Magnetite is a common mineral in many ore deposits and their host rocks, and contains a wide range of trace elements (e.g., Ti, V, Mg, Cr, Mn, Ca, Al, Ni, Ga, Sn) that can be used for deposit type fingerprinting. In this study, we present new magnetite geochemical data for the Longqiao Fe deposit (Luzong, ore district) and Tieshan Fe-(Cu) deposit (Edong ore district), which are important magmatic-hydrothermal deposits in eastern China.

Textural features, mineral assemblages and paragenesis of the Longqiao and Tieshan ore samples have suggested the, presence of two main mineralization periods (sedimentary and hydrothermal) at Longqiao, among which the hydrothermal period comprises four stages (skarn, magnetite, sulfide and carbonate); whilst the Tieshan Fe-(Cu) deposit comprises four mineralization stages (skarn, magnetite, quartz-sulfide and carbonate).

Magnetite from the Longqiao and Tieshan deposits has different geochemistry, and can be clearly discriminated by the Sn vs. Ga, Ni vs. Cr, Ga vs. Al, Ni vs. Al, V vs. Ti, and Al vs. Mg diagrams. Such difference may be applied to distinguish other typical skarn (Tieshan) and multi-origin hydrothermal (Longqiao) deposits in the MLYRB. The fluid-rock interactions, influence of the co-crystallizing minerals and other physicochemical parameters, such as temperature and fO(2), may have altogether controlled the magnetite trace element contents of both deposits. The Tieshan deposit may have had higher degree of fO(2), but lower fluid-rock interactions and ore-forming temperature than the Longqiao deposit. The TiO2-Al(2)o(3)-(Mgo + Mno) and (Ca + Al + Mn) vs. (Ti + V) magnetite discrimination diagrams show that the Longqiao Fe deposit has both sedimentary and hydrothermal features, whereas the Tieshan Fe-(Cu) deposit is skarn-type and was likely formed via hydrothermal metasomatism, consistent with the ore characteristics observed.