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1
Pan, Yuanming, and Michael E. Fleet. "Mineralogy and genesis of calc-silicates associated with Archean volcanogenic massive sulphide deposits at the Manitouwadge mining camp, Ontario." Canadian Journal of Earth Sciences 29, no. 7 (July 1, 1992): 1375–88. http://dx.doi.org/10.1139/e92-111.
Повний текст джерелаАнотація:
Skarn-like calc-silicate rocks are reported in spatial association with the Archean Cu–Zn–Ag massive sulphide deposits at the Manitouwadge mining camp, Ontario. Calc-silicates in the footwall of the Willroy mine occur as matrix to breccia fragments of garnetiferous quartzo-feldspathic gneiss and as lenses within garnetiferous quartzo-feldspathic gneiss and are composed of clinopyroxene, garnet, calcic amphiboles, wollastonite, plagioclase, K-feldspar, epidote, quartz, calcite, magnetite, and minor sulphides. Calc-silicates within the main orebody of the Geco mine are characterized by clinopyroxene, calcic amphiboles (Cl–K-rich hastingsitic and ferro-edenitic hornblende, ferro-edenite (up to 4.7 wt.% Cl); and ferroactinolite (6.7 wt.% MnO)), garnet, epidote (including an epidote rich in rare-earth elements and Cl), calcite, quartz, and abundant sulphides. Calc-silicates within the basal 4/2 Copper Zone of the Geco mine contain garnet, gahnite, sphalerite, ferroactinolite (8.5 wt.% MnO), epidote, quartz, biotite, plagioclase, chlorite, muscovite, K-feldspar, and pyrosmalite (with Mn/(Mn + Fe) ratio ranging from 0.21 to 0.61, and up to 3.9 wt.% Cl). The calc-silicates probably represent metasomatic remobilization of dispersed Ca (and Cl) from sea-floor hydrothermal alteration of mafic to intermediate volcanic rocks and are only indirectly related to the hypothesized syngenetic ore-forming processes for the associated base metal sulphide deposits. The calc-silicates formed initially at about 600 °C and 3–5 kbar (1 kbar = 100 MPa) in a mildly reducing environment (from 1 log unit above to 1 log unit below the fayalite–magnetite–quartz buffer) during the upper-amphibolite- to granulite-facies regional metamorphism and were altered subsequently at lower temperatures (<500 °C).
2
Abu-Alam, T. S., K. Stüwe, and C. Hauzenberger. "Calc-silicates from Wadi Solaf region, Sinai, Egypt." Journal of African Earth Sciences 58, no. 3 (October 2010): 475–88. http://dx.doi.org/10.1016/j.jafrearsci.2010.05.004.
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3
Fleet, Michael E., and Yuanming Pan. "Crystal chemistry of Rare Earth Elements in fluorapatite and some calc-silicates." European Journal of Mineralogy 7, no. 3 (May 19, 1995): 591–606. http://dx.doi.org/10.1127/ejm/7/3/0591.
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4
Oliver, Nick, and Vic Wall. "Metamorphic plumbing system in Proterozoic calc-silicates, Queensland, Australia." Geology 15, no. 9 (1987): 793. http://dx.doi.org/10.1130/0091-7613(1987)15<793:mpsipc>2.0.co;2.
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5
Luitel, Prakash, and Suman Panthee. "Geological study in Tal - Talekhu section of Manang District along the Besisahar – Chame Road." Bulletin of the Department of Geology 22 (December 15, 2020): 25–28. http://dx.doi.org/10.3126/bdg.v22i0.33411.
Повний текст джерелаАнотація:
The section between Tal to Talekhu of Manang District lacks the detailed geological study. The geological mapping in the scale of 1:50,000 followed by the preparation of geological cross-section and lithostratigraphic column has been done in the present study. The studied area lies partially in the Higher Himalayan Crystalline and the Tibetan Tethys Sequence. The units of the Higher Himalayan Group from Tal to Talekhu consists mainly of vigorous to faintly calcareous gneiss, migmatitic gneiss, quartzite, granite, etc. They are named as the Calc. Silicate Gneiss and Paragneiss and the Orthogneiss and Granite units. The lowermost part of the Tibetan Tethys consisted of metamorphosed calcareous rocks containing silicates and feldspar, so this unit is termed as the Marble and Calc. Gneiss. The section is about 9 km in thickness and is highly deformed with presence of igneous rocks at many places.
6
Luitel, Prakash, and Suman Panthee. "Geological study in Tal - Talekhu section of Manang District along the Besisahar – Chame Road." Bulletin of the Department of Geology 22 (December 15, 2020): 25–28. http://dx.doi.org/10.3126/bdg.v22i0.33411.
Повний текст джерелаАнотація:
The section between Tal to Talekhu of Manang District lacks the detailed geological study. The geological mapping in the scale of 1:50,000 followed by the preparation of geological cross-section and lithostratigraphic column has been done in the present study. The studied area lies partially in the Higher Himalayan Crystalline and the Tibetan Tethys Sequence. The units of the Higher Himalayan Group from Tal to Talekhu consists mainly of vigorous to faintly calcareous gneiss, migmatitic gneiss, quartzite, granite, etc. They are named as the Calc. Silicate Gneiss and Paragneiss and the Orthogneiss and Granite units. The lowermost part of the Tibetan Tethys consisted of metamorphosed calcareous rocks containing silicates and feldspar, so this unit is termed as the Marble and Calc. Gneiss. The section is about 9 km in thickness and is highly deformed with presence of igneous rocks at many places.
7
Zahm, Alain. "The compositional evolution of calc silicates from the Salau skarn-deposit (Ariège, Pyrénées)." Bulletin de Minéralogie 110, no. 6 (1987): 623–32. http://dx.doi.org/10.3406/bulmi.1987.8005.
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8
Singh, Vishnu Kumar, and Rajesh Kumar Sahoo. "Occurrence of Manganese Mineralization in Rayavalasa and Tudi Villages of Eastern Ghat Mobile Belts, Andhra Pradesh." International Journal of Research Publication and Reviews 03, no. 11 (2022): 2924–33. http://dx.doi.org/10.55248/gengpi.2022.31102.
Повний текст джерелаАнотація:
In this paper, we have reported small bands of Manganiferous quartzite at S. Gopalapuram, Tudi, .Some other small occurrences also observed as float ore/boulders and/or small manganese ore observed north of Nandala-meta, Tangidi and Rayavalasa The pockets of Mn ores are lithologically controlled but the disposition of manganese bands are structur-ally controlled, localized near the hinge zones and at some parts in the limb areas. The Mn-rich silicates are converted to manganese ore due to leaching or oxidation. The relict phases of silicate with Mn-rich rim and inclu-sions indicate that they were derived during leaching. Some features such as colloform bands, relict silicates and rare pseudomorphs, indicate its secondary nature formed due to the alteration of manganiferous silicates. Braunite, and psilomelane are represented as the primary minerals. secondary minerals are made up of psilomelane, cryptomelane, py-rolusite, and goethite and are formed in the low grades of metamorphism. Analytical val-ues of manganese (Mn) in bedrock samples collected from the Mn-enriched horizons of calc-granulite and khondalite rock types range from 0.16% to 39.70%. The analytical results of float ore samples have maximum values of upto 23.64%
9
Barnes, Christopher J., Jarosław Majka, Michał Bukała, Erika Nääs, and Sabine Rousku. "Detrital zircon U-Pb geochronology of a metasomatic calc-silicate in the Tsäkkok Lens, Scandinavian Caledonides." Geology, Geophysics and Environment 47, no. 1 (April 23, 2021): 21–31. http://dx.doi.org/10.7494/geol.2021.47.1.21.
Повний текст джерелаАнотація:
The Tsäkkok Lens of the Seve Nappe Complex in the Scandinavian Caledonides comprises eclogite bodies hosted within metasedimentary rocks. These rocks are thought to be derived from the outermost margin of Baltica along the periphery of the Iapetus Ocean, but detrital records from the sedimentary rocks are lacking.Many metasedimentary outcrops within the lens expose both well-foliated metapelitic rocks and massive calc-silicates. The contacts between these two lithologies are irregular and are observed to trend at all angles to the high-pressure foliation in the metapelites. Where folding is present in the metapelites, the calc-silicate rocks are also locally folded. These relationships suggest metasomatism of the metapelites during the Caledonian orogenesis. Zircon U-Pb geochronology was conducted on sixty-one zircon grains from a calc-silicate sample to investigate if they recorded the metasomatic event and to assess the detrital zircon populations. Zircon grains predominantly show oscillatory zoning, sometimes with thin, homogeneous rims that have embayed contacts with the oscillatory-zoned cores. The zircon cores yielded prominent early Stenian, Calymmian, and Statherian populations with a subordinate number of Tonian grains. The zircon rims exhibit dissolution-reprecipitation of the cores or new growth and provide ages that span similar time frames, indicating overprinting of successive tectonic events. Altogether, the zircon record of the calc-silicate suggests that the Tsäkkok Lens may be correlated to Neoproterozoic basins that are preserved in allochthonous positions within the northern extents of the Caledonian Orogen.
10
Huraiová, Monika, Patrik Konečný, and Vratislav Hurai. "Niobium Mineralogy of Pliocene A1-Type Granite of the Carpathian Back-Arc Basin, Central Europe." Minerals 9, no. 8 (August 15, 2019): 488. http://dx.doi.org/10.3390/min9080488.
Повний текст джерелаАнотація:
A1-type granite xenoliths occur in alkali basalts erupted during Pliocene–Pleistocene continental rifting of Carpathian back-arc basin (Central Europe). The Pliocene (5.2 Ma) peraluminous calc-alkalic granite contains unusually high concentrations of critical metals bound in Nb, Ta, REE, U, Th-oxides typical for silica-undersaturated alkalic granites, and syenites: columbite-Mn, fergusonite-Y, oxycalciopyrochlore, Nb-rutile, and Ca-niobate (fersmite or viggezite). In contrast, it does not contain allanite and monazite—the main REE-carriers in calc-alkalic granites. The crystallization of REE-bearing Nb-oxides instead of OH-silicates and phosphates was probably caused by strong water deficiency and low phosphorus content in the parental magma. Increased Nb and Ta concentrations have been inherited from the mafic parental magma derived from the metasomatized mantle. The strong Al- and Ca-enrichment probably reflects the specific composition of the mantle wedge modified by fluids, alkalic, and carbonatitic melts liberated from the subducted slab of oceanic crust prior to the Pliocene-Pleistocene rifting.
11
Oliver, Nicholas H. S., Victor J. Wall, and Ian Cartwright. "Internal control of fluid compositions in amphibolite-facies scapolitic calc-silicates, Mary Kathleen, Australia." Contributions to Mineralogy and Petrology 111, no. 1 (June 1992): 94–112. http://dx.doi.org/10.1007/bf00296581.
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12
Ghent, E. D., and M. Z. Stout. "MINERAL EQUILIBRIA IN QUARTZ LEUCOAMPHIBOLITES (QUARTZ - GARNET - PLAGIOCLASE - HORNBLENDE CALC-SILICATES) FROM SOUTHEASTERN BRITISH COLUMBIA, CANADA." Canadian Mineralogist 38, no. 1 (February 1, 2000): 233–44. http://dx.doi.org/10.2113/gscanmin.38.1.233.
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13
Delpino, Sergio H., and Jorge A. Dristas. "Dolomitic marbles and associated calc-silicates, Tandilia belt, Argentina: Geothermobarometry, metamorphic evolution, and P–T path." Journal of South American Earth Sciences 25, no. 4 (June 2008): 501–25. http://dx.doi.org/10.1016/j.jsames.2007.06.001.
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14
Torres-Ruiz, J., A. Pesquera, and V. López Sánchez-Vizcaíno. "Chromian tourmaline and associated Cr-bearing minerals from the Nevado-Fildbride Complex (Betic Cordilleras, SE Spain)." Mineralogical Magazine 67, no. 3 (June 2003): 517–33. http://dx.doi.org/10.1180/0026461036730114.
Повний текст джерелаАнотація:
AbstractChromian tourmaline, in association with other Cr-bearing minerals (amphibole, mica, epidote, chlorite, titanite, rutile and chromian spinel), occurs in fine calc-schist levels within metacarbonate rocks from the Nevado-Filabride Complex, SE Spain. Electron microprobe analyses of tourmaline and coexisting minerals document both chemical differences dependent on the host-rock type and an irregular distribution of Cr at grain scale. Tourmaline is Na-rich dravite, with average Mg/(Mg+Fe) ratios of 0.83 and 0.63 a.p.f.u. and Cr contents of 0.32 and 0.18 a.p.f.u., in dolomitic and ankeritic marbles, respectively. Tourmaline contains small but significant concentrations of Zn (av. 0.01 a.p.f.u.) and in ankeritic marble it also contains Ni (av. 0.04 a.p.f.u.). Zn-rich chromian spinel appears as small relict inclusions in silicates, with average Cr, Fe, Al and Zn contents of 1.201, 1.241, 0.411 and 0.107 a.p.f.u., respectively. Amphibole, epidote, mica and chlorite show average Cr contents of 0.088, 0.138, 0.115 and 0.267 a.p.f.u., respectively, in dolomitic marbles, and 0.103, 0.078, 0.065 and 0.185 a.p.f.u., respectively, in ankeritic marbles. Cr-silicates formed through metamorphic reactions involving detrital Cr-rich spinel, in addition to clay minerals and carbonates. The B necessary to form tourmaline was probably derived from the leaching of underlying evaporitic rocks.
15
Mora, Claudia I., and John W. Valley. "Prograde and retrograde fluid-rock interaction in calc-silicates northwest of the Idaho batholith: stable isotopic evidence." Contributions to Mineralogy and Petrology 108, no. 1-2 (July 1991): 162–74. http://dx.doi.org/10.1007/bf00307335.
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16
Cartwright, I., I. S. Buick, T. R. Weaver, J. K. Vry, and N. H. S. Oliver. "Patterns of fluid flow in Proterozoic calc‐silicates: Fluid channelling and variations in fluid fluxes and intrinsic permeabilities." Australian Journal of Earth Sciences 42, no. 3 (June 1995): 259–65. http://dx.doi.org/10.1080/08120099508728200.
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17
FITZSIMONS, I. C. W., and S. L. HARLEY. "Garnet coronas in scapolite-wollastonite calc-silicates from East Antarctica: the application and limitations of activity-corrected grids." Journal of Metamorphic Geology 12, no. 6 (November 1994): 761–77. http://dx.doi.org/10.1111/j.1525-1314.1994.tb00058.x.
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18
Jiménez-Franco, Abigail, Carles Canet, Pura Alfonso, Eduardo González-Partida, Abdorrahman Rajabi, and Edgar Escalante. "The Velardeña Zn–(Pb–Cu) skarn-epithermal deposits, central-northern Mexico: New physical-chemical constraints on ore-forming processes." Boletín de la Sociedad Geológica Mexicana 72, no. 3 (November 28, 2020): A270719. http://dx.doi.org/10.18268/bsgm2020v72n3a270719.
Повний текст джерелаАнотація:
The Velardeña mining district is economically the most important of Durango state. The ore deposits occur in different skarn zones developed within the intrusive contact between Mesozoic limestones and Eocene granitic stocks and dikes. The most important ore deposits are related to the Santa María dike and Reyna de Cobre porphyritic stock (separated from each other by 10 km). They occur as irregularly shaped replacement masses developed near the intrusive contact and have a skarn paragenesis dominated by calc-silicates and sulfides. The mineral assemblages show replacement textures and are dominated by calcic clinopyroxene (Di97-53Hd42-02Jh04-01) and garnet (Ad100-57Grs43-00) in the exoskarn, with wollastonite particularly abundant in the endoskarn. Hydrous silicates are actinolite, epidote, and chlorite, whereas sulfides include pyrite, sphalerite, pyrrhotite, galena, chalcopyrite, and sulfosalts. Scheelite, hematite, quartz, and calcite are also present. According to sphalerite geobarometry, the skarns formed at hypabyssal depths (~3–4 km). They developed by a succession of replacive mineralizing events, including (a) a prograde stage at temperatures from ≥470 to 335 °C in conditions of low f (CO2), followed by (b) a retrograde stage from 335 to 220 °C. There was a general increase in f (O2), accompanying the temperature decline during the formation of the system, which accounts for a process of mixing with cooler, oxidizing, and dilute water. During the retrograde stage, wollastonite, calcic garnet and clinopyroxene formed. On the other hand, hydrous silicates, sulfides, sulfosalts, scheelite, and hematite crystallized during the retrograde stage. Skarn mineralization is crosscut by veins of calcite, fluorite, adularia, and sphalerite. The vein mineralization formed at temperatures below 200 °C. The different ore deposits of Velardeña constitute a telescoped skarn–epithermal mineral system.
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Voudouris, P., I. Graham, K. Mavrogonatos, S. Su, K. Papavasiliou, M. V. Farmaki, and P. Panagiotidis. "MN-ANDALUSITE, SPESSARTINE, MN-GROSSULAR, PIEMONTITE AND MN-ZOISITE/CLINOZOISITE FROM TRIKORFO, THASSOS ISLAND, GREECE." Bulletin of the Geological Society of Greece 50, no. 4 (July 28, 2017): 2068. http://dx.doi.org/10.12681/bgsg.14258.
Повний текст джерелаАнотація:
Mylonitized manganiferous schists and calc-silicate layers intercalated within amphibolite- to greenschist facies mica schists from the Trikorfo area (Thassos Island, Greece), host an unusual Mn-rich paragenesis of metamorphic silicate minerals, most of them in large, gemmy crystals. The silicates occur both in layers subparallel to the foliation and within discordant veins cross-cutting the metamorphic fabric. Piemontite (up to 12.7 wt. % Mn2O3), Mn-rich epidote (up to 7.8 wt. % Mn2O3), Mn-rich andalusite (up to 15.6 wt. % Mn2O3), Mn-poor pink clinozoisite-epidote (up to 0.87 wt. % Mn2O3), Mn-poor pink zoisite (up to 0.21 wt. % Mn2O3), spessartine (up to 47.7 wt. % MnO) and Mn-rich grossular (up to 3.6 wt. % MnO) are associated with diopside, hornblende, phlogopite, muscovite, tourmaline, hematite and iron-bearing kyanite. The studied assemblages are indicative of high fO2 conditions due to the presence of highly oxidized pre-metamorphic Mn-rich mineral associations. They developed during prograde metamorphism of a Mn-rich sedimentary protolith(s), followed by re equilibration to post-peak metamorphic conditions, vein formation and metasomatism during retrograde metamorphism accompanying the exhumation of the Thassos Island during the Oligocene-Miocene. Alternatively, the skarn similar mineralogy of the calc-silicate layers could have been formed by fluids released by granitoids during contact metamorphism. The studied area represents a unique mineralogical geotope. Its geological-mineralogical heritage should be protected through establishment of a mineralogical-petrological geopark that will also promote sustainable development of the area.
20
Kontonikas-Charos, Alkis, Cristiana L. Ciobanu, Nigel J. Cook, Kathy Ehrig, Roniza Ismail, Sasha Krneta, and Animesh Basak. "Feldspar mineralogy and rare-earth element (re)mobilization in iron-oxide copper gold systems from South Australia: a nanoscale study." Mineralogical Magazine 82, S1 (February 28, 2018): S173—S197. http://dx.doi.org/10.1180/minmag.2017.081.040.
Повний текст джерелаАнотація:
ABSTRACTNanoscale characterization (TEM on FIB-SEM-prepared foils) was undertaken on feldspars undergoing transformation from early post-magmatic (deuteric) to hydrothermal stages in granites hosting the Olympic Dam Cu-U-Au-Ag deposit, and from the Cu-Au skarn at Hillside within the same iron-oxide copper-gold (IOCG) province, South Australia. These include complex perthitic textures, anomalously Ba-, Fe-, or REE-rich compositions, and REE-flourocarbonate + molybdenite assemblages which pseudomorph pre-existing feldspars. Epitaxial orientations between cryptoperthite (magmatic), patch perthite (dueteric) and replacive albite (hydrothermal) within vein perthite support interface-mediated reactions between pre-existing alkali-feldspars and pervading fluid, irrespective of micro-scale crystal morphology. Such observations are consistent with a coupled dissolution-reprecipitation reaction mechanism, which assists in grain-scale element remobilization via the generation of transient interconnected microporosity. Micro-scale aggregates of hydrothermal hyalophane (Ba-rich K-feldspar), crystallizing within previously albitized areas of andesine, reveal a complex assemblage of calc-silicate, As-bearing fluorapatite and Fe oxides along reaction boundaries in the enclosing albite-sericite assemblage typical of deuteric alteration. Such inclusions are good REE repositories and their presence supports REE remobilization at the grain-scale during early hydrothermal alteration. Iron-metasomatism is recognized by nanoscale maghemite inclusions within ‘red-stained’ orthoclase, as well as by hematite in REE-fluorocarbonates, which reflect broader-scale zonation patterns typical for IOCG systems. Potassium-feldspar from the contact between alkali-granite and skarn at Hillside is characterized by 100–1000 ppm REE, attributable to pervasive nanoscale inclusions of calc-silicates, concentrated along microfractures, or pore-attached. Feldspar replacement by REE-fluorcarbonates at Olympic Dam and nanoscale calc-silicate inclusions in feldspar at Hillside are both strong evidence for the role of feldspars in concentrating REE during intense metasomatism. Differences in mineralogical expression are due to the availability of associated elements. Lattice-scale intergrowths of assemblages indicative of Fe-metasomatism, REE-enrichment and sulfide deposition at Olympic Dam are evidence for a spatial and temporal relationship between these processes.
21
Schiffman, Peter, Dennis K. Bird, and Wilfred A. Elders. "Hydrothermal mineralogy of calcareous sandstones from the Colorado River delta in the Cerro Prieto geothermal system, Baja California, Mexico." Mineralogical Magazine 49, no. 352 (June 1985): 435–49. http://dx.doi.org/10.1180/minmag.1985.049.352.14.
Повний текст джерелаАнотація:
AbstractThe Cerro Prieto geothermal system provides a unique opportunity for the detailed study of calc-silicate mineral transitions between the diagenetic clay-carbonate and greenschist facies within the terrigenous sediments of the Colorado River delta. In this system, progressive devolatization reactions within carbonate-cemented, quartzofeldspathic sediment have produced a distinct hydrothermal mineral zonation at temperatures between 200–370°C and fluid pressures below 0.3 kbar. Descriptive and compositional data are presented for these minerals which include wairakite, epidote, prehnite, actinolite, clinopyroxene, garnet, sphene, biotite, microcline, and calcite. Partitioning of octahedral Fe, Mg, and Al between coexisting authigenic silicates is comparable with data from higher temperature metamorphic rocks and demonstrates an approach to local equilibrium within this system. Calculated fugacities of oxygen at temperatures above 300°C are (with rare exception) more reducing than that defined by the quartz-fayalite-magnetite buffer, a result consistent with the scarcity of hematite and grandite and the ubiquitous presence of organic material in Cerro Prieto sandstones.
22
Munyanyiwa, Hubert. "Mineral assemblages in calc-silicates and marbles in the Zambezi mobile belt: their implications on mineral-forming reactions during metamorphism." Journal of African Earth Sciences (and the Middle East) 10, no. 4 (January 1990): 693–700. http://dx.doi.org/10.1016/0899-5362(90)90035-d.
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Li, Hao, Gideon Lambiv Dzemua, and Qi Liu. "Beneficiation Studies of the Low-Grade Skarn Phosphate from Mactung Tungsten Deposit, Yukon, Canada." Minerals 11, no. 4 (April 15, 2021): 421. http://dx.doi.org/10.3390/min11040421.
Повний текст джерелаАнотація:
A preliminary beneficiation study of low-grade skarn phosphate rocks from Mactung tungsten deposit, along the Yukon and Northwest Territories border in Canada, was carried out through standard Bond Work Index, grinding test and laboratory batch flotation tests. The skarn phosphate sample assayed 12.65% P2O5 (about 30% apatite), 31.71% CaO and 35.46% SiO2. The main gangue minerals included calcite, quartz, calc-silicates, amphibole, feldspar, and pyrrhotite. The sample had a Bond Work Index of 19.04 kWh/t, belonging to a hard ore category. The beneficiation study of the skarn phosphate sample was carried out using “direct–reverse flotation” method. The direct flotation was carried out using sodium carbonate, sodium silicate solution (water glass) and sodium oleate. Sulfuric acid and phosphoric acid were used in the reverse flotation of the carbonate gangue. One phosphorous rougher flotation, one bulk cleaner flotation and one carbonate reverse flotation at ore grind size of 86% passing 53 µm led to a phosphate concentrate assaying 28.68% P2O5, 12.06% SiO2, 0.72% MgO and 46.98% CaO, at a P2O5 recovery of 70.9%.
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Schmid, Robert, Leander Franz, Roland Oberhänsli, and Shuwen Dong. "High-Si phengite, mineral chemistry and P-T evolution of ultra-high-pressure eclogites and calc-silicates from the Dabie Shan, eastern China." Geological Journal 35, no. 3-4 (July 2000): 185–207. http://dx.doi.org/10.1002/gj.863.
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Paoli, Dini, Petrelli, and Rocchi. "HFSE‐REE Transfer Mechanisms During Metasomatism of a Late Miocene Peraluminous Granite Intruding a Carbonate Host (Campiglia Marittima, Tuscany)." Minerals 9, no. 11 (November 4, 2019): 682. http://dx.doi.org/10.3390/min9110682.
Повний текст джерелаАнотація:
The different generations of calc‐silicate assemblages formed during sequential metasomatic events make the Campiglia Marittima magmatic–hydrothermal system a prominent case study to investigate the mobility of rare earth element (REE) and other trace elements. These mineralogical assemblages also provide information about the nature and source of metasomatizing fluids. Petrographic and geochemical investigations of granite, endoskarn, and exoskarn bodies provide evidence for the contribution of metasomatizing fluids from an external source. The granitic pluton underwent intense metasomatism during post‐magmatic fluid–rock interaction processes. The system was initially affected by a metasomatic event characterized by circulation of K‐rich and Ca(‐Mg)‐rich fluids. A potassic metasomatic event led to the complete replacement of magmatic biotite, plagioclase, and ilmenite, promoting major element mobilization and crystallization of K‐feldspar, phlogopite, chlorite, titanite, and rutile. The process resulted in significant gain of K, Rb, Ba, and Sr, accompanied by loss of Fe and Na, with metals such as Cu, Zn, Sn, W, and Tl showing significant mobility. Concurrently, the increasing fluid acidity, due to interaction with Ca‐rich fluids, resulted in a diffuse Ca‐metasomatism. During this stage, a wide variety of calc‐silicates formed (diopside, titanite, vesuvianite, garnet, and allanite), throughout the granite body, along granite joints, and at the carbonate–granite contact. In the following stage, Ca‐F‐rich fluids triggered the acidic metasomatism of accessory minerals and the mobilization of high-field-strength elements (HFSE) and REE. This stage is characterized by the exchange of major elements (Ti, Ca, Fe, Al) with HFSE and REE in the forming metasomatic minerals (i.e., titanite, vesuvianite) and the crystallization of HFSE‐REE minerals. Moreover, the observed textural disequilibrium of newly formed minerals (pseudomorphs, patchy zoning, dissolution/reprecipitation textures) suggests the evolution of metasomatizing fluids towards more acidic conditions at lower temperatures. In summary, the selective mobilization of chemical components was related to a shift in fluid composition, pH, and temperature. This study emphasizes the importance of relating field studies and petrographic observations to detailed mineral compositions, leading to the construction of litho‐geochemical models for element mobilization in crustal magmatic‐hydrothermal settings.
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Bahramnejad, E., S. Bagheri, and A. Zahedi. "Petrology and mineral chemistry in the Calc-silicates of the Deh-salm metamorphic complex, East of Lut block: evidence of progressive metamorphism to the granulite facies." Iranian Journal of Crystallography and Mineralogy 29, no. 1 (March 1, 2021): 149–64. http://dx.doi.org/10.52547/ijcm.29.1.149.
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Rumsey, M. S., M. D. Welch, A. R. Kampf, and J. Spratt. "Diegogattaite, Na2CaCu2Si8O20·H2O: a new nanoporous copper sheet silicate from Wessels Mine, Kalahari Manganese Fields, Republic of South Africa." Mineralogical Magazine 77, no. 8 (December 2013): 3155–62. http://dx.doi.org/10.1180/minmag.2013.077.8.09.
Повний текст джерелаАнотація:
AbstractDiegogattaite (IMA2012-096), Na2CaCu2Si8O20·H2O, is a new mineral from the Wessels mine in the Kalahari manganese fields of South Africa. It occurs as a minor phase with other copper-bearing silicates, Cu-rich pectolite, sugilite, quartz, aegirine and undifferentiated Fe-Mn oxides. Diegogattaite is pale turquoise through teal blue. It is found as sub-mm sized grains in a main crystalline patch 3–4 mm in size, and is currently known from only one sample. The mineral is transparent with a vitreous lustre and may have a good cleavage on {001}. It is brittle, with an uneven fracture and a very pale-blue streak. It is non-fluorescent in short- and long-wave UV light and has an estimated Mohs hardness of ∼5–6. Diegogattaite is biaxial (–), α = 1.598(2), β = 1.627(2), γ = 1.632(2); 2Vmeas = 44.0(6)°, 2Vcalc = 44.5°; dispersion: strong r < v, orientation: X = b, Y ≈ ⊥(001), Z ≈ a; pleochroism X colourless << Y ≈ Z blue green. The calculated density is 3.10 g/cm3. Electron-microprobe analysis gave: Na2O 8.07, CaO 7.3, CuO 20.5, FeO 0.36, SiO262.4, H2O(calc) 2.34, total 100.97 wt.%. A charge-balanced formula on the basis of 21 oxygen a.p.f.u. is: Na2.00Ca1.00Cu1.98Fe0.04Si7.99H2O21. Diegogattaite is monoclinic, space group C2/m, a = 12.2439(6) Å, b = 15.7514(4) Å, c = 10.6008(3) Å, β = 125.623(2)°, V = 1661.87(10) Å3 and Z = 4. The five strongest lines in the X-ray powder pattern are [dobs in Å (Iobs)(hkl)]: 4.25(75)(002,22,220), 3.951(77)(040), 3.261(100)(31,13), 2.898(89)(042,03,003), 2.332(66)(331,43,62,260,043). The crystal structure of diegogattaite was determined by single-crystal X-ray diffraction to final agreement indices of R1 = 0.027, wR2 = 0.071 and GoF = 1.090. It represents a completely new silicate topology based upon a double-sheet of SiO4 tetrahedra composed of connected 6482 cages. The structure of diegogattaite is related to those of synthetic nanoporous Na-Cu-Si-O-(OH)-H2O (CuSH) compounds, which are of interest to the solid-state chemistry community as potential ion-exchangers, catalysts and molecular sieves. The structure of diegogattaite forms a bridge between these structures and those of the gillespite-group minerals, including wesselsite. The close spatial association of wesselsite and diegogattaite suggests a possible reaction between them that may point to a synthetic route for the production of novel alkaline-earth-based nanoporous copper silicates.
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Voudouris, Panagiotis, Vasilios Melfos, Constantinos Mavrogonatos, Alexandre Tarantola, Jens Gӧtze, Dimitrios Alfieris, Victoria Maneta, and Ioannis Psimis. "Amethyst Occurrences in Tertiary Volcanic Rocks of Greece: Mineralogical, Fluid Inclusion and Oxygen Isotope Constraints on Their Genesis." Minerals 8, no. 8 (July 28, 2018): 324. http://dx.doi.org/10.3390/min8080324.
Повний текст джерелаАнотація:
Epithermally altered volcanic rocks in Greece host amethyst-bearing veins in association with various silicates, carbonates, oxides and sulfides. Host rocks are Oligocene to Pleistocene calc-alkaline to shoshonitic lavas and pyroclastics of intermediate to acidic composition. The veins are integral parts of high to intermediate sulfidation epithermal mineralized centers in northern Greece (e.g., Kassiteres–Sapes, Kirki, Kornofolia/Soufli, Lesvos Island) and on Milos Island. Colloform–crustiform banding with alternations of amethyst, chalcedony and/or carbonates is a common characteristic of the studied amethyst-bearing veins. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), propylitic and zeolitic types. Precipitation of amethyst took place from near-neutral to alkaline fluids, as indicated by the presence of various amounts of gangue adularia, calcite, zeolites, chlorite and smectite. Fluid inclusion data suggest that the studied amethyst was formed by hydrothermal fluids with relatively low temperatures (~200–250 °C) and low to moderate salinity (1–8 wt % NaCl equiv). A fluid cooling gradually from the external to the inner parts of the veins, possibly with subsequent boiling in an open system, is considered for the amethysts of Silver Hill in Sapes and Kassiteres. Amethysts from Kornofolia, Megala Therma, Kalogries and Chondro Vouno were formed by mixing of moderately saline hydrothermal fluids with low-salinity fluids at relatively lower temperatures indicating the presence of dilution processes and probably boiling in an open system. Stable isotope data point to mixing between magmatic and marine (and/or meteoric) waters and are consistent with the oxidizing conditions required for amethyst formation.
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Voudouris, P., I. Psimis, C. Mavrogonatos, C. Kanellopoulos, M. Kati, and E. Chlekou. "Amethyst occurrences in Tertiary volcanic rocks of Greece: mineralogical and genetic implications." Bulletin of the Geological Society of Greece 47, no. 1 (September 5, 2013): 477. http://dx.doi.org/10.12681/bgsg.11026.
Повний текст джерелаАнотація:
Epithermal-altered volcanic rocks in Greece host gem-quality amethyst veins in association with various silicates, carbonates, oxides, sulfides and halides. Host rocks are Oligocene to recent calc-alkaline to shoshonitic lavas and pyroclastics of intermediate- to acid composition. The amethyst-bearing veins occur in the periphery of porphyry-type and/or high-sulfidation epithermal mineralized centers in northern Greece (e.g. Sapes, Kirki, Kornofolia/Soufli, Lesvos island) and on Milos island in the active Aegean Volcanic Arc. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), argillic, propylitic and zeolitic types. Precipitation of amethyst in the northern Greece occurrences, took place during the final stages of the magmatic-hydrothermal activity from near-neutral to alkaline fluids, as indicated by the presence of gangue adularia, calcite, smectite, chlorite, sericite, pyrite, zeolites (laumontite, heulandite, clinoptilolite), analcime and minor amounts of barite, halite, epidote and fluorite in the quartz veins. Amethyst at Milos Island (Chondro Vouno and Kalogries-Vani areas), is accompanied by barite, smectite and lepidocrocite. Colloform-crustiform banding with alternations of amethyst, chalcedony and/or carbonates is a common characteristic of the studied amethyst-bearing veins. Fluid inclusion- and mineralogical data suggest that the studied amethyst were formed at: 174-246 °C (Sapes area), 100-175 °C (Kirki and Kornofolia areas) and 223-234°C (Lesvos island). The amethyst formation requires oxidizing conditions and is probably the result of mixing between meteoric or seawater with upwelling hydrothermal fluids. The involvement of seawater in the studied mineralization is supported by the presence of halite and abundant barite in the veins. Finally, the studied amethyst deposits should be evaluated as potential gemstone sources in Greece.
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Cubley, Joel F., and David R. M. Pattison. "Metamorphism and deformation of the Grand Forks complex: implications for the exhumation history of the Shuswap core complex, southern British Columbia." Canadian Journal of Earth Sciences 49, no. 11 (November 2012): 1329–63. http://dx.doi.org/10.1139/e2012-066.
Повний текст джерелаАнотація:
The Grand Forks complex (GFC) is an elongate, north–south-trending metamorphic core complex in the Shuswap domain of southeastern British Columbia. It comprises predominantly upper-amphibolite- to granulite-facies paragneisses, schists, orthogneisses, amphibolites, and calc-silicates of the Paleoproterozoic to Paleozoic Grand Forks Group. The GFC is juxtaposed against low-grade rocks of the Quesnel terrane across two bounding Eocene normal faults: the Kettle River fault (KRF) on the east flank and the Granby fault (GF) on the west flank. Peak metamorphic Sil + Kfs ± Grt ± Crd (Sil, sillimanite; Kfs, potassium feldspar; Grt, garnet; Crd, cordierite) assemblages in paragneiss and Hbl ± Opx ± Cpx (Hbl, hornblende; Opx, orthopyroxene; Cpx, clinopyroxene) assemblages in amphibolite in the GFC formed at 750 ± 25 °C, 5.6 ± 0.5 kbar (1 kbar = 100 MPa; 20 ± 2 km depth). Stratigraphically overlying Sil + St-bearing pelitic schists (St, staurolite) within the complex record peak conditions of 600 ± 15 °C, 5.5 ± 0.25 kbar. Crd + Ilm + Spl (Crd, cordierite; Ilm, ilmenite; Spl, spinel) and Crd + Qtz (Qtz, quartz) coronal textures in paragneiss, and Cpx + Opx + Pl + Mt (Pl, plagioclase; Mt, magnetite) symplectites in amphibolite, formed at 735 ± 20 °C, 3.3 ± 0.5 kbar, indicating high-temperature, near-isothermal decompression of the GFC of ∼2.3 ± 0.7 kbar (∼8.2 ± 2.5 km) from peak conditions. Transitional greenschist–amphibolite metamorphic assemblages in the hanging wall of the KRF indicate conditions of ∼425 ± 25 °C and 2.2 ± 0.6 kbar (∼8 ± 2 km depth), with local contact metamorphism around Jurassic intrusions as high as 630–650 °C at ∼2.5 ± 0.5 kbar. The pressure contrast across the Kettle River fault prior to greenschist facies displacement was ∼0.8 ± 0.7 kbar, for a vertical offset of ∼2.9 ± 2.5 km. This is similar to estimates for the Granby fault on the west flank of the GFC. The GFC therefore experienced a two-stage exhumation history: early high-temperature decompression at upper-amphibolite- to granulite-facies conditions, followed by low-temperature exhumation at greenschist-facies conditions owing to movement on the Eocene Granby and Kettle River faults.
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SEARLE, MICHAEL P., and JON COX. "Subduction zone metamorphism during formation and emplacement of the Semail ophiolite in the Oman Mountains." Geological Magazine 139, no. 3 (May 2002): 241–55. http://dx.doi.org/10.1017/s0016756802006532.
Повний текст джерелаАнотація:
The metamorphic sole along the base of the Semail ophiolite in Oman records the earliest thrust slice subducted and accreted to the base of the ophiolite mantle sequence. In the Bani Hamid area (United Arab Emirates) a c. 870 m thick thrust slice of granulite facies rocks includes garnet+ diopside amphibolites, enstatite+cordierite+sillimanite+spinel±sapphirine quartzites, alkaline mafic granulites (meta-jacupirangites) quartzo-feldspathic gneisses and calc-silicates. The latter contain garnet+diopside+scapolite+plagioclase±wollastonite. P–T conditions of granulite facies metamorphism are in the range 800–860°C and 10.5±1.1 kbar to 14.7±2.8 kbar. Garnet+clinopyroxene+hornblende+plagioclase amphibolites from the metamorphic sole record peak P–T conditions of 840±70°C and 11.6±1.6 kbar (THERMOCALC average P–T mode) and 840–870°C and 13.9–11.8 kbar (conventional thermobarometry) with low degrees of partial melting producing very small melt segregations of tonalitic material. Pressure estimates are equivalent to depths of 57–46 km beneath oceanic crust, much deeper than can be accounted for by the thickness of the ophiolite. 40Ar39Ar hornblende ages from the amphibolites range from 95–93 Ma, synchronous with formation of the plagiogranites in the ophiolite crustal sequence (95 Ma), eruption of the Lasail (V2) volcanic sequence and deposition of Cenomanian–Turonian radiolaria in metalliferous sediments between the Geotimes (V1) and Lasail (V2) lavas. Protoliths of the metamorphic sole were Triassic–Jurassic and early Cretaceous Haybi volcanic rocks, Exotic limestones and quartzites and were clearly not equivalent to the Semail ophiolite rocks, showing that initiation of subduction could not have occurred at the ridge axis. Heat for metamorphism was derived from the mantle sequence harzburgites and dunites which were at or around 1100–1500°C. All data from the sub-ophiolite metamorphic sole in Oman and the United Arab Emirates indicate that the ophiolite was formed in a Supra-Subduction zone setting and that obduction occurred along a NE-dipping high-temperature subduction zone during Late Cretaceous times.
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Searle, Michael P., Alan G. Cherry, Mohammed Y. Ali, and David J. W. Cooper. "Tectonics of the Musandam Peninsula and northern Oman Mountains: From ophiolite obduction to continental collision." GeoArabia 19, no. 2 (April 1, 2014): 135–74. http://dx.doi.org/10.2113/geoarabia1902137.
Повний текст джерелаАнотація:
ABSTRACT The tectonics of the Musandam Peninsula in northern Oman shows a transition between the Late Cretaceous ophiolite emplacement related tectonics recorded along the Oman Mountains and Dibba Zone to the SE and the Late Cenozoic continent-continent collision tectonics along the Zagros Mountains in Iran to the northwest. Three stages in the continental collision process have been recognized. Stage one involves the emplacement of the Semail Ophiolite from NE to SW onto the Mid-Permian–Mesozoic passive continental margin of Arabia. The Semail Ophiolite shows a lower ocean ridge axis suite of gabbros, tonalites, trondhjemites and lavas (Geotimes V1 unit) dated by U-Pb zircon between 96.4–95.4 Ma overlain by a post-ridge suite including island-arc related volcanics including boninites formed between 95.4–94.7 Ma (Lasail, V2 unit). The ophiolite obduction process began at 96 Ma with subduction of Triassic–Jurassic oceanic crust to depths of > 40 km to form the amphibolite/granulite facies metamorphic sole along an ENE-dipping subduction zone. U-Pb ages of partial melts in the sole amphibolites (95.6– 94.5 Ma) overlap precisely in age with the ophiolite crustal sequence, implying that subduction was occurring at the same time as the ophiolite was forming. The ophiolite, together with the underlying Haybi and Hawasina thrust sheets, were thrust southwest on top of the Permian–Mesozoic shelf carbonate sequence during the Late Cenomanian–Campanian. Subduction ended as unsubductable cherts and limestones (Oman Exotics) jammed at depths of 25–30 km. The Bani Hamid quartzites and calc-silicates associated with amphibolites derived from alkali basalt show high-temperature granulite facies mineral assemblages and represent lower crust material exhumed by late-stage out-of-sequence thrusting. Ophiolite obduction ended at ca. 70 Ma (Maastrichtian) with deposition of shallow-marine limestones transgressing all underlying thrust sheets. Stable shallow-marine conditions followed for at least 30 million years (from 65–35 Ma) along the WSW and ENE flanks of the mountain belt. Stage two occurred during the Late Oligocene–Early Miocene when a second phase of compression occurred in Musandam as the Arabian Plate began to collide with the Iran-western Makran continental margin. The Middle Permian to Cenomanian shelf carbonates, up to 4 km thick, together with pre-Permian basement rocks were thrust westwards along the Hagab Thrust for a minimum of 15 km. Early Miocene out-of-sequence thrusts cut through the shelf carbonates and overlying Pabdeh foreland basin in the subsurface offshore Ras al Khaimah and Musandam. This phase of crustal compression followed deposition of the Eocene Dammam and Oligocene Asmari formations in the United Arab Emirates (UAE), but ended by the mid-Miocene as thrust tip lines are all truncated along a regional unconformity at the base of the Upper Miocene Mishan Formation. The Oligocene–Early Miocene culmination of Musandam and late Cenozoic folding along the UAE foreland marks the initiation of the collision of Arabia with Central Iran in the Strait of Hormuz region. Stage three involved collision of Arabia and the Central Iran Plate during the Pliocene, with ca. 50 km of NE-SW shortening across the Zagros Fold Belt. Related deformation in the Musandam Peninsula is largely limited to north and eastward tilting of the peninsula to create a deeply indented coastline of drowned valleys (rias).
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Thwee Aye, May, Subagyo Pramumijoyo, Arifudin Idrus, Lucas Donny Setijadji, Akira Imai, Naoto Araki, and Johan Arif. "The mineralogy of gold-copper skarn related porphyry at the Batu Hijau deposit, Sumbawa, Indonesia." Journal of Applied Geology 3, no. 1 (September 2, 2015). http://dx.doi.org/10.22146/jag.7177.
Повний текст джерелаАнотація:
Clacic gold-copper bearing skarn in the Batu Hijau porphyry deposit is located in the western part of Sumbawa Island, Indonesia. Skarn mineralizations were found at the deep level of the deposit (-450m to -1050mL) by drilling program 2003. No evidence around Batu Hijau has limestone although most skarn are metasomatiz ed from carbonate-rich rock as limestone or marble. Most skarn-type metasomatic alteration and mineralization occurs at the contact of andesitic volcanic rock and intermediate tonalite porphyry intrusion and within intermediate tonalite in some. Although both endoskarn and exoskarn can be developed, it has no clear minerals to known the endoskarn. Exoskarn is more principle skarn zone. The formation of skarn occurred two min stages: (1) prograde and (2) retrograde. The prograde stage is temporally and spatially divided into two sub-stages as early prograde (sub-stage I) and prograde metasomatic (sub-stage II). Sub-stage I begin immediately after the intrusion of the tonalite stock into the calcium rich volcanic rocks. Then, sub-stage II originated with segregation and evolution of a fluid phase in the pluton and its invasion into fractures and micro-fractures of host rocks developed during sub-stage I. The introduction of considerable amount of Fe, Si and Mg led to the large amounts of medium- to coarse-grained anhydrous calc-silicates. From the texture and mineralogy, the retrograde metasomatic stage can be divided into two sub-stages: (a) early retrograde and (sub-stage III) and (b) late retrograde (sub-stage IV). During sub-stage III, the previously formed skarn zones were affected by intense multiple hydro-fracturing phases in the gold-copper bearing stocks. Therefore, the considerable amounts of hydrous calc-silicates (epidote), sulfides (pyrite, chalcopyrite, sphalerite), oxides (magnetite, hematite) and carbonates (calcite) replaced the anhydrous calc-silicates. Sub-stage IV was coexisting with the intrusion of relatively low temperature, more highly oxidizing fluids into skarn system, bringing about partial alteration of the early-formed calc-silicates and developing a series of very fine-grained aggregrates of chlorite, clay, hematite and calcite.
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Mokhtari, Mir. "The mineralogy and petrology of the Pahnavar Fe skarn, In the Eastern Azarbaijan, NW Iran." Open Geosciences 4, no. 4 (January 1, 2012). http://dx.doi.org/10.2478/s13533-012-0106-y.
Повний текст джерелаАнотація:
AbstractThe Pahnavar calcic Fe-bearing skarn zone is located in the Eastern Azarbaijan (NW Iran). This skarn zone occurs along the contact between Upper Cretaceous impure carbonates and an Oligocene granodioritic batholith. The skarnification process can be categorized into two discrete stages: prograde and retrograde. The prograde stage began immediately after the initial emplacement of the granodioritic magma into the enclosing impure carbonate rocks. The effect of heat flow from the batholith caused the enclosing rocks to become isochemically marmorized in the pure limestone layers and bimetasomatized (skarnoids) in the impure clay-rich carbonates. Segregation and evolution of an aqueous phase from the magma that infiltrated to the marbles and skarnoids through fractures and micro-fractures took place during the emplacement of magma. The influx of Fe, Si and Mg from the granodiorite to the skarnoids and marbles led to the crystallization of anhydrous calc-silicates (garnet and pyroxene).The retrograde stage can be divided, in turn, into two distinct sub-stages. During earliest sub-stage, the previously formed skarn assemblages were affected by intense hydro-fracturing; in addition, Cu, Pb, Zn, along with H2S and CO2 were added. Consequently, hydrous calc-silicates (epidote and tremolite-actinolite), sulfides (pyrite, chalcopyrite, galena and sphalerite), oxides (magnetite and hematite) and carbonates (calcite) deposited the anhydrous calc-silicates. The late-retrograde sub-stage was due the incursion of colder oxidizing fluids into the skarn system, causing the alteration of the previously formed calc-silicate assemblages and the development of fine-grained aggregates of chlorite, illite, kaolinite, hematite and calcite.The lack of wollastonite in the mineral assemblage, along with the garnet-clinopyroxene paragenesis, suggests that the prograde stage formed under temperature and fO2 conditions of 430–550°C and 10−26–10−23, respectively.
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"CATHODOLUMINESCENCE MICROSCOPY OF THE KOKCHETAV ULTRAHIGH-PRESSURE CALC-SILICATE ROCKS: WHAT CAN WE LEARN FROM SILICATES, CARBON-HOSTING MINERALS, AND DIAMOND?" Геология и геофизика 56, no. 1 (2015). http://dx.doi.org/10.15372/gig20150106.
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"The precursor principle and the possible significance of stratiform ores and related chemical sediments in the elucidation of processes of regional metamorphic mineral formation." Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 328, no. 1602 (August 25, 1989): 529–646. http://dx.doi.org/10.1098/rsta.1989.0050.
Повний текст джерелаАнотація:
This contribution is concerned with the regional metamorphism of fine-grained (pelitic) sedimentary materials, and with the pelitic components of coarser sediments. It emphasizes the possible importance of purely chemical sedimentary rocks, and the preservation of chemical patterns within them, in the elucidation of some regional metamorphic mineralogical processes. The materials and examples used come largely from the category of exhalative sediments, of which stratiform metallic sulphide orebodies and their associated exhalites are important members. A few examples come from volcanic rocks that have been altered by exhalative processes. The special significance of chemical sediments stems from their propensity for the development of highly complex metamorphic silicate mineral assemblages within relatively minuscule volumes of rock, and from their commonly sharply defined chemical bedding and chemical sedimentary facies patterns. As the primary nature of such chemical bedding and chemical layering and zoning in completely unmetamorphosed materials is observable and known, and as their sharp boundaries and other well-defined features can be examined in a full range of unmetamorphosed to highly metamorphosed environments, they may be used as extremely sensitive markers for the detection and measurement of any chemical movement that may have taken place during regional metamorphism. Detailed examination of such evidence appears to indicate a general lack of diffusion and reaction, and a common lack of attainment of mineral equilibrium, in the development of the regional metamorphic silicate assemblages of a number of such stratiform ore deposits and their associated exhalative materials. This, together with the common interbedded nature of metamorphic silicate, sulphide, carbonate, etc., and the faithful maintenance of primary sedimentary chemical facies patterns within many exhalative metasediments suggests that the silicates, like the accompanying sulphides and associated compounds, may derive directly and in situ from early-formed precursor materials rather than from extensive elemental diffusion and metamorphic reaction. That particular clays and zeolites derive from specific precursors in many instances has been recognized for a long time. That many metamorphosed bedded oxides (including quartz), together with carbonates, sulphates, sulphides and authigenic silicates such as the feldspars, have derived from sedimentary: diagenetic precursors is self-evident and unavoidable, and establishes precursor derivation for at least some regional metamorphic minerals as a principle, not an hypothesis. What is not known, however, is the extent to which this principle applies to the broader spectrum of metamorphic silicates. The present contribution examines this problem. The evidence of ‘ metamorphic ’ silicates in a range of unmetamorphosed and littlemetamorphosed rocks, in present ocean-floor sediments, in unmetamorphosed volcanic alteration products and in modern geothermal systems is examined. The preservation of possible precursor materials in a variety of rocks, and the synthesis of a number of ‘ metamorphic ’ minerals by low-temperature solution experimentation and in low-temperature industrial products is considered. It is deduced that most of the well-known regional metamorphic minerals may in fact be produced directly from low-temperature sedimentary/diagenetic/alteration materials, and that such precursors may be of simple or complex kind. It is suggested that the direct derivation of regional metamorphic silicates from precursors may resolve the problem of the elusive metamorphic mineral reaction, and that the principal regional metamorphic grade indicators may be the temperatures of precursor transformations rather than temperatures of reactions. Several implications of the precursor principle are then examined: its significance in the interpretation of zoning of regional metamorphic mineral assemblages and mineral chemistry; in considerations of metamorphic grade and the development of grainsize; in the identities of certain metamorphic equilibria, intergrowths and ‘retrograde’ materials; and in the deduction of earlier environments of rock formation and alteration. In this general connection it is proposed that the overall regional metamorphic process may be substantially indigenous: that through their primary nature certain materials, e.g. some andesitic-dacitic volcaniclastic rocks, may be predisposed to metamorphose themselves, and that this may be accentuated by the petro-tectonic setting in which they form, e.g. island arc - eugeosynclinal provinces, with their characteristically inter-related calc-alkaline volcanism, riftrelated palaeogeographical features and highly patterned heat flow. Effects of climate may be superimposed on this: some of the more highly developed regional metamorphic zoning may arise in calc-alkaline volcanic sediments deposited in tropical island arc shelf areas, and in sediments laid down in large saline lakes of continental volcanic rift provinces. From all this it is proposed that the ambit of regional metamorphic petrology may be much wider than currently visualized. Just as precursor-derived oxides, carbonates, sulphates, graphite, pyrite, etc., of high-grade metasedimentary rocks may give clear indications concerning the nature and environments of formation of the original sediments, so the metamorphic silicates may yield subtle insights into palaeoprovenance, palaeogeography, palaeoclimate and a variety of weathering, volcanic alteration, sea-floor hydrothermal and other regimes. The application of metamorphic mineralogy and mineral chemistry to the search for stratiform ores in metamorphosed terranes may constitute one of the major advances in mineral exploration in the near future. It appears that there is considerable scope for further searching for possible precursor material in a variety of rocks and modern sediments (especially those of the present-day volcanic-sedimentary milieu), extension of clay and mixed-layer clay-chlorite-zeolite mineral synthesis in low-temperature-pressure laboratory experiment, and for the investigation of the behaviour of these synthetic products at metamorphic temperatures and pressures.
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Mikaeili, Khadijeh, Saeid Baghban, Mohammad Reza Hosseinzadeh, David R. Lentz, and Mohsen Moayyed. "Genesis of the Brazin Iron Skarn Deposit, Nw Iran: Analysis of Formation Conditions of Calc-Silicates and the Evolution of Fluids Responsible for the Massive Magnetite Precipitation." SSRN Electronic Journal, 2022. http://dx.doi.org/10.2139/ssrn.4261684.
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Mikaeili, Khadijeh, Saeid Baghban, Mohammad Reza Hosseinzadeh, David R. Lentz, and Mohsen Moayyed. "Genesis of the Brazin Iron Skarn Deposit, NW Iran: Analysis of formation conditions of calc-silicates and the evolution of fluids responsible for the massive magnetite precipitation." Journal of Geochemical Exploration, January 2023, 107162. http://dx.doi.org/10.1016/j.gexplo.2023.107162.
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Khan, T., M. A. Khan, M. Q. Jan, and M. Latif. "The Kohistan between Gilgit and Chilas, northern Pakistan: regional tectonic implications." Journal of Nepal Geological Society 14 (November 1, 1996). http://dx.doi.org/10.3126/jngs.v14i0.32317.
Повний текст джерелаАнотація:
In this paper, we present geological description of an area located between Gilgit and Chilas within the Kohistan terrane. This terrane has been considered an intra-oceanic island arc, formed due to northward subduction of the Neo-tethyan lithospheric plate. At present, it is squeezed between the Karakoram Asian and Indian continental plates. Both the contacts are marked by suture zones, that is, Shyok (MKT) in the north and Indus (MMT) sutures in the south, respectively. The investigated area consists of plutonic, metamorphosed volcanic and sedimentary rocks, the Chilas Complex, and the Kamila Amphibolite. The metamorphosed volcanic and sedimentary rocks are packaged into the Jagfot Group. This group comprises basal turbiditic sediments, intercalated with amphibolites and calc-silicates (the Gilgit Formation), followed upward by the Gashu-Confluence Volcanics = Chait Volcanic Group, and finally the Thelichi Formation = Yasin Group of Aptian-Albian age. The Thelichi Formation comprises a volcanic base (Majne volcanics) and overlying turbidites, local intercalation of marbles, volcaniclastics and lava flows. Greenschist and amphibolite facies are common in the Jaglot Group, and particularly the sillimanite in the Gilgit Formation. A pair of anticline (the Gilgit anticline) and syncline (the Jaglot syncline) make up the structural scenario. On the basis of field geology, we conclude that the entire Jaglot Group and its equivalents, the Yasin Group, Chait Volcanic Group in Kohistan, and Burjila Formation, Bauma Harel Formation and Katzarah Formation in Ladakh show intra-oceanic back-arc basin rather than island arc affinities as suggested in the past.
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Hassan, Mahmoud Hussein, Mohamed Amlas, Al Zein A. Al Zein, and Han Run Sheng. "Details Geological Mapping and Petrological Characteristics of EL Shereik Study Area, River Nile State, North Sudan." Journal of Geography, Environment and Earth Science International, May 10, 2019, 1–23. http://dx.doi.org/10.9734/jgeesi/2019/v21i130118.
Повний текст джерелаАнотація:
The present study focused on details geology of the lithostratigraphy, phenomena and petrogenesis, with full classification of rock units and correlate by the regional geology in the study area. The previous studies, focused on regional geology, which can be divided in Bayuda Terrane, represented by Dem El Tor Shear Zone (DTSZ), its Precambrian to Tertiary ages (isotopic signatures of later cooling 590 to 550 Ma), with dominated by metamorphic and intrusive rocks belonging to the Pre-Nubian basement complex. The study area lies at El Shereik, River Nile State, Sudan. It is characterized by low-lying bed plains, covered with superficial deposits, with an arid climate. The techniques of this work, represented in an official, field works and laboratory test, with used Land Sat Images ETM. And Nubian Arabian Shield, represented by the Keraf Shear Zone (KSZ), its Precambrian to Phanerozoic ages (Neoproterozoic, Pb isotope ages dating, of forms is -730 -710Ma and ended in -565Ma), with dominated by metamorphic, ophiolitic mélange, volcano-sedimentary sequences, and Phanerozoic sediments. But through this detailed surveyed, we discovered different types of rock units; they were found as accumulated and highly deformed, affected by various thrusting faults. collected more than 40 samples, through six traverses, for classification and petrographic studies and classified more than 9 types of rooks units didn’t mentioned before in previous study, all of them well exposed as following: metamorphic rocks, included, migmatites, calc-silicates, wollastonite, talc-schist, carbonaceous (dolomitic marble), amphibolites, graphitic schist, mica schist, quartzo-feldspathic schist, and grey gneiss, While the Igneous rocks, consisted of dykes, as dolerite, trachy-basaltic, Rhyolite porphyry, pegmatites, diorite, and quartz veins, whereas the superficial deposits, included, of aeolian, fluvial, and collovial. These rocks extend and spread to the outside of the limits of the study area and most of them oriented parallel with KSZ SE - NW region and a few of them are oriented E-W, This is maybe due to the collusion of the contact boundary between KSZ and DTSZ Bayuda Tehran. Talc-schist, Wollastonite and graphitic schist, represent a strategic stockpile besides gold mining. Studies conducted with DTSZ, its old age, occurred before Neoproterozoic compared to KSZ. Because it has the first deformation of the folding of pre- KSZ proportion to the presence of folding in the west and east of the Nile zone, according to the border between Bayuda Terrane and Nubian Arabian Shield, as the suggest result. And the previous studies of the ages dating confirm it.
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"METEORIZACIÓN E HIDROGEOQUÍMICA DE LOS RÍOS QUILISH Y PORCÓN EN LA CUENCA PORCÓN." Revista ECIPeru, January 17, 2019, 11–14. http://dx.doi.org/10.33017/reveciperu2008.0004/.
Повний текст джерелаАнотація:
METEORIZACIÓN E HIDROGEOQUÍMICA DE LOS RÍOS QUILISH Y PORCÓN EN LA CUENCA PORCÓN WHEATHERING AND HYDROGEOCHEMISTRY´S QUILISH AND PORCÓN RIVERS IN THE PORCÓN BASIN Carlos Malpica Sandoval, Hugo Rivera Mantilla, Sandra Rumay Villarreal y Víctor Vargas Rodríguez DOI: https://doi.org/10.33017/RevECIPeru2008.0004/ RESUMEN Con los resultados obtenidos, podemos señalar que la meteorización produjo reacciones de hidrólisis, oxidación, disolución de silicatos, sulfuros y azufre originando minerales secundarios, iones y coloides (arcillas, H4SiO4, SiO2, Fe2O3, FeOOH, Fe(OH)3, Al(OH)3, Ca2+, Mg2+, Al3+, Fe3+, Na+, K+, 2 4SO , Pb2+, H2AsO-4, Cu2+), parte de los productos de la meteorización entran al sistema hidrológico y otra parte permanece en el suelo debido a su baja movilidad o por intercambio catiónico o aniónico; estas reacciones están determinadas por la energía libre, Eh y pH. El análisis hidrogeoquímico se basa en la energía libre, constante de equilibrio, índice de saturación, diagramas Eh-pH, rNa/rCl y rCl/rHCO3-2, resultando agua de naturaleza cálcica-sódica, debido a la meteorización de los silicatos. Basándonos en los resultados obtenidos de los datos de energía libre determinamos que todas las reacciones están relacionadas con el índice de saturación, y basándonos en el diagrama Eh-pH, el hierro y aluminio reaccionan formando hidróxidos. Estudios petrológicos (30 muestras) y análisis hidrogeoquímico (9 muestras de agua), determinaron que los iones, coloides y moléculas originados por la meteorización de los silicatos y sulfuros que se encuentran en el río se deben a contaminación natural. Palabras claves: Energía libre, índice de saturación, diagrama Eh-pH, disolución, hidrogeoquímica. ABSTRACT With the results, we can point out that the wheathering produced reactions of hydrolyse, oxidation, silicate´s dissolution, sulphurs and sulphur reactions; originating secondary minerals (clays, H4SiO4, SiO2, Fe2O3, FeOOH, Fe(OH)3, Al(OH)3, Ca2+, Mg2+, Al3+, Fe3+, Na+, K+, SO42-, Pb2+, H2AsO-4, Cu2+), part of the weathering products going to the hydrologic system, and another part remains in the soil due to its low mobility, or for cationic or anionic interchange; these reactions are determined by the free energy, Eh and pH. The hydrochemistry analysis is based on the free energy, constant of balance, saturation index, graphs Eh-pH, rNa/rCl and rCl/rHCO3-2and, standing out to be calc-sodic water, due to the silicates weathering. Basing on the results obtained of the information of free energy, we determined that all the reactions are related to the saturation index and basing on the graph Eh-pH, the iron and aluminium react forming hydroxides. Petrologic studies (30 samples) and hydrogeochemistry analysis (9 water samples), determined that the ions, colloids and molecules that are in the river owe to natural pollution. Keywords: Free energy, saturation index, Eh-pH diagram, dissolution, hydrogechemistry.
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Chakrabarti1, C. K., B. N. Upret, and A. K. Ghosh. "Geochemistry of the Ganesh Himal zinc-lead deposits, central Nepal Himalaya." Journal of Nepal Geological Society 30 (December 1, 2004). http://dx.doi.org/10.3126/jngs.v30i0.31679.
Повний текст джерелаАнотація:
A dolomite hosted strata-bound high-grade (19-25%) zinc-lead sulphide deposit occurs, between 4,000 m and 5,100 m over an area of 5 km2 in the ~ 7 km wide MCT zone of the Ganesh Himal area of central Nepal. The host crystalline milky white sugary dolomite occurs in a repeated sequence of garnet-mica schist, quartzite, calc-schist and concordant amphibolite of older Lesser Himalayan sequence (Upper Nawakot Group), all showing ductile deformation. The rocks along with the ore have undergone at least three phases of deformation. A series of overturned, steep northerly dipping and NE to ENE plunging anticlines and synclines form the dominating structure, characterised by disharmonic shape of the dolomite host rock because of apparent squeezing out from limbs into the axial regions. Compared to their strike lengths, the ore bodies and the host rock bodies have long extension along the plunge direction. The ore has a very simple composition of sphalerite-galena-pyrite with a little pyrrhotite, magnetite and chalcopyrite. Chemically, it consists mainly of zinc along with iron, lead, silver and very low silica, silicates and alumina. Concentrations of trace and rare elements are very low. Ore body types vary from dissemination and bands to massive sulphide lenses, arranged en echelon parallel to the schistosity/ bedding. The rocks of the area were subjected to almandine-amphibolite facies of metamorphism, to 750±150 MPa pressure and 500 °C to 750 °C temperature conditions. The latest thermal event was as young as ~12 Ma. The lead isotope data are interpreted to establish an age of 875 to 785 Ma for the Ganesh Himal deposits, while sulphur isotope data imply an age greater than 650 Ma. The Ganesh Himal deposit appears to be Vindhyan equivalent in the Himalaya, showing highest metal values as on date. Only two out of six occurrences in the area have been explored so far. The ore reserve estimates stand at 2.4 million tonnes with 14.66% zinc, 3.01 % lead, and 23.5 g/t silver. Taking into account all the occurrences the Ganesh Himal basin might have had 861,000 tonnes zinc and 182,000 tonnes lead at the minimum. The lithologic sequence represents a shallow marine facies of deposition. The δ34 S values for Ganesh Himal sulphides indicate that the sulphur was probably produced by biogenic reduction of contemporaneous seawater sulphate. The lead isotope ratios of Ganesh Himal deposit fall on a single-stage growth curve, on which also fall many big deposits of the world, indicating that the Ganesh Himal zinc-lead deposit has high potential. The primary control of the mineralisation is stratigraphic, the present ore body configuration being controlled by south vergent folding related with the metamorphism and thrusting along the MCT. Pyrite framboids and geochemical characters of ore indicate that the mineralisation is syngenetic sedimentary, and it may have been deposited in association with a bioherm or reef in an anoxic environment. The source of metal ions is not clear yet, but the contemporaneous basic rock bodies providing the metal ions could be a possibility.