基岩地球化学金矿勘查的异常圈定与评价

针对金矿化的具体地质特征，研究了确定背景值、异常下限和异常分级的一套方法。在大比例尺基岩地球化学勘查中，应用目标追踪法，分别采集了背景场和异常场两类介质［１］。在确定背景值、异常下限时，将每类介质中的全部样品测试结果，按ｘ＋３ｓ公式剔除到不能再剔除为止，使剩余样品在基本服从正态分布的前提下，取其平均值作为背景值；最后一次被剔除样品的平均值作为异常下限；在每次被剔除样品的平均值中，选择与上下相邻变化梯度显著的平均值作为异常分级的界线值；并将它们与地质特征相联系，使地球化学异常圈定中最重要的３个参数被赋予地质涵义，分级界线与金的成矿阶段相对应，对异常的评价能够得到正确的结论。

ANOMALY DEFINITION AND EVALUATION OF GOLD FOR BEDROCK GEOCHEMICAL EXPLORATION

aking into account of geological characteristics of gold mineralization,the authors has proposed a series of methods to define the background value, threshold and anomaly classification. The "target tracing prospecting" method is favourable to collect two kinds of materials for two kinds of geochemical fields: background field and anomaly field in large-scale bedrock geochemical exploration. The data of each variable are processed to submit the normal distribution law according to the principle that if a value is larger than x 3s, here x is the mean of a variable and s is the standard deviation, it should be rejected. The procedure is carried out untill the value is not more than x 3s,and the final result of x and the mean of rejected data of the last step are considered as the background and threshold for the corresponding variables.The midvalues of two or the largest intervals of means of whole steps are taken to be the limits for different anomaly levels. It is important to find the relationship between geochemical limits and geological characteristics or gold-forming substages in order to give geological implication to each of the three important parameters for the anomaly definition and to take reliable conclusion for anomaly evaluation.