Discussion On Geological Characteristics,Source Of Ore-forming Material And Genesis Of Huanglong Gold Deposit In Hanyin,Shaanxi Province

The northern Shiquan-Hanyin gold belt in the southern Qinling tectonic belt is one of the important polymetallic metallogenic belts in the Qinling area.There are many gold occurrences in this gold belt,and the geological characteristics of Huanglong gold deposit are typical.The gold deposit is located in the northern part of Hanyin County,South Qinling Mountains.The exposed strata are mainly the Lower Silurian Meiziya Formation（S₁m）.It has undergone multiple stages of tectonic deformation and magmatic activity,and has complex structural characteristics.Although the predecessors have carried out more research work here and achieved certain research results,there are still some controversies about the source of ore-forming fluids and the source of ore-forming materials.Based on the geological characteristics of the deposit,this study mainly discusses the ore-forming fluid properties,material sources and genesis of the deposit by analyzing the characteristics of fluid inclusions in quartz veins,in-situ analysis of major and trace elements of pyrrhotite and in-situ S isotope test.Mainly obtained the following understanding:（1）The ore bodies in the Huanglong gold deposit are stratoid,and the occurrence is basically consistent with the S₂ tectonic foliation and surrounding rock of the main metallogenic period.The main ore-controlling structure is brittle-ductile shear zone（RF4）.The alteration types most closely related to gold mineralization are biotite phenocryst crystallization,pyritization,pyrrhotization and so on.（2）The ore-bearing quartz vein fluid inclusion temperature measurement results show that the homogenization temperature range is mainly between 170°C～300°C,the salinity value is between 0～12%,the density value is between 0.7g/cm3～0.9g/cm³,the average metallogenic pressure is 61.12 Mpa,and the average metallogenic depth is 1.73 km.In general,the fluid has the characteristics of medium-low temperature,medium-low salinity and low density,and the metamorphic secreted water and atmospheric precipitation are the main sources of ore-forming fluid.（3）The electron probe test results of pyrrhotite in the main metallogenic period show that the corresponding chemical molecular formula of pyrrhotite is Fe_0.838S-Fe_0.911S,abbreviated as Fe₆S₇-Fe₈S₉,mainly monoclinic type,indicating that its metallogenic temperature is low.The genesis is characterized by metamorphic hydrothermal-magma hydrothermal,mainly metamorphic hydrothermal,indicating that the ore-forming materials are mainly derived from the strata,and few parts are derived from magma.（4）The LA-ICP-MS in-situ micro-area trace element test results of pyrrhotite in the main metallogenic period show that pyrrhotite is rich in Ni and poor in Co,and the content of As is low,resulting in limited space for gold enrichment.It is difficult to replace iron with isomorphism and exist in the form of fissure gold or wrapped gold.（5）The results of in-situ S isotope test of pyrrhotite in the main metallogenic period show that the value ofδ³⁴S（‰）is between 11.54 and 14.69.Theδ³⁴S of pyrrhotite in the metallogenic period has the characteristics of mixed sulfur,and S is derived from strata and magma.（6）Based on the comprehensive analysis of the ore-forming geological characteristics,ore-forming fluid characteristics and ore-forming material sources,it is considered that the genetic type of Huanglong gold deposit is medium-low temperature hydrothermal deposit,and the industrial type is brittle-ductile shear zone altered rock type gold deposit.