利用铅同位素研究金属矿床地气物质来源:甘肃蛟龙掌铅锌矿床研究实例

Tracing source of geogas with lead isotopes: A case study in Jiaolongzhang Pb-Zn deposit, Gansu Province

地气测量方法能够用来勘查隐伏矿和盲矿,但由于其机理还处在假说阶段,方法自诞生以来一直受到质疑。研究地气物质来源有助于对地气形成机理的认识。采用超净环境控制、高纯酸提纯和高纯制水等方法,成功地实现捕集材料空白Pb小于0.5ng/mL。利用美国国家标准局SRM981铅同位素标准物质和SRM982富集铅同位素稀释剂,采用ICP-MS法首次实现低含量地气铅同位素比值的测定。矿区黄土、红层、围岩和矿石铅同位素组成由质谱法测定。结果显示,背景区地气样品由于铅同位素含量低,其铅同位素组成偏离矿区已知地质母体,可能主要受到捕集剂空白干扰所致;异常区地气铅同位素组成明显不同于背景区,样品点位于近矿围岩和矿石硫化物之间,且更靠近矿石硫化物,说明异常区地气样品有深部矿石硫化物铅的加入,从而为地气用于覆盖区矿产勘查提供了可靠的理论依据。

Geogas survey can be used as a powerful tool for mineral exploration in covered area. People doubt the geogas, however, because of uncertainty of its formation mechanism. The study of geogas source is helpful to understanding the formation of geogas. The blank Pb in liquid collectors is successfully lowered to less than 0. 5 ng/mL by environment control, purifying the solvent wall rocks, mineralizations and ores were determined geogas were measured by HP4500 ICP-MS through and water. The Pb isotope compositions in loess, red layer, by VG-354 spectrometer made in Great Britain and those in optimizing the operating parameters. To acquire accuracy results, the lead isotope ratios were corrected with the dead time and internal standard mass bias. The Pb isotope compositions in geogas from the background area are different from those in a single medium including loess, red layer, wall rocks and ores and might be greatly impacted by blank Pb in the geogas collectors and geogas in soils. The Pb isotope compositions in the geogas anomalies above the orebodies are totally different from those in the background and indicate that some anomalous Pb might be added to geogas. The Pb isotope compositions in geogas give evidence that some metals in anomalous samples survey can play an important role originated from deep orebodies, therefore, support geogas in mineral exploration in overburden.