Abstract Widespread Ni-Mo sulfide mineralization in South China during the early Cambrian may have affected the seawater chemistry and biodiversity of this region, but its underlying causes are not well-understood. To better understand the formation of sulfide ores in early Cambrian marine systems, this study evaluated the paragenesis and sulfur isotopic composition (δ34S) of sediment-hosted Ni-Mo sulfide ores in the lower Cambrian Niutitang Formation of the Nanhua Basin of South China. Petrographic analysis revealed three types of sulfide aggregates: (1) ubiquitous framboidal and euhedral pyrite (Py-1), (2) a MoSC phase (i.e., Mo mineralization) that was cogenetic with larger pyrite cubes or nodules (Py-2), and (3) intergrown millerite (NiS), sphalerite (ZnS) and veined pyrite (Py-3) (i.e., Ni-Zn mineralization) characterized by laminated and veined textures. Alternating precipitation of Mo and Ni-Zn sulfides was caused by intermittent emission of Mo-Fe or Ni-Zn-rich hydrothermal fluids into euxinic mid-depth waters of the Nanhua Basin, representing a sedimentary exhalative (SEDEX) process. The different sedimentary ore textures are each associated with a characteristic δ34S distribution. At all study sites, the syngenetic Py-1 phase yields δ34S of −15.7 to + 1.9‰, consistent with a seawater sulfate source that was variably fractionated through microbial sulfate reduction (MSR). In the Nayong and Zunyi areas, δ34S values of −11.8 to +4.4‰ are associated with the MoSC phase, and −20.6 to −6.8‰ with the Py-2 phase. In the Zhangjiajie area, Py-2 yields similar values (−25.1 to −10.8‰) but MoSC higher and less variable values (+8.6 to +18.7‰). These phases are thought to contain a mixture of sulfur sourced from seawater sulfate (via MSR) and hydrothermal fluids in varying proportions. A mode of Ni-Zn sulfides δ34S values between −9.1 and +8.0‰ is likely to represent the isotopic composition of hydrothermal sulfur inputs to the Ni-Zn mineralization. As a consequence, both hydrothermal emissions and biogenic production of H2S had a significant influence on seawater chemistry, with consequences for contemporaneous evolution of early marine animal life (e.g., the small shelly fauna and Chengjiang Biota) in the early Cambrian Nanhua Basin.

中文翻译：

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华南早寒武世南华盆地SEDEX矿石岩相学及硫同位素组成

摘要 早寒武世华南地区广泛的镍钼硫化物矿化可能对该地区的海水化学和生物多样性产生了影响，但其深层原因尚不清楚。为了更好地了解早寒武世海相系统中硫化矿的形成，本研究评估了华南南华盆地下寒武统牛蹄塘组沉积物中镍钼硫化矿的共生作用和硫同位素组成（δ34S）。岩石学分析揭示了三种类型的硫化物聚集体：(1) 无处不在的 framboidal 和自形黄铁矿 (Py-1)，(2) 与较大的黄铁矿立方体或结核 (Py-2) 共生的 MoSC 相（即 Mo 矿化）， (3) 共生的闪锌矿 (NiS)、闪锌矿 (ZnS) 和脉状黄铁矿 (Py-3)（即，Ni-Zn 矿化）以层状和脉状结构为特征。Mo 和 Ni-Zn 硫化物的交替沉淀是由于富含 Mo-Fe 或 Ni-Zn 的热液间歇性排放到南华盆地的富氧中深水体中引起的, 代表了沉积喷出 (SEDEX) 过程。不同的沉积矿石结构各自与特征性的 δ34S 分布有关。在所有研究地点，同生 Py-1 相产生 -15.7 至 + 1.9‰的 δ34S，与通过微生物硫酸盐还原 (MSR) 可变分馏的海水硫酸盐来源一致。在纳雍和遵义地区，-11.8～+4.4‰的δ34S值与MoSC相有关，-20.6～-6.8‰与Py-2相有关。在张家界地区，Py-2 产生相似的值（-25.1 至 -10.8‰），但 MoSC 更高且变量值更小（+8. 6 到 +18.7‰）。这些相被认为包含来自海水硫酸盐（通过 MSR）和不同比例的热液流体的硫混合物。Ni-Zn 硫化物 δ34S 值介于 -9.1 和 +8.0‰ 之间的模式可能代表了 Ni-Zn 矿化的热液硫输入的同位素组成。因此，热液排放和 H2S 的生物产生对海水化学有显着影响，对早期寒武纪南华盆地早期海洋动物（如小型贝类动物群和澄江生物群）的同时进化产生影响。0‰可能代表Ni-Zn矿化的热液硫输入的同位素组成。因此，热液排放和 H2S 的生物产生对海水化学有显着影响，对早期寒武纪南华盆地早期海洋动物（如小型贝类动物群和澄江生物群）的同时进化产生影响。0‰可能代表Ni-Zn矿化的热液硫输入的同位素组成。因此，热液排放和 H2S 的生物产生对海水化学有显着影响，对早期寒武纪南华盆地早期海洋动物（如小型贝类动物群和澄江生物群）的同时进化产生影响。