Actual traces of mantle fluid from alkalic-rich porphyry and deep xenoliths in Liuhe, Yunnan, and its implication to geology

There are quite a few mantle xenoliths and one special Fe-rich melt xenolith in aegirine syenite porphyry, Liuhe, Yunnan province. Petrographic research shows that black opaque material that is Fe-rich glass, which are widely distribute reticulate along intergranular cracks of minerals, crystals fissues and cleavage in association with metasomatic alteration in the mafic-ultramafic xenoliths and their host rocks, and the Fe-rich melt xenolith have the analogous nature. The materials are detected by electron microprobe analysis, SEM and energy spectrum analysis. It is found that they are a kind of submicroscopic cryptocrystal solid of electronic microscopic grade which is mainly composed of silicates, quartz and, especially, carborundum and ferrite and ilmenite and gray hematite et al. for mantle guide minerals. These minerals show the characteristics of liquation in the back-scattered electron image. It is concluded that the compositions and characteristics of the materials are actual traces of supercritical and molten-lava mantle fluid. The metasomatic alteration caused by mantle fluid expressed in silication, potash alteration together with metalliferous mineralization in varying degrees and retrograde reaction in order of pyroxene→amphibole→biotite→chlorite in dark minerals of host body and deep xenoliths. Based on the discussions above, we probe into geologic significances of mantle fluid for polymetal mineralization in this investigated area.