Experiments on the partitioning of cations between arsenopyrite and (Zn2+,Co2+,Ni2+,Mn2+,Mg2+)Cl2 aqueous solution were conducted at 500 and 600 ℃, 1 kb. The cations tended to concentrate into arsenopyrite in the following order:
Co2+ > Ni2+ ≥ Fe2+ > Zn2+ > Mg2+ > Mn2+.
The optimum ionic radius for arsenopyrite is situated between Co2+ and Fe2+ (around 0.77 Å).
Experiments on the partitioning of the cations between cobaltite and (Zn2+,Ni2+,Fe2+,Mn2+,Mg2+)Cl2 aqueous solution were also conducted at 500-800 ℃, 1 kb. The concentration tendency of the cations into cobaltite was as follows:
Co2+ > Ni2+ > Fe2+ ≥ Zn2+ ≥ Mg2+ > Mn2+.
This order is the nearly same as that of arsenopyrite. However, cobaltite shows larger difference in the partition coefficient between Co2+ and Fe2+ than arsenopyrite. This is because the optimum ionic radius for arsenopyrite is situated somewhat in the Fe2+ side than cobaltite (around 0.76 Å).
The partition coefficient - ionic radius (PC-IR) curves for arsenopyrite and cobaltite are steeper than those for silicate and multiple oxide minerals. This suggests that the selectivity of sulfide minerals to the cations is stronger than silicate and multiple oxide minerals. Zn2+ shows a negative anomaly, reflecting that Zn2+ prefers a 4-fold coordinated site. Although Ni2+ shows a positive anomaly, the degree of anomaly is smaller than that of the multiple oxide minerals having the peak of the PC-IR curves near Fe2+. Because the peaks of the PC-IR curves for mafic silicate minerals are situated in the vicinity of Ni2+ and they does not show a remarkable anomaly, it is considered that the magnitude of the anomaly of Ni2+ is proportional to the distance between the ionic radius of Ni2+ and the position of the optimum ionic radius of the mineral.
Information collected from geological newsmagazines in 2018 is reviewed. First topic is mineral resources such as mineral commodity summary in USA and gold deposits in Ethiopia. Second topic is regional geology. Visiting points of Corsica and Oman are introduced. The Qinling orogenic belt is reviewed in detail. As third topic, the Anthropocene is overviewed, especially discussion whether the Holocene was over. In addition, the meeting on future of national geological survey is introduced.
A field excursion to a selenite outcrop near the Zao hot spring and to the Zao volcano was held as one of the final events of the 2018 Annual Meeting of the Japan Association of Mineralogical Sciences on September 19, 2018. The formation processes of the selenite in the outcrop are summarized as follows: 1) the selenite was formed by sulfate ions in hot water originated from the Zao hot spring, in combination with Ca ions in host rocks; 2) the selenite favors neutral pH conditions in which smectite is stable, however there is no selenite occurrence in an acidic alteration zone where kaolinite and pyrite are stable. The Zao hot spring is closely connected with a large explosion of the volcano, and the selenite was formed by sulfate-rich acid water from the hot spring, therefore the hot spring and selenite are two of the blessings of the Zao volcano.