The Artulândia prospect area: A newly discovered Paleoproterozoic Zn–Pb–Cu-(±Ag–Bi) VHMS mineralization in Campinorte Magmatic Arc, Central Brazil

Abstract

The Artulândia prospect area is a recently-mapped, non-auriferous VHMS mineralization within Paleoproterozoic rocks in Central Brazil. The mineralization is hosted in a felsic-dominated bimodal volcano-sedimentary sequence that formed during the onset of Campinorte Magmatic Arc. The Zn–Pb–Cu-(±Ag–Bi) VHMS mineralization occurs as massive sulfide lenses and sulfide disseminations. Surrounding the sulfide lenses, two proximal hydrothermal assemblages are identified: (i) Tremolite-spessartine (±clinochlore-epidote) assemblage, associated with the sphalerite-pyrite aggregates and (ii) Clinochlore-carbonate (±tremolite-talc-serpentine) assemblage encompassing chalcopyrite, galena, and sphalerite. Besides these two assemblages, three others are considered distal to the mineralization, and interpreted to represent the stringer zone: (i) Biotite-spessartine (±chamosite-tourmaline) assemblage, with disseminated sphalerite + pyrite + galena, (ii) Biotite-sericite-carbonate (±chamosite) assemblage, with disseminated pyrite + sphalerite and (iii) Biotite-carbonate assemblage, with pyrite and traces of sphalerite intergrown with biotite lamellae. The mineralogy of the assemblages results from the Paleoproterozoic, syn-volcanic metamorphism (Neoproterozoic, Brasiliano Orogeny) of hydrothermal alteration minerals. The mineralogy and mineral chemistry data of the assemblages show that proximal assemblages formed under great influence of Fe–Mg–Ca-rich fluids. The highest grades of base metals are restricted to the sulfide lenses: Zn (1.4% wt.), Pb (1.0% wt.%), and Cu (1.8% wt.). Anomalous contents of Mo (>180 ppm), Bi (>700 ppm) and Ag (>60 g/t) occur in the proximal hydrothermal assemblages. Gold grades as high as 270 ppb are directly related to chalcopyrite-enriched zones. The δ34S measurements in pyrite vary from +8.77‰ to +10.99‰. These values are compatible with Paleoproterozoic deposits in which the isotope composition reflects a mix of seawater and leached sulfur from host rocks.