矿床地球化学国家重点实验室知识库

The similar to 260Ma Taihe layered intrusion is one of the mafic-ultramafic intrusions host giant magmatic Fe-Ti oxide ore deposit in the central Emeishan Large Igneous Province. It outcrops similar to 3km long and similar to 2km wide, and has a thickness of similar to 1.2km. According to mineral assemblages and petrography textures, the intrusion can be divided into three lithologic zones: Lower Zone (LZ), Middle Zone (MZ) and Upper Zone (UZ). The LZ comprises (olivine) gabbros and thick massive Fe-Ti oxide ores. The MZ consists of six cyclic units, which are comprised of (apatite) magnetite clinopyroxenites and (apatite) gabbros from the base to the top. The UZ is comprised of Fe-Ti oxide-poor apatite gabbros. The apatite magnetite clinopyroxenites of the Taihe MZ contain 5% similar to 12% apatite, 20% similar to 35% Fe-Ti oxides and 50% similar to 60% silicates which occur as cumulus phases together with apatite. The magnetite compositions of the apatite magnetite clinopyroxenites are characterized by high TiO2, FeO, MnO and MgO contents and its variations are similar to those of the Panzhihua intrusion. Meanwhile, the ilmenite compositions display the negative correlations between FeO and TiO2, and MgO, respectively. The FeO of ilmenite is positively correlated to Fe2O3 and MnO, respectively. These features suggest that magnetite and ilmenite crystallized from the Fe-Ti-P-rich silicate magma rather than immiscible nelsonitic melts. It thus can be concluded that the origin of apatite magnetite clinopyroxenites is resulted from crystal fractionation associated with gravitational sorting and setting. In the LZ, magnetite inclusions in olivine contain relatively high Cr2O3 (0.07% similar to 0.21%), whereas the Cr2O3 (0.00% similar to 0.03%) of magnetite inclusions in olivine from the MZ abruptly decreased. The Cr2O3 contents of magnetite inclusions in olivine are positively correlated with An content of plagioclase and Cr content of clinopyroxene. It confirms the replenished parental magmas formed the MZ rocks are different from the relatively primitive parental magmas formed the LZ rocks and ores. The MZ Fe-Ti-P-rich magma may be produced by the Fe-Ti enriched magma from a deep-seated magma chamber mixing with the extensively evolved P-rich magma in a middle level magma chamber. The relatively low Ti + V contents of magnetite of the UZ and the top of MZ suggest the compositions of these magnetites may be modified by magmatic hydrothermal resulted from late stage of magma differentiation.