Wyniki wyszukiwania - BazTech

1

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

Štemprok M., Seifert T.

Mineralogia

|

2011

|

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.

2

Spatial variability of recent sedimentation rates in the Eastern Gotland Basin (Baltic Sea)

Hille S., Leipe T., Seifert T.

Oceanologia

|

2006

|

No. 48 (2)

297-317

EN

n order to study recent sedimentation rates in the Eastern Gotland Basin, 52 short sediment cores collected from the deepest part (< 150 m) of the Basin in 2003 were investigated. The upper parts of all the cores were distinctly laminated and dark in colour, followed by a homogeneous, greyish lower part. The thickness of the laminated sequences varied from 17 to 300 mm. 210Pb dating analyses of selected cores revealed that the change from non-laminated to laminated sediments happened about 100 years ago, indicating a shift from predominantly oxic bottom water conditions to anoxic conditions. Used as a time marker, this shift in the sediment texture enabled sediment accumulation rates to be estimated for all sediment cores. The observed mean linear sedimentation rate for the whole basin was 0.93 š 0.67 mm y-1. The respective bulk sediment accumulation rates ranged from 10.5 to 527 g m-2 yr-1 with an average of 129 š 112 g m-2 yr-1, indicating a high spatial variability of sedimentation rates within the basin. This agrees very well with the long-term sedimentation pattern since the Litorina transgression. The observed pattern clearly reflects the hydrographic conditions at the seafloor as studied by modelled near-bottom current velocities.

3

Warm waters of summer 2002 in the deep Baltic Proper

Feistel R., Nausch G., Mohrholz V., Łysiak-Pastuszak E., Seifert T., Matthäus W., Krüger S., Hansen I. S.

Oceanologia

|

2003

|

No. 45 (4)

571-592

EN

From October 2002 until March 2003 surprisingly warm, oxygenated waters were frequently encountered in the Baltic Sea in the area between the Bornholm and Fa*rö Deeps from the halocline down to the bottom. Owing to their ventilation effect in the stagnating deep waters, their occasional observations have partly been incorrectly attributed to the inflow events of October 2002 or January 2003. The emergence of some of these waters can be traced back to the exceptional summer weather conditions in August and September 2002 in central Europe. The warm waters played a remarkable renewal pacemaker role for the subsequent important winter inflow of January 2003. The evolution of this summer inflow is described and possible causes are discussed.