Hydrothermal footprint related to regional-scale shear zone-controlled scheelite mineralization, Seridó W-skarn system, northeastern Brazil

Abstract

Tungsten deposits and occurrences in the Seridó Mineral Province represent metasomatic assemblages that differ from the garnet-diopside skarn deposits described in the area. The six W(±Mo ± Au) selected for study show no spatial association with carbonate rocks or igneous intrusions, but are strongly controlled by regional-scale N20°E-trending shear zones formed during the Neoproterozoic-Ediacaran (ca. 615 Ma to 530 Ma) Brasiliano Cycle. Throughout the area, this orogenic event affected both basement and supracrustal rocks, forming scheelite-bearing rocks in both domains. The alteration process is characterized by three mineral associations: (1) diopside-amphibole-feldspars (DAF), (2) amphibole-feldspars (AF), and (3) biotite-rich (BR); and each deposit or occurrence may present one, two or all mineral assemblages. Some of the studied locations are also spatially associated with the mineralized garnet-diopside skarns (MGDS) of the province, where the three mineral associations generally occur tens to hundreds of meters below them. These associations represent a continuously evolving system that records changes in physicochemical properties over time. These changes are documented by mineral chemistry analyses for pyroxene, amphibole, feldspars, biotite, epidote group minerals, titanite and apatite. Earlier, higher temperature metasomatism enriched the system in Mg, Fe, Ca, Ba and REE, whereas later, lower temperature stages are characterized by an enrichment in Na, K, Si, W and Mo. The studied mines and occurrences provide important information on the distal, deeper hydrothermal alteration haloes of tungsten skarn deposits in the Seridó Mineral Province.