The paper reports on the results of studies of supergene sulfate mineralization found in a tunnel of the Pyatigorskiy Proval cave. The sulfate minerals include humberstonite K3Na7Mg2(SO4)6(NO3)2·6H2O, sid-eronatrite Na2Fe(SO4)2(OH)·3H2O, metasideronatrite Na2Fe(SO4)2(OH)·H2O, natrojarosite NaFe3(SO4)2(OH)6, tamarugite NaAl(SO4)2·6H2O, and epsomite MgSO4·7H2O, which were identifed by electron probe micro-analysis, powder X-ray difraction and infrared spectroscopy. The presence sulfate sulfur can be related to both the oxidation of sulfde grains, which were found in some samples, and the oxidation of gaseous H2S air oxygen. Humberstonite and metasideronatrite are found for the frst time in Russia.

Keywords: sulfates, Pyatigorsky Proval cave, hypogene karst, humberstonite, sideronatrite, metasidero-natrite, natroyarosite, tamarugite, epsomite.

Received 10.11.2020, accepted 28.02.2021

O.Ya. Chervyatsova, State Natural Reserve Shulgan-Tash, Zapovednaya 14, Irgyzly, Republic of Bashkortostan, 453585 Russia; kittary@yandex.ru 

A.V. Kasatkin, Fersman Mineralogical Museum of RAS, Leninskiy Pr. 18/2, Moscow, 119071 Russia 

N.V. Chukanov, Institute of Problems of Chemical Physics RAS, Chernogolovka, Moscow oblast, 142432 Russia 

F. Nestola, Department of Geosciences, University of Padova, Via G. Gradenigo 6, Padova, 35131 Italy

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