Trace element geochemistry of magnetite: Implications for ore genesis of the Talate skarn Pb-Zn (-Fe) deposit, Altay, NW China

摘要

The Talate skarn Pb-Zn (-Fe) deposit is hosted in the Kangbutiebao Formation of the Abagong polymetallic belt, Altay (NW China). The Talate magnetite comprises the magmatic-hydrothermal/hydrothermal disseminated and massive magnetite types and formed during the early skarn and quartz-magnetite stage. The magmatic-hydrothermal disseminated magnetite is Nb-Ta-Ti-depleted, whereas the hydrothermal disseminated magnetite associated with skarn alteration is geochemically similar to the Ca-skarn (with slight Ta-Mg-Ni depletions). The massive magnetite ores have similar Ni concentrations with the Ca-skarn, but contain minor depletions in Sn, Sc, Ta, Nb, Mg and Co, probably attributed to magma-host rock interactions. The Talate hydrothermal disseminated magnetite contains lower Sn than magnetite from typical skarn deposits, and likely resulted from cassiterite crystallization as it is found coprecipitated with disseminated magnetite. Both magmatic-hydrothermal and hydrothermal disseminated magnetite are characterized by narrow Ti concentration range and variable Co/Ni ratios, which likely reflect rapid cooling rate and significant fluid-rock interaction during multiple successive stages of skarn alteration, as the Co has a higher solubility over the Ni in the ore-forming fluid. Whereas the Talate massive magnetite contains wider Ti concentration range and in some cases with 120 degrees triple junctions, the Co/Ni ratios (mostly 0.1) of these massive magnetite grains fall within the bracket of Kangbutiebao Formation (Co/Ni = similar to 1) and the magmatic deriving fluid (Co/Ni = similar to 0.01), which was probably generated by equilibration fluid-rock interaction. The high (Al + Mn) and low (Ti + V) and Ni/(Cr + Mn) values for all the Talate hydrothermal magnetite support a typical skarn origin, and the textural and trace element features of the Talate magnetite are analogous to those of typical Ca-skarn Fe deposits worldwide. (C) 2017 Elsevier B.V. All rights reserved.