Fengmei Chai

Geochronology and Geochemistry of the Kuwei Mafic Intrusion, Southern Margin of the Altai Mountains, Northern Xinjiang, Northwest China: Evidence for Distant Effects of the Indo-Eurasia Collision

The Kuwei mafic intrusion, consisting of hornblende gabbro, gabbro, gabbro norite, and olivine norite, lies in the southern Altai Mountains, northern Xinjiang. A combined field, geochronological, and geochemical study of the Kuwei intrusion is reported here. This study provides the first reliable SHRIMP U‐Pb zircon dating results for the intrusion, and these yielded an age of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Lamprophyre or Lamproite Dyke in the SW Tarim Block? —Discussion on the Petrogenesis of These Rocks and Their Source Region

47\pm 1

Mesozoic Mo-W-Ag-Pb-Zn mineralization in the Nannihu area, western Henan Province, China

\end{document} Ma, which is the first documented report of Eocene magmatism in the region. The chondrite‐normalized rare earth element patterns for the Eocene intrusions are flat, and most of the incompatible elements are comparably depleted. Thus, geochemical data suggest that the Kuwei mafic intrusion was produced by partial melting of asthenospheric mantle that was slightly contaminated by lithospheric material. We interpret the 47‐Ma magmatism to result from asthenospheric mantle upwelling following the progressive India‐Eurasian collision. Although the Kuwei intrusion is laterally beyond the limit of Eocene deformation normally attributed to the India‐Asia collision, the timing of magmatism in the intrusion suggests that lateral extension may have initially affected a wider region than the area later thickened by convergence in the Tibetan Plateau. The Kuwei intrusion and other plutons likely related to it may have been emplaced into dilational jogs in fault systems activated by the India‐Asia collision. The emplacement depth is estimated to be ∼6 km, based on geobarometric determinations. Erosion was imperceptible before 25 Ma but has worn away an average of 0.024 cm of uplift every year since 25 Ma. The 6 km of exhumation since the late Oligocene is also attributed to far‐field effects of the India‐Asia collision.

Mesozoic Au-Ag-Pb-Mo mineralization in the Xiong’ershan area, western Henan Province, China

The Au-telluride district of the Pingyi area, western Shandong, mainly comprises the Guilaizhuang and Lifanggou gold deposits. The former is hosted in cryptoexplosive breccia of the Tongshi complex with a zircon SHRIMP U-Pb weighted mean age of 175.7±3.8 Ma. The latter occurs in dolomitic limestone, micrite and dolomite of the Early Cambrian Zhushadong Formation. Fluid inclusion studies indicate that the inclusions of both Au telluride deposits are both of vapor-liquid two-phase NaCl-H2O type. Homogenization temperatures of the fluid inclusions vary from 103 to 250°C, and the ice melting temperatures range from −2.5 to −13.5 °C, corresponding to a salinity range of 4.65 to 17.26 wt.% NaCl equiv. The δ34S values of pyrite associated with gold mineralization exhibit a narrow range of −0.71 to 2.99‰, implying that the sulfur was probably derived from the mantle or magma. The δ18OSMOW values of vein quartz and calcite range from 11.5 to 21.5‰, corresponding to the δ18Ofluid values of −1.13 to 10.9‰, and the δD values of the fluid inclusions between −70 and −48‰. The isotope data suggest that the ore-forming fluids of the two gold deposits were derived from the mantle, and mixed with meteoric water at shallow levels. Pressure release and boiling of the fluids played an important role in the ore-forming processes of the two deposits.

Geochemistry of the Kalatongke layered intrusion, Xinjiang NW China: Implications for the genesis of a magmatic Cu-Ni sulfide deposit

ABSTRACT The mineralogical, petrological and geochemical studies on Keliyang ( ) potassic dykes have been carried out to understand their rock types, the petrogenesis and the nature of their mantle sources. They are potassic lamprophyre, not lamproites as the previous researchers believed. In this study, the whole-rock major and trace element compositions of another 6 lamproite dykes recently discovered are reported. Major elements were determined by X-ray fluorescence spectrometry (XRF) techniques, while REE and trace elements were determined by inductively coupled plasma mass spectrometry (ICP-MS). They can be classified into phlogopite-diopside lamprophyre, leucite-diopside lamprophyre and granular carbonatite-bearing diopside lamprophyre on the basis of their mineral components. They are all characterized by relatively low SiO2 (41. 31%–44. 84%), TiO2 (0.75%–0.86%) and high MgO (7.30%–11.33%), K2O (4.01%–6.01%) concentrations with K2O/KNa2O ratios of 2.77–12.49. In addition, they display enrichment in large-ion lithophile elements (LILEs, e. g., Rb, Sr, Ba) and LREE, but a relative depletion in high-field-strength elements (HFSEs, e. g., Nb, Ta, Zr, Hf and Ti). They display similar chondrite-normalized REE patterns with slight negative Ea anomalies (δEu=0.64–0.82), and high initial 87Sr/86 ratios, which resemble those of high K/Ti and low-Ti potassic magmas formed in subduction-related settings. Consequently, we suggest that the parental magma was generated by partial melting of the phlogopite-amphibole-bearing garnet Iherzolite within the lithospheric mantle that might have been metasomatized by a potassium-bearing fluid released from a subduction oceanic crust.

Geology, petrology and geochemistry of the Baishiquan Cu-Ni-bearing mafic-ultramafic intrusions in Xinjiang, NW China

On the basis of previous studies, this paper provides a preliminary summary of recent research on mafic-ultramafic intrusions and related magmatic Cu-Ni sulfide ore deposits in northern Xinjiang. The authors argue that there is still a need to study some key problems concerning the origin and tectonic settings of these intrusions and sulfide deposits.

Discussion on approximated estimation method of the three-parameter lognormal distribution

There are many Mesozoic hydrothermal Mo-W-Ag-Pb-Zn deposits in the Nannihu area, west Henan Province, which is located in the eastern part of the Jinduicheng-Nannihu Mo-W polymetallic metallogenic belt of the southern margin of the North China Craton. Deposit types in the Nannihu area include porphyry-skarn Mo-W deposits, skarn polymetallic pyrite deposits, and structurally-hosted, altered-rock Ag-Pb-Zn deposits. These deposits show a consistent spatial-temporal association with Late Jurassic magmatism. Sulfur and lead isotopic compositions indicate that ore was mainly derived from the lower crust. Hydrogen-oxygen isotope compositions indicate that ore fluids were derived from primary magmatic water in the early stages, and a mixture of magmatic and meteoric water in the later stage. During a period of tectonic regime transitions in eastern China in the Late Jurassic, underplating of mafic magma, partly remelting of the lower crust, and intrusion of acid magmas developed successively, resulting in extensive mineralization in the area.

The association of mafic–ultramafic intrusions and A-type magmatism in the Tian Shan and Altay orogens, NW China: Implications for geodynamic evolution and potential for the discovery of new ore deposits

The Xiong’ershan district is located on the southern margin of the North China Craton and is the second largest Au area in Henan Province, China. It contains Mesozoic hydrothermal Au and Ag, Pb and Mo deposits. The deposits can be classified into different types: cryptoexplosive breccia type Au deposits, structural alteration type Au, Ag and Pb deposits, and porphyry type Mo deposits. The porphyry type Mo deposit formed earlier than other types of deposits. Various deposits formed in an extensional environment that resulted from rapid lithospheric thinning in eastern China during 140–120 Ma, and the combination of a tectono-thermal event and deep deep-seated magmagtic ore fluids and meteoric water that resulted in the formation of large-scale hydrothermal mineralization.