Morphological and compositional study of quartz and cassiterite of the Mocambo Granite, South Pará Tin Province, Amazonian Craton

Rubem Santa Brígida Barros Neto,Claudio Nery Lamarão,Gisele Tavares Marques,Cristina Valle Pinto-Coelho

doi:10.1590/2317-4889202020190096

Rubem Santa Brígida Barros Neto, Claudio Nery Lamarão + Show 2 more

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https://doi.org/10.1590/2317-4889202020190096

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Abstract

Quartz and cassiterite crystals of granite, greisens, and quartz veins from Mocambo Granite, Carajás Province, were studied by scanning electron microscopy — cathodoluminescence and electron microprobe. Five types of quartz were identified: Qz1, magmatic and Qz2, Qz3, Qz4, and Qz5 hydrothermal. Qz1, anhedric to subhedric, luminescent and fractured at different intensities, predominating in less evolved rocks. Qz2, with low luminescence, is younger than Qz1; it occurs as irregular patches, filling fractures or forming veins that cut Qz1. Qz3, non-luminescent, resulting from continuous alteration, dissolution, and recrystallization processes; fills fractures that cut Qz1 and Qz2. Qz4 occurs in the most evolved and hydrothermalized rocks and in greisens bodies mineralized in cassiterite; is euhedral to subhedral, exhibits well-defined zoning, and has been interpreted as later than the previous one. Qz5 has poor luminescence; occurs in mineralized veins with wolframite and, secondarily, cassiterite. Qz1 shows Ti enrichment, while Qz4 associated with cassiterite is enriched with Al. Well-formed cassiterite crystals exhibit concentric zoning and low Fe, Ti, W, Nb and Mn contents. Qz5-associated cassiterite crystals form inclusions in the wolframite, suggesting that cassiterite and wolframite precipitated from hydrothermal processes at different times.

Highlights

Quartz and cassiterite crystals of granite, greisens, and quartz veins from Mocambo Granite, Carajás Province, were studied by scanning electron microscopy — cathodoluminescence and electron microprobe
(2013, 2014), who showed that quartz is an excellent marker of the magmatic evolution and hydrothermal alterations that acted on mineralized granites of the Amazonian Craton (North of Brazil) and sandstones of the Parnaíba Basin (Northeast of Brazil), with quartz veins containing orange opal
The Velho Guilherme Intrusive Suite (VGIS), located in the Carajás Province, Amazonian Craton, is composed of several anorogenic granite plutons affected by hydrothermal processes at different intensities, commonly mineralized in tin and other rare metals (Abreu and Ramos 1974, Teixeira et al 2002, 2005, Lamarão et al 2012)

Summary

Introduction

Quartz and cassiterite crystals of granite, greisens, and quartz veins from Mocambo Granite, Carajás Province, were studied by scanning electron microscopy — cathodoluminescence and electron microprobe. The Velho Guilherme Intrusive Suite (VGIS), located in the Carajás Province, Amazonian Craton, is composed of several anorogenic granite plutons affected by hydrothermal processes at different intensities, commonly mineralized in tin and other rare metals (Abreu and Ramos 1974, Teixeira et al 2002, 2005, Lamarão et al 2012). Granites in this suite are, a good target for morphological and compositional studies of the different types of quartz and associated mineralization. The main objective of this work was to morphologically, texturally, and compositionally characterize quartz crystals and to correlate them with the intensity of the hydrothermal alteration and mineralization present in rocks and greisen bodies, in addition to characterizing the morphology and composition of cassiterite crystals

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