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Pyrite morphology was studied at large gold deposits of Kyrgyzstan. All three deposits are of different geological types: Kumtor is a black shale hosted gold deposit with gold reserves estimated at about 1000 tonnes; the Makmal is a gold skarn deposit (60 tonnes); Taldy-Bulak Levoberezhny is a gold porphyry deposit (110 tonnes). Pyrite is the main ore mineral.
Makmal Deposit Overall, 16 morphological types of pyrite crystals were identified and divided into five major groups. Both the number and percentage of different pyrite types in different rocks are varying.
Therefore, at the deposit we can see how the shape of pyrite crystals evolved: at the early pre-ore stages it was a cube; later a cube combined with a pentagon-dodecahedron, then a pentagon-dodecahedron, and finally octahedron faces.
Kumtor Deposit This deposit is located in the backarc magmatic belt of the Middle Tien Shan. Here the average pyrite content is 12%. 21 types of pyrite crystals have been identified at the deposit. Out of the three simple shapes the major are {210} and {100}. The widespread combinations are {100}+{210} and {210}+{100}. The octahedron faces are poorly developed and found only occasionally. Besides that, the insignificant vertical variability of ore-bearing pyrite crystals indicates that the deposit under study is very large.
Taldy-Bulak Levoberezhny This deposit occurs on the active continental margin of the Kazakh microcontinent. The pyrite content in ores is 12-15%. Pyrite is the main gold mineral. 18 types of pyrite were identified. The most gold-bearing are the crystals that take the shape of a pentagon-dodecahedron in combination with a cube and an octahedron.
Conclusion To summarize, at the three different-type gold deposits of Kyrgyzstan the pyrite content in ores is different ranging from 2% to 20%. At all deposits the ore formation process was followed by metasomatic alteration of rocks. The main ore mineral is pyrite. Pyrite crystals take the shape of a cube, a pentagon-dodecahedron, an octahedron, or their combinations. During the pre-ore stage the pyrite crystal habit was a cube; during the ore stage it was a cube combined with pentagon-dodecahedron, a pentagon-dodecahedron, or a pentagon-dodecahedron with poorly developed octahedron faces; and during the final post-ore stage it was an octahedron. Thus, clear pyrite evolution can be seen: {100}{100}+{210}{210}{210}+{111}{111}.
Within mineralized zones pyrite crystals typically take the shape of a pentagon-dodecahedron or its combinations with a cube or an octahedron. Within non-mineralized zones pyrite crystals take the shape of a cube or an octahedron. Besides, mineralized zones contain more types of pyrite crystals (8-12) as compared to the host rocks (2-5). Pyrite typomorphic features are good visual indicators that gold will likely be present in the area and can be used to evaluate the potential of gold mineralization. These features supplement the gold deposit modeling data base.
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