Trends in Mercury Anomaly Amplitude along Faults within the Norris-Mammoth-La Duke Corridor, in and Adjacent to Yellowstone National Park, WY and MT

Abstract

Hg anomalies occur in soils over mapped faults at thermal areas and at intermediate locations along faults that interconnect them. Using established criteria for anomaly threshold identification, we find significant anomalies as large as 180 and as small as 20 ppb in the north boundary between Mammoth Hot Springs and La Duke Spring. Anomaly amplitudes vary along faults in a way that suggests depletion of Hg in aquifers associated with the faults, and amplitude trends suggest flow direction that are in agreement with those inferred by other investigators. Hg depletion is large along fault segments where gas venting is observed, and it is small on segments that lack visible surface manifestations. In several cases we observe discrete amplitude increase in the inferred "downstream" directing. Such augmentation north of Mammoth appear to reflect input of Hg bearing water from intersecting faults "upstream". South of Mammoth a similar increase in attributed to an unmapped fault.