Characteristics Of Gold-Bearing Pyrite From The Jiadi Gold Deposit In Southwestern Guizhou And Its Implications For Mineralization

As a newly discovered carlin-type gold deposit in basalts in southwestern Guizhou in recent years,the shelf-bottom gold deposit has attracted the attention of many scholars and achieved a lot.Previous studies have shown that arsenic-bearing pyrite is the main gold-bearing mineral in the southwest of Guizhou.However,the gold-bearing Pyrite and the gold enrichment regularity in the gold deposits at the bottom of the shelf have not been deeply studied,it restricts the follow-up scientific research and prospecting work.Based on the field investigation and indoor microscopic lithofacies observation,the pyrite in the mining area is divided into three stages:pre-mineralization,mineralization and post-mineralization,the typical pyrite in each stage are strawberry-shaped Pyrite,self-shaped-semi-self-shaped Pyrite(with ring structure),fine pentagonal-dodecahedron Pyrite and self-shaped coarse-grained Pyrite(with ring structure).The EPMA results show that there is a negative correlation between S and As in the pyrite of the gold deposit,and there is a certain correlation between Au and As,the pyrites are characterized by high S and Fe,low As and Au before mineralization,high S and Fe,low As and Au at the core of pyrites and high As,Au,low S and Fe at the annulus of pyrites,High S and Fe,low As and Au at the core of pyrites after mineralization,there was a significant difference between these two bands(high As without Au).According to the mineral characteristics and interrelation,the order of the gold-bearing Pyrite in the mining area is as follows:Strawberry-Shaped and Low-Arsenic and Ring-Free pyrite(without gold)?hydrothermal pyrite(without gold or with little gold)?hydrothermal arsenic-bearing ring pyrite(with gold)and homogeneous ring-free fine pyrite(with gold)?high-arsenic ring pyrite(without gold).The in-situ sulfur isotope results show that the?³⁴S value of pyrite before mineralization is characterized by sedimentary sulfur,and the core and girth of pyrite during mineralization and after mineralization show magmatic sulfur characteristics,and the content characteristics of pyrite in different stages,it is suggested that the ore-forming materials mainly come from the deep mantle,and some of the crustal materials are mixed in.Gold migrated from deep to shallow in the form of sulfur complex,and existed in the state of"invisible gold".The occurrence state of gold in the gold deposit may be sub-micron to nano-scale gold particles formed by supersaturation of Au content,there is also an Au ion form due to the unsaturation of Au content.Based on the above understanding,a possible metallogenic process for the Jiadi gold deposit is preliminarily constructed,there is magmatic activity related to mineralization in the study area,the deep faults in the region and the faults in the study area provide a channel for the upwelling of ore-forming hydrothermal fluids,and the reductive fluids containing H₃As O₃⁰,[Au(HS)₂]^-,and H₂S-rich fluids migrate to regions where the pressure decreases,finally,it fills in the tectonic fracture zone in the second member of the Mount Emei basalts and the tectonic alteration bodies between the Permian and the Upper Permian,resulting in intense hydrothermal alteration(mainly Fe metasomatism in the iron dolomite and completion of pyrite mineralization),to form a rich deposit of gold.