Visible-Near Infrared–Short-Wave Infrared Spectroscopy and Mineral Mapping of Hydrothermal Alteration Zones at the Brejuí W-Mo Skarn Deposit, Seridó Mobile Belt, Borborema Province, Brazil
Manoel Augusto Corrêa da Costa, João Luís Carneiro Naleto, Mônica Mazzini Perrotta, Lena Virgínia Soares Monteiro, C. R. de Souza Filho
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引用次数: 0
Abstract
The Brejuí W-Mo skarn deposit is the main scheelite deposit of the Seridó tungsten province (Borborema province, NE Brazil). It constitutes the largest Brazilian W ore reserve. The orebodies are hosted in the metasedimentary Jucurutu Formation of the Seridó Group (650–610 Ma), close to the margin of the Neoproterozoic Acari pluton (Brasiliano orogeny). Skarns include prograde and retrograde mineral assemblages. Infrared spectral analysis shows that the skarns mainly reflect retrograde mineral assemblages, formed in three different hydrothermal alteration stages with overprinting. Mineral phases spectrally detected include (1) vesuvianite, actinolite, and phlogopite (alteration stage 1), (2) epidote, prehnite, and illite (alteration stage 2), and (3) laumontite, montmorillonite, chlorite, and gypsum (alteration stage 3; main ore zone). Phlogopite chloritization and actinolite recrystallization were observed in the main W-Mo skarn orebodies. Chloritization is marked by a displacement in the Fe-OH–related absorption wavelength (2,246.5–2,250.5 nm). A spectral index using spectral mixtures of laumontite + montmorillonite + actinolite is proposed here to map mineralized skarn layers (WO3 + Mo ≥ 0.1%) in drill cores. It was used to vector to richer mineralized bodies of the Brejuí deposit successfully and may be applied to similar skarn deposits with the same aim.
期刊介绍:
The journal, now published semi-quarterly, was first published in 1905 by the Economic Geology Publishing Company (PUBCO), a not-for-profit company established for the purpose of publishing a periodical devoted to economic geology. On the founding of SEG in 1920, a cooperative arrangement between PUBCO and SEG made the journal the official organ of the Society, and PUBCO agreed to carry the Society''s name on the front cover under the heading "Bulletin of the Society of Economic Geologists". PUBCO and SEG continued to operate as cooperating but separate entities until 2001, when the Board of Directors of PUBCO and the Council of SEG, by unanimous consent, approved a formal agreement of merger. The former activities of the PUBCO Board of Directors are now carried out by a Publications Board, a new self-governing unit within SEG.