Kaolinization – a tool to unravel the formation and unroofing of the Pleystein pegmatite-aplite system (SE Germany)

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, 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, thermo analytical 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 no 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 alkalinisation 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

Deep exploration using long-offset transient electromagnetics: interpretation of field data in time and frequency domain

In the framework of the Deep Electromagnetic Soundings for Mineral Exploration project, we conducted ground-based long-offset transient-electromagnetic measurements in a former mining area in eastern Thuringia, Germany. The large-scale survey resulted in an extensive dataset acquired with multiple high-power transmitters and a high number of electric and magnetic field receivers. The recorded data exhibit a high data quality over several decades of time and orders of magnitude. Although the obtained subsurface models indicate a strong multi-dimensional subsurface with variations in resistivity over three orders of magnitude, the electrical field step-on transients are well fitted using a conventional one-dimensional inversion. Due to superimposed induced polarization effects, the transient step-off data are not interpretable with conventional electromagnetic inversion. For further interpretation in one and two dimensions, a new approach to evaluate the long-offset transient-electromagnetic data in frequency domain is realized. We present a detailed workflow for data processing in both domains and give an overview of technical obstructions that can occur in one domain or the other. The derived one-dimensional inversion models of frequency-domain data show strong multi-dimensional effects and are well comparable with the conventional time domain inversion results. To adequately interpret the data, a 2.5D frequency-domain inversion using the open source algorithm MARE2DEM (Modeling with Adaptively Refined Elements for 2-D EM) is carried out. The inversion leads to a consistent subsurface model with shallow and deep conductive structures, which are confirmed by geology and additional geophysical surveys

Psycho-social correlates of medication serum levels in patients with seizures: implications for education of patients

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67536/2/10.1177_001789697002900301.pd