Abstract—

The limited literature data on gold-bearing albite–pyroxene rodingites are summarized for the Agardag ultramafic massif in southern Tuva. These data are supplemented by new mineralogical, geochemical, thermobarogeochemical, and isotopic–geochemical results in order to reveal the physicochemical mineral formation conditions and sources of ore matter and fluids on gold deposition in rodingites. Rodingites and associated schistose nephritoids are near-fault metasomatites and are confined to a latitudinal tectonic zone in antigorite serpentinites. They formed in two stages. Stage I minerals (pyroxene, albite, etc.) are rodingites and stage II minerals (Na-bearing actinolite, albite, etc.) are nephritoids and veinlets that intersect rodingites. Disseminated sulfides of the Cu–S series (chalcocite, digenite, etc.) and Au minerals (tetra-auricupride and electrum) were deposited during both stages. The temperature regime (500–250°C) and low amount of CO₂ in fluid (\({{{\text{X}}}_{{{\text{C}}{{{\text{O}}}_{{\text{2}}}}}}}\) = 0.017–0.025) correspond to the formation conditions of typical bimetasomatic rodingites. The degree of oxidation of gas components in fluids CO₂/(CO₂ + Σreduced gases) increases from rodingites (0.189) to nephritoids (0.299) and antigorite serpentinites (0.738). The O isotopic composition of silicates and calculated O isotopic composition of the fluid during antigorite serpentinization (5.8 to 7.6‰ δ¹⁸О_fl and –66 to –69‰ δD_fl) correspond to juvenile and magmatic water in contrast to metamorphic water during nephritization and rodingitization (6 to 9.9‰ δ¹⁸О_fl and –39 to –46‰ δD_fl) with involvement of heavy oxygen that was subjected to the sedimentary cycle. It is suggested that the magmatic ore-bearing fluid (7.3–7.6 wt % NaCl-equiv) separated from gabbroic melts. The oxidized fluid was modified to a reduced fluid during interaction with ultramafic rocks. The mafic and ultramafic rocks were the source of Na, REE, Au, Ag, Cu, and Ni. Deformations with the formation of veins and filling of veinlets are favorable for a high local gold concentration.

中文翻译：

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Agardag超镁铁质地块（俄罗斯南图瓦）的含金Rodingite及其成因问题

摘要—

总结了图瓦南部Agardag超镁铁质岩块的含金钠长石-辉绿岩Rodite的有限文献数据。这些数据通过新的矿物学，地球化学，热压地球化学和同位素-地球化学结果得到补充，以揭示理化矿物的形成条件以及在Rodingite中金沉积的矿石物质和流体的来源。Rodingite和相关的片岩类肾上腺素是近断层交代岩，并局限于蛇纹石蛇纹岩中的一个纬向构造带。他们分为两个阶段。第一阶段的矿物（辉石，钠长石等）是针铁矿，第二阶段的矿物（含钠的阳起石，钠长石等）是与软锰矿相交的类肾上腺和细脉。铜-S系列的弥散性硫化物（菱锰矿，重辉石等））和金矿物质（四金铜和电子）在两个阶段均沉积。温度范围（500–250°C）和少量CO₂ in fluid（\（{{{text {X}}} _ {{{\ text {C}} {{{\ text {O}}} _ {{\ text {2}}}}}}} \） = 0.017–0.025）对应于典型的双变质碳镁辉石的形成条件。流体中CO ₂ /（CO ₂ +Σ还原的气体）中气体成分的氧化程度从软锰矿（0.189）增加到类肾上腺素（0.299）和蛇绿蛇纹石（0.738）。硅酸盐中的O同位素组成和流体的计算的氧气同位素组成叶蛇纹石蛇纹石期间（5.8至7.6‰δ ¹⁸ О _FL和-66至-69‰δD _FL）nephritization期间对应于在对比变质水少年和岩浆水和rodingitization（6至9.9‰δ ¹⁸ О_FL和-39至-46‰δD _FL）与进行沉积循环重氧的参与。建议从辉长岩熔体中分离出岩浆含矿流体（7.3-7.6 wt％NaCl当量）。在与超镁铁质岩石相互作用期间，氧化的流体被改性为还原的流体。镁铁质和超镁铁质岩石是钠，稀土，金，银，铜和镍的来源。矿脉的形成和矿脉的充填对高局部金含量有利。