The First Occurrence of Platinum Group Minerals in Ultramafic Rocks of the Kyzyr–Burlyuk Massif (Western Sayan Mountains,Russia)

Geology of Ore Deposits - For the first time, platinum group minerals (PGMs) have been revealed in dunites and apodunite serpentinites of the Kyzyr–Burlyuk ultramafic massif in the...     

Geochemical Evolution and Ore-Bearing Metasomatic Rocks of the Baga-Gazryn Multiphase Massif of Rare-Metal Li–F Granites (Mongolia)

Doklady Earth Sciences - This paper considers the geochemical evolution of igneous and metasomatic rocks in the Baga-Gazryn Massif on the basis of new precision analytical data. The Baga-Gazryn...     

High-Temperature Metasomatism of the Layered Mafic–Ultramafic Massif in Kiy Island,Belomorian Mobile Belt

The paper presents results of a detailed petrologic study of metasomatites and their host metagabbroids in the northwestern part of Kiy Island, Onega Bay, White Sea. The first evidence is acquired that coronitization and amphibolization of the host rocks took place at the peak of Svecofennian metamorphism at Т = 700–640°C, Р = 9–10 kbar, and \({a_{{H_2}O}}\) = 0.2–0.3. Accompanying metasomatism has formed a number of long (up to several meters long) melanocratic hornblendite and garnet–amphibole veins 0.3–2 m thick. In this area, metasomatites of another type make up single relatively thin amphibole–zoisite lenses that sometimes host ruby-like corundum. The fluid phase that induced metasomatism was poor in salts (Na,K)Cl, and hence, the rocks do not contain sodic plagioclase, and their amphibole is tschermakite but not pargasite. The compositions of the metasomatites of the two types are proved to be complementary, and this indicates that they were most likely produced by high-temperature metasomatism but not via the removal of components by fluid from migmatization zones.     

Tectono-Geochemistry of Superimposed Mineralization in the Bainaimiao Ore Field, Inner Mongolia

Combining geomechanics with geochetnistry, this paper makes a rather systematic study on the stratigraphic division, tectonic evolution and ore genesis of the Bainaimiao ore field and, on such a basis, puts forward some new ideas. It has been emphatically pointed out that, in addition to the prominent E-W structural zone that controls the Cu-Mo deposits, there also exist N-S and NE structures which dominate Pb-Zn and Au mineralizations respectively. The formation of the copper deposit was attributed to the superimposition of three successive stages of mineralization related to volcano-sedimentation and metamorphic and magmatic hydrothermal activities respectively.     

Characteristics of Volcanic Rocks in the Shoshonite Province, Eastern China, and Their Metallogenesis

The shoshonite province in eastern China is characterized by extensive distribution (ca. 80000 km2) of Late Jurassic-Early Cretaceous (165-100 Ma) shoshonite series with subordinate high-K calc-alkali series. It was formed in a dominantly tensile stress field. In comparison with their analogues in island arcs and active continental margins in other countries, the volcanic rocks in the shoshonite province have their specific characteristics in petrology, mineralogy and geochemistry as well as related mineralization association, which are the comprehensive reflection of the special composition and structure of the mantle and crust of the province and the special Mesozoic regional tectonic setting.     

Minerogenic Model of Chrysotile Deposits in Ultramafic Rocks

Most chrysotile deposits occur in ultramafic rocks of the ophiolite suite. The chrysotile deposits dis-cussed in the present paper were formed through metasomatism and infilling-crystallization in a continentalserpentinization environment after plate convergence, where ultramafic rocks were replaced byhydrothermal solutions consisting mainly of deep-circulating heated water derived from atmospheric precip-itation. The critical state for the formation of asbestos in ultramafic rock bodies might be reached bysuperposition of multiple stages of serpentinization. Favourable fracture systems and relatively stable geo-logical environment are important conditions for forming chrysotile deposits. Three subtypes of chrysotiledeposits could be formed in different tectonic settings and under different minerogenic geochemical condi-tions.     

Formation Conditions of Ferromagnesian Metasomatic Carbonates in the Lower Riphean Terrigenous–Carbonate Rocks of the Southern Urals

Lithology and Mineral Resources - Ferromagnesian carbonate metasomatites in limestones of the Lower Riphean Suran Formation in the Avzyan ore region (Bashkir meganticlinorium) are represented by...     

Mineralogy of Copper in Sulfide-Free Endogenic Pb–Zn–Sb Mineralization of the Pelagonian Massif,Republic of North Macedonia

Geology of Ore Deposits - Behavior of copper in sulfide-free metasomatic ores of the Pelagonian massif, Republic of North Macedonia has been studied. It is shown that the highest copper activity...     

Factors of Localization and Forecasting of Ore Mineralization in the Dzhusa Pyrite–Polymetallic Deposit (Southern Urals)

An analysis of tectonic displacements along fractures and faults revealed changes in the character of tectonic deformations that resulted from tectonic evolution of the Magnitogorsk island arc. Structural conditions of localization of ore mineralization of various types were investigated in the open pit of the Dzhusa deposit. The block diagram of an ore shoot of the Dzhusa deposit, which is confined to intersection of NW-striking and sublongitudinal faults was constructed. Trends in the distribution of sites with enriched mineralization are slightly different for various metals. The obtained data make it possible to predict the localization of rich ore bodies at deeper levels of the deposit and to reveal new prospecting ore sites in the Terensai ore field.     

Differentiated Mafic–Ultramafic Intrusions of the Kruglogorsky Type in the Noril’sk Area: Petrology and Ore Potential

Intrusions of the Kruglogorsky type are an integral part of magmatic formations in the Noril’sk area. The marginal portions of these intrusions are composed of microdolerite, dolerite, and contact gabbrodolerite. The central parts of the intrusions consist of leucogabbro and of olivine-free, olivine-bearing, and olivine gabbro-dolerite. Leucogabbro is a characteristic rock of this type of intrusions and sometimes composes up to half of the thicknesses of the rock units. The rocks with plagioporphyritic textures are widespread. Olivine-free, olivine-bearing, and olivine gabbro-dolerite occur as horizons with indistinct boundaries, which are unevenly distributed over the vertical sections of the lithological units. The olivine is the most magnesian (Fo_89-64) and richest in Ni (up to 0.23 wt % NiO) in the olivine gabbro-dolerite. The clinopyroxene is represented by augite (Fs_12-29). The rock-forming minerals are typically zoned. The Sr isotopic composition of the rocks (calculated for an age of 250 Ma) varies within a considerable range (⁸⁷Sr/⁸⁶Sr = 0.705972–0.708006), due to metasomatic alterations. The variations in the Nd and Sr isotopic composition of the Kruglogorsky intrusion are close to those in rocks of the Noril’sk-type ore-bearing intrusions. The olivine-bearing and taxitic gabbro-dolerite host Pt–Cu–Ni ore mineralization, which are of economic value for disseminated ores of the Talnakh area.     

The Evolution of Alpine Ultramafic Rocks and Partial Melting of the Upper Mantle

Ultramafic rocks of Tibet and Xinjiang are the products of partial melting of the upper mantle. The evolution of their mineral composition is marked by two parallel evolutionary series: one is the progressive increase of the 100 Mg/(Mg+Fe~(2+) ratio of silicate minerals in order of lherzolite→harzburgite→dunite, i.e. the increase in magnesium; the other is the increase of the 100 Cr/(Cr+Al) ratio of accessory chrome spinel in the same order, i. e. the increase in Chromium. The above-mentioned evolutionary trends are contrary to that of magmatic differentiation. The evolution of fabrics of ultramafic rocks is characterized by progressive variation in order of protogranular texture→melted residual texture, symplectic texture and clastophyritic texture→equigranular mosaic texture and tabular mosaic texture. Experiments of partial melting of lherzolite have convincingly shown that the evolution of Alpine ultramafic rocks resulted from the partial melting of pyrolite. Various subtypes of them represent different degrees of partial melting. The vertical zoning marked by more basic rocks in the upper part and more acid rocks in the lower actually belongs to the fusion zoning of pyrolite.     

190Pt–4He Dating of Placer-Forming Minerals of Platinum from the Chad Alkaline–Ultramafic Massif: New Evidence of the Polycyclic Nature of Ore Formation

Doklady Earth Sciences - The results of 190Pt–4He dating of placer-forming platinum-group minerals (PPMs) from the placer deposits of Mokhovoi Creek, its tributaries, and eluvial and...     

U–Pb Age and Hf–Nd–Sr Isotopic Systematics of Vein Rocks of the Volkovsky Massif,Middle Urals,Russia

This paper reports chemical, geochronological, and Hf–Nd–Sr isotopic-geochemical data on granite, leucogabbro, and microgabbro porphyrite vein bodies in the gabbro of the Volkovsky massif. It was proved that the vein granite and leucogabbro are genetically related to the leucogabbro–anorthosite–plagiogranite (anorthosite–granite) series of the Urals Platinum Belt. The granite was dated by U-Pb laser ablation inductively coupled plasma mass spectrometric method at 409.0 ± 2.3 Ma. The rock has ⁸⁷Sr/⁸⁶Sr_{(409 Ма)} = 0.70358, high ε_{Nd(409 Ма)} = 6.4–6.5, and ε_{Hf(409 Ма)} ≥ 10.8. Similar values of ⁸⁷Sr/⁸⁶Sr_{(409 Ма)} = 0.70370 and ε_{Nd(409 Ма)} = 5.9 were obtained for the vein leucogabbro. The isotopic-geochemical data are consistent with existing concept of the formation of the leucogabbro–anorthosite–plagiogranite (anorthosite–granite) series through partial melting of the olivine gabbro. The measured ¹⁴³Nd/¹⁴⁴Nd = 0.512939 value obtained for the microgabbro porphyrite reflects their more radiogenic composition and likely a mantle source. The granite, associated leucogabbro, and microgabbro porphyrite were emplaced at the final magmatic stage in the massif evolution. This event marks the upper age boundary of the Au–Pd mineralization related to the gabbroic rocks. The vein rocks lack any signs of the mineralization. However, it is highly probable that they were sources of energy and fluid for reworking of the earlier olivine gabbro and redeposition of ore components in this rock.     

First Data on Au–Sb Mineralization of the Ariadnoe Ultramafic Intrusion,Primor’e

Doklady Earth Sciences - A new promising source of mineral deposits is found in the southern part of the Far East of Russia: the Ti-bearing intrusions of ultramafic rocks of the Sikhote-Alin...     

Age and Ore Matter Sources of Au-Sulfide Mineralization of the Tanadon Deposit,Republic of North Ossetia–Alania,Greater Caucasus

The results of geochronological, petrological–mineralogical, and isotope-geochemical studies of the Tanadon gold deposit in the Greater Caucasus (Republic of North Ossetia–Alania) have made it possible to determine the age of ore veins and identify ore matter sources of sulfide mineralization. The Tanadon deposit is localized in Paleozoic synmetamorphic granitic rocks at the southern margin of the epi-Hercynian Scythian Plate, which is included in the tectonic zone of the Main Caucasus Range. The orebodies are represented by quartz veins varying in thickness and containing complex sulfide mineralization (pyrite, arsenopyrite, chalcopyrite, pyrrhotite, galena, sphalerite, stannite, cobaltite, and bismuthinite). Arsenopyrite is the main repository of invisible gold. Mineralogical data provide evidence for hydrothermal ore formation, which proceeded at least in two stages, giving rise to earlier pyrite + arsenopyrite and later galena + sphalerite + chalcopyrite mineral assemblages. The Tanadon deposit is a zone of intense young magmatic activity. Neointrusions widespread therein are related to the Early Pliocene Tsana Complex (trachyandesitic dikes, ~4.7 Ma in age) and to the Late Pliocene–Early Pleistocene Tepli Complex (dacitic necks, ~1.4 Ma). According to K–Ar dating of sericite from ore-bearing veins, the Tanadon deposit formed synchronously with Early Pliocene dikes of the Tsana Complex. The total duration of the hydrothermal process likely did not exceed hundreds of thousands of years. As follows from Pb-isotope-geochemical data, hydrothermal processes coeval with Early Pliocene magmatic activity, as well as geological relationships between ore-bearing veins and trachyandesitic dikes, show that the sulfide mineralization of the Tanadon deposit is genetically related to the intrusive Tsana Complex. The main source of ore components is represented by hydrothermal solutions produced in an Early Pliocene melt spot localized beneath the considered part of Greater Caucasus. In the adjacent territory of Georgia, a number of ore objects similar in structure and mineral composition to the Tanadon deposit are also genetically and spatially related to the intrusions of the Tsana Complex. Therefore, the Tsana Complex should be regarded as productive and the areas occupied by Early Pliocene intrusive bodies as promising for Au-bearing arsenopyrite and base-metal mineralization.     

Mineralization of pegmatites in parts of the Oban Massif, Southeastern Nigeria： A preliminary analysis

The Oban Basement Massif of southeastern Nigeria is composed of metamorphosed rocks including phyllites, schists, gneisses and amphibolites cut by pegmatitic dykes of varying length and thickness, which intruded the metamorphic rocks. Preliminary geochemical study and analysis of these pegmatites from western Oban Massif at Uyanga, Akwa Ibami, Iwuru I, Iwuru Ⅱ and Igbofia showed that the pegmatites are highly albitized. This is incon-sistent with earlier postulations that the pegmatites in this part of Nige...     

Globular Phyllosilicates of the Glauconite–Illite Series in the Cambrian and Ordovician Rocks of the Eastern Baltica (Northern Estonia,Western Lithuania,and Western Latvia)

Lithology and Mineral Resources - The mineralogical, structural and crystal-chemical features of seven samples of globular phyllosilicates of the glauconite–illite series (GPS) from the Lower...     

Composition and evolution of PGE mineralization in chromite ores from the Il’chir ophiolite complex (Ospa–Kitoi and Khara-Nur areas,East Sayan)

Data are presented on chromitites from the northern and southern sheets of the Il’chir ophiolite complex (Ospa–Kitoi and Khara-Nur (Kharanur) massifs). The new and published data are used to consider similarities and differences between ore chrome-spinel from the chromitites of the northern and southern ophiolite sheets as well as the species diversity of PGE minerals and the evolution of PGE mineralization. Previously unknown PGE minerals have been found in the studied chromitites.Ore chrome-spinel in the chromitites from the northern sheet occurs in medium- and low-alumina forms, whereas the chromitites from the southern sheet contain only medium-alumina chrome-spinel. The PGE minerals in the chromitites from the southern sheet are Os–Ir–Ru solid solutions as well as sulfides and sulfoarsenides of these metals. The chromitites from the northern sheet contain the same PGE minerals and diverse Rh–Pt–Pd mineralization: Pt–Ir–Ru–Os and isoferroplatinum with Ir and Os–Ir–Ru lamellae. Areas of altered chromitites contain a wide variety of low-temperature secondary PGE minerals: Pt–Cu, Pt–Pd–Cu, PdHg, Rh2SnCu, RhNiAs, PtAs2, and PtSb2. The speciation of the PGE minerals is described along with multiphase intergrowths. The relations of Os–Ir–Ru solid solutions with laurite and irarsite are considered along with the microstructure of irarsite–osarsite–ruarsite solid solutions. Zoned Os–Ir–Ru crystals have been found. Zone Os82–99 in these crystals contains Ni3S2 inclusions, which mark off crystal growth zones. Different sources of PGE mineralization are presumed for the chromitites from the northern and southern sheets.The stages of PGE mineralization have been defined for the chromitites from the Il’chir ophiolite belt. The Pt–Ir–Ru–Os and (Os, Ru)S2 inclusions in Os–Ir–Ru solid solutions might be relics of primitive-mantle PGE minerals. During the partial melting of the upper mantle, Os–Ir–Ru and Pt–Fe solid solutions formed syngenetically with the chromitites. During the late-magmatic stage, Os–Ir–Ru solid solutions were replaced by sulfides and sulfarsenides of these metals. Mantle metasomatism under the effect of reduced mantle fluids was accompanied by PGE remobilization and redeposition with the formation of the following assemblage: garutiite (Ni,Fe,Ir), zaccariniite (RhNiAs), (Ir,Ni,Cu)S3, Pt–Cu, Pt–Cu–Fe–Ni, Cu–Pt–Pd, and Rh–Cu–Sn–Sb. The zoned Os–Ir–Ru crystals in the chromitites from the northern sheet suggest dissolution and redeposition of Os–Ir–Ru primary-mantle solid solutions by bisulfide complexes. Most likely, the PGE remobilization took place during early serpentinization at 450–600 ºC and 13–16 kbar.During the crustal metamorphic stage, tectonic movements (obduction) and a change from reducing to oxidizing conditions were accompanied by the successive transformation of chrome-spinel into ferrichromite–chrome-magnetite with the active participation of a metamorphic fluid enriched in crustal components. The orcelite–maucherite–ferrichromite–sperrylite assemblage formed in epidote-amphibolitic facies settings during this stage.The PGE mineral assemblage reflects different stages in the formation of the chromitites and dunite-harzburgite host rocks and their transformation from primitive mantle to crustal metamorphic processes.     

Relationship Between Pb-Zn and Au-Ag Mineralization of Kengdenongshe Polymetallic Deposit in Eastern Segment of the Eastern KunlunEI北大核心CSCD

The Kengdenongshe deposit is a newly discovered large Au-Ag-Pb-Zn polymetallic deposit in the eastern Kunlun metallogenic belt, and the genetic relationship between Pb-Zn-rich ore bodies and Au-rich ore bodies in this deposit is controversial. Therefore, comparative studies of mineralization, alteration, and fluid inclusions in the two types of ore bodies were carried out with the statistical analysis of the correlation among ore-forming elements of Au, Ag, Pb and Zn. The results show that, from north to south, the mineralization changes gradually from Pb-Zn-rich to Au-rich with the wall-rock alteration from silicification-epidotization to baritization-marbleization-silicification. In addition, the structures of Pb-Zn-rich ores indicate a hydrothermal sedimentary origin with the late hydrothermal superposition, while those of Au-rich ores show features of hydrothermal origin. Besides, based on the study of fluid inclusions in this mining area, the ore-forming fluid of Pb-Zn-rich ores is low temperature (focus on 150-170°C) and low-medium salinity (1.74%-10.24% NaCleqv), while that of Au-rich ores displays low-medium temperature (manily 130-250°C) with low-medium salinity (0.35%-10.24% NaCleqv). Pb-Zn and Au-Ag show positive correlation (correlation coefficient r>0.25), but Au is poorly correlated with Pb and Zn (correlation coefficient r<0.15). However, to due to the late stage hydrothermal superimposition, Au is rather well correlated with Pb in high grade ores. In summary, there may exist two epochs of mineralization in the Kengdenongshe polymetallic deposit. The early one is Pb-Zn mineralization stage with characteristics of hydrothermal sedimentary origin, and the ore-forming fluid may be derived from the mixture of magmatic water and seawater. While the later one is Au mineralization stage, having characteristics of hydrothermal origin with subsequent hydrothermal superimpositions, and the ore-forming fluid is mainly derived from magmatic water that mixed with meteoric water. © 2018, Science Press. All right reserved.