Antimony deposits in the Variscan Armorican belt, a link with mafic intrusives?

Abstract

International audienceThe Variscan Armorican belt was the World leading producerof antimony at the beginning of the twentieth century. However,geological controls on the deposits remain unconstrained.Here, we illustrate the field setting ofmineralisations and perform a statistical analysis using GeographicalInformation System software, geophysical and geologicaldata. The analysis shows that Sb deposits are spatiallycorrelated with high-density and magnetic zones. This mayreflect the presence of mafic/ultramafic bodies at depth – asuggestion that is further supported by numerous occurrencesof doleritic dykes throughout the region. Future antimonyprospecting should focus on the high-density and high-magneticzones which comprise about 18% of the Armorican massif.Links between Sb deposits and mafic intrusions arerecognised elsewhere in the West European Variscan belt,emphasising that these may be key for antimony prospectingin deformation belts

A Sb ± Au mineralizing peak at 360 Ma in the Variscan belt

“…Although there is no apparent genetic relationships between Sb ± Au mineralization and base metal VMS through the Armorican Massif, it could be interesting to investigate potential relationships between these two events, because Lescuyer et al (1997) did not evaluate the extent of the magmatism (responsible for VMS deposits) outside the basins. Based on our data and the recent works of Pochon et al (2016aPochon et al ( , b, 2018, we infer that this mafic magmatism and the related thermal anomaly might have affected the external whole domains of the belt around 360 Ma. Indeed, the Central Iberian Zone (i.e.…”

“…This magmatic event is therefore coeval with the high-pressure metamorphic event identified in the South Armorican Domain (Bosse et al, 2000(Bosse et al, , 2005 and with the beginning of the bulk dextral wrenching of the CAD (Gumiaux et al, 2004). As mentioned in the introduction, this mafic magmatic event has strong spatiotemporal and likely genetic relationships with some Sb ± Au deposits from the CAD (Pochon et al, 2016a, 2018. Note that the base metal VMS-type deposits recognized in the Châteaulin Carboniferous Basin (Figs.…”

“…Then, subsequent fluid flows driven by thermal effect, as evidenced by granite emplacements or migmatization during post-orogenic collapse, are missing all together and make therefore this Late Carboniferous fluid flows scenario unlikely. Furthermore, recent works by Pochon et al (2016aPochon et al ( , b, 2018 highlighted a strong spatial and temporal relationship between a widespread mafic magmatism at ca. 360 Ma and the Le Semnon Sb ± Au mineralization ( Figs.…”

Native antimony emplaced by methane‐rich hydrothermal fluid in an orogenic fault‐zone

“…These settings have produced 40% of the world's antimony and have been mined in terranes ranging in age from Archaean, such as the "Antimony Line" in South Africa (Davis, Paterson, & Griffiths, 1986;Jaguin et al, 2013;Pearton & Viljoen, 1986) and the Wiluna deposit in Western Australia (Czarnota, Blewett, & Goscombe, 2010;Hagemann & L€ uders, 2003), to Phanerozoic, such as Hilgrove in New South Wales, Australia (Ashley & Craw, 2004;Boyle, 1990), Baogutu in northwest China (An & Zhu, 2010;Zheng, Zhu, An, Huang, & Qiu, 2015), La Lucette in France (Chauris & Marcoux, 1994;Pochon et al, 2016) and the Sarylakk and Sentachan deposits in Sakha-Yakutia, Russia (Bortnikov, Gamunin, Vilent'eva, Prokof'ev, & Prokop'ev, 2010). The deposits are hosted by low-grade, greenschist facies regionally metamorphosed rocks and may include stratabound gold-antimony mineralized rocks.…”

Polygenic chamosite from a hydrothermalized oolitic ironstone (Saint-Aubin-des-Châteaux, Armorican Massif, France): crystal chemistry, visible–near-infrared spectroscopy (red variety) and geochemical significance

“…At Saint-Aubin-des-Châteaux, the oolitic ironstone was subjected to very-low-grade metamorphism (anchizone) and is mainly composed of siderite and chamosite, with abundant organic matter (vitrinite reflectance R = 3.9 ± 0.2%). Later, this ironstone was hydrothermally altered by early Variscan polyphase fluid flow (Gloaguen et al, 2007;Tartèse et al, 2015) related to a 360 Ma mafic magmatism (Pochon et al, 2016a(Pochon et al, , 2016b. This fluid flow induced specific mineralizations (Pochon et al, 2017(Pochon et al, , 2018, including the Saint-Aubin-des-Châteaux sulfide ore (Pochon et al, 2019).…”