The Ruš orebody is located in Spodnje Jezersko in the southern Karavanke Alps, northeast of Kranj. The ore is present in Paleozoic rocks, being restricted to the boundry between the Upper Devonian limestones and the Carboniferous clastites of the Hochwipfel Formation. The latter being deposited within the foreland basin of the Variscan mountains in the subducting Paleotethys Ocean.
The main ore mineral of the deposit is sphalerite, while galenite, pyrite and tetrahedrite are also present. Based on mineral structures and paragenesis, sphalerite mineralization occurred in two phases. In the first phase mineralization of Sph 1 occured in the form of fillings between clasts or veins, and is characterized by black, dark brown or grayish-green colors, while the mineralization of Sph 2 occured later, in the form of veins and impregnations, and is characterized by orange and beige colors.
LA-ICP-MS analysis of trace elements of sphalerites, shows that Sph 2 contains higher values of Cu, Ga, Ge and Ag, than Sph 1. Correlations between trace elements show that these elements were incorporated into sphalerite by coupled substitution, e.g. 2Zn2+ ↔ Ga+3 + Cu+. Using the concentrations of trace elements we calculated the sphalerite precipitation temperatures between 56 to 241 °C, with the GGIMFis geothermometer, and determined an intermediate sulfidation state of sphalerites. We assume that the higher values of Cu, Ga, Ge and Ag in Sph 2 are the result of the mixing of a fluid that was Cl-rich and carried Zn, and a fluid in which trace elements were present in the form of hydroxides, e.g. Ga(OH)3.
We conclude that, based on the Paleozoic host rocks, the compressive tectonic regime of the deposit, low-temperature precipitation (<250 °C) and the enrichment of sphalerite with trace elements, especially Ga, the Ruš orebody is a low-temperature zinc deposit of the Mississippi-Valley type.
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