Abstract:The Pangkuam deposit is a large-sized copper-gold deposit newly discovered in Laos. Previous studies held that the gold mineralization in the study area was closely related to the magmatic activity with the subduction of the Paleo-Tethys oceanic plate and crust vanishing; nevertheless, such an argument has not been supported by convincing geochemical evidence. In the study area, 13 samples of volcanic rock and intrusive rock were collected in order to analyze the content of main elements, trace elements and rare earth elements (REE). The research result shows that the andesitic intrusive rocks have the geochemical features of calc-alkaline volcanic rocks in an island arc environment. Tectonic discrimination diagram indicates that the rocks belong to an oceanic arc environment, related to the subduction of the oceanic plate. The formation process occurred in an oceanic subduction zone. The magma of volcanic rock and intrusive rock originated from the mantle wedge with crystallization differentiation. The lamprophyre was formed by the mantle melting, which was enriched during the plate subduction. Based on a comparison with the geochemical features of REE and trace elements of several deposits in Chatree magmatic belt, the authors hold that volcanic rocks and gold deposits in the two mining areas originated from the same stage of tectonomagmatic mineralization process. The result has further demonstrated that there existed an important regional mineralization process at the Loei tectonic magmatic belt in the Late Permian-Early Triassic period.

Abstract:There are a large number of late Paleozoic intermediate to acid intrusions exposed along the tectonic-magmatism belt of western Junggar Basin, Xinjiang. It is of great significance to know the magmatic evolution of this tectonic-magmatism belt through the petrogenesis and emplacement periods. However, there are still no accurate isotopic chronologic and geochemical data of partial small rock bodies, such as Kuergakexi granite, which has restricted the understanding of their genetic types and emplacement ages. In this paper, the petrogenic age and genetic type of Kuergakexi granite were investigated through field geological survey, LA-ICP-MS zircon U-Pb isotopic dating and geochemical analysis. The results show that Kuergakexi granite is mainly composed of granodiorite with an outcrop area of 0.55 km², and prove that the zircons yielded a LA-ICP-MS U-Pb age of 312.9±2.9 Ma (n=20, MSWD=0.072), indicating that intrusive time of the granodiorite is the early Late Carboniferous. The values of major elements indicate that these granodiorites are characterized by high Si, intermediate Al and rich alkali, and low Mg, with A/CNK ratios ranging from 0.99 to 1.20. The trace elements are enriched in large ion lithophile elements such as Rb, Ba, K, but strongly depleted in high field strength elements such as Nb, Ta, Ti, P and heavy rare earth elements, with slightly negative Eu anomalies (δEu=0.68~0.82). These features suggest that the Kuergakexi granite belongs to calc-alkaline series, weakly peraluminous I-type granite. A comparison between Kuergakexi granite and other small intrusions such as Bieluagaxi granite and Baogutu granite shows that they have significant similarities in petrogenic age and geochemical characteristics. It is thus held that the Junggar Ocean continued its deep subduction from the south to the north during the early Late Carboniferous. The source of the granodiorite might have been the lower juvenile crust derived from the depleted mantle that had been metasomatized by fluids released from subduction slabs.

Abstract:The Hekoulinchang porphyry tin-polymetallic deposit is located in the Wandashan epicontinental accretional terrane, which is a part of China's eastern margin in the Circum-Pacific Metallogenic Belt. On the basis of previous geological and geochemical studies, this paper first reports ICP-MS zircon U-Pb age of 121.4±0.5 Ma for granite porphyry, which indicates that the deposit was formed in late period of Late Cretaceous. Geochemical analysis indicates that rock samples of the Hekoulinchang granite porphyry show high content of SiO₂(61.21%~73.81%), K₂O (3.74%~4.61% ) and lower content of Na₂O (0.06%~0.20%). The Hekoulinchang granite porphyry can be classified as high K calc-alkaline A-type granites. The magmatism in this area occurred in an extensional tectonic setting, and the diagrams of Yb-(La/Yb)_N and Rb-K/Rb show that mantle-derived materials played an important role in the generation of the magma. The lithospheric thinning in eastern China took place in the Late Mesozoic, and maximally thinned in Early Cretaceous (130~120 Ma). It is thus considered that the lithospheric thinning was related to the subduction of paleo-Pacific plate in the east, which resulted in the lithospheric thickening and subsequent delamination, leading therefore to the direct contact between the asthenospheric mantle and the crust. The heating from the asthenosphere on the crust subsequently caused the W-Sn ore-related deep-seated magma to trigger the fluids to circulate and leach out ore-forming elements from sedimentary rocks underlain by the wall rock of the deposit, thus forming the Hekoulinchang porphyry tin-polymetallic deposit in endo-and exo-contact zone between the strata and the intrusion. The Hekoulinchang porphyry tin-polymetallic deposit is the first case in Wandashan epicontinental accretional belt which has an affinity with Sikhote-Alin tin province, and its discovery offers a new thought of tin exploration in Northeast China.

Abstract:Based on detailed petrographical and mineralogical compositional features of biotite from the granodiorite porphyry around the Jinjiwo deposit in the Jiurui ore district, the authors not only established the physicochemical conditions of the mineral formation but also explored its significance for rock and ore formation. Major element composition of the biotite phenocrysts of the samples was measured by the electron probe micro-analyzer (EPMA). The Ti content and the Mg/(Mg+Fe) ratios of the biotite from the Jinjiwo granodiorite porphyry are 0.44~0.47 apfu (atoms per formula unit) and 0.58~0.62, respectively, and the compositions of these biotite are plotted in both the domain of the primary magmatic biotite and that of the Mg-rich biotite. These features suggest that the biotite phenocrysts of the samples are all eastonite, and that these analyzed biotites display the Mg-rich and Fe-poor characteristics. The oxidation coefficient and the MF values of biotites are 0.31~0.67 and 0.38~0.41, respectively. Biotite has 13.27%~14.28% MgO, 3.59%~8.93% K₂O, 0.26%~3.28% Na₂O, 15.74%~17.30% FeO, 3.93%~4.19% TiO₂, and 13.52%~14.19% Al₂O₃, respectively. It contains about 2.00~2.24 apfu of tetrahedral Al^Ⅳ and 0.15~0.41 apfu of octahedral Al^Ⅵ. The TAl content of biotite can be used to figure out the solidification pressure of the granitoid. Considering the composition of biotites together with experimental results of the former research, which falls on or above Fe₂O₃-Fe₃O₄ buffer in the Fe³⁺-Fe²⁺-Mg diagram, the authors consider that the biotites from granodiorite porphyry in the study region were crystallized under the condition of temperatures 734~748℃ and pressures 71~89 MPa, corresponding to solidification depth 2.7~3.3 km. The above characteristics suggest that the Jinjiwo granodiorite porphyry belongs to high potassium Ca-alkaline series, showing the typical syntexis type (or I-type) granitoid derived from a crust-mantle mixing source, and that the pluton was formed in a relatively high oxygen fugacity environment, which was beneficial to copper mineralization.

Abstract:All REE deposits in the Mianning-Dechang REE ore belt of western Sichuan Province are closely related to syenite-carbonatite complex in genesis. Despite the similar geological backgrounds, syenite-carbonatite complexes have various occurrences. Also, various types of zircons in these syenites rather than carbonatite exhibit the forms of fresh zircons (type Ⅰ), recrystallization zircons (type Ⅱ), hydrothermal fluid altered zircons (type Ⅲ), and ore-forming fluids altered zircons (type Ⅳ). All these types of zircons were examined carefully by BSE images, CL images, Raman spectra, EMPA, and some other means. Type Ⅰ and type Ⅱ zircons have nearly identical crystal structures, chemical composition and BSE images, with edges of Type Ⅱ zircons being recrystallized and having well-developed crystal structure because of their smaller full-widths at half-maximum FWHM; type Ⅲ zircons have the murky transmissive images, destroyed sieve texture and more increased FWHM, some thorite inclusions and decreased Zr and relatively high content of U, Th, Hf, Ce; type Ⅳ zircons have experienced more serious alteration by ore-forming fluids with many thorite inclusions, more destroyed sieve texture and the most increased FWHM, and high concentrations of U, Th, Hf as well as La, Ce, Nd, Sm. Different zircons show various morphologies, inclusions, degrees of destroyed texture and isomorphous substitutions between U, Th, Hf, Ce and Zr, which, in turn, suggests the evolution from magmatic to hydrothermal processes in the formation of REE deposits.

Abstract:The Huanggangliang Fe-Sn deposit is located in a late Paleozoic accretionary orogenic belt within the southern segment of the Da Hinggan Mountains. Two types of sphalerite occur in skarn, i.e., disseminated sphalerite and lamellar sphalerite. High-precision trace elements analysis was performed for the two types of sphalerite by LA-ICP-MS, and the results indicate that they are syngenetic. The sphalerite presents high concentrations of Mn, Cu, As and In, low concentrations of Ga, Ge and Cd, and wide-ranged concentrations of As, Sn, Bi and Pb. Cu, Sn, Bi and Pb occur as independent minerals, and Mn, Fe, Ga, Ge, Cd, In and Sb enter the lattice of sphalerite in the form of isomorphism. Low In/Ga and In/Ge ratios and Zn/Cd ratios from 233 to 250 suggest that the sphalerite was formed under a moderate-high temperature condition. Cd/Fe ratios below 0.1 and Cd/Mn ratios below 0.5 indicate that the formation of sphalerite was related to magmatism, and the In-Ge discrimination diagram of ore deposit genesis also suggests skarn type. According to comparing these results with other studies of sphalerite from typical ore deposits and in consideration of geological features of the deposit, the authors hold that the Huanggangliang Fe-Sn deposit is a moderate-high temperature skarn-type deposit related to the Yanshanian magmatism.

Abstract:Nominally anhydrous minerals, i.e., clinopyroxene (Cpx), orthopyroxene (Opx) and olivine (Ol), from peridotite xenoliths hosted by Cenozoic basalts in Muchang, Maguan, southeastern Yunnan Province, were investigated by micro-Fourier transform infrared spectrometry (FTIR). Most of Ol and all the Cpx and Opx grains contain structural water in the form of OH. The range of the average core water content (H₂O) of multi grains (>10) in the same sample from the analyzed Muchang peridotites is 160×10^-6~557×10^-6, 85×10^-6~207×10^-6 and 5×10^-6~12×10^-6 for Cpx, Opx and Ol respectively. The whole-rock water content recalculated according to mineral volume proportions varies from 46×10^-6 to 137×10^-6, much richer than that in the North China Craton. Elemental fractionation suggests that the peridotite xenoliths are relicts of primary mantle with partial melting. Low (La/Yb)_N (0.22~0.57) and high Ti/Eu (4 076~6 772) of clinopyroxenes suggest that Muchang lithospheric mantle has undergone low mantle metasomatism by silicate melt. Apparently, the large-scale Neo-Tethys oceanic crust subduction and fluid metasomatism contributed to the rich water in Muchang, which implies that the mantle in Muchang was the new proliferative mantle and the geological evolution differed from that of the North China Craton in Cenozoic.

Abstract:Iron isotopic compositions of siderite minerals from the carbonate rocks in the Mansa siderite deposit of Mengla County in Yunnan Province were studied for the first time in order to discuss the genesis and ore-forming environment of the deposit. Fe isotopes of siderite from the Mansa deposit show a relatively small negative range: δ⁵⁶Fe values of siderite range from -0.337‰ to -0.201‰ (averagely -0.261‰), whereas δ⁵⁷Fe values from -0.518‰ to -0.289‰ (averagely -0.380‰), implying that the Fe isotopic compositions are rather homogeneous and enriched in light iron isotope. Detailed Fe isotope studies of the Mansa siderite deposit show a close relationship between metallogenesis and hydrothermal process, and hence the deposit was formed in a partial submarine environment with rapid accumulation after the effusion of the ore-bearing hydrothermal solution.

Abstract:Such factors as detrital composition, major elements, trace elements and rare earth elements of sedimentary rocks can reflect the information of provenance, and are hence widely used to determine sedimentary provenance type and tectonic setting. An analysis of detrital petrology and geochemistry shows that the provenance of the basin around west Bogda came from the upper earth crust, and felsic rocks were predominant, with the mixture of a small portion of andsitic and basic rocks. The tectonic setting of this area should be active continental margin; nevertheless, as the original rock was formed in a continental island arc environment, a part of the tectonic background displays the continental arc environment. This research provides evidence for studying the structural evolution of the Chaiwopu Basin and North Tianshan Mountains, and is also of great significance for the exploration of oil and gas resources in Chaiwopu Basin and Junggar Basin.

Abstract:In this paper, microscopic observation, X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma (ICP) and electron probe micro-analyzer (EPMA) technologies were used to investigate the characteristics of petrography, mineral and chemical composition of Nanhong agates from Baoshan, Yunnan Province. Moreover, scanning electron microscopy (SEM), energy disperse spectroscopy mapping (EDS-Mapping) and laser confocal microscope Raman were used to investigate the morphologic structure, chemical component and mineral phase composition of colored minerals. The results show that Nanhong agate mainly consists of quartz (>95%) and the most common structures are fiber and granular structures. Nanhong agate has some auxiliary minerals including coesite and calcite and contains two kinds of water for adsorbed water and structure water. The colored minerals could be divided into four categories, i.e., medicine balls mineral grains with diameter less than 1 μm, flocculent globular aggregations with 2~10 μm, needle-like mineral particles and irregular shape mineral types, and all of them have iron minerals. Furthermore, micro Raman study shows that the color of Nanhong agate results from iron minerals, and goethite and hematite could bring red and yellow color respectively. The value of Nanhong agate depends on content form and distribution of iron minerals. This study not only provides useful reference information for Nanhong agate research and has important significance for completing the knowledge system and promoting Nanhong agate culture but also offers a new way for investigating gemstones by using micro Raman technology.