分形含量梯度法在地球化学异常圈定中的应用

Application of Fractal Content-Grads Method to Geochemistry Anomaly Delineation

地球化学异常下限的确定对于圈定异常,指导找矿非常关键.传统的均值加固定系数乘标准差计算常下限的方法只适用于地球化学数据呈正态分布或对数正态分布的情况,但是在实际情况中,地球化学元素的含量分布并不只局限于正态分布或对数正态分布,而是具有典型的分形特征,在处理化探数据时采用分形方法能有效地克服传统方法的不足.本文以青海省大柴旦镇柴达木山南坡一带1∶1万土壤地球化学测量数据为例,首先用分形含量面积法确定各元素的异常下限值,圈定化学异常区域,在异常区域内再用分形含量梯度法圈定异常浓集中心,进而确定各元素异常的分带性.与均值加2倍标准差作为异常下限相比,用分形含量面积法圈出的异常面积更大一些,对弱小异常的识别更为理想.经后期工程验证,用分形含量梯度法圈出的异常浓集中心与圈定发现的矿体吻合较好,比用传统的均值加固定系数乘标准差确定浓集中心的方法更为客观,这说明分形含量梯度法在圈定地球化学异常浓集中心时是实用而有效的.

Determination of lower limit for geochemical anomaly is the key to delineate geochemical anomalies and guide prospecting.The traditional mean plus the value that the fixed coefficient by standard deviation way of determining thresholds is only suitable for the geochemical data that are of positively normal distribution or lognormal distribution patterns.However,geochemical distribution of elements is not confined to normal distribution or lognormal distribution,but with typical fractal characteristics.Fractal method can effectively overcome the deficiency of the traditional method.Based on the 1 ∶ 10000 soil geochemical data in the south slope of Caidamu in dacaidan town area of qinghai province as an example.Using the fractal content-area method to determine single-element geochemistry of the anomaly lower limit,re-use concentration gradient method of fractal to delineate abnormal concentration center and then to determine the abnormal zonation.Compared with the method that mean plus 2 times the standard deviation is the anomaly threshold,the area outlined by using fractal content-area method is bigger,and is better coincidence with the mineralization-concentrated areas.By the late engineering verification,the geochemical concentration focus enclosed by using fractal content-grads method shows better co.incidence with the delineation of ore body.It is more objective than the traditional way that the mean plus fixed coefficient by the standard deviation of enclosing the geochemical concentration focus.The result shows that content-grads method is feasible and effective for enclosing the geochemical concentration focus.