a low trend, and Eu has a significantly negative anomaly; Zr/Hf=3.13~23.31, and Nb/Ta=0.28~7.67.In combination with the mineral characteristics, it is believed that the ore-bearing rock masses are all highly differentiated granites.From the bottom to the top of the ore-forming rock mass, except for some hidden rock masses that show the characteristics of the top zone, the ore-forming rock masses all show obvious facies belt characteristics, and the characteristic mineral mica changes more obviously, towards light-colored mica and evolution in lithium-richer direction; the ore-forming rocks are the associated or transitional combination of biotite granite, two-mica granite and muscovite granite.The mineralizing granite includes both S-type highly differentiated granite and topaz A-type granite, and topaz A-type granite.Granite and S-type granite are symbiotic and were formed by melting of the S-type granite.Combined with regional research data, the authors hold that the deposits were formed in the subduction accretive orogenic process under the background of ocean-continent convergence:westward subduction of the Paleo-Pacific plate led to the occurrence of intracontinental subduction on the southeast margin of the Yangtze Block, which resulted in the northwest margin of the intrusive (rock) arc of the southeast coast pushing over the southeast margin of the Yangtze Block, forming many "collision type" granite Nb-Ta deposits.