Outline of Mineralization in Zoned Granitic Pegmatites

Brotzen, Otto

doi:10.1080/11035895909449134

Cited by 17 publications

(5 citation statements)

References 52 publications

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“…Thirdly, similar spherulites were found in chalcedony and quartz, which would be unsurprising if both formed from a silica gel precursor and represented various stages of its crystallisation. We also note that silica gels were previously considered as potential precursors for quartz cores of pegmatites [20][21][22]. Furthermore, it has been asserted that quartz cores were partially squeezed out from some pegmatites of the Central Urals (Russia) to form radiating quartz veins that serve as vectors to mineralised cavities [105], which can be readily explained by invoking a silica gel precursor.…”

Section: Discussionmentioning

confidence: 85%

“…Many of the previous studies that have advocated the presence of hydrosilicate fluids focused on processes that are typically regarded as marking the magmatic-hydrothermal transition, such as the formation of greisens [3,18,19], pegmatites [20][21][22][23] and porphyrytype deposits [25,26]. In these cases, hydrosilicate fluids could exsolve [4] or gradually fractionate [45] from aluminosilicate melts, or precipitate from H 2 O-CO 2 fluids of magmatic origin [14].…”

Section: Discussionmentioning

confidence: 99%

“…This array includes low-temperature (200-800 • C) and low-pressure (0.05-3 kbar) hydrosilicate fluids with >40 wt.% of SiO 2 and >10 wt.% of H 2 O, which have been variably referred to as heavy fluids, silicothermal fluids, hydrosilicate liquids, silica gels or colloidal silica [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Fluids with similar compositions were long invoked in petrogenetic models of a wide range of geological systems, such as agates [16], quartz veins [17], greisens [3,18,19], pegmatites [20][21][22][23][24] and porphyry-type deposits [25,26]. However, many of these models have received little attention in the recent literature [27][28][29][30][31][32][33][34][35][36], probably because they were generally derived by interpretation of mineral and rock textures and lacked supporting evidence from inclusions in minerals and human-accessible environments.…”

Section: Introductionmentioning

confidence: 99%

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Inclusions of Amorphous and Crystalline SiO2 in Minerals from Itrongay (Madagascar) and Other Evidence for the Natural Occurrence of Hydrosilicate Fluids

2022

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Experimental studies increasingly often report low-temperature (200–800 °C) and low-pressure (0.05–3 kbar) hydrosilicate fluids with >40 wt.% of SiO2 and >10 wt.% of H2O. Compositionally similar fluids were long suggested to potentially exist in natural systems such as pegmatites and hydrothermal veins. However, they are rarely invoked in recent petrogenetic models, perhaps because of the scarcity of direct evidence for their natural occurrence. Here we review such evidence from previous works and add to this by documenting inclusions of hydrosilicate fluids in quartz and feldspar from Itrongay. The latter comprise opal-A, opal-CT, moganite and quartz inclusions that frequently contain H2O and have negative crystal shapes. They coexist with inclusions of CO2- and H2O-rich fluids and complex polycrystalline inclusions containing chlorides, sulphates, carbonates, arsenates, oxides, hydroxides and silicates, which we interpret as remnants of saline liquids. Collectively, previous studies and our new results indicate that hydrosilicate fluids may be common in the Earth’s crust, although their tendency to transform into quartz upon cooling and exhumation renders them difficult to recognise. These data warrant more comprehensive research into the nature of such hydrosilicate fluids and their distribution across a wide range of pressure and temperature conditions and geological systems.

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Section: Discussionmentioning

confidence: 85%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Inclusions of Amorphous and Crystalline SiO2 in Minerals from Itrongay (Madagascar) and Other Evidence for the Natural Occurrence of Hydrosilicate Fluids

2022

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“…Generalized types of chondrite-normalized REE patterns observed for CGM are presented in Fig. 3 Vasil 'ev et al (2008, 2009) G18, Liha river, Mambasa, Ituri, DRC columbite-(Fe) Angermeier et al (1974) Högsbo, Göteborg area, Sweden columbite-(Mn); X Mn :~0.55 Brotzen (1959); Romer and Smeds (1996) (Table 2). Type-2 CGM are characterized by HREE N 4 MREE N ( Fig.…”

Section: Ree Concentration and Distribution Patterns Inta-(nb) Oxidesmentioning

confidence: 99%

Rare earth element geochemistry of columbite-group minerals: LA-ICP-MS data

et al. 2010

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New data on rare earth element (REE) concentrations and distribution patterns of columbite-tantalite minerals from Ta-ore provinces worldwide are presented. The REE geochemistry was studied by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Five major types of chondrite-normalized REE distribution patterns are defined for columbite-group minerals (CGM) from lithium-caesium-tantalum (LCT) pegmatites and rare-metal granites. Features to discriminate between the types include (1) the shape of the pattern (e.g. flat or concave), (2) calculated ratios between groups of the REE (e.g. heavy REEN/middle REEN), and (3) the presence and intensity of anomalies (e.g. Ce*, Eu*). Four pegmatites in central and southern Africa are used as case studies to discuss application of the types of REE patterns in individual deposits. The REE fractionation during progressive evolution of the melt in a pegmatite body (either Nb → Ta or Fe → Mn fractionation lines, or both) results in smaller heavy REEN/middle REEN ratios whereas replacement of primary CGM by secondary CGM produces modifications in the light REEN patterns and the heavy REEN/middle REEN ratios also. Critical features of REE patterns such as highly variable heavy REEN/middle REEN ratios or striking differences in the appearance of Eu anomalies are discussed considering structural data of the host minerals and the differentiation behaviour of the pegmatitic melt. In general, CGM from each individual Ta-ore province are characterized by a predominance of one type of REE distribution pattern. Consequently, these patterns are suitable for tracing the origin of tantalum ore concentrates (e.g. as a forensic tool).

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“…They are composed mainly of potash feldspars, plagioclases, quartz and micas. According to Brotzen (1959) classification of pegmatites, these pegmatitic bodies represent the simple type. As the ideal simple pegmatite containe feldspars, biotites and quartz, with subordinate hornblende, muscovite and tourmaline, while as the complex pegmatite contains abundant muscovite and lithium minerals such as lithium mica and spodumene.…”

Section: Introductionmentioning

confidence: 99%

Geochemical Contributions of Ree's Bearing Pegmatites, Within Kadabora Granitic Pluton, Central Eastern Desert, Egypt

2019

Egyptian Journal of Geology

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Pegmatitic bodies are encountered within the Kadabora granite to which they are spatially and genetically related. These bodies bearing REEs, U, Th, Y, Zr, Hf, Nb, Ta, and Cs. The mineralized pegmatites are characterized by high ΣREEs contents ranging from 3404 ppm to 15196 with an average of 7516ppm. The assemblage of the accessory minerals encountered in the mineralized pegmatites are zircon, allanite, fergusonite, uranothorite, betafite, samarskite, pyrochlore, bastnaesite, cerianite, rutile, euxenite and opaques. Each of these minerals is bearing certain trace elements ; zircon (Zr, Hf , Th); fergusonite (U, Th, Zr); uranothorite (Th, U); betafite (U, Nb, Ta); samarskite (Nb, Ta, U); pyrochlore (Nb, Ta); bastnaesite (REEs); cerianite (Ce, Th, Nb, Ta, Zr) and rutile (Ti). The REEs distribution pattern in the mineralized pegmatites reflects the role of these minerals as REEs accumulators e. g. betafite, bastnaesite and cerianite host LREEs while zircon, allanite and samarskite host HREEs.The REEs pattern is characterized by HREEs enrichment relative to LREEs with convex tetrad effect and a sharp negative Eu anomaly. This well demonstrated pattern reflects highly differentiated rocks associated with self strong hydrothermal interaction. It seems that parent magma has undergone extensive magmatic differentiation, during associated with syngenetic interaction of aqueous hydrothermal fluids resulted in the tetrad effect of REEs distribution forming highly mineralized pegmatites.

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Outline of Mineralization in Zoned Granitic Pegmatites

Cited by 17 publications

References 52 publications

Inclusions of Amorphous and Crystalline SiO2 in Minerals from Itrongay (Madagascar) and Other Evidence for the Natural Occurrence of Hydrosilicate Fluids

Inclusions of Amorphous and Crystalline SiO2 in Minerals from Itrongay (Madagascar) and Other Evidence for the Natural Occurrence of Hydrosilicate Fluids

Rare earth element geochemistry of columbite-group minerals: LA-ICP-MS data

Geochemical Contributions of Ree's Bearing Pegmatites, Within Kadabora Granitic Pluton, Central Eastern Desert, Egypt

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