Hydrogeochemistry of ground and surface waters associated with massive sulphide deposits, Bathurst Mining Camp, New Brunswick: Halfmile Lake and Restigouche deposits

A deposit-scale study of hydrochemical processes has been conducted at the Halfmile Lake and Restigouche massive (Zn-Pb-Cu-Ag) sulphide deposits, Bathurst Mining Camp (BMC), New Brunswick, Canada. Both the Halfmile Lake and Restigouche deposits are hosted in a deformed sequence of Ordovician (465 Ma) felsic volcanic rocks with similar topography and climate. Groundwater flow is dominated by fracture-flow. The two deposits differ in that the Halfmile Lake deposit is steeply dipping with steep structures whereas the Restigouche deposit is closer to surface with shallower structures.;Groundwaters were collected using flow-through bailers and a straddle-packer system that permits recovery of groundwaters from a discrete depth interval. In fracture-controlled rocks, straddle-packer groundwater compositions are more depth representative than bailer groundwaters.;Geochemical modelling and stable isotopic compositions indicate that shallow Ca-HCO3 groundwaters are produced by modern meteoric recharge and the major solutes are controlled by dissolution of fracture and vein carbonate and silicate hydrolysis. The Ca-SO4 groundwaters reflect oxidation of the sulphide minerals by modern recharge waters. Deeper brackish to saline groundwaters from the Restigouche, Heath Steele, Brunswick ;Interaction between oxygenated recharge waters at the Restigouche and Stratmat Main Zone deposits has resulted in elevated levels of metals (e.g., up to 4000 m g/L Pb and 5300 m g/L Zn) which, based on geochemical modelling and borehole geophysics (self-potential anomalies), are produced by sulphide oxidation.;Surface waters collected from the Halfmile Lake and Restigouche deposit primarily represent groundwater discharge based on the compositional and stable isotopic similarity with shallow groundwaters. Geochemical and isotopic modelling indicates that the major solute compositions are controlled primarily by the underlying lithologies and dissolution of carbonate.;Although sulphide-associated metals (Zn, Cd, Pb, Cu, Fe) in surface waters at the Halfmile Lake and Restigouche deposits are low compared to streams draining other deposits and mine tailings, anomalously high values (with respect to local background) occur proximal to the Restigouche massive sulphides. The generally neutral pH values in the BMC results in more subtle base metal anomalies in surface waters which indicates that detailed sampling is required for hydrogeochemistry to be an effective exploration tool in the BMC. Groundwaters have higher base metal abundances and display greater contrast between anomalous and background compositions such that groundwaters have potential in better outlining mineralized targets during a drilling program.* (Abstract shortened by UMI.).;*The appendices are presented on CD-ROM in Microsoft Excel and Adobe Acrobat format with "xl" and "pdf" suffixes, respectively. The files are readable on Macintosh computers as well as Windows 95 and Windows NT.