RING ZONING OF THE NEOGENE GOLD AND COPPER METALLOGENY IN THE METALIFERI MTS., ROMANIA

The Neogene metallogeny in the Metaliferi Mts. is included in the so-called Golden Quadrilateral which represents the most important metallogenic unit of Romania and which comprises the largest gold deposits in Europe (e.g. Rosia Montana and Sacaramb).

During the 1970s, 10 porphyry copper structures have been discovered in the area, of which, the best know is that of Rosia Poieni – a “copper counterpart” of the gold-silver deposit in Rosia Montana. The epithermal low-sulfidation gold-silver and porphyry copper mineralization is commonly represented by ring structures centred on porphyry-type columns.

The vertical zoning of local mineralized bodies was first pointed out in 1941 (Ghitulescu and Socolescu) and later sustained by Borcos (1994). In some circumstances, a lateral zoning could be described which separated the Au mineralization from Au – base metal ore concentrations, such as in the case of Magura, Hondol and Coranda. In our view, the lateral ring zoning model may be generalized for the Neogene metallogeny in the Metaliferi Mts.

Such a model reflects the spatial distribution of mineralised areas within this unit – i.e. gold-silver veins distributed in a circular manner around “porphyry roots” – Bolcana, Musariu, Valea Arsului, Rosia Poieni, Bucium Tarnita. The zoning process has evolved during two stages:

1) the Upper Cretaceous (K2) stage – when initial zones have formed within the major batholithic domes: i.e., copper, polymetallic and gold-silver, with a pattern analogous to the Fersman zoning model. This idea is sustained by the fluid inclusion data determined on bornite and quartz, pointing to temperatures of 970-1170o C, if the partitioning is accepted of Cu and Au (Te, As, Sb) in saline volatile-rich/melt inclusions during the primary boiling at the magmatic stage.

2) During a second stage (Neogene)caldera-like circular volcanism has differentially remobilised the initial peri-batholithic zones. Intrusive columns with associated porphyry mineralization formed in the central, peak areas of the magmatic bodies. Simultaneously, epithermal gold-silver mineralization accumulated in the satellite volcanoes and ring shaped structures have formed which confer the metallogenic specificity of the Golden Quadrilateral.

References:

Borcos M. (1994) - IGCCP Project No. 356, Field trip guide, GIR, 43 pp.

Ghitulescu T.P., Socolescu M. (1941) - An. Inst. Geol., 21, p. 181 – 464.