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Economic By-Products in Copper Porphyries: Silver in the Ascutita Cu-Porphyry, Romania

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posted on 2022-11-07, 16:36 authored by Adam E Eskdale, Daniel James Smith, Vlad-Victor Ene, M Negulici, D Onescu

The Ascutita porphyry Cu-Mo prospect is located in the SW Poiana Rusca Mountains, Romania. Current assessment estimates a resource of 110 Mt @ 0.15 % Cu-equivalent. In relatively low-grade deposits such as this, by-products such as Ag (2–3 ppm) are important in determining the economic feasibility of the overall orebody. Assayed Cu and Ag have a clear downhole correlation. In the absence of other silver-bearing minerals, or correlations of Ag with other sulphides (e.g., Pb indicating Ag-bearing galena) this suggests Cu-sulphides are instead the dominant hosts of Ag. Petrography of 21 samples from various drillholes show chalcopyrite is the dominant Cu-sulphide present, spatially associated to two stages of pyrite. LA-ICP-MS analysis determined that both chalcopyrite and Stage 3 pyrite (younger) co-host the Ag. Chalcopyrite hosts Ag mostly in solid solution, whilst pyrite hosts Ag within a variety of complex, sulphosalt micro-inclusions undetectable on an SEM, but apparent on time-resolved LA-ICP-MS spectra. These micro-inclusions lock in Cu and Ag, with a bulk median Ag content of 0.79 ppm. The pyrite also contains mean concentrations of 52 ppm Bi and 46 ppm Se: both typically penalty-incurring elements at smelters. The chalcopyrite has a greater Ag concentration than the pyrite (median = 30.3 ppm with potential for 181 ppm), presumably in solid solution. The lattice-bound Ag partitioned into the chalcopyrite through monovalent, simple substitution of Ag+ for Cu+. Occurrence of Ag in the main Cu-bearing phase at Ascutita raises the possibility of combined recovery, and this study demonstrates the value of trace element analysis in geometallurgical assessments of orebodies.


Reid doctoral scholarship of Royal Holloway University of London

Department of Geography, Geology, and the Environment at the University of Leicester

UKRI Interdisciplinary Circular Economy Centre for Technology Metals (TechMet)

Engineering and Physical Sciences Research Council

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School of Geography, Geology and Environment, University of Leicester


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