Study On Three-dimensional Electrical Structure And Gold Metallogenic Model Of Sanhetun Mining District In Duobaoshan,Heilongjiang Province

The Nenjiang-Heihe tectonic mélange belt,which was formed by the Paleogene collocation of the Xing’an Massif and the Songnen Massif.It is one of an important gold metallogenic belt in northern China.Sanhetun mine is located at the southwest end of this gold belt.It is the most typical volcanic-hydrothermal gold deposit in the belt.Due to the thick surface Quaternary overburden and insufficient deep geophysical exploration,it has largely restricted the research on the metallogenic model and the breakthrough of deep mineralization in this area.This paperis based on the China Geological Survey Project undertaken by East China University of Technology.AMT three-dimensional exploration in Sanhetun mine area were carried out to obtain the three-dimensional electrical structure of the deep part of the study area.The three-dimensional spatial distribution of the main lithological interfaces and fracture structures were identified through the electrical structure to deepen the study of gold mineralization patterns in the study area.The paper first obtains reliable AMT responses in the study area by cross-referencing and power spectrum picking techniques.The results of the phase tensor analysis reveal that the deep part of the study area exhibits a strong three-dimensionality.Non-linear conjugate gradient(NLCG)3D inversion of the processed AMT data using the electromagnetic 3D forward inversion software MT3 DINV to obtaining a 3D electrical structure model of the Sanhetun mine.The model reflects that the shallow part of the volcano-sedimentary basin in the study area exhibits a low resistance anomaly.This electrical reflection corresponds to the Cretaceous sand mudstone volcanic rocks.The continuous distribution of high resistance anomalies at depth indicates that the Carboniferous intrusive rocks.The transition zone between high and low resistance reveals the deep spreading of ductile shear zones,fractures and other ore-conducting and storage structures.We summarize the gold mineralization pattern in the Sanhetun mine area at a depth of2,000 meters combining regional geological,geochemical and available geophysical data:Ore-forming fluids transported upward along deep fractures and ductile shear zones in an Early to Middle Jurassic extensional tectonic setting.Late Carboniferous intrusive rocks with gold elements leached out and intruded contributed to the first phase of mineralization.Transport of gold elements carried by deep magmatic eruptions along newly formed and reactivated ductile shear zones and basin margin fractures towards the Sanhetun volcanic basin margin in the context of Early Cretaceous-age extensional partitioning.As the temperature decreases gold elements are gradually precipitated and enriched,and superimposed on the mineralization formed earlier.