Evolution of a hydrothermal ore-forming system recorded by sulphide mineral chemistry: A case study from the Plaka Pb-Zn-Ag Deposit, Lavrion, Greece

Laser ablation inductively-coupled plasma mass spectrometry and electron probe microanalysis were used to investigate the trace-element contents of sphalerite, chalcopyrite and pyrite from the Plaka Pb-Zn-Ag deposit, Lavrion, Greece. Using petrographic observations, the analytical results could be linked to the temporal evolution of the Plaka ore-forming system.
Sphalerite chemistry (Ga, Ge, In, Mn and Fe content) reliably records the temperature evolution of the system, with formation temperatures estimated by sphalerite geothermometry reproducing microthermometric results from previous fluid inclusion studies. Chalcopyrite chemistry also shows systematic variations with formation temperature, particularly for Cd, Co, Ge, In, Sn and Zn concentrations. Pyrite was only found in association with early high-temperature mineralisation, and no clear temperature trends could therefore be identified. We note, however, that its Se content is consistent with formation at the temperatures estimated from sphalerite chemistry.
In addition to these observations, comparing the results for the three investigated minerals allowed us to identify different classes of trace elements according to their temporal and spatial distribution in the ore-forming system. For instance, In concentrations appear to be highest in early high-temperature sulphide assemblages from the southern part of the deposit, while Ge concentrations are highest in late low-temperature assemblages from any part of the deposit.
These results demonstrate that the detailed study of multiple minerals in a single ore-forming system, well documented in terms of geology, paragenesis and conditions of formation, still has considerable untapped potential to provide important new insights into ore-forming processes.