The Characteristic Of Mineralogy And Geochemistry Of Tourmaline In Boron Deposits Of Houxianyu In Liaoning Province

The author has studied the mineralogy and geochemistry of the tourmaline intourmaline-rich rocks in the Houxianyu borate deposit, Liaoning, and discussed thesignificances of the chemistry of tourmaline and their host rocks to understanding of thegenesis of borates and associated rocks.The tourmalines in the studied area are Mg-and Fe-rich, falling into schorl-draviteseries in the Mg-Fe-Al plot. The Mg/Fe ratio of the tourmaline vary with the distance fromthe borates, i.e., more Mg-rich towards the borates. Those proximal to the borates usuallyexhibit declining of Mg from core to rim;and those distal to the borates are generally Fe-richand Fe content decreases towards the rim. Meanwhile, the tourmalines vary in their color,grain size, morphology and internal zoning. In general, the hanging wall rocks are moretourmaline-rich than those in the footwall, and the tourmalinite are hosted in the hanging wall.In rocks distal to the borates, tourmaline exhibits pronounced positive correlation betweenMg/Fe ratio and Na20.The chemistry of the tourmaline reflects the evolution of fluids during the rock-andborate-forming process. The early phase tourmaline resulted from metamorphism ofboron-rich sediments, which was followed by metasomatism-related precipitation oftourmaline. During the evolution of fluids in the evaporation basin, Mg, Na, and K becameenriched in the later phase, resulting in Mg/Fe zoning in the tourmalines. The chemistry ofthe tourmalines suggests a genetic correlation with their host rocks, i.e., the clastic rocksprovided Al, Mg and Fe for formation of the tourmalines.The thermo-luminescence of the tourmaline provides an indicator for borate explorationin the area, the intensity of luminescence increase towards borates.Both mineralogy and geochemistry of the tourmalines suggest that the tourmalinesformed via metamorphism and metasomatism. The protolith of the tourmaline-rich leptynitesmight be metasomatized sediments that subsequently experienced metamorphism. The spatialaffiliation between the tourmalines and borates also suggests a genetic link between them.The results of this study may provide exploration indicator, and also promoteunderstanding of the genesis of the borate deposits in the region.