Abstract The variably serpentinized mantle peridotites of the Late Neoproterozoic Ess ophiolite (Western Saudi Arabia) are highly altered along shear zones and thrust planes to form erosion-resistant listvenites. The listvenites are distinguished petrographically and geochemically into three types: carbonate, silica-carbonate and silica (birbirite) listvenites. Geochemical analyses are consistent with expectations from petrography: carbonate listvenite is low in SiO2 content but high in MgO, Fe2O3, and CaO relative to silica-carbonate and birbirite, which is remarkably high in SiO2 at the expense of all other components. The total REE contents are low in silica-carbonate and carbonate listvenites but highly enriched in birbirite, with a large positive Eu anomaly. The host serpentinites have all the characteristics typically associated with highly depleted mantle harzburgite protoliths in supra-subduction fore-arc settings: bulk compositions are low in Al2O3 and CaO with high Mg# [molar Mg/(Mg + Fe)], relict Cr-spinel has high Cr# [molar Cr/(Cr + Al)] and low TiO2, and relict olivine has high Mg# and NiO content. The Cr-spinel relics are also found in the listvenites; those in serpentinite and carbonate listvenites have significantly higher Mg# than those in silica-carbonate and birbirite, suggesting re-equilibration of Cr-spinel in the later phases of listvenitization. The varieties of listvenite capture successive stages of fluid-mediated replacement reactions. The carbonate listvenite appears to have developed syn-contemporaneously with serpentinization, whereas silica-carbonate listvenite and birbirite formed later. The listvenite formation resulted in leaching and removal of some components accompanied by deposition of others in the solid products, notably CO3, SiO2, REE (especially Eu), Au, Zn, As, Sb and K. Our data show that listvenitization concentrated gold at sub-economic to economic grades; measured gold concentrations in the host serpentinite are 0.5–1.7 ng/g, versus 4–2569 ng/g in carbonate listvenite, 43–3117 ng/g in silica-carbonate listvenite and 5–281 ng/g in birbirite. The listvenite deposits in the Jabal Ess area merit further exploration for gold.

中文翻译：

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来自沙特阿拉伯西部阿拉伯地盾的新元古代埃斯蛇绿岩碳化地幔部分的含金利斯特文岩的岩石成因

摘要 晚新元古代埃斯蛇绿岩（沙特阿拉伯西部）的可变蛇纹石化地幔橄榄岩沿剪切带和冲断面发生高度蚀变，形成抗侵蚀的利斯特文岩。从岩石学和地球化学上将李斯特文岩分为三种类型：碳酸盐、二氧化硅-碳酸盐和二氧化硅（水钠沸石）李斯特文岩。地球化学分析与岩相学的预期一致：碳酸盐李文石的 SiO2 含量低，但 MgO、Fe2O3 和 CaO 相对于二氧化硅-碳酸盐和水钙沸石高，SiO2 的含量非常高，但会牺牲所有其他成分。稀土元素总含量在二氧化硅-碳酸盐和碳酸盐listvenite 中较低，但在水沸石中高度富集，具有大的Eu 正异常。宿主蛇纹岩具有所有典型的与超俯冲前弧环境中高度耗竭的地幔菱镁矿原岩相关的特征：整体成分中 Al2O3 和 CaO 含量低，Mg#[摩尔 Mg/(Mg + Fe)]，残余 Cr-尖晶石具有高 Cr# [摩尔 Cr/(Cr + Al)] 和低 TiO2，而残橄榄石具有高 Mg# 和 NiO 含量。在listvenites中也发现了Cr-尖晶石遗迹。蛇纹石和碳酸盐利斯特云石中的 Mg# 显着高于二氧化硅-碳酸盐和水钠铝石中的 Mg#，这表明 Cr-尖晶石在利斯特维特化的后期阶段重新平衡。各种listvenite 捕获流体介导的置换反应的连续阶段。碳酸盐李斯特文似乎与蛇纹石化同时发育，而二氧化硅-碳酸盐listvenite和birbirite后来形成。Listvenite 的形成导致一些成分的浸出和去除，伴随着固体产品中其他成分的沉积，特别是 CO3、SiO2、REE（尤其是 Eu）、Au、Zn、As、Sb 和 K。我们的数据显示，listvenitization 将金浓缩到次经济到经济等级；在主体蛇纹石中测得的金浓度为 0.5-1.7 ng/g，而碳酸盐李斯特石为 4-2569 ng/g，二氧化硅-碳酸盐李斯特石为 43-3117 ng/g，水钠钙石为 5-281 ng/g。Jabal Ess 地区的listvenite 矿床值得进一步勘探黄金。我们的数据显示，listvenitization 将黄金集中在次经济到经济等级；在主体蛇纹石中测得的金浓度为 0.5-1.7 ng/g，而碳酸盐李斯特石为 4-2569 ng/g，二氧化硅-碳酸盐李斯特石为 43-3117 ng/g，水钠钙石为 5-281 ng/g。Jabal Ess 地区的listvenite 矿床值得进一步勘探黄金。我们的数据显示，listvenitization 将黄金集中在次经济到经济等级；在主体蛇纹石中测得的金浓度为 0.5-1.7 ng/g，而碳酸盐李斯特石为 4-2569 ng/g，二氧化硅-碳酸盐李斯特石为 43-3117 ng/g，水钠钙石为 5-281 ng/g。Jabal Ess 地区的listvenite 矿床值得进一步勘探黄金。