Paragneiss

paragneiss

[′par·ə‚nīs]
(geology)
A gneiss showing a sedimentary parentage.

Paragneiss

 

a metamorphic rock formed in the earth’s crust from sedimentary rocks (sandstones and argillaceous schists) that recrystallized in the deep zones of the earth’s crust in an amphibolite facies of metamorphism. Paragneiss consists of quartz and feldspars with admixtures of other minerals, typically andalusite, sillimanite, disthen, staurolite, cordierite, and tourmaline. The varieties of paragneiss are distinguished according to the admixture content. A certain excess of alumina, caused by the content of clay material in the primary sediments, is typical of paragneiss. In contrast to paragneiss, orthogneiss is formed through transformation of magmatic rocks.

References in periodicals archive ?
The host rocks at Patrie are orthogneiss, amphibolites and paragneiss. It is this unique geological setting that attracted Sphinx to the Patrie project.
The Sioule metamorphic series is composed by three lithostructural units, which are from top to bottom [34]: (i) an upper unit of cordierite-bearing migmatite and biotite-sillimanite gneiss, corresponding to the UGU; (ii) an intermediate unit composed by biotite-muscovite paragneiss, corresponding to the LGU; and (iii) a lower unit formed by biotite-muscovite micaschists, which is correlated with the PAU.
The Charles Prospect is a 1-km-long gold prospect hosted in biotite-rich paragneiss with quartz veins and up to 15% sulphides (pyrite, pyrrhotite), marked by several high-grade grab samples (up to 42.34 g/t Au).
U-Pb age and Lu-Hf Isotope Systematics of Detrital Zircons from Paragneiss of the Bulun Block (Sharyzhalgai Uplift of the Siberian Craton Basement).
(1990) the high-grade metamorphic rocks in both the Chuggin Road and Lime Hill units include biotite, bioitite-cordierite, and sillimanite-bearing paragneiss, migmatitic paragneiss, marble, quartzite, amphibolite, and tonalitic orthogneiss.
In the study area lithological units is outcrops the second to fourth periods, which from old to new are as follows: phyllite, ouartzite, paragneiss, marble, shell, sandstone with tufa, volcanic rocks, crystalline limestone locally with fosolina, metamorphic volcanic and tufa, cherty limestone, phyllite, metamorphic quartzarenite, micaschist, metadolomite, amphibolite, limestone, shale and sandstone, schist hornfels, orthogneiss, granodiorite, oput rock, shale and phyllite sandstone, granite, granodiorite, diorite, dolomitic lime, radiolarit breccia, rodist lime, orbitoline, radiolarat, black and blue marl with limestone, alluvium.
The main rocks composing the massif in the profile zone are paragneiss, metabasite and their interbedding, granite and metasedimentary rocks.
This paragneiss has a metamorphic age obtained by U-Pb SHRIMP from zircon rims of ~ 472 Ma (Pankhurst et al., 2006).
On slopes with crystalline shists, gneiss, paragneiss in composition appears geomorphological processes of lateral erosion in Valsan catchment, rill wash on slopes with medium values, creeping on steep slopes; tumble down on rocky slopes and landslides on slopes with medium values with consistent layers of depositions.
3) contains a calcite marble horizon, roughly 2 km long by < 10 m wide, intercalated in a sequence of mafic metavolcanic rocks and paragneiss. The marble has returned highly anomalous values of light rare-earth-elements (La, Ce, Nd), which locally reach 1.59% [(REE).sub.2] [O.sub.3] (Lataille showing; Madore et al.
Cal Graphite holds a 100% interest in mining claims in the township of Butt, near Huntsville, where crystalline flake graphite occurs in mafic gneiss and paragneiss. An open-pit mine and a processing plant with an initial milling capacity of 3,000 t/d ore, which could be expanded to 5,000 t/d, was completed during the year and production started during October.
Copper mineralization at Mythril is hosted in a variably altered, foliated granodiorite intrusion, previously interpreted as a quartz-feldspar paragneiss based on limited outcrop exposures.