English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The host rocks of the Estrela Cu-Au deposit in the Serra dos Carajas region are andesites and gabbros of the Grao Para Group, of the Itacaiunas Supergroup, formed at 2.7 Ga. The deposit is in a 400-600 m thick sequence ofaltered andesites and gabbros still presenting relict ophitic to subophitic-type igneous textures. The gabbros and andesites are possibly related to magmatic are origin, as suggested by Se/Ti ratios of 0.02-2.28 x 10 -3 for the gabbros and 3.25 x 10 -3 _ 1.67 X 10 -3 for the andesites. The andesites present higher REE content (LREE = 90.50 a 471.67 ppm) than the gabbros (LREE = 43.76 a 230.57 ppm), what may reflect the original igneous content or an advanced alteration stage. The host roeks of the Estrela Cu-Au Deposit have been affected by an early calcic-sodie alteration followed by a potassic alteration, accompanied by ferrifieation and sulfidation, which transformed the igneous protoliths into biotite-rich rocks. The early calcic-sodic alteration is represented by hastingsite, Fe-pargasite, Fe-homblende, oligoclase-andesine, albite, quartz, magnetite and minor Fe-biotite, Fe-epidote and chlorite. The potassic alteration overprinted the calcic-sodic mineral assemblage and is characterized by siderophyllite, biotite, Fe-epidote, fluorite, radioactive minerais, quartz, chamosite, dravite, schorlite, magnetite, chalcopyrite, pyrite, pyrrhotite, molybdenite and minor bornite. The late alteration stage is a greisenization developed at localized sites mainly in the andesites. The greisen mineralogy is quartz, zinwaldite, Li-muscovite, dravite-schorlite, fluorite, topaz, titanite, F-apatite and chlorite. Calcite, chamosite, topaz, quartz and tourmaline veins post date the mineralization and greisenization. This alteration sequence suggests that the hotter fluids, assoeiated with the potassic alteration and albitization were oxidizing alkaline and held high K and CI activities in addition to high Na:Ca ratios. During the cooling path a deereasing in the Na:Ca ratio probably occurred accompanied by a sharp increasing of F activity, as evidenced by the massive presence of fluorite. During the greisenization stage the fluids became reducing and aeidic permitting the stabilization of the Li-muscovites and the other greisen mineral assemblages.

ALTERAÇÃO HIDROTERMAL DAS ROCHAS MÁFICAS DO ALVO ESTRELA (Cu-Au), SERRA DOS CARAJÁS, PARÁ