The San Albino deposit is an orogenic gold occurrence hosted by a low-angle thrust that is the site of a new open-pit mine in northern Nicaragua. The deposit is hosted in greenschist facies rocks of the Jurassic metasedimentary Neuvo Segovia Formation. The schist was uplifted and exposed during arc accretion and Cretaceous thin-skin deformation, forming the NE-striking Colon fold-and-thrust belt. Deformation included emplacement of the 119 to 113 Ma NE-trending Dipilto batholith into the regionally metamorphosed clastic rocks about 5 km northwest of the San Albino deposit. Mineralization is dominated by three laminated quartz vein systems (i.e., San Albino, Naranjo, Arras) that broadly follow shallowly dipping (approx. 30°) carbonaceous shears roughly concordant to schistosity along the limbs of a doubly plunging antiform. The three main parallel shears are each separated by about 90 m and individually reach a maximum thickness of about 8 m. Maximum thickness of ore zones is where post-ore local folding and reverse motion along the shallow shears has duplicated the laminated low-angle gold-bearing veins (D₂ and early D₃). Additional gold was added to the veins, with abundant sulfides, during a subsequent brecciation event of the early formed quartz veins that accompanied progressive thrusting (late D₃). This predated boudinage of the veins during continued compression and thrust loading (D₄); high gold grades are particularly notable along pyrite- and arsenopyrite-bearing stylolites formed during D₄ pressure solution. The D₂ to D₃ gold event is likely coeval with Albian uplift of the Dipilto batholith and with back thrusting in the schist aided by the stress inhomogeneities provided by the igneous complex.Low-angle thrust-controlled orogenic gold deposits may represent world-class exploration targets because of their large linear footprints, although they are traditionally looked at as less favorable exploration targets relative to gold systems developed more commonly along high-angle reverse faults. Our case study of the San Albino deposit shows that although low-angle deposits are not inherently misoriented for failure like the more common subvertical reverse fault-related deposits, they may be sites of significant pressure buildup due to hydrothermal mineral precipitation during initial water-rock interaction or slight temperature decreases along the low-angle flow path. Resulting fluid cycling may lead to thick laminated vein development, such as seen at San Albino, where especially high-grade zones may be associated with local steepening and/or dilational zones within the broader, low-angle vein-hosting shear system.

中文翻译：

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尼加拉瓜圣阿尔比诺：低角度、逆冲控制的造山金矿床

圣阿尔比诺 (San Albino) 矿床是一个由低角度逆冲断层孕育的造山金矿，是尼加拉瓜北部一个新露天矿的所在地。该矿床赋存于侏罗纪变沉积 Neuvo Segovia 组的绿片岩相岩石中。片岩在弧增生和白垩纪薄皮变形过程中抬升暴露，形成北东向的结肠褶皱逆冲带。变形包括将 119 至 113 Ma NE 走向的 Dipilto 基岩侵位到圣阿尔比诺矿床西北约 5 公里处的区域变质碎屑岩中。矿化主要由三个层状石英脉系统（即 San Albino、Naranjo、Arras）主导，这些系统大致遵循浅倾（约 30°）碳质剪切​​，大致与沿着双倾角反形态四肢的片理一致。三个主平行剪切机各自相距约 90 m，最大厚度分别达到约 8 m。矿带的最大厚度是矿后局部褶皱和沿浅剪切力的反向运动复制了层状低角度含金矿脉（D ₂和早期D ₃）的地方。在早期形成的石英脉的后续角砾化事件中，伴随着渐进的逆冲（D ₃晚期），额外的金被添加到矿脉中，并含有丰富的硫化物。这早于静脉在持续压缩和推力负载期间的布丁（D ₄）；_{高金品位在 D 4}压溶过程中形成的含黄铁矿和毒砂的缝合线沿线尤为显着。D ₂至 D ₃金矿事件可能与 Dipilto 岩基的阿尔布阶隆升同时发生，并且在火成岩复合体提供的应力不均匀性的帮助下，片岩中发生反向逆冲。小角度逆冲控制的造山金矿床可能代表世界级金矿床由于其大的线性足迹，它们传统上被视为不太有利的勘探目标，但相对于沿高角度逆断层更常见的金矿系统而言，它们被视为不太有利的勘探目标。我们对圣阿尔比诺矿床的案例研究表明，尽管低角度矿床本质上并不像更常见的与垂直逆断层相关的矿床那样因失败而定向错误，但它们可能是由于初始水岩期间热液矿物沉淀而产生显着压力的场所。相互作用或沿着低角度流动路径轻微的温度降低。由此产生的流体循环可能导致厚层状静脉发育，例如在圣阿尔比诺（San Albino）所见，其中特别高品位的区域可能与更广泛的低角度静脉托管剪切系统内的局部陡峭和/或扩张区域相关。