Mineralization Of The Jinya And Nakuang Carlin-like Gold Deposits In Northwest Guangxi

A large number of Carlin-like gold deposits have been found in the Youjiang basin,many researches have been carried out on Shuiyindong and Jinya gold deposits,but the commons between different deposits,evolution and composition of ore-forming fluid,material source were rarely researche.In this paper,the Jinya and Nakuang gold deposits in NW Guangxi were selected as the research object by detailed field investigation in geological characteristics,at the same time,observe the gold-bearing sulfide under microscope and scanning electron microscopy,using in situ trace element analysis and in situ sulfur isotope tracer study on the common place of gold mineralization,composition and evolution of ore-forming fluid,material source,to explore the metallogenic process.This paper will give the following conclusions:The Jinya and Nakuang gold deposits were hosted in Middle Triassic Baifeng Formation and development the same alteration such as sulfuration,silicificationa,carbonatation.The gold-bearing minerals are pyrite and arsenopyrite.In addition,the evolution of ore-controlling structures in this two gold deposits were show they both go through from compression to extension.According to the observation of pyrite and arsenopyrite by microscope and scanning electron microscope,the Jinya and Nakuang can be divided into Py1,Py2,Py3,Py4 and Apy.Combine with the Au content in multistage pyrie and asrenpyrite we can know the metallogenic stage in Jinya is Py4 and Apy,Nakuang metallogenic stage is Py3 and Py4.Au is existed as solid solution in gold-bearing sulfide both of Jinya and Nakuang.the Jinya and Nakuang gold deposits have the characteristics of Au,As,Sb,Pb,Bi,Cu,Zn,etc.The Jinya gold deposit is obviously high Au,poor of Co and Ni,slightly enriched Cu in metallogenic stage,is contrary to pre mineralization stage.The Nakuang gold deposit was show slightly enriched Au,Cu and As in metallogenic stage,the other trace elements in this stage do not change so much.The results of the in situ sulfur isotope analysis in Jinya show that the?³⁴S values of Py4 and Apy in metallogenic stage were-7.0‰^-6.1‰and-6.1‰^-5.1‰,respectively;before the metallogenic stage the?³⁴S values range from-9.0‰^-6.6‰in Py2,-8.8‰^-6.2‰in Py3.The?³⁴S values of Nakuang metallogenic stage Py3 and Py4 were-12.9‰^-7.1‰and-9.3‰⁷.3‰;the?³⁴S values range from-11.4‰^-9.2‰and-11.8‰^-10.0‰,which was form in the Py2 and Apy stage before metallogenic;The?³⁴S values in Jinya and Nakuang are both negative which was showing the characteristics of sedimentary source,but we found the?³⁴S values in metallogenic stage is much closer to zero than before metallogenic stage,which may indicate the addition of magma.Based on the study of geochronology,metallogenic dynamics background and deposit structure,the occurrence of Jinya and Nakuang gold deposits was closely to the extension after Indosinian compression.Under the tectonic system of compression to extension,the formation fluid and the Au-bearing magmatic fluid migrated along the deep fault to the deposite fault and fracture zone then the gold deposits were formed after reaction with the wallrocks.