Abstract:The formation of giant deposits in the collisional environment usually undergoes multiple stages of magmatism, but the genetic relationship between different stages of magmas and the formation mechanism of ore-forming porphyry magma has not been effectively restricted. The giant Qulong porphyry copper deposit, located in the hinterland of Qinghai-Tibet Plateau, has several stages of Miocene magmas, including pre-ore granodiorite (also known as RMCL pluton), ore-forming granite porphyry (P and X porphyry), and post-ore high-Mg diorite porphyry (HMD), and diorite enclaves are found in the granodiorite. Such abundant magmatic sequence provides a good opportunity for the systematic study of the formation mechanism of ore-forming magma of porphyry deposits in collisional environment. This paper systematically analyzed the zircon trace elemental and Hf-O isotopic compositions of various types of magmatic rocks in Qulong and estimates the redox state of Miocene magmas in the Qulong mining area, which constrain the origin and evolution of the magma, especially the formation process of ore-forming porphyry.The results show that the zircons in the RMCL pluton and the diorite enclaves before mineralization have high Ce/Ce^* ratios (average values of 111 and 117, respectively) and similar Hf-O isotopic compositions, with the value of εHf(t) of +7~+10 and +7~+9 respectively, and the value of δ¹⁸O of +5.6‰~+7.1‰ and +4.7‰~+7.0‰ respectively. Whereas zircons from the ore-forming P porphyry have similar δ¹⁸O values (+4.6‰~+6.4‰), but the Ce/Ce^* ratios (29~405, with an average of 149) and the values of εHf(t) (+5~+10) change variably. Zircons from the post-ore high-Mg diorite porphyry (HMD) have similar δ¹⁸O values (+5.2‰~+6.3‰) with the P porphyry, but lower εHf(t) values (+3~+7) and changeable Ce/Ce^* ratios (34~252, with an average of 159).
The positive εHf(t) value and moderate-high δ¹⁸O value of the RMCL pluton and diorite enclaves indicate that they were originated from the juvenile lower crust. The low εHf(t) and δ¹⁸O values of the HMD show that it was formed from the evolved mantle with a strongly altered Hf isotopic composition. The zircon Hf isotopic composition of the P porphyry, varies between the RMCL pluton and the HMD, showing that it was originated from magma mixing between the crust-derived magma (represented by RMCL pluton) and the mantle-derived magma (represented by HMD). Among the Qulong Miocene magmatic rocks, the zircon Ce/Ce^* ratio from the HMD is the highest, indicating that the magma represented by the diorite porphyry also has the highest oxygen fugacity. Therefore, the addition of mantle-derived material during the formation of the P porphyry can provide water and raise the oxygen fugacity of the magma, which promotes the decomposition of saturated sulfides. The whole process is one of the keys to the mineralization of the P porphyry.

Abstract:The Jiudingshan porphyry-skarn Cu-Mo deposit, located in the Sanjiang-Tethys metallogenic domain, is related to the left trending strike-slip fault of Jinshajiang-Ailaoshan tectonic belt. Field observations have identified the metal zonation in Jiudingshan, including the Mo-Cu mineralization in the inner porphyry system, Cu-Mo mineralization in the skarn system from the intrusion-carbonate contact zone, and the weakly Pb-Zn mineralization in the distal wall rocks. Trace element analyses on zircons from ore-bearing monzogranitic porphyry and porphyritic-like granite have yielded an average Ce⁴⁺/Ce³⁺ ratios of 218.0 and 218.6, respectively, which demonstrates an oxidative condition. Hydrothermal garnets from skarn system are well zoned and exhibit a large variation in Al and Fe contents. The dark cores of garnet are belong to andradite and enriched in LREEs, Mo and W, whereas the bright rims share an increase in Al and are enriched in Eu, U and Cu. Further Cu-Ag-Pb-Zn-Mo-W-Bi-Sn-As-Sb-Ti analyses on mineralized intrusions and orebodies have indicated a similar zonation observed in the field. The metals, like Cu, Ag and W, are commonly enriched in the same pattern while Mo shares no relationship with Cu. It can be concluded that an sulfur-unsaturated magma was more easily enriched and brought the Cu and Mo under high oxygen fugacity condition. The transition of Fe-rich to Al-enriched endmember in garnet from skarn system has suggested a fluid boiling process under a less oxidative condition. This process would inhibit the transportation of Mo complexes into skarn system but has the negligible impact on the solution of Cu, which finally led to the high Mo/Cu orebodies in porphyry system and high Cu/Mo orebodies in skarn system.

Abstract:This paper presents the petrology and geochemistry of the middle-late Jurassic adakitic granites (165~153 Ma) in the southeast edge of Dayao Mountain in the southwestern part of the Qinhang junction zone, and discusses its characteristic attribute of adakitic and TTG rocks. The SiO₂ content of the rocks varies from 63.76% to 72.13%. The rocks show adakitic features with high Al₂O₃(≥ 15%), low MgO(<3%), depleted HREE, positive Eu anomaly (some of them are weakly negative Eu anomaly), low Y(≤ 18×10^-6) and Yb(≤ 1.9×10^-6), high Sr(>300×10^-6) and Sr/Y(>20). Combined with the study of regional tectonic evolution, it is considered that the Jurassic adakitic granite was formed in the intracontinental extensional tectonic setting, which is the product of partial melting of the thickened lower crust in the continental intraplate (uplift area), and belongs to the intracontinental non-arc environment I-type granite. The Jurassic adakitic granites are similar to the two high-pressure TTG subclasses of low-Mg andesite/diorite series (LMA) and Mg andesite/diorite series (MA). They are the inheritance characteristics of arc-type rocks melting in the lower crust of the Paleozoic subduction accretion zone, and belong to non-subduction genesis, which has nothing to do with the Mesozoic Paleo-Pacific subduction slab melting process. They are highly coincident with the early Paleozoic subduction accretion zone in the southern margin of Dayao Mountain, and closely adjacent to the early Paleozoic TTG intrusive rock assemblage, suggesting that they may have originated from the partial melting of basaltic rocks in the oceanic subduction zone or the lower crust of the continental margin arc in the early Paleozoic, so they have the characteristic attributes of oceanic subduction.

Abstract:Leucogranitics rocks, crop out in the eastern Tethys Himalaya Cuonadong dome, southern Tibet, have characteristic minerals such as muscovite, garnet and tourmaline, and show the characteristics of highly differentiated magmatic rocks. From two-mica granite, tourmaline granite to garnet granite, alkaline feldspar is orthoclase, plagioclase evolved from oligoclase to albite, the content of Al₂O₃ and Na₂O in muscovite increased gradually, reflecting the evolution trend of granite towards aluminum-rich and sodium-rich. In the two-mica granite, the X_Fe and Al^Ⅵ of biotite increase gradually, which indicates that there is crystallization differentiation evolution in the two-mica granites. The variation of the contents of X_vac, Al, Mg and Fe in tourmaline reflects the increase of Na content in the magmatic crystallization environment from tourmaline granite to granite pegmatite, indicating that the degree of crystallization differentiation of granite pegmatite is higher than that of tourmaline granite. The characteristics of garnet with high X_Fe and X_Mn values are also the marks of highly fractionated granites. The Cuonadong two-mica granite was formed by long-term crystallization of a crystal mush composed of early magmatic crystalline minerals and residual parent magma, while tourmaline granite and garnet granite are formed by derivative melts separated from crystal mush.

Abstract:Yuanjiang River is an important source of diamond placer in Hunan Province, where the garnet and diamond are common heavy minerals in placer. It is of great significance for revealing the source and formation conditions of diamond placer in Hunan Province to analyze and screen garnets related to diamond. In this paper, detrital garnets (160 grains, 80 grains of DJZ-7-1 sample and 80 grains of DJZ-10-1 sample) in Chenxi area of Yuanjiang River, and inclusion garnets in diamond (5 grains) in Hunan Province were selected and analyzed by mineralogical, geochemical and statistical methods. The results show that the fluvial detrital garnets are mainly Fe-Al and Mn-Al garnet series, a few of them contain diamond inclusions. Cluster analysis, linear discriminant analysis and logistic regression analysis indicate that some G3 eclogite garnets may have genetic relationship with diamonds. Major and trace elements are certain differences between the two sites; analysis result shows that the garnets of DJZ-7-1 samples are more closely related to diamond. Based on the analysis of the Si value of detrital garnets (>3.02) and the limited temperature and pressure conditions of Hunan diamond in previous study, it is considered that Hunan diamond may be formed in the mixing area of peridotite and eclogite with a depth of less than 220 km, which is the dominant source area of lamproite-type diamond. Therefore, it is suggested that G3 garnet and lamproite should be further searched in the upper part of Chenxi, Yuanjiang River, in order to prospect the primary diamond deposits in Hunan Province.

Abstract:In order to discuss the characteristics of the tectonic alteration zone and the origin of the fluorite deposit in Daping, North Fujian, the characteristics of major, rare earth and trace elements in the tectonic alteration zone of Daping fluorite deposit are studied. The results show that the alteration of Daping fluorite ore is mainly consisted of sericitization, silicification and fluorite mineralization, and that the fluorite mineralization zone is characterized by low total rare earth elements, enrichment of heavy rare earth elements and high CaO and F contents. According to the ore structure of fluorite mine and its alteration characteristics, it has proved that the Daping fluorite deposit consists of at least three ore-forming stages, and belongs to the post-magmatic mesothermal-epithermal filling type.

Abstract:The Sandaomingshui deposit, located at the western part of the Beishan district, is a recently discovered medium-sized Cu-Zn deposit. Aim to understand its genesis type and controlling factors, geological characteristic of the Sandaomingshui Cu-Zn deposit is studied in this paper. According to the alteration features, mineral assemblages and crosscutting relationships, the mineralization and alteration process have be divided into the early-(stage Ⅰ), middle-(stage Ⅱ) and late-mineralization (stage Ⅲ) stages. The early-mineralization stage is characterized by the occurring of pyrite±chalcopyrite±sphalerite and pyrite-sphalerite±chalcopyrite veins, and disseminated pyrite-chalcopyrite-sphalerite assemblage, with chlorite±sericite alteration occurred in wall rocks, which are similar to VMS-type deposits. The middle-mineralization stage, main mineralization stage, is marked by phyllic alteration and chalcopyrite-pyrite-sphalerite assemblage, in which Cu-Zn-rich minerals (chalcopyrite and sphalerite) occurred during ductile deformation. The late-mineralization stage is featured by the quartz±chalcopyrite±molybdenite±pyrite and calcite veins, with unconspicuous alteration, which were hosted by open fractures. According to the alteration and mineralization features of the Sandaomingshui Cu-Zn deposit and regional mineralization characteristics, Cu-Zn mineralization of the Stage Ⅰ was likely VMS-type. The stage Ⅱ Cu-Zn mineralization overprinted on the stage I and formed the major Cu-Zn orebodies of the Sandaomingshui, which was controlled by ductile shear zones. The stage Ⅲ Cu-Mo mineralization superposed on the earlier Cu-Zn mineralization.

Abstract:The detrital heavy minerals are relatively stable and contain important genetic information. The EPMA composition analysis of them can provide the provenance and basin tectonic setting. The first member of Shoush-angou Formation is mainly composed of sandstone and conglomerate,and the second member is mainly composed of siltstone and mudstone. The assemblages of heavy minerals in the sandstones are mainly composed of zircon, spinel and garnet, suggesting that the provenance rocks were magmatic and metamorphic rocks. The results of electron probe microanalysis show that tourmalines were derived mainly from lithium-poor granite and metasedimentary rocks, spinels were sourced from island arc basalts and mid ocean ridge basalts, and garnets from the source of high-grade metabasic rocks. Comprehensive provenance analysis shows that they were mainly derived from Diyanmiao ophiolite,Xilinhot complex and basalts of Benbatu Formation. Combined with regional geological correlation, the sediments of Shoushangou Formation were formed in a backarc basin, suggesting that the Paleo-Asian Ocean was not closed in the Early Permian.

Abstract:In nature, copper mainly occurs in sulfide minerals. At present, only the sulfur β-factors of several Cu-bearing sulfides and the iron β-factor of chalcopyrite have been determined, and the β-factors determined by different researchers are different, impeding the application of S and Fe isotopes as powerful tracers in tracing the formation and evolution of porphyry copper deposits. In this study, the first-principles methods are used to compute the reduced partition function ratio of S isotopes (10³lnβ_34-32) for Cu-bearing sulfides as well as the reduced partition function ratio of Fe isotopes (10³lnβ_57-54) for Cu-Fe sulfides in the temperature range of 0~1 000℃. 10³lnβ_34-32 decreases in the order of covellite>cubanite>chalcopyrite ≈ villamaninite>bornite>chalcocite, and 10³lnβ_57-54 decreases in the order of cubanite ≈ chalcopyrite>low-bornite>high-bornite>intermediate-bornite>intermediate-Cu₈Fe₄S₈. 10³lnβ_34-32 of Cu-bearing sulfides displays weak correlations with S coordination number, the average metal-sulfur bond length, and the average bond lengths of all the bonds formed by S, while 10³lnβ_57-54 of Cu-Fe sulfides displays an approximately negative correlation with the average Fe-S bond length. S isotope fractionation caused by the phase transition of chalcocite is very large, while S isotope fractionation caused by the phase transition of bornite is negligible. The results of this study can provide theoretical evidence for tracing porphyry copper deposits and other types of sulfide deposits.

Abstract:The southwestern Tianshan high- and ultrahigh-pressure metamorphic belt is a rare example of metamorphosed accretionary mélange exhumed from great depths, as a result of the closure of the paleo-Tianshan Ocean. The internal structure of the subduction complex is still controversial. Taking a~4 km-long N-S cross section in the Muzaerte area as an example, this paper summarizes the field occurrences, mineralogy and metamorphic evolution of the southwestern Tianshan high- and ultrahigh-pressure metamorphic belt. These studies suggest that there expose two types (i.e., UHP and HP) of lawsonite eclogites, but most of them were strongly retrogressed and deformed at blueschist- and greenschist-facies conditions. These metabasic rocks constitute two eclogite belts, including northern and southern, that are separated by a fault. The Muzhaerte UHP lawsonite eclogites and their host rocks experiencedsimilar peak metamorphism, constituting the western termination of the UHP metamorphic belt of southwestern Tianshan. Compared with the eastern Akeyazi UHP eclogites, they are different in terms of deformation features, rock assemblages and metamorphic experiences, probably indicating that deeply subducted slab occurred different metamorphic and transform evolution along-strike variations of tectonometamorphic processes during exhumation. These results are fundamental to unravel the metamorphic evolution of subducted accretionary mélange and related geodynamics during slab subduction and uplift.

Abstract:Using conventional gemmological instruments along with electron probe microanalysis, electron paramagnetic resonance spectroscopy and ultraviolet visible spectroscopy, the samples of yellow and brown tremolite jade were studied, discussing the causes and differences of coloration elements in different dark and light samples. The main reasons for the coloration of yellow tremolite jade are the charge transfer transition of O^2-→Fe³⁺and the ⁶A₁→⁴T₂(D) transition of Fe³⁺, while the coloration of brown tremolite jade is mainly caused by ⁶A₁→⁴E(D) and ⁶A₁→⁴T₂(D) transitions of Fe³⁺ and Jahn-Teller effect of Mn³⁺ ions. The charge transfer transition of O^2-→Fe³⁺ in yellow tremolite jade leads to the absorption at 412~500 nm in the visible region, which is an important factor for forming and controlling the color of yellow tremolite jade, while the yellow green light absorption caused by Mn³⁺ in brown tremolite jade shows the complementary color of yellow green. In addition, the charge transfer of Fe²⁺-Fe³⁺ and Fe²⁺(⁵T₂)+Fe³⁺(⁶A₁)→Fe²⁺(⁵E)+Fe³⁺(⁶A₁) are also part of the reasons for the coloration of brown and yellow tremolite jade.

Abstract:The transformation of well-crystallized macrogranular gibbsite to boehmite has been studied by hydrothermal method, at 165℃, 175℃, 185℃ and 195℃ for 12 h, respectively. Samples have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) before and after autoclaving. The transformation of gibbsite to boehmite is a dissolution-precipitation mechanism, rather than a solid-state process. The rate of transformation of gibbsite to boehmite in water vapour was faster than the rate in water. The size of obtained boehmite crystal (4~7 μm) reduced to thirtieth of the macrogranular gibbsite (120~200 μm), indicating that well-crystallized macrogranular gibbsite can be used to produce particulate boehmite. Because boehmite firstly crystallized on the outside surface of gibbsite particles during the period of gibbsite to boehmite, which keep the pseudomorphism of gibbsite particles with the double-layer structure, the hydroxide particles of aluminum were obtained by controlling the temperature and reaction time. Moreover, the hollow particles of boehmite aggregation were perhaps formed.