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@PHDTHESIS{Chatziliadou:51191,
author = {Chatziliadou, Maria},
othercontributors = {Kramm, Ulrich},
title = {{R}b-{S}r {A}lter und {S}r-{P}b {I}sotopencharakteristik
von {G}angmineralisationen in paläozoischen {G}esteinen am
{N}ordrand des linksrheinischen {S}chiefergebirges ({R}aum
{S}tolberg-{A}achen-{K}elmis) und {V}ergleich mit den
rezenten {T}hermalwässern von {A}achen-{B}urtscheid},
address = {Aachen},
publisher = {Publikationsserver der RWTH Aachen University},
reportid = {RWTH-CONV-113503},
pages = {VIII, 144, [ca. 150] Bl. : Ill., graph. Darst.},
year = {2009},
note = {Zusammenfassung in dt. und engl. Sprache; Aachen, Techn.
Hochsch., Diss., 2009},
abstract = {Vein mineralizations of different age and formation were
studied in the northern Eifel area and its foreland. The
focus was put on microstructure, geochemistry and isotopic
composition to characterize discrete fluid flow events and
to date their generations. Samples from the geothermal well
RWTH – 1 representing Variscan vein mineralizations, from
the Pb – Zn vein mineralizations of the mining district
Stolberg – Aachen – Kelmis with special emphasis on
veins from the limestone quarry Hastenrath of Postvariscan
age and from the recent thermal springs of Aachen and
Burtscheid were investigated. RWTH – 1 sank down in the
town of Aachen in 2004 is situated within the Aachen fold
and thrust belt and reached a final depth of 2544 m. From
top to the base the bore hole exposed Upper Carboniferous,
Upper Devonian and Lower Devonian carbonate and
siliciclastic sediments. Three core cuts display intensive
hydrothermal veining with variable orientations. These veins
are mm to cm wide and represent extension structures with
characteristics of deformation and recrystallization in
minerals of the rim parts. Calcite, ankerite, dolomite,
chlorite, quartz and occasionally pyrite are the typical
vein minerals with chlorite found along the vein margins and
the carbonates generally in the centre. Crack-seal processes
indicate brittle deformation and multiple reactivations of
the opening. The chemical compositions of the chlorite from
veins of the first and second cored section of the well
indicate formation temperatures of 290°C to 370°C.
Homogenization temperatures of fluid inclusions found in the
vein minerals are < 390°C (Lögering, 2008). These
temperatures reflect typical Variscan metamorphic
temperatures along the northern part of the Rhenohercynian
fold belt (Behr et al., 1993, Muchez et al., 2000). The
precipitation of the carbonate minerals within the veins is
attributed to cooling of a fluid phase and its change in pH
by reaction with the carbonate-bearing wall rocks during
uprise in the fault systems of the rocks (compare also
Lögering, 2008). The pronounced factionation of rare earth
elements suggests that the components of the precipitated
carbonate minerals in the veins cannot be derived from the
immediate wall rocks aside the veins but must have come from
more distant rock volumes. Independant from the
stratigraphic level these carbonates are characterized by a
significant Eu anomaly which is interpreted to show a
carbonate formation at increased temperatures. Initial
87Sr/86Sr ratios of calcite and chlorite of the veins cannot
become identical at any times. Thus a Rb-Sr isochrone age of
the mineral assemblage of the veins cannot be obtained.
Model calculations for the chlorite – carbonate mineral
pairs using a paleo-mixing of different Sr isotope
compositions suggest a model age of 218±15 Ma (Beiss, 2008)
which is similar to 40Ar/39Ar ages of the vein chlorites of
182±18 Ma (Sindern et al., 2008). Of course these "ages" do
not correspond to the Variscan formation of the veins. The
initial 87Sr/86Sr ratios of carbonate minerals and chlorite,
both from the veins, and the fractions of the corresponding
host rocks soluble in HCl show a considerable variation for
Carboniferous times. Calcite varies from 0,71107±1 to
0,72119±1, Chlorite from 0,71513±4 to 0,72628±3 and the
soluble part of the host rocks from 0,71049±1 to
0,72138±1. This variation in Sr composition may be an
effect of intensive interaction of the fluid phase with the
corresponding wall rocks of the veins but can also be
interpreted as distinct fluid pulses with individual Sr
compositions. In any case, since chlorite is always higher
in 87Sr/86Sr than the associated carbonates the two phases
cannot be precipitated simultaneously. Chlorite may have
formed by interaction of a fluid phase with the country
rocks or, chlorite experienced a late alteration. Likewise,
the carbonate components are not exclusively derived from
the wall rocks. Pb isotope compositions of pyrite
(206Pb/204Pb = 18,229 – 18,254; 207Pb/204Pb = 15,589 –
15,592) characterize the Variscan mineralizations. The Lower
Carboniferous limestone of the Hastenrath quarry shows
87Sr/86Sr ratios of 0,70812±1 and 0,70817±1 which is
typical for a marine formation. For the source of C delta13C
of this rock suggests formation waters. Diagenetic processes
within this limestone are documented by small-scale
branching structures composed of dolomite. The structures
are cross cut by non-oriented calcite veins with Sr isotope
compositions distinctly higher radiogenic than the
surrounding country rocks. Sr of these veins has an unknown
source. The structures of the Paleozoic limestones are block
faulted perpendicular to their strike by NW –SE trending
faults which exhibit a Pb – Zn vein mineralization typical
for the Stolberg – Aachen – Kelmis mining district.
Three different mineralized zones can be distinguished
within the veins (zones 1, 2, 3) which indicate at least
three crack – seal processes and thus at least three
periods of fluid flow. The brecciated zone 1 marks the first
fracture sealing process. It contains fragments of galena
crystals, chalcopyrite, bornite, quartz, dolomite, ankerite
and blocks of the wall rocks fixed in a calcitic matrix. The
second fracture sealing phase (zone 2) is composed
exclusively of large crystals of calcite. Zone 3 is made of
calcite which is overgrown by collomorphic sphalerite.
Within this ZnS inclusions of galena, chalcopyrite and
bornite are found. In parts of the sphalerite the Cd content
is very high (up to 6,5 $wt.-\%).$ Within one of the
investigated veins the minerals are symmetrically deposited
on the limestone wall rocks. The central part of this veins
contains a small filling of lignite coal. It marks the
fourth fracture sealing phase. The transport of this lignite
coal into the centre of the vein may be explained by
tectonic shearing along the fault. The homogenization
temperatures of fluid inclusions in calcite from sealing
zones 1, 2 and 3 are distinctly different. The total span
covers 80,7°C to 179,7°C. The salinity varies from 10,24
to 23,08 $wt.-\%$ NaCl equivalent and thus are within the
range of Postvariscan NaCl – CaCl2 – H2O fluids of other
occurrences of the northern margin of the Rhenohercynian
fold belt. The REE distribution patterns of calcite of zones
1, 2 and 3 are similar to those of the wall rocks. All
carbonate minerals exhibit a small negative Eu anomaly
indicating a reducing character of the fluid phase. delta18O
of calcite increases from zone 1 to zone 3, delta13C
decreases. The delta are characteristic for hydrothermally
crystallized carbonate minerals. delta13C of calcite from
zone 3 (-7,53 - $-8,70\%)$ may be interpreted as a mixture
of C from the wall rocks and C from a hydrothermal source
higher in temperature. Late stage calcite formations in
limestone caves of the Hastenrath quarry show similar C and
O isotopic compositions than calcite from zone 3 of the
veins. Sphalerite from zone 3 occurrences were dated by Rb
– Sr. The isochron reflects an age of 134,3±1,3 Ma which
defines a period of formation at the turn from the Jurassic
to the Cretaceous. The large range of 87Sr/86Sr ratios for
calcite even from single zone 1, 2 or 3 indicates the
complex conditions of formation. The range of Pb isotope
ratios of calcite of the veins, galena and sphalerite is
small and very similar to other occurrences of Postvariscan
mineralizations of the northern Eifel area. The Pb ratios
suggest a crustal source of this lead and a possible
remobilization by repeated hydrothermal pulses from mixed
and homogenized sources. Pb–Zn vein mineralizations of
Diepenlienchen, Albertsgrube, Altenberg and Bleiberg in
Belgium and Thermae 2002, Netherlands, represent equivalents
to the mineralization of the limestone quarry Hastenrath.
Sphalerite in its collomorphic appearance, galena, pyrite,
marcasite, the carbonates calcite, dolomite, ankerite and
siderite, and quartz are prominent minerals. In contrast to
Hastenrath the sphalerite here is rich in Fe (< 5,81
$wt.-\%).$ This Fe enrichment is interpreted to show
elevated temperatures during crystallization. Carbonate
minerals of Bleiberg are characterized by a positive Eu
anomaly while die other occurrences show negative Eu’s.
The Sr isotope compositions of carbonates vary considerably,
and similar to Hastenrath also for Bleiberg several fracture
sealing generations of calcite are recognized (Muchez et
al., 1994). The Pb isotope compositions of galena,
sphalerite and pyrite plot into the field of Postvariscan
mineralizations defined by Krahn (1988) as do these minerals
of Hastenrath. The Rb–Sr systematics date the
crystallization of sphalerite to 129,9±9,7 Ma for
Diepenlienchen, to 137,1±1,7 Ma for Altenberg, and to
134,5±4,1 Ma for Thermae 2002. Thus, within the limits of
error, all these vein-type Pb – Zn mineralizations of the
mining district Stolberg – Aachen – Kelmis took place at
the turn from the Jurassic to the Cretaceous as defined by
Odin (1994). This age marks a time of block faulting in
Central Europe which is related to phases of opening of the
North Atlantic Ocean. It is characterized by intensive
hydrothermal activities and a wide-spread formation of ore
deposits. The thermal spring waters along the Aachen and the
Burtscheid thrust system document recent fluid flow. Their
chemical composition is used here for a comparison with the
Variscan and Postvariscan fluid flows. The mineralizations
of the springs reflect several geochemical processes.
Subrecent sinter formations are a direct segregation product
of the springs. Catchment areas, transport routes and
geochemical enrichment and depletion processes can be
modelled by new Sr and Pb isotope compositions of the
thermal water and, thus, are used to refine the genetic
models of Pommerening (1993) and Herch (1997). The 87Sr/86Sr
of the thermal water ranges from 0,71607±1 to 0,71618±1
and reflects mixtures of several ground water types which
took part in different water-rock interactions. In any case,
the Sr compositions are distinctly more radiogenic than sea
water during the whole Phanerozoic. Sr sources of the Aachen
and Burtscheid waters will be Paleozoic siliciclastic and
carbonate rocks, possibly also evaporitic sediments. The
spring precipitations exhibit 87Sr/86Sr ratios of 0,71600±1
to 0,71615±1 which falls into the range of Sr compositions
of the waters. Pb isotope compositions of the spring waters
and their precipitations scatter over a wide range. This
scatter may be caused by complex mixing of different ground
waters characzerized by different Pb sources. This is
suggested since Pb compositions of the Variscan and
Postvariscan ore deposits described above scatter in a very
similar way. An anthropogenic contamination of the springs
by lead, however, cannot be excluded. The Variscan,
Postvariscan and recent fluid flow documented for the NW
Rhenohercynian belt is correlated to deformation processes,
block faulting and fold and thrust processes. The results of
geochemical and isotope investigations presented here refer
to multiple fluid mobilizations and complex genetical
processes which are related to spatial – temporal
variations of tectonics and fluid supply.},
keywords = {Mineralchemie (SWD) / Geochemie (SWD) / Datierung (SWD) /
Isotopendatierung (SWD) / Vererzung (SWD) / Zinkblende (SWD)
/ Carbonate (SWD)},
cin = {541110 / 530000},
ddc = {550},
cid = {$I:(DE-82)541110_20140620$ / $I:(DE-82)530000_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-opus-27157},
url = {https://publications.rwth-aachen.de/record/51191},
}
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