Spatio-temporal structure and prospecting of Dabu tungsten polymetallic ore field,Ganxian,Jiangxi Province
The Dabu ore field,located in the eastern part of the Nanling metallogenic belt,is an important component of the Yudu-Ganxian tungsten polymetallic ore cluster,where more than 50 tungsten polymetallic deposits/occur-rences have been discovered,including quartz vein type,skarn type,greisen type and veinlet-disseminated type.All kinds of mineralization are distributed around the Dabu granitic complex.The Dabu complex has characteris-tics of multiple phases stages based on the field observation,which,however,lacks systematic research,especial-ly on the relationship between various phases stages of magmatism and different types of mineralization.In this study,zircon grains from different phases of the Dabu complex were dated by LA-(MC)-ICP-MS to constrain the time framework of magmatism.Dating results are(429.1±4.7)Ma,(430.0±5.8)Ma,(431.8±4.7)Ma and(158.3±4.1)Ma,showing two groups of ages in Caledonian and early Yanshanian.Furthermore,trace elements and Hf iso-topes were analyzed,showing that both the two phases of granits belong to the high-K,calc-alkaline and peralu-minous,S-type granites.In detail,the Eu negative anomaly is more obvious in the early Yanshanian phase than that of the Caledonian phase.The εHf(t)values of zircon grains from the Caledonian and Yanshanian phases are-6.3～-1.3 and-11.4～-7.1,respectively,corresponding to the two-period model ages of 1.49～1.82 Ga and 1.66～1.93 Ga,indicating that the parent magma was formed by partial melting of the crust during Mesoproterozoic.The trace element characteristics of zircon show that both Caledonian and Yanshanian phases had continental crust source regions and had similar crystallization temperatures.But the early Yanshanian phase has a higher de-gree of crystallization differentiation and higher F content and has a stronger correlation with tungsten mineraliza-tion than that of the Caledonian phase.Our study indicates that the tungsten mineralization in the Dabu ore field are concentrated in 159～155 Ma,which was formed immediately after the emplacement of the early Yanshanian granitic magma.Based on the study of magmatic and metallogenic age framework in the Dabu ore field,com-bined with the analysis of granite metallogenic specificity and metallogenic geological conditions,the exploration model of tungsten polymetallic ore in Dabu ore field is established,and the prospecting direction of veinlet-dis-seminated type,greisen type and inner zone quartz vein type tungsten ore deposits is figured out.It is predicted that the buried intrusive body of early Yanshanian age in the Northeast of Dabu pluton has the potential to find"Helong"quartz vein type and veinlet-greisen type tungsten deposits.
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