Magmato-hydrothermal space: A new metric for geochemical characterisation of metallic ore deposits

Abstract

“Magmato-Hydrothermal Space” is a new mathematical construct where 24 ore and pathfinder elements are used to quantify ore-element signatures. Quantification allows relationships between ore deposit samples to be mapped. The broad-scale view of Magmato-Hydrothermal Space reveals three important trends: (1) Zn-Pb sediment-hosted mineralisation to igneous-associated Cu-Au mineralisation, (2) Cu-Au mineralisation to Au-only mineralisation, and (3) ultramafic associated magmatic Ni-Cu-PGE mineralisation through Cu-Au mineralisation to granitoid-associated Mo, W and Sn mineralisation. The view provided by Magmato-Hydrothermal Space reveals that there is a spectrum of ore element signatures that mirrors the spectrum of ore deposit classes described in the literature.Geochemical variations within individual ore deposit classes are examined for orogenic-Au, VHMS, epithermal and sediment-hosted Cu samples. Sub-groups within each of these classes are compared on element enrichment diagrams and described in the context of Magmato-Hydrothermal Space. Orogenic Au samples are divided into two sub-groups of As-Sb rich mineralisation and four sub-groups of relatively As-Sb poor mineralisation. The As-Sb poor sub-groups include a Te-Cu-Ag rich sub-group that overlaps with the porphyry Cu class and a Te-W-(Bi-Mo) rich class dominated by granitoid hosted deposits. The VHMS class ranges from a Cu-rich sub-group that overlaps with porphyry Cu and IOCG classes through a Cu-Zn sub-group to two Zn-Cu sub-groups, one of which overlaps with the SHMS class. The epithermal class is divided into Zn-rich, Cu-rich and base metal – poor sub-groups.