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Thermal dehydration of a natural hydrous ferric sulfate Fe(SO4)(OH)?2H2O was studied using x-ray-phase and thermal analyses. This mineral was found in the hypergenesis zone of the Khangalas gold deposit, Eastern Yakutia, Russia. A comparative analysis of the sample with known hypergenic hydrous ferric sulfates with a similar Fe2O3:SO3 ratio close to 1:1 was performed. The dissimilarities between the founded mineral and its possible polymorphs – butlerite and parabutlerite are identified. The mineral is less stable and begins to break down at 60 °C. Water loss in the first two endothermic peaks (120 and 255 °C) is about 16%, which is close to the loss of two H2O molecules. At 120 °C a new previously unknown phase X is formed, which persists to temperatures of ~255-280 °C. No analogs to the X ray pattern of this phase could be found. The interplanar distances and intensities of its main lines are as follows: d (I) -9.3(100), 4.66(25), 3.53(42), 3.32(10), 2.144(8) A. It is likely that this phase is a hydrous sulfate Fe(SO4)(OH)·0.5H2O, that has not yet been identified in nature. Completely water and OH group disappear by 450 °C, while the mass loss is ~24 %. For temperatures of ~300 °C and higher, the dehydration processes for all the minerals of the studied group are almost identical. When further heating occurs, the mineral is completely dehydrated and anhydrous ferrous sulfates are formed. The final stage of the decomposition of anhydrous ferrous sulfate after heating the sample to 700 °C – hematite formation. [ABSTRACT FROM AUTHOR]

Characteristic features of the petrographic and chemical compositions as well as the age of basic dikes in the Nastenka site of the Malo-Tarynskoe orogenic gold ore deposit (MTD), located in the central part of the Yana-Kolyma metallogenic belt, northeast Russia, are considered. The dikes are composed of light greenish-gray porphyritic rocks replaced by sericite-chlorite-albite-carbonate substance with ore and epidote components, in which relics and fragments of primary igneous minerals are noted. The obtained Rb-Sr erochron dates of the dikes rocks determine their age at 162±4 Ma (I0 = 0.7128 ± 0.0002), which suggests them to be the earliest magmatic formations of the Malo-Tarynskoe deposit. The calculated formation temperature for the whole rock samples (from Ti- and Zr-geobarometers) is between 747-787 °C and 671-709 °C. Intrusion of the dikes occurred under a relatively high oxygen fugacity (ΔNiO-Ni = -0.08 – +0.83), within the nickel-nickel buffer. The genetic connection of gold mineralization with deep magmatic chambers, which are the source of basic rocks of the dike complex at the Nastenka site of the Malo-Tarynskoe orogenic gold ore deposit, is assumed. [ABSTRACT FROM AUTHOR]