Study On The Geological Characteristics Of Gold-Copper Deposits And The Occurrence Of Au,Ag,Te And Bi Elements In The Fengshan Orefield,Southeast Hubei Province

Fengshan orefield is a representative skarn Au-Cu mineralization district in the west of the middle and lower Yangtze River Valley,it consists of many skarn Cu-Au deposits and sedimentary rock-hosted gold deposits.This study makes the Jilongshan and Fengshan deposits as the examples of the skarn Cu-Au deposits and makes the Zhulintang and Caojiashan deposits as the examples of the sedimentary rock-hosted gold deposits.Based on microscope,scanning electron microscopy observations,electron microprobe analysis,zircon U-Pb and sulfur isotope,we now obtain several conclusions,as follows:(1)The Jilongshan and Fengshan skarn deposits' ore bodies are mainly hosted in the contact zone between the carbonate of the Lower Triassic Daye Group and granite diorite porphyry.The mineralization process can be divided into four stages,including a prograde skarn stage,a retrograde skarn stage,a quartz-sulfides stage and a carbonate stage,and the precipitation of Au and Cu occurs in the quartz-sulfides stage.Microscope and electron microprobe analysis suggests Au and Ag occur mainly as visible Au minerals(native gold,electrum)and visible Ag minerals(hessite,matildite),respectively,and Au minerals occurs mainly as inclusions in chalcopyrite and tetrahedrite or bornite.Abundant Te-Bi minerals,such as tetradymite and aikinite,have also been observed in the skarn Au-Cu deposits,which means during the process of metallogenesis Bi and Te may be quite significant for the enrichment of Au and Ag.(2)In the Zhulintang and Caojiashan gold deposits,microscope and electron microprobe analysis suggest Au and Ag occur mainly as visible Te-Au-Ag minerals,which hosted in the veins composed of sericite,pyrite and quartz or Mn-bearing calcite and Pb-Cu sulfides,respectively.At the same time combined with related ore deposits geological characteristics with epithermal gold deposits and sedimentary rock-hosted gold deposits,we determined the sedimentary rock-hosted gold deposits occurs in the Fengshan orefield belong to the distal-disseminated gold deposits.(3)In consideration of other evidences,such as zircon U-Pb and sulfur isotope,we propose that both of the Caojiashan and Zhulintang gold deposits are intrusionrelated gold deposits,and the distal-disseminated gold deposits and porphyry-skarn Cu-Au deposits belong to the same magmatic-hydrothermal metallogenic system.