UDC 549.548.321
V.M. Kvasnytsya 1, E.V. Naumenko 2, I.V. Kvasnytsya 3, E.E. Grechanovskaya 1.
1 M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
34, Acad. Palladin Ave., Kyiv-142, Ukraine, 03142
E-mail: vmkvas@hotmail.com
2 National Scientific Museum of Natural History of the NAS of Ukraine
15, Bohdan Khmelnytsky Str., Kyiv, Ukraine, 01601
3 Kyiv Taras Shevchenko National University. Educational-Scientific Institute "Institute of Geology"
90, Vasylkivska Str., Kyiv, Ukraine, 03022
Language: Ukrainian
Mineralogical journal 2018, 40 (4): 36-44

Intergrown wurtzite-sphalerite crystals from the Muzhiivo gold-polymetallic deposit in Transcarpathia were studied using goniometry, scanning electron microscopy, X-ray spectral, X-ray fluorescent and X-ray diffraction analysis. Wurtzite-sphalerite crystals are found in a low-grade vein of the deposit (on upper horizon no 130, ore body no 8). The vein consists of galena, sphalerite and wurtzite-sphalerite, upwards it changes to calcite, aragonite, and barite. A 2-3 cm layer of galena and sphalerite is a substrate for massive aggregates of up to 2 cm large subparallel crystals of wurtzite-sphalerite. In cavities of the aggregates idiomorphic crystals of wurtzite-sphalerite occur in size up to several millimeters, rarely up to 5-7 mm. These columnar crystals have growth forms of both polymorphs of ZnS. Overgrowths of microscopic pyrite and chalcopyrite crystals are found on wurtzite-sphalerite. Chemical composition of wurtzite-sphalerite is (in wt. %): Zn - 59.65, Fe - 6.18, Cd - 0.30, Mn - 0.26; S - 33.29. X-ray studies of crystals have shown the presence of reflections of sphalerite and wurtzite. Wurtzite has been identified as hexagonal polytype 10H, the intensity of its X-ray reflections is not high. Wurtzite-sphalerite crystals are hexagonally pyramidal and hexagonally prismatic with well-defined horizontal hatching. Simple forms of the pyramid are defined as a combination {1 0 -1 2} + {2 0 -2 5} + {1 0 -1 3}. The heads of crystals have a typical sphalerite form, a combination of positive tetrahedron and cube. On prismatic crystals these forms form scepters. The main axis of the hexagonal pyramid and prism coincides with one of the trifold axis of sphalerite faceting on the crystal head. That is, the L6 wurtzite is parallel to L3 sphalerite and, accordingly, (0001) wurtzite is parallel to (111) sphalerite. Probably such crystals are polysynthetic twins of these phases of both polymorphs of ZnS on (111). Rapid crystallization from supersaturated solutions with a slight excess of sulfur at relatively low temperatures is a probable cause of growth of such pyramidal and prismatic crystals of ZnS.
Keywords: wurtzite-sphalerite, pyramidal crystals, polytype 10Н, Muzhiivo gold-polymetallic deposit, Transcarpathia.

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