Vetorização geoquímica, caracterização e modelamento 3D de alterações hidrotermais em sistemas cupro-auríferos: exemplo do Complexo Sossego (PA), Província Mineral de Carajás

Abstract

The copper-gold Sossego Complex, Pista, Sequeirinho/Baiano, and Curral/Sossego sectors, is in the southern portion of the Carajás Mineral Province, along with a WNW-ESSE regional shear zone. The main host lithologies that take place at the Complex are granitoids, felsic metavolcanic rocks, and mafic to ultramafic intrusive rocks. This work involved the application of multivariate statistical techniques to define geochemical units and vectors to help with geological interpretation, exploratory guides, and geometallurgy of the Complex concerning the mineralization. Overall, the use of those techniques revealed a good correlation between elemental data and the geochemical units proposed, which allowed coherently defining of the units, major elements, and probable hydrothermal mineralogical paragenesis for the deposits. Individual analyses and elemental correlation of chosen elements in probability diagrams, histograms, binary, ternary, and boxplots were carried out and aimed at identifying the geochemical features and their relation to the mineralogical association. At the Pista sector, at least five geochemical units occur (sodic, sodic-silica, potassic-chloritic, magnesian, and potassic feldspathic), where are highlighted the units with a higher concentration of sodium and silica for zones closer to the orebody. Geochemical vectors that predominate over this sector and that can be considered as trackers or contaminants about the ore zones are As, Al, Ag, Hf, Sr, Te, Zr, Mo, Na, Pb, S, La, W, and U, directly associated with sodic-silica and sodic geochemical units. Ternary diagrams have shown an indicator of paragenesis, which comprises a vector from an initial phase of sodic evolving to potassic. At Sequeirinho/Baiano sector, occur nine geochemical units (sodic, sodic-silica, sodic-ferric, sodic-calcic, calcic-ferric, ferric, magnesian, potassic-chloritic, and potassic feldspathic) in which the paragenesis is observed from the distal to the proximal zones concerning the orebody. Over distal zones, higher sodium concentration is observed, evolving to medium concentration of sodium and calcium, achieving high iron, calcium, and magnesium content nearby the mineralization, showing that the geochemical units related to the copper mineralization of high-grade are calcic-ferric and ferric. Elements such as Ag, As, Bi, Cd, Co, Fe, Ga, Ge, In, Ni, P, Pb, S, Se, Te, and V (secondary Ca, Mg, Mn, Re, Sb, Sn, Th, and U) were the main vectors directly associated with mineralization and calcic-ferric to ferric units. Ternary diagrams of this sector suggest two probable paragenesis vectors, both from initial stages of the sodic unit, although, one of them showed an evolution towards sodic-ferric and the other to a sodic-calcic stage and evolving to calcic-ferric unit afterward. In the Sossego/Curral sector occur seven geochemical units (sodic, sodic-silica, sodic-potassic, potassic, chloritic, ferric, and calcic). This sector has revealed a complex correlation between hydrothermal zoning and geochemical units because of its geological features (breccias, veins, veinlets, and late dissemination). The graphics show that geochemical units that display an affinity with mineralized zones are chloritic, calcic, and ferric (breccia and vein zones). Over the chloritic unit, the highlighted elemental vectors are Ag, Be, Bi, Ca, Ce, Cu, La, Mn, Mo, Ni, P, and S (secondary K, Al, Mg, and Fe). Ferric geochemical unit happens mainly associated with chloritic and calcic zones, although it is not similar due to high iron concentration (>15% Fe), and the main geochemical vectors are As, Cd, Ce, Co, Fe, Ga, Ge, In, La, Re, S, Sb, Se, Sn, Te, U, and Y (secondary Ag, Be, Ca, Cs, Li, Mg, Mn, Mo, and V). The calcic unit corresponds to calcite, actinolite, and epidote-rich intervals in breccias and veinlets that cut chloritic rocks. Its main geochemical vectors are Al, Ca, Cr, Mn, Sc, Sr, V, and Zn (secondary Ag, As, Cd, Co, Fe, Ga, In, S, Se, and Sr). The probable paragenesis vector points to an initial sodic stage, evolving to a potassic stage followed by chloritic. Spatial materialization of the units and geochemical vector was made by 3D modeling obtained by statistical results that were developed, displaying a better visual geological understanding of hydrothermal flow, probable chemical/mineralogical paragenesis, and correlation with mineralization. This work will contribute in the future to the understanding of lithology, structural, and geochemistry of the Sossego Complex, besides provisioning geometallurgical data. This work can benefit open pit operations with direct or indirect reduction of cost, safety increment, and better operational performance of the ore processing.