Evolução magmática, alteração hidrotermal e gênese da mineralização de ouro e cobre do Palito, Província Aurífera do Tapajós (PA) / Magmatic evolution, hydrothermal alteration and geneseis of gold-copper mineralization at Palito, Tapajós Gold Province (PA)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

The Palito porphyry type copper-gold deposit is located in the central region of the Amazonian craton, in the Tapajós Gold Province (TGP), in an area that is dominated by intermediate to felsic granitic and volcanic rocks of late Paleoproterozoic age. Three lithotypes make up this deposit. The Palito Granite, with porphyritic features, is the host rock for gold and copper mineralization, and it is the youngest unit in the sequence, intrusive in the Rio Novo Granite and Fofoquinha Granodiorite. Three main wall-rock alteration zones have been recognized: potassic, propylitic, and sericitic zones. The potassic alteration is volumetrically the most important, affecting mainly the granitic bodies of Palito and Rio Novo, the propylitic alteration constitutes an outer halo within the Palito and Rio Novo granites, and the sericitic alteration is related to mineralization predominantly within the Palito granite. The ore bodies within the Palito Granite are mainly associated with sheared sulphide-bearing quartz veins trending predominantly NW-SE within shear zones and hydrothermalized stockworks. Gold is also disseminated within the Palito Granite. Shearing possibly remobilized elements, which later were concentrated in the shear zones and stockworks. Oxygen isotope analyses of the hydrothermal alteration zones and mineralized veins have been carried out on quartz (18OVSMOW = 8.8 to 11.2); K- feldspar (7.9 to 8.8); sericite (1.7 to 6.9); chlorite (2.4) and calcite (9.0 to 23.9). Stable isotope analyses of the ore sulphides show 34S values that range from 1.2 to 3.6 , reflecting a magmatic source. For the 18OH2O calculation a temperature of 350 ºC was considered, resulting in values for quartz from 3.2 to 5.6 , and for K-feldspar, from 4.8 to 5.7; values for sericite range from 1.1 to 6.3, for chlorite, -2.6, and for calcite, from 6.2 to 21.1. The isotopic results for quartz and K-feldspar suggest that the ore fluids were mainly derived from magma in the early stage of mineralization. 18O values for sericite and chlorite, however, indicates interaction of meteoric waters during the sericitization and chloritization processes. Fluid inclusion studies of quartz crystals suggest an very early stage of fluid exsolution, indicated by low salinities with a range from 0,6 to 1.5 wt.% NaCl equiv., at higher temperatures (429 to 462 ºC), followed by boiling processes, and posterior fluid-mixing stages, as indicated by high variability of salinities from 0.3 to >28.8 wt.% NaCl equiv., and homogenization temperatures that range between 101 a >400 oC, all suggesting a magmatic-hydrothermal source for the mineralization. The geological features of the deposit, styles and types of hydrothermal alteration, stable-isotopes and fluid inclusion analyses indicate that the Palito mineral deposit represents a magmatic-hydrothermal porphyry type developed in a continental margin magmatic arc.

ASSUNTO(S)

pórfiro metalogênese porphyry gold and copper ouro e cobre metallogenesis

ACESSO AO ARTIGO

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