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Geochemistry, mineral chemistry and P-T evaluation of metasediments of Bahram-Gur complex, ES Sanandaj-Sirjan zone, Iran

Sadegh Hadiseh Rahimi, Moeinzadeh Hesam, Nakashima Kazu

Mineralogia

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2019

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Vol. 50, iss. 1/4

34--68

EN

The Bahram-Gur area in the southeastern part of the Sanandaj–Sirjan metamorphic zone, contains metabasites and metasediments. The metasedimentary rocks are mainly garnet schists and garnet-staurolite schists that were metamorphosed under amphibolite facies conditions. The rocks consist of garnet ± staurolite, biotite, muscovite, chlorite and quartz. The geochemistry of the Bahram-Gur metasediments classifies them as quartziferous sedimentary rocks. The protoliths of the metasedimentary rocks were close to greywackes from an ensialic arc basin depositional setting, with a source comprising mostly mixture of acid and intermediate magmatic rocks in the upper continental crust. The metamorphic conditions of formation of the Bahram-Gur metasedimentary are investigated by geothermobarometric methods. The results show that the metasedimentary rocks formed at temperatures of 600-750°C and pressures of 5-7.5 kbar.

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The Baklia Fault Zone – a regional strike-slip zone splitting Prins Karls Foreland (Svalbard

Ziemniak G., Czerny J., Manecki M., Kośmińska K.

Geology, Geophysics and Environment

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2016

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Vol. 42, no. 1

142--143

EN

Prins Karls Foreland (PKF) is a westernmost island of Svalbard Archipelago belonging to the Southwestern Basement Province. The island consists of low-metamorphic facies probably Neoproterozoic metasediments, divided into two, northern and southern parts. Both parts are characterized by similar geological structures but different stratigraphy. New discoveries presented here result from joint, Norwegian Polar Institute and AGH UST Krakow expeditions in 2013 and 2014. Thorough characteristics of the location and character of a strike-slip fault splitting PKF (the Baklia Fault Zone) is presented here for the first time. To date, one succession has been distinguished in the lithostratigraphy of PKF’s basement. The northern part of the island consists of two groups: the Scotiafjellet Group and Grampianfjella Group (Dallmann et al. 2015). They comprise low-metamorphic metasediments (chlorite zone of greenschist facies), mostly slates, metapsamites and carbonates. Stratigraphic units of the southern part represent slightly higher, biotite metamorphic zone, and have been considered to be conformably underlying Scotiafjellet Group. The uppermost Peachflya Group and Geikiebreen Group (mostly phyllites with metavolcanics and carbonates) are in thrust contact with underlying Ferrierpiggen Group, comprising schistose diamictites. The Ferrierpiggen Group is a tectonic unit stratigraphically discontinuous at top and bottom. Isolated klippe of the Ferrierpiggen Group separated from Scotiafjellet Group by tectonic boundary is present in the northern part of PKF (Harland et al. 1979, 1993). These complexes have undergone the Caledonian metamorphism followed by D 1 deformation producing SE directed folding and thrusts. D 2 deformation was coaxial, but not coplanar with D 1. D 2 deformation occurred probably in Mid-Cenozoic and resulted in refolding and thrusting, followed by formation of a dextral shear zone along Scotiadalen (Morris 1989). D 3 deformation is connected with transtensional formation of the Forlandsundet Graben along NNW-SSE faults finishing the West Spitsbergen Orogeny (WSO) (Manby 1986). Distinct difference in the stratigraphy of southern and northern parts of PKF is apparent. The presence of the fault dividing the island was indicated before (Hjelle et al. 1979), but no single fault has been recognized during detailed mapping later on (Harland et al. 1979, Morris 1982, Manby 1986, Morris 1989). Mapping and structural measurements conducted by the authors in the area of Selvågen led to the discovery of the major fault zone (the Baklia Fault Zone – BFZ) dividing PKF into two terrains. The BKF have N-S trend from Haukebukta in the west coast, through the slopes of Alasdairhornet (where it trapped few hundred meters long slab of the Ferrierpiggen Group rocks), to the southern Scotiadalen. Approaching Selvågen, the fault zone bends slightly to the NNE-SSW. The zone is filled with breccias and mixture of different lithologies with slabs of rocks derived from both limbs of the fault zone. The width of the zone measures approximately 100–250 meters. To the east, it is accompanied by at least three narrow subparallel faults. The age of the BFZ is unknown. A brittle character of deformation may suggest that it is Cenozoic in age. En échelon normal faults with a drop to the north, which associate BFZ may be considered as a Riedel shears R 1 formed at the beginning of a strike-slip movement. Structural measurements on slickensides as kinematic indicators revealed that normal faulting was associated with both, dextral and sinistral shear (not simultaneous). A main movement connected with dextral shearing occurred probably earlier, during late stages of the early Cenozoic crustal shortening. The extended width of the fault zone and the presence of a mixture of rock material from both terranes suggest the significant lateral displacement that might reach tens of kilometers. The BFZ cuts through the boundary faults of the Forlandsundet Graben displacing them sinistrally by approximately one kilometer. This suggests that sinistral movement was probably associated with rejuvenation of the fault during late stages or after the Forlandsundet Graben formation. There are several regional implications of BFZ. The stratigraphic relationship of southern and northern terranes is unclear. The presence of BFZ at the boundary of the Scotiafjellet and Peachflya groups does not exclude their stratigraphic succession but makes it impossible to define. The field observations suggest that BFZ may be Cenozoic in age. It has similar tectonic style and orientation to other strike-slip zones present along western Svalbard coast. Strong tectonic deformation suggests displacement of the northern terrain of PKF by tens of kilometers. Even though southern terrain can be directly correlated with Oscar II Land, more research is needed to correlate more exotic northern terrain of PKF with the basement rocks in the southern parts of Spitsbergen. Ongoing research towards dating and detail structural characterization of this regional fault zone will allow for reconstruction of pre-Tertiary position of this part of Archipelago.

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Złoto w żyłach kwarcowo-siarczkowych z wiercenia DB-4 (rejon Doliny Będkowskiej, Południowa Polska)

Mikulski S. Z., Markowiak M., Oszczepalski S.

Biuletyn Państwowego Instytutu Geologicznego

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2008

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nr 429

99-111

PL

W wyniku aktualnie przeprowadzonych przez Państwowy Instytut Geologiczny badań materiału rdzeniowego z archiwalnego wiercenia DB-4 z rejonu Doliny Będkowskiej (południowa część bloku małopolskiego) udokumentowano występowanie złota w szarozielonych i brunatnych metasedymentach ediakaru. Podwyższone zawartości złota (maks. do 15 ppm) stwierdzono w próbkach punktowych kilku interwałów głębokościowych, przede wszystkim z głębokości 253,0 i 584,5 m. W strefach tych występują liczne żyłki kwarcowe (grubości do 10 cm), kwarcowo-kruszcowe oraz węglanowe. Złotonośna mineralizacja kruszcowa związana jest z żyłkowo-impregnacyjnymi wystąpieniami pirytu i sfalerytu, którym towarzyszy galena, chalkopiryt oraz podrzędnie arsenopiryt. Złoto i elektrum występująw postaci wrostków w pirycie, żyłek sfalerytowo-galenowych (tnących piryt), jak również w formie drobnoziarnistych wydzieleń (<0,1 mm średnicy) w kwarcu. Elektrum cechuje zmienna zawartość srebra, od 19,7 do 46,9% wag. W profilu otworu wyraźnie zaznacza się pozytywna korelacja ztota z arsenem, ołowiem i miedzią, a także z wysokimi koncentracjami cynku. W strefach złotonośnych oprócz sylifikacji stwierdzono epidotyzację, chlorytyzację oraz kalcytyzację skał klastycznych. Obecność intruzji granodiorytowej w pobliżu otworu oraz licznych górnokarbońsko-dolnopermskich dajek skał magmowych - dacytów, diabazów i andezytów, przecinających strukturalnie zdeformowane metasedymenty ediakaru, wskazuje na związek mineralizacji złotonośnej z rozwojem późnowaryscyjskich pomagmowych procesów hydrotermalnych w strefach oddziaływania intruzji i aktywności tektonicznej.

EN

Recent Polish Geological Institute investigations of the DB-4 drillhole cores from Będkowska Valley (southern part of Małopolska block) documented occurrence of gold in grey-greenish and brown Ediacaran metasedimentary rocks. Elevated concentrations of gold (up to 15 ppm) have been revealed in isolated samples from several intervals, mostly at depths of 253.0 and 584.5 m. Numerous quartz veinlets (up to 10 cm thick), quartz-sulphide and carbonate veinlets occur within those intervals. Gold-bearing mineralization coexists with pyrite and sphalerite veinings and impregnations in association with galena, chalcopyrite and minor arsenopyrite. Gold and electrum occur in a form of inclusions in pyrite, sphalerite-galena veinlets (which crosscut pyrite), and as fine-grained exsolutions(<0.1 mm in size) in quartz. Electrum is characterized by variable contents of silver, in a range from 19.7 to 46.9 wt %. In DB-4 profile, gold shows a positive correlation with arsenic, lead, copper, and zinc. Gold-hosted rocks display silification, epidotization, chloritization and calcitization. Granodiorite intrusion in the vicinity of drillhole and numerous intrusion-related Upper Carboniferous-Lower Permian dacite, diabase and andesite dikes which cut across the Ediacaran structurally-deformed metasediments implies that the formation of gold-bearing mineralization may relate to evolution of late-Variscan postmagmatic hydrothermal processes in zones affected by magmatic and tectonic activity.