Trace Element Geochemistry Of Gold Deposits And Copper Deposits In Shizishan Ore-Field In Tongling, Anhui Province

The Shizishan copper-gold district is one of the most representative ore-field in Tongling ore assembly district of Anhui province.More than tens deposits have been discovered and the scale of the ore-field is large to super-large.It has been explored and stdied,but controversy remains regarding on the origin of the ore-forming material and the genesis of the deposits.Based on the knowledge of the regional geological setting,the trace element and REE data of wall rocks,ores and altered rocks and minerals in gold and copper deposits in Shizishan ore-field are collected to analyse the relation among ores and altered rocks and related host sedimetary rocks and magmatic rocks.Then,quartz samples in ores in different stage are selected to analyse the trace element and REE compositions of fluid inclusion. According to the contrasting of the differences of trace element and REE from the related wall rocks and ores to minerals and to fluid inclusions in quartz between gold deposits and copper deposits,the trace element geochemical behavior in mineralization and ore-forming mechanism of gold and copper deposits in Shizishan ore-field are discussed.Firstly,the trace element geochemical characteristics indicate that the mineralization is closely associated with magmatism and the ore-forming material may mainly come from the magmatic roccks and partly from the wall sedimentary rocks.Secondly,they also show that the ore-forming fluids of gold deposits and copper deposits are mainly magmatic hydrothermal solution and have the same evolution tendency.Thirdly,the characteristics of Eu negative anomaly reflect the ore-forming fluids of gold deposits originated from the differentiation of magma at low pressure,and the ore-forming fluids of copper deposits originated from the differentiation of magma at high pressure and at the deeply of the earth curst.Fourthly,the ore-forming fluids of gold deposits and copper deposits are hydrothermal fluids ore-forming material enriched,and the quartz-sulphide stage is the best stage for ore-forming material enrichment.Fifthly,the REE distribution patterns of garnets are characterized by straight-line type and kick-down-line type,and both of them are enriched in LREE,the REE patterns of skarns are basically controlled by REE partition behavior in the garnets.Sixthly,the REE distribution patterns of parts of skarns in copper deposits are characterized by kick-down-line debt in La and Ce,and are enriched in LREE, which indicates that those skarns formed in magmatism,and the magmatic skarn is proved. While the REE distribution patterns of the skarns in gold deposits and the other part of skarns in copper deposits are characterized by straight-line type,which indicates that those skarns formed from hydrothermal metasomatism.The lastly,the comparison studies of REE between fluid inclusions and quartz show that there are many differences in REE characteristics,such as the REE contents are lower and are richer in LREE in quartz than in fluid inclusions,those reflect that the host form of REE are different between mineral garnets and fluid inclusions in quartz.