Study On The Genesis And Structural Controlling Regularity Of Sanhe Pb-Zn Deposit In Genhe County, Inner Mongolia

The Sanhe Pb-Zn deposit in Genhe county,Inner Mongolia is a typical medium-sized hydrothermal vein-type deposit that located in the northern part of the Deerbuer metallogenic belt.Taking it as the main research object,the paper summarizes the geological characteristics of the deposit,analyzes and discusses the genesis of the deposit as well as establishes its metallogenic model based on detailed field investigations and indoor comprehensive analysis.From the ore-controlling fault kinematics,spatial geometry of the lower plane of ore-controlling faults and relation with spatial variation of ore thickness etc.aspects,the ore-controlling law of the structure in the mining area was studied and summed up,which provides an important basis for guiding the further prospecting and exploration of the main ore veins.The research content and major results obtained are as follows:1.The Sanhe Pb-Zn deposit is a typical hydrothermal vein-type deposit.The ore bodies occurred in veins that controlled mainly by NW and NWW strike faults.The main metal minerals of the ore are pyrite,chalcopyrite,sphalerite and galena etc.According to the characteristics of the ore mineral assemblage,ore structure,and vein cross-cutting relationships,the lead-zinc mineralization in the mining area can be classified into hydrothermal and superficial oxidation two phases.The former phase isdivided into dolomite±pyrite;?II?pyrite-quartz;?III?quartz-polymetallic sulfide;?IV?pyrite-fluorite-calcite±galena±sphalerite and?V?ore-free calcite five stages progressively.2.Based on petrographic and thermometric analysis of fluid inclusions developed in the ore of different mineralization stages,the ore-forming fluid was proposed as a kind of medium-low temperature,low salinity solution of NaCl-H₂O system.Hydrogen-oxygen isotope composition of fluid inclusions reflects that the ore-forming fluids of the early mineralization stage mainly came from magmatic solutions.With mineralization process progressed,meteoric water continued to join in.The sulphur-lead isotope composition of the ore minerals indicates that the ore-forming materials came from a mixed source of the mantle and the crust.Based on the above evidence,the conclusion that the ore deposit belongs to medium-low temperature hydrothermal origin of mixed solution from magmatic fluid and meteoric water was put forward.3.The LA-ICP-MS zircon U-Pb dating method was used to determine the diagenetic age of ore-bearing volcanic rocks and multi-phase intrusive dikes that cutting through the ore veins?bodies?.The results show that the ages of ore-bearing volcanic formations are 167.6±1.9Ma¹68.9±1.9Ma;the forming ages of various dikes are 127.7±1.1Ma¹38.0±1.1Ma.Meanwhile,the Rb-Sr isochronal age of sphalerite taken from ores is142.22±0.47Ma,which is between the diagenetic ages of ore-bearing volcanic rocks and ore veins cutting dikes.Therefore,it is inferred that the mineralization age of the deposit is Early Cretaceous.Based on regional tectonic evolution history,it is concluded that Sanhe lead-zinc deposit was formed in the tectonic setting of collapsing process of thickened lower crust after the closure of the Mongolian-Okhotsk Ocean in the Early Cretaceous.4.The mineralization in the area is strictly controlled by faults.The ore-controlling faults are a set of conjugate NWW and NW compressive-torsional faults.The former is dominated by rightward thrust movement and the latter is by leftward thrust movement.The characteristics and enrichment of mineralization are obvious in the ore-bearing faults.Among them:the thicker and larger ore bodies in the NWW strike faults occurred in the convex-concave?wave peak-wave valley?transition zones and the sag?valley?structural parts of the lower planes of the faults,and the distribution of ore bodies show no obvious lateral trending in space;while in the NW strike faults thicker and larger ore bodies mainly occurred in the concave?wave valley?-convex?wave peak?transition and sag?wave valley?structural parts of the lower planes of the faults.The ore bodies take on obvious SE lateral trending at medium angles in space,the angles generally are 45°⁵0°±.The numerical simulation results of the spatial occurrences and distribution of industrial ore bodies in the ore–controlling faults have been used to predict the location of buried ore bodies in the No.1-4 and No.21 etc.five major ore veins and a total of 12 prospecting target areas have been identified which provides directions for further exploration work in the mining district.