Barite (BaSO4) is a common mineral in sandstone that must be removed during separation of detrital zircon (ZrSiO4). One widespread technique for the removal of barite exploits its lesser tenacity by milling the barite and zircon mixture in a ball mill. Here we test the extent to which such milling affects zircon and thus whether the milling could introduce bias into the detrital zircon sample. We then describe a new chemical technique for the removal of barite from detrital zircon. We find that milling a mixture of barite and zircon both breaks and causes loss of zircon grains, potentially introducing bias into a detrital zircon sample. Boiling barite in a 0.94 molar aqueous solution of sodium carbonate for 4 h converts most grains to barium carbonate. The barium carbonate grains are opaque white and thus visually distinguishable from zircon, allowing separation by hand under a stereoscopic microscope. Alternatively, the barium carbonate grains can be dissolved by boiling in 16 wt% nitric acid for 30 min. In our experiments, boiling zircon in sodium carbonate solution and/or concentrated (65 wt%) nitric acid cleaned the surfaces of and the cracks in the grains but did not visibly change the zircon surfaces in other ways. Boiling only in concentrated nitric acid did not measurably affect the U-Pb and Lu-Hf isotopic systems in zircon interiors, and boiling in a sodium carbonate solution followed by concentrated nitric acid did not detectably alter the Lu-Hf isotopic system. However, boiling in a concentrated sodium carbonate solution followed by concentrated nitric acid did disturb the U-Pb isotopic system in zircon interiors. We recognize this disturbance due to a ~0.5% reduction in 206Pb/238U dates of treated zircon. Our results highlight the importance of proper technique during zircon isolation to minimize the introduction of bias into the sample.

中文翻译：

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两种从碎屑锆石中去除重晶石的工艺试验

重晶石 (BaSO4) 是砂岩中的常见矿物，必须在碎屑锆石 (ZrSiO4) 分离过程中去除。一种去除重晶石的普遍技术通过在球磨机中研磨重晶石和锆石混合物来利用其较低的韧性。在这里，我们测试了这种铣削对锆石的影响程度，从而测试了铣削是否会给碎屑锆石样品带来偏差。然后，我们描述了一种从碎屑锆石中去除重晶石的新化学技术。我们发现，研磨重晶石和锆石的混合物既会断裂又会导致锆石颗粒丢失，从而可能会导致碎屑锆石样品出现偏差。将重晶石在 0.94 摩尔碳酸钠水溶液中煮沸 4 小时，可使大多数颗粒转化为碳酸钡。碳酸钡颗粒是不透明的白色，因此在视觉上与锆石不同，允许在立体显微镜下用手分离。或者，可以通过在 16 wt% 硝酸中煮沸 30 分钟来溶解碳酸钡颗粒。在我们的实验中，在碳酸钠溶液和/或浓（65wt%）硝酸中煮沸锆石清洁了晶粒表面和裂纹，但没有以其他方式明显改变锆石表面。仅在浓硝酸中沸腾不会显着影响锆石内部的 U-Pb 和 Lu-Hf 同位素系统，并且在碳酸钠溶液和浓硝酸中沸腾不会显着改变 Lu-Hf 同位素系统。然而，在浓碳酸钠溶液和浓硝酸中沸腾确实扰乱了锆石内部的 U-Pb 同位素系统。由于~0，我们认识到这种干扰。处理过的锆石的 206Pb/238U 日期减少了 5%。我们的结果强调了锆石分离过程中适当技术的重要性，以最大限度地减少引入样品的偏差。