| The Anqing-Guichi ore-cluster area is located in the Lower Yangtze river Metallogenic Belt,which is rich in mineral resources.Numerous Cu-Au-Mo deposits have been discovered.Yanshanian magmatic rocks are widely developed in this area and are closely related to copper-gold mineralization.As a newly discovered skarn-type deposit in the area,the Baoshujian copper polymetallic deposit had not been taken research before.As a typical porphyry deposit,great breakthroughs in ore prospecting have been made in the Mashi copper deposit,however its deep and peripheral areas still have great prospecting potential.In this paper,the Baoshujian copper polymetallic deposit and the Mashi copper deposit are used as objects.We carried out whole-rock major and trace elements,zircon U-Pb geochronology,whole-rock Sr-Nd-Pb isotopes,in-situ zircon Lu-Hf isotopes on intrusive rocks and the ?34S values in ore,to explore the genesis of rocks and the formation mechanism of the ore deposits.It will provide guidance for finding the similar deposits.Igneous rocks related to mineralization belong to the high-potassium calc-alkaline and calc-alkali series,with high Sr/Y,La/Yb ratios and low Y and Yb contents.The geochemical characteristics are shown as arc magmatic rocks and adakitic rocks.The rocks in Mashi show a different Eu negative anomaly than the Baoshujian,which may be the result of mixing of the adakitic magma and the depleted Neoproterozoic lower crust.Zircon U-Pb gechronological data show that the Baoshujian magmatic rocks were formed at ca.148.6 ±3.2Ma,and the Mashi magmatic rocks were formed at ca.145.2±2.4Ma,both of which are the early Yanshanian Magmatism in the Lower Yangtze River Metallogenic Belt.The ancient crustal materials were involved in the rock formation.The whole rock Sr-Nd-Pb isotopes and in-situ zircon Lu-Hf isotopes indicate that partial melting of the subducted oceanic slab and sediments was the first stage of the rock formation.The ?34S values in ore indicate the ore-forming materials are derived from magmatic hydrothermal fluids mixed with strata.The Eu anomaly characteristics and Ce4+/Ce3+ratios of zircon indicate that the magma forming rock had high oxygen fugacity,which was beneficial to the migration of ore-forming materials such as Cu,Au and Zn,and eventually form the deposit.Based on the regional geological background,we propose a model about the two deposits.During the Mesozoic,the ancient Pacific plate subducted beneath the continental lithosphere in Anqing-Guich ore-cluster area,forming an enriched mantle.At about 145Ma,the melt generated by the partial melting of the subducted oceanic slab and sediments was mixed with the melt generated from the enriched mantle,producing the adakitic magma.The magma reached the shallow crust,forming ore-bearing intrusive rocks,and providing the ore-forming materials for the deposit. |
PDF Full Text Request