Description: The Zhubu magmatic Ni-Cu-PGE sulfide deposit is hosted in a mafic-ultramafic intrusion which is part of the Emeishan large igneous province in southwest China. The Zhubu intrusion is composed of a layered sequence (750 x 400 x 600 m) with subhorizontal modal layering and a subvertical marginal zone of 〈40 m across. The marginal zone is composed of lherzolite and olivine websterite with minor gabbroic rocks. The layered sequence is composed of lherzolite, websterite, gabbro, and gabbrodiorite from the base to the top. The Zhubu intrusion can be explained by two stages of formation, an early conduit stage for the marginal zone and a late in situ differentiation stage for the layered sequence. Most important Ni-Cu-PGE mineralization in the intrusion occurs as disseminated sulfides within the marginal zone. Olivine crystals from the marginal zone contain 81 to 84 mol % Fo and 1,600 to 1,900 ppm Ni. The rims of zoned olivine phenocrysts in the Emeishan picrites have similar Fo contents but significantly higher Ni contents (2,300–2,600 ppm). The olivine data indicate that the parental magma of the Zhubu ultramafic rocks is similar to the transporting magma of the Emeishan picrites in MgO/FeO ratios but depleted in Ni due to sulfide segregation before olivine crystallization. The initial concentrations of PGE in the Zhubu magma, estimated from bulk sulfide compositions, are 7 ppb Pd, 9.3 ppb Pt, and 0.8 ppb Ir, similar to the values in the Emeishan picrites. Like the Emeishan picrites, the Zhubu intrusive rocks are characterized by light REE enrichments. Negative Nb anomalies relative to Th and Ta, which are rare in the Emeishan picrites, are present in the Zhubu samples. The ( 87 Sr/ 86 Sr) i and Nd values of the Zhubu intrusive rocks vary from 0.709591 to 0.710692 and from –2 to –3, respectively. The trace element and isotope compositions indicate that the Zhubu magma was contaminated by crustal materials, supporting the interpretation that sulfide saturation in the magma was triggered by crustal contamination. The area where the lower part of the conduit may have been brought up by faulting should be the focus of future exploration at Zhubu.

Description: Magmatic-hydrothermal ore deposits in collisional orogens are new targets for modern mineral exploration, yet it is unclear why they preferentially occur in some specific tectonic environments within these orogenic belts. We integrate geologic and geochemical data (especially zircon U-Pb dating and Lu-Hf isotope data) for Mesozoic-Cenozoic magmatic rocks and associated ore deposits in the Lhasa terrane, a highly endowed tectonic unit within the Himalayan-Tibetan orogen, and provide the first example in a continental collision terrane of the application of zircon Hf isotope data to image the lithospheric architecture and its relationship with ore deposits. Three crustal blocks are identified within the Lhasa terrane by the Hf isotope mapping method. They include a central long-lived Precambrian microcontinent with local reworking and two surrounding juvenile Phanerozoic crustal blocks with significant mantle contributions to constituent magmatic rocks. The three crustal blocks are bounded by two E-W–trending terrane-boundary faults, and each block is cut by two N-S–striking concealed faults. Isotopic signatures of zircons from the juvenile crustal blocks indicate that the Phanerozoic continental crust grew from several Mesozoic volcanic-plutonic arcs and by underplating of mantle-derived magmas generated during Mesozoic accretion and Cenozoic collision. Mesozoic subduction-related porphyry Cu-Au deposits and Cenozoic collision-related Cu-Mo deposits are exclusively located in regions with high Hf (〉5) juvenile crust. Cu enrichment during differentiation of high f o 2 arc magmas is the key for the formation of Mesozoic subduction-related porphyry Cu-Au. By contrast, remelting of the lower crustal Cu sulfide-rich magmatic cumulates within the juvenile crust is interpreted to have played a key role in the formation of Cenozoic collision-related Cu-Mo deposits. Granite-related Pb-Zn deposits cluster in the oldest crustal regions or developed along the margin of the old crustal block bounded by lithospheric faults. The porphyry Mo deposits are localized along the reworked margins of the old crustal block. It is suggested that crustal reworking released Mo from the old crust to form porphyry Mo deposits, whereas leaching of Pb and Zn from the Paleozoic carbonate cover strata by felsic intrusion-driven fluids is critical to the formation of Pb-Zn ore deposits. Skarn Fe-Cu ore deposits are typically localized along a terrane boundary fault, i.e., lithospheric discontinuity, through which crust-derived felsic melt mixed with Cu-rich mantle-derived mafic magmas ascending upward. Associated granitoid rocks usually bear microgranular mafic enclaves and show a zircon Hf isotope array from negative to positive Hf values (–7.3 to +6.7), supporting mixing of juvenile mantle and evolved crustal sources. The Hf isotope maps show temporal-spatial relationships between crustal structure and the location of ore deposits, demonstrating that the structure, nature, and composition of the crust controlled the localization of ore deposits and the migration of ore-forming metals in the terrane. This study shows that the lithospheric architecture of an orogenic terrane can be imaged by Hf isotope mapping to provide mappable units which can be used to explore for ore deposits at the terrane scale.