Characteristics And Genesis Of Magmatic Rocks In The Chating Cu-Au Ore District,Xuancheng City,Anhui Province

The Chating Cu-Au deposit in the Xuancheng City of Anhui Province is a newly discovered porphyry deposit in the Middle and Lower Yangtze River Valley Metallogenic Belt(MLYB)in recent years.In this paper,we conducted the zircon LA-ICP MS U-Pb dating,major elements,trace elements(REEs),Sr-Nd-Pb isotopes and zircon Hf isotope geochemical study on the revealed magmatic rocks from the drilling holes of the ore deposit.So as to know its geological and geochemical characteristics,and to discuss the origin of the magma and petrogenesis of the rocks.The major intrusive rock types of the Chating Cu-Au deposit included quartz diorite porphyrite,diorite porphyrite and spessartite.The LA-ICP MS U-Pb zircon ages of the ore-bearing quartz-dioritic porphyrite is 137.8±1.3Ma,diorite porphyrite is 135.9±1.2Ma,spessartite is 138.0±1.3 Ma,showing that it is the produce of the magmatism late Jurassic.The major volcanic rocks of the Chating ore district is crystal-debris tuff and amphibole andesite.And the ages of those two kinds volcanic rocks are 130.2±1.2Ma and 132.2±1.6Ma respectively,showing that it is the produce of the magmatism at early Cretaceous.The volcanic rocks are with characteristics of low K,ALK and Ti content,showing that they belong to high-k calc-alkaline volcanic rock series.The intrusive rocks have high alkalinity and high Na contents,also belonging to high-K calc-alkaline series.They are enriched in light rare earth elements and large ion lithophile elements(K,Rb,Sr,Ba),depleted in high field strength elements(Nb,Ta,Ti,Ce).They have no visible negative Eu anomalies.The(87Sr/86Sr)i values of the intrusive rocks in the ore district are ranging from 0.706403 to 0.707903,?Nd(t)values are low,ranging from-7.4 to-13.3,In-situ Hf isotope analyses were carried out on the zircon grains from the magmatic rocks,and their ?Hf(t)values ranges from-4.25 to-11.75(t=137.8Ma).These characteristics show that the magma were mainly generated from enriched lithospheric mantle-derived magma.The petrogenetic process may have the same experience as those of the Tongling ore district in the fault uplift of MYLB.So the genetic mechanism of the intrusive rocks is that the magma come from partial melting of enriched lithospheric mantle and partial melting of lower curst,the mixed magma intruded to deep magma chamber and contaminated the material of the upper crust,and before the magma shallow-intruded and solidified it may take place a certain degree fractional crystallization.