Study On The Ore Controlling Structures Features Of The Hadamengou Gold Field In Inner Mongolia

The Hadamengou gold field has experienced a long and complex geological evolution, forming multi-stage structures, which strictly controled the formation and evolution of the gold veins. However, for such a long time, the research of geological structures and ore-controlling structures has always been relatively weak. Therefore, through these studies a better understanding of the structural deformation and the ore controlling structures features could be achieved.Based on the basic theory of structural geology, by the means of field measured geological profile, drill core logging and sample analysis, the following conclusions can be made from this paper: the structural deformation in this area could be divided into five stages. The first stage was ductile shear deformation, which formed the ductile shear zones, flexible folding and mineral stretching lineation; the second stage was lateral extrusion deformation,which formed the second-stage folds represented by the Wulashan anticlinorium, the piedmont fault, the fault filled by the piedmont potassic alteration zone and a part of joints; the third stage was extrusion deformation, which formed the third-stage folds, thrust nappe faults(probably imbricated thrust nappe fault) and a part of joints; the fourth stage was tensile deformation, making the previous thrust faults subjected to tensile and being opened, then filled by gold bearing hydrothermal; the fifth stage was extensional strike-slip deformation, which formed the ore-breaking fault system, and a part of joints.By measuring the distance between center lines of the main gold veins within the study area, in the N-S direction, with the interval of 1km in the E-W direction,a conclusion can be made that the distance between adjacent veins varies in 528 m ~ 564 m, the mean value is 543.5m, showing the gold veins arranged equidistantly and parallel to each other. Drilling exploration line profile and CSMAT profile show that in the section the dip angle of gold veins in the superficial is large, while to the deep, the angle becomes small gradually. Thus, the ore-bearing fault is most probably normal fault which superimposed on the early imbricated thrust faults. The ore-breaking faults mainly extend along the NW,NE and NNE direction, most of which distribued in the NE side of the F116 fault(exactly the location of Dabagou), probably obstructed by the F116 fault.The ore-controlling structures features are as follows: the NEE trending piedmont fault is the dominant structure in the Hadamengou gold field, and other faults which are filled by various kinds of rock dikes and gold veins are the secondary structures derived from the fault. In the early indosinian stage,the paleo-Asian Ocean subducted underneath the northern margin of North China plate, and a series of nearly EW trending(imbricated) thrust faults formed in the North of the fault. In the Indosinian-Yanshan stage, the tectonic environment of the northern margin of North C hina plate changed from collision orogenic to post-collision extensional environment, during when the Hadamengou area suffered a tectonic reverse. As a result,the early(imbricated) thrust faults were opened by tensile stress, filled by potassic hydrothermal with abundant gold, forming the gold veins.