The geochronology of the Haobugao skarn Zn-Pb deposit (NE China) using garnet LA-ICP-MS U-Pb dating

The Haobugao skarn Zn-Pb ore deposit (reserves of 0.29 Mt @ 4.24% Zn, 0.15 Mt @ 2.25% Pb) is located in the southern Great Xing' an Range (SXGR) Cu-Mo-Ag-Au-Pb-Zn-Fe metallogenic province in northeastern China. The ore bodies mainly occur near the contact zones between the early Cretaceous granite and the lower Permian carbonates and sometimes in distal locations. Two types of garnet are identified, i.e., green and fine-grained garnet (Grt A), and brown and coarse-grained garnet (Grt B). The Grt A contains a wider compositional range (Adr(71.46-95.07)Grs(0.16-24.10)), whereas the Grt B contains a relatively narrow compositional range (Adr(87.65-97.52)Grs(0.07-0.11)). The Grt A displays chondrite-normalized HREE-enriched and LREE-depleted patterns with negative Eu anomalies, suggesting that the Grt A was likely crystallized from a nearly neutral fluid. In contrast, the Grt B is LREE-enriched, HREE-depleted with pronounced positive Eu anomalies, indicating that the Grt B was probably formed from a mildly acidic fluid. The Grt A contains lower U contents than the Grt B, implying that the Grt A was likely formed under a relatively oxidized condition, while the Grt B crystallized from a more reduced condition. Skarn mineralization at Haobugao (139.10 +/- 5.40 and 140.70 +/- 1.89 Ma, garnet LA-ICP-MS U-Pb ages) and Zn-Pb mineralization (138.27 +/- 0.14/0.69/0.81 and 138.82 +/- 0.07/0.68/0.80 Ma, molybdenite ID-N-TIMS Re-Os ages) were associated with the emplacement of the granitoids dated from 143.49 +/- 0.76 to 140.85 +/- 0.75 Ma (zircon LA-ICP-MS U-Pb ages). The integrated geochronological data suggest that the ore-related granitoids, skarn, and Zn-Pb mineralization in the Haobugao deposit all formed in the early Cretaceous, which occurred in an extensional tectonic setting associated with regional Paleo-Pacific slab roll-back. This study highlights the reliability and viability of garnet U-Pb dating for constraining the timing of skarn formation, and utilizing its age with textural and trace element concentrations could well reconstruct the ore-forming process of skarn deposits.