The Mineral Chemistry of Magnetite and Its Constraints on Ore-Forming Mechanism in the Sandaozhuang Skarn-Type W-Mo Deposit in East Qinling

The Sandaozhuang super-large W-Mo deposit is located in the southern margin of North China Craton, within well-known East Qinling Mo mineralization belt, and one typical skarn-type deposits China. Based on EMPA LA-ICP-MS analyses, major trace elements were presented, mineral chemistry magnetite at various stages was discussed. Combining field observations, petrography, geochemical characteristics, can be classified into three types, namely early-magmatic-stage high-temperature (Mag1), potassic-alteration-stage (Mag2), retrograde-alteration-stage (Mag3). Mag1 Mag2 magnetites primarily occurred granites association with potassium (K) feldspar biotite, whereas Mag3 associated metallic sulfide minerals that mainly vein-like structures skarn. Mag1, Mag2, distinguished as having magmatic, magmatic–hydrothermal transition, hydrothermal origins, respectively. All types exhibit a depletion high-field-strength (HFSEs) such Zr, Hf, Nb, Ta, Ti, large-ion lithophile (LILEs) including Rb, K, Ba, Sr, compared to mean continental crust composition. Conversely, they are enriched Sn, Mo, V, Cr, Zn, Ga. showed no significant Co, Ni, Cu, Bi, indicating influence coexisting sulfides composition limited. There systematic variations from Mag3, which exhibited similar patterns element spider rare earth diagrams, Y/Ho ratio, consistent source for magnetite. changes V Cr contents (Ti + V) vs. (Al Mn) diagram reflected evolution ore-forming fluids an initial increase oxygen fugacity subsequent decrease, well gradual decrease temperature during skarn mineralization. early high-oxygen-fugacity magmatic became W by fluid interaction. rapid change properties retrograde alteration stage led precipitation scheelite molybdenite.