铂矿化探:取子样误差与控制方法

通过对颗粒铂分布与取子样误差关系的讨论 ,发现在铂矿地球化学勘查中 ,铂分析的取子样误差主要出现在铂异常的查证和异常源追踪阶段 ,导致误差的主要因素是随着与矿床或矿体的不断接近 ,样品中铂含量迅速增高 ,可能出现铂的颗粒效应。为了使铂分析的误差控制在 5 0 %之内 ,建议在铂矿地球化学勘查的不同阶段 ,采取不同的子样量分析铂。在区域化探阶段 ,大多数样品仍可采用取 1 0 g子样分析铂 ;而在异常追踪和查证阶段 ,由于样品中的铂含量往往大于 1 0ng/ g ,土壤、水系沉积物样品中颗粒铂粒径通常为 5～ 2 0 μm ,故建议取 2 0 g子样分析可保证大多数样品的分析误差控制在 5 0 %之内。文献中报道的取 5g、1 g样品获得的铂分析数据 ,使用时应慎重

GEOCHEMICAL EXPLORATION FOR PLATINUM DEPOSITS:CONTROL OF ERRORS DUE TO SUB-SAMPLING FOR ANALYSIS OF Pt WITH DIFFERENT GRAIN SIZES

The theoretical discussions on the distribution of grain size of particles containing Pt and the sub-sampling for analysis of Pt reveal that the significant errors in analysis of Pt arose mainly from those samples taken in the stages of follow-up and source-tracking of geochemical anomalies. The main factor causing the error is that the contents of Pt are increasing rapidly along with being close to the sources of geochemical anomalies, so the “nugget effect” exists. To keep the errors less than 50%, I suggest to vary the sub-sample size at the different stages of geochemical exploration. At the stage of regional geochemical exploration, a sample size of 10 g for Pt analysis might be suitable for most of samples. At the stage of follow-up and source-tracking of geochemical anomalies, the contents of Pt in samples are often larger than 10 ng/g. A preliminary study of the distribution of grain size of particles containing Pt shows that the grain size for rocks, soils and stream sediments ranges from 5 to 20 μm. It is therefore suggested that the sub-sample size of 20 g be taken to ensure the error less than 50%.