Abstract The Cuiaba deposit, located in the Quadrilatero Ferriferro district (QF) in the southeastern part of the Minas Gerais state, is the largest underground mine in Brazil (5.78 Moz resources of 10.26 g/t Au - 1.18 Moz of ore reserves and 6 Moz of overall production). This world-class orogenic gold deposit is part of the Rio das Velhas greenstone belt, a typical association of mafic volcanic rocks, banded iron formation (BIF), carbonaceous and micaceous phyllites, metamorphosed to the greenschist facies conditions. Historically, economic gold production at Cuiaba derives from BIF-hosted, replacement-style sulfide (pyrite and pyrrhotite) ores. More recently, economically significant shear-zone-related gold mineralization in quartz-carbonate veins systems, hosted in metamafic rocks, were identified. They are associated with distal (chlorite-), intermediate (carbonate-) and proximal (sericite-dominant) hydrothermal alteration zones. Structures related to the gold-bearing quartz-carbonate veins were generated during a single, progressive ductile to brittle deformational event (D1), with the compositional banding Sb and the flexural foliation Sf created in the early stages of deformation. As deformation progressed, shear zones, isoclinal folds, the mylonitic foliation Sm, the mineral lineation Lmin and the intersection lineation Lint were formed simultaneously to the main stage of hydrothermal fluid input. Flanking folds and flanking shear bands represent the late stage of deformation and the final hydrothermal fluid pulse. Four quartz-carbonate vein systems are identified: V1, V2, V3 and V4. The V1 mineralized system is an Sm-controlled fault-fill type, associated with the principal, gold-bearing fluid input stage. The V2 veins are also mineralized, controlled by the Sf foliation and subdivided in three sub-types, according to internal crystal orientation: V2a extensional, V2b oblique-extensional and V2c, a fault-fill vein. The extensional array V3 veins are also controlled by the Sm foliation, whereas the extensional, breccia-style V4 system has veins associated with flanking structures. The structural analysis of veins indicates a shortening vector rotation during D1 accompanied by hydrothermal fluid input. Since all vein systems are related to the D1 event, each one defining an incremental deformational stage, they provide information about the hydrothermal fluid evolution at Cuiaba. A proposed evolutionary model for the vein systems suggest that the ore-forming fluid responsible for gold mineralization was channeled along shear zones and dispersed out into the Sb and Sf structures. The internal vein features and the trapping temperatures of quartz from each vein system indicate a progressively decrease in tectonic activity.

中文翻译：

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来自巴西 Quadrilátero Ferrífero 的 Rio das Velhas 绿岩带、BIF 托管的世界级 Cuiabá 矿床变质岩中石英-碳酸盐脉中与剪切带相关的金矿化：脉分类和结构控制

摘要 Cuiaba 矿床位于米纳斯吉拉斯州东南部的 Quadrilatero Ferriferro 区 (QF)，是巴西最大的地下矿山（5.78 Moz 资源，10.26 g/t Au - 1.18 Moz 矿石储量和 6 Moz总产量）。这个世界级的造山金矿床是 Rio das Velhas 绿岩带的一部分，该带是典型的基性火山岩、带状铁层 (BIF)、碳质和云母千枚岩的组合，变质为绿片岩相条件。从历史上看，库亚巴的经济黄金生产来自 BIF 托管的替代型硫化物（黄铁矿和磁黄铁矿）矿石。最近，在变质岩中的石英-碳酸盐脉系统中发现了具有经济意义的与剪切带相关的金矿化。它们与远端（绿泥石-）有关，中间（碳酸盐岩）和近端（绢云母为主）热液蚀变带。与含金石英-碳酸盐脉相关的结构是在单一的、渐进的延性至脆性变形事件 (D1) 中产生的，在变形的早期阶段产生了成分带 Sb 和弯曲叶理 Sf。随着变形的进行，剪切带、等斜褶皱、糜棱片理Sm、矿物线理Lmin和交叉线理Lint与热液流体输入的主要阶段同时形成。侧翼褶皱和侧翼剪切带代表变形后期和最终热液脉冲。确定了四个石英-碳酸盐脉系统：V1、V2、V3 和 V4。V1 矿化系统是 Sm 控制的断层充填类型，与主、含金流体输入阶段。V2 脉也被矿化，由 Sf 叶理控制并根据内部晶体取向细分为三个亚型：V2a 伸展型、V2b 斜伸展型和 V2c，一种断层填充型脉。伸展阵列 V3 脉也受 Sm 叶理控制，而伸展的角砾岩型 V4 系统具有与侧翼结构相关的脉。脉的结构分析表明在 D1 期间伴随着热液输入的缩短矢量旋转。由于所有脉系统都与 D1 事件有关，每个脉系统都定义了一个增量变形阶段，因此它们提供了有关库亚巴热液演化的信息。提出的脉系统演化模型表明，负责金矿化的成矿流体沿着剪切带被引导并分散到 Sb 和 Sf 结构中。来自每个脉系统的石英的内部脉特征和捕集温度表明构造活动逐渐减少。