Models and case history studies of deep-penetrating geochemical exploration for concealed deposits in basins

In the past twenty years, more and more mineral deposits were discovered in basins. The traditional geochemical exploration methods are not effective in mineral exploration of concealed deposits in basins. Deep-penetrating geochemistry provides a new approach for exploration in basins. The case history studies from the concealed sandstone-type uranium deposit hosted in a sedimentary basin, the concealed Ag-polymetallic deposit in a volcanic basin, the concealed Cu-Ni deposit in a basin covered by metamorphic rocks and the concealed Au deposit covered by loess have led the authors to reach the following conclusions:(1) Uranium is converted to uranyl ionsUO₂²⁺ under the oxidizing condition and is easy to migrate under the influence of groundwater movement along sandstone pore structure and tectonic fissures; the uranyl ions are absorbed on clay minerals after migrattion to earth's surface, because clay layers have a net negative charge, which needs to be balanced by interlayer cations; leaching of mobile forms of elements in soils and separation of fine-grained soils can be used to determine the orebodies; (2) The Yueyang Ag-polymetallic deposit was nearly formed in the same period as the volcanic rock; Ore-bearing fluid migrated to earth's surface along tectonic fissures in the formation process of the deposit; mobile forms of metals in ore-bearing fluid were absorbed on clay minerals; leaching of mobile forms of elements in soils and separation of fine-grained soils can be used to determine the orebodies in volcanic basins; anomalies of elements are directly displayed over the blind orebodies; (3) the contact zone between intrusive mass and metamorphic rock generated a lot of tectonic fissures in the process of emplacement of the ultrabasic intrusion; and the fluid would take ore-forming elements Cu and Ni and migrate to earth's surface and form cyclic anomaly; (4) ore-forming elements Au and Ag in the form of complexes, nano-scale elemental or alloy particles taken by fluid migrated upward in the oreforming process of Au deposits in Luoning basin; compound or nanoparticles which dissociated from orebodies or rocks could penetrate loess pores and migrated upward to earth's surface and were absorbed on clay minerals; separation of fine-grained soils can be used to determine the orebodies. In this paper, the authors built deep-penetrating geochemical models for mineral deposits in basins based on application effects, anomaly shapes, characteristics of the covers, occurrences of the ore-forming elements, and migration patterns. The above results will provide theoretical and technical support for geochemical exploration in basins.