Improvement of the Anomaly Spot-checking Method in Sample Analysis during a Geochemical Reconnaissance Survey

In order to meet the double goals of picking up real geochemical anomalies and monitoring inner laboratory analytical quality during multiple element analysis of geochemical samples, a multi-interval and element-grouping sampling procedure (MIEGSP) based on the statistical method of geochemical anomalies is proposed. The MIEGSP mainly includes:(1) the set of each element's (logarithmic) measurements supposed to obey normal distribution and is divided into successive intervals including low/high value outlier ones and cumulative frequency distributions. Each measurement is assigned to a specific interval. (2) Target elements are grouped, total anomaly number (TAN), high anomaly number (HAN) and low anomaly number (LAN) in each group are calculated. (3) The samples with gold anomaly are randomly picked up according to the ratios of each interval, whereas samples with other element anomaly are orderly picked up from those samples characterized by higher TAN, HAN and LAN values. (4) If necessary, supplementary samples are randomly picked up from certain analytical batches. The MIEGSP takes into account, not only geochemical anomalies and experimental analysis anomalies, but also supplements of non-anomalies and analytical batch balance sampling. It has resolved the paradox between limited sample amount and the lack of sampling representativeness. An EXCEL program for anomaly sampling based on the Macros (VBA) was developed. The MIEGSP has been successfully applied to routine analysis of geochemical reconnaissance survey samples.