Constraints on the Genesis of Yellow Fluorite in Hydrothermal Barite Fluorite Veins of the Erzgebirge, Eastern Germany: Evidence From Optical Absorption Spectroscopy, Rare-Earth-Element Data, and Fluid-Inclusion Investigations

Abstract

The optical absorption spectra of yellow fl uorite crystals from hydrothermal barite-fl uorite veins of the Erzgebirge, eastern Germany, are characterized by a broad absorption band with a peak at 433 nm that shows a subtle vibronic structure. The optical absorption behavior of the crystals is attributed to the presence of O 3 centers in the structure; the O 3 molecules were incorporated during crystallization. The presence of the O 3 centers implies that a very specifi c chemical reaction must have taken place during crystallization, under particular physicochemical conditions. Thermal stability constraints of the yellow coloration suggest that the fl uorite formed at low to moderate temperatures (below 250 to 400°C), which agrees with homogenization temperatures determined on fl uid inclusions entrapped in the crystals (below 150°C). The crystals have a middle-rare-earth-element-enriched signature. The depletion of the light rare-earth elements in the fl uorite-forming fl uids was caused by the precipitation of Ce-rich phases prior to the formation of fl uorite, whereas the incorporation of the heavy rare-earth elements into fl uorite was suppressed by the formation of carbonate complexes in the hydrothermal fl uids. Fluid-inclusion data show that fl uorite formation occurred in a comparably stagnant environment typifi ed by the mixing of fl uids of different salinity and composition, namely a highly saline, CaCl 2-and NaCl-rich brine that contained some Na 2 SO 4 , Na 2 CO 3 , NaHCO 3 , CaSO 4 , and SrSO 4 , as well as a NaCl-dominated fl uid of distinctly lower salinity. Fluorite precipitation from the cooling hydrothermal fl uids occurred in a relatively reducing environment under near-neutral conditions. We propose a chemical reaction that may have led to the formation of O 3 centers in the structure, and that may also explain the formation of the yellow coloration of fl uorite in other hydrothermal systems. In particular, fl uorite precipitation in some Mississippi-Valley-type deposits apparently occurred under very similar environmental conditions.

Superposition of burial and hydrothermal events: post‐Variscan thermal evolution of the Erzgebirge, Germany

“…The Mesozoic mineralisation consists of predominantly barite–fluorite–sulphide and hematite–barite veins penetrating the metamorphic basement (e.g. Trinkler et al ., ; Seifert, ; Romer et al ., ).…”

Fluid inclusions, muscovite Ar–Ar age, and fluorite trace elements at the Baiyanghe volcanic Be–U–Mo deposit, Xinjiang, northwest China: Implication for its genesis

“…Its geochemistry allows direct reconstruction of the chemistry of the hydrothermal fluids sourced from the magma-fluid system. Fluorite REE patterns and the size of individual tetrads are also helpful for characterizing the evolution of hydrothermal fluids (Constantopoulos, 1988;Graupner et al, 1999;Jebrak et al, 1985;Monecke et al, 2002;Möller and Dulski, 1999;Morozov et al, 1996;Trinkler et al, 2005). Based on field observations, the bertrandite in the Baiyanghe deposit is intergrown with dark-purple fluorite and muscovite (Fig.…”

Geoquímica de lantánidos de los yacimientos de fluorita de los distritos mineros de Taxco y Zacualpan, sur de México: implicaciones sobre el origen y la evolución de los fluidos

“…Más recientemente la geoquímica de lantánidos en fluoritas ha sido utilizada por muchos autores como indicadora del tipo y del origen de los fluidos asociados (p. ej., Grappin y Treuil, 1979;Ruiz et al, 1980;Chatagnon y Galland, 1982;Strong et al, 1984;Jebrack et al,1985;Ekambaram et al, 1986;Constantopoulus, 1988;Eppinger y Closs, 1990;Subías et al,1994;Bau y Dulski, 1995;Fanlo et al, 1998;Bosze y Rakovan, 2002;Gagnon et al, 2003;Trinkler et al, 2005;Soussi et al, 2012;Makin et al, 2014). Esta posible utilización como mineral trazador se debe a la facilidad que presentan los átomos de Ca de la fluorita (CaF 2 ) de ser sustituidos por cationes de igual carga y radio iónico parecido.…”