Understanding Geochemical Anomaly Formation Through Transported Cover and Implications for Mineral Exploration: The Australian Experience

摘要

As mineral exploration inevitably moves into regions dominated by transported cover, conventional geochemical techniques are less applicable and thus, increasingly, there is a need for new innovative approaches. But to develop new approaches it is necessary to identify and understand the operating mechanisms capable of transferring metals from buried mineralisation upwards through cover to the surface. In recently completed Australian CSIRO-AMIRA industry project, biological and gaseous mechanisms of vertical metal migration from source to surface were shown to be particularly important in vadose environments. One example of upward element transfer by vegetation occurred in an area of up to 35-m-thick transported cover, where elevated metal concentrations in trees and near-surface caliche reflected underlying Au mineralisation. In another example, microbial communities showed an unusual bacterial activity in the soil over mineralisation. Similarly, metals and hydrocarbons, detected by gas collectors, were transferred to surface as gases and/or aerosols and located the presence of buried mineralisation. Experimental trials have shown that geochemical anomalies can form rapidly but temporal studies suggest the migration of elements may vary in time and in intensity. It is anticipated that our results should promote confidence in mineral exploration in Australia and elsewhere using geochemistry in cover materials.