Mineralogical Characteristics And Geological Significance Of Skarn And Biotite In Daruoluolong Copper Deposit,Tibet

The Daruoluolong skarn copper deposit is the first middle Late Jurassic skarn copper polymetallic deposit related to the North subduction of Bangong-Nujiang ocean found in the middle of the Bangong-Nujiang metallogenic belt.The study of the diagenetic and metallogenic process of the deposite is helpful to enrich the metallogenic theory of the middle of the Bangong-Nujiang metallogenic belt and guide the reginal prospecting and exploration.In order to study the metallogenic process and the genesis of metallogenic rocks,this paper focuses on the skarn minerals and the protogenetic biotite of metallogenetic rocks.Through detailed geological records,systematic identification under the microscopic examination and the electron prob analysis,the research on the geological characteristics,mineralogy and mineralogy,petrogenesis and metallogenetic process of the deposits are carried out,the metallogenic model of Daruoluolong deposit is preliminarily established.The main achievements of this paper are as follows:1.The three ore bodies in Daruoluolong deposit are all layered and stratoid in skarn.The ore structure are mainly vein,disseminated and cloddy.The ore texture are mainly crystallization,metasomatism and exsolution.The main metal minerals are chalcopyrite,pyrite,bornite,molybdenite,magnetite and arsenopyrite,while the main non-metal minerals are skarn,biotite,quartz and calcite.2.The metallogenic progress of Daruoluolong deposit can be divided into three metallogenic periods: magmatic period,hydrothermal period and exogenous period,and then the hydrothermal period is divided into skarn stage,oxide stage,quartz-sulfide stage and quartz-carbonate stage.3.The vertical zoning characteristics of skarn are found out: from metallogenic body to contact zone,the skarn type from garnet-pyroxene skarn to pyroxene-garnet skarn,the pyroxene content in skarn minerals increases,the mineral grain of pyroxene increases,the garnet content decreases,the color changes from dark brown to light yellow green,the mineral grain increases,the content of andradite garnet intendes to decrease,and the content of grossular increases;the mineralization zoning is shown as copper,molybdenum mineralization to copper,iron mineralization.4.Based on the study of skarn minerals,the change of metallogenic environment is judged.The skarn minerals are mainly garnet and pyroxene.The garnet belongs to the andradite-grossular series(And62.17~81.48Gro17.45~36.59Pyr+Spe+Alm0.7~2.56),pyroxene belongs to the sahlite-hedenbergite series(Di4.83~63.72Hd35.45~94.00Jo0.63~1.46).The mineral assemblage and mineral chemical characteristics show that the skarn stage is in the environment of faintly acid and high oxygen fugacity,in the quartz-sulfide stage,the metallogenic environment changes from relatively oxidized environment to relatively reduced environment.5.Starting from protogenetic biotite,the genesis of metallogenetic rock is discussed.It is found that granodiorite porphyry is I-type granite,crystallized in high temperature and high oxygen fugacity environment,which belongs to the calc alkaline series of orogenic belt,with the genetic characteristics of crust mantle mixed source.