C.Y. Feng’s research while affiliated with Chinese Academy of Geological Sciences and other places

The Galinge skarn iron deposit is located at the junction between the Qimantag metallogenic belt in the East Kunlun Mountains and the Qaidam Basin. There are two types of Fe-Ti oxides coexisting assemblages in the Galinge skarn deposit: one is the hydrothermal magnetite-ilmenite coexisting assemblage (HYM) which was discovered in No. 2 II ore group, whereas the other one is the igneous magnetite-ilmenite coexisting assemblage (IGM) which is developed in the fresh mafic basaltic andesite. This research aimed to analyze the distinctive composition and significant thermodynamic features of the HYM and IGM. The HYM shows an intergrowth with ferromagnesium spinel, and the crystallographic orientation of growing ilmenite lamellae are parallel to the (111) planes of the magnetite octahedron. Based on the equilibrium of oxidation, the equilibrated temperatures range between 581.8C and 688.9℃, and the oxygen fugacities vary between 10-14.74 and 10-17.94. The IGM is mainly in equilibrium with silicate minerals in the mafic magma. The equilibrated temperatures of the IGM range between 690.73℃ and 740.26℃, and the range of oxygen fugacities is 10-15.44-10-17.30. It is reasonably inferred that the primary metallogenic temperature might have reached 700℃, approaching the crystallographic temperature of water saturated magma. Therefore, the HYM was formed after the primary cooling procedure of the early high-temperature and high-salinity hydrothermal fluid which evolved from the magma. Because of the infiltration metasomatism between the hydrothermal fluid and the mafic igneous rocks, large amounts of metal elements such as Fe, Ti, Al, Mg and Cu were leached out. In the early high temperature setting, Ti and Al were incorporated into the magnetite, and consequently the oxyexsolution of titaniferous magnetite resulted in the intergrowth of magnetite and ilmenite. As the oxyexsolution did not rapidly re-equilibrate under new conditions, the iron-titanium oxide relationship could be preserved and hence could indicate the equilibrium temperature and the oxygen fugacity of the oxidation.

The Saishitang copper deposit is an important skarn deposit located in the Southeast of Ngola Mountain Area, Eastern margin of East Kunlun orogenic belt. The skarn occurs along the contact between Indosinian quartz diorite and middle-lower Triassic T1-2b2 lithologic section. The ore bodies which are stratoid or lenticular mainly occur in exoskarn. The T1-2b2 lithologic section consists of intermediate volcanic rocks, marble and metamorphic siltstone. Cu mineralization is adjacent to the metamorphic andesitic tuff and andesite spatially. Petrography studies of Cu-bearing skarn show four stages of skarn formation and ore development, including skarn stage, retrograde alteration stage, quartz-sulfide stage and quartz-carbonate stage. Skarn stage consists of garnet, pyroxene and wollastonite and retrograde alteration stage dominates by epidote, amphibole and magnetite. In quartz-sulfide stage a large amount of sulfides were precipitated. Electron microprobe analysis shows that components of garnet and pyroxene are Gro0.00~91.00And7.02~100.00(Pyr+Alm+Spe)0.00~4.27 and Di12.80~91.75Hd2.41~79.80(Jo+Jd+Opx)0.00~13.47, respectively. The result indicates that the skarn in Saishitang deposit belongs to typical calcic skarn. High concentrations of grossular and epidote are found in skarns located closer to the contact between quartz diorite and andesite. Andradite is richer near the marble with wollastonite and Mn-bearing hedenbergite. Mineralogical characteristics and compositional variations suggest: from skarn stage to quartz-sulfide stage, the property of fluid changed episodically with two redox fluctuations at least, probably resulting from the influx of meteoric waters in ore-forming fluid. Saishitang copper deposit is a skarn deposit. The quartz diorite-dominated intrusions carrying plenty of heat and fluids intrude into middle-lower Triassic strata. The materials exchange between intrusions and wall rocks may be the mechanism of the development of skarn and ore bodies in Saishitang deposit, accompanying the bimetasomatism between marble and metamorphic siltstone and intermediate volcanic rocks.

The Xingguo-Ningdu ore cluster in southern Jiangxi Province, located in the convergent zone of the eastern Nanling EW-trending metallogenic belt and the western Wuyishan NE-trending metallogenic belt, possess several different type of W-Sn polymetallic deposits. However, little research has been done for these deposits. Based on detailed field investigations, high-precision isotope dating on the Zhangjiadi Mo-W deposit, the time-space distribution of W-Sn ore deposits in Cathaysia Block and their geodynamic settings are studied in this paper. SHRIMP zircon U-Pb age for porphyritic fine to medium-grained biotite granite from the Zhangjiadi ore deposit is 154.1 ± 1.8Ma. Molybdenites separated from the quartz vein type orebody in the Wangnipai ore block and the greisen orebody in the Liujiazhuang ore block yield Re-Os isochron ages of 158.4 ± 3.1Ma (weighted mean age 157.7 ± 1.4Ma) and 161.9 ± 3.2Ma (weighted mean age 157.9 ± 1.6Ma), respectively, which are corresponding to Late Jurassic period. The studied molybdenites show quite low Re contents (9.58 × 106 - 22.65 × 106), suggesting a continental crustal source of the ore metals. Integrated with the latest research results, it is concluded that the W-Sn deposits formed during 240-210Ma, 170-150Ma and 130-90Ma, and are centered by the largest scale in southern Jiangxi Province and southern Hunan Province, and become younger in the east, west, south and north directions. We suggest that the Yanshanian large-scale magmatic and ore-forming processes may have occurred in a Jurassic intraplate extensional geodynamic setting during the Mesozoic lithosphere extension in South China.