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The Zhaheba ophiolite is an ocean relic of the Zhaheba-Aermantai oceanic slab, a branch of the early Paleozoic Paleo-Asian Ocean. The peridotites consist mainly of harzburgite, lherzolite and minor dunite, chromitite. This study describes the whole-rock geochemistry and mineral chemistry of the Zhaheba peridotite and chromitite for the purpose of constraining their tectonic environment and genesis. The major oxides and the trace element concentrations of the peridotites are comparable with abyssal peridotite, but fall outside the field of SSZ (suprasubduction zone) peridotite and the fore-arc peridotite. The massive chromites belong to the high-Cr group, with an average Cr# (Cr/(Cr + Al)) atomic ratio) value of chromian spinel of 0.77, whereas the average Mg# value is 0.60. The disseminated chromites give a lower concentration of Cr2O3 (38.96–42.15 wt.%, average 40.35 wt.%) and lower Cr# values (0.50–0.56, average 0.53), but slightly higher contents of MgO (13.23 wt.%) and Mg# (0.61) than the massive chromites. In the diagrams of Cr#-Mg#, NiO-Cr# and TiO2-Cr#, the massive chromites fall in the field of boninite, and the disseminated chromite in the peridotite plot fall in the field of abyssal peridotite and mid-oceanic ridge basalt (MORB). The massive chromitites, with high-Cr, display a boninite affinity, whereas the disseminated chromite plot in the high-Al and abyssal peridotite type field may be generated by the extension of the Zhaheba ocean in the MOR environment then experienced deep subduction and exhumation. The calculated degrees of partial melting for the massive chromites are 21%−22%, and for the disseminated chromites in peridotites the degrees are 17%−18%. The calculated values of fO2 for the massive chromites range from −1.44 to +0.20, and the values for the disseminated chromites range from −0.32 to +0.18. The inferred parental melt composition for massive chromitite falls in the field of boninite in an arc setting, whereas the disseminated chromite in peridotites are in the field of a MORB setting. This indicates that the parental magmas of the former were more refractory than the latter. A two-stage evolution model for the chromites was proposed, in which disseminated chromites were first formed in an MOR environment and then modified by later-stage melts and fluids, and formed massive chromites were formed in an SSZ setting during intra-oceanic subduction.

The recently discovered Daping tungsten deposit is located about 25 km north of Tongcheng County, Hubei Province, in the northern margin of the Sijiapu granite deposit of the Mufushan composite batholith. The ore body is produced in the northeast-oriented greisenization granite and quartz vein, and belongs to the greisen-vein-type scheelite deposit. The resources of the Daping W deposit have a value of 7935 t W and the average grade is 0.201% WO3. Based on mineralogical and petrographic studies, scheelite is classified into two types. A study of the geochemical characteristics of rare earth elements (REEs) and trace elements indicated that some scheelite specimens showed LREE depletion. Meanwhile, the total amount of scheelite rare earth elements (REEs) is low and the ratio of LREE/HREE ranges from 0.40~2.72 in the Daping W deposit. The contents of REEs and trace elements in the two types of scheelite differ significantly. Type I scheelite has an average ∑REE content of 195.65 ppm, an LREE/HREE value of 0.5, an Eu anomaly (δEu) of 0.78, Mo of 366.20 ppm, Sn of 22.62 ppm, and Sr of 264.80 ppm. However, type II scheelite features an average ∑REE of 111.28 ppm, an LREE/HREE ratio of 1.43, a δEu of 1.56, Mo of 188.48 ppm, Sn of 0.15 ppm, and Sr of 829.93 ppm. The content level of Mo in the two types of scheelite is not high, indicating that this whole metallogenic environment is a reduction environment. However, this is a complex process. The presence of type I scheelite with negative Eu anomalies and relatively high Mo content indicates that the ore-forming environment in the early period of the greisen stage was relatively oxidizing. In contrast, type II scheelite contains large amounts of Sr and large positive Eu anomalies, which are likely to be released from plagioclase in the granite during greisenization. The extremely low composition of Mo in type II scheelite is closely related to the reducing environment in the later period of the greisen stage. Because Mo probably exists in its Mo4+ state, it may be difficult for it to replace W6+ in the scheelite lattice. Additionally, comparing the contents of Sn and Sr in different types of scheelite shows that the metallogenic environment changes from relative oxidation to the reduction of scheelite. The variation in trace elements and REEs in scheelite over time reflects a complex magmatic–hydrothermal mineralization environment. Additionally, the Ar–Ar system dating results for muscovite that is closely associated with scheelite in the greisenization granite vein indicate that a muscovite 40Ar/39Ar plateau age of about 133 Ma represents the time of tungsten mineralization. This muscovite 40Ar/39Ar dating result is close to the previous zircon U-Pb age data of the biotite monzogranite (ca. 140–145 Ma), which is the largest intrusion in the orefield. Meanwhile, the new age data reported here confirm that the Daping tungsten deposit represents a Mesozoic magmatic–hydrothermal mineralization event with a setting of lithospheric extension in the Mufushan composite batholith.