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The Forcarei Norte and Lalín pegmatite fields, Galicia, Northwest of Spain
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
M. Fuertes-Fuente, A. Martin-Izard
Group F2. Beryl pegmatites. These occur as dykes with a well-developed internal structure. The border zone has a granitic texture and its mineralogy is albite, quartz, muscovite and K-feldspar, with tourmaline, garnet (72%Alm., 27%Sps., 1%Prp.) and phospates. The phosphates are Mn-rich apatite, eosphorite-childrenite, montebrasite and probable xanthoxenite (from EMA). Eosphorite-childrenite and montebrasite often appear together as patches replacing the feldspars. The wall-zone is characterized by an increase in grain size and the main minerals have a squeletal habit showing intergrowths between them. The mineralogy is quartz, muscovite and albite, the accessory minerals being abundant beryl, garnet, zircon and Mn-rich apatite. The garnet varies between almandine (65.3%Alm., 32.8%Sps., 1.7%Prp) and spessartine (51.5%Sps., 38%Alm., 0.3%Prp., 0.5%Grs.). The intermediate zone is formed by centimetric pertitic microcline with graphic texture. In the core of these bodies a blocky and coarse-grained monomineralic zone of quartz occurs. Irregular bands or patches of saccharoidal albite with minor quartz, muscovite and zircon occur aleatory distributed along the bodies.
Geochemical characteristics and structural setting of lithium–caesium–tantalum pegmatites of the Dorchap Dyke Swarm, northeast Victoria, Australia
Published in Australian Journal of Earth Sciences, 2023
B. R. Hines, D. Turnbull, L. Ashworth, S. McKnight
The Mount Wills Granite is a Silurian S-type granite, forming an elongate, northwest-trending pluton, located south and west of the Dorchap Range, and west of the Glen Wills area (Figure 2). It is a fine- to coarse-grained muscovite–biotite leucogranite with accessory tourmaline, garnet (spessartine–almandine), and topaz (Figure 4e; Morand et al.,2005). Pegmatitic phases associated with the Mount Wills Granite are common, as are numerous roof pendants. Four muscovite K–Ar dates obtained from the Mount Wills Granite indicate an intrusion age of 414 ± 16 Ma, with a single sample suggestive of regional metamorphism at 399 ± 10 Ma (Richards & Singleton, 1981), possibly associated with the intrusion of the nearby Anglers Rest Granite (Figure 2), metasomatic fluid movements during regional metamorphism associated with the Tabberabberan Orogeny or hydrothermal fluid movements along northeast-trending structures of the adjacent Glen Wills goldfield. The Mount Wills Granite is dextrally displaced by the Dunstan’s Fault, and additional brittle faults post-dating regional high-grade metamorphism host narrow-vein gold mineralisation at Glen Wills (Morand et al., 2005). Common miarolitic cavities containing quartz, orthoclase, muscovite, and tourmaline suggest a shallow level of intrusion for the Mount Wills Granite (English, 1988; Morand et al., 2005). Metasediments intruded by the Mount Wills Granite sit within the cordierite zone, indicating a depth of emplacement no greater than 9 km (based on a temperature of 550 °C; Morand et al., 2005).
Origin and evolution of nephrites, diopsidites and giant diopside crystals from the contact zones of the Pounamu Ultramafics, Westland, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2023
SEM–EDS analyses for Fe in garnet have been recalculated on the basis of stoichiometry into FeO and Fe2O3 contents using the formulae of Droop (1987) and then compositions recast into end-member molecules using the calculations of Locock (2008). Garnet occurs in diopsidite specimen OU86924 in two forms (Figure 6). Analysis of the pale green rounded grains reveals a significant Cr concentration (up to 10.6 wt.% Cr2O3) with the average core composition (n = 11, Table 3) corresponding to uvarovite30-spessartine3-almandine4-grossular46-andradite16. Some grains are chemically zoned, with rims relatively depleted in Cr2O3 and enriched in Fe2O3. Colourless garnet has a more skeletal interstitial form (Figure 6) and continues the trend of Cr depletion and Fe3+ enrichment observed in the rounded porphyroblasts, reaching uvarovite13-spessartine6-almandine4-grossular30-andradite46.5 (Table 3).
Physico-chemical characterization of detrital sillimanite and garnet: Insights into REE elements, crystal structure and morphology
Published in Marine Georesources & Geotechnology, 2022
Rajan Girija Rejith, Mayappan Sundararajan, Sreekantaiyer Ramaswamy, Abdul Azeez Peer Mohamed, Manavalan Satyanarayanan
The Raman spectra clearly discriminate sillimanite from other A12SiO5 polymorphs such as andalusite and kyanite and confirm that the garnet belongs to almandine group, not any other silicate garnets such pyrope and spessartine. The XPS provides data on the oxidation state and bonding of major elements such as Al2p, Si2p, and O1s in sillimanite and Fe2p, Al2p, O1s, and Si2p in garnet. The major oxides, rare earth elements, and trace elements present in the minerals were estimated using ED-XRF and HR-ICPMS. The estimation of Al2O3, SiO2, and Fe2O3 helps to determine the possibility of choosing these minerals for the production of synthetic mullite and abrasive materials. The REE content derived using the HRICPMS allows the possibility of REE extraction from these minerals in the near future. The SEM-EDS provides evidence of surface morphological changes such as conchoidal fractures, removal of blocks, grooves, irregular pits, impact V's, and solution channels which occurred due to physical and chemical processes occurring during the movement and deposition of these minerals. These results facilitate in determining the grade of minerals for selecting their potential applications.