Types of endogenous geochemical fields and their significance for prospecting

Abstract

When prospecting ore deposits in Trans-Baikal region the endogenous geochemical fields (EGF) are taken as the main search element, as was proposed by L.V. Tauson (1983). Such fields are classified into: geochemical fields of dispersion (GFD), concentration (GFC) and removal (GFR). With regard to their formation conditions they are subdivided into magmatic (associated with magmatic chambers), intratelluric (associated with activity of intratelluric emanations), hydrothermal-metamorphic (vadose-thermal solutions), metamorphogenic, and sedimentary-metamorphogenic ones. Magmatic EGFs are divided into three groups: magmatic, pneumatolytic, and hydrothermal stages. This study identified their polygenetic origin and association with ore-magmatic systems. The geochemical fields of ore zones, fields, and deposits result from the late and post-magmatic processes; they also include the EGF of host rocks and those which altered at pre-ore stage of the natural system development.At ore deposits the EGFs are responsible for supply and redistribution of elements through the entire ore formation process. The fields were divided into EGF of poor concentration (contrast coefficient CC normalized after background to 10), mean (CC >10–100), and intense (CC >> 100). The EGF intensity progressively increases at the hierarchy stage: “host rock—pre-ore metasomatite—syn-ore hydrothermalite—ore body—ore pillar”.To summarize, the fields, ore districts, zones, and deposits are characterized by diverse patterns of dispersion, concentration, and removal.The specific features of composition, structure, and zonal distribution of elements in geochemical fields are exemplified by some gold-bearing zones of the Trans-Baikal region. The paper reports new approaches to investigating these natural formations. The authors promote transition from the generally accepted evaluation of a halo separation to the volumetric survey of endogenous geochemical fields (GFD, GFC, and GFR included) of ore deposits and ore-magmatic systems, in general. The acquired evidence supports the assumption that endogenous geochemical fields should be regarded as a complete system differentiated in space and time preserving specifics and pattern of the internal structure.