Genesis And Nano Characteristic Of Colloform Pyrite From Xinqiao Deposit In Tongling Metallization Cluster

As a representative stratiform iron sulfide deposit in Tongling metallization cluster in the Middle-Lower Yangtze Metallogenic Belt,the mineralization and mechanism of the Xinqiao iron sulfide deposit remains a topic of debate.The colloform pyrite ore is an important constituents of the stratabound sulfide orebodies in the Xinqiao deposit,and its formation and genesis are still controversial which on the contrary limits identification of the stratabound sulfide orebody.In addition,the particle sizes of pyrite in the colloform pyrite ores range from nanometer to sub-micrometer diameter which displays homogenous,thus colloform pyrite may be a kind of important nanomineral resources.In this study,the nanomineralogy,microstructure characteristics of colloform pyrite in Xinqiao deposit are carried out using powder X-ray diffraction(XRD),optical microscope,field emission scanning electron microscopy(SEM),and high-resolution transmission electron microscopy(TEM)to investigate mineral compositons,morphology,further discuss genesis and mechanism of the iron sulfide deposit.The results indicate that colloform pyrite ore mainly consist of microcrystalline pyrite with nanometer-and submicrometer-sized particles and the granular pyrites are dominated by euhedral-subhedral cubic morphology.In the ore detrital quartz and illite are discriminated by SEM and TEM.In addition organic matter fragments are also present in colloform pyrite by the analysis of SEM,TEM and EDS,and microcrystalline pyrites are co-existing with organic material.These systemic data indicate that the colloform pyrite from Xinqiao deposit is direct precipitation through biogeochemistry mechanism in the sub-closed marine basin instead of magmatic hydrothermal process.This colloform pyrite layer may also act as geochemical barrier or precipitant for the Mesozoic copper mineralization.Due to nanometer particles,the oxidation kinetics of pyrite in the colloform pyrite ores are quite different from those of macrocrystalline pyrite.Analysis of oxidation products of colloform pyrite by X-ray diffraction(XRD)and scanning electron microscopy(SEM)reveals that the oxidation of colloform pyrite proceeds in two stages under ambient conditions without flushing.The first stage is characterized by the formation of Fe(II)oxidation products such as rozenite and melanterite,whereas the second stage is characterized by the formation of Fe(III)sulfates such as rhomboclase and romerite.The oxidation kinetic experiments were designed to investigate the size-controlled oxidation rate of colloform pyrite and the results show that the oxidation of colloform pyrite in aqueous solution can be described by a zero-order kinetic model,proceeding 36.8 times faster than for macrocrystalline pyrite.These data indicate that the colloform pyite from Xinqiao deposit have a good nano effect.