Age and geochemistry of granites in Gejiu area, Yunnan province, SW China: Constraints on their petrogenesis and tectonic setting

Abstract

Gejiu is one of the largest polymetallic tin ore districts in the world. Located at the westernmost end of the South China tungsten–tin province (or Nanling tungsten–tin province), it is a granite-related (Gejiu granite) magmatic-hydrothermal system. Nine samples from two phases of Gejiu granitic intrusions have been analyzed by SHRIMP and/or LA-ICPMS zircon U–Pb techniques, yielding ages ranging from 77.4 ± 2.5 Ma to 85.0 ± 0.85 Ma. Whole rock analysis shows that both phases are high-K and alkali-rich granites and their ACNK values fall mainly into a small range of 1.0–1.1. Moreover, Harker diagrams indicate that granites experienced strong fractional crystallization during magmatic evolution. Most granites display relative enrichment in LREE and strong Eu depletion. The whole rock average ε Nd( t) values of the Gejiu granites vary from − 9.3 to − 6.9, whereas a range of − 8.12 < ε Hf( t) < 1.21 is defined by magmatic zircons. Sr–Nd–Hf isotope data indicate that the granites have been mainly derived from crustal melts with minor input of mantle component. Two stage Nd and Hf model ages, together with isotopic characteristics, indicate that the Gejiu granite magmas were possibly derived from partial melting of Mesoproterozoic continental crust, with minor input of mantle-derived melts, followed by extensive fractional crystallization.