5:15 PM - 7:15 PM
[HRE12-P04] Geochemical characteristics of groundwaters, hot spring waters, lake waters, and sediments in Lake Abhe, Djibouti
Keywords:lithium, boron, Sediment, Lake Abhe, Djibouti
Djibouti is situated in the southeastern part of the Afar Depression, between three tectonic plates, the Nubian plate at the west, the Somali plate at the southeast, and the Arabian plate at the northeast. Lake Abhe is situated in the southwestern part of Djibouti, near the border with Ethiopia. Although usually there is no inflow, River Awash is connecting to Lake Abhe, and there is no out-flow rivers, so the water level of the lake is regulated by evaporation. In Lake Abhe, travertines form from hot spring waters, when water level of the lake is relatively high. There are some hypotheses regarding the origins of lithium in the lake. One of the hypotheses is that lithium in brines of the lake originates from hydrothermal fluids. This study aims to reveal the geochemical characteristics of groundwaters, lake waters, hot spring waters, and sediments close to the sampling points of waters. We employed methods of ICP-MS, AAS, and XRD analyses, and microscopy.
Hot springs around Lake Abhe are located along a fault. All water samples have pH values between 7.9 and 10.2. with an average of 9.2, indicating a slightly alkaline. Major cations and anions in the lake water samples are in the order of Na > K > Ca > B > Li and Cl- > SO42- > HCO3, respectively. Those of groundwaters and hot springs water are Na > Ca > K > Mg > B > Li and Cl- > SO42- > HCO3, respectively. Among the major cations of the lake water, Na alone contributed 94 %, whereas K and Ca contributed only 3.5 % and 1.6 %, respectively. Among the major anions, Cl- alone contributed 60 %, whereas SO42- and HCO3- contribute 25 % and 15 %, respectively. As for the groundwater and hot springs water, Na alone contributed 70 %, whereas Ca, K, and Mg contribute 13 %, 8 %, and 5 %, respectively, and among the major anion, Cl- contributes 70 %, whereas SO42- and HCO3- contribute 20 % and 10 %, respectively. Lithium concentrations of the lake waters, hot spring waters, and groundwaters range from 2.1 to 3.2 mg/L, 0.2 to 0.4 mg/L, and 0.02 to 0.2 mg/L, respectively. Boron concentrations of the lake waters, hot spring waters, and groundwaters range from 23.1 to 43.1 mg/L, 1.3 to 2 mg/L, and 3.1 to 4.8 mg/L, respectively. Lithium concentrations of the sediments near the water sampling points of the lake waters, hot spring waters, and groundwaters are 11.7–87.1 ppm, 22.6–66.4 ppm, and 7.5–10.2 ppm, respectively, whereas boron concentrations of those are 5.2–63.7 ppm, 0.9–92.7 ppm, and 5.7–105.7 ppm, respectively.
The sediments from the lake are mainly clay composed of plagioclase, calcite, illite, kaolinite, and montmorillonite. The sediments near the hot springs are composed of plagioclase, pyroxene, calcite, quartz, and smectite. The travertine is composed mainly of calcite.
Hot springs around Lake Abhe are located along a fault. All water samples have pH values between 7.9 and 10.2. with an average of 9.2, indicating a slightly alkaline. Major cations and anions in the lake water samples are in the order of Na > K > Ca > B > Li and Cl- > SO42- > HCO3, respectively. Those of groundwaters and hot springs water are Na > Ca > K > Mg > B > Li and Cl- > SO42- > HCO3, respectively. Among the major cations of the lake water, Na alone contributed 94 %, whereas K and Ca contributed only 3.5 % and 1.6 %, respectively. Among the major anions, Cl- alone contributed 60 %, whereas SO42- and HCO3- contribute 25 % and 15 %, respectively. As for the groundwater and hot springs water, Na alone contributed 70 %, whereas Ca, K, and Mg contribute 13 %, 8 %, and 5 %, respectively, and among the major anion, Cl- contributes 70 %, whereas SO42- and HCO3- contribute 20 % and 10 %, respectively. Lithium concentrations of the lake waters, hot spring waters, and groundwaters range from 2.1 to 3.2 mg/L, 0.2 to 0.4 mg/L, and 0.02 to 0.2 mg/L, respectively. Boron concentrations of the lake waters, hot spring waters, and groundwaters range from 23.1 to 43.1 mg/L, 1.3 to 2 mg/L, and 3.1 to 4.8 mg/L, respectively. Lithium concentrations of the sediments near the water sampling points of the lake waters, hot spring waters, and groundwaters are 11.7–87.1 ppm, 22.6–66.4 ppm, and 7.5–10.2 ppm, respectively, whereas boron concentrations of those are 5.2–63.7 ppm, 0.9–92.7 ppm, and 5.7–105.7 ppm, respectively.
The sediments from the lake are mainly clay composed of plagioclase, calcite, illite, kaolinite, and montmorillonite. The sediments near the hot springs are composed of plagioclase, pyroxene, calcite, quartz, and smectite. The travertine is composed mainly of calcite.