Petrogenesis of Karamaili alkaline A-type granites from East Junggar, Xinjiang (NW China) and their relationship with tin mineralization

Abstract

Several types of granites including alkaline granites and alkali feldspar granites are distributed in the Karamaili tectonic belt of East Junggar, Xinjiang, China. Some medium-small tin deposits are located within or near the contact zones of the granitic intrusions. The alkaline granites share all the features commonly observed in peralkaline A-type granites. They contain alkalic mafic minerals such as riebeckite and aegirine; have high contents of SiO 2 , alkalis, Rb, Th, Zr, Hf, REE (except Eu), and high ratios of FeO*/MgO and Ga/Al; and show strong depletions in Ba, Sr, Eu in the spidergrams. Laser ablation-ICPMS U-Pb zircon geochronology indicates a crystallization age of ca. 305 Ma for the granites; TIMS analyses of the granites found high ε Nd (T) values of +5.9 to +6.5. Considering their geochemical features, alkaline granites most likely formed by fractional crystallization of granodioritic magmas, which were probably produced by partial melting of lower crustal basaltic to andesitic rocks formed from oceanic crustal materials that were deeply buried during late Paleozoic subduction and accretion. Six molybdenite samples from the Sareshike tin deposit in East Junggar yielded an isochron age of 307 ± 11 Ma (2σ) and a weighted mean model age of 306.5 ± 3.4 Ma, consistent with zircon U-Pb ages of the alkaline granites. Low Re contents (0.323-0.961 ppm) in the molybdenite suggest that they originated from crustal sources related to the alkaline granites. Considering their identical ages, close spatial distribution, and similar sources, we argue that the A-type granites have a genetic relationship with the tin mineralization, and that the same association may be important elsewhere.

Zircon U-Pb and Hf isotopes of volcanic rocks from the Batamayineishan Formation in the eastern Junggar Basin

“…The interval covers late Proterozoic to early Paleozoic [61], and late Paleozoic [5]. Through contrasting geochemical features between the basalts and granitoids of the late Carboniferous in the Junggar area, and combining these observations with previous investigations [3,9,22], it can be regarded that the granitoids were generated by partial melting of juvenile basement rocks, which were triggered by the upwelling of the asthenosphere. Conversely, the basaltic magmas were emplaced at the same time as the granitoids, and were derived from partial melting of deep asthenospheric mantle or depleted lithospheric mantle.…”

“…This idea is supported by the granitoids on the east and west sides of the Junggar Basin. Granitoids with high ε Nd (t) values apparently were not melting products of mantle-derived ultramafic rocks, but most likely generated by partial melting of juvenile basic-intermediate crustal materials [2,3,22]. Although some scholars have reported Precambrian or even Archean magmatic zircons from the igneous and sedimentary rocks around the Junggar area [36,44,54,55], which could be interpreted to indicate the existence of Precambrian crystalline rocks, further investigation is needed to identify where these old zircons came from, and how they were incorporated into the Paleozoic rocks.…”

“…However, limited agreement has been reached regarding its formation because of its complicated tectonic evolution and intense magmatic activities, and many important issues remain controversial. Han et al [1] suggested that the basement of the Junggar Basin is dominated by underplated mantle-derived basic rocks gauging from the high ε Nd (t) values of regional granitoids, whereas Chen and Arakawa [2] and Su et al [3] argued for a basement origin of Paleozoic remnant oceanic crust and arc complex. The reason for this discrepancy is mainly because of the poor exposure of basement rocks around or within the basin.…”

Tin isotope analysis of cassiterites from Southeastern and Eastern Asia

“…In contrast, SPEX2 was used to evaluate the performance of column chemistry using TRU resin, in which the sample solution was first introduced into the column as 0.5M HCl. SPEX1, dissolved in HNO 3 and HF, was not used for this purpose because conversion to the chloride form requires evapo- Imai et al (1972), 2) Haraguchi and Kikuchi (1952), 3) Shibata and Ishihara (1974), 4) Nagahara (1978), 5) Park and MacDiarmid (1964), 6) Tanaka et al (1971) Ikeda et al (1983), 9) Council of Underground Resources Development (1956), 10) Adachi (1997), 11) Shibata (1939), 12) Shibata et al (1962), 13) Suzuki et al (1994), 14) Ishihara and Wu (2001), 15) Su et al (2007), 16) Tang et al (2007), 17) Tang et al (2009), 18) Chen et al (1999), 19) Zhang et al (2007), 20) Wang (1983), 21) Qin et al (2006), 22) Chen et al (1992), 23) Li (1988), 24) Xu and Zhu (1988), 25) …”

Sr, Nd and O isotopic characters of quartz syenite in the Weiya magmatic complex from eastern Tianshan in NW China: Melting of the thickened juvenile lower crust

“…This belt seems to be one of the most important sites of juvenile crustal formation in the Phanerozoic . The juvenile nature is characterised by positive to around zero ε Nd (t) values and low initial Sr isotopic ratios of many Paleozoic granitoid plutons in the CAOB, such as those in Russian Transbaikalia (Wickham et al, 1996;Kovalenko et al, 2004), Kazakhstan (Heinhorst et al, 2000), northern Xinjiang (NW China, Han et al, 1997;Hu et al, 2000;Jahn et al, 2000;Jahn, 2002, 2004;Chen and Arakawa, 2005;Su et al, 2007;Zhao et al, 2008;, northern Inner Mongolia (N China, Chen et Shi et al, 1999;Zhou et al, 2004); KHF, Kumix-Hongliuhe Fault;ASF, Aqqikkudug-Shaquanzi Fault;KF, Kangguer Fault;Indosinian intrusive names: TH, Tianhu biotite granite (220 Ma, Li et al, 2005); WY, Weiya complex (246-233 Ma, Zhang et al, 2005a); NY, North Yamansu biotie granite (227.9 Ma, Lei et al, 2010). Insert (modified from Chung et al, 2004) Shu et al, 2004b).…”