The Genetic And Its Prospecting Significance Of Amphibole-rich Veins In Fine-grained Olivine Gabbro At Top Of Qinggangping,Baima

Amphibole-rich veins with a width of 2~5 mm are generally developed at top of Panzhihua-type iron ore host rock. This paper reports the electron microprobe analyses for the representative plagioclases, magnetites, ilmenites, amphiboles, biotites and apatites in amphibole-rich veins, alteration zone and fine-grained olivine gabbro at top of Qinggangping, Baima. Petrographic observations show that the mineral forms in veins are the large particles of amphibole(3~5 mm) with ilmenites, plagioclases and calcites filling in the meantime. In the alteration zone the minerals are amphiboles, plagioclases, biotites, magnetites and ilmenites with general mineral alteration(e.g. biotite chloritization). The dissolution edge of plagioclase is also well developed. And in the host rock close to alteration zone there are major minerals as plagioclases and clinopyroxenes(similar content) and minor minerals such as amphiboles, biotites, magnetites and ilmenites. There are also apatites and sulfides(pyrite and chalcopyrite) around the titanium oxides. The olive gabbro away from veins is fresh and major minerals are plagioclases and clinopyroxenes(similar content). The rock also contains a small amount of olivines, amphiboles, biotites, magnetites and ilmenites. Electron microprobe data shows that the An of plagioclases far from the alteration zone is higher than the An of plagioclases in the veins and the alteration zone. The plagioclases in fresh host rock are mainly labradorites. The plagioclases in the alteration zone are mainly andesines. And albites appear in the veins. Based on an aluminum-in- amphibole geobarometer, the pressures recorded by the amphibole from core to rim show a fluctuating trend. The temperature and oxygen in the equilibrium of magnetite and ilmenite are calculated by using the magnetite-ilmenite geothermobarometry. The results show that the equilibrium temperature of magnetite and ilmenite is about 546~574 ℃, and the oxygen(logfO2) is about-20.41~-23.83. According to the Ti-Mg/(Mg+Fe) graphic of the biotites, the crystallization temperature of the biotite in the host rock close to alteration zone is between 700 ℃ and 720 ℃. Through the discussion and analysis, we draw the conclusion:(1) The top and side part of Qinggangping mafic intrusion firstly concrete to be the fine-grained olivine gabbro. Then it plays the role of a shielding layer for fluid mineralization in deep.(2) The plagioclases in the veins and alteration zone enrich Na. Calculated by the hornblende core to the edge of the electron microprobe data, pressures show a characteristic of fluctuation. It indicates the presence of fluid and fluid ultra-pressure is formed due to fluid expansion. From the amphibole rich veins to alteration zone to the host rock, mineral crystallization temperature decreases, corresponding to the fluid diffusion characteristics from higher temperature to the lower.(3)The amphibole-rich veins in shallow can be used as an indicator for deposits in deep. So, this provides a way for the exploration of iron ore-deposits in deep.