AN EXPERIMENTAL INVESTIGATION OF THE PANZHIHUA IGNEOUS COMPLEX, SW CHINA-ADDRESSING THE GENESIS OF FE-TI-V OXIDE ORE DEPOSITS

The Late Permian Panzhihua layered gabbroic intrusion of SW China hosts one of the largest magmatic Fe-Ti-V oxide deposits within the Emeishan large igneous province and is coeval with peralkaline granitic rocks.The largest oxide ore body is found at the base of the intrusion which is unlike other layered intrusions where the Fe-Ti oxide deposits are located in the uppermost portions. This study attempts to model the genesis of the Panzhihua layered intrusion, including the formation of the ore deposit, using a starting composition equal to high-Ti Emeishan basalt at atmospheric pressure. The experiments were conducted between 1312^oC and 1102^oC and lasted between six and sixty-five hours. The experimental results show that the first mineral to crystallize at 1274^oC is iron-titanium oxide with a composition within the titanomagnetite series. Following the crystallization of the Fe-Ti oxides are clinopyroxene (Wo_39-52En_39-52Fs_8-16) at 1188^oC and plagioclase (An_67-41) and orthopyroxene (Mg# = 89-92) at 1162^oC. The compositional range of the silicate minerals matches those measured from the rock of the Panzhihua layered gabbro. The low temperature residual glass compositions are enriched in SiO₂, Al₂O₃, Na₂O and K₂O and depleted in TiO₂, FeO, MgO and CaO. Chromium-rich magnetite only appears in the first crystallized oxides at the highest temperature (1274^oC). The results of the experiment indicate that the early crystallization sequence of the parental magma is dominated by Fe-Ti oxide and can explain why the largest oxide ore deposits of the Panzhihua intrusion are found in the lowermost layers. Furthermore the residual glass compositions are similar to spatially associated peralkalinesilicic rocks found in close proximity to the layered gabbro and suggest that the two rock types form a coherent igneous complex.