Dual and Multi Energy XRT and CT analyses applied to coppermolybdenum mineralizations in porphyry deposits
Abstract
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. Five samples from the Niaz porphyry copper (Mo)-deposit in northwest Iran, representing each a specific alteration zone were investigated by dual energy (DE) and multi energy (ME) X-ray transmission (XRT) as well as X-ray computed tomography (CT). These
non-destructive techniques are powerful tools for locating metal concentrations and evaluating porosities. Two samples come from the potassic phyllic zones: (1) A microgranular quartz- diorite is composed of sericitized albite, chloritized biotite and quartz veinlets. Ore phases are chalcopyrite, Fe-sulfides, galena. Magnetite, barite and Ti-oxides also occur. (2) A granular quartz-monzonite is composed of sericitized feldspars, quartz, amphibole, biotite, chlorite and ankerite. Ore phases are molybdenite and Cu-sulfides. Veins are filled with galena and Cu-Bi-sulfides (+Cd, Sb, As). A coarse-grained diorite composed of feldspars, amphiboles, epidotes, biotite, chlorite and calcite characterizes the propylitic alteration zone. Apatite, zircon, sphene, magnetite and ilmenite are present. Ore phases are molybdenite, galena, pyrite, Te-Bi phases and sphalerite. A microgranular quartz-diorite hosting quartz, feldspars, amphibole, biotite, kaolinite and siderite represents the phyllic-argillic mineralized zone. Ore phases are various Cu-sulfides. Minor barite, monazite, thorite and galena occur. The peripheral part of the
porphyry is a coarse-grained skarn composed of chlorite, amphiboles, garnet, epidote, diopside, quartz, calcite and apatite. Ore phases are chalcopyrite, pyrite, Ag-sulfides and Te-Bi clusters attached to galena. Scheelite, magnetite, sphalerite and galena are observed in sulfides. Analysis of reconstructed three-dimensional CT volume data revealed structure information as well as two or three different groups of elements (low, medium and high effective atomic number). With these data, priorly calibrated by SEM, mine-geologists can assign grey values to minerals based on densities. Thus, it is possible to locate rapidly mineralization and evaluate porosities 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 due to its high time consumption, XRT can be used as a real-time process on conveyor belts. This information contribute to ore body modelling and predicting optimal process parameters like crushing or sorting.