Elemental mobility patterns and metallogenic implications of the Tongshan porphyry Cu-Mo-Au deposit, Heilongjiang Province, NE China

• Geochemical migration of elements is quantitatively calculated. • The distinct association of W-Bi-Tl enrichment and Zr-Hf-REE depletion with Cu mineralization provides robust geochemical indicators for exploration • Chlorite chemistry tracks fluid evolution and controls the mobility of specific trace elements. Quantifying element mobility within the well-defined alteration zones of porphyry Cu systems is critical for reconstructing metallogenesis and defining exploration vectors. This study integrates whole-rock geochemistry and chlorite mineral chemistry to constrain fluid-rock interaction processes in the Tongshan porphyry Cu deposit. Chlorite geothermometry indicates that the Chlorite-Epidote ± Muscovite mineral assemblages occurred at 280–320 °C, with compositional variations (e.g., SiO 2 , Al 2 O 3 , FeO and MgO) tracking the physicochemical evolution of ore-forming fluids. Chlorite crystallization might be elevated fluid pH, thereby exerting a primary control on the mobility of trace elements such as Fe, Mg, Cr, As, and Sr. Mass-balance calculations reveal that intense hydration (LOI gains up to + 56 %) induced rock volume expansion and pressure reduction, likely triggering fluid boiling and subsequent metal precipitation. The propylitic zone is identified as the primary host for ore deposition in the deposit, exhibiting extreme Cu enrichment (up to + 5423 %) that contrasts with widespread REE depletion (−27.4 % to −77.3 %). This geochemical decoupling reflects the differential stability of metal complexes, wherein high-temperature fluids mobilized REEs while promoting the destabilization and precipitation of Cu. A robust geochemical footprint was also identified, in which W, Bi, Tl, Zr, and Hf strongly correlate with Cu (R 2 > 0.56). These elements, combined with the distinct REE depletion pattern, serve as effective vectoring indicators for targeting concealed orebodies. These findings in this study establish a comprehensive element-mobility framework that elucidates metal enrichment mechanisms in the propylitic zone and provides a practical geochemical toolkit for exploration in the Tongshan porphyry Cu deposit and analogous porphyry systems.