Late-Variscan multistage hydrothermal processes unveiled by chemical ages coupled with compositional and textural uraninite variations in W-Au deposits in the western Spanish Central System Batholith

Authors

  • S.M. Timón-Sánchez Instituto Geológico y Minero de España, IGME Plaza de la Constitución 1, Planta 3ª, 37001 Salamanca, Spain http://orcid.org/0000-0001-5919-6691
  • F.J. López-Moro Departamento de Geología, Universidad de Salamanca Plaza de Los Caídos s/n, 37008 Salamanca, Spain
  • R.L. Romer Deutsches GeoForschungsZentrum, GFZ Telegrafenberg 14473 Postdam, Germany
  • D. Rhede Deutsches GeoForschungsZentrum, GFZ Telegrafenberg 14473 Postdam, Germany
  • A. Fernández-Fernández Departamento de Geología, Universidad de Salamanca Plaza de Los Caídos s/n, 37008 Salamanca, Spain
  • C. Moro-Benito Departamento de Geología, Universidad de Salamanca Plaza de Los Caídos s/n, 37008 Salamanca, Spain

Keywords:

Uraninite, U-Pb dating, W-Au deposits, Spanish Central System Batholith, Variscan belt.

Abstract

The scheelite skarn from Los Santos and the W-Au veins from El Cabaco district, located in the Spanish Central System Batholith (SCSB), are some of the best-known tungsten ore deposits in Spain. Uraninite is an accessory mineral in both deposits, which underwent several hydrothermal flow events. Chemical and textural characteristics, as well as electron microprobe U-Th-Pb uraninite chemical data from the different stages of the skarn and the vein-type mineralizations, are presented here. Based on these data the uraninite was able to be classified into two groups. Group I uraninite has an octahedral habit and occurs as inclusions in K-feldspar relicts of the leucogranite related to Los Santos skarn formation. It shows high Th (6.95 to 8.51wt.% ThO2) and high Rare Earth Elements (REEs) contents (0.55 to 1.38wt.% ∑REE2O3). Group II uraninite occurs i) associated to El Cabaco granite, in a greenish selvage-style greisen and its reddish envelope and in the mineralized rimming quartz veins and ii) in Los Santos high-temperature endoskarn and anorthite skarn, where it is associated with U-rich mica. This uraninite type has lower Th and ∑REE2O3contents than Group-I uraninite. The mineral chemistry and the assemblage and textural relationships suggest that Group-I uraninite is magmatic and the attained U-Th-Pb chemical age of 300±4Ma is interpreted as the magmatic age of the skarn-forming aplite granites in the western part of the SCSB. Group-II uraninite includes two events: i) hydrothermal uraninite, which yields an age of 295±2Ma, dates a strong alkali mobilization and early tungsten deposition and ii) a later hydrothermal process, around 287±4Ma, that resulted in sulfides and late scheelite precipitation and widespread silicification. Finally, the gold deposition is younger than this silicification according to textural criteria. Therefore, W-Au deposits in the western part of the SCSB were formed by superposition of several processes that took place some 15Ma after the skarn-forming granite crystallized. Comparable W, W-Au and U deposits in the Variscan orogenic belt show a similar timing of hydrothermal events, suggesting that the hydrothermal history was controlled by large-scale Late-Variscan tectonic processes.

Author Biography

S.M. Timón-Sánchez, Instituto Geológico y Minero de España, IGME Plaza de la Constitución 1, Planta 3ª, 37001 Salamanca, Spain

DEPARTAMENTO DE INVESTIGACIÓN EN RECURSOS GEOLÓGICOS

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Published

2019-01-31

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Articles