The genetic relationship between organic-rich source rocks and Hg deposits remains the subject of debate. This paper evaluates the role of organic-rich source rocks in cinnabar ore formation in the Terlingua mining district, Texas, which was deposited at relatively shallow depths in Cretaceous sedimentary rocks spatially related to intrusive alkali igneous rocks.The mineralization formed at ~45 bar and ~200°C. The aqueous ore-forming fluid had a pH of ~5 to 7 and was H₂S saturated. Cinnabar was deposited as a result of H₂S oxidation through mixing and cooling with local meteoric water. Both Hg⁰_(org) and Hg⁰_(aq) species were likely important in cinnabar ore formation. However, recent studies on the solubility of Hg⁰ in hydrocarbons show that at cinnabar saturation, Hg⁰ is more than an order of magnitude more soluble in hydrocarbons (Hg⁰_(org) = 163 mg/kg) than Hg⁰ in water (Hg⁰_(aq) = 10.8 mg/kg). Despite their proximity in some deposits, conditions of ore formation of the rare Hg oxychloride and sulfate minerals are not compatible with conditions under which most cinnabar ores formed, requiring fO2 conditions orders of magnitude more oxidizing, a relatively high chloride ion activity (>10^–1), and alkaline conditions, with pH > 10.Mass dependent fractionation versus mass independent fractionation of Hg isotope data from Hg-bearing minerals in Terlingua support a genetic link to the source of Hg being the organic-rich marls and tuffaceous black shales of the Lower Eagle Ford Formation. This source rock is chronostratigraphically equivalent to the Lower Cretaceous oceanic anoxic event (OAE-2), which defines the Cenomanian-Turonian boundary. OAE-2 represents the culmination of a global anoxic ocean event at ~94.1 Ma, believed to be a consequence of volcanic activity associated with a large igneous province. Mercury was sequestered by the organic-rich source rocks of the Lower Eagle Ford Formation and associated coeval ash and tuffs.Tabular igneous bodies that intruded and uplifted the local stratigraphy formed the Terlingua monocline and provided a source of heat for hydrothermal activity and maturation of organic matter. The subsequent generation and migration of liquid hydrocarbons and formation brines from the Lower Eagle Ford Formation transported Hg⁰_(org) updip toward the hinge line of the Terlingua monocline where mixing with oxygenated meteoric water and subsequent oxidation of H₂S produced the cinnabar-rich ores.

中文翻译：

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阐明碳氢化合物在朱砂 (HgS) 矿石形成中的作用：德克萨斯州西南部大弯国家公园 Terlingua 矿区的汞矿化模型

富含有机质烃源岩和汞矿床之间的成因关系仍然是争论的主题。本文评估了德克萨斯州 Terlingua 矿区富含有机物烃源岩在朱砂矿形成中的作用，朱砂矿沉积在白垩纪沉积岩中相对较浅的位置，在空间上与侵入性碱性火成岩有关。矿化形成于 ~45 bar 和〜200°C。含水成矿流体具有～5至7的pH并且是H ₂ S饱和的。朱砂是通过与当地大气水混合和冷却而发生 H ₂ S 氧化而沉积的。Hg ⁰ _(org)和 Hg ⁰ _(aq)物种可能对朱砂矿石的形成很重要。^{然而，最近对Hg 0}在烃类中溶解度的研究表明，在朱砂饱和状态下，Hg ⁰在烃类中的溶解度（Hg ^{0 (org) = 163 mg/kg）比Hg 0}在水中的溶解度（Hg 0 _(org) = 163 mg/kg）高出一个数量级以上。 ⁰ _{（水溶液）} = 10.8 毫克/千克）。尽管在一些矿床附近，稀有的氯氧化汞和硫酸盐矿物的矿石形成条件与大多数朱砂矿石的形成条件并不相容，要求 fO2 条件更具氧化性、相对较高的氯离子活性 (>10 ^{– 1} ) 和碱性条件，pH > 10。来自 Terlingua 含汞矿物的汞同位素数据的质量依赖分馏与质量无关分馏支持汞来源与富含有机物泥灰岩和凝灰质黑色页岩的遗传联系。下伊格尔福特地层。该烃源岩在年代地层上相当于下白垩统海洋缺氧事件（OAE-2），它定义了塞诺曼阶-土伦阶边界。OAE-2 代表约 94.1 Ma 的全球缺氧海洋事件的顶峰，据信是与大型火成岩省相关的火山活动的结果。汞被下 Eagle Ford 组的富含有机物的烃源岩以及相关的同时代灰烬和凝灰岩所封存。侵入并抬升当地地层的板状火成体形成了 Terlingua 单斜，并为热液活动和有机物成熟提供了热源。事情。随后来自下 Eagle Ford 地层的液态烃和地层卤水的生成和迁移将 Hg ⁰ _(org)向上倾输送至 Terlingua 单斜斜线的铰链线，在那里与含氧大气水混合以及随后 H ₂ S 的氧化产生了富含朱砂的物质。矿石。