Petrogenesis Of Early Cretaceous Granitoids And Fe-Mo Polymetallic Mineralization In Yongding-Dehua Area,Southwestern Fujian Province

The southwestern Fujian Province is one of the most economically significant Fe?Cu ore belts in southeastern China coastal region and even in South China.This belt hosts more than 120 Fe polymetallic deposits,with typical ore deposit represented by the Makeng-type skarn Fe-Mo polymetallic deposit.The Fe-Mo polymetallic mineralization is intimately related to the Early Cretaceous granitoids which are mainly concentrated in Yongding-Dehua area,eastern part of the belt.However,these granitoids remain poorly studied,which results in highly debates on their distribution,petrogenetic mechanism and coupling relationship with the Fe-Mo polymetallic mineralization.This study presents systematic petrological,geochronological,mineralogical and petrogeochemical data for the representative ore-bearing granitic intrusions,including Shierpai?Dapai plutons and Yongfu batholith,to depict their petrographic,and geochemical characteristics,as well as to comprehensively elucidate their genetic types,magma sources,evolutions and emplacement ages.This study also determines the ore geology and isotopic geochemical compositions of typical Fe-Mo polymetallic deposits.On this basis,the genetic relationship between Early Cretaceous magmatism with Fe-Mo metallogenic events and their tectonic background are systematically discussed.Main observations obtained and conclusions are as follows:1.Zircon U-Pb chronological ages reveal the studied granitoids were mainly emplaced at 142?128Ma.Integrated with regional chronological and petrologic data for coeval granitoids,we propose that there exists an Early Cretaceous granitoid belt in Yongding-Dehua area.The granitoid association is syengranite-biotite monzogranite-granodiorite(porphyry),and they were formed at 145?125Ma.2.The elemental geochemical results show the granitoids are metaluminous to weakly peraluminous and have high Si,K and low Mg,Ca concentrations.They are variously enriched in K?Rb?Th?U?Y and REEs,whereas obviously depleted in P,Ti,Sr,Ba,Nb,Ta,and have moderate to prominent Eu negative anomalies with flat right-sloping REE patterns.All these observations indicate the Early Cretaceous granitoids in Yongding-Dehua area belong to High-K calc-alkaline and highly fractionated I-type granites.3.Combined with Sr-Nd-Hf isotopic compositions,we suggest these granitoids were most likely formed by mixing of Paleoproterozoic basement(the Mayuan Group)-derived felsic magmas and deep-seated mantle components,and subsequently experienced high degrees of fractional crystallization.Mantle-derived magmas were not only directly involved in the generation of the Early Cretaceous granitoids,but also of that material contributions gradually increased with time,suggesting crust-mantle interactions played a progressive role in their petrogenesis.4.Our geological survey,geochemistry and geochronology data for typical ore deposits suggest the Fe-Mo polymetallic mineralization is closely related to the early Cretaceous granitoids in Yongding-Dehua belt,and mainly occurred at 145?130Ma.The S-Pb-O-Re isotopic analyses indicate the ore-forming fluids and metal elements may derived from crust-derived magma,similar to the Early Cretaceous highly-differentiated granitoids.After comprehensive comparisons,we consider that the intrusion of Early Cretaceous granitic magma contributed to form skarn-porphyry Fe-Mo polymetallic mineralization,and they were likely formed in the back-arc extension environment caused by the rollback of the paleo-Pacific plate during Early Cretaceous.5.Comparison with previous known metallogenic series in southwestern Fujian Province and adjacent areas,we redefined the Fe-Mo polymetallic deposit related metallogenic series as "the Fe,Mo,Pb,Zn,and Cu metallogenic series associated with the Early Cretaceous granitoids",and further put forward the main Fe-Mo polymetallic ore deposit prospecting types and directions for the studied area.