Banca de QUALIFICAÇÃO: Juliana de Araujo Carvalho
Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.STUDENT : Juliana de Araujo Carvalho
DATE: 30/08/2023
TIME: 14:00
LOCAL: Sala de videoconferência e Teams
TITLE:
KEY WORDS:
IOCG, footprint, hydrothermal alteration, copper
PAGES: 112
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:
Inserted in the northern portion of the Carajás Province, in the context of the Cinzento shear zone, Salobo represents the largest copper deposit in Brazil. The region below the final pit proposed for the deposit is referenced as Salobo Deep, where deep exploratory drillholes were executed to investigate a panel of ~700m of depth and 1800m of strike. Petrographic, hyperspectral and geochemical data from three boreholes (~3000m) were integrated in order to map the spatial distribution, magnitude, mineralogical characteristics and geochemical effects of hydrothermal processes from the most distal portions to the mineralized zone. Based on petrographic studies four distinct main lithological groups were separated and comprise granitic rocks (granites, granodiorites, tonalites); mafic rocks (gabbro and amphibolite), hydrothermally altered rocks (garnet-grunerite rocks, garnet-biotite, magnetitite, albitite) and recent intrusive lithotypes (Young Salobo granite and gabbroic dykes). The extensive hydrothermal alteration zone is characterized by albitization and silicification in the distal halo. The sodic-calcic to calcic-ferric intermediate halo is marked by the increase in the proportion of actinolite, biotite, chlorite, and garnet appearance. The proximal halo is defined by significant ferric metasomatism (grunerite, garnet, tourmaline, biotite, magnetite ± fayalite), potassic-ferric alteration (biotite ± garnet, quartz and magnetite, grunerite, tourmaline) and the extreme of iron alteration (magnetitite). The copper-gold mineralization consists mainly of bornite and chalcocite. Propilitization and albitization II characterize post-mineralization alterations. The spectral parameters and the mineralogical proportion obtained from the hyperspectral scanning carried out at some intervals, helped to map the main mineral assemblage that characterize the hydrothermal alteration zone with centimetric resolution and evidenced the direct relationship between the garnet abundance and zones of high copper content, demonstrating that the application of spectroscopy technique is a robust tool in obtaining mineralogical information. The geochemical data analysis highlighted the elements association related to the main lithotypes, alteration and mineralization, characterizing in a simplified way, a central zone marked by ferric hydrothermalism with higher Cu, Au and Ag contents and a clear Na depletion, between two predominantly granitic units with relatively high Na grades and moderate contents of Ca, Mg, Fe, Cr and V. The geochemical and mineralogical data reflect the characteristics of and IOCG system with the classic association of Fe, Cu ± Au, enriched in Ag, Bi, Co, F, Mo, U, F, La, Ce and suggest the mineralization control associated with iron rich zones independent of specific lithotypes.
COMMITTEE MEMBERS:
Presidente - 3167909 - ADALENE MOREIRA SILVA
Interno - 404825 - CESAR FONSECA FERREIRA FILHO
Interno - 6404885 - NILSON FRANCISQUINI BOTELHO
Interno - ***.539.401-** - REINHARDT ADOLFO FUCK - UnB
Interna - 2341034 - ROBERTA MARY VIDOTTI