MULTIPLE HOST PHASES OF MERCURY IN THE EARLY PALEOZOIC ROAD RIVER GROUP OF NORTHERN YUKON, CANADA

In order to use mercury (Hg) concentrations as a geochemical proxy for ancient episodes of enhanced volcanism, it is necessary to identify the sedimentary host phases of Hg. By normalizing Hg concentrations to host phase concentrations, researchers can deconvolve the relative contribution of host phase to the Hg trends expressed in stratigraphic columns. Typically, organic matter, sulfide minerals, or clay minerals are identified as host phases on the basis of a high Pearson correlation coefficient (e.g., >0.6) between Hg concentrations and whole rock concentrations of total organic carbon, total sulfur, and aluminum, respectively. The dominant host phase may change throughout a stratigraphic section. To explore the expression of host phase variation, we analyzed 776 samples for whole rock geochemistry, mineralogy, and Hg concentrations from the upper Cambrian–Middle Devonian Road River Group of the Yukon, Canada, which comprises a near complete record of deep-marine deposition along the northeastern edge of the Great American Carbonate Bank. Instead of using single correlation coefficients for our analysis of this extensive dataset (which would only provide summary statistics of the relationship between Hg and different host phases), we developed a moving window method that measures correlation coefficients for many ~100 m intervals in our 2300 m measured stratigraphic section. For the Road River Group, of the 244 intervals that we evaluated, 9 intervals had Hg hosted in organic matter, 17 intervals had Hg hosted in clay minerals, 53 intervals had Hg hosted in sulfide minerals, 20 intervals had Hg hosted in two host phases, and 125 intervals had host phases that were indeterminable or statistically insignificant. Our results illustrate that the sedimentary host of Hg can vary in a single stratigraphic column. We believe that changes in host phase may be controlled by a wide range of physical and environmental processes, such as sedimentation rates, hydrothermal or groundwater discharge, and/or diagenesis. On the basis of our findings, we hypothesize that one or more of these processes likely played a role in the expression of Hg in the Road River Group.