Collofrom And Idiomorphic Pyrite In Baocun Copper-gold Deposit At Tongling,Anhui Province:Minerology,Trace Elements And Genetic Implications To Collofrom Pyrite And Its Metallogenic Implications To Copper-gold Deposit

The Baocun copper-gold deposit is an important deposit in the Shizishan orefield.It is one of the representative skarn deposit in Tongling metallization cluster.Based on the systematic data collection of geological characteristics,mineralogy,deposit geochemistry of Baocun copper-gold deposit and Tongling mineralization cluster.Pyrite is as aimed minerals through field surveys and indoor works including polarizing microscope,powder X-ray diffraction(XRD),Raman spectroscopy(RS),field emission scanning electron microscopy(SEM)and high-resolution transmission electron microscopy(TEM).Multi-grain distribution pyrite in the Baocun deposit was carried out to illuminate colloform pyrite genesis,and discuss its implication for Mesozoic copper(gold)mineralization in Tongling mining cluster.The pyrite in the Baocun deposit can be divided into three types according to the particle size: colloform pyrite,fine-grained pyrite,and coarse-grained pyrite.Colloform pyrite is mainly composed of nanometer and sub-micrometer pyrite with euhedralsubhedral morphology coexisting with a minor of detrital quartz and clay miernals(maybe illite).In addition,the colloform pyrite with ring structure occurred in the Baocun deposit.Marcasite mainly presented in the dark ring.Fine-grained pyrite is cut by hydrothermal quartz veins.There is a clear recrystallization for pyrite at the edge of the hydrothermal quartz veins,and a small amount of sphalerite is identified in the veins.The coarse-grained pyrite is cut more clearly by quartz veins and is accompanied by chalcopyrite.SEM observations and LR identification show that colloform pyrite ores from the Baocun deposit contains some organic matter.It is residue of post-degradation of primary sedimentary organic matter,which maybe indicate that the colloform pyrite in the Baocun deposit is resulting from biochemical sedimentary processes.The trace element compositions of pyrite shows that colloform pyrite has been affected by laterhydrothermal processes which inducing nanometer pyrite recrystallization.The larger the particle size,the more thydrothermal elements are enriched in the pyrite.However some trace elements origining from sedimentary processes are still retained in colloform pyrite.Nanometer pyrite in colloform pyrite has higher chemical reactivity.The sulfur loss in the pyrite will occur during hydrothermal processes.The element sulfur and sedimentary organic matter in the ores can provide a reducing environment and precipitation agent for sulfide minerals formation during the Mesozoic copper-gold mineralization in the Tongling mineralization cluster and regional metallogenic zone.