Geochemical Studies on the Minerals Obtained by Dry Valley Drilling Project

[摘要] Calcium carbonate in Lake Vida was found in a thin flat form having alternating bands of brown and white. This sample contained some rounded quartz that might be originated from the Beacon sandstone. From the data of X-ray diffraction of the mineral, the calcium carbonate is a typical calcite. The logarithmic mol ratio of Mg to Ca in the solution that formed the calcite is calculated as -0.25～-0.8, while sea water has a value of 0.86. The ground water collected from the Lake Vanda drilling hole has a value of -0.4. Using the distribution coefficient of alkaline earth element in calcite, the minerals in Lake Vida may have been deposited from Sr- and Mg-poor solution as compared with sea water. Gypsum crystals were found in the fractures of the core No. 4. And in the ice block in the core, thin flat hexagonal sheets of gypsum crystals were also found. The ground water collected at Vida is almost in equilibrium with calcium sulfate, but the lake water is supersaturated with it. δD and δ^<18>O of the crystal water of the gypsum is -263 ‰ and -27.7‰, respectively. These values indicate that the crystal water is equilibrium with the lake water. These data suggested that the minerals were formed from such a solution as the water of the Lake Vida.