Characteristics Of Ore-controlling Structures Of The Huachanggou Gold Deposit,Mian-lue Area,Shaanxi Province

The South Qinling area is located at the western section of Qinling-Dabie metallogenic province.It is the intersection part of the Qinling-Qilian-Kunlun metallogenic domain and the circum-Pacific metallogenic domain,and is one of the important metallogenic belts.The Huachanggou gold deposit is located on the northwest part of the Mianxian-Lueyang-Ningqiang metallogenic belt which belongs to the Shaanxi-Gansu-Sichuan metallogenic province.Structure types resulted from multi-period superposition in this region are complex.In this paper,we carry out systematic studies of geological characteristics of ore deposits,tectonic deformation features in the field and micro-structural analysis by microscope.Combined with the results of previous studies,the following consulsions are obtained:?1?The study area is located at the South Qinling accretionary complex belt.Rock assemblage in the Huachanggou area is composed of schistositized matrix?schist,phyllite?and different types of blocks?spilite and limestone?.?2?Tectonic events in Huachanggou area during Indosinian are multiple and three phases are identified in the matrix and blocks:schistosity?D₁?,interlayer tight folds?D₂?and east-west strike slip shear?D₃?;D₁ event formed east-west strike structures in the mining area;Axis of fold in D₂ event is consistent with foliation and may be the product of progressive shear deformation after compression;Strike-slip in D₃ event can be divided into sinistral and dextral types,but the latter is perdominant relative to the former.Locally,superposition of three phases of deformation is observed.?3?Each stage has special impact on gold deposits:the schistositilization?D₁?formed main structural framework of the mining area,resulting in separation of the schistositilization belt.During this process,long axis of blocks,such as spilite and limestone,extends in parallel to the foliation.The tight folds?D₂?make the metallogenic material?auriferous pyrite?transfers to the hinge of folds,causing enrichment of ore bodies.The strike-slip?D₃?along the east-west direction contributes to the formation of ductile shear belts.Ductile shear belts intensely reform the auriferous pyrite,leading to formation of microcracks,which may supply space for gold deposition.This plays an important role in the enrichment of ore bodies and belongs to host structures.?4?By comparative studies,the three-stages deformation structures?schistositilization,tight folds,and strike-slip?of Huachanggou mining area is corresponding to the extrusion,thrust shear and accompanying adjustment of the forward pressure during the collision period between the Yangtze block and the North China block.?5?It is believed that the Huachanggou gold deposit is formed during the Indosinian Qinling collision stage,based on new geochronological study carried out on the ore-bearing spilite and previous results.Combined with impact of abovementioned structures on formation of the Huachanggou gold deposit,it shows that the structure and mineralization are not only consistent in time,but also formation of the ore body is mainly controlled by the orogenic process of the South Qinling during Indosinian.Based on previous researches on the mineral chemistry of the Huachanggou ore,it is considered that the Huachanggou gold deposit is a typical orogenic gold deposit.