In the Kalahari Copperbelt, the mechanism of regional scale Cu-Ag mineralization has remained intensely debated between early diagenesis and a single pass during a regional deformation event. At the Zone 5 Cu-Ag deposit in northwestern Botswana, the orebody is hosted preferentially by chemically reduced metasedimentary rocks that overly oxidized, hematite-bearing arkosic sandstone. An early diagenetic mineralizing event has been identified which is characterized by fine-grained stratiform pyrite, including recrystallized framboidal pyrite, intergrown with diagenetic mineral assemblages in the host-rock. Diagenetic pyrite is in textural equilibrium with chalcopyrite, sphalerite, galena, and (Fe-Co-Ni) sulfarsenide. These minerals were subsequently overprinted by a more intense, multi-stage, structurally-controlled hydrothermal Cu-Ag mineralization event related to the Damaran orogeny (~600–480 Ma). The hydrothermal Cu-Ag mineralization was deposited from hot (~236–265°C), high salinity (19–24.6 wt% NaCl equiv.) hydrothermal ore fluids. Petrographic results reveal an apparent overlap in trace metal associations (Cu, Fe, As, Zn, Pb, Ni, Co) between the two mineralizing events, which can be explained by remobilization of precursor sulfides. The major Ag-carriers in the ore are chalcocite, covellite, and bornite. The δ³⁴S values of diagenetic pyrite range from −35.8 to +11.4‰, whereas those of hydrothermal epigenetic sulfides, including pyrite, range from −28.0 to +3.0‰. We propose that the hydrothermal sulfides had acquired some bacterially-reduced sulfur from earlier-formed minerals. The δ¹⁸O and δ¹³C values of quartz and calcite associated with the hydrothermal mineralization are typical of Neoproterozoic sediment-hosted Cu-Ag deposits. However, the δ¹⁸O isotopic values of the calcite gangue are anomalously depleted, which is likely due to recrystallization under metamorphic conditions. Our studies at Zone 5 indicate that the Zone 5 Cu-Ag deposit is the result of a multi-stage mineralization history that includes both diagenetic and epigenetic events (punctuated by >400 m.y.) facilitated by a strong litho-structural control.

中文翻译：

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博茨瓦纳西北部卡拉哈里铜带 Khoemacau Zone 5 矿床中铜银矿化的成岩和表观成因

在喀拉哈里铜带，区域尺度的铜银矿化机制在早期成岩作用和区域变形事件中的单程之间一直存在激烈的争论。在博茨瓦纳西北部的 5 区 Cu-Ag 矿床，矿体主要由化学还原的变沉积岩组成，这些变沉积岩过度氧化、含赤铁矿的长石砂岩。已经确定了一个早期的成岩成矿事件，其特征是细粒层状黄铁矿，包括重结晶的扇形黄铁矿，与主岩中的成岩矿物组合共生。成岩黄铁矿与黄铜矿、闪锌矿、方铅矿和（Fe-Co-Ni）硫砷化物处于结构平衡状态。这些矿物随后被更强烈的、多阶段的、与达马兰造山运动（~600-480 Ma）相关的受结构控制的热液Cu-Ag矿化事件。热液 Cu-Ag 矿化由热（~236–265°C）、高盐度（19–24.6 wt% NaCl equiv.）热液矿液沉积。岩相学结果显示，两个矿化事件之间的微量金属缔合（Cu、Fe、As、Zn、Pb、Ni、Co）存在明显重叠，这可以通过前体硫化物的再迁移来解释。矿石中的主要银载体是辉铜矿、铜蓝和斑铜矿。δ Co）在两个矿化事件之间，这可以通过前体硫化物的再迁移来解释。矿石中的主要银载体是辉铜矿、铜蓝和斑铜矿。δ Co）在两个矿化事件之间，这可以通过前体硫化物的再迁移来解释。矿石中的主要银载体是辉铜矿、铜蓝和斑铜矿。δ^{成岩黄铁矿的34} S 值范围为 -35.8 至 +11.4‰，而包括黄铁矿在内的热液表生硫化物的 34 S 值范围为 -28.0 至 +3.0‰。我们提出热液硫化物从早期形成的矿物中获得了一些细菌还原的硫。与热液成矿作用相关的石英和方解石的δ ¹⁸ O 和δ ¹³ C 值是新元古代沉积物为主的Cu-Ag 矿床的典型特征。然而，δ ¹⁸方解石脉石的 O 同位素值异常减少，这可能是由于变质条件下的再结晶。我们在 5 区的研究表明，5 区铜银矿床是多阶段成矿历史的结果，包括成岩和表观成因事件（间断 > 400 米），由强大的岩石结构控制促成。