Abstract:A series of granites crop out to the northeast of Erenhot City, near the China-Mongolian border. Zircon U-Pb dating and whole-rock elemental and Sr-Nd isotopic analysis were performed for four granitic plutons. The Halatumiao syenogranite intruded into the Middle-Devonian strata, showing geochemical features of aluminous to weakly peraluminous A-type granite, with A/CNK of 0.98~1.04, and its LA-ICP-MS zircon U-Pb age is 317.5±2.8 Ma (the Late Carboniferous). The Saiyinwusu, Yaguoaobao, and Gancihuduge plutons intruded into the Carboniferous strata, and their LA-ICP-MS zircon U-Pb ages range from 270.1±2.7 Ma to 273.8±1.6 Ma (the Early Permian). The Saiyinwusu pluton consists of biotite monzogranites, granodiorite, and syenogranite, while the Gancihuduge pluton is biotite monzogranites, and both plutons show transitional charac-teristics of I-and A-type granites. All the four granitic plutons are characterized by positive εNd(t) values ranging from +3.2 to +5.8 and variable I_Sr values from 0.703 58 to 0.709 92. Sr-Nd isotopic characteristics show that these granites are juvenile and thus are indicative of crustal growth. Combined with regional data, the study area probably have been subjected to an extensional setting during the Late Carboniferous to the Early Permian.

Abstract:There are abundant Paleozoic granites in China's Altay orogenic belt, which played an important role in the tectonic evolution. In this study, LA-ICP-MS zircon U-Pb dating yielded the ²⁰⁶Pb/²³⁸U ages of 407±3 Ma and 491±3 Ma for the gneissic granite and gneissic tonalite of the Aobaote pluton in Qinghe area respectively, suggesting early Devonian and terminal Cambrian period. The gneissic granite is of calc-alkaline or alkali-calc nature, and belongs to magnesian granite. It is metaluminous-slightly peraluminous with the A/CNK values being 0.98~1.08 and normative corundum values being less than 1. And there are high Y values of 27.2×10^-6~40.5×10^-6 and Th values of 10.2×10^-6~27.0×10^-6, which increase with increasing Rb. The above characteristics indicate that the gneissic granite belongs to I-type granite. There are low SiO₂ values of 60.28%~64.01% for the gneissic tonalite, and its A/CNK values show that its protolith was metaluminous-slightly peraluminous. Together with its trace element characteristics, the authors hold that the gneissic tonalite is characterized by I-type granite. Synthetic analysis shows that the gneissic granite and gneissic tonalite were formed by the subduction.

Abstract:In order to further understand the crust reworking process related to the early Paleozoic intracontinental orogeny in the Cathaysia Block, this paper presents detailed studies of lithology, petrography and zircon U-Pb dating of the Fuhuling migmatites in western Guangdong Province. With the increasing migmatization, these rocks can be divided into three rock types: migmatized para-metamorphic rock, stromatic migmatite and migmatitic granite (diatexite). According to lithological and petrographic characteristics, the Fuhuling migmatites can be divided into three suites: paleosomes, melanosomes, and leucosomes. LA-ICP-MS zircon U-Pb dating results together with a comparison with the data of metamorphic basements from this region suggest that the protolith (paleosome) was meta-sedimentary rocks deposited in the Neoproterozoic, and the migmatization occurred at 441~435 Ma, related to the early Paleozoic intracontinental orogeny in South China.

Abstract:Mesozoic granite is widely distributed in southeast China, which can be divided into Nanling and southeast coastal granitic belts. Due to the effect of tectonism, the depth of Moho and the thickness of lithosphere together with the emplacement age of granite bodies decrease eastward, but the temperature at the depth increases eastward. Radioactive heat-producing element content determinations of granites from surface and drill holes within Nanling region and Southeast coastal region show that the average radioactive heat generation ratios are 5.18 and 3.01 μW/m³, respectively, and that the Fogang granitic body exhibits the highest value of 7.56 μW/m³. In addition, the thermal contribution rate mainly comes from the radioactive decay heat of Th and U with ⁴⁰K thermal contribution being less than 10%. The new data obtained by the authors, in combination with previous geological, geophysical and geothermal data, indicate that the contribution rate from the crust to the surface heat flow in Nanling region and Southeast coastal region is about 60%~65% and 40%~45%, respectively. The result suggests that Nanling region is of “hot crust-cold mantle” type and the Southeast coastal region is of “cold crust-hot mantle” type lithospheric thermal structure.

Abstract:Apatite is a ubiquitous accessory mineral in many geological settings and is stable over a wide range of pressure and temperature. With halogens, rare earth elements (REEs), strontium, yttrium and other minor elements, apatite can reflect the formation of rocks and change of fluid composition. Apatite is one of the most common accessory minerals in eclogites and high pressure veins from HP-UHP metamorphic belt in Chinese southwest Tianshan Mountains, Xinjiang. The occurrences of apatites include inclusions, intergranular grains and vein apatites. This study mainly focused on the apatites whose diameters are larger than 0.1 mm and which were formed at or after the stage of peak metamorphism. According to the results of major element analysis, all the apatites are fluorapatites. The concentration of fluorine ranges between 1.44% and 3.56%, and that of chlorine is below 0.09%, which suggests that the salinity of the fluid in equilibrium with apatites is low. The results of LA-ICP-MS analysis suggest that all the apatites have relatively high concentrations of Sr, Y and REEs, low concentrations of large ion lithophile elements (LILEs, such as Rb and Ba) and high field-strength elements (HFSEs, such as Zr, Nb, Hf, Ta and Ti), and various values of total rare earth elements (∑REE) from 10×10^-6 to 660×10^-6. Based on the ∑REE and their differentiation, all the samples can be divided into three types: LREEs enrichment with low ∑REE, flat pattern with medium ∑REE and MREEs enrichment with high ∑REE. An euhedral elongated apatite displays a growth zoning with the concentrations of REEs gradually decreasing from core to rim, which may reflect the growing process of the apatite and change of fluid composition.

Abstract:East Tianshan, one of the important ore concentration belt in China, is characterized by a large number of mafic-ultramafic intrusions with magmatic Cu-Ni sulfide mineralization in a concentrated area. These small mafic-ultramafic intrusions are distributed in three groups, i.e., Baixintan, Huangshan, and Tulaergen, from west to east. The large-sized deposits mainly occur in the Huangshan intrusion group. The rocks mainly consist of olivine, bronzite, clinopyroxene, hornblende and plagioclase together with a small amount of Cr-spinel and phlogopite. Systematic and comparative studies of the mineralogy of rocks from ore-hosting mafic-ultramafic intrusions in East Tianshan were conducted in this paper. The estimated crystallization temperatures based on Cr-spinel and olivine pair from Huangshan intrusion group were from 1 143 to 1 257℃, which are slightly lower than those from Baixintan and Tulaergen groups (1 283~1 301℃). The estimated pressures show similar widths of 0.31~0.33 GPa calculated by clinopyroxene geobarometer for all the three intrusion groups. The characteristics of hydrous minerals and the fact of earlier crystallization of clinopyroxene than plagioclase indicate that the primitive magmas of the intrusions in East Tianshan were substantially hydrous. The clinopyroxenes in sulfide-bearing intrusive rocks have higher Al/Ti ratio, and the compositions of Cr-spinel and olivine crystals are within or close to the field of island arc volcanic basalts. Based on the regional tectonic evolution, the authors hold that the primitive magmas of sulfide-bearing mafic intrusions in East Tianshan were generated by partial melting of a metasomatic mantle, which was modified by slab-derived fluids associated with the previous subdction events. Mineral comparisons indicate that the ore-hosting intrusions in the Huangshan group have more orthopyroxene and andesine as well as lower Cr^# of Cr-spinel and Ca content in olivine. The new data obtained from this study, together with previous results, indicate that the higher SiO₂ and Al₂O₃ content in the parental magma of Huangshan intrusions group might have resulted from higher degree of crustal contamination, which also reduced the crystallization temperature of the magma.

Abstract:Located in the west of Xiangshan area, the Julong'an uranium deposit has undergone strong chloritization. Based on detailed field investigation and indoor petrographic observation, the authors studied the production state, association relation and chemical composition by applying the electron microprobe technology to the drill hole samples and investigated geochemical features of the chlorite deposit and its relationship with uranium mineralization. Some conclusions have been reached: ① There are four types of chlorites: chlorite from biotite alteration, chlorite from feldspar alteration, colloidal chlorite and uranium-associated chlorite; ② The major chlorites in the deposit are chlorophaeite and brunsvigite, with a small amount of chamosite. The temperature of chlorite varies from 190.5 to 269.9℃, with an average of 224.5℃, suggesting a medium and low temperature condition; ③ The chlorite deposit was formed in a relative reduction environment, with the two formation mechanisms being dissolution-precipitation and dissolution-migration-precipitation; ④ The process of chloritization changed the physical and chemical properties of surrounding rocks and accelerated uranium activation and preenrichment.

Abstract:The Xuebaoding deposit is located in northern Longmen Mountain of Sichuan Province. The deposit lies mainly in the contact marble between Pankou and Pukouling granites. The deposit is characterized not only by the coarse-grained beryl, scheelite, cassiterite and fluorite but also by mineral zones in ore veins. The typical ore veins can be grouped into three parts. In the first part, granite is the main host rock, and beryl, cassiterite, muscovite with diameters less than 1 cm and K-feldspar with diameters up to 20 cm (fd1, fd2 and fd3) can be found. Part Ⅲ is the most important part of the ore veins with coarse-grained fluorite, beryl, scheelite, cassiterite, albite (Ab4 and Ab5), muscovite and apatite up to 20 cm. All the K-feldspar and albite with various kinds of morphology are distributed throughout these veins. EPMA, XRF and ICP-MS were employed to examine the chemical composition of minerals. Tabular beryls in the Xuebaoding deposit are rich in Li, Rb, Cs, belonging to a type of beryl between Na-Li and Li-Cs beryls. Scheelites are rich in REE+Y (>350×10^-6). Muscovite is enriched in Li, Rb, Cs, suggesting a kind of Li-bearing muscovite. Apatite is a type of F-bearing fluorapatite. F-feldspar and albite are very pure with chemical composition of fd1 (Or 95.34~93.96), fd2 (Or 96.28~97.88), fd3 (Or 95.74~98.39), Ab4 (Ab 99.19~100) and Ab5 (Ab 99.58~100). According to the morphology, and locations, K-feldspar and albite samples were named fd1 to fd5 separately: fd1, fd2 and fd3, Ab4 (in marble host rock) and Ab5 (in marble host rock Li, Rb, Cs, W, Sn, Be were highly concentrated in the hydrothermal fluids during the late stage of the evolution and crystallization differentiation as various types of complex such as SnF2 from the melt. With the increasing temperatures of emplaced magma, the reduced volume of magma after its emplacement led to the formation of fissures in marbles, which also resulted in the fluid immiscibility. Fluid immiscibility might have been induced by the pressure released by extension joints, thereby facilitating the mineralization found in Part III. To constrain the formation age of Xuebaoding deposit, the author selected muscovite with coarse-grained beryl from Part III for Ar-Ar dating and obtained the age of 195.7±2.5 Ma.

Abstract:The Hucun copper deposit, located in the south of the Shizishan deposit in Anhui Province, is a typical skarn-type copper polymetallic deposit, which is mainly characterized by copper-gold orebodies in the shallow and copper-molybdenite orebodies in the depth. A systematic study of its ore-forming fluids of the shallow skarn-type copper deposit indicates that three evolutionary stages could be recognized in its rock-forming and ore-forming process, i.e., skarn stage (StageⅠ, subdivided into Ⅰ-1 and Ⅰ-2), quartz sulfide stage (StageⅡ, subdivided into Ⅱ-1, Ⅱ-2a and Ⅱ-2b stages) and carbonate stage (Stage Ⅲ). The results also show that there are three main types of fluid inclusions, namely liquid-rich phase (Type Ⅰ), subcrystal (Type Ⅱ) and gas-rich phase (Type Ⅲ). The evolution of ore-forming fluids at different stages are as follows: it was of high temperature (543~631℃) and moderate-high salinity (14.8%~20.1% and 44%~50.1%) at Stage Ⅰ, medium temperature (172~298℃) and low-moderate salinity (5.9%~16.9%) at StageⅡ, and medium-low temperature (158~247℃) and low-moderate salinity (1.7%~6.2%) at Stage Ⅲ. H-O isotope studies indicate that ore-forming fluid originated from magmatic water and then was mixed with meteoric water at the sulfide metallogenic stage. Geochemical characteristics of fluid inclusions reveal that the temperature was the main controlling factor for the shallow orebodies, the copper migrated at high temperature and then the ore-forming materials began to precipitate and concentrate to mineralize when the temperature rapidly fell with the continuous mixing of meteoric water and ore-forming fluids.

Abstract:Noble gases are widely used as geochemical tracers. In this study, noble gas isotopes of olivine and pyroxene in nephelinites from Wajilitag of Northwest Tarim large igneous province were analyzed. The results show low ³He/⁴He ratios (2.0~2.4 Ra and 0.65~0.85 Ra, respectively) and low ⁴⁰Ar/³⁶Ar ratios (342.3~651.7, slightly higher than atmospheric value). This feature can be interpreted as being influenced by the paleo-subduction. It is inferred that the south Tianshan oceanic plate subducted southward beneath the Tarim plate in the early Paleozoic and the subducting plate brought the fluid enriched with U or ⁴He and atmospheric components into the deep mantle. Furthermore, the nephelinite magma was produced by low degree partial melting of the mantle source region with the involvement of the mantle plume.