Vol 8, No 3 (2022)
Minerals and mineral assemblages
Fahlores from porphyry Cu-(Mo) deposits of the Urals
Abstract
The paper describes chemistry of tetrahedrite-tennantite group minerals from three porphyry deposits of the Urals: Mikheevskoe and Tomino porphyry copper deposits on the South Urals and Talitsa Mo porphyry deposit on the Middle Urals. In the deposits studied tetrahedrite-tennantite group minerals deposited either with late mineral assemblages of the porphyry stage or within late subepithermal veins. They vary in composition from tennantite to tetrahedrite with variable Fe and Zn contents. Contents of Cd, Co, Te, Bi, Ag, Se Te, Bi, Ag, S are usually insignificant. However argentotetrahedrite-(Fe) was described within the latest assemblage at the Mikheevskoe deposit, while tennantite-tetrahedrite-(Cd) was noted overgrowing bornite at the Tomino deposit. Most tetrahedrite group minerals do not establish complicated chemical zoning: they are either homogeneous or comprise a core of intermediate tennantite-tetrahedrite composition and a rim with dominating tetrahedrite end-member. This evidences relatively quiet deposition environment with no dramatic variations of PTx parameters which is rather typical for porphyry systems. Comparison with published data shows the tetrahedrite group minerals studied are similar to those from «transitional» subepithermal mineralization.
5-22
Ore minerals of the Buranovskoe tungsten deposit (Southern Urals)
Abstract
Primary and supergene Pb, Bi, Te, Cu, Mo, Ag, Au and Hg minerals are found in samples from the dumps of the Buranovskoe tungsten deposit (Chelyabinsk oblast). The paper presents the most complete list of mineral species of the deposit based on available literature and our data. Fourteen tellurides and sulfotellurides are identified. They occur as individual grains and intergrowths with each other or simple sulfides and form numerous inclusions in fahlores in quartz-scheelite veins. Among the oxidation products of fahlores, galena and tetradymite, we found rare supergene minerals – telluroperite and perite, which form a limited solid solution series, as well as choloalite and a Ag and Hg sulfide-iodide corresponding to hanauerite by its chemical composition. The findings of telluroperite and hitachiite are the first at the territory of the Russian Federation and perite and choloalite are found for the first time in the Urals.
23-46
REE minerals in black shales of the paleoproterozoic mikhailovka formation (Baikal-Patom highland, Siberia)
Abstract
The paper characterizes REE mineralization from carbonaceous metapelites of the Paleoproterozoic Mikhailovka Formation, which is the most ancient gold-bearing horizon of the Lena province (Bodaibo district, Irkutsk region). The conditions of metamorphism of the studied samples do not exceed those of chlorite-muscovite subfacies of greenschist facies (ilmenite-pyrrhotite isograde). The metamorphic allanite is a main REE host, which crystallized before the last stage of plastic deformation and folding. The matter source for its formation is related to REE and Th absorbed on organic matter and clay minerals, as well as the detrital monazite. Late hydrothermal-metasomatic processes resulted in its replacement by hydroxycarbonates (hydroxybastnaesite, ancylite) and hydrous phosphates of light REEs (rhabdophane?), while Th precipitated as a hydrous silicate. Findings of low-temperature metamorphic monazite and xenotime are also described.
47-66
Jonassonite from the Belogorskoe iron deposit (Sikhote-Alin)
Abstract
The paper describes a rare Au–Bi sulfide (jonassonite) from the Belogorskoe iron deposit (Sikhote-Alin), the ore bodies of which are composed of metalliferous sediments that underwent contact metamorphism (T ~550 °С, Plithostatic ~1.5 kbar) and late hydrothermal processes (T 350–415 and 271 °С or slightly lower). Jonassonite is found in products of hydrothermal alteration of metamorphic bustamite-andradite (with a low amount of Mn-bearing hedenbergite, scheelite, lollingite and baryte) rocks composed of calcite, fluorite, native bismuth, bismuthinite, joseite A, an unnamed AgBiS2 phase, cosalite, Mo-bearing scheelite, povellite-molybdenite and other minerals. Jonassonite is intergrown with anhedral calcite aggregates in andradite and forms grains with sections (~5 × 7 µm) close to ellipsoid shape. The mineral contains up to 2.29 wt. % Te, which most likely isomorphically substitutes S. Jonassonite formed at a temperature not exceeding 271 °C during hydrothermal alteration of metamorphic mineral assemblages.
67-78
Studies of mineral composition of ores of the Kumtor deposit (Central Tien Shan) by QXRD and XRF methods
Abstract
Samples of various mineral ore types of the Kumtor gold deposit (Central Tien Shan) were studied using XRF method on a TORNADO M4 analyzer by digital processing of images of the elemental scanning maps to reveal the possibilities of this method to measure the mineral composition of ores without using the AMICS electronic mineral database. During the experimental work, the optimal parameters of elemental analysis and scanning of samples were selected, which allow maximum information with minimal time and expenses. The experimental analyses enabled us to estimate the semi-quantitative content of major ore-forming non-metallic and ore minerals and to establish the possible presence of minerals previously unknown in the composition of ores (barytocalcite, viterite, ferrinatrite, etc.). The macro- and microscopical identification of these minerals is problematic, although their relative content locally reaches several weight percents.
79-101