Repty: Sulphur isotope composition of the Brunswick No.12 massive sulphide deposit, Bathurst Mining Camp, New Brunswick: implications for ambient environment, sulphur source, and ore genesis

摘要

We welcome M. Solomin's discussion of our paperon the origin of sulphur in the world-class Brunswick No. 12massive sulphide deposit and the ambient seafloor conditions atthe time of its formation. It allows us to not only respond to analternative interpretation of our data presented by the dicusser, butalso to address broader fundamental questions related to thegenesis of massive sulphides in the Bathurst Mining Camp inparticular and ancient seafloor sulphide deposits in general. Thesequestions include, why are seafloor hydrothermal deposits moreprevalent at certain times in Earth history than at others? Why aremany seafloor massive sulphide deposits hosted by laminatedcarbonaceous sediments representing reduced seafloor conditions?What is the origin of sulphur in massive sulphide deposits with δS values significantly greater than values for reduced sulphurmeasured in modern seafloor hydrothermal systems and predictedby chemical modelling? Is an ambient reduced water column anessential requirement for the formation and preservation of manyseafloor massive sulphide deposits, particularly giant volcanogenicmassive sulphide (VMS) deposits?Reduced sulphur (as dissolved sulphide)plays an essential rolein the precipitation of sulphides at or near the seafloor. The redoxconditions at the time of sulphide formation are also importantsince they determine the extent of sulphide oxidation at theseafloor and whether or not sulphide particles in buoyanthydrothermal plumes or density-stratified brine pools are destroyedby seawater oxidation or settle to the seafloor to form beddedsulphide deposits. The constraints on the seafloor environment andsulphur isotope compositions are discussed below.