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Mineralogical and geochemical evidence for two-stage silicification of serpentinized peridotites from the Szklary Massif (NE Bohemian Massif)

Cieślik Błażej, Kierczak Jakub, Pietranik Anna

Mineralogia

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2022

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Vol. 53, iss. 1

20--35

EN

Previously unknown exposures of silicified serpentinites have been documented within the Szklary Massif, which is a fragment of the tectonically dismembered Central Sudetic Ophiolite (NE Bohemian Massif). On the basis of textural, mineralogical and chemical differences, two types of silicified serpentinites have been distinguished in this study (Type I and Type II). Type I is characterized by well-preserved primary minerals cut by numerous veinlets filled with microscale euhedral quartz crystals. Studied samples of Type I are enriched in silica (from 62 to 69 wt.% SiO2) and depleted in magnesium (from 10 to 19 wt.% MgO) in comparison to serpentinized peridotites from the Szklary Massif. Type II is almost exclusively composed of amorphous or poorly crystalline silica, with microquartz aggregates being the most abundant form. Silicified serpentinites of Type II show extremely high values of silica (from 83 to 90 wt.% SiO2) and low magnesium concentrations (from 4 to 8 wt.% MgO). Both types of silicified serpentinites have elevated content of REE and many other trace elements generally regarded as incompatible. We infer that the earlier silicification event was caused by the percolation of Si-rich hydrothermal fluids derived from igneous rocks, which intruded this area from ca. 380 to 330 Ma. A subsequent silicification event is the result of silica remobilization during intense chemical weathering under tropical conditions, which could have occurred between Late Cretaceous and Miocene.

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Geologiczny profil ociosów historycznych wyrobisk podziemnej trasy edukacyjnej w Szklarach

Kaczan W.

Hereditas Minariorum

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2017

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Vol. 4

231--240

PL

W sztolni „Robert”, będącej częścią dawnej kopalni niklu w Szklarach sporządzone zostały szkice terenowe ociosów wyrobisk oraz pobrano próbki skalne. Na podstawie obserwacji przeciętych i wyszlifowanych powierzchni próbek, przeprowadzonych makroskopowo i z wykorzystaniem mikroskopu stereoskopowego wykonano uproszczone opisy petrograficzne skał. Efektem powyższych działań są geologiczne profile ociosów podparte opisem sytuacji geologicznej w sztolni. W sprawozdaniu zawarto także zdjęcia najbardziej interesujących fragmentów wyrobisk obiektu.

EN

Geological profiling of side walls has been done in “Robert” adit, which is a part of historical nickel mine in Szklary-Huta (SW Poland). Creating the field sketches and collecting the rock samples combined with stereo microscopic analysis made it possible to draw geological profiles of side walls. The report includes macroscopic description of rock samples, fragments of geological profiles of side walls and photos of the most interesting geological objects in Underground Education Route in Szklary.

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Pokrywa zwietrzelinowa masywu Szklar i jej niklonośność [The Szklary massif nickel-bearing weathering cover]

Niśkiewicz J.

Geologia Sudetica

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2000

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Vol. 33, nr 2

107-130

EN

The thickness of the weathering cover on the Szklary Massif ranges from zero (no cover) to 76 metres. The weathered rock forms troughs and sinks of different shapes and depths. Its form indicates that a fissure network played an important role in the evolution of the weathering processes. The fissures allowed the weathering processes to penetrate deeply. The weathering cover is composed of alteration products of three rock varieties: serpentinites, metamorphic and magmatic rocks. The author distinguished 9 varieties of serpentinite, 6 varieties of metamorphic rock and 3 varieties of magmatic rock weathering covers. The thickness of these covers ranges from several cm to 47.9 metres. The weathering cover types of the three different rock varieties generally have sharp boundaries, while within a given rock variety, the weathering cover types have boundaries which, as a rule, are poorly expressed. The nickel in the weathered rocks of the Szklary massif is genetically related to serpentinite rocks containing from 0.18 to 0.28 wt % Ni. The largest nickel concentration occurs in the weathering cover of the central area, at Mount Szklana Góra. The serpentinite weathering covers are the main centre of nickel concentration, while the metamorphic and magmatic rock weathering covers have higher nickel contents where they are in contact with the serpentinite weathering covers, or if they were within the scope of activity of local nickel-bearing weathering solutions.

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Heavy minerals in the serpentinite weathering cover of the Szklary massif

Sachanbiński M., Piórewicz R., Michalin R.

Geologia Sudetica

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2000

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Vol. 33, nr 2

131-141

EN

Forty minerals were identified belonging to the heavy mineral (d > 2.98 g/cm3) suite of the Szklary massif. They are: actinolite, almandine, anthophyllite, apatite, biotite, brunsvigite, chlorite, chromite, chrysolite, zircon, enstatite, epidote, ferroplatinum, goethite, haematite, hornblende, clinochlore, leucoxene, magnesioferrite, magnetite, magnesite, molibdenite, monacite, muscovite, niggliite (PtSn), olivine, orthopyroxenes, an osmium-bearing phase (Ba2CaOsO6), native palladium, pyrope, native platinum, pleonaste, rutile, native silver, talc, tremolite, trevorite, tourmaline, native gold and zoisite. The mineralogical characteristics of the most common phases are presented in this paper, and three paragenetic groups of heavy minerals are distinguished.

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Gold in the serpentinite weathering cover of the Szklary massif, Fore-Sudetic Block, SW Poland

Michalin R.

Geologia Sudetica

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2000

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Vol. 33, nr 2

143-150

EN

he average gold content in the serpentinite and weathered serpentinite rocks of the Szklary massif (20 samples from the surface and 38 samples from boreholes) is about 4.97 ppb; for the individual rock types: 0.72 ppb for the fresh serpentinite, 3.83 ppb for the weathered serpentinite, and 2.59 ppb for the serpentinite residual soil. The highest gold content was recorded for the talc-rich rocks - 27.84 ppb, while the chalcedony veins accompanying the weathered serpentinite rocks contain 12.03 ppb. The gold distribution in the serpentinite weathering cover has characteristics typical of gold migration in laterite debris. The increased gold content often associated with the lithological boundaries and with the water-table level has a clear connection with a higher content of other elements, such as Cu, As, Sb, Ni and Zn. However, elevated gold content in the chalcedony veins was not observed to be related to an increase in the amount of chalcophile metals. The native gold in the serpentinite weathering cover usually forms separate irregular blades up to 0.2 mm long, which are isolated or, rarely associated with oxides (chromite, magnetite) and silicates (enstatite, tremolite, anthophyllite). The narrow rims of gold around the rock-forming minerals indicate its secondary nature. The gold bearing phase (Au+Sb+Cu) was also identified, occurring as rare fine grains up to 10 micrometres in length.