Saussurite

Abstract: Results of 40Ar/39Ar step heating for muscovite, potassium feldspar, and plagioclase from the ca. 1240 Ma Elzevir trondhjemite in the Central Metasedimentary Belt of the Canadian Grenville Province have been combined with earlier data and used to deduce a thermal history for the eastern Elzevir terrane following the Ottawan orogeny (1050–950 Ma). Muscovite yielded precise plateau dates of ca. 900 Ma, whereas the potassium feldspar displayed disturbed age spectra with ca. 730–760 Ma dates for broad "plateau" regions. This age difference could be explained by slow cooling or by thermal overprinting at 760–800 Ma that has updated the microcline. The plagioclase spectra provide evidence for a low-temperature hydrothermal event ca. 380 Ma ago that has generated sericite in saussurite and has caused partial argon loss from the microcline. This result agrees with the other plagioclase thermochronometry and paleomagnetism on the Cordova gabbro 25 km to the west but provides a lower estimate for the upper age brac...

Abstract: The Shagari Bala area lies in the Skardu district of Gilgit-Baltistan province. It is located within the Kohistan-Ladakh island arc on the east side of Nanga Parbat Haramosh massif. Deosai volcanics and the meta-volcanics of the Burji-La Formation, mainly exposed in the study area are the focus of this study. The Deosai volcanics are partially to highly altered porphyrictic rocks while the meta-volcanics of the Burji-La Formation are metamorphosed to greenschist facies. The Deosai volcanics also have suldes-bearing mineralized altered zones which exhibit leaching of chalcopyrite and pyrite to malachite, azurite and limonite. The petrographic studies show that the Deosai volcanics have porphyritic texture and mainly comprised of plagioclase and hornblende phenocrysts. Plagioclase phenocrysts are generally partially altered but the completely altered phenocrysts are also not common. Hornblende phenocrysts are usually replaced by chlorite and epidote. Phenocrysts of plagioclase and hornblende along with alkali feldspar, quartz and ores are embedded in felsophyric groundmass. The feldspar phenocrysts and the groundmass are generally altered to kaolinite, sericite and saussurite. The meta-volcanics of the Burji-La Formation consists of amphibole (mainly tremolite/actinolite with lesser amount of hornblende), plagioclase, epidote, alkali-feldspar, chlorite and ores. Epidote and chlorite are the alteration products of hornblende while kaolinite, sericite and saussurite are the alteration product of feldspar. The gain and loss in gold, silver and base metals in the hydrothermally altered suldes-bearing mineralized altered zone have been evaluated on the basis of enrichment and depletion factors. Multifold enrichment of Au, Ag and Cu are found in these zones. However, this enrichment is not of economic importance. The geochemical studies show that the Deosai volcanics are dacite to rhyodacite in composition while the meta-volcanics of Burji-La Formation show basalt to basaltic-andesite in composition. The spider diagrams of both Deosai volcanics and the meta-volcanics of the Burji-La Formation exhibit enrichment of large ion lithophile elements as compared to high eld strength elements while well-dened negative and positive anomalies have been observed for Nb and Sr respectively. The major and trace elements data of Deosai volanics and the meta-volcanics of the Burji-La Formation were evaluated for identifying the paleotectonic environment of their formation. It has been noticed that the studied volcanics are of calcalkaline character which have been originated in the island arc type of setting mainly involving subduction related magmatism.

Abstract: A fine network of aplites, pegmatites, and veins, together with partially assimilated granitic xenoliths, reveals the progress of differentiation within a set of lamprophyric dikes. First, intratelluric augite and biotite were replaced by pargasite, with simultaneous precipitation of more pargasite and of intermediate plagioclase and saussurite. These were followed by albite as aplite, by microcline and muscovite as micropegmatite, and by epidote and calcite as veins. A quantitative analysis shows that the dike rock corresponds to Camptonose III.I.5.3.4, and suggests that the average amphibole is low in lime and perhaps high in potash.