Micro-Analysis Of Metamorphism And Deformation In Hongtoushan Copper–Zinc Deposit,Liaoning Province

Hongtoushan copper–zinc deposit is the only large–scale Archean Volcanogenic Massive Sulfide(VMS)deposit in China.It is located in the Hunbei granite–greenstone terrane,and more than 100 VMS deposits have been found within this terrane.Moreover,Hongtoushan copper–zinc deposit has been intensely deformed and metamorphosed.Zircons LA–ICP–MS U–Pb dating shows that the supracrustal rocks formed at around 2550 Ma,indicating that Hongtoushan copper–zinc deposit formed at late Neoarchean(?2550 Ma).Furthermore,its tectonic setting was back–arc extension.The felsic metamorphic volcanic rocks(biotite plagioclase gneiss)originated from the partial melting of the lower crust.The mafic metamorphic volcanic rocks(plagioclase hornblende gneiss and garnet anthophyllite gneiss)were derived from partial melting of spinel lherzolites,and experienced significant metasomatism(fluid and melt)and various degrees of crustal contamination.Multiple sulfur isotope analyses(³²S,³³S,³⁴S and ³⁶S)show that the?³⁴S values of sulfides are–0.01–+1.60,and no difference among different places of sulfides,resembling the typical mantle–derived sulfur isotopic compositions.The?³³S values rang from–0.20–0.14,with the mean?³³S value of–0.05‰,and the most of them are negative.It suggsets that they are slightly negative mass–independent fractionation(MIF)of sulfur.These indicate a magmatic sulfur source with?3.5%seawater S.In the process of metamorphism and deformation,some trace elements of sulfides in Hongtoushan copper–zinc deposit were enriched,some were depleted,and some are unchanged.For example,Co,Ni and Co/Ni in pyrite,In and Mn in sphalerite;Se and Sn in Chalcopyrite,which are sensitive to temperature change during its substitution,were changed.According to the characteristics of variation of trace elements in sulfides,it is considered that the formation temperature of metamorphic sulfide is higher than that of the initial sulfides,and they all were formed in a reducing environment.Combined with previous research results,it is considerate that the physical deformation and recrystallization are the main processes without the addition of other materials in the process of metamorphism and deformation.