Geodynamic controls of epithermal mineralisation in the Gutii Neogene volcanic region (Baia Mare, Romania.)

The gold-bearing massive sulphides have generally been related to three volcanic episodes, though recent Ar-Ar dating suggests only two. The relationships between mineralisation and associated hydrothermal facies, and the stratigraphic position of the volcanic rocks as determined by palaeontology, suggest that volcanic activity and its associated mineralisation migrated with time from NNW to SSE of the district. The main Pannonian period of mineralisation is correlated with a major break in volcanic activity and evidence of phreatomagnetic explosion in most mines, where breccia veinlets, dykes and pipes all contain a very wide range of clast sizes and origins. The presence of several generations of breccia dykes, some containing mineralised and hydrothermally altered pebbles, show how their evolution was related to sinistral strike-slip faulting and how the mineralising phenomena generally followed a sequence from Pb-Zn-Cu through Sb to a gold-bearing association. Pb isotope signatures are usually closely spaced, not varying for a particular generation of ore within a single mine but only from one mine to another. Such signatures are typical of Neogene mineralisation deriving from a single crustal source.
The gold-bearing massive sulphides have generally been related to three volcanic episodes, though recent Ar-Ar dating suggests only two. The relationships between mineralisation and associated hydrothermal facies, and the stratigraphic position of the volcanic rocks as determined by palaeontology, suggest that volcanic activity and its associated mineralisation migrated with time from NNW to SSE of the district. The main Pannonian period of mineralisation is correlated with a major break in volcanic activity and evidence of phreatomagnetic explosion in most mines, where breccia veinlets, dykes and pipes all contain a very wide range of clast sizes and origins. The presence of several generations of breccia dykes, some containing mineralised and hydrothermally altered pebbles, show how their evolution was related to sinistral strike-slip faulting and how the mineralising phenomena generally followed a sequence from Pb-Zn-Cu through Sb to a gold-bearing association. Pb isotope signatures are usually closely spaced, not varying for a particular generation of ore within a single mine but only from one mine to another. Such signatures are typical of Neogene mineralisation deriving from a single crustal source.