Abstract

The chemical composition of chlorites from the rocks that are conventionally classified as the residual weathering mantle of the Kolskii ophiolite massif was studied. The chlorites exhibit high Mg/ (Mg + Fe) atomic ratio values (Mg#) of 0.78–0.96 and elevated Si content (2.95–3.74 apfu), but are relatively poor in Al (1.28–2.66 apfu). In terms of octahedral occupancy (R^VI is 5.52–5.98 and [R³⁺]^VI is 0.87–2.04 apfu), they are classified as the trioctahedral subgroup. The NiO content in the chlorites varies from 0.2 to 21 wt %; in addition, the tabular low-Ni and high-Ni chlorite grains are often tightly intergrown. There is a pronounced negative correlation between NiO and MgO content. The crystallization temperature estimated using chlorite geothermometers varies widely. The crystallization temperature interval is 125–300°C or higher with a statistical maximum in the region of 175–300°C for the low-Ni chlorites and 50–250°С with a statistical maximum in the region of 75–125°С for the high-Ni chlorites. In addition, the high-Ni chlorites demonstrate a gradual decrease in temperature as the nickel content increases. This correlation indicates the important role of temperature as an ore generation factor during the formation of the oxide–silicate nickel deposits that are associated with the Kolskii massif. These tendencies support the conclusion that the hydrothermal processes not only preceded lateritization, but also played a significant part in the level of nickel concentration in phyllosilicates.

中文翻译：

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Kolskii地块（北乌拉尔）中含镍亚氯酸盐的测温法

摘要

研究了通常被归类为Kolskii蛇绿岩地块残余风化幔的岩石中亚氯酸盐的化学组成。亚氯酸盐的Mg /（Mg + Fe）原子比值（Mg＃）为0.78-0.96，Si含量较高（2.95-3.74 apfu），而Al相对较差（1.28-2.66 apfu）。就八面体占有率而言（R ^VI为5.52-5.98，[ R ³⁺ ] ^VI是0.87–2.04 apfu），它们被分类为三八面体亚组。亚氯酸盐中的NiO含量为0.2至21 wt％。此外，板状的低镍和高镍的亚氯酸盐颗粒通常紧密结合在一起。NiO和MgO含量之间存在明显的负相关性。使用亚氯酸盐地热仪估算的结晶温度变化很大。结晶温度区间为125-300°C或更高，低镍亚氯酸盐的统计最大值在175-300°C范围内，而50-250°С的统计最大值在75-125°С范围内用于高镍亚氯酸盐。另外，随着镍含量的增加，高镍亚氯酸盐的温度逐渐降低。这种相关性表明，温度是与Kolskii地块有关的氧化物-硅酸盐镍矿床形成过程中矿石成因的重要作用。这些趋势支持这样的结论：水热过程不仅在红土化之前，而且在页硅酸盐中镍浓度的水平中起着重要的作用。