Geochemical Anomaly And Prospecting Potential In The Ermuchang Area Of Nileke County,Xingjiang,China

The western Tianshan region in Xinjiang has experienced a complex history of geological evolution.From Carboniferous to Permian,this region underwent the closure of the Tianshan Ocean followed by plate subduction and intracontinental extension accompanied with extensive volcanism and associated mineralization.These mineral resources include porphyry Cu and volcanic-hydrothermal Cu,Fe,Au deposits.For further ore prospecting in the Ermuchang area of Nileke County in the western Tianshan where geochemical exploration is insufficient,a detailed stream sediment survey is carried out in this study.The Ermuchang area is located in the middle-north part of the western Tianshan Orogen and belongs to the Yining Block.Its northern part belongs to the Early Paleozoic Boluokenu continental marginal arc and the southern part belongs to the Late Paleozoic Awulale rift system of the Yili rift.The exposed strata in this area are dominated by Devonian,Carboniferous,Permian,Jurassic,and Tertiary in which the Carboniferous volcanic strata are closely associated with mineralization.Intrusive rocks are mainly Late Paleozoic granites which intruded into the Devonian and Carboniferous strata.Fractures are well-developed and are the main ore-controlling and ore-hosting structures.They are primarily NWW-SEE-and NW-SE-striking and subordinately NE-SW-striking.Based on a comprehensive study on regional geology and mineral resources of the Ermuchang area,a 1:50000 stream sediment survey is carried out.Sixteen elements include Au,Ag,Cu,Pb,Zn,As,Sb,W,Bi,Sn,Mo,Cr,Co,Ni,Nb,and Y have been analyzed.After statistical analysis,240 single-element and 14 composite anomalies are determined.The W,Sn,Mo,Bi,Y,and Nb anomalies are dominantly distributed in the northern part of the study area where magmatic rocks expose;the Pb,Zn,Au,Ag,As,and Sb anomalies are mainly controlled by NW-SE-striking fractures in the Kapuqike-Aersang area;and the Cu,Cr,Co,and Ni anomalies mainly occur in the Carboniferous strata(Cld and C2y).According to the classification of anomalies,seven anomalies(HS-4,HS-6,HS-9,HS-10,HS-11,HS-13,and HS-14)have been checked through large-scale geological mapping,1:10000 section of combined geophysical and geochemical exploration,and exploratory trench.One Pb-Zn ore occurrence,one Cu ore occurrence,and one magnetite ore occurrence are discovered.The Pb-Zn ore occurrence is in the HS-4 composite anomaly.The ore veins are dominantly controlled by S-N-striking fractures and hosted by NW-SE-striking fractures.IP profiles reveal that the mineralization zone has low-resistance and high-polarizability characteristics,indicating a good prospecting potential.Both the Cu and magnetite ore occurrences are in the HS-14 composite anomaly.The Cu occurrence is mainly controlled by the intermediate-mafic lava of C2y.The ore bodies are lenticular with a Cu grade of 0.18-2.5%and hosted by the NW-SE-and NE-SW-striking fractures.The magnetite ore occurrence is controlled by magnetite-bearing diorite and faults.The ore bodies have a grade of ca.20%and are hosted by the NW-SE-striking fractures.Finally,four metallogenic prospects(one A-class,one B-class,and two C-class)and seven prospecting targets(three A-class,one B-class,and three C-class)have been determined in the Ermuchang area.Based on mineralization features,the mineralization types in this area are divided into vein Pb-Zn ores,volcanic-hydrothermal Cu ores,and intermediate-mafic rock associated magnetite ores.