Ore deposits found in Proterozoic marine sedimentary basins supply much of the world's zinc. Many of the deposits formed contemporaneously with their host sediments when saline brines circulating from deeper in the basin reached the sea floor. Textural, geochemical and isotopic features of these SEDEX (‘sedimentary-exhalative’) deposits and their host sediments indicate that biologically active seeps, vents and brine pools were a feature of many ore-forming systems. In mineralised pockets of mid-Proterozoic basins, these ‘microbial oases’ were productive areas in an otherwise low productivity, anoxic, deep marine realm. Here we hypothesize that these metal-rich brines which circulated through organic matter-rich substrate also carried high levels of fixed nitrogen and stimulated distinct ecosystems at sites of mineralisation, or enhanced productivity more broadly in the basin. We tested this hypothesis with organic carbon and nitrogen analyses of samples of carbonaceous siltstone and shale from the 1.64 Ga Barney Creek Formation of northern Australia. The Barney Creek Formation hosts several SEDEX Zn systems, including one of the world's largest deposits at McArthur River Mine (the HYC deposit). Samples come from the mineralised edge of HYC and from correlated strata in drill cores at varying distances (1-60 km) from the deposit. The data reveal lower ratios of total organic carbon (TOC) to total nitrogen (TN) closer to the ore body. Strong correlations (${\mathrm{r}}^2>0.7$) between TOC and TN and the absence of excess N in the samples suggest that most N was buried as bound to organic matter. Bioavailable N was thus probably more abundant closer to HYC, consistent with fixed nitrogen input by hydrothermal fluids. If correct, our data may suggest that such a hydrothermal nitrogen point source enabled microbes to develop lower C:N ratios in their biomass. A hydrothermal nitrogen source is also supported by a gradient in ${\delta }^{15}$N values from = +4‰ proximal to the vent to +7.5‰ in distal sites, which may point towards recycling of ammonium from the underlying Wollogorang Formation (1.73 Ga). This unit has previously been identified as a source of over-mature hydrocarbons to the ore-forming fluid. We speculate that, during the mid-Proterozoic, fixed nitrogen carried by SEDEX hydrothermal brines may have locally offset the lack of aerobic nutrient remineralization that characterized most of the anoxic Precambrian deep ocean and thus stimulated biological productivity in areas where the brines reached the sea floor, and, possibly, more broadly as spent brines mixed into the water column.

在元古代海洋沉积盆地中发现的矿床提供了世界上大部分的锌。当从盆地深处循环的盐水到达海底时，许多沉积物与它们的宿主沉积物同时形成。这些SEDEX（“沉积物-呼出气”）沉积物及其宿主沉积物的质地，地球化学和同位素特征表明，具有生物活性的渗漏，喷口和盐水池是许多成矿系统的特征。在元古代中期盆地的矿化口袋中，这些“微生物绿洲”是原本生产力低下，缺氧的深海领域的生产区。在这里，我们假设这些通过富含有机物的底物循环的富含金属的盐水也携带高水平的固定氮，并在矿化位点刺激了独特的生态系统，或在流域更广泛地提高生产力。我们通过对来自澳大利亚北部1.64 Ga Barney Creek地层的碳质粉砂岩和页岩样品的有机碳和氮分析测试了该假设。Barney Creek地层拥有多个SEDEX Zn系统，其中包括McArthur River矿山中最大的矿床之一（HYC矿床）。样品来自HYC的矿化边缘，以及来自矿床不同距离（1-60 km）的钻芯中的相关地层。数据显示，靠近矿体的总有机碳（TOC）与总氮（TN）的比例较低。强烈的相关性（Barney Creek地层拥有多个SEDEX Zn系统，其中包括McArthur River矿山中最大的矿床之一（HYC矿床）。样品来自HYC的矿化边缘，以及来自矿床不同距离（1-60 km）的钻芯中的相关地层。数据显示，靠近矿体的总有机碳（TOC）与总氮（TN）的比例较低。强烈的相关性（Barney Creek地层拥有多个SEDEX Zn系统，其中包括McArthur River矿山中最大的矿床之一（HYC矿床）。样品来自HYC的矿化边缘，以及来自矿床不同距离（1-60 km）的钻芯中的相关地层。数据显示，靠近矿体的总有机碳（TOC）与总氮（TN）的比例较低。强烈的相关性（${\mathrm{[R}}^{\mathrm{2个}}>0.7$）在TOC和TN之间，并且样品中不存在过量的N，这表明大多数N被掩埋为与有机物结合。因此，生物可利用的氮可能更接近HYC，这与水热流体的固定氮输入相一致。如果正确，我们的数据可能表明这种水热氮点源使微生物能够在其生物质中形成较低的C：N比。水热氮源还受到梯度梯度的支持。${\delta }^{15}$N值从排放口近端的+ 4‰到远端部位的+ 7.5‰，这可能表明来自下面的Wollogorang组（1.73 Ga）的铵循环利用。该单元先前已被确定为成矿流体中过熟碳氢化合物的来源。我们推测，在元古代中期，SEDEX热液盐水携带的固定氮可能局部抵消了缺氧的营养矿物质再矿化的不足，而缺氧性矿物质再矿化是大多数缺氧前寒武纪深海的特征，因此刺激了盐水到达海床的区域的生物生产力。 ，并且可能更广泛地说是将废盐水混入水柱中。