In contrast to base- and precious-metal deposits associated with igneous activity, surface manifestations of ore formation at depth in continental sedimentary basins have not been recognized. Herein, the surface expressions of fluids capable of forming deeper red-bed copper deposits—a sediment-hosted stratiform copper deposit subtype—are documented from the central Andean Altiplano-Puna Plateau in northwest Argentina. Thermogene travertine and tufa of Quaternary age are common on the Altiplano-Puna Plateau but those at La Borita and Quebrada Angosta, both underlain by thick red-bed sedimentary sequences, are unusual in being well mineralized with copper, chiefly in the form of the arsenates, lavendulan, and conichalcite. La Borita travertine is also cut by a late, lead-bearing vein dominated by the chlorocarbonate, phosgenite. Drilling beneath the travertine at La Borita intersected up to ~ 250 m of anomalous zinc (up to 350 ppm), lead (up to 250 ppm), and arsenic (up to 500 ppm), but low copper, values in unaltered red-beds. Several sources for the copper, arsenic, and subsidiary base metals and accompanying silver in the travertine and distal tufa at La Borita and Quebrada Angosta have been considered, including in situ supergene oxidation of sulfides, exotic deposition peripheral to porphyry copper deposits undergoing supergene sulfide oxidation and enrichment, and direct magmatic fluid input. However, all these possible mechanisms are precluded by definitive geological, mineralogical, and geochemical evidence. The only viable travertine-forming fluid capable of metal introduction is a low-temperature, near-neutral to weakly alkaline, oxidized chloride brine. Such fluids are common in sedimentary basins, including those in the Altiplano-Puna Plateau, and are capable of leaching base metals, arsenic, and silver from red-bed sedimentary sequences and underlying rocks. If the metal-bearing fluids encounter reductants, they can generate red-bed copper deposits, as occurred in Eocene to Miocene red-bed strata throughout the Altiplano-Puna Plateau. In the absence of reductants, however, copper can continue to be leached, consistent with its absence in the red-beds beneath the travertine at La Borita. Bearing in mind the arid climate, evaporation may have induced precipitation of the travertine-hosted copper and accompanying elements, with arsenic abundance accounting for the prevalence of the copper arsenates.

与与火成岩活动相关的贱金属和贵金属矿床相比，大陆沉积盆地深处矿石形成的表面表现尚未得到认可。在这里，来自阿根廷西北部安第斯高原中部的安第斯高原-普纳高原中部记录了能够形成更深的红床铜矿床（一种沉积物承载的层状铜矿床亚型）的流体的表面表现。第四纪热成因石灰华和凝灰岩在高原-普纳高原上很常见，但在 La Borita 和 Quebrada Angosta 都被厚厚的红床沉积层序所覆盖，它们的铜矿化程度不同，主要以砷酸盐的形式存在, 薰衣草, 和 conichalcite。La Borita 石灰华也被一个晚期的含铅矿脉所切割，该矿脉以氯碳酸盐光气岩为主。在 La Borita 石灰华下方的钻探发现了高达约 250 m 的异常锌（高达 350 ppm）、铅（高达 250 ppm）和砷（高达 500 ppm），但在未改变的红层中铜含量较低. 已经考虑了在 La Borita 和 Quebrada Angosta 的石灰华和远端凝灰岩中铜、砷和次要贱金属以及伴随的银的几个来源，包括硫化物的原位表生氧化、斑岩铜矿床外围经历表生硫化物氧化的外来沉积和富集，并直接输入岩浆流体。然而，所有这些可能的机制都被确定的地质、矿物学和地球化学证据所排除。唯一可行的能够引入金属的石灰华形成流体是低温、近中性至弱碱性的氧化氯化盐水。这种流体在沉积盆地中很常见，包括在 Altiplano-Puna 高原的沉积盆地，并且能够从红床沉积序列和下伏岩石中浸出贱金属、砷和银。如果含金属流体遇到还原剂，它们会产生红床铜矿床，就像整个高原-普纳高原的始新世至中新世红床地层一样。然而，在没有还原剂的情况下，铜可以继续被浸出，这与 La Borita 石灰华下方的红床中没有铜是一致的。考虑到干旱的气候，蒸发可能导致钙华承载的铜和伴随元素的沉淀，砷的丰度是砷酸铜普遍存在的原因。并且能够从红床沉积序列和下伏岩石中浸出贱金属、砷和银。如果含金属流体遇到还原剂，它们会产生红床铜矿床，就像整个高原-普纳高原的始新世至中新世红床地层一样。然而，在没有还原剂的情况下，铜可以继续被浸出，这与 La Borita 石灰华下方的红床中没有铜是一致的。考虑到干旱的气候，蒸发可能导致钙华承载的铜和伴随元素的沉淀，砷的丰度是砷酸铜普遍存在的原因。并且能够从红床沉积序列和下伏岩石中浸出贱金属、砷和银。如果含金属流体遇到还原剂，它们会产生红床铜矿床，就像整个高原-普纳高原的始新世至中新世红床地层一样。然而，在没有还原剂的情况下，铜可以继续被浸出，这与 La Borita 石灰华下方的红床中没有铜是一致的。考虑到干旱的气候，蒸发可能导致钙华承载的铜和伴随元素的沉淀，砷的丰度是砷酸铜普遍存在的原因。它们可以生成红床铜矿床，就像在整个 Altiplano-Puna 高原的始新世至中新世红床地层中发生的那样。然而，在没有还原剂的情况下，铜可以继续被浸出，这与 La Borita 石灰华下方的红床中没有铜是一致的。考虑到干旱的气候，蒸发可能导致钙华承载的铜和伴随元素的沉淀，砷的丰度是砷酸铜普遍存在的原因。它们可以生成红床铜矿床，就像在整个 Altiplano-Puna 高原的始新世至中新世红床地层中发生的那样。然而，在没有还原剂的情况下，铜可以继续被浸出，这与 La Borita 石灰华下方的红床中没有铜是一致的。考虑到干旱的气候，蒸发可能导致钙华承载的铜和伴随元素的沉淀，砷的丰度是砷酸铜普遍存在的原因。