Abstract:Triassic Yushu volcanic rocks are mainly composed of dacites and distributed in the northern part of the North Qiangtang (NQ) terrane. Zircon LA-ICP-MS U-Pb ages of 230±2 Ma (MSWD=0.5) could be interpreted as the formation time of these volcanic rocks. Most samples from the Yushu volcanic rocks are characterized by high SiO₂ and Al₂O₃, obvious enrichment of large ion lithophile elements (LILEs: Rb, Ba, Th and U) and strong depletion of high field strength elements (HFSEs, such as Nb, Ta and Ti) relative to the primitive mantle. They exhibit high εNd(t) (-0.91～-0.53), low I_Sr (0.707) and positive εHf(t) (+3.81～+7.61), suggesting that they probably originated from partial melting of a juvenile crustal component. Compared with the other reported Triassic volcanic rocks of the (NQ), it could be found that most of the Middle to Late Triassic volcanic rocks (MLTV) are concentrated in the northern part or the southern part of the NQ. The Middle-Lower Triassic Yushu volcanic rocks from the south part of the NQ exhibit lower εNd(t) (-8.79～-1.77), higher I_Sr (0.706～0.714) and negative εHf(t) (-15.3～-10.1), implying these rocks might be derived from partial melting of the old crustal materials. Combined with the other new available observations, the authors hold that the Middle-Lower Triassic Yushu volcanic rocks in the southern part of the NQ were genetically related to the slab break-off during the collision between South Qiangtang terrane and NQ, whereas the southward subduction of the Ganzi-Litang Paleo-Tethyan ocean resulted in the generation of the Middle-Lower Triassic Yushu volcanic rocks from the northern part of the NQ.

Abstract:There are several types of xenoliths, such as monzonite, quartz diorite porphyry, black rock and greisen schlieren, in the alkali feldspar granite of the Yaogangxian tungsten deposit, Hunan Province. The xenoliths are different in geological and geochemical characteristics, sources and evolution paths, which implies the genesis and magma evolution history of the Yaogangxian granite. In this paper, the authors studied the petrology, geochemistry of the xenoliths, alkali feldspar granite, and monzonite batholiths formed in late Jurassic period. It is detected that the monzonite inclusion (Ⅰb) came from early crystallization of deep magma chamber similar to the monzonite batholith. The quartz diorite porphyry and black rock xenoliths seem to have been the residue of Precambrian metamorphic rocks in the melting. The greisen schlieren resulted from the transition from the alkali feldspar granite stage to the magma-hydrothermal stage. The fine biotite granite xenolith (Ⅲb) in the quartz porphyry was captured from the supplementary granite which was differentiated from the main magma, or from the granite pluton formed from the supplementary rocks. The granite (Ⅰ) was rich in volatiles, which resulted in strong contamination of the xenoliths, and a certain amount of fluorite, mica, tourmaline and sulfide minerals formed in the xenoliths. The Yaogangxian granite is a product of the intrusion of highly fractionated magma derived from the magma chamber equivalent to monzonite batholith. The quartz porphyry magma directly resulted from the residue of segregation from fractional crystallization of magma chamber, rather than from the alkali feldspar granite of Yaogangxian. It is suggested that the magma evolved in order of magma chamber (main) (coarse monzonite) → fine biotite granite (supplementary) → alkali feldspar granite → magma-hydrothermal transition fluid (tungsten mineralization) → quartz porphyry veins.

Abstract:The Lüjing pluton is one of the "Five Golden Flower" granite plutons in the Western Qinling. Its main lithologies includes porphyroid biotite admellite, phenocryst-bearing biotite adamellite, medium-fine-grained biotite monzonitic granite and coarse-grained biotite monzonitic granite. The zircon LA-ICP-MS dating for the porphyroid biotite admellite, coarse-grained biotite monzonitic granite and medium-fine-grained biotite monzonitic granite from this pluton yielded ages of 221±1 Ma (N=20, MSWD=0.11), 221±1 Ma (N=24, MSWD=0.04) and 218±1 Ma (N=15, MSWD=0.13), respectively. These ages suggest that they were formed during Late Triassic and the porphyroid biotite admellite was formed earlier than the medium-fine-grained biotite monzonitic granite. The rocks are of high-K calc-alkaline to shoshonite series and belong to peraluminous to strong peraluminous I-type granites with A/CNK varying from 1.02 to 1.16, Na₂O+K₂O from 7.65% to 8.84% and K₂O/Na₂O from 1.37 to 1.82. Their REE and trace elements are enriched in LREE, Rb, Th and K and differently depleted in Sr, Nb, P and Ti, with strong negative anomalies of Eu (δEu=0.30～0.70). Crystallization temperature of the Lüjing granites is from 736℃ to 818℃ by zircon thermometer. The geochemical features and formation ages of the Lüjing pluton are similar to those of the Zhongchuan pluton, which is also one of the "Five Golden Flower" granites, suggesting that the Lüjing pluton may have similar petrogenic mechanism and metallogenic potential to the Zhongchuan pluton.

Abstract:The pumpellyite in the eclogites from Uzkaya Salma area of the Belomorian mobile belt, Russia, was formed at the pre-eclogite stage under the condition of sub-greenschist facies. Pumpellyite occurs as inclusions in garnet porphyroblasts and is associated with titanite, rutile, clinopyroxene, chlorite, epidote and quartz. In addition, rare granulous pumpellyite occurs as isolated inclusions in the matrix diopside. According to the composition features of pumpellyite, pumpellyite mostly belongs to pumpellyite-(Al) and rarely belongs to pumpelltie-(Fe). According to the petrographic features and the calculation of phase equilibrium and mineral geothermobarometers, the authors divide the metamorphic evolution of pumpellyite-bearing eclogite into four stages: Stage Ⅰ, which is the pre-peak prograde metamorphic stage characterized by pumpellyite, chlorite, epidote, quartz inclusions within the garnet porphyroblasts, with p-T conditions being t=160～320℃, p=0.2～0.8 GPa according to the stable field of mineral assemblages of pumpellyite + chlorite + quartz and pumpellyite-(Fe) + epidote, based on experimental petrologic study. Stage Ⅱ, the peak eclogite-facies metamorphic stage, which is characterized by the mineral assemblage of garnet + omphacite (the symplectite of diopside and plagioclase) + rutile ± hornblende + quartz; the isopleths in garnet core and the Jd isopleths in omphacite reflect the metamorphic peak condition of 725～740℃ at 1.4～1.5 GPa for the rock. Stage Ⅲ, during which the initial decompressional retrogression began at the high granulite-facies stage characterized by garnet + diopside + hornblende + plagioclase + quartz; the garnet-clinopyroxene thermometer and An isopleths in plagioclase indicate that the p-T conditions t=725～750℃ and p=1.1～1.3 GPa. Stage Ⅳ, which is late retrogression under the condition of amphibolites-facies and is characterized by the mineral assemblage of hornblende+plagioclase±biotite+quartz, with p-T conditions t=670～700℃ and p=0.7～0.9 GPa according to the calculation of phase equilibrium and hornblende-plagioclase thermometer. In conclusion, the pumpellyite-bearing eclogite in Uzkaya Salma area of the Belomorian mobile belt, Russia, shows a clockwise p-T path and the corresponding geothermal gradient in the peak eclogite-facies metamorphic stage is 15℃/km. The initial pre-eclogite metamorphic evolution began under the condition of pumpellyite-epidote facies during subduction. The pumpellyite-bearing eclogite is characterized by isothermal decompression from the peak eclogite-facies to the high granulite-facies. The results obtained by the authors show that "cold" subduction of the plate might have occurred at the early stage of the evolution of the earth during Archean.

Abstract:Geology, geochemistry and isotopic geochemistry are reported for the subvolcanic rocks from the Ashele Cu-Zn deposit. The rocks are basaltic andesites belonging to low-K tholeiite series, and are characterized by intermediate SiO₂ (51.90%～52.85%), MgO (4.44%～5.08%), Al₂O₃ (14.94%～16.11%), TiO₂ (0.99%～1.03%) values and low K₂O (0.01%～0.27%) content. They have low REE values (ΣREE=38.07×10^-6～41.70×10^-6) and exhibit LREE depletion with LREE/HREE ratio of 0.57～0.61 and (La/Yb)_N ratio of 0.84～0.91, and positive Eu anomaly. The trace elements are characterized by enrichment of Sr, Ba, and Th and depletion of Nb, Ta, Zr and Hf. They show both compositional characteristics of the mid-ocean ridge basalt (MORB) and the island arc basalt (IAB). Relatively high εNd(t) values (+6.9～+7.6) suggest that their primitive magma was possibly generated by partial melting of a metasomatic mantle source modified by the subducted slab-derived fluid rather than by the slab-derived melt. Combined with the tectonic evolution of the southern margin of the Altay, the authors hold that the southern margin of the Altay was in an active continental margin setting during the late Paleozoic, and the Ashele Basin was in an island arc or forearc setting.

Abstract:Located in the inner zone of the middle part of the eastern Kunlun orogenic belt, the Shitoukengde mafic-ultramafic intrusion is composed of gabbro-lithofacie, pyroxenite-lithofacie and peridotite-lithofacie. Geological data of field indicate that the emplacement order of each lithofacie is gabbro-lithofacie→pyroxenite-lithofacie→peridotite-lithofacie. This study shows the average content of Ni in spinel is 258×10^-6; the olivine crystals are chrysolite with the forsterite content (Fo) ranging from 81 to 86, the content of Ni in olivine is from 471×10^-6 to 2 279×10^-6 and the average is 1 153×10^-6; En of Orthopyroxene is from 80.35 to 83.89, and the average is 82.51. Based on distribution coefficient of Mg-Fe between olivine and melts, the most Fo-rich olivines indicate that the primary magma of Shitoukengde intrusion belongs to high MgO basaltic magma containing about 10.5％ MgO. This intrusion is derived from 11.2％～14.0％ partial melting of mantle. The study of partial melting, primary magma, structural sign, rock assemblage, direct mineralized markers and mineral assemblage, Ni-content and Fo of olivine shows that the Shitoukengde intrusion has favorable conditions for the formation of copper-nickel deposit and the eastern Kunlun orogenic belt can be important nickel prospective region.

Abstract:Located in the Duobaoshan ore concentration area of Nenjiang County, Heilongjiang Province, the Sankuanggou deposit is a small skarn type iron-copper deposit. On the basis of field geological investigation, ICP-MS test, indoor rock ore appraisal, scanning electron microscopy (SEM) and energy spectrum analysis, the authors studied ore characteristics of the Sankuanggou deposit. Numerous minerals such as empties, ferberite, scheelite, cassiterite, native Bi, tellurobismuthite, wittichite, cobalt-pyrite, hessite, ellurobismuthite, electrum, zinc-bearing enargite, native gold, and kustelite were newly discovered. Useful metals such as copper, iron, zinc, tungsten, cobalt, indium and bismuth should be evaluated so as to understand the characteristics of these elements. In this way, the comprehensive utilization of these elements and the improvement of the economic values can be realized. The formation process of the Sankuanggou deposit can be divided into five stages, in which the endogenous ore-forming period can be divided into four phases, i.e., ① the dry skarn phase, ② the wet skarn phase, ③ the oxide phase, ④ the hydrothermal-sulfide phase, whereas the supergene period only has the supergene phase (phase 5). The iron mineralization occurred at the high temperature stage, whereas the copper mineralization was produced by hydrothermal metasomatism under the medium temperature condition.

Abstract:In this paper, the authors conducted a systematic study of the features of chemical components of different stages of sphalerite in the Huize lead-zinc deposit by using electron microprobe analysis (EMPA) and ICP-MS, so as to explore enrichment regularity and indicative significance of Fe, Zn, Cd, Ge, In and Ag. The results show that hydrothermal metallogenesis of the Huize deposit can be divided into four ore-forming stages, forming fine-grained pyrite, polymetallic sulfides, pyrite-galena and carbonate respectively. Sphalerite can be divided into two generations varying in color from black to red gradually. The early stage sphalerite exhibits enrichment of Fe and depletion of Zn, Cd, Ge, In and Ag. In contrast, the late stage sphalerite shows relative depletion of Fe and enrichment of Zn, Cd, Ge, In and Ag. The content of Cd and Ge has met the requirement of comprehensive utilization, and these two elements are mainly in the form of isomorphism in the sphalerite. Ore-forming temperatures range from 170 to 262℃ at the early stage and below 203 ℃ at the late stage, as shown by the content of FeS in the sphalerite. In combination with the sphalerite Zn/Cd ratios, it is suggested that the Huize lead-zinc deposit is a mesothermal deposit. Spatially, the flowing direction of the hydrothermal fluid was consistent with the strike of the orebodies. Compared with typical lead-zinc deposits, the In, Cd, Ga, Ge, Zn/ Cd, Ga/In and Ge/In of sphalerite in the Huize lead-zinc deposit show characteristics of Mississippi valley-type deposit.

Abstract:Maocaoping is a newly-discovered vein Cu deposit in western Lanping Basin of western Yunnan. The deposit contains abundant hydrothermal tourmaline, which has not been found in the other vein Cu deposits in this region. The authors investigated the characteristics of the tourmaline and analyzed its chemical composition so as to understand the evolution of the hydrothermal system, the factors controlling tourmaline growth and composition, and the ore-forming fluid sources. Mineralization at Maocaoping consists of Cu-bearing quartz-car_bonate-sulfide veins and associated Cu-barren hydrothermal alteration halos. Two types of tourmaline have been identified: ① tourmaline in the alteration halos (T1), which was formed relatively early; ② tourmaline in the veins (T2), which was formed relatively late. T1 tourmaline is anhedral, fine-grained, and aligned parallel to the mylonitic foliation of host rocks. It can be divided into two subtypes: metaclastic-hosted tourmaline (T1-Q) and marble-hosted tourmaline (T1-M). T2 tourmaline is euhedral, coarse-grained, and sub-parallel to the mylonitic foliation of host rocks or grows along or adjacent to the boundaries as comb tourmaline aggregates. The growth characteristics of T1 and T2 tourmaline suggest that the shear stress during the formation of tourmaline at Maocaoping was evolving from strong shearing through weak shearing to no shearing. Electron microprobe analyses of the tourmaline at Maocaoping show that all the tourmaline belongs to alkali group and dravite-schorl series, with dravite being dominant. T2 tourmaline has oscillatory zoning in back-scattered electron (BSE) images, suggesting their growth in an environment where physical and chemical properties fluctuated. The composition of tourmaline at Maocaoping is mainly controlled by the composition of the fluid phase. However, T1-Q tourmaline is slightly enriched in Al, and T1-M tourmaline is slightly enriched in Ca, suggesting that their compositions were slightly influenced by their host rocks, respectively. Tourmaline in Maocaoping is mainly dravitic and falls in 4, 5, 6 regions of the Al-Fe-Mg diagram, implying that the ore-forming fluid could not be derived from magmatic water of S-type granite with no interaction with the pathway rocks of fluid. The significantly higher Fe³⁺/(Fe³⁺+Fe²⁺) ratios in T2 tourmaline than in T1 tourmaline imply that the pre-ore stage had relatively low oxygen fugacity than the ore stage. These features, combined with the characteristics of ore-forming fluid and alteration, metal assemblages, and the lithology of host rocks in the other vein Cu deposits in western Lanping Basin, suggest that a reduced, CO₂_buffered pH value fluid (reduced sulfur>oxidized sulfur) was responsible for Cu transportation in the vein Cu deposits, and increasing oxygen fugacity of fluid might have played an important role in the Cu precipitation.

Abstract:Quartzite jade consists of tiny grained quartz crystallites, and the yellow color is the major color. However, due to lack of conclusive evidence and spectroscopic data, the coloration for the yellow color is unclear, although previous studies suggested that the yellow colored quartzite jade could be related to a very small quantity of nano-sized minerals. In this paper, yellow and red colored quartzite jades were collected from Longling of Yunnan Province, Huoshan of Anhui Province and Hezhou of Guangxi, and the coloration-related spectroscopic data were firstly obtained using the UV-Vis spectroscopic technique with first order derivative. It is found that the yellow colored quartzite jade is caused by goethite with characteristic absorption bands centered on 545～535, and 435 nm, and that the red colored quartzite jade is caused by hematite with absorption bands centered on 595～555 nm. For the mixed yellowish-red or reddish-yellow colouration, the first-order derivatives of the UV-Vis spectra show absorption bands centred on 595～555, 545～535, and 435 nm, indicating that the coloration results from a combination of hematite and goethite.

Abstract:The composition, migration and evolution of hydrothermal fluids as well as the precipitation mechanism are the essence and main difficulties in the study of hydrothermal deposit. Skarn deposit has long been one of the most important hydrothermal deposits in that hydrothermal fluid in this kind of deposit has complex evolution process with multiple stages. Diopside and garnet are the most typical minerals in skarn deposit. Garnets with oscillatory zoning have recorded the property, composition and evolutionary process of the fluids completely in skarn deposits, which suggests that the compositions of garnets of different series have a specific selectivity for physical and chemical environments of hydrothermal fluids at different stages. Chemical elements zoning of gar_ net result from periodic emersion between fluid mobility and mineral reprecipitation, which could indicate the mechanism of major and trace elements zoning in prograde skarn fluid. The values of Fe₂O₃ and Al₂O₃ in differ-ent garnets vary remarkably, which plays an important role in tracing redox environment at the process of fluid evolution. In addition, trace elements constitute a more sensitive probe for detecting fluid evolution to some extent, which could reflect an important process in petrogensis and metallogeny. The grossular is often enriched in Al, Ti, Zr and HREE; however, the andradite is enriched in As, W, Mo, Fe and LREE. In-situ electron microprobe analysis and LA-ICP-MS technology have played an important role in major and trace elements(including REE)analysis of garnets having oscillatory zoning in the process of ore-forming fluid evolution, which can reveal garnets growth mechanism, ore-forming environment and fluid property.

Abstract:According to the principles of thermodynamics, partial melting is a from of phase transition. The protolith will melt when it moves across the solidus along the p-T path. The incongruent partial melting, which is a usual behavior for the natural rocks, can leave a residuum with different bulk composition and mineral assemblage (lithology) from the protolith. Therefore, the residuum can be different from the protolith in "metamorphic facies" and lithology. The "C-type adakites" contain hydrous minerals such as hornblende and biotite, and they cannot be generated by dry melting. The experimental petrology studies show that the mafic (SiO₂ < 50%) system is much easier than intermediate or acidic systems in generating the "eclogitic" residuum during the dehydration melting under the condition p=1.0～2.0 GPa. Meanwhile, the major oxides other than silica in the protolith also control the portion of minerals in residuum and, subsequently, influence the content of Sr, Y and HREE in the melt. Accordingly, the geochemical signal of high Sr and low HREE for the "C-type adakite" is determined by multiple factors such as the p-T condition of melting, the major oxide composition and the trace element content of the protolith. The melts produced from mafic or intermediate-mafic protolith with high potash content (K₂O≈1.0%) contain too much aluminum or sodium, and differ significantly from the "C-type adakite" in composition. However, the mafic protolith with moderate potash content can generate high-silica "C-type adakite" with low degree of melting, but fails to produce the intermediate "C-type adakite".