Programa de Pós-Graduação em Geociências – CTG/UFPE

 

Defesa de Dissertação de Mestrado n.º 6 em 2020

 

Aluno(a): Isis Mayara Gomes da Silva

 

Orientador(a): Prof. Dr. João Adauto de Souza Neto

 

Coorientador(a): Prof.ª Dr.ª Thais Andressa Carrino

 

Título: “INTEGRAÇÃO DE DADOS GEOLÓGICOS, AEROGEOFÍSICOS E DE ESPECTROSCOPIA DE REFLETÂNCIA NA DEFINIÇÃO DE VETORES EXPLORATÓRIOS PARA O DEPÓSITO DE OURO SÃO FRANCISCO, FAIXA SERIDÓ - RN”

 

Data: 25/09/2020

 

Horário: 14h

 

Local: http://stream.meet.google.com/stream/323db8a2-d7b3-4eb9-9035-9aa448f86bca

 

Banca Examinadora:

 

Titulares:

 

1.º Examinador(a): Prof. Dr. João Adauto de Souza Neto (Orientador)

2.º Examinador(a): Prof. Dr. Lauro Cézar Montefalco de Lira Santos (PPGEOC/CTG/UFPE)

3.º Examinador(a): Dr.ª Rosa Elvira Correa Pabón (ITV)

 

Suplentes:

 

1.º Examinador(a): Prof. Dr. Gorki Mariano (PPGEOC/CTG/UFPE)

2.º Examinador(a): Prof. Dr. Wanilson Luiz Silva (UNICAMP)

 

Resumo:

 

The São Francisco deposit (lode gold deposit) is located in the municipality of Currais Novos (RN), belonging to the Seridó fold belt, inserted in the Borborema Province, which corresponds to a shear belt marked by supracrustal rocks from the Seridó Group (Neoproterozoic). This region is located in the Seridó metallogenetic Province, characterized by skarns (e.g. W-Mo, W-Mo-Au-Bi-Te, Cu), mineralized pegmatites (Nb-Ta, Be, gems) and lode gold deposits. This research aimed to integrate geological, airbone geophysical and reflectance spectroscopy data, allowing the mineralogical and spectral characterization of the São Francisco deposit. Regional airbone geophysics reveals a high magnetic response and a high value of K that delimit the deposit area. Petrographic and reflectance spectral data of surficial rocks and drill cores allowed the identification of the hydrothermal mineralogy. The deposit-forming hydrothermal alteration is mainly associated with the generation of muscovite and sericitic alteration in the mica schists of the Seridó Formation. Hydrothermal alteration minerals, such as calcite, chlorite and epidote occur in smaller proportions. The hydrothermal muscovite is associated with sulfides, such as pyrrhotite and arsenopyrite, and the ore paragenesis is characterized by gold+pyrrhotite+pyrite±ilmenite±chalcopyrite±arsenopyrite±galena. The occurence of altered mica shists, with predominance of muscovite and/or sillimanitte, and sulfide-rich quartz veins, show a positive correlation with a high gold content and a deep absorption feature of muscovite/sericite at 2200nm (Al-OH bond), in drill core rocks. Sulfide-rich quartz veins on the surface show diagnostic absorption features of jarosite (~430nm - Fe³⁺; 1470, 1848 and 2264nm - OH- bonds; 2394nm - S-O bond), a sulfate (KFe₃(SO₄)₂(OH)₆) derived from the weathering of sulfides. The association of muscovite with the mineral paragenesis of sulfides in subsurface, as well as jarosite mainly in sulfide-rich quartz veins in surface, define, respectively, hydrothermal (T~200-574°C) and supergenic (T<50°C) zones. These guide minerals, quickly identified by reflectance spectroscopy, characterize potential gold mineralized zones and, therefore, can be used as exploration vectors for the São Francisco deposit.

 

Palavras-chave: Hydrothermal alteration; Lode gold deposit; Reflectance spectroscopy; Airbone geophysics; Jarosite.