Abstract

The Valunistoe Au–Ag deposit is the third largest among epithermal deposits in Chukotka after the Kupol and Dvoinoe. It is located at the western closing of the East Chukotka flank zone of the Okhotsk-Chukotka volcanic belt. Volcanic domes (Pravogornenskaya, Zhil’ninskaya, Shakhskaya, Valunistaya, Shalaya, and Oranzhevaya, each is 3–6 km in diameter) have the main ore-controlling significance in the area; they form a chain elongated to the northeast, along the Kanchalan fault zone. Near the deposit, Upper Cretaceous volcanics are widespread: ignimbrites, lavas and tuffs ranging from rhyolite to basaltic composition, and lenses and interbeds of sedimentary rocks, subvolcanic bodies and dikes of andesites, basalts, and dacites. The structure of the deposit is caused by its localization within the limits of the eponymous (Valunistaya) volcanic dome. Twelve ore-bearing vein zones with thicknesses ranging from several to several tens of meters have been revealed at the deposit. The Glavnaya (Main) and Novaya (New) vein zones have been studied in detail; they are traced along their strikes to a distance of more than 1500 m and consist of en echelon veins 1.0 m thick on average, with lengths varying from 100 to 400 m. Based on the sampling data, Au and Ag contents in ores are 0–474.3 and 0–3794.23 g/t, respectively. Colloform-banded structures are frequently encountered, often combined with breccia structures. The main vein minerals are quartz and adularia; calcite, chlorite, fluorite, sericite, pyrophyllite, kaolinite, montmorillonite, gypsum, and epidote are less frequent. The main ore minerals are pyrite, acanthite, chalcopyrite, galena, sphalerite; secondary ore minerals are native Au and Ag and polybasite; rare ore minerals are pearceite, magnetite, hematite, marcasite, freibergite, tetrahedrite, bournonite, hessite, matildite, and others. Ores are characterized by an Au/Ag ratio from 1 : 5 to 1 : 10 and sulfidity (0.5–5%). Ores are enriched in many elements (Au, Ag, Sb, Cd, Pb, Cu, Zn, As, Se, Mo, Te, and Cr), with enrichment factors ranging from several times (Se, Mo, Te, and Cr), to tenfold (Cd, Pb, Cu, and Zn) and hundredfold (Sb) levels, reaching an excess of tens and hundreds thousand times for Au and Ag (Fig. 7). Ores are characterized by a low total REE and demonstrate positive Eu anomalies. Geochemical features are consistent with the mineral composition of ores. Full homogenization of fluid inclusions in quartz occurs at temperatures of 203–284°C and 174–237°C in calcite, while the salt concentration in both cases is from 0.2 to 0.7 wt % NaCl equiv. Fluid density changes from 0.87 to 0.56 g/cm³. The results give grounds to attribute the Valunistoe deposit to the low-sulfidized epithermal class. The data provided in the article are of practical value for regional forecast–metallogenic maps and can be used in searching for and appraising epithermal Au–Ag deposits.

中文翻译：

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瓦卢尼斯托超热金银沉积物（俄罗斯东楚科奇）：地质构造，矿物学-地球化学特征和成矿条件

摘要

在楚科奇的超热矿床中，Valunistoe Au-Ag矿床是仅次于Kupol和Dvoinoe的第三大矿床。它位于鄂霍次克-楚科奇火山带东楚科奇火山侧翼带的西侧。火山圆顶（Pravogornenskaya，Zhil'ninskaya，Shakhskaya，Valunistaya，Shalaya和Oranzhevaya，直径分别为3–6 km）在该地区具有主要的控矿意义。它们沿着坎恰兰断裂带形成向东北延伸的链条。在该矿床附近，上白垩纪火山很普遍：火成岩，熔岩和凝灰岩从流纹岩到玄武岩成分，以及沉积岩的透镜和夹层，安山岩的次火山体和堤防，玄武岩和dacites。沉积物的结构是由其在同名（Valunistaya）火山圆顶范围内的局部化引起的。该矿床发现了十二个含矿脉带，厚度范围从几米到几十米。对Glavnaya（主要）和Novaya（新）静脉带进行了详细研究。它们沿着其走向被追踪到超过1500 m的距离，由平均厚度为1.0 m的梯形脉组成，长度从100到400 m不等。根据采样数据，矿石中的Au和Ag含量分别为0-474.3和0-3794.23 g / t。经常出现带状带状结构，经常与角砾岩结构结合。主要矿脉矿物是石英和石楠；方解石，绿泥石，萤石，绢云母，叶蜡石，高岭石，蒙脱石，石膏和附子较少见。主要矿石矿物为黄铁矿、,石，黄铜矿，方铅矿，闪锌矿；次生矿石矿物为天然金和银以及多碱土矿。稀有矿石矿物为白云母，磁铁矿，赤铁矿，钙铁矿，贝氏体，四面体，勃朗石，黑铁矿，黑云母等。矿石的特征在于Au / Ag比为1：5至1:10，硫化度为（0.5-5％）。矿石富含多种元素（Au，Ag，Sb，Cd，Pb，Cu，Zn，As，Se，Mo，Te和Cr），其富集系数范围为数倍（Se，Mo，Te和Cr）到十倍（Cd，Pb，Cu和Zn）和百倍（Sb）的水平，Au和Ag达到数万倍（图7）。矿石的特点是总稀土元素含量低，并显示出正Eu异常。地球化学特征与矿石的矿物成分一致。石英中流体包裹体的完全均质化发生在方解石中的温度为203–284°C和174–237°C，两种情况下的盐浓度为0.2至0.7 wt％NaCl当量。流体密度从0.87变为0.56 g / cm³。结果为将瓦卢尼斯托矿床归因于低硫化超热类别提供了依据。本文提供的数据对于区域预测成矿图具有实用价值，可用于搜索和评估超热金银沉积物。