Clastic dominant-type massive sulfide deposits are well preserved in Upper Devonian carbonaceous mudstones in the Macmillan Pass district (Yukon, Canada). The Macmillan Pass deposits have been considered to be type examples of sedimentary exhalative Zn-Pb mineralization, whereby sulfides precipitated when hydrothermal fluids were vented into a euxinic (H₂S-bearing) water column. We propose a new mineralization model, documenting the mineralogical evolution of layered mineralization. We show that textures previously interpreted to form via depositional processes actually formed by subseafloor replacement of diagenetic barite. Mineral assemblages associated with barite dissolution in the layered mineralization include (1) barium carbonate phases (witherite, barytocalcite, and norsethite), which are intergrown with Zn-Pb sulfides and represent localized Ba mass transfer, and (2) barium feldspar (celsian, hyalophane) that is abundant in the mudstones surrounding the layered mineralization. The barium feldspar formed following transport of Ba in low-sulfate fluids on the margins of the subseafloor replacement system. This resulted in whole-rock Ba enrichments (up to 5 wt %) in mudstones 15 m below and above the layered mineralization. High Ba in these surrounding mudstones is coupled with decreasing K/Al ratios, indicative of secondary illite and kaolinite. The source(s) of fluids related to the diagenetic (barite, barytocalcite) and hydrothermal (ankerite) assemblages can be constrained using Sr isotopes. Whereas highly radiogenic ⁸⁷Sr/⁸⁶Sr values (>0.714) in ankerite correspond with host-rock alteration within the vent complex, the overlying barite and barytocalcite preserve lower ⁸⁷Sr/⁸⁶Sr values (<0.714), providing evidence of mixing between a radiogenic fluid (likely a formation water) and Late Devonian seawater. The complex mineralogy and paragenesis contained within the layered mineralization are linked to a protracted history of diagenetic and hydrothermal fluid events, all of which took place in and peripheral to a subseafloor replacement hydrothermal system.

中文翻译：

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麦克米伦Pass口（加拿大育空）碎屑优势型Zn-Pb±Ba矿床的矿物学演化-分层成矿作用中的海底重晶石置换

碎屑优势型块状硫化物矿床保存在麦克米伦district口地区（加拿大育空）的上泥盆统碳质泥岩中。Macmillan Pass矿床被认为是沉积性呼出气中Zn-Pb矿化的典型例子，当水热流体排入富余性（H ₂S轴承）水柱。我们提出了一个新的矿化模型，记录了分层矿化的矿物学演化。我们表明，先前解释为通过沉积过程形成的纹理实际上是由成岩重晶石的海底置换形成的。与层状矿化中重晶石溶解相关的矿物组合包括（1）与Zn-Pb硫化物共生并代表局部Ba传质的碳酸钡相（钙铁矿，重钙钙石和水钠钙石），以及（2）钡长石（celsian，透明玻璃质），在分层成矿作用周围的泥岩中含量丰富。钡长石是在海底置换系统边缘将Ba运入低硫酸盐流体后形成的。这导致在分层成矿作用之下和之上15 m的泥岩中，整个岩石中的Ba富集（最多5 wt％）。这些周围泥岩中的高Ba与降低的K / Al比相结合，表明次生伊利石和高岭石。可以使用Sr同位素限制与成岩作用（重晶石，重晶石方解石）和热液（铁矾石）组合有关的流体源。而高放射原性闪锌矿中⁸⁷ Sr / ⁸⁶ Sr值（> 0.714）对应于发泄复合体内的主岩蚀变，上覆的重晶石和重晶石保留较低的⁸⁷ Sr / ⁸⁶ Sr值（<0.714），提供了放射源流体之间混合的证据（可能是地层水）和泥盆纪晚期海水。分层矿化中包含的复杂矿物学和共生作用与成岩和热液流体事件的悠久历史有关，所有这些都发生在海底置换热液系统中和外围。