Zircon U-Pb geochronology of the Mesozoic intrusive rocks in the Tongling region:Implications for copper-gold mineralization

Abstract

Tongling region is one of the most important non-ferrous metal producers where the formation of Cu-Au deposits and other poly-metal deposits has close genetic relations with Mesozoic intrusions.In this study,LA-ICP-MS zircon chronology of three-type Mesozoic intrusives (i.e.,quartz diorite—monzonite and granodiorite assemblies related with Cu-Au-S-Fe ore-forming) was systematically investigated in Tongling region.The results of high precise zircon U-Pb ages possibly present the sequences of the intrusive evolutions in Tongling region as follows:granodiorite (141Ma) → pyroxene diorite-pyroxene monzodiorite (139Ma) →quartz diorite—quartz monzodiorite (135Ma,136Ma,137Ma).These high-precision zircon U-Pb ages manifest that the intrusive rocks possibly experienced immediately after crystallization.Laser ablation ICP-MS zircon U-Pb dating yielded two groups of ages (c.a.130 ～132 Ma and 138 ～140 Ma) for the intrusive rocks,which are the most important magmatic events in Tongling area related to Cu-Au mineralization.Combined the high-precision zircon U-Pb dates,Re-Os age of some ore deposit and zircon trace element measurements,two events of ore-forming periods are obtained:one is the ore-forming event with high Ce abnormality (molybdenite Re-Os age of 138 ～ 140Ma),which is closely related to those of copper and gold ore deposits;another is probably ore-forming event with low Ce abnormality (pyrite Re-Os age of about 126 Ma) closely related to those of iron and sulfur ore deposits in the Tongling region.