ISOTOPIC STUDY OF JAROSITE IN A GOSSAN ON THE WESTERN MARGIN OF GREENLAND ICE SHEET

Sulfate and sulfide minerals were sequentially extracted from an intact gossan containing jarosite. Samples were obtained by augering through oxidized material overlying sulfide-mineralized, Paleoproterozoic metasediments at a site located about 0.5 km from active face of the Russell Glacier near Kangerlussuaq, Greenland. Local hydrogeological conditions during jarosite formation (such as temperature, pH, and source of ground water) can be reconstructed from stable isotopes of oxygen and sulfur, improving the understanding of environmental conditions during retreat of an ice sheet. Although the mineral jarosite was discovered by the Opportunity rover at Meridiani Planum on Mars, the origin of jarosite on Mars remains unclear. The study of jarosite in Greenland may find application to reconstruction of environmental conditions on Mars. X-ray diffraction (XRD), inductively coupled plasma mass spectrometry, and sequential extraction of sulfur fractions were the methods used. Sulfur isotopic compositions of water-leachable sulfate (WLS), acid-leachable sulfate (ALS), acid-volatile sulfur (AVS), and chromium-reducible sulfur (CRS) were analyzed as well as oxygen isotopic compositions of WLS and ALS. XRD data reveal anorthite, quartz, albite, jarosite, muscovite, and microcline. Jarosite was the only sulfate-bearing mineral identified by XRD with abundance up to 8.4 wt % in the reddish yellow zone and below detection level in the underlying grayish black zone. The δ³⁴S values of WLS and ALS are generally lower than corresponding AVS and CRS. The averages of δ¹⁸O and Δ¹⁷O values of WLS and ALS are ‒11.9‰ and ‒8.3‰, ‒0.16‰ and ‒0.17‰ (VSMOW), respectively. Preliminary data suggest that 1) ALS from the Russell Glacier gossan is dominated by jarosite inferred to result from sulfide oxidation in subglacial melt water rather than present-day precipitation; 2) The WLS likely is derived from trace-level gypsum or kieserite; 3) CRS and AVS likely are original stratiform-hydrothermal minerals.