The Chemistry of Quartz in Granitic Pegmatites of Southern Norway: Petrogenetic and Economic Implicationsстатья из журнала
Аннотация: Trace element concentrations in quartz from 188 granitic pegmatites in the Froland and Evje-Iveland pegmatite fields, southern Norway, have been determined to establish exploration targets for high-purity quartz (HPQ) and to gain a better understanding of the genesis of pegmatites hosting HPQ deposits.Both pegmatite fields were formed during the Sveconorwegian (Grenvillian) orogeny (1145 to 900 Ma) at the western margin of the Fennoscandian Shield.In situ raster analyses within single quartz crystals were undertaken by laser ablation inductively coupled plasma mass spectrometry (spot size 75 µm) to assess levels of latticebound impurities, rather than mineral and fluid inclusions which are relatively easily removed during HPQ processing.Quartz in the Froland pegmatites has relatively pure and homogeneous compositions containing 46±24 µgg -1 Al, 8±3 µgg -1 Ti, 1.4±0.8µgg -1 Ge, and 11±7 µgg -1 Li.The Ti-in-quartz geothermobarometer gives an average pegmatite crystallisation temperature of 537±39 °C.Temperatures estimates are highest along the NW margin of the pegmatite field (>550°C), whereas the most differentiated pegmatites occur towards the NE.The area of greatest economic potential for HPQ lies just north of the central part of the field where individual pegmatites contain >1 Mt quartz with low average trace element contents of 67±11 µgg -1 .From mineral-chemical criteria, and a range of other geological factors, we propose that pegmatite melts in the Froland field were generated by fluid-present crustal melting at about 1060 Ma, in zones of localized high-strain deformation during progressive thrusting along the Porsgrunn-Kristiansand Fault Zone (PKFZ).Quartz in the Evje-Iveland pegmatites has more variable compositions with 69±57 µgg - 1 Al, 19±11 µgg -1 Ti, 2.3±1.8µgg -1 Ge, and 7±5 µgg -1 Li.From its Ti content, it crystallised at temperatures of 613±70°C.The regional spatial distribution of Ti-in-quartz temperatures appears irregular mainly due to the scattered distributions of chemical evolved pegmatites with "amazonite"-"cleavelandite" replacement zones which show crystallization temperatures down to 442 °C.Quartz from the Evje-Iveland pegmatites is unlikely to be of current economic interest due to its moderate to high trace element contents, heterogeneous chemistry and low volume.The Evje-Iveland pegmatites show no apparent genetic link to a granite intrusion.Instead they probably formed as a result of partial melting at depth of their amphibolite country rocks at around 910 Ma.This is related to a regional low-pressure/hightemperature metamorphic event at about 930-920 Ma.
Год издания: 2015
Авторы: Axel Müller, Peter M. Ihlen, Ben Snook, Rune Larsen, Belinda Flem, Bernard Bingen, Ben J. Williamson
Источник: Economic Geology
Ключевые слова: Geological and Geochemical Analysis, Geology and Paleoclimatology Research, earthquake and tectonic studies
Другие ссылки: Economic Geology (HTML)
Open Research Exeter (University of Exeter) (PDF)
Open Research Exeter (University of Exeter) (HTML)
Open Research Exeter (University of Exeter) (PDF)
Open Research Exeter (University of Exeter) (HTML)
Открытый доступ: green
Том: 110
Выпуск: 7
Страницы: 1737–1757