Abstract The Los Burros gold deposit is located within the Franciscan complex of the Nacimiento block, California. Although this deposit was mined during the late 19th and early 20th centuries, its origin and its relationship with the regional metamorphism and deformation are unclear. In order to better understand the mode of formation of the deposit, and its possible link with a post-subduction thermal anomaly, we performed a detailed geological and structural mapping within the Los Burros district, coupled with a (U-Th)/He thermochronological study on apatite and zircon. Fluid-inclusion and stable isotope (O and C) analyses of the ore deposit provide constraints on the temperature and potential source of the fluid(s) responsible for the Los Burros gold formation. Our results demonstrate that the Los Burros Au deposit formed from a metamorphic aqueous CO2-CH4 fluid at temperatures of ~300 °C. Results from Raman Spectroscopy of Carbonaceous Materials confirm the presence of a thermal anomaly in the range 260–320 °C near the Los Burros Mining District as previously inferred by vitrinite reflectance techniques. Our structural and preliminary thermochronological analyses show that the Los Burros Au deposit consists of a series of meter-wide, quartz-calcite-sulfide “en-echelon” veins, formed during a late transpressive event related to San Andreas fault activity and the subduction of a slab-window during the past 30 Ma. Our new data suggest that the thermal anomaly recorded in the vicinity of the Los Burros Mining District is not associated with a magmatic-derived hydrothermal system such as described within the epithermal McLaughlin deposit in Northern California, but rather with a late transpressive deformation event that uplifted deeply buried metamorphic rocks, possibly connected to a local metamorphic overprint.

中文翻译：

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Nacimiento 区块金矿化的结构和成因：Los Burros 矿床（加利福尼亚中部）

摘要 Los Burros 金矿床位于加利福尼亚州 Nacimiento 区块的 Franciscan 复合体中。虽然该矿床是在19世纪末20世纪初开采的，但其成因及其与区域变质变形的关系尚不清楚。为了更好地了解矿床的形成模式及其与俯冲后热异常的可能联系，我们在 Los Burros 地区进行了详细的地质和结构测绘，并结合 (U-Th)/He 热年代学研究磷灰石和锆石。矿床的流体包裹体和稳定同位素（O 和 C）分析提供了对负责 Los Burros 金形成的流体的温度和潜在来源的限制。我们的结果表明，Los Burros Au 矿床由变质的 CO2-CH4 水溶液在约 300 °C 的温度下形成。碳质材料的拉曼光谱结果证实了先前通过镜质体反射技术推断的 Los Burros 矿区附近 260-320 °C 范围内的热异常。我们的结构和初步热年代学分析表明，Los Burros Au 矿床由一系列米宽的石英-方解石-硫化物“梯形”矿脉组成，形成于与圣安德烈亚斯断层活动和过去 30 Ma 期间的平板窗口。