The Age of the Latest Thermal Overprint of Tin and Polymetallic Deposits in the Erzgebirge, Germany: Constraints from Fluorite (U-Th-Sm)/He Thermochronology

Abstract

The Erzgebirge region of Germany records two major episodes of hydrothermal activity, which includes a Late Carboniferous to Early Permian event associated with significant Sn-W mineralization that is related to late Variscan granite magmatism, and a Mesozoic episode of polymetallic vein mineralization. In contrast to the first event, the age of the younger hydrothermal activity is poorly constrained. For the latter, various geochronological methods yielded a wide age range from Permian to early Tertiary. Here we apply fluorite (U-Th-Sm)/He thermochronology (FHe) on both types of mineralization with a twofold goal: (1) to investigate the sensitivity and applicability of the new FHe method (Evans et al., 2005), and (2) to constrain the thermal history of ore deposits in the Erzgebirge region. Two hundred and thirty-three aliquots from seven mineralization localities have been dated. Fluorite from six deposits yielded Cretaceous FHe ages between 112 to 79 Ma, which are independent of their paragenesis. In contrast, fluorite from the Sadisdorf Sn-W deposit yielded an age of 234 Ma. The younger ages are interpreted as cooling ages indicating the time of the last thermal overprint, including possible hydrothermal activity, in the Erzgebirge. The oldest, Triassic FHe ages at Sadisdorf indicate that the Mesozoic thermal overprint only partially reset the (U-Th-Sm)/He system of the late Variscan mineralization. Thermal modeling based on FHe ages and He diffusion parameters in fluorite results in thermal histories comparable to the results from the well-established apatite-based thermal modeling. This study emphasizes the applicability of fluorite (U-Th-Sm)/He thermochronology, which is especially suited for ore deposits where apatite is lacking. Regional Geology and Post-Variscan Tectonic Evolution The Erzgebirge forms an antiform structure exposing high-to medium-grade metamorphic gneisses in the core surrounded by a sequence of low-grade metamorphic units, mainly composed of micaschists and phyllites. This metamorphic assemblage formed by crustal stacking during the Carboniferous (e.g., Werner and Lippolt, 2000) and was later intruded by late-to post-Variscan granitoids and locally covered by rhyolites (Kossmat, 1925; Romer et al., 2007; see Fig. 1b). The Erzgebirge is bordered in the east by the Lausitz thrust to the Cadomian basement of the Lausitz block (Linnemann and Romer, 2002). This fault is sealed by Cretaceous deposits that formed at the margin of the synsedimentary uplifting block in the east. The initially flexural margin was later transformed into a thrust (Linnemann and Romer, 2010). The Eger fault delimits the Erzgebirge toward the south (e.g., Kroner et al., 2007; Fig. 1b). The post-Variscan

Geologic and Metallogenic Framework of North Africa

“…Indeed, the emplacement during Pangean rifting and opening of the Tethys and Central Atlantic oceans of Triassic tholeiitic basaltic dikes, sills, and lava flows over large areas in Morocco, Algeria, and Tunisia (Marzoli et al 1999) was contemporaneous with the genesis of numerous significant ore deposits and districts including polymetallic Jbel Tighza (280.6-267.7 Ma, Watanabe 2002;Marcoux et al 2015;Magali et al this volume), Aouli Pb-Zn ± F ± Ba deposits (Margoum et al 2015), and El Hammam REE-rich F (205 ± 1 Ma, 40 Ar/ 39 Cheilletz et al 2010). Some mineralization related to the giant Imiter (Ag-Hg) deposit (254.7 ± 3.2 Ma, 40 Ar/ 39 Borisenko et al 2013), and the Bou Azzer (CoNi-Fe-As ± Au ± Ag) deposit (240 ± 10 Ma, Re/Os, Lendent 1960; 218 ± 8 Ma, Ar-Ar, Levresse 2001; 308 ± 31-310 ± 5 Ma, U-Pb and Sm-Nd, Oberthür et al 2009) also formed during this time span, coincident with Pangean rifting and opening of the Tethys and Central Atlantic oceans (Muttoni et al 2003;Martins et al 2008;Wolff et al 2015).…”

“…Regionally, this period is when most of Western Europe's polymetallic ± F ± Ba vein-type deposits formed (Sizaret et al 2009;Wolff et al 2015, and references herein). In North Africa, the Permian-Triassic period coincides with two major geodynamic events: opening of the Central Atlantic Ocean to the west as a result of the breakup of Pangea, and incipient opening of the Tethys Ocean to the east.…”

A cirkon (U-Th)/He kormeghatározás módszertani alapjai és alkalmazása fiatal (<1 Ma) vulkánkitörések datálására

“…: EVENSON et al 2014, AULT et al 2015, fluorit (pl. : EVANS et al 2005, WOLFF et al 2015, valamint a gránát (pl. : ACIEGO et al 2003).…”

“…: diagenetikus hőmér -sékleti hatások és hidrotermális események datálására, mély völgyek bevágódási ütemének megállapítására; HOUSE et al 1997, HAIDER et al 2013, REINERS & BRANDON 2006, SCHILDGEN et al 2007, WOLFF et al 2015. Abban az esetben, ha egy hirtelen a felszínre került, gyorsan lehűlt vulkáni kőzetet vizsgálunk, amely a kitörés során (geológiai idő ská -lán nézve) gyorsan áthaladt a részleges vissza tar tódási zóna hőmérséklet-tartományán, és amelyet nem ért későbbi hő -hatás (pl.…”

Geology, Fluid Inclusions, and Geochemistry of the Aouli Sulphide ± Fluorite ± Barite Vein Deposit (Upper Moulouya District, Morocco) and Its Relationships to Pangean Rifting and Opening of the Tethys and Central Atlantic Oceans

“…Indeed, the Zeida deposit exhibits many diagnostic features typical of so-called sandstone-hosted Pb deposits that contrast greatly with those of the epigenetic Mibladen MVT mineralization. Conversely, the Aouli vein deposit belongs to the large family of hydrothermal vein-type deposits or "filon péri--plutonique de départ acide" of Routhier (1963Routhier ( , 1980 that are spatially but not genetically related to granitoid intrusions and associated apophyses (Wolff et al 2015, and references herein)…”