The Chaijiagou Mo deposit (0.11 Mt Mo @ 0.07%) is located along the northern margin of the North China Craton. This study integrates ore geology, S–Pb–He–Ar–H–O isotopes, and fluid inclusion (FI) analyses to constrain the sources of ore-forming fluids and metals, as well as mineralization mechanisms. Three principal inclusion types were identified: liquid-rich, vapor-rich, and saline FIs. Microthermometry documents a progressive decline in homogenization temperatures and salinities from early to late mineralization stages: Stage 1 (360–450 °C; 5.3–11.3 and 35.4–51.5 wt.% NaCl equation), Stages 2.1–2.2 (320–380 °C and 260–340 °C; 5.4–11.8 and 33.8–44.5 wt.% NaCl equation), and Stage 4 (140–200 °C; 0.4–3.9 wt.% NaCl equation). Noble gas and stable isotope data reveal that the ore-forming fluids were initially dominated by crustally derived magmatic–hydrothermal components with a minor mantle contribution, subsequently experiencing significant meteoric water input. S–Pb isotopic compositions demonstrate a genetic relationship between mineralization and the ore-bearing granite porphyry, indicating a magmatic origin for both sulfur and lead. Fluid–rock interactions and fluid boiling were the dominant controls on molybdenite and chalcopyrite deposition during Stage 2, whereas mixing with meteoric waters triggered galena and sphalerite precipitation in Stage 3.

The Damiao Fe-Ti-P deposit, located within the Damiao anorthosite complex in northeastern China, features Fe-Ti oxide ores and nelsonites that occur as irregularly inclined stratiform-like bodies, lenses, or veins with sharp contacts against anorthosite and gabbronorite. This deposit is characterized by abundant titanomagnetite that hosts diverse ilmenite exsolution textures, including blocky, lamellar, and cloth-like forms. In this study, we investigate the geochemistry and mineralogy of ilmenite exsolutions in titanomagnetite to understand their formation mechanisms and implications for the ore-forming process. Detailed petrographic observations and electron microprobe analyses reveal that the exsolution textures result from multiple mechanisms: oxy-exsolution due to titanomagnetite oxidation; subsolidus re-equilibration between magnetite and ilmenite involving elemental diffusion of Fe, Ti, Cr, Co, and Ni; and exsolution related to lattice defects caused by rapid cooling. Thermodynamic modeling using Gibbs free energy calculations and the QUILF program indicates that blocky, lamellar, and cloth-textured ilmenite exsolutions formed at temperatures above and below the solid solution solvus under decreasing oxygen fugacity. Additionally, our results indicate that the exsolution of zircon and pleonaste at ilmenite grain boundaries is attributed to the saturation and precipitation of elements like Zr and Al, due to the oxidation of titanomagnetite, rather than interactions between ilmenite and adjacent clinopyroxene. Reconstruction of the cooling history suggests that the oxygen fugacity of oxide-apatite gabbronorites was significantly higher than that of Fe-Ti-P ores. This confirms that increasing oxygen fugacity during magma evolution promoted immiscibility, leading to the formation of nelsonitic melts and ultimately the development of Fe-Ti-P ores.