Abstract

The rare earth element (REE) composition of host rocks (dolomites, Neoproterozoic Pod’’emsk Formation) and manganese ores (manganese oxides and carbonates of supergene zone) are studied. The Pod’’emsk Formation is subdivided into the lower and upper subformations. The upper Pod”emsk subformation is characterized by the elevated manganese content and considered to be a Mn source for supergene ores of the deposit. Dolomites of the lower Pod’’emsk subformation show no pronounced cerium anomalies (\({{{\text{Ce}}} \mathord{\left/ {\vphantom {{{\text{Ce}}} {{\text{Ce}}_{{{\text{NASC}}}}^{*}}}} \right. \kern-0em} {{\text{Ce}}_{{{\text{NASC}}}}^{*}}}\)). They were formed in the absence or low concentrations of free oxygen in seawater. It is also probable that these dolomites experienced postsedimentary transformations, which could have resulted in the REE redistribution. Dolomites of the upper Pod’’emsk subformation from a karst depression (positive Ce/*Ce_NASC anomaly) were formed under anoxic conditions, in a hydrodynamically weakly active shallow-marine environment. The elevated cerium concentrations in the dolomites could be also associated with the introduction of oxidized Ce into the sedimentation basin with river colloids. The positive europium anomaly in the dolomites of the Pod’’emsk Formation (\({{{\text{Eu}}} \mathord{\left/ {\vphantom {{{\text{Eu}}} {{\text{Eu}}_{{{\text{NASC}}}}^{*}}}} \right. \kern-0em} {{\text{Eu}}_{{{\text{NASC}}}}^{*}}}\) = 1.22–2.16) could be related to the europium influx with subaquatic hydrothermal solutions (probably enriched in iron and manganese) or to the supply of europium with river runoff. Manganese was likely supplied in the Late Proterozoic sedimentation basin during the dolomite accumulation together with hydrothermal solutions and continental ablation. Manganese oxide ores show a sharp enrichment in HREE (by an order of magnitude), which likely occurred at the late (acidic) stage of supergene weathering as a result of LREE removal and HREE and yttrium retention in the weathering crust.

中文翻译：

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波罗津斯克锰矿床（克拉斯诺亚尔斯克州叶尼塞海脊）岩石和矿石中稀土元素分布的具体特征

摘要

研究了主岩（白云岩、新元古代Pod''emsk组）和锰矿（表生带的锰氧化物和碳酸盐）的稀土元素（REE）组成。Pod''emsk 组被细分为下部和上部子组。上部 Pod”emsk 亚组的特点是锰含量升高，被认为是矿床表生矿石的锰来源。下 Pod''emsk 亚组的白云岩没有显示出明显的铈异常（\({{{\text{Ce}}} \mathord{\left/ {\vphantom {{{\text{Ce}}} {{\text {Ce}}_{{{\text{NASC}}}}^{*}}}} \right. \kern-0em} {{\text{Ce}}_{{{\text{NASC}}} }^{*}}}\)）。它们是在海水中没有或低浓度的游离氧的情况下形成的。这些白云岩也很可能经历了沉积后转变，这可能导致 REE 重新分布。岩溶洼地上部 Pod''emsk 亚组的白云岩（Ce/*Ce _NASC正异常）是在缺氧条件下，在流体动力学较弱的浅海环境中形成的。白云岩中铈浓度的升高也可能与氧化铈进入沉积盆地与河流胶体有关。Pod'emsk组白云岩中铕正异常（\({{{\text{Eu}}} \mathord{\left/ {\vphantom {{{\text{Eu}}} {{\text{Eu}}_{{{\text{NASC}}} }^{*}}}} \right. \kern-0em} {{\text{Eu}}_{{{\text{NASC}}}}^{*}}}\） = 1.22–2.16）可以与铕通过水下热液（可能富含铁和锰）流入或与河流径流供应铕有关。锰可能在晚元古代沉积盆地的白云石堆积期间与热液溶液和大陆烧蚀一起供应。氧化锰矿石显示出高稀土元素的急剧富集（一个数量级），这可能发生在表生风化晚期（酸性）阶段，这是由于轻稀土去除和高稀土元素和钇在风化壳中的保留。