Copper porphyry exploration: Combination of X-ray investigations with other methods

Copper porphyries represent complex alteration zones, hosting variable grades of Cu- (Au-Mo), but also Pb, Zn, Te, Bi and Ag. Processing of these ores becomes more difficult and more expensive as metal grades are lower and highly variable. Reducing the operational costs while increasing the resource efficiency at constant production is the challenge for the mining industries. Samples from specific alteration zones of the Niaz porphyry copper (Mo)-deposit in NW Iran were analyzed by different methods (e.g. scanning electron microscopy (SEM), dual energy (DE) and multi energy (ME) X-ray transmission (XRT) as well as X-ray computed tomography (CT)). The alteration zones are potassic-phyllic, propylitic, phyllic-argillic and peripheral skarn. The propylitic alteration zone is characterized by a coarse-grained diorite composed of feldspars, amphiboles, epidotes, biotite, chlorite, and minor calcite. Ore phases are pyrite, molybdenite, galena Te-Bi phases and sphalerite. The phyllic-argillic mineralized zone is represented by a microgranular quartz-diorite composed of quartz, feldspars, amphibole, biotite, kaolinite and rare siderite. Ore phases are various Cu-sulfides. The peripheral part of the porphyry is a coarse-grained skarn composed of chlorite, amphibole, garnet, epidote, rare diopside, quartz calcite and apatite in the matrix and veins. Ore phases are chalcopyrite, pyrite, Ag-sulfides and Te-Bi clusters attached to galena. Analysis of reconstructed three-dimensional CT volume data revealed structural information as well as two or three different groups of elements (low, medium and high effective atomic number). With these data, in combination with other methods, mine-geologists can assign grey values to minerals based on densities. Thus, it is possible to locate rapidly mineralization in the alteration zones for unknown samples. With XRT, fractions of heavy and light materials can be revealed in two-dimensional radiographs. While CT is useful for a small selection of samples as it is time consuming, XRT can be used in real-time on conveyor belts.