Geochronology, petrogenesis and metallogenic implications of granitoids in the Xiaotuergen Cu deposit, Northern Chinese Altai Orogen, NW China: Constraints from zircon, apatite and whole-rock geochemistry
Geochronology, petrogenesis and metallogenic implications of granitoids in the Xiaotuergen Cu deposit, Northern Chinese Altai Orogen, NW China: Constraints from zircon, apatite and whole-rock geochemistry
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中国西北阿尔泰造山带小土尔根铜矿床花岗岩类的年代学、岩石成因和成矿意义：来自锆石、磷灰石和全岩地球化学的约束
DOI：
10.1016/j.oregeorev.2022.105041
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发表时间：
2022-07
期刊：
影响因子：
--
通讯作者：
Jiangtao Huang
中科院分区：
文献类型：
--
作者：
Xianke Fan;Xiaofei Pan;Zengqian Hou;John Mavrogenes;Yongguan Dong;Chunyan Yao;Jihua Qin;Jiangtao Huang
小吐尔根铜矿床是中国北方阿拉泰造山带中发现的第一个铜矿床。小吐尔根地区发育多期花岗岩侵入岩，包括花岗闪长斑岩、花岗斑岩和黑云二长花岗岩。其中，铜矿化与海西早期花岗闪长斑岩关系密切。然而，三个小吐尔根花岗岩类的确切侵位年龄、岩石成因、氧化还原状态和构造背景以及它们与成矿作用的关系尚不清楚。为了解决这些问题，本研究测定了锆石U-Pb定年、锆石原位微量元素含量、Hf同位素组成、磷灰石原位常量元素含量和全岩地球化学。区内可识别出三个不同的侵入相，按年龄大小依次为黑云二长花岗岩、花岗闪长斑岩和花岗斑岩，其年龄分别为400.2±1.6 Ma~399.6±2.4 Ma、390.3±1.6 Ma~377.1±1.6 Ma、381.0±2.0 Ma~378.7±1.2 Ma，表明它们侵位于早中泥盆世。地球化学资料表明，这些侵入岩为偏铝-弱过铝(A/CNK=0.91-1.28)，钙碱性-钾玄质I型花岗岩类。这两个Harker图趋势揭示了经历了不同演化过程的两种岩浆来源(黑云二长花岗岩与花岗闪长斑岩和花岗斑岩)。锆石Ce4+/Ce3+比值和氧逸度(LogfO2)值、磷灰石锰氧气压计和全岩Fe2O_3/FeO比值等多项指标一致表明，富饶的花岗闪长斑岩的母岩浆比两个贫瘠的侵入岩(黑云二长花岗岩和花岗斑岩)的母岩浆氧化程度更高。此外，富矿的花岗闪长斑岩中的磷灰石颗粒的氯含量和氯/氟比高于贫矿黑云二长花岗岩和花岗斑岩中的磷灰石颗粒，这可能是由于母岩浆的含水率较高以及岩石圈地幔流体参与其生成所致。因此，较高的磷灰石氯/氟比可以用来区分北阿拉泰造山带中赋存铜矿化的富饶的花岗岩类侵入岩。锆石Hf同位素组成显示出广泛的εHf(T)值(−4.2~+11.4，主要集中在+2~+8)。这些同位素特征结合年轻的锆石TDMC(Hf)年龄(655~1659 Ma；主要集中在850~1250 Ma)表明，小吐尔根花岗岩类很可能来自年轻下地壳的部分熔融，并与下伏地幔楔体的地幔物质有一定的相互作用。三个小吐尔根花岗岩类富含轻稀土元素和大离子亲石元素。
The Xiaotuergen Cu deposit is the ffrst Cu deposit described in the Northern Chinese Altai Orogen, Xinjiang, NW China. The multiple phases of granitic intrusions occur in the Xiaotuergen region, including the intrusions of granodiorite porphyry, granite porphyry, and biotite monzogranite. Among these types of intrusions, Cu mineralization is considered to be closely related to the early Hercynian granodiorite porphyry. However, the precise emplacement ages, petrogenesis, redox states, and tectonic setting of the three Xiaotuergen granitoids and the relationship between these granitoids and mineralization was unclear. To resolve these issues, zircon U–Pb dates, zircon in situ trace element concentrations, Hf isotopic compositions, apatite in situ major element concentrations, and whole-rock geochemistry were determined in this study. Three different intrusive phases are recognized within the district; in order of deceasing age, these phases are biotite monzogranite, granodiorite porphyry, and granite porphyry, which have the ages of 400.2 ± 1.6 Ma to 399.6 ± 2.4 Ma, 390.3 ± 1.6 Ma to 377.1 ± 1.6 Ma, 381.0 ± 2.0 Ma to 378.7 ± 1.2 Ma, respectively, suggesting that they were emplaced during the Early-Middle Devonian. Geochemical data show that these intrusions are metaluminous to weakly peraluminous (A/CNK = 0.91–1.28), calc-alkalic to shoshonitic I-type granitoids. The two Harker plot trends reveal derivation from two magma sources (biotite monzogranite vs granodiorite porphyry and granite porphyry) that experienced different evolutionary processes. Multiple indicators, including the zircon Ce4+/Ce3+ ratio and oxygen fugacity (logfO2) values, apatite Mn oxybarometer, and whole-rock Fe2O3/FeO ratio, consistently indicate that the parental magma of the fertile granodiorite porphyry was more oxidized than that of the two barren intrusions (biotite monzogranite and granite porphyry). Furthermore, apatite grains from the fertile granodiorite porphyry have higher Cl contents and Cl/F ratios than those of the ore-barren biotite monzogranite and granite porphyry, which may have resulted from the higher water content of the parental magma and increased lithospheric mantle-derived ffuid involvement in their generation. Thus, higher Cl/F ratios of apatite can be used to discriminate fertile granitoid intrusions that host Cu mineralization in the Northern Altai orogen. Zircon Hf isotopic compositions show widely ranging and mostly positive εHf (t) values (− 4.2 to +11.4, mainly concentrated between +2 and +8). These isotope characteristics in combination with young zircon TDMC (Hf) ages (655–1,659 Ma; mainly concentrated between 850 Ma and 1250 Ma) indicate that the Xiaotuergen granitoids were most likely derived from the partial melting of juvenile lower crust, with some interaction of mantle materials from the underlying mantle wedge. The three Xiaotuergen granitoids were enriched in light rare earth elements and large ion lithophi
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