Bachelor Thesis

Mudpots as proxies for volcanic, volatile As and Sb

Alexander Hurley (11/2012-09/2013)

Support: Britta Planer-Friedrich, Julia Arndt

Gas phase sampling of volatile metal(loid)s in hydrothermal systems still poses methodical difficulties. To avoid these, mudpot chemistry is proposed as a proxy for volatile metal(loid) exhalation. In comparison with hot springs, higher residence times for gas transported through mudpots, promoting solution into liquid phase, were assumed. Arsenic, antimony and thallium, were considered for a possible proxy functionality. Hence, mudpot chemistry has to be attributed to gas emissions of the hydrothermal system. Enrichment factors (Mg-normalized; liquid-bedrock ratio: logF(i)AQ=R) were used to infer non-surface contributions. Stable water isotope ratios (δ 2H, δ18O) and sulfur were utilized to determine liquid phase origin. 32 mudpots (replicates taken at 2) in Yellowstone National Park were sampled. Total metal(loid) concentrations (As, Sb, Tl, Mg) were obtained from liquid (filtered) and solid phase (altered host rock; microwave-extraction before analysis) via ICP-MS. As, Sb, Tl and S (liquid phase) species analysis was performed using IC-ICP-MS. δ2H and δ18O values were determined by TC-IRMS (external). Supporting parameters (temperature, pH, spec. conductivity) were recorded on site. Replicate sampling revealed parameter stability during the study period. Enrichment factors showed strong variations between elements (Tl < Sb < As) and thermal areas. A negative correlation between logF(As)AQ=R and pH was observed. Non-surface contribution of As or Sb, or both, were identified in 5 of 7 thermal areas, implying enrichment by hydrothermal processes. Hot springs showed higher logF(i)AQ=R for pH>3. δ2H, δ18O and sulfur allowed determining influence of meteoric water and identification of vapor-dominated systems to some extent. Inferring from species analysis, the presence of volatile arsenic compounds was likely. Methodical constraints did not allow a reliable designation of proxy functionality. However, sampling mudpot chemistry could allow to directly focus volatile metal(loid) exhalation, in contrast to hot springs, and should therefore be further investigated.