Tin Metallogenic Regularity And Exploration Prospecting Of The Xikengjing Ore Field In Huichang County,Jiangxi Province

The Xikengjing ore field in Huichang,Jiangxi Province,is located in the southern part of the Wuyi metallogenic belt in South China,and also to the west side of the intersection between the NNE Shicheng-Xunwufault belt and the Huichang circular structure.Strong deformation structure,extensively magmatic activities and large-scale tin polymetallic mineralization associated with the magmatism developed in the area.In recent years,with the strengthening of geological exploration,it has been proved that there is a good prospecting potential in the area,and especially important breakthruoghs in tin deposit exploration has been made.At present,many large and medium-sized tin mines have been found,such as Yanbei,Taoxiba,Fenghuangdong and Kuzhudong,which are distributed around the circular structure of the Mikengshan caldera.Although many previous studies on igneous rocks and tin deposits in the area have been carried out,chronological frameworks for magmatic rocks and the associated deposits as well as the regional metallogenic regularity are still not clear,which make further exploration unclear.In this study,we focused studies on petrology,mineralogy and U-Pb geochronology of zircon and cassiterite of both the Yanbei and Taoxiba tin deposits to identify the characteristics of the tin deposits and ore-controlling conditions.A“multiple-integrated” regional metallogenic model for the Xikengjing tin field is proposed.Various types of orebodies together occur in the contact zone of Mikengshan caldera,including the Yanbei porphyry,the Kuzhudong greisen,the Fenghuangdong altered rock and the Taoxiba cryptoexplosive interlaminar-fracturetypes.LA-ICP-MS zircon U-Pb dating yielded an age range of 136.1±1.6 to138.6±1.9Ma for the Mikengshan granite body,an age of 136.3±0.88 Ma for the Yanbei granite porphyry and an age of 109.9±1.1 Ma for the diorite porphyrite dike at Yanbei.Moreover,a cassiterite U-Pb age of 128.15±0.88 Ma from the #?orebody at Yanbei is first obtained.This tin mineralization age is consistent with one of the Yanbei granite porphyry.Some prospecting indicators are proposed:(1)All of the ore deposits and tin ore spot are located at the "juncture" where several groups of the fault zones with different directions intersect,especially near the conduit for volcanic-subvolcanic rocks;(2)The contact zone between ore-forming granitic rocks and wall-rocks(volcanic rocks),which has their occurrence change from steeply dipping to gently dipping on dip direction,especially where the contact surface is low-angle dipping,concave and complex,are more conducive to the formation of the rich and large orebodies;(3)Topazization,chloritization and sulfidization are closely related to tin mineralization and thus are potential indicators;(4)The concealed tin deposits is characterized by soil element anomalies of Sn,Cu and Ag and obvious high F content in primary halo;(5)Brownish red and honeycomb iron cap is a surface mark for exploring ore body.With the MRAS evaluation system of mineral resources and the comprehensive geological information prediction technology of deposit model,seven prediction areas(2 in class A and 5 in class B)are delineated,and the shallow tin ore resources above500 m were predicted to be 807,300 tons.Combined with field geological investigations,three prospecting targets for tin deposit,including the Songdong and Gongpokeng targets in Huichang county,and the Shitouao target in Anyuan county are identified.Further,the Songdong prospecting target is selected for drilling test,and 12-layer orebodies with accumulative apparent thickness of 27.94 m are discovered,among them the five industrial orebodies have 5 layers with accumulative apparent thickness of 10.33 m.