Study On Fault Fold Of Huijiabao Anticline And Relationship With Gold Mineralization,North Of Nanpanjiang Basin

The Nanpanjiang Basin came into being a series of dome structures after experienced the Indosinian-Yanshanian orogeny,and the domes controlled the distribution of low temperature deposits.Huijiabao anticline,located in the north of Nanpanjiang Basin,is an important metallogenic and ore-storing structure of Carlin-type gold deposits in southwestern Guizhou,which controls the distribution and occurrence of many low temperature gold deposits in the region.Through detailed field geological survey and structural analysis of the Huijiabao anticline,the formation process of the Huijiabao anticline is determined;the relationship between the Huijiabao anticline and deep thrust faults is analyzed;and the Huijiabao anticline is judged to be a fault-related fold,and the geometry and depth of the hidden thrust faults are calculated.The attitude of Huijiabao anticline strata is systematically measured and counted.According to the two measured sections,the data was projected by stereographic projection,and the fold patterns of the Huijiabao anticline is determined to be superiposed fold of NW trend vertical and horizontal fold and NE trend vertical and horizontal fold.Statistical analysis and stereographic projections are carried out on the cleavages in the region,we screened out the axial cleavages matched with NW trend and NE trend.According to the intersection relationship of the axial cleavages,we judge that the NE trend fold is superimposed on the NW trend fold.Combined with the stratigraphic and related chronological data involved in the superimposed deformation,it is determined that the structural style of the Huijiabao anticline is the result of the superimposed deformation from late Yanshanian to early Yanshanian.Using the Huijiabao anticline to study the geometry and depth of the hidden thrust fault,combined with the backlimb dip angle?2??,interlimb angle???,height of anticline?h?,the thickness of the referenced layer?h₀?,width of the anticline?AB?and thickness-change ratio of layering within the forelimb?t_?/t?are used to calculate the parameters associated with the thrust fault.The ramp dip angle of the thrust fault is 62°;the shortening rate of the Huijiabao anticline is about 3.8%;the fault-parallel distance of the fault is 3.32 km;the displacement on the fault surface is 0.39 km;and the depth of the hidden thrust fault is 7.67 km.Combined with the stratigraphic sequence histogram in the study area,it can be judged that the depth of the thrust fault is in the Cambrian system,and it develops along the black shale at the bottom of the Cambrian system.On this basis,it is considered that the activation of gold elements and the migration of gold-bearing fluids in the Shijiabao anticline gold deposit are all related to the detachment layer developed along the black shale at the bottom of the Cambrian system.Based on the analysis of the ore-bearing strata of the Shuiyindong section and the field survey phenomena,combined with the regional tectonic evolution,the Huijiabao gold deposit concentration area is the result of the formation of water-fractured breccia zone and gold ore enrichment is caused by the enrichment of ore-bearing fluid near the fault-tip line.Through identifying the weak strata of Cambrian,combined with the characteristics of regional tectonic evolution and Huijiabao anticline structure,we propose a three-stage tectonic-metallogenic model of tectonic-metallogenic material supply:the Indosinian orogeny and the initial activation of metallogenic materials?Indosinian Progressive nappe of orogenic belts and activation and preliminary enrichment of metallogenic materials?Intracontinental deformation of early Yanshanian and reactivation and re-enrichment of metallogenic materials.The structural superposition phenomenon in the late Yanshanian enriched the ore-forming type and development and distribution of the Huijiabao anticline.