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Harald G. Dill – One of the best experts on this subject based on the ideXlab platform.

  • kaolinization a tool to unravel the formation and unroofing of the pleystein pegmatite Aplite system se germany
    Ore Geology Reviews, 2015
    Co-Authors: Harald G. Dill, Reiner Dohrmann, Stephan Kaufhold, Sorin-ionut Balaban

    Abstract:

    Abstract The Hagendorf–Pleystein Pegmatite Province, SE Germany, is known for the largest feldspar–quartz pegmatite in Central Europe and renowned for its rare elements, e.g., Li, Nb, and Ta, giving rise to a spate of exotic minerals, mainly phosphates. Argillaceous rocks are scarce and eclipsed by the numerous mineralogical investigations on rare phosphates. These phosphate pegmatites are for the first time subjected to a clay mineralogical study, rendered possible by the newly discovered strongly kaolinized Aplite near the Kreuzberg Quartz Pegmatite at Pleystein. The supergene kaolin akin to the residual kaolin deposit at Tirschenreuth, SE Germany, was analyzed for its major and minor elements by XRF and micro-chemically by EMPA. Mineralogical investigations involved XRD, IR spectroscopy, thermoanalytical studies, CEC analyses and SEM-EDX. Supergene kaolinization forms a repository for heavy minerals critical for the interpretation of the emplacement of the Late Paleozoic pegmatites as well as a matrix for pegmatite-related trace elements and thereby may be used as an ore guide during exploration of these rare metal pegmatites. The resultant kaolin is also the protagonist in the story of exhumation and destruction of a pegmatite by weathering and erosion. Irrespective of the strength of kaolinization, Nb–Ta–Ti heavy minerals can be identified in the regolith atop the host pegmatite or Aplite and used for genetic interpretation of the primary mineralization and the origin of the felsic intrusive. Nb–Ta solid solution series (s.s.s.) have to be treated cautiously because of the disposition of Ta-enriched Nb–Ta oxide s.s.s. to undergo corrosion in their tantalite lamellae more easily than in their niobium-enriched zones. Kaolinization may alter the primary Nb/Ta ratio but not to the extent that Ta is released completely. The most strongly kaolinized new Aplite is the youngest member of a series of felsic intrusive rocks in the Pleystein pegmatite–Aplite system. The supergene kaolinization extending from the Miocene through the Pliocene can easily be correlated by “minero-stratigraphy” with the larger Tirschenreuth kaolin deposit. The four stages established in the area furnish evidence of gradual alkalinization of the meteoric pore fluids throughout the Neogene and the Quaternary. Youngest stages are found at Tirschenreuth, the oldest regolith stage is present at Pleystein.

  • The new Nb-P Aplite at Reinhardsrieth: A keystone in the lateral and depth zonations of the Hagendorf-Pleystein Pegmatite Field, SE Germany
    Ore Geology Reviews, 2015
    Co-Authors: Harald G. Dill, Radek Škoda

    Abstract:

    Abstract The Hagendorf–Pleystein Pegmatite Field (HPPF) is the largest pegmatite concentration in Central-Europe, which has been intensively studied for its mineralogy, mainly at Hagendorf-South pegmatite stock. It was not until recently that the lateral and depth zonations of the HPPF could be clarified when the newly discovered tabular Aplite at Reinhardsrieth Aplite has been found at transition into the so-called barren zone devoid of rare metals. Thereby the theory of the derivation of the HPPF felsic mobilizates as a result of a successive differentiation of a pegmatitic melt from the Flossenburg Granite has to be discarded. From the structural and lithological point of view, stock-like, well zoned pegmatites, e.g. Hagendorf-South, developed in the hinge zone, whereas tabular Aplites, such as Reinhardsrieth, evolved along the limb zone of strongly folded basement rocks. In the latter case, the accommodation space was smaller and the cooling of the felsic mobilizates much faster, giving rise to fine-grained aplitic rather than coarse-grained felsic mobilizates (chilled margin effect). During the incipient stages of the evolution in the HPPF, at Reinhardsrieth, a stronger impact of granitization can be determined than at the neighboring Aplites and pegmatites based upon the REE fractionation. A tripartite subdivision may be established for the various pegmatites and Aplites in the HPPF: (1) Barren zone (minor amounts of LREE in a system otherwise dominated by feldspar and quartz), (2) marginal zone (mainly Fe–Al phosphates plus columbite-(Fe)), (3) central zone (Fe–Zn–Li phosphates plus columbite-(Fe)). The afore-mentioned zonation shows an E–W trend and a bilateral symmetric arrangement of the various areas. There are significant indications of an oxidizing facies to substitute for a more reducing facies at the transition from the central into the marginal zone of the HPPF. The key mineral for the primary pegmatite mineralization in the marginal and central zones is columbite-(Fe). Its Mn/Fe ratios plotted vs. the Ta/Nb ratios allow for an assessment to what extent metamorphic and magmatic processes have contributed to the built-up of the pegmatites and Aplites in the HPPF. Even the most primitive “nigrine”-hosted columbites fit well into this pattern, forming a lithochemical halo in the roof rocks of the pegmatites. The heavy mineral aggregated of rutile–ilmenite (“nigrine”) giving host to the columbite as armored relicts got released from the basement rock on top of the pegmatites into the stream sediments where they are operative as an ore guide. The morphology of zircon in the stream sediments has been utilized as an economic ore indicator. The Zr silicate is also indicative of the temperature of formation and closely supports the tripartite zonation established above. Manganiferous apatite is a good depth-of-emplacement indicator for each Aplite and pegmatite, respectively. The higher the FeO + MnO content of apatite, the shallower the depth of emplacement of its host pegmatite or Aplite. Vivianite, in turn, marks the onset of the hydrothermal alteration of the pegmatites and Aplites and its Mn contents relate to the depth where alteration has taken place or emplacement of the secondary phosphates. The higher the Mn content the shallower the depth of alteration. Peculiar element ratios were selected to design some key diagrams so as to corroborate the field-based mineralogical and geological results in terms of zonation of genetic economic geology as well as to cater for applied economic geology as proximity indicators and ore guides when exploring for rare element pegmatite.

  • Kaolinization — a tool to unravel the formation and unroofing of the Pleystein pegmatite–Aplite system (SE Germany)
    Ore Geology Reviews, 2015
    Co-Authors: Harald G. Dill, Reiner Dohrmann, Stephan Kaufhold, Sorin-ionut Balaban

    Abstract:

    Abstract The Hagendorf–Pleystein Pegmatite Province, SE Germany, is known for the largest feldspar–quartz pegmatite in Central Europe and renowned for its rare elements, e.g., Li, Nb, and Ta, giving rise to a spate of exotic minerals, mainly phosphates. Argillaceous rocks are scarce and eclipsed by the numerous mineralogical investigations on rare phosphates. These phosphate pegmatites are for the first time subjected to a clay mineralogical study, rendered possible by the newly discovered strongly kaolinized Aplite near the Kreuzberg Quartz Pegmatite at Pleystein. The supergene kaolin akin to the residual kaolin deposit at Tirschenreuth, SE Germany, was analyzed for its major and minor elements by XRF and micro-chemically by EMPA. Mineralogical investigations involved XRD, IR spectroscopy, thermoanalytical studies, CEC analyses and SEM-EDX. Supergene kaolinization forms a repository for heavy minerals critical for the interpretation of the emplacement of the Late Paleozoic pegmatites as well as a matrix for pegmatite-related trace elements and thereby may be used as an ore guide during exploration of these rare metal pegmatites. The resultant kaolin is also the protagonist in the story of exhumation and destruction of a pegmatite by weathering and erosion. Irrespective of the strength of kaolinization, Nb–Ta–Ti heavy minerals can be identified in the regolith atop the host pegmatite or Aplite and used for genetic interpretation of the primary mineralization and the origin of the felsic intrusive. Nb–Ta solid solution series (s.s.s.) have to be treated cautiously because of the disposition of Ta-enriched Nb–Ta oxide s.s.s. to undergo corrosion in their tantalite lamellae more easily than in their niobium-enriched zones. Kaolinization may alter the primary Nb/Ta ratio but not to the extent that Ta is released completely. The most strongly kaolinized new Aplite is the youngest member of a series of felsic intrusive rocks in the Pleystein pegmatite–Aplite system. The supergene kaolinization extending from the Miocene through the Pliocene can easily be correlated by “minero-stratigraphy” with the larger Tirschenreuth kaolin deposit. The four stages established in the area furnish evidence of gradual alkalinization of the meteoric pore fluids throughout the Neogene and the Quaternary. Youngest stages are found at Tirschenreuth, the oldest regolith stage is present at Pleystein.

Jeremy T. Ross – One of the best experts on this subject based on the ideXlab platform.

  • Formation by silicate–fluoride + phosphate melt immiscibility of REE-rich globular segregations within Aplite dikes
    Contributions to Mineralogy and Petrology, 2018
    Co-Authors: Charles R. Stern, Julien Allaz, Markus B. Raschke, G. Lang Farmer, M. Alexandra Skewes, Jeremy T. Ross

    Abstract:

    Aplite dikes intruding the Proterozoic 1.42(± 3) Ga Longs Peak-St. Vrain Silver Plume-type peraluminous granite near Jamestown, Colorado, contain F, P, and rare earth element (REE)-rich globular segregations, with 40–46% REE, 3.7–4.8 wt% P2O5, and 5–8 wt% F. A combination of textural features and geochemical data suggest that the Aplite and REE-rich globular segregations co-existed as two co-genetic liquids prior to their crystallization, and we propose that they are formed by silicate–fluoride + phosphate (+ S + CO2) melt immiscibility following ascent, cooling, and decompression of what was initially a single homogeneous magma that intruded the granite. The REE distribution coefficients between the silica-rich Aplites and REE-rich segregations are in good agreement with experimentally determined distribution coefficients for immiscible silicate–fluoride + phosphate melts. Although monazite-(Ce) and uraninite U–Th–Pb microprobe ages for the segregations yield 1.420(± 25) and 1.442(± 8) Ga, respectively, thus suggesting a co-genetic relationship with their host granite, eNd1.42Ga values for the granites and related granitic pegmatites range from − 3.3 to − 4.7 (average − 3.9), and differ from the values for both the Aplites and REE-rich segregations, which range from − 1.0 to − 2.2 (average − 1.6). Furthermore, the granites and pegmatites have (La/Yb)N 100 and absence of an Eu anomaly in both the Aplites and segregations. These data are consistent with the Aplite dikes and the REE-rich segregations they contain being co-genetic, but derived from a source different from that of the granite. The higher eNd1.42Ga values for the Aplites and REE-rich segregations suggest that the magma from which they separated had a more mafic and deeper, dryer and hotter source in the lower crust or upper mantle compared to the quartzo-feldspathic upper crustal source proposed for the Longs Peak-St. Vrain granite.

  • formation by silicate fluoride phosphate melt immiscibility of ree rich globular segregations within Aplite dikes
    Contributions to Mineralogy and Petrology, 2018
    Co-Authors: Charles R. Stern, Julien Allaz, Markus B. Raschke, Lang G Farmer, Alexandra M Skewes, Jeremy T. Ross

    Abstract:

    Aplite dikes intruding the Proterozoic 1.42(± 3) Ga Longs Peak-St. Vrain Silver Plume-type peraluminous granite near Jamestown, Colorado, contain F, P, and rare earth element (REE)-rich globular segregations, with 40–46% REE, 3.7–4.8 wt% P2O5, and 5–8 wt% F. A combination of textural features and geochemical data suggest that the Aplite and REE-rich globular segregations co-existed as two co-genetic liquids prior to their crystallization, and we propose that they are formed by silicate–fluoride + phosphate (+ S + CO2) melt immiscibility following ascent, cooling, and decompression of what was initially a single homogeneous magma that intruded the granite. The REE distribution coefficients between the silica-rich Aplites and REE-rich segregations are in good agreement with experimentally determined distribution coefficients for immiscible silicate–fluoride + phosphate melts. Although monazite-(Ce) and uraninite U–Th–Pb microprobe ages for the segregations yield 1.420(± 25) and 1.442(± 8) Ga, respectively, thus suggesting a co-genetic relationship with their host granite, eNd1.42Ga values for the granites and related granitic pegmatites range from − 3.3 to − 4.7 (average − 3.9), and differ from the values for both the Aplites and REE-rich segregations, which range from − 1.0 to − 2.2 (average − 1.6). Furthermore, the granites and pegmatites have (La/Yb)N 100 and absence of an Eu anomaly in both the Aplites and segregations. These data are consistent with the Aplite dikes and the REE-rich segregations they contain being co-genetic, but derived from a source different from that of the granite. The higher eNd1.42Ga values for the Aplites and REE-rich segregations suggest that the magma from which they separated had a more mafic and deeper, dryer and hotter source in the lower crust or upper mantle compared to the quartzo-feldspathic upper crustal source proposed for the Longs Peak-St. Vrain granite.

Julien Allaz – One of the best experts on this subject based on the ideXlab platform.

  • Formation by silicate–fluoride + phosphate melt immiscibility of REE-rich globular segregations within Aplite dikes
    Contributions to Mineralogy and Petrology, 2018
    Co-Authors: Charles R. Stern, Julien Allaz, Markus B. Raschke, G. Lang Farmer, M. Alexandra Skewes, Jeremy T. Ross

    Abstract:

    Aplite dikes intruding the Proterozoic 1.42(± 3) Ga Longs Peak-St. Vrain Silver Plume-type peraluminous granite near Jamestown, Colorado, contain F, P, and rare earth element (REE)-rich globular segregations, with 40–46% REE, 3.7–4.8 wt% P2O5, and 5–8 wt% F. A combination of textural features and geochemical data suggest that the Aplite and REE-rich globular segregations co-existed as two co-genetic liquids prior to their crystallization, and we propose that they are formed by silicate–fluoride + phosphate (+ S + CO2) melt immiscibility following ascent, cooling, and decompression of what was initially a single homogeneous magma that intruded the granite. The REE distribution coefficients between the silica-rich Aplites and REE-rich segregations are in good agreement with experimentally determined distribution coefficients for immiscible silicate–fluoride + phosphate melts. Although monazite-(Ce) and uraninite U–Th–Pb microprobe ages for the segregations yield 1.420(± 25) and 1.442(± 8) Ga, respectively, thus suggesting a co-genetic relationship with their host granite, eNd1.42Ga values for the granites and related granitic pegmatites range from − 3.3 to − 4.7 (average − 3.9), and differ from the values for both the Aplites and REE-rich segregations, which range from − 1.0 to − 2.2 (average − 1.6). Furthermore, the granites and pegmatites have (La/Yb)N 100 and absence of an Eu anomaly in both the Aplites and segregations. These data are consistent with the Aplite dikes and the REE-rich segregations they contain being co-genetic, but derived from a source different from that of the granite. The higher eNd1.42Ga values for the Aplites and REE-rich segregations suggest that the magma from which they separated had a more mafic and deeper, dryer and hotter source in the lower crust or upper mantle compared to the quartzo-feldspathic upper crustal source proposed for the Longs Peak-St. Vrain granite.

  • formation by silicate fluoride phosphate melt immiscibility of ree rich globular segregations within Aplite dikes
    Contributions to Mineralogy and Petrology, 2018
    Co-Authors: Charles R. Stern, Julien Allaz, Markus B. Raschke, Lang G Farmer, Alexandra M Skewes, Jeremy T. Ross

    Abstract:

    Aplite dikes intruding the Proterozoic 1.42(± 3) Ga Longs Peak-St. Vrain Silver Plume-type peraluminous granite near Jamestown, Colorado, contain F, P, and rare earth element (REE)-rich globular segregations, with 40–46% REE, 3.7–4.8 wt% P2O5, and 5–8 wt% F. A combination of textural features and geochemical data suggest that the Aplite and REE-rich globular segregations co-existed as two co-genetic liquids prior to their crystallization, and we propose that they are formed by silicate–fluoride + phosphate (+ S + CO2) melt immiscibility following ascent, cooling, and decompression of what was initially a single homogeneous magma that intruded the granite. The REE distribution coefficients between the silica-rich Aplites and REE-rich segregations are in good agreement with experimentally determined distribution coefficients for immiscible silicate–fluoride + phosphate melts. Although monazite-(Ce) and uraninite U–Th–Pb microprobe ages for the segregations yield 1.420(± 25) and 1.442(± 8) Ga, respectively, thus suggesting a co-genetic relationship with their host granite, eNd1.42Ga values for the granites and related granitic pegmatites range from − 3.3 to − 4.7 (average − 3.9), and differ from the values for both the Aplites and REE-rich segregations, which range from − 1.0 to − 2.2 (average − 1.6). Furthermore, the granites and pegmatites have (La/Yb)N 100 and absence of an Eu anomaly in both the Aplites and segregations. These data are consistent with the Aplite dikes and the REE-rich segregations they contain being co-genetic, but derived from a source different from that of the granite. The higher eNd1.42Ga values for the Aplites and REE-rich segregations suggest that the magma from which they separated had a more mafic and deeper, dryer and hotter source in the lower crust or upper mantle compared to the quartzo-feldspathic upper crustal source proposed for the Longs Peak-St. Vrain granite.