The Soil Geochemical Characteristics And Prospecting Prediction Of Lalangmai Tungsten-Polymetallic District,Dulan County,Qinghai Province,China

The Lalangmai tungsten-polymetallic district located in the Dulan County,Qinghai Province,and its tectonic location is on the margin of the magmatic island arc belt on the northern slope of Eastern Kunlun,north of the Kunzhong Great Fault.A series of deposits are found in the region,such as Asiha Au deposit,Walenai Au deposit,Harizha Cu–Ag–Pb–Zn polymetallic deposit,and Halongxiuma Pb–Zn–Ag polymetallic deposit,etc.This region shows well geologic conditions for ore prospecting,but main metallogenic elements are Au,Cu,Pb,and Zn,etc.The tungsten ore prospecting work has not been made a breakthrough.Qinghai Geological Survey Institute has delineated a 1:50,000 scale stream sediment W–Sb element anomaly(HS Class-B₃⁶⁷WSb)in Lalangmai district,which displays W prospecting potential.In order to quickly evaluate ore prospecting potential,delineate the ore prospecting targets,and guide the deployment of the exploration engineerings.This paper relies on the Qinghai Geological Survey Fund Program and the Deep Resources Exploration and Mining of the National Key R&D Program of China?No.2018YFC0604105-05?.Based on field geological work such as mapping and soil geochemical survey,this paper comprehensively analyzes the ore-forming geological conditions and soil geochemical characteristics in the Lalangmai district,and delineates the ore prospecting target areas.The target areas were selected for engineering verification,and finally discover five skarn-type tungsten orebodies.This industry–university–research cooperation efficiently supports exploration engineerings deployment,achieves significant ore prospecting outcomes,and makes breakthroughs in prospecting tungsten prospecting in eastern Kunlun,providing new directions and ideas for regional ore prospecting.Through the study,main outcomes and understandings are obtained below:?1?In the Lalangmai district,stratas include Baishahe Formation gneiss?Pt₁b^a?,schist?Pt₁b^b?and marble?Pt₁b^c?.A NE-NW fault F₁is distributed in the northwestern part of the district.Magmatic rocks are characterized by multi-phase activities,exposing Caledonian tonalites,Variscan granodiorites,and Indosinian monzonitic granites.The skarn-type tungsten polymetallic mineralization was formed in the contact zone between the Caledonian tonalites and the Baishahe Formation marble section?Pt₁b^c?.?2?The statistics of mathematical parameters of soil geochemical elements in the district show that the enriched elements are W,Ag,As and Sb.The strongly differential elements include W,Sn,Mo,Au,Ag,As and Sb.According to multivariate statistical analysis,elements of the area are grouped into high-temperature ore-forming elements?W–Sn–Mo?and low-temperature ore-forming elements?Au–Ag–As–Sb?.?3?Using conventional statistics,EDA and content–area fractal methods,the anomaly thresholds of soil geochemical analysis elements were calculated respectively.According to comprehensive comparison,the EDA method was selected for anomaly threshold determination.Using the anomaly threshold determined by EDA,eight integrated anomalies were delineated in the district,including three Class-B1,two Class-B2 and three Class-B3 anomalies.Combined with soil geochemical anomaly characteristics and ore-forming geologic conditions,three ore prospecting targets were delineated within the district,including one Class-I and two Class-II targets.?4?Engineering verification was conducted on the delineated Class-I target.Trenching was used to reveal,trace and control the surface outcrops of ore bodies.Through depth verification by drilling,five skarn-type tungsten ore bodies were delineated.Orebody W?-1 has control length of 479 m at the surface and average thickness of 1.412 m,at 0.588%WO₃on average.Orebody W?-2 has control length of 641 m at the surface,control along hole depth of 226 m and average thickness of2.556 m,at 0.248%WO₃on average.Orebody W?-3 has control length of 492 m at the surface,maximum control along hole depth of 351 m and average thickness of2.317,at 0.402%WO₃on average.Orebody W?-4 has control length of 1320 m at the surface,maximum control along hole depth of 246 m,and average thickness of1.877 m,at 0.28%WO₃on average.Orebody W?-5 has control length of 204 m at the surface,control along hole depth of 251 m and average thickness of 3.765 m,at0.44%WO₃on average.Estimation of resources shows that the five ore bodies have2185241.9 t ore of Class 334 resource,which contained 7689.73 t WO₃;95718.78 t ore of Class 333 resource,which contained 472.01 t WO₃.These five orebodies have total 22830960.7 t ore of Class 333+334 resource,which contained 8161.73 t WO₃,indicating that the deposit is a small-sized scale and is potential of becoming a medium-large deposit.?5?This thesis show that mineral exploration in the eastern Kunlun metallogenic belt,the ore prospecting idea of being guided by soil geochemical survey,fast delineating ore prospecting targets and then performing engineering exploration and verification is feasible and also of referential significance to mineral exploration of other similar areas.