Petrology,Geochemistry And Geochronology Study On The Granites From Zhongba Rb-Nb-Ta Field In,Zijin County,Guangdong Province

Zhongba ore field in Zijin county,Guangdong province is located at the southeast end of Nanling metallogenic zone and the eastern part of Guangdong province folding-belt of Cathaysia Massif.Separate Rb ore body and Nb-Ta-containing Rb ore body were discovered in 2013 with estimated yield of 230,000 tons,indicative of superior metallogenic environment and a unique tectonic setting in this region.Rb-Nb-Ta rare metal deposits in this region show close association with Yanshannian intermediate acid magmatic rocks.So,it is very important to study the origin and formation of these magmatic rocks to gain better understanding of the tectonic evolution and crust mantle interaction in Nanling region.Three periods of granites in Zhongba ore field are stronglyperaluminous,rich in K and F,poor in Fe,Mg,Ca,Ti and P.They are enriched in Si O₂(67.96%?76.71%)and exhibit high TFe O/Mg O ratio(5.30?65.61,with average of 29.52).They have high rare earth element(REE)concentration and are enriched in light rare earth.These characteristics along with the seagull-type chondrite-normalized REE patterns indicate that these granite rocks are mostly A type granite.The high Rb/Sr ratio,low Zr/Hf ratio and low K/Rb ratio of the granites suggest high degree of differentiation and evolution,with the fourth period rocks showing the significant higher degree of evaluation than the first three periods.Zircon LA-MC-ICP-MS U-Pb dating of the medium-grained(porphyritic)biotite granite and the medium grained biotite granite produces age of 135.38±0.57Ma(MSWD=0.99)and 136.96±0.88 Ma(MSWD=2.2),respectively,belonging to early Cretaceous.The contents of F and Li vary obviously in granites of different stagesin Zhongba mining.The very high contents of F and Li of the fourth period of Yanshan magmatic rocks may be one of the most important contributing factors for the enrichment of Rb,Nb and Ta.