The Anarraaq clastic-dominated (CD) Zn-Pb-Ag deposit (Red Dog district, Alaska, USA) has an inferred mineral resource of 19.4 Mt at 14.4% Zn, 4.2% Pb, and 73 g/t Ag and is spatially associated with a separate ~1 Gt barite body. This study presents new cross sections and petrographic evidence from the Anarraaq area. The barite body, previously shown to have formed in a shallow subsurface environment akin to a methane cold seep, contains multiple generations of barite with locally abundant calcite masses, which are discordant to sedimentary laminae, and is underlain by an interval of massive pyrite containing abundant framboids and radiolarians. Calcite and pyrite are interpreted to have formed by methane-driven diagenetic alteration of host sediment at the sulfate-methane transition (SMT). The sulfide deposit contains two zones of Zn-Pb mineralization bounded by faults of unknown displacement. The dominant hydrothermal minerals are marcasite, pyrite, sphalerite, quartz, and galena. The presence of hydrothermal pseudomorphs after barite, early pyrite resembling diagenetic pyrite associated with the barite body, and hydrothermal quartz and sphalerite filling voids formed by dissolution of carbonate all suggest that host sediment composition and origin was similar to that of the barite body prior to hydrothermal mineralization. Rhenium-osmium isochron ages of Ikalukrok mudstone (339.1 ± 8.3 Ma), diagenetic pyrite (333.0 ± 7.4 Ma), and hydrothermal pyrite (334.4 ± 5.3 Ma) at Anarraaq are all within uncertainty of one another and of an existing isochron age (~338 Ma) for the Main deposit in the Red Dog district. This indicates that the Anarraaq deposit formed soon after sedimentation and that hydrothermal activity was approximately synchronous in the district. The initial Os composition of the Anarraaq isochrons (0.375 ± 0.019–0.432 ± 0.025) is consistent with contemporaneous seawater, indicating that a mantle source was not involved in the hydrothermal system. This study highlights the underappreciated but important role of early, methane-driven diagenetic processes in the paragenesis of some CD deposits and has important implications for mineral exploration.

中文翻译：

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阿拉斯加红狗区 Anarraaq 碎屑为主的 Zn-Pb-Ag 矿床形成的成岩控制

Anarraaq 碎屑为主 (CD) Zn-Pb-Ag 矿床（美国阿拉斯加州红狗区）的推断矿产资源量为 19.4 Mt，锌含量为 14.4%，铅含量为 4.2%，银含量为 73 克/吨，并且是空间伴生的带有单独的~1 Gt 重晶石体。本研究提供了来自 Anarraaq 地区的新横截面和岩相学证据。重晶石体，先前证明是在类似于甲烷冷渗流的浅表下环境中形成的，包含多代重晶石，局部富含方解石块，与沉积层不协调，下面是含有丰富的块状黄铁矿的间隔。 framboids 和放射虫。方解石和黄铁矿被解释为由在硫酸盐-甲烷转变 (SMT) 的宿主沉积物的甲烷驱动的成岩改变形成。硫化物矿床包含两个以未知位移断层为界的锌铅矿化带。主要的热液矿物有白铁矿、黄铁矿、闪锌矿、石英和方铅矿。重晶石之后的热液假晶、与重晶石体伴生的类似成岩黄铁矿的早期黄铁矿以及碳酸盐溶解形成的热液石英和闪锌矿充填空隙都表明宿主沉积物成分和成因与热液之前的重晶石体相似。矿化。Anarraaq 的 Ikalukrok 泥岩 (339.1 ± 8.3 Ma)、成岩黄铁矿 (333.0 ± 7.4 Ma) 和热液黄铁矿 (334.4 ± 5.3 Ma) 的铼-锇等时线年龄都处于不确定性范围内，并且存在于现有等时线年龄 (~ 338 Ma) 为 Red Dog 区的主要矿床。这表明 Anarraaq 矿床在沉积后很快形成，并且该地区的热液活动大致同步。Anarraaq等时线的初始Os组成（0.375±0.019-0.432±0.025）与同期海水一致，表明地幔源不参与热液系统。这项研究强调了早期甲烷驱动的成岩过程在一些 CD 矿床的共生过程中未被充分认识但很重要的作用，并对矿产勘探具有重要意义。表明地幔源不参与热液系统。这项研究强调了早期甲烷驱动的成岩过程在一些 CD 矿床的共生过程中未被充分认识但很重要的作用，并对矿产勘探具有重要意义。表明地幔源不参与热液系统。这项研究强调了早期甲烷驱动的成岩过程在一些 CD 矿床的共生过程中未被充分认识但很重要的作用，并对矿产勘探具有重要意义。