Sm-Nd age dating of garnet from the Heiniudong copper deposit in the Liwu copper mining district,western Sichuan

The Heiniudong copper deposit in the Liwu copper mining district is a newly found Cu-rich deposit in western Sichuan,and characteristic of polyphyletic,polyphase and polygenetic origins.Three phases of garnet are found in this deposit.Both the earliest garnet as bands along schistosity and subsequent one as grains are found to be filled by sulfides along fractures or around the grains.The latest garnet occurs as fine-grained crystalloblasts,and gives a Sm-Nd age of 101±26 Ma and an initial ¹⁴³Nd/¹⁴⁴Nd value of 0.511765±0.000025,which may be the age of the latest medium-to high-grade metamorphism.On the basis of the ³⁹Ar/⁴⁰Ar ages of biotite from the Heiniudong copper deposit(136.4±0.8 Ma) and Zhongzui copper deposit(143.4±1.9 Ma),and emplacement age of granites(K-Ar age of 131±5 Ma),the mineralization in individual deposits of the Liwu copper mining district has gone through a long period(15~20 Ma) of hydrothermal processes.