Major ions, δ~(18)O, δ~(13)C and ~(87)Sr/~(86)Sr compositions of water and precipitates from springs along the Cameroon volcanic line (Cameroon, west Africa): Implications for provenance and volcanic hazards

摘要

A combined study of major ions, delta O-18, delta D, C-13, Sr-87/Sr-86 isotopes, X-ray diffraction, scanning electron microscopy, and electron probe microanalyses on springs and spring mineral precipitates along the Cameroon Volcanic Line (CVL) was undertaken to understand water chemistry, and infer the type and origin of the precipitates. The waters are of evaporated Na + K-Cl and non-evaporated Ca + Mg-HCO3 types, with the more mineralized (electrical conductivity-EC of 13130 mu S/cm) Lobe spring inferred to result from interaction of circulating 49 degrees C waters with magmatic volatiles of the active Mt. Cameroon. Water mineralization in the other springs follows the order: Sabga A Sabga B Bambui B Bambui A Nyos Cave. But for the Nyos Cave spring, all other springs contain fluoride (up to 0.5-35.6 mg/l above WHO potable water upper limit). The Sabga spring contains arsenic (up to 1.3 mg/l above the WHO limits). The springs show low fractionation temperatures in the range of 19-43 degrees C. The Lobe and Sabga A springs are precipitating dolomite (CaMg(CO3)(2)), while the Nyos Cave, Bambui A, Bambui B and Sabga B springs precipitate trona ((Na3H(CO3)(2).H2O). Our data suggest a marine provenance for the carbonates, and point to a volcanic input for the Lobe, Nyos, Sabga A, and Bambui A springs. The latter springs are therefore proposed as proxies for monitoring volcanic activity for hazard mitigation along the CVL.