MINERALOGY AND GEOCHEMISTRY OF SUSPENDED SEDIMENTS FROM GROUNDWATERS ASSOCIATED WITH UNDISTURBED Zn Pb MASSIVE SULFIDE DEPOSITS, BATHURST MINING CAMP, NEW BRUNSWICK, CANADA

Abstract

Suspended sediments from groundwaters were recovered from two undisturbed massive sulfide deposits (Halfmile Lake and Restigouche) in the Bathurst Mining Camp, New Brunswick, Canada. Suspended sediments in most groundwaters are dominated by quartz and aluminum silicate minerals. Fe oxyhydroxides are probably present as surface coatings in addition to amorphous phases. Suspended sediments from groundwaters recovered from boreholes that intersect the Restigouche orebody near its surface expression consist primarily of Fe, Pb, and Zn sulfate and Fe sulfide minerals. In general, suspended sediments are depleted in the mobile elements K, Rb and Cs compared to host rock-types from both deposits. Suspended sediments show generally flat element-enrichment patterns normalized to respective felsic host-rocks for most other elements, but exhibit strong enrichments in Pb, Fe, Co, Zn, Ag, and Eu. Iron-oxide-rich suspended sediments from a borehole that penetrates massive sulfide gossan at the Halfmile Lake deposit are more strongly depleted in most elements relative to other sediments. At the Restigouche deposit, the degree of enrichment in Pb, Zn, Cu, and Ag in the suspended sediment is greater than for the deeper Halfmile Lake deposit. Compared to coexisting groundwaters, suspended sediments are relatively enriched in Al, Fe, Pb, and relatively depleted in Ca, Sr, and Mg. Potassium and Rb are generally more strongly fractionated into the suspended sediment phase than other mobile elements, suggesting that their abundance in the groundwaters is controlled by secondary phases (illite – white mica), consistent with SEM and XRD data. Comparisons of groundwaters, suspended material and host rocks yield important information regarding relative fractionation of major and trace elements among these reservoirs. Suspended sediments proximal to massive sulfide ore have elevated Fe/Ti and base-metal contents; with increasing distance away from mineralization, Al/(Al + Fe + Mn) values increase, base-metal contents decrease, and Zn/Pb values increase. The elevated base-metal content of suspended sediments associated with massive sulfides is important, as mining activities in the Bathurst mining camp can result in changes in groundwater Eh–pH conditions, potentially resulting in greater dispersion of metals that are presently strongly sorbed onto sediments.