The Alto Guaporé gold province, southwestern Amazon craton, contains gold deposits that have been mined since the beginning of the 18th century and these deposits, together, have modern-day, pre-mining gold resources of at least 1.8 Moz. The ore is associated with quartz vein systems along the southeastern part of the Aguapei belt, a ~35-km-wide and ~500-km-long, NNW-trending shear zone formed due to reactivation of a terrane-bounding suture. The Aguapei belt evolved by ca. 1150 to 1100 Ma rifting and deposition of siliciclastic sediments in an aulacogen basin, followed by deformation and low-grade metamorphism of the sedimentary sequences during 1100 to 900 Ma terrane collision along the craton margin. The deformation was characterized by a compressional regime until ca. 950 Ma and transition to a transpressional setting during the final 50 m.y.The gold deposits are hosted in a variety of structures that are second-order to the main Aguapei shear zone. The Ernesto and Pau-a-Pique deposits are located ~40 km apart and at jogs along the Aguapei belt. They are marginal to pre-ore igneous rocks, with Ernesto hosted in the basal part of the metasedimentary Fortuna Formation that overlies tonalite and Pau-a-Pique at the contact between metasedimentary rocks and diorite. Three deformational phases comprise the compressional (D₁ to D₂) to transpressional (D₃) tectonic events. In the Pau-a-Pique deposit and the deeper level of the Ernesto deposit, the ore-bearing veins are bedding parallel and follow D₂ strike-slip and reverse fault zones, respectively. However, the veins formed during D₃ reactivation of the older structures by an array of oblique accommodation faults. In contrast, ores at shallower levels of Ernesto, both in discordant and bedding-parallel veins, are hosted within a ~20-m-thick rigid metaconglomerate with associated dilation due to the structural complexity as sedimentary rocks of the Aguapei Group were folded around the dome-shaped roof of the pre-ore tonalite. The ores in both deposits, as well as in many other deposits of the province, are characterized by disseminated and vein-hosted pyrite. Gold occurs mainly as inclusions in the pyrite, with other hydrothermal phases comprising muscovite, Fe-Ti oxides, and minor apatite, chalcopyrite, and galena.Fluid inclusion data, coupled with stable isotope geochemistry and geothermometry, indicate that gold precipitated from a low-salinity, CO₂-rich fluid at ~300°C and ~2.5 kbar. The source for the fluid and gold was the interbedded pelites during devolatilization of the Aguapei Group sequence. The aqueous-carbonic fluid inclusions and the narrow range of δ¹⁸O values of quartz (12 ± 1‰) from many auriferous veins from the central part of the province represent a regional ore-forming fluid. The broad range of δD for hydrous minerals (–116 to –55‰) reflects influx of small amounts of meteoric water into the steeply dipping shear zones during postgold exhumation. The ⁴⁰Ar/³⁹Ar geochronology from hydrothermal muscovite indicates a widespread hydrothermal event along the belt between 928 and 920 Ma. Collectively, the geological, geochronological, and geochemical data suggest that metamorphic fluids migrated laterally into and then upward along the Aguapei belt and deposited gold in lower-order structures where strain gradients existed between lithounits. The province has many characteristics of large orogenic gold provinces worldwide and represents a highly prospective and underexplored target region for early Neoproterozoic gold, a time period that generally is not well endowed in gold ores.

中文翻译：

---

巴西西部亚马逊克拉通西南部上瓜波雷省的新元古代早期金矿床

亚马逊克拉通西南部的 Alto Guaporé 黄金省包含自 18 世纪初以来开采的金矿床，这些矿床共同拥有至少 1.8 Moz 的现代预开采金资源。该矿石与沿 Aguapei 带东南部的石英脉系统有关，这是一个约 35 公里宽、约 500 公里长的 NNW 向剪切带，由于地体边界缝合线的重新激活而形成。Aguapei 带由大约进化。1150-1100 Ma 裂谷和硅质碎屑沉积物沉积在 aulacogen 盆地，随后在 1100-900 Ma 地体碰撞期间沉积层序变形和低级变质作用沿克拉通边缘。变形的特征是压缩状态直到大约。950 Ma 并在最后 50 我 金矿床位于主要 Aguapei 剪切带的二级构造中。Ernesto 和 Pau-a-Pique 矿床相距约 40 公里，位于 Aguapei 带的缓坡处。它们位于前成矿火成岩的边缘，Ernesto 位于变沉积的 Fortuna 组的基底部分，该组位于变沉积岩和闪长岩之间的接触处，覆盖在云母岩和 Pau-a-Pique 之上。三个变形阶段包括压缩（D Ernesto 位于变沉积的 Fortuna 组的基底部分，该组位于变沉积岩和闪长岩之间的接触处，覆盖在钠长石和 Pau-a-Pique 上。三个变形阶段包括压缩（D Ernesto 位于变沉积的 Fortuna 组的基底部分，该组位于变沉积岩和闪长岩之间的接触处，覆盖在钠长石和 Pau-a-Pique 上。三个变形阶段包括压缩（D₁至 D ₂ ) 至横压 (D ₃ ) 构造事件。在 Pau-a-Pique 矿床和更深层次的 Ernesto 矿床中，含矿脉呈平行层理，分别沿着 D ₂走滑带和逆断层带。然而，在 D ₃期间形成的静脉通过一系列倾斜的调节断层重新激活旧结构。相比之下，Ernesto 较浅层的矿石，无论是在不协调的还是平行层理的矿脉中，都位于一个约 20 米厚的刚性变砾岩中，由于结构复杂，因为 Aguapei 组的沉积岩在周围折叠矿石前色调长石的圆顶形屋顶。两个矿床以及该省许多其他矿床中的矿石都以浸染和脉状黄铁矿为特征。金主要以包裹体形式存在于黄铁矿中，其他热液相包括白云母、Fe-Ti 氧化物和少量磷灰石、黄铜矿和方铅矿。流体包裹体数据，加上稳定的同位素地球化学和地球测温，表明金从低盐度，CO ₂- 在 ~300°C 和 ~2.5 kbar 下的富流体。流体和金的来源是 Aguapei 群层序脱挥过程中的互层泥质岩。来自该省中部多条含金矿脉的水相-碳酸流体包裹体和窄范围的石英δ ¹⁸ O值（12±1‰）代表了一种区域性成矿流体。含水矿物的 δD 范围很广（–116 到 –55‰）反映了在后金开采过程中少量大气水流入陡倾剪切带。的⁴⁰的Ar / ³⁹来自热液白云母的 Ar 年代学表明，在 928 至 920 Ma 之间沿着该带发生了广泛的热液事件。总的来说，地质、年代学和地球化学数据表明，变质流体横向迁移到阿瓜佩带然后向上迁移，并在岩石单元之间存在应变梯度的低阶结构中沉积金。该省具有世界范围内造山带金矿大省的许多特征，是新元古代早期金矿具有高度前景和未充分勘探的目标区域，该时期通常不具备金矿资源。