辽东翁泉沟硼镁铁矿矿床海相蒸发成因:来自稳定同位素地球化学证据

Marine evaporative genesis of Wengquangou ludwigite deposit in eastern Liaoning Province: Evidences from stable isotopic compositions

翁泉沟硼镁铁矿矿床呈层状赋存于南辽河群里尔裕组火山-沉积地层下部的钙镁硅酸盐岩中,是一个大型含铀硼镁铁矿矿床.文章运用LA-MC-ICP-MS硼同位素微区原位测试技术和MC-I CP-MS酸溶法硼同位素测试技术,获得硼镁铁矿矿石中δ11B值为6.9‰～8.2‰;硼镁石δ11B值为7.4‰～7.8‰;变粒岩（上盘）内电气石的δ11B值为4.2‰～4.8‰;蛇纹石化碳酸盐岩中的δ11B值为7.6‰～9.4‰.镁铁矿矿石内磁黄铁矿的δ34SV-CDT值为12.3‰～13.2‰,矿体上下层位中的蛇纹石化大理岩δ13CV-PDB值为-4.6‰～1.8‰,矿床外围同层位的大理岩δ13CV-PDB值为-1.2‰～0.1‰.文章结合该矿床内成矿地层中的蛇纹石化镁质大理岩、橄榄玄武岩和硼镁铁矿的共生关系,认为辽东地区硼酸盐矿床中的硼最初来自富硼海水,后经蒸发和变质作用而形成硼酸盐矿床.

The Wengquangou uranium-beating ludwigite deposit occurs in bedded form in the calcium-magnesium silicate rock strata of Lieryu Formation of Liaohe Group. Boron isotope measurement by in-situ LA-MC-ICP-MS and aqueous MC-ICP-MS technologies show that 3rib values of ludwigites range from 6.99‰ to 8.29‰ szaibelyites range from 7.4‰ to 7.89‰, tourmalines within the leptynite located on the hanging wall range from 4.2‰ to 4.8‰, while the serpentinized marbles range from 7.6% to 9.4‰. The 334SV_CDT of gangue mineral （pyrrhotite） values vary from 12.3‰ to 13.2‰. The δ^13Cv-PDB values of serpentinized marble within the borate ore deposit range from - 4.6%0 to 1.8%0, while the 3t3 Cv-pDB values of rdatively fresh marble located outside the borate ore district range from - 1.2‰ to 0.1‰. Combined with the geological bedded features of the dolomitic marbles, ludwigite and olivine basalts in the mining area, the authors hold that the source of boron in the Wenquangou ludwigite deposit might have come from a boron-rich seawater, whose evaporation and later metamorphism caused the formation of borates and carbonates.