Chemical and boron isotopic compositions of tourmaline from the Paleoproterozoic Houxianyu borate deposit, NE China: Implications for the origin of borate deposit

摘要: Abstract The Houxianyu borate deposit in northeastern China is one of the largest boron sources China, hosted mainly Paleoproterozoic meta-volcanic and sedimentary rocks (known as Liaohe Group) that are characterized by high concentrations. ore-body has intimate spatial relationship with Mg-rich carbonates/silicates Group, fine-grained gneisses (meta-felsic volcanic rocks) main country rocks. presence abundant tourmalinites tourmaline-rich quartz veins orebody provides an opportunity to study origin boron, nature ore-forming fluids, possible mineralization mechanism. We report chemical isotopic compositions tourmalines from tourmaline-bearing gneisses. Tourmalines chemically homogeneous, showing relatively Fe Na low Mg, δ11B values a narrow range +1.22‰ +2.63‰. rocks, however, commonly show compositional zoning, irregular detrital core euhedral overgrowth, have significantly higher REE (and more pronounced positive Eu anomalies), V (229–1852 ppm) Sr (208–1191 ppm) than those They varied B isotope ranging +4.51‰ +12.43‰, which plot intermediate between terrigenous sediments arc (as represented δ11B = +1.22‰ +2.63‰ this study) marine carbonates evaporates values. In addition, rim zoned tourmaline shows notably Ti, V, Sn, Pb, (particularly LREEs), but lower Fe, Co, Cr, Ni, Zn, Mn, core. These data suggest (1) (2) fluids should be temperature metamorphic related amphibolite-facies metamorphism foldbelt, leach boron-rich subsequently interacted evaporates, forming deposit, overgrowth