Numao gold deposit in the Iberian Variscan belt, Northern Portugal: Ore features and mineralization controls. A gold deposit in a W-Sn metallogenic province

The Numao gold deposit in the northern part of the Iberian Variscan belt is close to the regional first-order Vilarica-Manteigas fault system. The second and third-order structures controlled the gold mineralized bodies. These bodies consist of disseminated sulfides, arsenopyrite-quartz veins, and sulfides-scheelite-quartz veins. The scheelite occurrence predates the gold mineral assemblage and is lithologically controlled by host rocks with calc-silicate minerals. The ore mineral assemblage comprises scheelite, arsenopyrite, chalcopyrite, bismuth, and Au-Ag mineral phases, with minor pyrite, pyrrhotite, sphalerite, and galena. The hypogene gold minerals at Numao deposit are hosted by arsenopyrite, chalcopyrite, and silicate matrix in minor amounts. Chemically, gold fineness ranges from 663 to 841. The thermal evolution of the mineralization was estimated based on arseno-pyrite (381 to 502 degrees C) and chlorite geothermometers (264 to 341 degrees C). The multi-element and principal component analysis information was used to better identify geochemical patterns and trends in hydrothermal alteration. The gold-metal association (Au-As-W-Bi) was found to be similar to other gold deposits in the Eu-ropean Variscan belt.

Automated summary

The Numao gold deposit in the northern part of the Iberian Variscan belt is controlled by second and third-order structures near the regional first-order Vilarica-Manteigas fault system. The deposit consists of disseminated sulfides, arsenopyrite-quartz veins, and sulfides-scheelite-quartz veins. The ore mineral assemblage includes scheelite, arsenopyrite, chalcopyrite, bismuth, and Au-Ag mineral phases.