Graphite usually occurs in mineral/rock associations in the form of solid inclusions and plays an important role in tracing regional metamorphic degree, ore-forming temperature, fluid evolution, as well as the deep carbon cycle of the Earth. In this study, we investigate the placer black nephrite jade where the co-occurrence of abundant graphite inclusions and jade remains extraordinary. By employing petrographic, mineral-chemical, and Raman spectroscopic methods, we characterize the textures and crystallinity of graphite inclusions that exist in nephrite jade. EPMA and petrological data indicate that the main constituents of black jade are tremolite and graphite, with minor phases of diopside, calcite, dolomite, epidote, and apatite. Micro-Raman spectroscopic thermometry of carbonaceous material shows that most of the formation temperatures of graphite inclusions are between 378 and 556 °C, and only a few temperatures may be above 650 °C, indicating that graphite inclusions were formed at medium- to high-temperature metamorphic facies. The petrologic and spectral investigations of graphite inclusions in these nephrite jade samples show major metamorphic signatures with mixed features associated with fluid precipitation. Our results allow us to propose that primary nephrite jade was formed under multi-stage tectonic evolution conditions, and regional temperatures were predominately driven by the late continent–continent collision, while the ore-controlling temperatures of nephrite jade formation were found in a medium- to high-temperature environment.

The Jiaodong Peninsula is the most important gold mineralization area in China, and the formation of gold deposits is closely related to granitoids. The isotopic ages of the Early Cretaceous granodiorites in the northwestern Jiaodong Peninsula are concentrated in the range of 111~123 Ma, and are coeval with the formation of the gold deposits in the area. However, the studies on the geotectonic settings of the granodiorites, especially their petrogenesis and relationship with gold deposits in the northwestern Jiaodong Peninsula, are scarce. Based on field and petrographic observations, geochemistry, EPMA analysis, zircon U-Pb chronology, and Sr-Nd isotopes of the Early Cretaceous Zhouguan granodiorite in the Jiaodong area, the formation age of Zhouguan granodiorite is determined as 115 Ma ± 0.77 Ma; the analysis of EPMA shows that biotite is mainly composed of Fe-biotite and Mg-biotite, with its MgO content ranging from 9.797% to 11.635%. The crystallization temperature of biotite is in the range of 500 °C~625 °C and the emplacement depth of the rock mass is 3.98~8.71 km. The amphibole in the mass mainly includes magnesiohornblende, pargasite, and magnesiosadanagaite; among them, the former two are of crustal origin, while magnesiosadanagaite is of mantle origin. The crystallization pressure and depth of the former two are in the range of 0.75~3.02 kbar and 2.81~11.4 km, respectively, while the crystallization pressure and depth for the latter is 4.64 kbar and 17.53 km, respectively. The (⁸⁷Sr/⁸⁶Sr) values range from 0.710424 to 0.711074 and the (¹⁴³Nd/¹⁴⁴Nd) values range from 0.511530 to 0.511808. The parental magma of the Zhouguan granodiorite is highly oxidized with high-water content that is favorable for Au enrichment. Combined with the Nb-Y and Yb-Ta diagrams, a model describing the formation of Zhouguan granodiorite is proposed.