Zircon U-Pb and Lu-Hf Isotopic Dating of Magmatic Rocks in the Wunugetushan Porphyry Copper-Molybdenum Deposit, Inner Mongolia

The Wunugetushan copper-molybdenum deposit located in the northwest of the Erguna—Hulun fault is a large porphyry copper-molybdenum deposit. Magmatic rocks are widespread in the mining area.

In order to determine the emplacement age and tectonic setting of ore-hosting surrounding rock and ore-forming parent rock, and to discuss the petrogenesis and metallogenic dynamics.

Zircon U-Pb isotopes and zircon Lu-Hf isotopes of rocks were studied by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) and laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS).

(1) The zircons in the study area have a high content of REE with strong enrichment of HREE, δEu negative anomaly and δCe positive anomaly, and the REE distribution curves are left-inclined. (2) The anisomitic monzogranites are the ore-hosting rocks with a weighted average value of 200.96±0.88Ma, indicating that the rock mass was formed in early Jurassic. Zircon εHf(t) ranges from 0.1 to 5.8, single-stage Hf model ages (TDM) range from 643Ma to 882Ma, and two-stage Hf model ages (TDMC) range from 874Ma to 1235Ma. (3) The rhyolite porphyritic lavas are the ore-forming parent rocks with a weighted average value of 179.58±0.91Ma, indicating that the rocks formed in the Early Jurassic. Zircon εHf(t) ranges from 4.3 to 6.6, single-stage Hf model ages (TDM) range from 570Ma to 663Ma, and two-stage Hf model ages (TDMC) range from 802Ma to 952Ma.

The zircon Lu-Hf isotopic characteristics of the anisomitic monzogranites indicate that the magma source is a mixture of mantle and a small amount of ancient crust. The magma source area of the rhyolite porphyritic lavas is dominated by mantle-derived materials. The transition evolution process from crust source to mantle source from host rock to metallogenic parent rock is revealed.