Sequence of magma emplacement and sulfide saturation in the Gaojiacun–Lengshuiqing intrusive complex (SW China)

The Lengshuiqing area contains several small intrusions made up of peridotite ± quartz diorite ± granite spatially associated with the Gaojiacun pluton (gabbroids + peridotite + diorite). Ni–Cu sulfide ore occur at Lengshuiqing, hosted in peridotite. SHRIMP U–Pb zircon dating produced the ages of 803 ± 4.2 Ma (peridotite), 807 ± 2.6 Ma (oikocrystic hornblende gabbro), 809 ± 4.3 Ma (hornblende gabbronorites) for the Gaojiacun pluton and 807 ± 3.8 Ma (diorite, intrusion I), 817 ± 6.3 Ma (quartz diorite, intrusion II) and 817 ± 5 Ma (peridotite, intrusion 101) for Lengshuiqing. These ages suggest the emplacement of the Gaojiacun pluton later than the intrusions from Lengshuiqing. The olivine from Lengshuiqing does not contain sulfide inclusions and is relatively Ni-rich (1,150–1,550 ppm Ni), suggesting its crystallisation before the sulfide saturation that generated the Ni–Cu deposits. The olivine of the gabbros in the Gaojiacun pluton is Ni-poor (250–800 ppm), which indicates crystallisation from a severely metal-depleted magma after a sulfide saturation event. The olivine in the peridotites from the Gaojiacun pluton has 800–1,150 ppm Ni and contains sulfide inclusions. Moreover, geological evidence suggests the genesis of the peridotites from Gaojiacun in conduits that were ascending through the gabbroids. A sequence of at least three stages of magma emplacement is proposed: (1) Lengshuiqing; (2) gabbroids from Gaojiacun; (3) peridotites from Gaojiacun. Given the age differences, the intrusions at Lengshuiqing and the Gaojiacun pluton might have been produced by different magmatic events.