The Genesis Of Layered Iron Bodies Occurred In The Middle Zone Of Panzhihua Intrusion, Zujiabaobao Mine: Evidence From Quantitative Rock Textural Analysis

Panzhihua magmatic iron deposit is one of the most important iron resources in China and bu up Emeishan mantle plume. However, the metallogenic mechanism is still left controversial. In this article, the middle zone of Panzhihua instrusion in Zujiabaobao mine is investigated. With the analysis of quantitative clinopyroxene texture, the genesis of layered iron bodies has been put forward based on field and microscopic observation. In the aspect of petrography, the textures of clinopyroxene and plagioclase in dissolved samples have been obviously changed by dissolution and the dissolved parts were occupied by oxide. Crystal Size Distribution diagrams show that dissolved samples have steeper CSD slopes and are more curved at small granularity with higher oxide than those of the original. It is explained that the dissolution results in a more steep CSD slope and a coarsening-like CSD diagram. Spatial Distribution Pattern shows that crystals in the upper part are better sorted, however the lower underwent compaction from the former. Sorting have been recorded in the upper part and the lower are suffered from dissolution which results in bigger pore space. Rocks with larger space can not hold up the weight so compaction trend is shown up. It is shown that fluid exists during oxide forming processes revealed by dissolution of rock-forming minerals and fluid-rich amphibole together with serpentine around the dissolved minerals and interstitial oxide. Ti-magnetite/ilmenite geothermometer calculation shows that the equilibrium temperature in the dissoluted sample is 100℃ lower than in the undissoluted one. Fluid rich in iron injected into the unsolidificated body in the late crystallization stage, resulting in the dissolution, then filled the pore space. Iron formed when fluid escaped. Pervasive dissolution occurred in the lower part and iron-rich fluid escaped by compaction, so poor bulk ore body came into being. In the upper part, fluid moved horizontally without compaction, so rich layered iron body formed. This ore-forming pattern is similar to the transmagmatic fuild metallogenic model.