Dayu Zhang

Genesis of late carboniferous granitoid intrusions in the Dayinsu area, West Junggar, Northwest China: evidence of an arc setting for the western CAOB

ABSTRACT The Dayinsu area is located in the northern part of the West Junggar district near the border between China and Kazakhstan and is an important component of the Central Asian Orogenic Belt (CAOB). The Dayinsu area hosts numerous granitoid plutons in Devonian–Carboniferous volcano–sedimentary strata. The older Laodayinsu and Kubei (345–330 Ma) plutons are located in the west with the younger Bayimuzha and Qianfeng (330–325 Ma) plutons in the east. The whole-rock SiO2 contents of the four granitoid plutons range from 52.22 to 68.42 wt.% and total alkaline contents (K2O + Na2O) range from 4.94 to 9.16 wt.%. The granites are enriched in large ion lithophile elements and light rare earth elements with depletions in Nb, Ta, Ce, Pr, P, and Ti. The plutons are metaluminous with I-type signatures. The geochemistry of the intrusions suggests that they formed in a subduction zone setting, and subsequently underwent fractional crystallization during emplacement, with higher degrees of fractionation in the eastern sector than in the west. Similarities in the geochronology and geochemical characteristics of the granitoid plutons in Dayinsu to those in the Tabei district (west to Dayinsu area) suggest that both districts are part of the Carboniferous Tarbagatay Mountain intrusive event. The early Carboniferous (345–324 Ma) granitoid intrusions in the Tarbagatay Mountain likely formed in an island arc subduction setting during the evolution of the CAOB.

Petrogenesis and timing of emplacement of porphyritic monzonite, dolerite, and basalt associated with the Kuoerzhenkuola Au deposit, Western Junggar, NW China: implications for early Carboniferous tectonic setting and Cu–Au mineralization prospectivity

ABSTRACT The Kuoerzhenkuola epithermal Au deposit is located in the northern part of the West Junggar region of NW China and is underlain by a recently discovered porphyritic monzonite intrusion that contains Cu–Au mineralization. Zircon LA-ICP-MS U–Pb dating of this intrusion yielded an age of 350 ± 4.7 Ma. The porphyritic monzonite is calc-alkaline and is characterized by high concentrations of Sr (583–892 ppm), significant depletions in the heavy rare earth elements (HREE; e.g. Yb = 0.96–2.57 ppm) and Y (10.4–23.3 ppm), and primitive mantle-normalized multi-element variation diagram patterns with positive Sr and Ba and negative Nb and Ti anomalies, all of which indicate that this intrusion is compositionally similar to adakites elsewhere. The composition of the porphyritic monzonite is indicative of the derivation from magmas generated by the melting of young subducted slab material. The area also contains Nb-enriched basalts that are enriched in sodium (Na2O/K2O = 1.20–3.90) and have higher Nb, Zr, TiO2, and P2O5 concentrations and Nb/La and Nb/U ratios than typical arc basalts. The juxtaposition of adakitic rocks, Nb-enriched basalts, and dolerites in this region suggests that the oceanic crust of the expansive oceans within the West Junggar underwent early Carboniferous subduction. Magnetite is widespread throughout the Kuoerzhenkuola Au deposit, as evidenced by the volcanic breccias cemented by late hydrothermal magnetite and pyrite. In addition, the zoned potassic, quartz-sericite alteration, and propylitic and kaolin alteration in the deeper parts of the porphyritic monzonite are similar to those found in porphyry Cu–Au deposits. These findings, coupled with the mineralogy and geochemistry of the alteration associated with the Kuoerzhenkuola Au deposit, suggest that the mineralization in this area is not purely epithermal, with the geology and geochemistry of the porphyritic monzonite in this area suggesting that a porphyry Cu–Au deposit is probably located beneath the Kuoerzhenkuola Au deposit.

Characteristics of the Intracontinental Porphyry Deposits in the Middle‐Lower Yangtze River Valley Metallogenic Belt, Eastern China

world’s copper (Cu) and one fifteenth of the world’s gold (Au) (Sillitoe, 2010), with 97% of the giant-large porphyry Cu (Mo-Au) deposits being generated in magmatic arc setting (Richards; 2003; Cooke et al., 2005; Sillitoe, 2010). Nevertheless, recent studies indicate that important porphyry deposits may also be formed in subduction-unrelated environments, e.g., along continental collision-related orogeny and intracontinental setting (Hou et al., 2009; Chen, 2013; Zhou et al., 2011). The Middle-Lower Yangtze Metallogenic Belt (MLYB) is one of the most important Cu-Au-polymetallic metallogenic belts in eastern China, and has been studied extensively in the past (Zhou et al., 2008). Various models have been proposed concerning the regional metallogeny, with major ones including the “porphyrite iron deposit” (NW Group, 1978), “stratabound skarn deposits” (Chang et al., 1991) and the “superimposed metallogenic system” (Zhai et al., 1992; Chang et al., 2012). With the discoveries of large porphyry Cu-Au deposits at Shaxi and Shujiadian in the recent years addition to the previous discovered porphyry deposits such as Chengmenshan and Fengshandong and other deposits, porphyry deposits are becoming more important exploration targets in the MLYB. Their nature and origin are still controversial, and are attributed variably to be the products of intracontinental magmatism (Hou et al., 2009; Chen, 2013; Zhou et al., 2011) or of the subduction of the Paleo-Pacific Plate (Ling et al., 2009, 2011; Liu et al., 2010; Sun et al., 2010; Xie et al., 2012), and recent study are more and more tend to the former point (Chen et al., 2014; Lv et al., 2014; Wang et al., 2014). To further illustrate the differences between the porphyry deposits formed in intracontinental setting and magmatic (continental or island) arc setting, we have chosen typical continental margin arc porphyry deposits, i.e., Bingham Canyon (US) and Bajo de la Alumbrera (Central Andes); island arc porphyry deposits, i.e., Panguna (PNG) and Batu Hijau (Indonesia) to compare with the MLYB porphyry deposits. It is summarized that: 1. Distribution of magmatic (continental or island) arcgenerated porphyry deposits is commonly linear, and is parallel to the orogeny and perpendicular to the subduction zone (Sillitoe, 2010). The MLYB porphyry deposits are distributed along the Yangtze Fault, oblique to the PaleoPacific subduction zone. 2. Magmatic arc-generated porphyry metallogenic systems are commonly preceded by calc-alkaline or alkaline felsic volcanism (Sillitoe, 1973) that occurs ca. 0.5 ‒ 3 Ma prior to the porphyry emplacement, as evidenced at Bingham (Waite et al., 1997), Farallón Negro (Argentina; Sasso and Clark, 1998; Halter et al., 2004), Yerington (Dilles and Wright, 1988; Dilles and Proffett, 1995), Tampakan, Philippines (Rohrlach and Loucks, 2005) and Yanacocha (Longo and Teal, 2005). No coeval (or similar age) volcanism with the porphyry deposits has been documented in the MLYB. 3. Types of wall rocks vary in different deposits, suggesting porphyry Cu deposits are indiscriminative towards their wall rocks. Wall rocks for magmatic arcgenerated porphyry deposits are commonly volcaniclastic rocks, whereas wall rocks for the intracontinental MLYB porphyry deposits contain sandstone (e.g., Shaxi) and carbonates (e.g., Tongshankou). 4. Major metal sulfides in the MLYB include chalcopyrite, pyrrhotite, pyrite,and bornite. Pyrrhotite is closely associated with skarn, and may suggest the reducing nature of the wall rocks (Kósaka and Wakita, 1978; Perelló et al., 2003), in accordance with the formation of magmatic arc-generated porphyry deposits (Sillitoe, 2010). The MLYB porphyry deposits contain the same vein types as typical magmatic arc-generated porphyry deposits, but with different vein type proportion: ZHOU Taofa, WANG Shiwei, FAN Yu, YUAN Feng, ZHANG Dayu and Noel White, 2014. Characteristics of the Intracontinental Porphyry Deposits in the Middle-Lower Yangtze River Valley Metallogenic Belt, Eastern China. Acta Geologica Sinica (English Edition), 88(supp. 2): 667-669.

The Geochemical Identification on Mo-(Cu) and Cu-Mo Bearing Granitoids and Their Significance: Evidences from Chinese Mo-Bearing Intrusions

In recent years, whole-rock geochemistry has been used for tracing the petrogenesis of magmatism (Loucks & Ballard, 2002), however, metallogenic research according to the whole-rock geochemical characteristics of orebearing magmatism has been largely neglected. In this study, after systematically collecting all the published whole-rock geochemical data of Mo mineralization related granitoids in China, we tried to find their discriminative indicators to identify the Mo-Cu and Cu-Mo bearing granitoids, and further understand how these two types of Mo-bearing granitoids form during their evolution process. This study opens a window to research the features and evolution of ore-forming magmatism.