The Genesis Of The Nibao Gold Deposit In Pu'an County,Guizhou Province

The Nibao gold deposit is a representative Carlin-type gold deposit in the southwestern Guizhou Province.It is also an important part of the“Golden Triangle”of Dian-Qian-Gui,and has great economic value and research significance.In recent years,many scholars have carried out a lot of research on the geological background,element geochemistry and isotope geochemistry of typical gold deposits in the region,but there are still some controversies in the source of ore-forming materials and the genesis of the deposits.And There is little detailed research on the ore-bearing potential.Therefore,this paper studies the distribution patterns and in-situ S isotopic compositions of different types of pyrites in gold deposits and surrounding rocks in the Nibao gold deposit,and discusses the mineralization of the Nibao Carlin gold deposit,Material source and the genesis.The gold ore bodies of the Nibao deposit are mainly controlled and distributed in the faults of the area and the Longtan Formation in the La te Permian.Au is mainly found in ore and surrounding rocks,and arsenic-containing pyrite is the main gold-bearing sulfide.Combining field research and ore microscopic observation of mineralogy,the gold-bearing arsenic-containing pyrite in the Nibao gold mine is subdivided into three types,namely euhedral and subhedral pyrite?veined pyrite and other forms pyrite.the elemental composition and S isotope characteristics of three types of pyrite were obtained by EPMA and MC-ICP-MS.The result of the EPMA showed that the pyrite had good content of the gold,and the average content of Au was 0.016wt%.In addition to the elements of Fe and S,it also contained trace elements such as As,Au,Co,Cu and Sb.The S-As element has a positive correlation characteristic,indicating that As may enter the crystal lattice of pyrite by replacing S.The Au-As element correlation indicates that Au is mainly present in the gold-bearing minerals in the form of Au⁺,in which part of the arsenic-containing pyrite-containing Au is present in the form of nano-sized particles of natural Au?Au⁰?In the hot liquid.Fe-Au and S-Au do not have significant elemental correlation.The high Co/Ni ratio of pyrite shows that its genesis is mainly related to magma hydrothermal activity.Most of the pyrite samples subjected to in situ S isotope analysis were pyrites with good gold content after EPMA test.The change of?³⁴S value with time reflects the change of sulfur source from early deposition source to late stage Magma source.The other forms pyrite is formed in the early stage of mineralization.The geochemical characteristics are higher in S,Fe,As,Co,and Ni and the?³⁴S value is 0.0‰^-7.5‰through deposition.During the process of diagenesis,bacteria reduce a small amount of marine sulfate to derive the sulfur source.Euhedral and subhedral pyrite is formed in the main stage of the ore,contains higher As and Au contents and lower S and Fe contents,and its Co and Ni content does not change much.Its?³⁴S value is 0.1‰⁴.6‰,and a small amount of seawater sulfate with high?³⁴S value is mixed into the magma sulfur source.The later ore stage forms veined arsenic-bearing pyrite,which is mainly embedded in the pores of the host rock in the form of vein aggregates,which contain high concentrations of As,Co and Ni and low concentrations of S and Fe.The range of?³⁴S values of veined arsenic pyrite varies little from 0.3‰to 2.1‰,which is interpreted as a magma source.According to the analysis of S isotope and trace element characteristics of gold-bearing iron ore.Combined with the recent magma gravity and magnetic anomaly detection and fluid inclusion data,the ore-forming elements and materials in the Nibao gold deposit are mainly derived from the deep magmatic hydrothermal system,in which the formation may provide some ore-forming materials.