Abstract:The Pobei mafic-ultramafic belt is an impotant Ni-Cu sulfide metallogenic prospective province in Beishan area, eastern Xinjiang. About 20 intrusions (e.g., Bijiashan, Hongshishan, Cihai, Poyi, Poshi and Luodong) were recognized along the fault in this area and almost all the intrusions are associated with Ni-Cu sulfide deposits. The Hongshishan mafic-ultramafic complexs are located in the eastern part of the Pobei mafic-ultramafic belt and the southern part of the Baidiwa-Yunihe fault in this area. They intruded into quartz schist of the Lower Carboniferous Hongliuhe Formation. They are mainly composed of dunite, peridotite, troctolite, pyrox-enite, olivine gabbro, gabbro and diorite. These rocks were emplaced in two stages. The first stage consists of peridotite and olivine gabbro, and the second stage comprises gabbro and diorite. The dunite, pyroxene peridotite and troctolite are the host rocks for Ni-Cu sulfide ores. The platinum-group elements and Re-Os isotopic compositions of ore and rocks from the Hongshishan Ni-Cu sulfide-bearing mafic-ultramafic intrusions were analyzed, and the result shows that the total PGE content is quite low, ranging from 0.54×10^-9 to 15.84×10^-9 and increasing with the increase of sulfide content. The PGE primitive mantle-normalized patterns display a positive slope and low fractionation between IPGE and PPGE. PGE, Cu and Ni are depleted relative to the primitive mantle with low and a narrow Pd/Ir range (3.19～10.5), indicating a weak influence of later hydrothermal alteration. Furthermore, the Ir displays positive correlations with Pt, Pd, Os, Ru and Rh, indicating a weak contribution of the fractionation and the partial melt to PGE depletion. The Cu/Pd ratios(73×10³～1 670×10³)and Ti/Pd ratios (87×10³～2 857×10³)of these rocks suggest that sulfur in the primary magmas had reached saturation, and immiscible sulfides droplets were segregated from silicate magmas before their emplacement. The relationship between Ni/Cu and Pd/Ir indicates that the parental magma was high-magnesium basaltic magmas. Their γ_Os(t) and (¹⁸⁷Os/¹⁸⁸Os)_i are variable,ranging from +18 to +282 and from 0.148 3 to 0.481 3, respectively, suggesting that abundant crustal material was mixed with the ascending magma. The fractionation of olivine and contamination by crustal material probably triggered the sulfide saturation and segregation and the Ni-Cu-(PGE) mineralization as well. The intrusions were generated from the magma that had undergone crystallization differentiation of olivine and segregation of sulfides.

Abstract:Located in Lapeiquan area, northern Altun Mountains of Xinjiang, the Qilesayi pluton consisting mainly of gabbro and diorite intruded into the Lapeiquan Group. This paper has studied petrographic, geochemical and zircon U-Pb chronological characteristics of gabbro and diorite from Qilesayi pluton as well as their tectonic significance. Geochemical analyses suggest that the gabbro has high Al₂O₃ (13.47%～15.34%), FeO^T (10.77%～16.89%) and moderate MgO (5.15%～7.49%) values, whereas the diorite samples are characterized by low SiO₂ content (52.06%～54.23%) and high Mg^# values (58.63～62.45), belonging to the calc-alkaline series. The gabbro and diorite samples have features of low ΣREE content with low fractionation of LREE/LREE and no or slightly negative Eu anomalies, depletion of HFSE (Nb, Ta, Zr, Hf) and enrichment of LILE (Rb, Ba). These geochemical features imply an origin similar to that of the subduction-related tectonic setting. Zircon U-Pb ages obtained by LA-ICP-MS analyses from the gabbro and diorite samples are 477.5±3.3 Ma and 469.7±3.4 Ma, respectively, implying that these rocks were emplaced in the Early-Middle Ordovician period. Their petrogenic ages are similar to rock-forming ages of the adjacent Bashenkaogong gigantic phenocryst granitoid (474 Ma), Bashenkaogong-Xiemierbulake quartz diorite (481.6±5.6 Ma) and Jinyanshan granodiorite intrusive bodies (467.1±6 Ma), suggesting that they may be products of the same magmatism and constitute the basic-intermediate-acidic magmatic evolution series. Integrated with geochemistry, trace elements discrimination, geochronology and regional background, it is inferred that that the gabbro and diorite were formed in a subduction-related active continental margin arc. Meanwhile, this study proposes that the gabbro and diorite from Qilesayi pluton were derived from the southward subduction of an oceanic crust to Milanhe-Jinyanshan active continental margin during the Early Paleozoic period, and this provides the corroborating evidence for the further ascertaining of the existence of the Early-Middle Ordovician continental margin arc and subduction polarity of Hongliugou-Lapeiquan ophiolite mélange zone in the North Altun Mountains.

Abstract:The Shuangpengxi gold deposit, as one of the most important gold deposits in northwest China, is located in the Tongren ore concentration area of Qinghai Province. Gold mineralization occurs within skarn that lies between granodiorite and marble. The ore bodies are in lenticular and veinlike forms. Ores are mainly composed of chalcopyrite, pyrrhotine and pyrite. Gangue minerals comprise diopside, garnet, calcite and sericite. The main types of rock alterations are skarnization, silicification, carbonatization, brecciation and ferritization. The tectonic setting, material source and genesis of the ore deposit are discussed on the basis of trace elements, REE, fluid inclusions and isotope geochemistry of ores and wall rocks as well as characteristics of the ore deposit. Studies show that ores and granodiorite have similar chondrite-normalized REE patterns and are enriched in light REE with a moderate Eu negative anomaly but no Ce anomaly. Microthermometric homogenization measurements of the fluid inclusions show that temperatures are from 215℃ to 468℃, corresponding salinities vary from 1.40％ to 13.40％ NaCleq, and densities vary from 0.55 g/cm³ to 0.85 g/cm³. The metallogenic pressure is 2.25 MPa～20.61 MPa. and the ore- forming fluids belong to NaCl-KCl-CaCl₂-H₂O types, especially enriched in CO₂,CH₄ and C₂H₂. Sulfur isotopic compositions of sulfides from ores show that the values of δ³⁴S from the early depositional ores range from 2.2‰ to 7.0‰. The ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb ratios of ores range from 38.19 to 38.53, 15.581 to 15.641 and 18.058 to 18.710, respectively. According to the isotopic data, it is considered that the ore-forming materials were derived from the crust and the upper mantle. Studies show that the Shuangpengxi ore deposit might be a skarn gold deposit related to hypo-and mesothermal processes and belongs to the acid and intermediate-acid magmatic activities of Indo-Chinese and Yanshanian period.

Abstract:Located in the Sangjiang metallogenic belt, Laochang is one of the important noble metal and nonferrous metal ore-forming belts of southwestern China, whose geotectonic location is very unique with rich ore resources and lots of metal deposits. Laochang is one of the areas with significant breakthrough for new discovery of great thick porphyry molybdenum ore bodies in the depth since 2008. Geochemical characteristics of the concealed granite porphyry in the Laochang ore deposit were studied in this paper. Tectonic setting and genetic mechanism of the granite porphyry were investigated by using various discrimination diagrams. Petrologic research indicates that granite porphyry of this area is light gray and grayish white in color and has porphyritic texture and massive structure. Phenocrysts are mainly composed of orthoclase, quartz, plagioclase and biotite, whereas the matrixes are composed of equiaxial fine-grained orthoclase and quartz. It is concluded that chemical compositions of the concealed granite porphyry in Laochang are characterized by the similarity to China's granite porphyry in average SiO₂ (68.09%～73.48%), alkali enrichment (Na₂O+K₂O=7.73%～8.51%), K enrichment (K₂O/Na₂O=1.85～25.8), LREE enrichment, HREE depletion, (La/Yb)_N varying from 12.01 to 24.85, weak negative Eu anomaly (δEu varying from 0.79 to 0.99), and smoothly right-declined REE distribution pattern. Thus, the granite porphyry belongs to acid, aluminum medium-saturated, High-K calc-alkalic series of magmatic rock. A comprehensive study of geochemical characteristics by using discrimination diagrams and zircon features of concealed granite porphyry in Laochang indicates that the granite body was mainly derived from crust source mixed with minor mantle materials and formed at the main collision stage of the Cenozoic collisional oregeny of the Tibetan Plateau under the regional compressional environment. Zircon SHRIMP U-Pb dating of the Laochang granite porphyry yielded 44.6±1.1 Ma. The chronologic age shows that the granite porphyry was formed in Eocene. The petrogenesis and mineralization of the Laochang granite porphyry took place during the main collisional stage of the Cenozoic intracontinental collision orogeny, and this is consistent well with metallogenic peak period of porphyry type deposits in the Sangjiang region. Based on the results from Sr-Yb classification of granite-porphyry diagram, R₁-R₂ discriminating tectonic setting of granite-porphyry diagram and regional tectonic development, it is suggested that the Laochang granite porphyry was formed in the collisional setting. The magma, which was derived from partial melting of deep mantle initiated by collision, experienced upwelling through the core part of early developed rift, and became a major driving force for structural, magmatic and thermal events. The input of mantle material into the crust induced partial melting of the lower crust to form a potassium-rich ore-bearing magma with mixed sources of the crust and the mantle.

Abstract:Diagenesis and its corresponding cements are extensively developed in the upper Carboniferous phylloid algal reef and circumjacent limestone of Bianping Village, Houchang Town, Ziyun County. These cements are prominent and representative in Houchang Town. A study of crystal shape, fabric and cathodoluminescence images of cements as well as the contacts between cements can help determine paragenetic sequences, recognize diagenetic environments, and understand the porosity evolution in the phylloid algal reef limestones. During the syndiagenetic stage, wackestone and packstone sediments generally had low porosity and permeability, pores were filled with sea-floor micrite cement, biological encrustation and sea-floor cementation sediments rich in the fragments of phylloid algal thalli had high porosity and big pores, and marine botryoidal cement and isopachous acicular cement grew in the pores. During the early diagenetic stage, cementation supplied a great amount of cements, constructed rock framework, and consequently decided the features of the limestone rock. Blocky calcite spar and calcite microspar were formed in small pores, and radiating cement fans grew in big pores. During the epidiagenetic stage, extensive dissolution and cementation occurred. Vuggy or channel porosity was created by dissolution in the recharge area, and calcite precipitation was greatly increased in downflow areas. Meteoric phreatic cements include isopachous columnar calcite and blocky or equant calcite cement. Isopachous columnar cement is volumetrically more abundant. The porosity of the reef limestone was reduced dramatically through the early-stage cementation, so the reef limestone could prevent mechanical compaction. During the middle and late diagenetic stage, nearly all porosity was occluded by cements with low rates of fluid influx and efflux, and the remaining pores were filled with isopachous bladed cement and drusy or blocky calcite spar. Some preexisting cements were altered during the middle or late diagenetic stage, the color of isopachous bladed to columnar calcite cement changed from gray to white, and the color of botryoidal cement became more blackish due to hydrocarbon infiltration. Some isopachous bladed to columnar calcite cement could be dissolved, leaving mouldic pores filled subsequently and radiating cement fans formed simultaneously. Construction fracturing is one of the main types of diagenesis during the catagenesis stage. Rusty microcrystalline layers containing Fe₂O₃ line the wall of some fractures, and vadose pisoids and ferrugineous crystal silt containing Fe₂O₃ are deposited at the bottom of the cavities formed in the tectonic fractures, which indicates that they were formed in oxidizing vadose environments. Late-stage fractures are filled with coarse-grained white or green bladed and drusy or blocky calcite spar. The middle part of some of these fractures is filled with bitumen block. A reason for the phylloid algal reef limestone not becoming oil and gas reservoirs might be that the pores of the phylloid algal reef limestone were filled with cements before or during the late diagenetic stage, and no large interconnected secondary pores were created afterwards. Only limestone that has a great deal of secondary porosity generated during the catagenesis stage could become oil and gas reservoirs in the Nanpanjiang Basin.

Abstract:The Paleoproterozoic Badu Group in southwestern Zhejiang Province is the oldest metamorphic basement in the Cathaysia block, and its metamorphic grade was previously considered to be only of amphibolite facies. Recently, pelitic granulite with the typical mineral assemblage of garnet+sillimanite+perthite+antiperthite+biotite was discovered in the Al-rich gneiss of Suichang area. According to petrographic observation, micro-mineral composition and calculating results from garnet-biotite thermometer and GASP barometer, three stages of metamorphism were recognized in the pelitic granulite. The early prograde metamorphic stage (M₁) was detected on the basis of inclusions of biotite, muscovite and sillimanite in garnet. The peak metamorphic stage (M_2-3) is characterized by the presence of garnet, biotite, sillimanite and ternary feldspar, with a probable pT condition of 0.6～0.7 GPa at ca. 800～850℃. The post-peak retrograde metamorphic stage (M₄) was recognized according to the mineral assemblage of biotite, garnet, fresh plagioclase and muscovite, with a pT condition of 560～590℃ and 0.25～0.33 GPa. The garnet from the pelitic granulite developed both diffusion zoning and symplectite of plagioclase related to the lowering of temperature and pressure, respectively. A clock-wise pT path has been constructed for the pelitic granulite which is consistent with the thinning process of the thickened continental crust.

Abstract:The discovery of the intermediate and basic volcanic rocks in recent years in the Devonian strata in Dachang Guangxi has important significance in the explanation of the tin ore formation mechanism and the prospecting research. The authors analyzed its volcanic output characteristics, petrology and rock geochemistry and explored the relationship between the volcanic rock and the mineralization. The results show that the volcanic rocks are mainly basalt and andesite. The volcanic rocks are in conformable contact with the surrounding upper and lower rocks, with a lot of classic sedimentary structure characteristics of laminations and stripes, and the output position of the volcanic rocks contains a lot of marine fossils of tentaculitoid. The above evidence indicates that the eruption environment of the volcanic rocks is sea facies. The analysis shows that the ore is closely related to the layered volcanic rocks and shows consistency and continuity with the layered volcanic rocks, and ore sources may be related to the volcanism. It is concluded that the ore deposits in the study area should be of the type of marine volcanic-sedimentary exhalative hot water plus later superposition and alteration.

Abstract:As one of the Himalayan sediments-hosted base metal deposits in Sanjiang region, the newly-found Chaqupacha Pb-Zn deposit is less known. This paper deals with its history, current status and next targets of exploration. Mineralization anomalies were found in the ore deposit on the basis of 1∶200 000 and 1∶50 000 geochemical investigations in the period of 2002～2004. Subsequently, the ore bodies were delineated through 1∶10 000 investigations by means of geology, geochemistry and induced polarization (IP) sounding as well as trench excavation and drilling. It has been so far determined that the ore deposit has (332+333+334) Pb+Zn resources of 996 000 tons. Geological mapping shows that marl and mudstone in Miocene Wudaoliang Formation (Nw) unconformably overlies limestone in Permain Jiushidaoban Formaion (Pj) that rides on clastics in Permain Nayixiong Formation (Pn) in terms of a N-dipping thrust fault in the ore zone. This fault was interpreted as a pop up structure of a S-dipping thrust fault found in a drilling hole. Ore bodies in Kongmolong ore block hosted by Pj limestone are apparently better than those in Chaqupacha ore block that is hosted by Nw and Pn strata. Four E-W-striking anomaly belts of IP sounding and geochemistry occur in the Nw-dominated northern segment, the Pj-dominated middle segment, and the Pn-dominated southern segment in the ore deposit, respectively. Audio magnetotelluric (AM) sounding shows that limestone has higher resistivity than clastics, fault zone, water, and ores. It is suggested that Pre-Cenozoic carbonates are prime prospect targets forexploration of this type of ore deposits in Fenghuoshan-Nangqian fold-thrust belt. Within the ore district, the next exploration targets should be relatively lower AM sounding resistivity parts in limestone of Duocaima ore block where mineralization and IP sounding-geochemical anomaly are present on the surface.

Abstract:Dyke swarms are important in geological investigation. In order to provide valuable information for future research, this paper summarized the multidisciplinary research conclusions about dyke swarms in such aspects as tectonic setting, emplacement mode, genetic mechanism, lithology, geochemistry, isotopic geochronology, geometry and comparative planetology. Dyke swarms were primarily formed in an extensional setting and resulted from magmatic emplacement along the fracture system in lithospheric crust which was caused by magmatic activities such as mantle plumes. The emplacement modes of dyke swarms are mainly vertical and lateral emplacements, and may also be the combination of these two emplacement modes. The lithologic characteristics are varied, with most of the dykes being ultrabasic-basic rocks, suggesting a significant relativity between dyke swarms and hypogene magmatism. The geochemical characteristics of dyke swarms show the tectonic environments, magmatic evolution and source types of magmatic events. Geometrical characteristics of radiating giant dyke swarms have important indicating significance and the center of radiating giant dyke swarms is considered to be the location of the head of mantle plumes. Dyke swarms are important 'piercing points' and very helpful to the palaeocontinent reconstruction. The giant radiating system on the terrestrial planets (Venus) may be the dyke swarms and can imply that such a radiating system once existed in the earth. Dyke swarms have important research values and valuable geological significance in such aspects as paleocontinent reconstruction, implication of mantle plume center, tracing of mantle sources, volcanic edifices and evolvement of regional magmatism, thus playing a great role in geoscience.

Abstract:Natural rubies often show central grayish blue cores in their untreated state, which are usually considered to be of a low quality. Therefore, most rubies are artificially heat-treated at high temperatures to improve the color. During the heating process, the flux accompanied by the process is cooled down and becomes amorphous residues that remain in the fractures or surface cavities of ruby unintentionally, and thus the clarity and transparency of the ruby, to some extent, are enhanced. Subsequently rubies that have experienced the heat treatment are often identified as those with traditional filling treatment, by which the original thoughts of merely conducting artificial enhancement are misunderstood and the values of the rubies are influenced. This paper intends to remove the amorphous residues in the ruby on the experimental basis so as to reassign it to the acceptable range of pure heat enhancement, and in this way the appropriate value of the ruby could be shown on the gem market. The amorphous residues existent in natural rubies due to heat enhancement and treatment are cleared by immersing the rubies in the hydrofluoric acid (HF) with the concentration of 23% in which the glass residues that remain in the fractures and pits of ruby are readily dissolved so as to attain the goal of clearing. ICP-AES analysis of the hydrofluoric acid solution with the amorphous residue solute mentioned above was used to indicate the concentration of Si and Al, namely 28.60 μg/mL and 2.795 μg/mL respectively, by which the weight of the removed residues was roughly calculated so that the filling degree of the amorphous residues that unintentionally added to the ruby could be determined. Fourier transform infrared spectra of ruby specimens were determined before and after the clearing process for comparison. The infrared spectra of ruby prior to the clearing process showed that, in the range of 1 100～1 000 cm^-1, the ruby exhibited broad band positioned at 1 050 cm^-1 due to the unsymmetrical stretching vibration of ν_as (Si—O—Si), which indicated that the residues were amorphous. A sharp band centered at 744 cm^-1 in the 750～600 cm^-1 region corresponded to symmetrical stretching vibration of ν_s (Si—O—Si), whereas none of the characteristic Si—O vibrations caused by amorphous residues was detected by the infrared spectroscopy after the acid treatment of the ruby, and only a broad band in the range of 950～600 cm^-1 featured at 736 cm^-1 and 622 cm^-1 was shown, which was caused by the Al—O fundamental frequencies of corundum and thus displayed the characteristics of crystallized metal oxide, suggesting that the amorphous substances in ruby were removed thoroughly and ruby specimens eventually fell into the pure heat-treatment (enhancement) category rather than the glass filling treatment category. After the performance of clearing experiments on the ruby specimens, the fractures and pits on the surface of the rubies which had previously been covered by amorphous residues were clearly visible under the gemological microscope.

Abstract:The mantle plume hypothesis proposed by Morgan has been in controversy all the time in spite of the fact that it has greatly propelled the development of earth sciences. This paper makes a tentative discussion on the focus problems, probes into the possible causes for the deviation of the volcanic tracks from the present-day locus of the active volcanism and the unfixing of the hot spots, and proposes a new possible dynamic model for the generation and continual development of the mantle plume: the result of long-term action by extraterrestrial objects.