DIAGENESIS, SULPHUR AND GIANT ZINC DEPOSITS
Moore Institute Seminar Room, NUI Galway
Admission is free. (James Hardiman Library Main Entrance/Turn right under the stairs)
Zinc is among the top four mined metals in the world and societal demands require a long-term stable supply for a growing market. The largest Zinc deposits in the world are massive sulphide deposits formed in carbonaceous mudstones; many are of Paleoproterozoic and Lower Paleozoic age. In the Lower Palaeozoic deposits of the North American Cordillera, the sulphide bodies are spatially associated with stratabound barite.
The commonly accepted genetic model for these deposits involves the exhalation of a metal-bearing hydrothermal fluid onto the seafloor where it mixes with reduced and oxidized sulphur in a stratified water column (in a restricted basin). In this presentation Dr. Gleeson will show that, in fact, barite and pyrite are formed in the sediment by diagenetic processes that pre-date the hydrothermal system. The diagenetic assemblage forms below the seafloor at the sulphate methane transition zone. The hydrothermal system dissolves barite, and in situ S isotopic data from pyrites show that anaerobic oxidation of methane plays an important role in the generation of a sulphide "trap". The hydrothermal system is superimposed on this diagenetic environment but, typically, does not exhale onto the seafloor. As a result, complex biological-chemical-physical interactions in time and space in the diagenetic environment have an important control on the genesis and size of these important deposits.