Fluid inclusion study of the Horní Luby cinnabar deposit, Saxothuringian Zone, Bohemian Massif: clues for the metamorphic remobilization of mercury
Abstrakt
The stratiform deposit of mercury at Horní Luby near Cheb (Czech Republic) is hosted by Ordovician phyllites of Vogtland–Saxony Paleozoic Unit in the Saxothuringian Zone of the Bohemian Massif. Ore is represented by cinnabar disseminated within the phyllite and by lenticular bodies rich in massive cinnabar (lenses with a thickness of up to 1 m and length along the strike varying from less than 1 m up to 20 m).
Cinnabar is accompanied by pyrite and locally also siderite. The P–T history of the mineralization was deciphered by the study of fluid inclusions.
Early fluids are fluid trapped in secretion quartz. This fluid underwent several heterogenization events starting from approximately 300 °C and continued down to 200–150 °C.
Metamorphic quartz of secretion origin crystallized at ~300 °C, while hydrothermal pyrite crystallized at 220–210 °C and cinnabar at 195–160 °C. The formation of the richest ore was associated with the replacement of metamorphic quartz in phyllites by the cinnabar in weakly alkaline solutions.
The cinnabar is pure phase, free of admixtures (Bi, Sb, Zn, Fe, and Cu). It is accompanied by minute blebs of Hg-bea-ring sphalerite (11–12 wt. % Hg) that might indicate earlier presence of the zincian metacinnabar and more complex metamorphic history of the ore.
The primary source of mercury is thought to be Lower Paleozoic submarine volcanism. The formation of ore bodies is, however, associated with metamorphic mobilization of mercury during the late stages of the Variscan orogeny.
Despite being relatively small, the mercury deposit at Horní Luby competed with the mines in Idrija (Slovenia) and Almadén (Spain) in the 16th century. The production of mercury at Horní Luby is estimated to have corresponded to c.10–30 % of the mercury production in the mines of Idrija and Almadén at that time.
In addition to Venice, the mercury from Horní Luby was also supplied to Nürnberg, Antwerp and Lyon.