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

Adam Eskdale, D J Smith, V V Ene, M Negulici, D Onescu

Research output: Contribution to journalArticlepeer-review


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.
Original languageEnglish
Article number105135
JournalOre Geology Reviews
Early online date30 Sept 2022
Publication statusPublished - Nov 2022

Cite this