PETROLOGIA DO MAGMATISMO ASSOCIADO À MINERALIZAÇÃO DO TIPO OURO PÓRFIRO DA PROVÍNCIA AURÍFERA JURUENA-TELES PIRES (MT)

Abstract

In the northern Mato Grosso State, in the Juruena-Teles Pires gold Province, primary gold mineralization is related to oxidized I-type calc-alkaline plutons. Serrinha deposit is the type-area and is host in the Matupa granitic Massif, with 1872 ± 12 Ma. Gold mineralization in the Serrinha Deposit is disseminated and restricted to the intense hydrothermal alteration areas where it is associated to pyrite, sericite, chlorite and/or albite. Hydrothermal magnetite and rutile occur with pyrite. Serrinha gold Deposit is similar to disseminated deposits genetically related to granite magmas classified as porphyry gold. The Matupa Massif comprises a biotite granite batholith, called Matupa Granite, which outcrops as isotropic undeformed and weakly-fractured blocks. The Matupa Granite is subsolvus, medium to coarse grained, equigranular to porphyritic. Hornblende is very rare and magnetite, titanite, zircon, fluorapatite, allanite, monazite and ilmenite are accessory minerals. Comagmatic rhyolitic dykes and younger diabase dykes, chemically similar to tholleiitic continental basalts, crosscut the granite. The Matupa Granite is calc-alkaline, similar to I-type granites developed in orogenic terrains, specially in volcanic arc and post-collisional settings. The biotite granite is characterized by 68-75 w.t.% SiO 2 , 13-14 w.t.% Al 2 O 3 , high MgO/TiO 2 ratio (2.56), K 2 O/Na 2 O ratio higher than 1, 1-2 w.t.% Ca, high Ba and Sr, medium Zr and Rb, low Nb, Y, Ga, Zn, F, Sn, W, Cu, Mo, Ta, Cl and Li contents. S ETR = 250 ppm, La/Yb ratios @ 30 and Eu/Eu* ratio @ 0.35. The initial crystallization pressure of the Matupa Granite, based on hornblende geobarometer, was 3.3 to 4.5 Kb. T DM values lie between 2.34 and 2.47 Ga and may represent either the continental crust crystallizing age ( e Nd (t) = -2.7 a -4.3), considering a unique source for the original granitic magma, or mixing of mantelic and crustal sources. The occurrence of disseminated gold deposits related to oxidized I-type granites in the Juruena-Teles Pires gold Province is analogous to associations present in world-class porphyry-style deposits and constitutes an important target in the search for gold in the northern region of the State of Mato Grosso.