Powerful laboratory and real time examination tools for copper porphyry exploration

Copper porphyries represent complex alteration zones, hosting variable grades of Cu- (Au-Mo), but also Pb, Zn, Te, Bi and Ag. Moreover, environmental harmful elements, such as As or Cd are present. It is therefore crucial that mining companies get reliable chemical and mineralogical drill core data from the earliest exploration state on to avoid project failure and to obtain three-dimensional models for mine and processing planning. Systematic sensor-based drill core logging and material sorting coupled with smart data evaluation is the ideal solution for accurate in-field and in-plant real time decision making to reduce waste and anticipate dysfunction during metal production. Risks and operational costs can be reduced while increasing resource efficiency.
In this paper, as an example, specific alteration zones of the Niaz porphyry copper (Mo)-deposit in north-western Iran were investigated by laser-induced breakdown spectroscopy (LIBS), X-ray Fluorescence (XRF), time-gated Raman spectroscopy, dual energy X-ray transmission (DE-XRT), multi energy X-ray transmission (ME-XRT) and X-ray computed tomography (CT). Most of these instruments were combined in the EIT RawMaterials project ANCORELOG. The sensor results were compared and evaluated against laboratory results obtained by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), and optical microscopy for calibration.
Fast LIBS, Raman and XRF core-scanner instruments clearly allow to distinguish the alteration zones: The potassic-phyllic alteration zone is characterized by two differently mineralized rock types: (i) the Cu-mineralized quartz diorite where the key minerals are chlorite and barite, quartz, albite/oligoclase, muscovite and the major ore mineral is chalcopyrite; (ii) the Cu-Mo-mineralized monzonite, where carbonates, orthoclase and albite/oligoclase are the key minerals. Ore minerals are molybdenite and chalcopyrite. The propylitic alteration zone is characterized by a coarse-grained diorite. Key minerals are orthoclase, epidote, sphene and apatite. Molybdenite is the major ore mineral. The phyllic-argillic mineralized zone is represented by a microgranular quartz-diorite. Key minerals are kaolinite-dickite, quartz, albite, muscovite-sericite and apatite. The major ore mineral is chalcopyrite. The peripheral part of the porphyry is a coarse-grained skarn with andradite, calcite, tremolite and epidote as key minerals. The major ore mineral is chalcopyrite. LIBS elemental mapping clearly reflects the ore mineralogy and texture. Analysis of reconstructed three-dimensional CT volume data revealed structural information as well as two to three different groups of grey values. After calibration, eg by SEM or LIBS, mine-geologists can assign these grey values to minerals or elements with low (eg Al, Si), medium (eg Fe, Cu), and high (eg Mo) effective atomic numbers. Our study shows that sensor-based characterization of successive alteration zones and Cu-Mo mineralized zones is possible for unknown samples. XRF, Raman spectroscopy, LIBS and XRT can be used and adapted in-field on mine and exploration sites as well as in plants. Selected samples of drill cores can then be sent for CT analysis and detailed LIBS imaging.