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Geochemical and tectonic constraints on the genesis of iron formation-hosted magnetite-hematite deposits at the Guanhães Block (Brazil) by contact metasomatism with pegmatite intrusions
Ore Geology Reviews ( IF 3.3 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.oregeorev.2020.103931
Flávia Cristina Silveira Braga , Carlos Alberto Rosière , João Orestes Schneider Santos , Steffen G. Hagemann , Lenoid Danyushevsky , Pedro Valle Salles

Abstract The Horto-Baratinha (HBD) and Cuite (CTE) are two high-grade iron ore deposits (>60% wt. Fe) located in the Guanhaes Tectonic Block (GB), at the eastern margin of the Sao Francisco Craton bordering the late Neoproterozoic–Cambrian Aracuai-West Congo Orogenic belt. The orebodies are hosted by Orosirian to early Statherian metamorphic banded iron formation (IF) associated with quartzite and aluminous schists. The metasedimentary units are time-correlated with the Serra da Serpentina and Serra de Sao Jose Groups exposed in the Southern Espinhaco fold-thrust belt. They occur as tectonic slivers inserted in the pre-Rhyacian gneissic rocks and the granitic plutons of the Statherian Borrachudos Suite that comprise the GB. In the GB, the IF was intruded by anatectic pegmatites of Ediacaran to Cambrian crystallization age with the development of massive, granular magnetite-rich high-grade orebodies at the contact zone, contrasting with the hosting schistose quartz-hematite IF. The Fe-mineralization of the IF during the Brasiliano Orogeny developed in three distinct stages. (1) Syn- to late-collisional stage (ca. 580-560 Ma) with partial Fe enrichment along sheared zones, crystallization of oriented platy hematite crystals and development of discontinuous lens-shaped schistose high-grade orebodies. (2) Syn- to late-collisional stage (ca. 560-530 Ma) with the formation of massive magnetite bodies by contact metamorphic-metasomatism with the pegmatite. (3) Late- to post-tectonic stage with the oxidation of magnetite to kenomagnetite, martite and crystallization of granular hematite, probably by increased input of meteoric fluids during gravitational collapse of the Aracuai-West Congo Orogen (ca. 530-490 Ma). In the HBD deposit, the first mineralization stage was unimportant for the enrichment of the IF that exhibit Fe contents of 32.45 to 43.50 wt.%.Whole-rock data indicates that the massive hematite-magnetite high-grade iron ore pods exhibit Fe contents between 50.24-69.46 wt.%, and increasing content of Al2O3, MgO and CaO and the trace elements Zr, Y, Zn, and Ni near the contact with pegmatite, associated with the presence of interstitial silicates and carbonates in their composition. Lamellar hematite exhibit very low contents of trace elements as in other specularitic IFs and orebodies from the eastern Sao Francisco Craton. A consistent increase in the content of trace elements, mainly Mg, V, Cr, Mn, Co, Ni, Zn, and Ga, is observed in kenomagnetite. Granular hematite grains are enriched an Al, Ti, Zr, Nb, Mo, Sn, Sb, Hf, Ta, and W. Notably, Mn and Ti may occur in relatively high concentrations in kenomagnetite and hematite with the crystallization of ilmenite inclusions, associated with the contact-metasomatic stages.

中文翻译:

通过伟晶岩侵入体接触交代作用对巴西关汉斯地块含铁磁铁矿-赤铁矿矿床成因的地球化学和构造约束

摘要 Horto-Baratinha (HBD) 和 Cuite (CTE) 是两个高品位铁矿床 (>60% wt. Fe),位于 Guanhaes 构造块 (GB),位于圣弗朗西斯科克拉通 (Sao Francisco Craton) 的东部边缘,与晚新元古代-寒武纪阿拉奎-西刚果造山带。矿体位于奥罗斯纪至早期斯塔瑟纪变质带状铁地层 (IF),与石英岩和铝质片岩有关。变沉积单元与南部 Espinhaco 褶皱逆冲带中出露的 Serra da Serpentina 和 Serra de Sao Jose 群具有时间相关性。它们以构造裂片的形式出现,插入到瑞亚阶前片麻岩和构成 GB 的 Statherian Borrachudos Suite 的花岗岩岩体中。在 GB 中,IF 被埃迪卡拉纪至寒武纪结晶时代的深熔伟晶岩侵入,在接触带发育块状、粒状富含磁铁矿的高品位矿体,与寄宿的片状石英-赤铁矿 IF 形成对比。巴西造山运动期间 IF 的铁矿化分三个不同的阶段发展。(1) 碰撞后期(约580-560 Ma),沿剪切带部分Fe富集,定向片状赤铁矿结晶,不连续透镜状片状高品位矿体发育。(2) 同碰撞后期(约 560-530 Ma),通过与伟晶岩接触变质交代形成块状磁铁矿体。(3) 晚期至后构造阶段,磁铁矿氧化为钾磁铁矿,黑铁矿和粒状赤铁矿的结晶,可能是由于阿拉奎伊-西刚果造山带(约 530-490 Ma)重力坍塌期间流星液的输入增加。在 HBD 矿床中,第一矿化阶段对于 IF 的富集并不重要,其 Fe 含量为 32.45 至 43.50 wt.%。全岩数据表明,块状赤铁矿-磁铁矿高品位铁矿荚的 Fe 含量介于50.24-69.46 wt.%,增加 Al2O3、MgO 和 CaO 以及与伟晶岩接触附近的微量元素 Zr、Y、Zn 和 Ni 的含量,这与它们的组成中存在间隙硅酸盐和碳酸盐有关。片层状赤铁矿的微量元素含量非常低,与圣弗朗西斯科克拉通东部的其他镜面岩和矿体一样。在钾磁铁矿中观察到微量元素的含量持续增加,主要是 Mg、V、Cr、Mn、Co、Ni、Zn 和 Ga。粒状赤铁矿晶粒富含 Al、Ti、Zr、Nb、Mo、Sn、Sb、Hf、Ta 和 W。值得注意的是,Mn 和 Ti 可能以相对较高的浓度存在于钾磁铁矿和赤铁矿中,伴随钛铁矿夹杂物的结晶,伴生与接触交代阶段。
更新日期:2021-02-01
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