Journal articles on the topic 'Sodic metasomatism'
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Gu, Shangyi, Guojiang Wan, and Jianquan Mao. "Sodic metasomatism in a dacite weathering profile in Pinxiang, Guangxi, China." Chinese Journal of Geochemistry 26, no. 4 (November 2007): 434–38. http://dx.doi.org/10.1007/s11631-007-0434-7.
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Albino, George V. "Sodium metasomatism along the Melones Fault Zone, Sierra Nevada Foothills, California, USA." Mineralogical Magazine 59, no. 396 (September 1995): 383–99. http://dx.doi.org/10.1180/minmag.1995.059.396.02.
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AbstractAlbitite, locally aegirine- and riebeckite-bearing, formed as a result of sodium metasomatism of felsic dykes and argillites along the Melones Fault Zone near Jamestown, California. Pyrite, magnetite, hematite and titanite are common in small amounts in altered dykes. The dykes were originally plagioclase-hornblende porphyritic, and had major and trace element abundances typical of calc-alkaline rocks, whereas they now have Na2O contents as high as 11.40%. Associated fracture-filling veins are dominated by albite, but locally include aegirine, analcime, paragonite, calcite and sodic scapolite. Quartz is present in most albitic rocks, but is absent in riebeckite- and aegirine-bearing samples. Albitization predated CO2 metasomatism and formation of sericite-pyrite assemblages that are typical of gold deposits of the Mother Lode Belt.Alkaline fluids responsible for Na-metasomatism had elevated Na+/K+ and Na+/H+ relatively high fO2, and low aH4SiO4. The presence of titanite indicates fluid. The presence of titanite indicates fluid XCO2 was low, in contrast to fluids that formed later carbonate-bearing assemblages. Sodic scapolite suggests that, at least locally, the fluids attained very high salinities.Mass balance calculations indicate that alteration involved addition of large amounts of sodium, and the removal of SiO2 and K2O. Textural preservation, combined with volume factors calculated from specific gravity and whole rock analytical data, indicate that Na-metasomatism was essentially isovolumetric.Sodium-rich zones along the Melones Fault Zone are closely associated with fault-bounded bodies of ultramafic rock, typically altered to talc-carbonate or quartz-magnesite-Cr muscovite assemblages. Carbonatization and talc-forming reactions in the ultramafic rocks may lead to SiO2-undersaturated fluids. Expansion of the muscovite stability field in terms of Na+/K+-Na+/H+, as a result of incorporation of Cr (up to 7.7% Cr2O3) in muscovite, would result in H+- and K+-depletion as the fluid interacts with ultramafic rocks. This could lead to fluids with elevated Na+/K+ and high pH, as documented in this occurrence.
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Hellebrand, Eric, and Jonathan E. Snow. "Deep melting and sodic metasomatism underneath the highly oblique-spreading Lena Trough (Arctic Ocean)." Earth and Planetary Science Letters 216, no. 3 (November 2003): 283–99. http://dx.doi.org/10.1016/s0012-821x(03)00508-9.
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Cinelu, S., and M. Cuney. "Sodic metasomatism and U–Zr mineralization: A model based on the Kurupung batholith (Guyana)." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A103. http://dx.doi.org/10.1016/j.gca.2006.06.120.
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Fiannacca, Patrizia, Miguel A. S. Basei, Rosolino Cirrincione, Antonino Pezzino, and Damiano Russo. "Water-assisted production of late-orogenic trondhjemites at magmatic and subsolidus conditions." Geological Society, London, Special Publications 491, no. 1 (February 6, 2019): 147–78. http://dx.doi.org/10.1144/sp491-2018-113.
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AbstractPeraluminous granites and trondhjemites make up small plutonic bodies intruded into high-grade paragneisses in the Peloritani Mountains, marking the beginning of late Variscan granitoid magmatism in southernmost Italy. The granites range from low-Ca monzogranites to alkali feldspar granites, while the trondhjemites vary from trondhjemites s.s. to low-Ca trondhjemites. Relatively high radiogenic (87Sr/86Sr)i ratios (mostly from 0.7073 to 0.7125) and negative εNd values (mostly from −5.66 to −8.73) point to crustal sources for all the granitoids. Major and trace element compositions indicate an absence of genetic relationships between the trondhjemites s.s. and the low-Ca granitoids, but possible relationships between the low-Ca trondhjemites and the granites. All of the studied granitoids have near-pure melts compositions, consistent with H2O-fluxed and dehydration melting of metasediments for the trondhjemites and the granites, respectively. However, the unusual compositions of the low-Ca trondhjemites and microstructural evidence in these rocks for pervasive subsolidus replacement of magmatic feldspars by secondary sodic plagioclase indicate that they were derived instead from metasomatic alteration of the granites. Thus, water may be involved in the production of trondhjemites in two different ways, driving water-fluxed melting in the magma source and driving alkali metasomatism at the sites of granite emplacement in the upper crust.
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Nardi, Lauro V. S., Jorge Plá-Cid, Maria de Fátima Bitencourt, and Larissa Z. Stabel. "Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif." Anais da Academia Brasileira de Ciências 80, no. 2 (June 2008): 353–71. http://dx.doi.org/10.1590/s0001-37652008000200014.
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The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism.
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Krátký, Ondřej, Vladislav Rapprich, Martin Racek, Jitka Míková, and Tomáš Magna. "On the Chemical Composition and Possible Origin of Na–Cr-Rich Clinopyroxene in Silicocarbonatites from Samalpatti, Tamil Nadu, South India." Minerals 8, no. 8 (August 17, 2018): 355. http://dx.doi.org/10.3390/min8080355.
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Mineralogical and chemical data are presented for a suite of Na–Cr-rich clinopyroxenes associated with chromite, winchite (sodium-calcium amphibole), titanite and calcite in Mg-Cr-rich silicocarbonatites from the Samalpatti carbonatite complex, Tamil Nadu, South India. The Mg-Cr-rich silicocarbonatites occur as 10–30 cm large enclaves in pyroxenites. The chemical composition of the pyroxenes differs among individual enclaves, with variable proportions of diopside, kosmochlor and jadeite-aegirine end-members. These compositions fill a previously unoccupied space in the kosmochlor-diopside-jadeite+aegirine ternary plot, indicating a distinct origin of kosmochlor-rich pyroxene compared with previous findings from diverse settings. The Na–Cr-rich clinopyroxene has low ΣREE = 9.2 ppm, with slight enrichment in LREE (LaN = 7), coupled with low HREE (YbN = 0.6), and flat HREE, paralleled by a significant fractionation of Nb/Ta (2408) and Th/U (26.5). Sodic metasomatism (fenitization) associated with either carbonatite emplacement at shallow levels or during carbonatite ascent through the upper mantle most likely was the major process operating in the area. We suggest two scenarios of the formation of Na–Cr-rich pyroxene: (1) from mantle-derived chromian mineral phases (spinel and/or garnet) through fenitization, with subsequent corrosion by growing winchite due to volatile influx; (2) via metasomatic reaction of Cr-rich garnet in mantle peridotite due to reaction with Na-rich carbonatite melt. Collectively, the appearance of kosmochlor may play an important role in deconvolving metasomatic processes, and fenitization in particular. If combined with petrologic experiments, it could improve our understanding of the origin and subsequent history of chemical signatures of carbonate-rich materials in the mantle.
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Almeida, Delia Del Pilar M. de, Vitor P. Pereira, Adriane Machado, Henrique Zerfass, and Ricardo Freitas. "Late sodic metasomatism evidences in bimodal volcanic rocks of the Acampamento Velho Alloformation, Neoproterozoic III, southern Brazil." Anais da Academia Brasileira de Ciências 79, no. 4 (December 2007): 725–37. http://dx.doi.org/10.1590/s0001-37652007000400012.
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A mineralogical study was carried out in mafic and felsic volcanic rocks of the Acampamento Velho Alloformation at Cerro do Bugio, Perau and Serra de Santa Bárbara areas (Camaquã Basin) in southern Brazil. The Acampamento Velho bimodal event consists of two associations: lower mafic at the base and upper felsic at the top. Plagioclase and alkali-feldspar were studied using an electronic microprobe, and magnetite, ilmenite, rutile, illite and alkali-feldspar were investigated through scanning electron microscopy. The rocks were affected by a process of late sodic autometasomatism. In mafic rocks, Ca-plagioclase was transformed to albite and pyroxenes were altered. In felsic rocks, sanidine was partially pseudomorphosed, generating heterogeneous alkali-feldspar. In this association, unstable Ti-rich magnetite was replaced by rutile and ilmenite. In mafic rocks, the crystallization sequence was: (1) Ti-rich magnetite (?), (2) pyroxene and Ca-plagioclase, (3) albite (alteration to Ca-plagioclase), (4) sericite, chlorite and calcite (alteration to pyroxene), and kaolinite (alteration to plagioclase/albite). In felsic rocks: (1) zircon, (2) Ti-rich magnetite, (3) sanidine, (4) quartz. The introduction of late Na-rich fluids, generated the formation of (5) heterogeneous alkali-feldspar, (6) ilmenite and rutile from the Ti-rich magnetite, (7) albite in the spherulites. Finally, alteration of sanidine, vitroclasts and pumice to (8) illite.
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Miyazoe, T., M. Enami, T. Nishiyama, and Y. Mori. "Retrograde strontium metasomatism in serpentinite mélange of the Kurosegawa Zone in central Kyushu, Japan." Mineralogical Magazine 76, no. 3 (June 2012): 635–47. http://dx.doi.org/10.1180/minmag.2012.076.3.14.
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AbstractStrontium-rich epidote, including epidote-(Sr) and epidote with major amounts of Sr (i.e. epidote containing up to 17.3 wt.% SrO), was found in pumpellyite schist and epidote blueschist in a tectonic block in the serpentinite mélange of the Kurosegawa Zone, central Kyushu, Japan. The tectonic block is 20 m wide and made primarily of lawsonite blueschist, with subordinate amounts of pumpellyite schist and epidote blueschist. The pumpellyite schist typically occurs at the edge of the block and is composed mainly of pumpellyite with subordinate amounts of strontium-poor epidote, albite and chlorite, and thin veins of fine-grained calcite and clinopyroxene. Epidote-(Sr) forms rims around strontium-poor epidote, fills fractures in strontium-poor epidote and also occurs interstitially between pumpellyite aggregates and along the boundaries between pumpellyite and calcite-clinopyroxene veins. The epidote blueschist is found between the pumpellyite schist and lawsonite blueschist, and consists mainly of sodic amphibole, epidote and titanite, with albite veining. Strontium-rich epidote occurs as rims, replacing Sr-poor epidote near the albite vein. The bulk strontium contents of the rocks are as follows: lawsonite blueschist (200 ppm), epidote blueschist (2800 ppm) and pumpellyite schist (~10,700 ppm). The chemical and petrological characteristics of the Sr-rich epidote-bearing metabasites suggest that the infiltration of a metamorphic fluid promoted extensive Sr metasomatism during the later stages of high-pressure metamorphism.
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Fedo, C. "Potassic and sodic metasomatism in the Southern Province of the Canadian Shield: Evidence from the Paleoproterozoic Serpent Formation, Huronian Supergroup, Canada." Precambrian Research 84, no. 1-2 (August 1997): 17–36. http://dx.doi.org/10.1016/s0301-9268(96)00058-7.
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TSIKOS, H., and J. M. MOORE. "Sodic metasomatism in the Palaeoproterozoic Hotazel iron-formation, Transvaal Supergroup, South Africa: implications for fluid-rock interaction in the Kalahari manganese field." Geofluids 5, no. 4 (October 20, 2005): 264–71. http://dx.doi.org/10.1111/j.1468-8123.2005.00117.x.
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Leão-Santos, Marcelo, Roberto Moraes, Yaoguo Li, Maria Irene Raposo, and Boxin Zuo. "Hydrothermal Alteration Zones’ Magnetic Susceptibility Footprints and 3D Model of Iron Oxide-Copper-Gold (IOCG) Mineralization, Carajás Mineral Province, Brazil." Minerals 12, no. 12 (December 9, 2022): 1581. http://dx.doi.org/10.3390/min12121581.
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Brownfield areas are important targets of exploration; however, the extensive drilling present in these areas has not fully exploited their prospective potential. The appropriate use of drill hole cores in these areas can play an important role in deep exploration. We present a case study of iron oxide-copper-gold (IOCG) Furnas Southeast deposit, located in the Carajás Mineral Province, Brazil. This deposit has disseminated chalcopyrite, bornite and gold mineralization associated with a silicic (Si), potassic (K), calcic (Na), sodic-calcic (Na-Ca) hydrothermal alteration, and intense iron metasomatism with massive magnetite (Fe) alteration. Petrophysical hand-held equipment measurements were carried out on drill core samples with the purpose of studying the potential roles that magnetic susceptibility properties can play in high-grade mineralization. The results indicate that the geological complexity of the IOCG deposit is readily reflected in the extensive variation of the measurements. The statistical analysis shows how the detailed characterization of this physical property carried out for this mineral association could effectively define and describe ore, and the magnetic susceptibility footprints of hydrothermal alteration zones. Furthermore, we were able to perform a magnetic susceptibility 3D modeling of diamagnetic, paramagnetic, and ferrimagnetic responses strictly correlated with known orebody. Thus, petrophysical analyses can form a quantitative geological criterion for ore delineation.
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Byrne, Kevin, Guillaume Lesage, Sarah A. Gleeson, Stephen J. Piercey, Philip Lypaczewski, and Kurt Kyser. "Linking Mineralogy to Lithogeochemistry in the Highland Valley Copper District: Implications for Porphyry Copper Footprints." Economic Geology 115, no. 4 (June 1, 2020): 871–901. http://dx.doi.org/10.5382/econgeo.4733.
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Abstract The Highland Valley Copper porphyry deposits, hosted in the Late Triassic Guichon Creek batholith in the Canadian Cordillera, are unusual in that some of them formed at depths of at least 4 to 5 km in cogenetic host rocks. Enrichments in ore and pathfinder elements are generally limited to a few hundred meters beyond the pit areas, and the peripheral alteration is restricted to narrow (1–3 cm) halos around a low density of prehnite and/or epidote veinlets. It is, therefore, challenging to recognize the alteration footprint peripheral to the porphyry Cu systems. Here, we document a workflow to maximize the use of lithogeochemical data in measuring changes in mineralogy and material transfer related to porphyry formation by linking whole-rock analyses to observed alteration mineralogy at the hand specimen and deposit scale. Alteration facies and domains were determined from mapping, feldspar staining, and shortwave infrared imaging and include (1) K-feldspar halos (potassic alteration), (2) epidote veins with K-feldspar–destructive albite halos (sodic-calcic alteration), (3) quartz and coarse-grained muscovite veins and halos and fine-grained white-mica–chlorite veins and halos (white-mica–chlorite alteration), and two subfacies of propylitic alteration comprising (4) prehnite veinlets with white-mica–chlorite-prehnite halos, and (5) veins of epidote ± prehnite with halos of chlorite and patchy K-feldspar. Well-developed, feldspar-destructive, white-mica alteration is indicated by (2[Ca-C] + N + K)/Al values <0.85, depletion in CaO and Na2O, enrichment in K2O, and localized SiO2 addition and is spatially limited to within ~200 m of porphyry Cu mineralization. Localized K2O, Fe2O3, and depletion in Cu, and some enrichment in Na2O and CaO, occurs in sodic-calcic domains that form a large (~34 km2) nonconcentric footprint outboard of well-mineralized and proximal zones enriched in K. Water and magmatic CO2-rich propylitic and sodic-calcic–altered rocks form the largest lithogeochemical footprint to the mineralization in the Highland Valley Copper district (~60 km2). Calcite in the footprint is interpreted to have formed via phase separation of CO2 from a late-stage magmatic volatile phase. Several observations from this study are transferable to other porphyry systems and have implications for porphyry Cu exploration. Feldspar staining and shortwave infrared imaging highlight weak and cryptic alteration that did not cause sufficient material transfer to be confidently distinguished from protolith lithogeochemical compositions. Prehnite can be a key mineral phase in propylitic alteration related to porphyry genesis, and its presence can be predicted based on host-rock composition. Sodic-calcic alteration depletes the protolith in Fe (and magnetite) and, therefore, will impact petrophysical and geophysical characteristics of the system. Whole-rock loss on ignition and C and S analyses can be used to map enrichment in water and CO2 in altered rocks, and together these form a large porphyry footprint that extends beyond domains of enrichment in ore and pathfinder elements and of pronounced alkali metasomatism.
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Davey, James, Stephen Roberts, and Jamie J. Wilkinson. "Copper- and cobalt-rich, ultrapotassic bittern brines responsible for the formation of the Nkana-Mindola deposits, Zambian Copperbelt." Geology 49, no. 3 (November 20, 2020): 341–45. http://dx.doi.org/10.1130/g48176.1.
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Abstract The Central African Copperbelt (CACB) is Earth’s largest repository of sediment-hosted copper and cobalt. The criticality of these elements in battery technology and electricity transmission establishes them as fundamental components of the carbon-free energy revolution, yet the nature and origin of the hydrothermal fluids responsible for ore formation in the CACB remain controversial. Here, we present microthermometric, scanning electron microscopy and laser ablation–inductively coupled plasma–mass spectrometry analyses of fluid inclusions from the Nkana-Mindola deposits in Zambia. We find that base metal concentrations vary by one to two orders of magnitude between “barren” and “ore” fluids, with concomitant distinctions in major salt chemistry. Primary fluid inclusions, hosted by pre- to synkinematic mineralized quartz veins, are characterized by high homogenization temperatures (∼200–300 °C) and salinities, with K/Na >0.8 and elevated metal concentrations (102 to 103 ppm Cu and Co). Conversely, barren, postkinematic vein quartz contains lower homogenization temperature (∼110–210 °C) and lower-salinity primary inclusions, characterized by K/Na <0.8 with low metal contents (<102 ppm Cu and Co). We propose a model in which high-temperature, sulfate-deficient, metalliferous, potassic residual brines, formed during advanced evaporation of CaCl2-rich, mid-Neoproterozoic seawater, were responsible for ore formation. During basin closure, lower-temperature, halite-undersaturated fluids interacted with evaporites and formed structurally controlled, sodic metasomatism. Reconciliation of these fluid chemistries and base metal concentrations with reported alteration assemblages from a majority of Zambian Copperbelt deposits suggests highly evolved, residual brines were critical to the formation of this unique metallogenic province.
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Yaxley, G. M., and David H. Green. "Experimental reconstruction of sodic dolomitic carbonatite melts from metasomatised lithosphere." Contributions to Mineralogy and Petrology 124, no. 3-4 (August 23, 1996): 359–69. http://dx.doi.org/10.1007/s004100050196.
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DVORNIK, Gennadiy Petrovich. "Types of metasomatic rocks: temperature conditions, buildups, features of composition, minerageny." NEWS of the Ural State Mining University 1, no. 1 (March 23, 2020): 63–72. http://dx.doi.org/10.21440/2307-2091-2020-1-63-72.
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The relevance of the work is due to the importance of metasomatic rocks associated many ore and non-metallic mineral resources. Purpose of the work: study of temperature conditions of formation, the characteristics of the chemical and mineral composition, the mineralogy of metasomatites. Results. The extended classification of the main types of metasomatic rocks (alkaline, basic, acidic) formed in the early alkaline and acid stages of the hydrothermal process is given. Temperature conditions of formation, features of chemical and mineral composition and metasomatite mineralogeny are considered. Alkaline metasomatites are subdivided into potassium (pyroxene phenites, microclinites, biotite-orthoclase metasomatites, gumbaites) and sodium (nepheline-pyroxene phenites, albites, sodic alterations). Deposits of tungsten, molybdenum, gold and uranium are associated with potassium metasomatites (gumbaites), and deposits of beryllium, lithium, tantalum, and niobium are associated with sodium metasomatites (albite). The main metasomatic rocks (basificates) include calcium and iron-magnesian metasomatites (calcareous and magnesian skarns, diopside-lapis lazuli metasomatites, rhodingites, kamaforites, carbonatites, apocarbonate calcites, dolomite-ankerite, magnesite and sideroplesite metasomatites). The formation of deposits of iron, boron, and phlogopite is associated with skarn; deposits of rare-earth elements, tantalum, niobium, and apatite are associated with carbonatites. Acid metasomatites are subdivided into aluminous and siliceous. Aluminous metasomatites include propylites, chloritolites, microcline-sericite and tourmaline-sericite metasomatites, secondary quartzites, argillizated rocks. Alumina deposits (kaolins, bentonites) are associated with secondary quartzites. Siliceous metasomatites include the largest number of species: uralite metasomatites, greisens, listvenites and berezites, chlorite-sericite-quartz and sericite-quartz metasomatites, charoitites, serpentinites, nephrites, anthophyllite metasomatites, carbonate-talc metasomatites and talcites, magnetite quartzites, jaspers, jasperoids. There is a group of metasomatites among them consisting of quartz in association with hydrous alumosilicates (muscovite, topaz, and chlorite). The other group includes low-alumina metasomatites, the mineral composition of which is dominated by hydrous calcium and magnesian silicates (charoite, serpentine, antophyllite, tremolite, talc). The third group is represented by metasomatites of quartz composition (magnetite quartzites, jaspers, jasperoids). The formation of deposits of iron, tin, tungsten, molybdenum, gold, polymetals, nonmetallic raw materials (asbestos, talc, charoite, nephrite, jasper) is associated with siliceous metasomatites. Conclusions. According to the formation temperature, high-temperature (above 500o С), medium-temperature (500–300о С) and low-temperature (below 300o С) metasomatic rocks are distinguished. The average compositions of alkaline metasomatites are characterized by high concentrations of potassium or sodium oxides, the predominance of feldspars (orthoclase, microcline, albite) in association with pyroxenes, carbonates. The main metasomatites are distinguished by high contents of calcium, magnesium and iron oxides at low silica concentrations prevailing in the mineral composition of silicates (pyroxenes and garnets) or carbonates (calcite, dolomite, magnesite, breunnerite). The composition of acid metasomatites is characterized by high concentrations of alumina or silica, the predominance of hydrous aluminosilicates, silicates and quartz.
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Francis, P. W., R. S. J. Sparks, C. J. Hawkesworth, R. S. Thorpe, D. M. Pyle, S. R. Tait, M. S. Mantovani, and F. McDermott. "Petrology and geochemistry of volcanic rocks of the Cerro Galan caldera, northwest Argentina." Geological Magazine 126, no. 5 (September 1989): 515–47. http://dx.doi.org/10.1017/s0016756800022834.
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AbstractAt least 2000 km3 of relatively uniform dacitic magma have been erupted from the Cerro Galan caldera complex, northwest Argentina. Between 7 and 4 Ma ago several composite volcanoes predominantly of dacitic lava were constructed, and several large high-K dacitic ignimbrites were erupted. 2.2 Ma ago the > 1000km3 Cerro Galan ignimbrite was erupted. The predominant mineral assemblage in the ignimbrites is plagioclase-biotite-quartz-magnetite-ilmenite; the Cerro Galan ignimbrite also contains sanidine. Fe-Ti oxide minerals in the Cerro Galan ignimbrite imply temperatures of 801–816 °C. Plagioclase phenocrysts in the ignimbrites typically have rather homogeneous cores surrounded by complex, often oscillatory zoned, rims. Core compositions show a marked bimodality, with one population consisting of calcic cores surrounded by normally zoned rims, and a second of sodic cores surrounded by reversely zoned rims. The older ignimbrites do not show systematic compositional zonation, but the Cerro Galan ignimbrite exhibits small variations in major elements (66–69% SiO2) and significant variations in Rb, Sr, Ba, Th and other trace elements, consistent with derivation from a weakly zoned magma chamber, in which limited fractional crystallization occurred. The ignimbrites have 87Sr/86Sr = 0.7108–0.7181; 143Nd/144Nd = 0.51215–0.51225, and δ18O = + 10 to + 12.5, consistent with a significant component of relatively non-radiogenic crust with high Rb/Sr and enriched in incompatible elements. Nd model ages for the source region are about 1.24 Ga. 87Sr/86Sr measurements of separated plagioclases indicate that Anrich cores have slightly lower 87Sr/86Sr than less calcic plagioclases, suggesting a small degree of isotopic heterogeniety in different components within the magmas. Pb isotope data for plagioclase show restricted ranges (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb = 18.87–18.92, 15.65–15.69 and 39.06–39.16 respectively), and suggest derivation from Proterozoic crustal material(> 1.5 Ga).Contemporaneous satellite scoria cones and lavas are high-K basalts, basaltic andesites and andesites with SiO2 = 51–57%; K2O = 2–3% and normative plagioclase compositions of An37–48, and may be derived from a mantle source containing both ‘subduction zone’ and ‘within plate’ components. 87Sr/86Sr ranges from 0.7055 to 0.7094 and 143Nd/144Nd from 0.51250 to 0.51290. Variation diagrams such as MgO: SiO2 show two trends, one indicating closed system fractional crystallization and the other crustal contamination. AFC modelling of the open system rocks indicates a parental mantle-derived mafic magma which is itself enriched in K, Rb, Ba, U, Ta/Sm, Ta/Th and Sr, and has 87Sr/86Sr = 0.705–0.706, while the contaminant need not be more radiogenic than the dacitic ignimbrites.The Cerro Galan dacitic magmas are interpreted in terms of a deep and uniform region of the central Andean continental crust repeatedly melted by emplacement of incompatible-element-enriched, mantle-derived mafic magmas, a proportion of which may also have mixed with the dacite magmas. A component of the crustal material had a Proterozoic age. The magmas derived by crustal melting were also enriched in incompatible elements either by crystal/liquid fractionation processes, or by metasomatism of their source regions just prior to magma generation. Much of the crystallization took place in the source region during the melting process or in mid-crustal magma chambers. The magmas may have re-equilibrated at shallow levels prior to eruption, but only limited compositional zonation developed in high-level magma chambers.
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Byrne, Kevin, Robert B. Trumbull, Guillaume Lesage, Sarah A. Gleeson, John Ryan, Kurt Kyser, and Robert G. Lee. "Mineralogical and Isotopic Characteristics of Sodic-Calcic Alteration in the Highland Valley Copper District, British Columbia, Canada: Implications for Fluid Sources in Porphyry Cu Systems." Economic Geology 115, no. 4 (June 1, 2020): 841–70. http://dx.doi.org/10.5382/econgeo.4740.
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Abstract The Highland Valley Copper porphyry Cu (±Mo) district is hosted in the Late Triassic Guichon Creek batholith in the Canadian Cordillera. Fracture-controlled sodic-calcic alteration is important because it forms a large footprint (34 km2) outside of the porphyry Cu centers. This alteration consists of epidote ± actinolite ± tourmaline veins with halos of K-feldspar–destructive albite (1–20 XAn) ± fine-grained white mica ± epidote. The distribution of sodic-calcic alteration is strongly influenced by near-orthogonal NE- and SE-trending fracture sets and by proximity to granodiorite stocks and porphyry dikes. Multiple stages of sodic-calcic alteration occurred in the district, which both pre- and postdate Cu mineralization at the porphyry centers. The mineral assemblages and chemical composition of alteration minerals suggest that the fluid that caused sodic-calcic alteration in the Guichon Creek batholith was Cl bearing, at near-neutral pH, and oxidized, and had high activities of Na, Ca, and Mg relative to propylitic and fresh-rock assemblages. The metasomatic exchange of K for Na, localized removal of Fe and Cu, and a paucity of secondary quartz suggest that the fluid was thermally prograding in response to magmatic heating. Calculated δ18Ofluid and δDfluid values of mineral pairs in isotopic equilibrium from the sodic-calcic veins and alteration range from 4 to 8‰ and −20 to −9‰, respectively, which contrasts with the whole-rock values for least altered magmatic host rocks (δ18O = 6.4–9.4‰ and δD = −99 to −75‰). The whole-rock values are suggested to reflect residual magma values after D loss by magma degassing, while the range of hydrothermal minerals requires a mixed-fluid origin with a contribution of magmatic water and an external water source. The O-H isotope results favor seawater as the source but could also reflect the ingress of Late Triassic meteoric water. The 87Sr/86Srinital values of strongly Na-Ca–altered rocks range from 0.703416 to 0.703508, which is only slightly higher than the values of fresh and potassic-altered rocks. Modeling of those data suggests the Sr is derived predominantly from a magmatic source, but the system may contain up to 3% seawater Sr. Supporting evidence for a seawater-derived fluid entrained in the porphyry Cu systems comes from boron isotope data. The calculated tourmaline δ11Bfluid values from the sodic-calcic domains reach 18.3‰, which is consistent with a seawater-derived fluid source. Lower tourmaline δ11Bfluid values from the other alteration facies (4–10‰) suggest mixing between magmatic and seawater-derived fluids in and around the porphyry centers. These results imply that seawater-derived fluids can infiltrate batholiths and porphyry systems at deep levels (4–5 km) in the crust. Sodic ± calcic alteration may be more common in rocks peripheral to porphyry Cu systems hosted in island-arc terranes and submarine rocks than currently recognized.
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Mian, I., and M. J. Le Bas. "Sodic amphiboles in fenites from the Loe Shilman carbonatite complex, NW Pakistan." Mineralogical Magazine 50, no. 356 (June 1986): 187–97. http://dx.doi.org/10.1180/minmag.1986.050.356.01.
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AbstractThe carbonatites at Loe Shilman, near Khyber in NW Pakistan, fenitize their country rocks to form a metasomatic zone c.100 m wide of alternate dark blue (mafic) and pale grey (felsic) banded fenites which grade into unfenitized bedded slates and phyllites. The Na-amphiboles in the banded fenites form a complete solid solution series between magnesio-arfvedsonite and magnesio-riebeckite which coexist with varying proportions of aegirine, albite, and K-feldspar, with or without phlogopite or biotite.The amphiboles show a gradual decrease in Na2O, K2O, Mg ratio [100Mg/(Mg + FeT + Mn)] and iron oxidation ratio, and an increase in total iron away from the carbonatite contact. The pleochroism correlates with the chemistry and distance from the carbonatite contact.The Mg ratio decreases from 74 to 35 away from the carbonatite contact. The iron oxidation ratio [100Fe3+/ (Fe3+ + Fe2+)] decreases in the magnesio-arfvedsonite for the first 30 metres from the carbonatite contact, and then increases in the magnesio-riebeckite from 40 to 60 metres from the carbonatite contact. K relative to Na decreases away from the contact in the amphibole, and the decrease in K causes an increase in vacancy in the A site. The main variation in the chemistry in this solid solution series is due to (K,Na)A+(Mg,Fe2+)c ⇌ □ + (Fe3+)c substitution.
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Kerrich, R., D. F. Strong, A. J. Andrews, and L. Owsiacki. "The silver deposits at Cobalt and Gowganda, Ontario. III: Hydrothermal regimes and source reservoirs–evidence from H, O, C, and Sr isotopes and fluid inclusions." Canadian Journal of Earth Sciences 23, no. 10 (October 1, 1986): 1519–50. http://dx.doi.org/10.1139/e86-145.
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The Ag–, Co–Ni–sulpharsenide deposits of the Cobalt–Gowganda district are characterized by relatively uniform light-stable-isotope systematics, where δ18O in quartz spans 11.1–16.0‰; in K-feldspar, 10.1–12.3‰; in albite, 8.1–14.4‰; in actinolite, 6.0–7.6‰; in chlorite, 3.2–5.6‰; and δD in chlorite = −42 to −35‰. The temperature of hydrothermal silicate deposition was 150–230 °C, as calculated from Δquartz–chlorite, and triple to quadruple isotopic concordancy is locally preserved amongst quartz, chlorite, actinolite, and K-feldspar or albite. Filling temperature modes at 230 and 330 °C exist for primary inclusions in quartz and carbonates. Ore-forming hydrothermal fluids were isotopically characterized by δ18O = −2.5 to + 5‰, δD = −40 to + 5‰, interpreted to reflect isotopically and chemically evolved formation brines from Huronian aquifers, ultimately derived from marine pore fluids, and Proterozoic meteoric water recharge of the sedimentary basin. The restricted range of δ18Oquartz, Δquartz−chlorite, and δDchlorite from a large population of veins implies that the ore-forming fluids were tapped from a large reservoir, or reservoirs, relatively uniform with respect to temperature, δ18O, and δD.Quartzes in silicate selvages, wall rocks, and carbonate-dominated gangue are isotopically comparable, signifying fluid-dominated conditions and the initial precipitation of carbonates from fluids isotopically similar to those involved in the silicate stage and at comparable temperatures. Vein dolomites (δ18O = 21 to 23.1‰) continued to exchange down to temperatures of 110–140 °C in the presence of fluids where δ18O = 3 ± 2‰, during thermal attenuation of the ore-forming reservoir. Vein calcites (δ18O = 1.7 to 15.7‰) record late incursion of meteoric waters where δ18O = −8 to −22‰ at temperatures of ~50 °C. The population of vein carbonates clusters at δ13C = −3.1 to −5.3‰, and this is probably also close to the carbon-isotope signature of the hydrothermal fluid. The source of carbon is uncertain.Actinolites possess age-corrected 87Sr/86Sr = 0.715 to 0.729, for 2200 Ma, close to estimates for the contemporaneous Huronian ratio (0.7053–0.714) but more radiogenic than contemporaneous Archean volcanics (0.7017–0.7021) or the Nipissing diabase (0.7060–0.7061). On this basis, Sr is interpreted to have been derived principally from the Huronian sedimentary reservoir.Fluid inclusions in quartz and calcite of both mineralized and barren veins in the Cobalt and Gowganda mining camps and environs show five different types type I (L), type II (L + halite), type III (L + V), type IV (L + V + H), and type V (V), with types III and IV being most abundant. A histogram of all mine data shows modes around 100, 230, and 330 °C, with a range from > 560 to < 100 °C. No carbon dioxide was observed in the inclusions, although the dominance of calcite and dolomite in the veins attests to its presence during mineralization. Several samples show evidence of aqueous boiling, allowing a direct pressure determination of about 600 bar (60 MPa). The fluids were highly saline NaCl–CaCl2 brines, with up to 54 wt.% NaCl equivalent and highly variable Na/Ca ratios. Fluid inclusions in samples of barren veins from Lundy Township, outside the areas of known mineralization, do not appear to be significantly different from those of the mineralized veins, indicating that the hydrothermal fluids were active throughout a large area of the Huronian basin; this is corroborated by the disturbance of Pb- and Sr-isotope systems in the Nipissing, Huronian, and Archean.The Nipissing diabase likely served as a heat source to mobilize metals and advect formation brines, which may have derived the metals from either or all of the Huronian sediments or the Archean volcanics Nipissing diabase and sedimentary rocks. We suggest a genetic scheme for the veins involving CO2 effervescence and aqueous boiling inducing pH increase and thereby mediating rapid precipitation of ore minerals coeval with and followed by carbonates. This process explains most of the presently known major and minor characteristics of the vein systems and their host rocks, including the chloritic and sodic metasomatism of the Archean and Huronian rocks, abundant calcite, the compositional and mineralogical variability of the ore minerals, the textural variability of both the carbonates and ore minerals, the paragenetic sequence of alteration and mineralization, the distribution of ore minerals with respect to the diabase and other rocks, the relatively narrow vertical extent of mineralization, variations in ore grade and tonnage, and the distribution of economic deposits on the periphery of the Huronian basin.
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Shi, Guang-Hai, Wen-Yuan Cui, Peter Tropper, Chang-Qiu Wang, Gui-Ming Shu, and Haixa Yu. "The petrology of a complex sodic and sodic?calcic amphibole association and its implications for the metasomatic processes in the jadeitite area in northwestern Myanmar, formerly Burma." Contributions to Mineralogy and Petrology 145, no. 3 (June 1, 2003): 355–76. http://dx.doi.org/10.1007/s00410-003-0457-y.
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Cooper, Alan F., Lorraine A. Paterson, and David L. Reid. "Lithium in carbonatites — consequence of an enriched mantle source?" Mineralogical Magazine 59, no. 396 (September 1995): 401–8. http://dx.doi.org/10.1180/minmag.1995.059.396.03.
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AbstractThe rare Li-mica taeniolite is described from the Dicker Willem carbonatite complex, Namibia, and from the Alpine carbonatitic lamprophyre dyke swarm at Haast River, New Zealand. At Haast River, taeniolite occurs in sodic and ultrasodic fenites derived from quartzo-feldspathic schists and rarely in metabasites, adjacent to dykes of tinguaite, trachyte and a spectrum of carbonatites ranging from Ca- to Fe- rich types. In Namibia, taeniolite is present in potassic fenites derived from quartz-feldspathic gneisses and granitoids at the margin of an early sövite phase of the complex and in a radial sövite dyke emanating from this centre.The occurrence of taeniolite in these totally disparate carbonatite complexes, together with examples of lithian mica from other carbonatite complexes worldwide, raises the question of the status of Li as a ‘carbonatitic element’. We argue that lithium is not a consequence of crustal assimilation or interaction, but reflects the geochemical character of the magmatic source. Li, an overlooked and little-analysed element, may be an integral part of metasomatic enrichment in the mantle, and of magmas derived by partial melting of such a source.
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Comin-Chiaramonti, Piero, Angelo De Min, Aldo Cundari, Vicente A. V. Girardi, Marcia Ernesto, Celso B. Gomes, and Claudio Riccomini. "Magmatism in the Asunción-Sapucai-Villarrica Graben (Eastern Paraguay) Revisited: Petrological, Geophysical, Geochemical, and Geodynamic Inferences." Journal of Geological Research 2013 (May 16, 2013): 1–22. http://dx.doi.org/10.1155/2013/590835.
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The Asunción-Sapucai-Villarrica graben (ASV) in Eastern Paraguay at the westernmost part of the Paraná Basin was the site of intense magmatic activity in Mesozoic and Tertiary times. Geological, petrological, mineralogical, and geochemical results indicate that the following magmatic events are dominant in the area: (1) tholeiitic basalt and basaltic andesites, flows and sills of low- and high-titanium types; (2) K-alkaline magmatism, where two suites are distinguished, that is, basanite to phonolite and alkali basalt to trachyte and their intrusive analogues; (3) ankaratrite to phonolite with strong Na-alkaline affinity, where mantle xenoliths in ultramafic rocks are high- and low-potassium suites, respectively. The structural and geophysical data show extensional characteristics for ASV. On the whole, the geochemical features imply different mantle sources, consistently with Sr-Nd isotopes that are Rb-Nd enriched and depleted for the potassic and sodic rocks, respectively. Nd model ages suggest that some notional distinct “metasomatic events” may have occurred during Paleoproterozoic to Neoproterozoic times as precursor to the alkaline and tholeiitic magmas. It seems, therefore, that the genesis of the ASV magmatism is dominated by a lithospheric mantle, characterized by small-scale heterogeneity.
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Sommer, Carlos A., Evandro F. Lima, Lauro V. S. Nardi, Joaquim D. Liz, and Breno L. Waichel. "The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins." Anais da Academia Brasileira de Ciências 78, no. 3 (September 2006): 573–89. http://dx.doi.org/10.1590/s0001-37652006000300015.
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The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources.
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Lucci, Federico, Giancarlo Della Ventura, Alessandra Conte, Manuela Nazzari, and Piergiorgio Scarlato. "Naturally Occurring Asbestos (NOA) in Granitoid Rocks, A Case Study from Sardinia (Italy)." Minerals 8, no. 10 (October 10, 2018): 442. http://dx.doi.org/10.3390/min8100442.
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All six minerals defined as “asbestos” by the existing regulation on asbestos hazard, i.e., actinolite, tremolite, anthophyllite, crocidolite and amosite amphiboles, and the serpentine-group mineral chrysotile are typical constituents of mafic and ultramafic magmatic rocks of ophiolitic sequences. However, little is known about the presence and distribution of naturally occurring asbestos (NOA) in plutonic felsic rocks. The Isadalu magmatic complex outcropping in central Sardinia and belonging to the post-variscan Permian volcanic cycle, is described here as an interesting occurrence of fibrous amphiboles in granitoid rocks. Field work and collected mineralogical/petrological data show that NOA fibers from the Isadalu complex belong compositionally to the actinolite-tremolite series. They were generated by metasomatic growth on pristine magmatic hornblende, at ca. 470 °C at 1 kbar, during sodic-calcic hydrothermal alteration. In terms of environmental hazard, the Isadalu complex represents a high-value case study, since the actinolite-bearing felsic rocks outcrop in a strongly anthropized area. Here, towns with local and regional strategic infrastructures (dams, pipes, hydroelectric power plants, water supply, roads) have been developed since the last century, also using the granitoid asbestos-rich stones. The aim of this study is to demonstrate that NOA and relative hazard are not univocally connected to a restricted typology of rocks. This result should be taken into account in any future work, procedure or regulation defining asbestos occurrences in natural environments.
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Souza, Márcio Roberto Wilbert de, Rommulo Vieira Conceição, Daniel Grings Cedeño, and Roberto Vicente Schmitz Quinteiro. "Study of silica-undersaturated magmas through the Kalsilite- Nepheline-Diopside-Silica system at 4.0 GPa and dry conditions." Geologia USP. Série Científica 18, no. 2 (July 24, 2018): 87–102. http://dx.doi.org/10.11606/issn.2316-9095.v18-126120.
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This study experimentally investigates the Kalsilite-Nepheline-Diopside-Silica system at high pressure and temperature, with emphasis on silica-undersaturated volume (leucite-nepheline-diopside — Lct-Nph-Di; and kalsilite-nepheline-diopside — Kls + Nph + Di — planes), at 4.0 GPa (~120 km deep), temperatures up to 1,400ºC and dry conditions, to better understand the influence of K2O, Na2O, and CaO in alkali-rich silica-undersaturated magma genesis. In the Lct-Nph-Di plane, we determined the stability fields for kalsilite (Klsss), nepheline (Nphss) and clinopyroxene (Cpxss) solid solutions, wollastonite (Wo) and sanidine (Sa); and three piercing points: (i) pseudo-eutectic Kls + Nph + Di + liquid (Lct62Nph29Di9) at 1,000ºC; (ii) Kls + Sa + (Di + Wo) + liquid (Lct75Nph22Di2) at 1,200ºC; and (iii) pseudo-eutectic Kls + Di + Wo + liquid (Lct74Nph17Di9) at 1,000ºC. Kalsilite stability field represents a thermal barrier between ultrapotassic/potassic vs. sodic compositions. In the plane Kls-Nph-Di, we determined the stability fields for Klsss, Nphss and Cpxss and two aluminous phases in smaller proportions: spinel (Spl) and corundum (Crn). This plane has a piercing point in Kls + Nph + Di(± Spl) + liquid (Kls47Nph43Di10) at 1,100ºC. Our data showed that pressure extends K dissolution in Nph (up to 39 mol%) and Na in Kls (up to 27 mol%), and that these solid solutions, if present, determinate how much enriched in K and Na an alkaline magma will be in an alkaline-enriched metasomatic mantle. Additionally, we noted positive correlation between K2O and SiO2 concentration in experimental melts, negative correlation between CaO and SiO2, and no evident correlation between Na2O and SiO2.
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Qiu, Kunfeng, Haocheng Yu, Mingqian Wu, Jianzhen Geng, Xiangkun Ge, Zongyang Gou, and Ryan D. Taylor. "Discrete Zr and REE mineralization of the Baerzhe rare-metal deposit, China." American Mineralogist 104, no. 10 (October 1, 2019): 1487–502. http://dx.doi.org/10.2138/am-2019-6890.
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Abstract Although REE (lanthanides + Sc + Y) mineralization in alkaline silicate systems is commonly accompanied with Zr mineralization worldwide, our understanding of the relationship between Zr and REE mineralization is still incomplete. The Baerzhe deposit in Northeastern China is a reservoir of REE, Nb, Zr, and Be linked to the formation of an Early Cretaceous, silica-saturated, alkaline intrusive complex. In this study, we use in situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon and monazite crystals to constrain the relationship between Zr and REE mineralization at Baerzhe. Three groups of zircon are identified and are differentiated based upon textural observations and compositional characteristics. Type Ia zircons display well-developed oscillatory zoning. Type Ib zircons are darker in cathodoluminescence images and have more irregular zoning and resorption features than type Ia zircons. In addition, type Ib zircons can locally occur as overgrowths on type Ia zircons. Type II zircons contain irregular but translucent cores and rims with oscillatory zoning that are murky brown in color and occur in aggregates. Textural features and compositional data suggest that types Ia and Ib zircon crystallized at the magmatic stage, with type Ia being least-altered and type Ib being strongly altered. Type II zircons, on the other hand, precipitated during the magmatic to magmatichydrothermal transition. Whereas the magnitude of the Eu anomaly is moderate in the barren alkaline granite, both magmatic and deuteric zircon exhibit pronounced negative anomalies. Such features are difficult to explain exclusively by feldspar fractionation and could indicate the presence of fluid induced modification of the rocks. Monazite crystals occur mostly through replacement of zircon and sodic amphibole; monazite clusters are also present. Textural and compositional evidence suggests that monazite at Baerzhe is hydrothermal. Types Ia and Ib magmatic zircon yield 207Pb-corrected 206Pb/238U ages of 127.2 ± 1.3 and 125.4 ± 0.7 Ma, respectively. Type II deuteric zircon precipitated at 124.9 ± 0.6 Ma. The chronological data suggest that the magmatic stage of the highly evolved Baerzhe alkaline granite lasted less than two million years. Hydrothermal monazite records a REE mineralization event at 122.8 ± 0.6 Ma, approximately 1 or 2 million years after Zr mineralization. We therefore propose a model in which parental magmas of the Baerzhe pluton underwent extensive magmatic differentiation while residual melts interacted with aqueous hydrothermal fluids. Deuteric zircon precipitated from a hydrosilicate liquid, and subsequent REE mineralization, exemplified by hydrothermal monazite, correlates with hydrothermal metasomatic alteration that postdated the hydrosilicate liquid event. Such interplay between magmatic and hydrothermal processes resulted in the formation of discrete Zr and REE mineralization at Baerzhe.
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Oliveira Chaves, Alexandre. "New geological model of the Lagoa Real uraniferous albitites from Bahia (Brazil)." Open Geosciences 5, no. 3 (January 1, 2013). http://dx.doi.org/10.2478/s13533-012-0134-7.
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AbstractNew evidence supported by petrography (including mineral chemistry), lithogeochemistry, U-Pb geochronology by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and physicochemical study of fluid and melt inclusions by LA-ICP-MS and microthermometry, point to an orogenic setting of Lagoa Real (Bahia-Brazil) involving uraniferous mineralization. Unlike the previous models in which uraniferous albitites represent Na-metasomatised 1.75 Ga anorogenic granitic rocks, it is understood here that they correspond to metamorphosed sodium-rich and quartz-free 1.9 Ga late-orogenic syenitic rocks (Na-metasyenites). These syenitic rocks are rich not only in albite, but also in U-rich titanite (source of uranium). The interpretation of geochemical data points to a petrogenetic connection between alkali-diorite (local amphibolite protolith) and sodic syenite by fractional crystallization through a transalkaline series. This magmatic differentiation occurred either before or during shear processes, which in turn led to albitite and amphibolite formation. The metamorphic reactions, which include intense recrystallization of magmatic minerals, led uraninite to precipitate at 1.87 Ga under Oxidation/Reduction control. A second population of uraninites was also generated by the reactivation of shear zones during the 0.6 Ga Brasiliano Orogeny. The geotectonic implications include the importance of the Orosirian event in the Paramirim Block during paleoproterozoic Săo Francisco Craton edification and the influence of the Brasiliano event in the Paramirim Block during the West-Gondwana assembly processes. The regional microcline-gneiss, whose protolith is a 2.0 Ga syn-collisional potassic granite, represents the albitite host rock. The microcilne-gneiss has no petrogenetic association to the syenite (albitite protolith) in magmatic evolutionary terms.