化探异常的多背景问题

The multi-background problem in geochemical anomaly

通常把多个地质单元中的不同背景值简称为化探异常的"多背景"。两个以上1∶5万图幅联测或工作区存在多个地质单元、数据存在多个母体分布的情况是很普遍的,有些测区不同岩性或地层单元的元素背景差异可以达到数倍至数十倍,这种情况下采用全区统一背景圈定异常,会在高背景区出现大范围与矿无关的异常,而在低背景区掩盖了可能反映隐伏矿体的弱异常。笔者提出采用多个地质单元分别统计元素背景值和异常下限,在多背景情况下用衬度圈定化探异常的处理方法,并比较了该方法与采用全区统一背景圈定异常的差异,以及对异常评价结果的影响。基于多背景圈定的异常,没有边界效应和异常位移现象,同时消除了高背景单元中的大范围外带异常,显示出了一些可能具有寻找隐伏矿前景的低缓异常,突出了找矿信息。在工作区存在多个地质单元,且各单元背景差异明显时,极力推荐采用多单元的多背景圈定异常。

Different geochemical anomalies caused by different geological units are called Geochemical “Multi?Background” for short. There commonly exists more than one geological unit in numbers of 1 ∶50 000 mapping. The geochemical anomaly values of some ele?ments in different geological units can reach the difference as much as several to dozen times. In this case if we only use single anomaly value to draw the geochemical anomaly map, a large anomaly may appear in the high background area not related to ores; on the contra?ry, it is probable that nothing appears in the low background area which may contain a concealed ore boy. This paper discusses the difference of geochemical anomaly maps between single background and multi?background. According to the multi?background, there exist no boundary effects and displacement phenomena in the geochemical anomaly map, meanwhile the large anomaly in high back?ground can be eliminated, and thus only the anomaly in low background that indicates the concealed orebody is displayed. The authors highly recommend using multi?background method to draw the geochemical anomaly map when there are many significantly different ge?ological units in the work area.