A wide application of modern precision research techniques to the studies of Pitkyaranta ores allowed us to find increased
contents of indium (to 0.33%), silver (447 g/t), gold (0.2–0.4 g/t), and palladium (0.2 g/t). A series of rare minerals previously
not found here was also discovered. Among ore minerals, these are roquesite, zavartskite, electrum, stutzite, altaite, bismite,
glaucodot, cervelleite, hedleyite, pavonite, cannonite, plantnerite, lindkvistite, ashoverite, etc. The discovery of roquesite
and electrum is the most important in terms of metallogeny. Roquesite (indium sulfide) is found in Karelia for the first time.
The highest indium contents in direct correlation to those of zinc are characteristic for polymetallic ores of the Pitkyaranta
ore fields with sphalerite as the concentrating mineral (to 0.5% of In). The predicted zinc resources are evaluated to ∼2.5
million t for the Pitkyaranta group of ore deposits, and to 400 000 t for the Hopunvaara region. Respectively, the resources
of indium amount to ∼2400 t (total) and 600 t for the Hopunvaara region. 相似文献
Data on the composition, inner structure, and age of volcanic and siliceous-terrigenous complexes and granitoids occurring
in association with them in the Caledonian Lake zone in Central Asia are discussed in the context of major relations and trends
in the growth of the Caledonian continental crust in the Central Asian Foldbelt (CAFB). The folded structures of the Lake
zone host basalt, basalt-andesite, and andesite complexes of volcanic rocks that were formed in distinct geodynamic environments.
The volcanic rocks of the basalt complex are noted for high concentrations of TiO2 and alkalis, occur in association with fine-grained siliceous siltstone and siliceous-carbonate rocks, are thus close to
oceanic-island complexes, and were likely formed in relation to a mantle hotspot activity far away from erosion regions supplying
terrigenous material. The rocks of the basalt-andesite and andesite complexes have lower TiO2 concentrations and moderate concentrations of alkalis and contain rock-forming amphibole. These rocks are accompanied by
rudaceous terrigenous sediments, which suggests their origin in island-arc environments, including arcs with a significantly
dissected topography. These complexes are accompanied by siliceous-terrigenous sedimentary sequences whose inner structure
is close to those of sediments in accretionary wedges. The folded Caledonides of the Lake zone passed through the following
evolutionary phases. The island arcs started to develop at 570 Ma, their evolution was associated with the emplacement of
layered gabbroids and tonalitetrondhjemite massifs, and continued until the onset of accretion at 515–480 Ma. The accretion
was accompanied by the emplacement of large massifs of the tonalite-granodiorite-plagiogranite series. The postaccretionary
evolutionary phase at 470–440 Ma of the Caledonides was marked by intrusive subalkaline and alkaline magmatism. The Caledonides
are characterized by within-plate magmatic activity throughout their whole evolutionary history, a fact explained by the accretion
of Vendian-Cambrian oceanic structures (island arcs, oceanic islands, and back-arc basins) above a mantle hotspot. Indicators
of within-plate magmatic activity are subalkaline high-Ti basalts, alkaline-ultrabasic complexes with carbonatites and massifs
of subalkaline and alkaline gabbroids, nepheline syenites, alkaline granites, subalkaline granites, and granosyenites. The
mantle hotspot likely continued to affect the character of the lithospheric magmatism even after the Caledonian folded terrane
was formed. 相似文献
Zoned quartz and feldspar phenocrysts of the Upper Carboniferous eastern Erzgebirge volcano-plutonic complex were studied by cathodoluminescence and minor and trace element profiling. The results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends, magma mixing and recharge events, and suggest that much heterogeneity in plutonic systems may be overlooked on a whole-rock scale. Multiple resorption surfaces and zones, element concentration steps in zoned quartz (Ti) and feldspar phenocrysts (anorthite content, Ba, Sr), and plagioclase-mantled K-feldspars etc. indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern Erzgebirge volcano-plutonic complex. Generally, feldspar appears to be sensitive to the physicochemical changes of the melt, whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas. The regional distribution of mixing-compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late-Variscan granites and associated volcanic rocks.
Quartz phenocrysts from 14 magmatic phases of the eastern Erzgebirge volcano-plutonic complex provide information on the relative timing of different mixing processes, storage and recharge, allowing a model for the distribution of magma reservoirs in space and time. At least two levels of magma storage are envisioned: deep reservoirs between 24 and 17 km (the crystallisation level of quartz phenocrysts) and subvolcanic reservoirs between 13 and 6 km. Deflation of the shallow reservoirs during the extrusion of the Teplice rhyolites triggered the formation of the Altenberg-Teplice caldera above the eastern Erzgebirge volcano-plutonic complex. The deep magma reservoir of the Teplice rhyolite also has a genetic relationship to the younger mineralised A-type granites, as indicated by quartz phenocryst populations. The pre-caldera biotite granites and the rhyodacitic Schönfeld volcanic rocks represent temporally and spatially separate magma sources. However, the deep magma reservoir of both is assumed to have been at a depth of 24–17 km. The drastic chemical contrast between the pre-caldera Schönfeld (Westfalian B–C) and the syn-caldera Teplice (Westfalian C–D) volcanic rocks is related to the change from late-orogenic geotectonic environment to post-orogenic faulting, and is considered an important chronostratigraphic marker. 相似文献