Recent investigation on several secondary minerals formed in old mining galleries in the Cârnic district (Roşia Montană, Romania) enabled us to characterize ten minerals. Out of these ten identified minerals, the discovery of jokokuite is the first reported occurrence in the Carpathians. A second mineral identified as apjohnite represents a new occurrence in Romania. Along with these two rare minerals, some other species of the halotrichite group (pickeringite, halotrichite, apjohnite, and dietrichite), iron sulfates, and K-Al sulfates were identified. Minerals were identified using light microscopy, X-ray diffraction, infrared, and scanning electron microscopy with energy dispersive spectroscopy. The chemical composition of some samples was determined with inductively coupled plasma atomic emission spectrometry. The precipitation of these sulfates is largely controlled by cations substitutions and changes in the temperature, relative humidity, and evaporation along the sampled gallery. The general sequence of sulfate deposition at the investigated site includes the following main steps: (1) oxidation of pyrite by meteoric water seepage through dacites to create ferrous sulfate and sulfuric acid solutions; (2) chemical reaction between dacites and sulfuric acid from which other cations (Al3+, Zn2+, Mn2+, K+) are released into solution; and (3) precipitation of various hydrated sulfates as a result of a combination of dehydration/hydration, oxidation, and neutralization reactions that take place under different microclimatic settings.
Onac, Bogdan P.; Vereș, Daniel; Kearns, Joe; Chirienco, Mirona; Minuț, Adrian; and Breban, Radu
Secondary sulfates found in an old adit from Rosia Montana, Romania,
Studia UBB Geologia
Available at: http://scholarcommons.usf.edu/geologia/vol48/iss1/art3