GEOLOGY

The gabbro-diabase massif of Nowa Ruda is a small geological unit in the Central Sudetes, built of several types of igneous rocks, mainly varieties of gabbro and diabases. It runs NNW to SSE, covering an elongated area of approx.15 km2 between Nowa Ruda and the surrounding area of ​​Bożkow, for a distance of about 9 km. Two small isolated occurrences of gabbro south of Sokolec and serpentinite in the Przygórze surrounding area, belongs geologically to the same unit. Modern-day it is believed that all massifs of mafic/ultramafic rocks in the vicinity of Góry Sowie (eng. Owl Mountains, germ. Eulengebirge), the oldest part of the Sudetes and one of the oldest in Europe, form together one unit called the Sudetes Ophiolite. It includes massifs: Mt.Ślęża, Gogołów-Jordanów, Nowa Ruda, Braszowice-Brzeźnica and Szklary. Parts of Sudetes Ophiolite consists of peridotite, pyroxenite, troctolite are elements of the upper mantle series. All overlying gabbro varieties, diabases, basaltoid veins and basaltic pillow lava representing remains of the seafloor.
The Nowa Ruda Massif shows a significant variation of mafic rocks, of which two main zones have been identified: the northern, built of gabbro and the southern, built of the diabase. From the south, the diabase is surrounded by a series of weakly metamorphosed rocks, mainly sandstone and phyllite, often with quartz lenses, probably of the Devonian age (Kłodzko Metamorphic Complex). From the north and east, the Massif is surrounded by the Lower Permian sediments (Rotliegendes), in the south-eastern part with small vulcanite intrusions. The western part of the massif surface is occupied by the Upper Carboniferous sediments, building the Nowa Ruda syncline, that belongs to the north-eastern, Polish part of the Permo-Carboniferous Intra-Sudetic Basin. During the Carboniferous, on the western slope of the Massif intensive weathering processes took place, combined with local sedimentation, leading to a creation of markedly diversified morphology on the surface. A series of smaller, sedimentary basins of erosive origin were formed, with local material from gabbro or diabase in conglomerates. In the south in the area of Bożków, gabbro, diabase and amphibolite rocks are also mentioned as
conglomerate components. The volume of these sediments differs. On the elevations separating the basins they are often missing, whereas in the central parts of the depressions the thickness can reach more than 20m. Above are red (and less often gray) shales named argilites. The range of argilites in the Słupec basin is much smaller than in the Nowa Ruda basin, maximum thickness of argilites does not seem to exceed several metres. Directly on them, the Nowa Ruda coal basin of industrial importance occurs in the Silesian series (Namurian A, Westphalian A and B layers), formed in several smaller sedimentation basins created on both sides of Massif (Miłków, Nowa Ruda, Nowy Dzikowiec, Słupiec).

The Nowa Ruda massif has repeatedly been elevated and sunk. The oldest elevation was the lower Devonian period. From that time until the beginning of the Westphalian, the whole structure constituted the land, opposed to the area located to the east of it, where marine sedimentation of the Upper Devonian and Kulm (Central European Dinantium) took place. In the old quarry of the upper Devonian limestone in Dzikowiec, conglomerates with ingredients of gabbro were found, which contradicts the age marked by the method Sm / Nd - 351 ± 16 Ma ( and 353 ± 21 Ma for Mt. Ślęża).

PETROGRAPHY

In the northern part of Nowa Ruda Massif, there are coarse-grained rocks, representing the deepest levels of magma solidification turning in the centre to finer grained. The oldest part created by peridotite, pyroxenite and troctolite occurs only in the Wolibórz-Przygórze area. The characteristic feature of the rocks of this region is the local stratification, manifested by the occurrence of parts clearly enriched with dark minerals and their opposite, nearly monomineral plagioclase zones, which together with the structures typical for plutonic rocks proves crystallisation in situ with the absence of any disturbance. Subsequently, the olivine-gabbro was created in the area of Nowa Ruda, turning into a non-olivine gabbro of Slupiec/Dzikowiec, in which there also appears a lamprobolite in augite, demonstrating the change of crystallization to the conditions more close to the surface. The last stage was the creation of a diabase in the southern part, the product of the fast solidification of magma in relatively shallow zones. The contact between gabbro and diabase is a several dozen-metres strip of mylonite, perfectly visible in the working quarry Słupiec. There is no proof of the similar age of gabbro-series and the diabase.

Overiew of rocks:

Olivine-gabbro - also called 'black gabbro', contains labradorite with 65-69% on anorthite (without iridescent optical effect), diallage, olivine, bronzite.

Gabbro - also called 'non-olivine-gabbro' or 'green gabbro'; contains labradorite with 50-60% on anorthite, diallage, ferrosilite (ferrohypersthene) and basaltic hornblende (lamprobolite).

Troctolite (in Poland also as 'pstrągowiec') - mostly on the Kmiotek Hill in Wolibórz, contains labradorite-bytownite series creating fine-grained masses in which olivine crystals are stuck, and an accessory diallage and hypersthene.

Anorthosite - sometimes called 'Plagioclasite' occurring locally, nearly monomineralic rock contains mostly plagioclase with 67-75% of anorthite, with the addition of diallage and an accessory apatite.

Peridotite - variously named depending on the author (also diallage-peridotite, olivine-pyroxenite, wehrlite), create melanocratic masses in the troctolites, composed of strongly transformed olivines, diallage and an accessory hypersthene.

Lamprophyre - hornblende, diallage, K-feldspar, (also mentioned kersantite and spessartite)

Diabase - fine grained to aphanitic equivalent to diallage gabbro

'Gabbro Pegmatites' - post-magmatic and metasomatic-hydrothermal origin contains labradorite-bytownite series, augite, hornblende, olivine, biotite, ilmenite

Gabbro aplites - labradorite, albite, K-feldspar, hornblende, zircon, titanite, apatite

Mylonite - in the tectonic zone exposed in Słupiec quarry excavation, with relics of primary minerals (labadorite, diallage) in conjunction with the cataclasis and total obliteration of the original composition and abundance of secondary minerals, locally with pyrite.

In all types of gabbro-diabase rock, dispersed ore mineralization occurs. The most common are Fe-Ti oxides resulting from the breakdown of solid solutions existing at high temperatures between magnetite - ilmenite - ulvöspinel and ilmenite - hematite. This mineralization is accompanied by dispersed sulphide mineralization with pyrrhotite, chalcopyrite, sphalerite. In olivine-gabbros and troctolites also with pentlandite. Sometimes automorphic pyrites are locally found in euhedral cubes of up to 1 cm edges.

HYDROTHERMAL MINERALISATION

In the period before the end of World War II, when this part of Silesia belonged to Germany, there were several works mentioning the occurrence of hydrothermal mineralization. Mostly, they concerned the Carboniferous rocks, made available by numerous mine and adits. In the rocks of the massif, only the occurrence of veins with chrysotile in troctolites are mentioned. In the kersantite from the hill near Wolibórz, a quartz veins with members of the dolomite-ankerite series, calcite and chalcopyrite was found, in paragenesis typical for Upper-Carboniferous series.
Intensive mining exploitation of this region, primarily between 1960s and 1980s, allowed to reach many rock series, previously inaccessible, as a result of which hydrothermal minerals were repeatedly encountered. It seems that the oldest paragenesis is calcite - epidote - chlorite - albite - quartz, but predominatly almost monomineral quartz veins were mentioned, reaching up to several metres. They are not prolonged in the above lying Carboniferous rocks, ending in the weathered gabbro. Also often quartz-calcite veins occur, sometimes with sulphide mineralization, monomineral calcite veins and lenses, as well with prehnite and zeolites: stilbite-Ca, chabasite, scolecite, laumontite and analcime. The peculiarities of the massif are the milky or pinkish white, fibrous calcite veins, which are pseudomorph after chrysotile.

Common hydrothermal mineralisation in Upper-Carboniferous series continue into the older rocks, mostly in the areas of sedimentary basins with argillite complex, created on the surface of gabbro-diabase. Minerals of that origin are dolomite-ankerite, barite, calcite, anhydrite, sulphides - pyrite, marcasite, sphalerite, chalcopyrite, galena, millerite, bornite, chalcocite, covellite, also hematite, goethite, malachite. Mineral fluides, interacting with the gabbro components, leads to the formation of prehnite and zeolites. As a great rarity millerite needles up to 3 mm length in prehnite was found in Słupiec, within hydrothermal vein in gabbro.

[K.Andrzejewski, March 2018]

Localities in this Region

Other Regions, Features and Areas that Intersect

References