A major Ti-bearing mineral in Emeishan basalts:The occurrence,characters and genesis of sphene
峨眉山高钛玄武岩中主要的赋钛矿物——榍石的产状、特征及成因

The form of the mineral of the titanium existing in Emeishan basalt have been mentioned by few scholars. Using by thin section identification, chemical-rock, X-ray diffraction, energy spectroscopy electronic probe (SEM) and cathodeluiminescence, this paper analysed the Emeishan basalt from well cores in Zhougong mountain-Hanwang field of southwestern of Sichuan Province in detail, and discussed the main mineral which occurred in titanium and its formation. (1) SiO2 between 46.4% and 48.3% and TiO2>3% showed that the Emeishan basalt generally belonged to high-Ti and alkaline Emeishan basalt series. Many layers have so much cryptocrystal sphene(>5%),but have few magnetite and ilmenite. (2) The cryptocrystal sphene mainly formed in mist shape, snowflake, sesamepoint like, branch shapea and distributed in microcrystalline feldspar, the intramarginal of solution pores and cave and crack, in a small amount is grain distributed in microcrystalline feldspar and chlorite. (3) The result of electronic probe showed that the highest content of TiO2(39.069%)was ilmenite, in the second was sphene (17.143%~38.648%), the third was magnetite(5%~10%)and the highest content was 12.293% in it, other minerals basically all less than 1%. (4) Element analysis showed that the content of Ti (2.49%~24.97%) in sphene is obviously higher than magnetite (2.68%~9.21%) and hematite (3.64%), its quite clear to ilmenite (19.51%). The result from the analyses was that: The abundant increasing cryptocrystal sphene in the Emeishan basalt may be the late magma products or altered product after the period of the magma. Expressed that a large number of cryptocrystal sphene found in Emeishan basalt for the first time was a major Ti-bearing mineral in high-Ti Emeishan basalt. The content of the cryptocrystal sphene in Emeishan basalt is one of the major marks to differentiate between 'high-Ti' and 'low-Ti' basalt.