Origin of mineralising fluids in Irish-type deposits: constraints from halogens.

A preliminary study of halogen compositions of fluid inclusions from the Tynagh and Silvermines lead-zinc deposits and veins hosted by the Lower Palaeozoic basement in Ireland has identified a complex range of fluid mixtures but suggests that seawater or evaporated seawater had a fundamental role in most of the fluid types recognised. The 10-15 wt% NaCl equiv. principal ore-fluid end-member observed in the basement and in the overlying deposits probably originated as partially evaporated seawater or seawater which had been dehydrated by fluid-rock interaction. The end-member saline fluid found at Tynagh has the halogen composition of a Cr-rich fluid. The involvement of evaporitic brines provided a potentially important constraint on the timing and genesis of Irish base metal deposits.
A preliminary study of halogen compositions of fluid inclusions from the Tynagh and Silvermines lead-zinc deposits and veins hosted by the Lower Palaeozoic basement in Ireland has identified a complex range of fluid mixtures but suggests that seawater or evaporated seawater had a fundamental role in most of the fluid types recognised. The 10-15 wt% NaCl equiv. principal ore-fluid end-member observed in the basement and in the overlying deposits probably originated as partially evaporated seawater or seawater which had been dehydrated by fluid-rock interaction. The end-member saline fluid found at Tynagh has the halogen composition of a Cr-rich fluid. The involvement of evaporitic brines provided a potentially important constraint on the timing and genesis of Irish base metal deposits.