Geological,Geochemical Characteristics And Formation Mechanism Of The Yangliweigou Gold Deposit In West Qiling Orogen

The West Qinling is our important metallogenic zone,and the Yangliweigou gold deposit is located in the Diebu-Wudu metallogenic belt of the West Qinling,which is a representative Carlin-like gold deposit.Through the observation of the veins in the field and the identification of the minerals under the microscope,the mineralization process of the deposit is divided into the quartz-pyrite phase(Ⅰ),the quartz-arsenic-containing pyrite phase(Ⅱ),and the late calcite phase(Ⅲ).The line scan and surface scan analysis of the energy spectrum can intuitively find the distribution law of elements,semi-quantitatively discover different characteristics of minerals at different stages,and the electronic probe accurately quantifies the content of elements,and finds the inherent laws of element composition.The main metal minerals in the stage are all pyrite: the first stage crystal form is mainly self-shaped cubes,a small part is pentagonal dodecahedron,the particle size is relatively fine,and As and Au elements are poor.Stage Ⅱ is the main mineralization stage.Arsenic-bearing pyrite is mainly cubic,pentagonal dodecahedron,with coarser grain size,generally 0.30-1.00 mm,and rich in As and Au elements.The mineralization in this stage is the strongest.In stage Ⅲ,pyrite is mostly in its fine-grained structure,distributed along the veins of quartz and calcite.The H-O isotope study of quartz shows that the ore-forming fluids of the Yangliweigou gold deposit are mainly derived from the mixing of magmatic water and atmospheric precipitation,and the hydrothermal fluid has a strong water / rock reaction with the surrounding rocks,and material exchange occurs.The C-O isotope of hydrothermal calcite indicates that the carbonate rock is dissolved,and the heat source of the dissolution may also be provided by magmatic activities.At the same time,in the field,there are many diorite veins developed on both sides of mineralization in boreholes,which indicates that magmatic activities may contribute to the mineralization process.The in-situ micro-isotope S isotope of pyrite reveals that the source of S is mainly seawater sulfated sulfur mixed with crust-derived magmatic sulfur.Before the mineralization,the abundance values of Au and As elements in the strata are high,and the crust-derived magma differentiates out of hydrothermal fluid,which migrates upward along the deep faults in the area and reacts with the strata on both sides,especially the black rock series.Extraction of Au,S and other ore-forming materials in the formation.By the second stage,the As-rich fluid formed by the precipitation and permeation of the formation by atmospheric precipitation mixes with the upward-moving ore-bearing hydrothermal fluid in the NW and NNE faults.In this process,the evolution from S-rich As-poor to As-rich S-poor as a whole increases the oxygen fugacity of the system,resulting in the precipitation and enrichment of Au.