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Título

MULTISTAGE HYDROTHERMAL FLUID CIRCULATION EVIDENCED BY LITHOGEOCHEMISTRY OF PADRE SERRANE AND CORREGO DO OURO TARGETS, PAPAGAIOS GOLD DEPOSIT, SÃO FRANCISCO CRATON

Texto do resumo

The Córrego do Ouro and Padre Serrane targets belong to the Papagaios gold deposit, located northestern portion of the Pitangui Greenstone Belt, São Francisco Craton. The gold mineralization is hosted primarily in metavolcanic mafic-ultramafic rocks and subordinately in carbonaceous phyllites, and it is controlled by regional ENE-WSW shear zones. . The results of this research showed that there are three main hydrothermal alteration zones in metavolcanic mafic-ultramafic sequences ranging up to 100 meters away from the mineralization. These zones were formed by multiple hydrothermal alteration processes such as chloritization, carbonatization, sericitization, silicification and sulfidation and can be defined as i) Distal actinolite-chlorite ± clinozoisite zone; ii) Intermediate calcite-ankerite ± talc zone; iii) Proximal quartz-sericite zone and iv) mineralized zone. There are two phases of hydrothermal alteration. The first and main process corresponds to the formation of well-defined alteration zones by processes such as chloritization, carbonatization and silicification. The main lodes comprise gold-sulfide assemblages in silicified zones, where gold occurs freely and associated with sulfide assemblages of sphalerite + galena + chalcopyrite + pyrite ± arsenopyrite ± marcasite.The second process does not present evident zoning and corresponds to a pervasive chloritic-sericitic alteration with associated pyrite and arsenopyrite. It overlaps the silicified zones through veinlets controlled by the incipient mylonitic foliation. Principal component analysis of drill core lithogeochemical assays indicate two geochemical clusters. The first one corresponds to Ni-Co-V-Mo association and it indicates the volcanic mafic host rock signature. The second one is represented by Au-As-Pb-Zn and comprises the mineralization signature, suggesting that the presence of arsenopyrite, galena and sphalerite could be used as a pathfinder for gold mineralization. The downhole geochemical profile of the drill cores shows that there is an increase on gold grade in carbonaceous phyllites compared to silicified zones in metabasalts, which suggests a possible stratabound mineralization control. Also, the second hydorthermal alteration process, characterized by chloritic-sericitic hydrothermal alteration, presents different geochemical signatures from the silicification zones. The downhole geochemical profiles also shows that the silificiation zones hosts the greatest gold grade, which is associated with Cu-Pb-Zn, while the chloritic-sericitic zones have low contents of Au-Cu-Pb-Zn and high concentration of As. This results reinforces the occurrence of a tardi-telescoping process during the orogenic stage that implicates in a multistage metallogenic evolution of gold mineralization at the Papagaios gold deposit.

Palavras Chave

Greenstone Belt Pitangui; Papagaios gold deposit; Orogenic gold; drill core lithogeochemistry