北京怀柔云蒙山地区花岗岩风化过程的地球化学基因

地球化学基因是近两年提出的一种新的地球化学示踪技术,本文选择北京怀柔云蒙山地区两个邻近的花岗岩风化剖面(编号为B和C)来分析岩性地球化学基因和金矿化地球化学基因的属性特征.剖面B样品的化学蚀变指数CIA变化为51.3～58.9,WIG的范围为89.4～68.6,属于初始风化程度;剖面C样品的CIA变化为52.4～78....

Geochemical genes related to granite weathering in the Yunmengshan area of Beijing,China

The geochemical gene technique is a new geochemical tracing technique formally proposed over the past two years. In this investigation, samples from two adjacent weathering profiles (B and C) developed in granite in the Yunmengshan area of Beijing, China were collected to test two geochemical genes named lithogene and gold metallogene. In samples from profile B, the chemical index of alteration (CIA) varied between 51.3-58.9, and the weathering index of granite (WIG) varied between 68.6-89.4, indicating incipient weathering in this profile; while in samples from profile C, CIA varied between 52.4-78.4, and WIG between 25.3-84.8, indicating intermediate weathering in profile C. The noticeable difference of weathering degrees between the two adjacent profiles indicates that different micro-environment may result in significantly different weathering products in the same granite. The lithogene similarity between samples and fresh granite varied from 85% to 100% in profile B and 90% to 100% in profile C, while the gold metallogene similarity between the two varied from 85% to 100% in profile B and 80% to 100% in profile C. With respect to top soil, the similarity of lithogenes varied from 80% to 100% in profile B and 90% to 100% in profile C, and the gold metallogene similarity varied from 85% to 100% in profile B and 80% to 100% in profile C. According to the criterion that gene similarity above 80% indicates similar genes, the lithogene and gold metallogene illustrate not only good heredity and inheritance in each profile but also high similarity between the two profiles. Besides, with respect to the ideal gold ore (gold metallogene 12020202020), the similarity of gold metallogenes varied from 25% to 50% in profile B and 30% to 50% in profile C. According to the criterion that mineralization can be recognized when the gold metallogene similarity reaches 40%, one mineralization layer of ca. 1 m thickness can be recognized in each profile. Thus, the gold metallogene may also be used as an integrated geochemical indicator in gold exploration.