Abstract
The Tocantinzinho gold deposit, located in the Tapajós Mineral Province, Amazonia, Brazil, is considered the largest gold deposit in the region. It is a stockwork-disseminated gold deposit, hosted in a 1982 ± 8 Ma hydrothermalized monzogranite of the Creporizão Intrusive Suite, with petrographic and geochemical characteristics of volcanic arc to post-collisional granites. Gold is mainly associated with phyllic alteration. Primary fluid inclusions trapped in the mineralization stages are H2O–NaCl and unsaturated and homogenize either to the vapor or to the liquid with Th(t) of 300–430 °C, salinity of 2–16 wt % NaCl eq. and density from 0.43 to 0.94 g/cm3. At these conditions, Au is expected to be transported as Au(HS)2− complexes and ore is deposited as the result of boiling in the first mineralizing stages and of mixing between magmatic fluid and meteoric water during the phyllic alteration. Compared with other deposits, Tocantinzinho has similarities with magmatic-hydrothermal oxidized calc-alkaline granite-related gold deposits classified as porphyry gold deposits but we classify as a porphyry-style gold deposit, as it lacks some characteristics of the Phanerozoic porphyry-type deposits. The results from this study can be used to elaborate and guide prospection models in Amazonia and in similar Proterozoic terrains.
Highlights
Located in the Tapajós Mineral Province (TMP) (Figure 1), Tocantinzinho is a stockwork gold deposit showing evidence of hydrothermal alteration
Chemical and fluid inclusion data obtained in this research, we suggest that the studied hydrothermal fluid may have a magmatic origin and a strong influence from meteoric fluids
The same description can be applied to other similar Paleoproterozoic granite-related gold deposits in the Tapajós and Juruena-Teles Pires Amazonian gold provinces [20]
Summary
Located in the Tapajós Mineral Province (TMP) (Figure 1), Tocantinzinho is a stockwork gold deposit showing evidence of hydrothermal alteration. Several gold deposits can be found to the north of the province alongside the Jamanxim and Crepori rivers but currently, considering its gold production, Tocantinzinho is considered the largest gold deposit in the region, with estimated annual production of 4.3 tons milled, an Au grade of 1.42 g/t and 170.000 oz of gold production/year [5,6,7]. Geological mapping programs run by the Brazilian Geological Survey (Minerals Research and Resource Company/CPRM) and collaborators have produced a better geological understanding of the province [5]. Academic papers from universities and research institutes—most of them dedicated to studying specific mineral deposits—have contributed to increased knowledge about the region [8,9,10,11,12,13,14,15,16,17,18,19]
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