Abstract

Chrome spinels in carbonate veins of the Onguren Complex, East Siberia, Western Baikal region are predominantly ferrichromite and chrommagnetite (MgO ≤ 0.3 wt %, Mg# ≤ 0.04, Al₂O₃ ≤ 2.5 wt %; Cr# 0.91–1.00, Fe²⁺/Fe³⁺ 0.8–1.4) with a high ZnO content (0.9–4.6 wt %). In the calcite vein, titanian chrome-magnetite is transformed into Cr-bearing titanomagnetite, which decomposes into Ti-depleted magnetite and ilmenite at temperature of 970–1000°С and \({{f}_{{{{{\text{O}}}_{{\text{2}}}}}}}\) approximately of +0.5…+0.7 QFM. In the dolomite vein, ferrichromite and chrome-magnetite grains contain relict cores of subferrialumochromite (Al₂O₃ 10.6–14.4 wt %, Cr# 0.63–0.73, Fe²⁺/Fe³⁺ 4.1–5.2, MgO ≤ 0.52 wt %) with elevated ZnO (3.7–5.1 wt %), TiO₂ (3.2–4.1 wt %), and MnO (0.6–1.1 wt %). Ferrichromite and chrome-magnetite are formed during the high-temperature (>600°C) metamorphism of the vein. Superimposed deformations under greenschist facies conditions lead to the formation of magnetite rims around chrome-magnetite grains.

中文翻译：

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西贝加尔湖地区Onguren建筑群的碳酸盐脉中的铬尖晶石

摘要

在Onguren复杂的碳酸盐脉铬尖晶石，东西伯利亚，西贝加尔区域中主要ferrichromite和chrommagnetite氧化镁（MgO≤0.3重量％以下，Mg＃≤0.04，AL ₂ ö ₃ ≤2.5％（重量）; CR＃0.91-1.00，铁^{2 +} / Fe ³⁺ 0.8–1.4），具有较高的ZnO含量（0.9–4.6 wt％）。在方解石脉中，钛矿铬磁铁矿转变为含铬的钛磁铁矿，然后在970–1000°С的温度下分解成贫钛的磁铁矿和钛铁矿，并且\（{{f} _ {{{{\\ t​​ext { O}}} _ {{\ text {2}}}}}} \\）大约为+ 0.5…+ 0.7 QFM。在白云岩脉中，亚铁铬铁矿和铬磁铁矿晶粒含有亚铁铬铁矿（Al ₂ O ₃10.6–14.4 wt％，Cr＃0.63–0.73，Fe ²⁺ / Fe ³⁺ 4.1–5.2，MgO≤0.52 wt％），ZnO（3.7–5.1 wt％），TiO ₂（3.2–4.1 wt％）升高，和MnO（0.6–1.1 wt％）。亚铁矿和铬磁铁矿是在静脉高温（> 600°C）变质过程中形成的。格林希斯特相条件下的叠加变形导致在铬磁铁矿晶粒周围形成磁铁矿边缘。