The La Belliere gold district, in the Ligerian domain of the Armorican Massif is the third one of France in term of production. It shows gold-bearing quartz veins neighboring with a complex network of Sb veins, hosted in the Neoproterozoic metasedimentary basement of the Mauges Nappe. New structural data, mineralogical, textural and geochemical assays have been carried out to clarify the gold and Sb veins relationships. Our results favor of two-step hydrothermal event with an early deep-seated gold event followed by a late shallower Sb event. The gold-bearing quartz veins are hosted by N60°E to N90°E sinistral strike-slip faults. These veins exhibit a four-stage paragenesis: 1) early barren quartz filling, 2) arsenopyrite-pyrite with minor scheelite assemblage, 3) gold and base metal sulfides crystallized after a ductile/brittle deformation stage, and 4) pyrite-carbonate coeval with a late brittle stage. These results support a continuous evolution model from a deep emplacement level (12 to 9 km) to a shallow one (7 to < 5 km) with a brutal change in the P/T conditions that triggered the deposition of gold (stage 2) controlled by a seismic-valve mechanism. On the contrary, Sb veins correspond to open space vein types, hosted in a N20°W to N20°E conjugated strike-slip fault network arranged in a Riedel shear model, controlled by N130-140°E regional dextral strike-slip shear zone associated to the South Armorican Shear Zone system. A two-stage evolution is recognized, the first one consists of early pyrite-arsenopyrite with microcrystalline quartz, followed by a late stibnite stage formed after geodic quartz deposition. Quartz texture argues for a shallow emplacement (< 5 km) of veins controlled by a suction-pump mechanism. Chronologically, the gold vein opening complies with a NE-SW maximum shortening direction different from the late-Variscan stress field responsible for the dextral Armorican shear zone during late Carboniferous, and constrains an indirect dating. Thus, a Visean age is proposed for the formation of gold veins. The overall features of gold deposits are close to those of mesozonal orogenic gold deposits in Europe. Conversely, Sb-bearing veins are generated by a N-S shortening during the late Carboniferous. The Sb event, distinct in time from the earlier gold one, might correspond to a different expression of the so-called “epizonal” type in the orogenic gold model. It is proposed that the Late Carboniferous “Or 300” event is not the unique metallogenic period for gold deposition in the French Variscan domain. Our study highlights the role of the sinistral strike-slip shearing of possible Visean age, in the gold metallogenesis of the Ligerian domain.

中文翻译：

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La Bellière 金锑区（French Armorican Massif）：由 Variscan 走滑构造控制的两阶段演化模型

位于Armorican Massif 的Ligerian 地区的La Belliere 黄金区是法国第三大生产区。它显示了含金石英脉与复杂的 Sb 脉网络相邻，位于 Mauges Nappe 的新元古代变沉积基底中。已经进行了新的结构数据、矿物学、结构和地球化学分析，以阐明金和 Sb 矿脉的关系。我们的结果有利于两步热液事件，早期深部金事件，随后是较晚的浅层 Sb 事件。含金石英脉位于 N60°E 至 N90°E 的左旋走滑断层中。这些矿脉表现出四阶段共生：1) 早期贫瘠的石英充填，2) 毒砂-黄铁矿与少量白钨矿组合，3) 金和贱金属硫化物在韧性/脆性变形阶段后结晶，和 4) 黄铁矿-碳酸盐同时期具有晚期脆性阶段。这些结果支持了从深位（12 至 9 公里）到浅位（7 至 < 5 公里）的连续演化模型，其中 P/T 条件发生了剧烈变化，触发了金沉积（第 2 阶段）控制通过地震阀机制。相反，Sb 脉对应于开放空间脉类型，位于 N20°W 至 N20°E 共轭走滑断层网络中，排列在 Riedel 剪切模型中，受 N130-140°E 区域右旋走滑剪切带控制与 South Armorican 剪切区系统相关。认识到一个两阶段的演化，第一个阶段由早期黄铁矿-毒砂和微晶石英组成，然后是大地石英沉积后形成的晚期辉锑矿阶段。石英纹理支持浅层定位（< 5 公里）的静脉由抽吸泵机制控制。从年代上看，金矿脉开口符合 NE-SW 最大缩短方向，不同于晚石炭纪右端 Armorican 剪切带的晚瓦利斯坎应力场，并限制了间接定年。因此，提出了形成金矿脉的维氏时代。金矿床总体特征与欧洲中带造山型金矿床相近。相反，含 Sb 的脉是由晚石炭纪期间 NS 缩短产生的。Sb 事件在时间上与早期的黄金事件不同，可能对应于造山金模型中所谓的“上位”类型的不同表达。推测晚石炭世“Or 300”事件不是法国瓦里斯坎地区金沉积的唯一成矿期。我们的研究强调了可能的 Visean 时代的左旋走滑剪切作用在 Ligerian 区域的金成矿作用中的作用。