ZONED TUNGSTENOAN MOLYBDENITE FROM A FENITIZED MEGAXENOLITH IN THE KHIBINA ALKALINE COMPLEX, KOLA PENINSULA, RUSSIA
Zoned tungstenoan molybdenite occurs in a fenite (~80 modal % nepheline) within a strongly heterogeneous fenitized megaxenolith (~0.2 km) enclosed by nepheline syenite, in the Khibina alkaline complex, Kola Peninsula, Russia. Molybdenite forms euhedral crystals (~50–60 m in length), enclosed by pyrr...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.488.7063 http://rruff.info/doclib/cm/vol38/CM38_1377.pdf |
| Summary: | Zoned tungstenoan molybdenite occurs in a fenite (~80 modal % nepheline) within a strongly heterogeneous fenitized megaxenolith (~0.2 km) enclosed by nepheline syenite, in the Khibina alkaline complex, Kola Peninsula, Russia. Molybdenite forms euhedral crystals (~50–60 m in length), enclosed by pyrrhotite, and abundant veinlets among silicates. The crystals are zoned with respect to tungsten, which is strongly enriched in the central zone. This area is 5–6 m across and contains up to 5.85 wt. % W (0.05 atoms per formula unit). Tungsten-rich zones of the molybdenite veinlets contain the same concentration of W as the central zone of the euhedral crystals, implying similar conditions of formation. There is thus a substantial solid-solution between molybdenite and tungstenite. We attribute the outward zoning to W-poor molybdenite in terms of increasing fugacity of oxygen and decreasing fugacity of sulfur, apparently in the presence of a reduced H2S–CH4-rich fluid of subalkaline character. The existence of locally reducing conditions in the fenite(s) at Khibina also is implied by the adjacent occurrences of titanium-and niobium-rich sulfides and a graphite-like material. |
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