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

IF 5.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Economic Geology Pub Date : 2024-07-04 DOI:10.5382/econgeo.5085

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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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.

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巴西博博雷马省塞里多移动带 Brejuí W-Mo 矽卡岩矿床的可见近红外-短波红外光谱分析和热液蜕变带矿物绘图

布雷朱伊 W-Mo 矽卡岩矿床是塞里多钨省（巴西东北部博博雷马省）的主要白钨矿床。它是巴西最大的白钨矿储量。矿体赋存于塞里多组（650-610Ma）的变质Jucurutu岩层中，靠近新新生代Acari岩体（巴西造山运动）的边缘。矽卡岩包括顺生和逆生矿物组合。红外光谱分析显示，矽卡岩主要反映了逆行矿物组合，形成于三个不同的热液蚀变阶段，并带有叠印。从光谱上检测到的矿物相包括：(1) 蔷薇岩、阳起石和辉绿岩（蚀变阶段 1）；(2) 表长石、绿泥石和伊利石（蚀变阶段 2）；(3) 褐铁矿、蒙脱石、绿泥石和石膏（蚀变阶段 3；主矿区）。在主要的钨钼矽卡岩矿体中观察到辉绿岩绿泥石化和阳起石重结晶。绿泥石化的特征是与 Fe-OH 有关的吸收波长（2,246.5-2,250.5 纳米）发生位移。这里提出了一种光谱指数，它使用了白云石+蒙脱石+阳起石的光谱混合物，用于绘制钻孔岩芯中的矿化矽卡岩层（WO3 + Mo ≥ 0.1%）。该方法已成功用于布雷朱伊矿床富矿化体的定向，也可用于具有相同目的的类似矽卡岩矿床。

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来源期刊

Economic Geology 地学-地球化学与地球物理

CiteScore

10.00

自引率

6.90%

发文量

120

审稿时长

6 months

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.