The Kiaka orogenic gold deposit (Burkina Faso), located in the Paleoproterozoic domain of the West African Craton, is characterized by a two-stage gold mineralization hosted in volcano-sedimentary metamorphic rocks that was formed during the Eoeburnean (2.20–2.13 Ga) and Eburnean (2.13–2.05 Ga) orogenic cycles. These two stages include an early disseminated low-grade gold mineralization and a late vein-hosted high-grade gold mineralization. Paragenetic studies indicate that the first gold stage was coeval with the deposition of hydrothermal tourmaline. The aim of this paper is twofold: (i) to determine the processes responsible for deposition of the economic disseminated gold mineralization and (ii) to identify the source of the mineralizing fluids. For this purpose, we performed an in situ study on tourmaline by combining electron probe microanalysis and secondary ion mass spectrometry measurements of boron isotopes. Hydrothermal tourmaline hosted in metamafic volcanic rocks and metagreywackes has a dravite composition but shows different δ11B values falling within the two intervals of − 25.1 to − 22.0‰ and − 19.6 to − 15.1‰, respectively. Our results suggest that tourmaline formed from a distal, high-temperature (ca. 400 °C), reduced, and low-salinity hydrothermal fluid that interacted with the local host rocks. Based on the modeling of tourmaline–fluid boron isotope fractionation, we propose a metamorphic fluid origin derived from devolatilization of deeply buried muscovite schists during the regional prograde to peak metamorphism prior ca. 2.13 Ga. This metamorphic fluid–rock interaction model may possibly extend to other orogenic gold deposits in the West African Craton.

中文翻译：

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来自 Kiaka 造山带金矿床（布基纳法索、西非克拉通）的电气石的化学和硼同位素组成作为成矿过程的代表

Kiaka 造山带金矿床（布基纳法索）位于西非克拉通的古元古代域，其特征是两阶段金矿化存在于火山沉积变质岩中，形成于 Eoeburnean（2.20-2.13 Ga）和Eburnean (2.13–2.05 Ga) 造山旋回。这两个阶段包括早期浸染的低品位金矿化和晚期脉状高品位金矿化。共生研究表明，第一个黄金阶段与热液碧玺的沉积同时期。本文的目的是双重的：(i) 确定负责经济扩散金矿化沉积的过程和 (ii) 确定矿化流体的来源。以此目的，我们通过结合电子探针微量分析和硼同位素的二次离子质谱测量，对电气石进行了原位研究。赋存于变镁铁质火山岩和变灰岩中的热液碧玺具有辉石成分，但显示出不同的 δ11B 值，分别落在 - 25.1 至 - 22.0‰ 和 - 19.6 至 - 15.1‰ 的两个区间内。我们的研究结果表明，电气石是由与当地主岩相互作用的远端、高温（约 400 °C）、还原和低盐度的热液形成的。基于电气石-流体硼同位素分馏模型，我们提出了一种变质​​流体来源，该变质流体起源于大约 10 年前的区域前移至峰值变质作用期间深埋白云母片岩的脱挥发分。2.13 嘎。