Petrologic characteristics and Rb-Sr age dating of lamprophyre dikes of Tsagaan Tsahir Uul gold deposit, Mongolia

Abstract

Geochemical, mineralogical and geochronological investigations have been carried out on the lamprophyre dike in the Tsagaan Tsahir Uul gold deposit area, Bayankhongor, Central Mongolia. The lamprophyre is composed of olivine, amphibole, and clinopyroxene as phenocrysts with plagioclase, potassium feldspar, biotite, and amphibole as the groundmass. The amphibole is mostly pargasite; some grains are rich in titanium and constitute kaersutite. Pyroxene is slightly enriched in titanium. Although the olivine ranges from Fo 92.9 to Fo 84.6 , a distinct compositional variation between the core and rim in a single grain is lacking. Mineral assemblage and chemical characteristics are close to those of calc alkaline lamprophyres (CALs). An Al 2 O 3 versus TiO 2 tectonic discrimination diagram of the shoshonitic and potassic igneous rock shows that the Tsagaan Tsahir Uul lamprophyre might have originated within an intra plate tectonic setting. The high Ti content of the lamprophyre also suggests that the magma could have originated in an intra continental tectonic setting. Small but similar intrusions emplaced during the Permian period are spatially and temporally associated with the main gold and copper mineralization in the Bayankhongor metallogenic belt. The obtained age of the lamprophyre dike (248.61 ± 18.5 Ma) demonstrates that its intrusion was a contemporary event. This was the youngest plutonic body in the Tsagaan Tsahir Uul area, which is close in age to the gold bearing quartz veins. Although there is no direct genetic evidence associating the auriferous veins and the lamprophyre in the field, they occur together and possibly share a similar tectonic setting.

Dioritic intrusions of the Slavkovský les (Kaiserwald), Western Bohemia: their origin and significance in late Variscan granitoid magmatism

“…This anomaly is strongly negative in the dioritic intrusions. CAL (Jargalan et al 2007) as a mafic end member shows the best overlap with the dioritic intrusions except of some REE (Eu, Yb). Thus, a mafic magma of calc-alkaline lamprophyre composition seems to be the most likely parental magma for the dioritic intrusions in the Slavkovský les.…”

“…SAB continental sodic-alcali basalt (Kelemen et al 2004). CAL calc-alkline lamprophyre, selected samples under 50% SiO 2 (Jargalan et al 2007). GR granite OIC (Kováříková et al 2007) it has a cumulate character.…”

“…plagioclase (20%) (black/white lines) and fractional crystallization after mixing (black/grey lines). The models are calculated for three different mafic end members a calc-alkaline lamprophyre (Jargalan et al 2007); b sodic-alkali basalt (Kelemen et al 2004); c ocean island basalt (BVSP 1981). Average OIC granite was used as felsic end member in all cases were subsequently used by voluminous granitic magmas during the repeated late Variscan magmatic activity.…”

“…This sample has high amounts of Cr, Ni, Co and low contents of incompatible elements, especially Ba and Sr. Higher content of Rb and Cs in this sample is probably caused by secondary enrichment. We used three different enriched mantle-derived magmas reported in the literature as mafic end members to document the differences between various sources and to select the most suitable one: (a) calc-alkaline lamprophyre from Mongolia (CAL; Jargalan et al 2007); (b) continental sodic-alkali basalt from Turkey (SAB; Kelemen et al 2004); (c) Hawaian ocean island basalts [OIB; Basaltic Volcanism Study Project (BVSP) 1981]. For the calculation, we used average values of basalts and lamprophyres with an SiO 2 content that is lower than in dioritic intrusions (Table 6).…”

EARLY MESOZOIC LAMPROITES AND MONZONITOIDS OF SOUTHEASTERN GORNY ALTAI: GEOCHEMISTRY, Sr-Nd ISOTOPE COMPOSITION, AND SOURCES OF MELTS

“…Многочисленные K-Ar датировки, выполненные в 60-70-х годах ХХ столетия, демонстрируют широкий спектр возрастов, соответствующих среднему триасу-ранней юре (~ 230-169 млн лет) [Оболенская, 1971]. Более поздние результаты Ar-Ar, Rb-Sr и U-Pb датирования позволили существенно «сузить» возрастные рамки становления комплекса (~ 250-234 млн лет, ранний-средний триас) [Борисенко и др., 2003, 2010Врублевский и др., 2004;Jargalan et al, 2007;Павлова и др., 2008;Васюкова и др., 2011]. Предполагается, что наблюдаемый возрастной интервал может указывать на двухэтапное (250-242 и 237-234 млн л.н.)…”