传统填图法在半覆盖区的改进——第四系岩性填图法

传统地质填图方法一般按成因划分第四系填图单位,但在半覆盖区,往往存在第四系不同成因物质混杂堆积的现象,若按成因划分填图单位,则会造成混乱。笔者在填图实践中,尝试按岩性划分第四系填图单位,这一做法能避免这种混乱,且有利于第四系中基岩信息的发掘,并能为勘查地球化学工作提供景观依据,这种新式填图方法可称为"第四系岩性填图法"。用岩性划分第四系填图单位需要使用统一的分类命名方案,本文使用了按碎屑特征进行分类的方案,主要考虑第四系松散堆积中碎屑的粒径、形态和含量变化。第四系岩性填图法中填图单位的划分需要参照这一分类命名方案,并可选用颜色、构造、次要碎屑类型等修饰性要素做为辅助划分依据。填图单位划分一般在踏勘和剖面实测中完成,第四系岩性填图法剖面测制较为复杂,除采用传统垂向测制方法外,还需运用横向测法和横向-垂向联合测法,通过剖面工作,可细化填图单位划分方案,并可评价不同填图单元基岩恢复的可靠性。第四系岩性填图法除需要编制传统地质图外,还需要编制基岩推断地质图或是在报告中制作插图以阐述此成果。

Quaternary Petrography-based Mapping Method: A Modified Mapping Technique for Mineral Exploration in the Partially Covered Area

Mapping units (MU) of Quaternary sediments generally used now in regional geological survey are genesis-MUs in nature for they are classified according to depositing process. Though the genesis-MU method has been broadly used in the past decades, muddle would occur in the partially covered area because of mixture of the Quaternary sediments of different origins. In this study, the authors developed a new mapping method, named petrography-based Quaternary mapping method (PBQMM), for mineral exploration in the partially covered area with the purpose of avoiding such confusion. In this method, MUs are classified according to petrographic features; as for Quaternary sediments, such factors as shape, size, and content of gravel-size fragments are the key elements referred. Based on these elements, base type and integrated name can be determined to distinguish Quaternary sediments of different locations. Like the traditional mapping method, the PBQMM can extract information on distribution and petrography of Quaternary sediments; nevertheless, it can deduce bedrock information, and help enhancing and explaining geochemical anomalies. To get the additional information efficiently, researchers should seek and survey geological profiling revealing Quaternary sediments as well as bedrock. Traditional geological map and deducted bedrock geological map are both needed in the PBQMM so as to express the information correctly.