A novel conceptual model of intrusion related gold bearing systems and exploration tools

Despite numerous debates conducted in the last two decades, the concept of intrusion related gold systems IRGS remains controversial and sometimes befuddling. The key issue drifts from case to case, i.e., initial to subsequent proposed classifications, presence of gold in reduced fluids-porphyritic environments, non-porphyry gold in orogenic terrains and participation of non-magmatic gold fluids in depositional processes. Trying to avoid atypical or particular aspects of certain deposits, a genuine metallogenetic depiction intends to enhance the intrusion related systems meaning. Gold is either a major constituent or a mere byproduct. A vertical metal zonation develops from surface to depth: Au, Ag → Cu, Pb, Zn → Cu, Au → Cu, Mo (Au), W → Fe, Cu, Au (Co,W) → U, Ce, La. Whether the relationship between different intrusion related occurrences is well known at shallow depth (epithermal, mesothermal, porphyry), so far less knowledge and understanding is assigned to deep seated mineralization (porphyry, Iron Oxides- Copper-Gold/IOCG). A specific relationship between those two deep seated ore styles emerges, that is the IOCG, confined to magmatic-hydrothermal type, is situated in the root zone of a deep porphyry system. Complementary information about updated classic exploration tools encompasses specifically geochemical association, geophysical signature, key alteration minerals, Au/Ag ratio and, last but not least, type minerals that contain/include gold in each intrusion related environment. A further valuable tool is given by the estimate of Au grade range specific to each gold bearing mineral sample in shallow or deep seated setting