Study On The Geochemical Characteristics Of Hongnipo Mine Section Of Lala Copper Deposit In Huili,Sichuan Province

The Hongnipo mine section of Lala copper deposit in Huili,Sichuan Province is located in the mid-west of Xikang Yunnan axis,which ore bodies occur in the lower member of Tianshengba Formation and upper member of Luodang Formation of Hekou Group.The main ore-bearing formation is the metamorphosed and sodic volcanic-sedimentary sequences of Hekou Group of Pre-Sinian system.Predecessors have conducted a large number of geological explorations and scientific researches on the Hongnipo mine section of Lala copper deposit,but have divergences on the issue of deposit genetic type for a long time.So,this paper selects the study on the geochemical characteristics of Hongnipo mine section of Lala copper deposit in Huili,Sichuan Province as the subject,focusing on the geochemical characteristics of Hongnipo mine section of Lala copper deposit,including geochemical characteristics of ore-bearing formation,isotopic geochemistry and fluid inclusions to provide more rich dates for the cause of Hongnipo mine section of Lala copper deposit.The research work of this paper has made the following main achievements and innovative knowledges.The characteristics of the metamorphosed volcanic rocks are sodic.On the TAS rock classification map of mineral deposits,the cast point is distributed in the basic rocks and the transition to the neutral rocks;On the SiO2-K2 O rock classification map,Except one sample,they all fall on calc alkaline series and its marginal range.The incompatible elements of rocks are enrichment,the Nb,Ta is relatively negative,changes in contents of Ti elements is large,and the Rb which belongs to the large ion Pro rock elements is also enrichment,its characteristics are similar to island arc volcanic rocks.In the Ti/100-Zr-3Y diagram of basalt tectonic environment,the albite rocks in this area basically fall into the calc alkaline series;In the Hf/3-Th-Ta diagram of basalt tectonic environment,almost all samples are falling into the range of arc-alkali alkaline part,except one sample.The REE distribution patterns of albitite are LREE slightly enrichment and Hree flat,Except 3 samples of Eu positive anomaly,other samples show positive Eu anomaly is not obvious,indicating that the magma is probably from the mantle,and contaminated by the crust.Geochemical studies of S and Pb isotopes show that the range of ?34S is 0.11³.37‰,of which 80% of the samples are between 1-3‰ with the tower effect is significant closed to the mantle sulfur.Therefore,the results represent the mantle-derived source of sulfur in the Hongnipo mine section of the Lala copper deposit.The lead isotopic compositions in total rock and metal sulfide changes greatly in Hongnipo mine section of Lala copper deposit,and it is characterized by rich radioactive lead,which indicates that lead is from different sources and may be related to the mixing of metamorphic volcanic rocks and metamorphic sedimentary rocks in the region.The types of mineral fluid inclusions of Hongnipomine section of Lala copper deposit include:the salt crystal inclusions?NaCl-KCl-H₂O?,CO2 inclusions?H₂O-CO2?and saline solution inclusion?NaCl-KCl-H₂O?.After testing the homogenization temperature and freezing point of the selected fluid inclusions,and calculating the salinity,density and pressure of inclusions,at last we roughly calculated the mineralization depth.The homogenization temperature data of fluid inclusions mainly concentrated in three intervals:100°C¹50°C,240°C³10°C and 330°C³50°C,which can be explained to be that the deposit formation had experienced multi metallogenic periods.According to conversion of inclusions freezing point,the salinity W?NaCl?ranges are between 5²5wt% and 5²5wt%.Results show that the ore-forming fluid has high salinity that means high salt ore-forming fluid properties.According to the relation equation about inclusions homogenization temperature,salinity and density,we can calculate that the scope of fluid density ofthe Hongnipo mine section of Lala copper deposit is from 0.954¹.277g/cm3,which shows that the ore-forming fluid density range is wide,illustrating the polyphyly of sources of ore-forming fluids.According to the relationship between salinity and pressure of the salt crystal fluid inclusion,metallogenic pressure of Hongnipo mine section of Lala copper deposit is 15.0²0.0MPa by stress calculation formula.If only considering lithostatic pressure,the metallogenic depth of Hongnipo mine section of Lala copper deposit is in roughly ranged in 600⁸00m by converting metallogenic pressure into metallogenic depth.In summary,the relationship between geochemical characteristics,metallogenic temperature,ore-forming material source,types of ore-forming fluid,and metallogenic model reveals that the Hongnipo mine section of the Lala copper deposit is a IOCG deposit.