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An overview of the association between lamprophyric intrusions and rare-metal mineralization

Štemprok M., Seifert T.

Mineralogia

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2011

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Vol. 42, iss. 2/3

121--162

EN

Granite-related rare metal districts in orogenic settings are occasionally associated with lamprophyre dikes. We recorded 63 occurrences of lamprophyres in bimodal dike suites of about 200 granite bodies related to rare metal deposits. Most lamprophyres occur in Paleozoic and Mesozoic metallogenic provinces in the northern hemisphere. Lamprophyres which are associated with rare metal deposits are calc-alkaline (kersantites, minettes, spessartites) or more rarely alkaline lamprophyres (camptonites, monchiquites) which occur in the roof zone of complex granitic bodies as pre-granitic, intra-granitic, intra-ore or post-ore dikes. Most lamprophyres are spatially associated with dominant felsic dikes and/or with mafic dikes represented by diorites or diabases. Diorites and lamprophyres occasionally exhibit transitional compositions from one to another. Lamprophyres share common geochemical characteristics of highly evolved granitoids such as enrichment in K and F, increased abundances of Li, Rb, and Cs and enrichment in some HFSE (e.g. Zr, U, Th, Mo, Sn, W). Lamprophyres in rare metal districts testify to accessibility of the upper crust to mantle products at the time of rare metal mineralization and possible influence of mantle melts or mantle-derived fluids in the differentiation of granitic melts in the lower crust.

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Late Palaeozoic lamprophyres and associated mafic subvolcanic rocks of the Sudetes (SW Poland): petrology, geochemistry and petrogenesis

Awdankiewicz M.

Geologia Sudetica

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2007

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Vol. 39

11-97

EN

Lamprophyric magmatism in the Sudetes, in the eastern part of the European Variscides, occurred during a period of post-collisional extension in the Carboniferous. The lamprophyres (minettes, vogesites, spessartites, kersantites) and associated mafic rocks (monzonites, micromonzodiorites) were emplaced as dyke swarms and as scattered veins that cut the crystalline basement and, locally, the overlying molasse deposits. The dyke swarms are adjacent to major regional dislocations, represent distinctive magmatic centres that are related to separate magmatic systems and each are characterized by specific parental melts that have undergone individualised shallow-level differentiation processes. The two largest dyke swarms are associated with the Karkonosze and Kłodzko-Złoty Stok granitoid massifs: these show the widest geochemical and petrographic variation, due to more advanced differentiation in long-lived magmatic systems. In contrast, a small dyke swarm emplaced in the SW part of the Orlica-Śnieżnik Dome, unrelated to granites, is strongly dominated by minettes only. Geochemical characteristics of the mafic rocks studied herein vary from (ultra)potassic in the minettes to calc-alkaline in the micromonzodiorites and from primitive (Mg# = 80-60 in many lamprophyres) to evolved (Mg# down to 30 in some micromonzodiorites). Some richterite minettes show Nb-enriched trace element patterns, but negative Nb anomalies are more typical. Richterite minettes posesess ?Nd300 and 87Sr/86Sr300 values that range from +1.9 to -8.3, and from 0.7037 to 0.715, respectively. The other rocks in this study show negatively correlated Nd and Sr isotopic ratios, between these extremes. The geochemical data suggest three types of mantle source for the lamprophyres and associated mafic rocks: (1) An asthenospheric, depleted and later re-enriched source; (2) A lithospheric source contaminated by subducted crustal rocks; (3) A lithospheric source metasomatized by subduction-related fluids. The richterite minette magmas originated from low degrees of partial melting, under high H2O/CO2 conditions, of garnet-phlogopite-peridotites. The Nb-enriched and Nb-depleted minettes are derived from sources (1) and (2), respectively. Kersantite magmas originated from source (3). The factors of source mixing, variable depths and degrees of melting, and aggregation of melts all influenced the compositions of other primitive minette and vogesite magmas. The other rocks studied (spessartites, monzonites, micromonzodiorites) are variably differentiated. Zoning and other disequilibrium textures in phlogopite, biotite, amphibole and clinopyroxene phenocrysts, together with the presence of xenocrysts, xenoliths and enclaves (cognate, restitic, migmatitic) constrain several processes that were involved in the shallow-level evolution of magmas: mixing, fractional crystallization, assimilation of crustal rocks. However, post-magmatic replacement of the igneous phases by albite, chlorite, epidotes, actinolite, blue amphiboles, titanite, carbonates, prehnite, pumpellyite and grossularite-andradite partly obscures the magmatic assemblages and textures. There are four more general results of this study. First, there is evidence for a strong heterogeneity of the upper mantle and of the presence of subduction-modified mantle beneath the Sudetes during the Late Palaeozoic. Second, the lamprophyre magmas originated and evolved in spatially and petrologically distinct, vertically extensive magmatic systems that spanned the asthenospheric and lithospheric mantle and the lower/middle crust. Third, a broad spectrum of source-related and shallow-level magmatic processes gave rise to the emplacement of primitive, mantle-derived magmas and of variably evolved magmas. Fourth, close links existed between late Variscan tectonics, the location of lamprophyric magmatism, and the shallow-level emplacement processes of mafic dykes.

3

Datowanie diabazów i lamprofirów świętokrzyskich metodą K-Ar i Ar-Ar

Migaszewski Z. M.

Przegląd Geologiczny

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2002

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Vol. 50, nr 3

227-229

PL

Kilka próbek dabazów i lamprofirów z Gór Świętokrzyskich poddano datowaniom KAr i ArAr. Przedział wiekowy tych skał waha się od 391,7 do 254,5 Ma, czyli od dewonu dolnego po najwyższy perm (IUGS, 2000). Wymienione wartości świadczą o długotrwałym i wieloetapowym procesie tworzenia się diabazów i lamprofirów świętokrzyskich. Cykl magmowy na obszarze Gór Świętokrzyskich zapoczątkowały prawdopodobnie diabazy z Zalesia. Czy jego zamknięcie stanowiły diabazy z Prągowca? - pozostaje w dalszym ciągu pytaniem bez odpowiedzi. Wiek skał magmowych potwierdza wcześniejsze przypuszczenia o związku co najmniej części wkładek tufów i tufitów występujących w profilu dewońsko-karbońskim Gór Świętokrzyskich z wulkanizmem lokalnym.

EN

Several samples of diabases and lamprophyres from the Holy Cross Mts were radiometrically dated using K-Ar and Ar-Ar methods. The results obtained indicated 391.7 through 254.5 Ma, e.g. the Lower Devonian through uppermost Permian. These studies confirm the stratigraphic and tectonic data on the long-lasting and multiphasic formation of diabases and lamprophyres. The magmatic cycle seems to have been initiated with the Zalesie diabases and completed with the Prągowiec diabases. The age of igneous rocks also confirms the previous premises on the local origin of some Devonian and Lower Carboniferous tuff and tujfite interbeds.