Experiments on the Element Distribution between the Granodiorite JG‐1a and 2M NaCl Hydrothermal Solution at Temperatures of 300 to 800°C and a Pressure of 1 kb

Abstract

Abstract:The distribution of Na, K, Ca, Mg, Mn and Fe between the granodiorite JG-1a, one of the geochemical standard rocks, and 2M NaCl aqueous solution was experimentally determined at temperatures of 300 to 800°C and a pressure of 1 kb using standard cold seal-type pressure vessels. The solid run products melted partially at 800°C. Only K shows a significantly different behavior from the experiments using the basalt JB-1a (Uchida and Tsutsui, 2000) due to the presence of orthoclase in the JG-1a. The transition elements tend to be preferably partitioned into the aqueous chloride solutions with increasing temperature. At 800°C and 1 kb, the Fe concentration of the aqueous chloride solutions reached up to 5,000 ppm, and the Mn concentration up to 350 ppm. The distribution coefficient, K D,i = C i,sol /C i, rock , is in the order of Na>K≈Mn≈Ca> Fe≈Mg at 300°C, but changed in the order of Mn>N≈K≈Fe>Ca>Mg at 800°C. The distribution coefficients of the divalent cations for the JG-1a are higher than those for the JB-1a. The distribution coefficient of the transition elements, Fe and Mn, increases significantly with increasing temperature. The thermodynamic analysis for aqueous speciation revealed that this is attributable to the formation of the tri-chloro complexes of the transition elements at higher temperatures.

Relationship Between Solidification Depth of Granitic Rocks and Formation of Hydrothermal Ore Deposits

“…According to the experiments, the formation constants of higher‐order chloride complexes of divalent metals increase with decreasing pressure and increasing temperature. Because the solidus temperature is relatively high at lower pressures under water‐saturated conditions, it is expected that hydrothermal solutions with a high potential of mineralization will be discharged from granitic magmas under low pressure conditions, combined with the temperature effect on the partitioning of metals between rocks and hydrothermal solutions (Uchida et al , 2003). In other words, metals such as Pb, Zn, Cu and Fe, which generally dissolve in hydrothermal solutions in the form of chloride complexes, are preferentially partitioned into hydrothermal solutions, and hydrothermal solutions rich in these metals (ore‐forming hydrothermal solutions) are released from the granitic rocks in shallow environments.…”

Physical and Chemical Diversity of Seafloor Hydrothermal Systems and Presentation of Associated Chemolithoautotrophic Ecosystem

“…Note that high-temperature phase separation (A) produces relatively CO2poor vapor (A' ) , whereas low-temperature phase separation (B) generates nearly pure CO2 vapor (B' ) . Scott, 1996, 2002) ることは 他の実験的研究からも確認されており (Urabe, 1985(Urabe, , 1987Uchida and Tsutsui, 2000;Uchida et al, 2003…”