Abstract:The Dingqing ophiolite is located in the eastern segment of the Bangong Co-Nujiang suture zone which is juxtaposed with the Yarlung Zangbo suture zone, and is an important area for finding chromite deposits in China. The ophiolite body is distributed in the southeast direction, with a total area of nearly 600 km². It is mainly composed of mantle peridotite, pyroxenite, gabbro, diabase, basalt, plagiogranite, siliceous rock and argillaceous rock. According to the spatial distribution, the Dingqing ophiolite is divided into east and west ophiolite bodies. On the basis of previous work, 83 chromite ore spots were discovered through geological mapping, measured sections, trench recording and drilling, including 27 in the east ophiolite body and 56 in the west ophiolite body. According to the production characteristics of the chromite spots and types of wall rock, Dingqing chromite can be divided into four types:Type I:chromite orebodies are vein-like, the wall rock is stripe-like or lenticular dunite and massive harzburgite; Type Ⅱ:chromite orebodies are lenticular, podiform or irregularly agglomerated, the wall rock is thin-shelled dunite and porphyry or massive harzburgite; Type Ⅲ:chromite is diffusely distributed in dunite, and the wall rock is stripe-shaped dunite and massive or porphyry harzburgite; Type IV:chromite orebodies are produced in stripes, and the wall rock is stripe-like or lenticular dunite and directional harzburgite. According to the structural characteristics of chromitites, they are mainly divided into four types:massive, vein, disseminated and disseminated stripe. Massive and veined chromitites are the main types of chromitites, a small amount is disseminated and disseminated stripe, with a small amount of nodular or bean-like structure developed in local dunite. In this study, 13 representative chromite ore spots were selected for detailed studies of petrology, mineralogy, and mineral chemistry. According to the mineral chemistry characteristics of chrome spinel in the chromitites, the chromite bodies can be divided into four types, i.e., high chromium (Cr^#78-85), medium-high chromium (Cr^#60-74), medium chromium (Cr^#30-51) and low chromium (Cr^#9-14)(Cr^#=100×Cr/(Cr+Al)). The east ophiolite body contains medium-high chromium and medium chromium type chromitite, with the lack of high chromium type chromitite; the west ophiolite body contains high chromium and medium chromium type chromitite, and lacks medium-high chromium type chromitite. At the same time, there is a very low Cr# chromitite in the east rock mass and the west rock mass, which is tentatively assigned to "low chromium type chromitite". These different types of chromitites have a certain correspondence with the field output, and may also restrict their geneses. This content will be expanded in subsequent articles. A comparison with Luobusa podiform chromitite and peridotite in mineral assemblages and mineral chemistry shows that they have many similar characteristics, even with the probable existence of a good prospecting space.

Abstract:The emplacement mechanism of ophiolites is a scientific problem in the plate tectonics which has not been clearly explained till now, and such a situation restricts resolving many secondary questions. In this paper, a new analytical model is proposed on the basis of combination of the key published data and the field observations. The large length of the ophiolite belt suggests a close relation between its formation and the converging plate process; the two phases of arc magmatism in the Gandise magmatic arc indicate translation of the tectonic features at the converging plate edges; there are not sufficient geological, petrological and mineralogical constraints in the previous reports about boninite; the universal discovery of the strongly reduced crystal populations suggests that the obduction process of ophiolite was related to the large scale activity of the deep fluids. Accordingly, a new model of ophiolite emplacement is proposed and called fluid-assisting model, in which the processes such as rollback and break-off of the subducted plate, fluid-lithosphere interaction, and oceanic lithosphere dome seem to have been the essential factors controlling ophiolite emplacement.

Abstract:The lead stable isotope geochemistry of regional metallogenic belts is an effective means for making regional geochemical zoning, tracing diagenetic ore-forming sources, and elucidating the genesis of deposits. Based on the unique tectonic setting of China, the authors have traced the diagenesis of large-sized and superlarge porphyry copper deposits and copper-nickel sulfide deposits in China based on the geochemical field of the lead isotope composition of the upper mantle in China for sources of ore-forming materials. Some conclusions have been reached:1. The porphyry copper deposit and the copper-nickel sulfide type ore-forming parent rock inherit the lead isotope composition of the upper mantle of the adjacent land mass; 2. The lead isotope composition of the ore-bearing rock mass and ore minerals of the two types of deposits is obviously consistent with each other, and the two traces are homologous; the lead isotope composition of the shell fused granite and surrounding strata is different from that of the ore; 3. In addition to inheriting different lead isotope composition characteristics of the mantle on each land mass, the lead isotope composition of rock and ore in the porphyry copper deposits and the copper-nickel sulfide deposits of each land mass also trace the "block effect" of the coupling between the crust and the mantle layers. At the same time, the lead isotope composition of the upper mantle may exhibits "delay effect".

Abstract:Important implications for the interior workings, constituent, circulation between crust and mantle, convection between core and mantle of the Earth can be drawn by studying diamonds and their hosted rocks. Based on the geological comparison of metallogenic kimberlites from super-giant deposits in Botswana and Mengyin and Wafangdian deposits in China, the authors put forward some exploration suggestions and prospecting clues as follows:(1) Kimberlite is an unique diamondiferous rock in Botswana, whereas lamproite is a main hosted -rock in South China craton including two important lamproite zones along the Jiangnan orogenic belt and northern margin of South China craton. Kimberlite is dominantly distributed in the North China craton, which is composed of three kimberlitic zones along Tanlu fault, Trans-North China orogen and northern margin of North China. Two industrial value diamondiferous kimberlite deposits are distributed in the Tanlu zone. (2) In-situ U-Pb age and Sr, Nd isotopic data of perovskites show that 86-97 Ma Orapa kimberlites and 456-470 Ma Mengyin and Wafangdian kimberlites have low ⁸⁷Sr/⁸⁶Sr ratios of 0.703-0.705, medium εNd(t) values ranging from -0.09 to 5, indicating that primary kimberlitic magmas were likely derived from primitive mantle or convective lower mantle. (3) Primary kimberlites in Botswana dominantly occur as pipes, while in China they mainly occur as irregular fissures, expressed as dykes and lesser extent sills. Crater facies are pervasively observed in Orapa and Jwaneng kimberlite pipes in comparison with hypabyssal (or root zone) facies in Mengyin and Wafangdian pipe clusters. (4) Orapa A/K1 and Jwaneng mines are a few diamondiferous kimberlitic pipes yielding predominantly eclogitic xenoliths and E type diamond. In contrast, Letlhakane, Damtshaa and Karowe mines also occur in Orapa cluster, Mengyin and Wafangdian mines from the Tanlu kimberlite belt have mainly peridotite xenoliths as well as P type and E type diamonds. (5) Some exploration suggestions and prospecting clues of diamondiferous kimberlites are presented as follows:(A) Deep faults cutting through on-craton and off-craton subcontinental lithospheric mantle play a role in the emplacement of kimberlites; (B) Soil sampling for kimberlite indicator minerals such as picroilmenite and garnet, Cr-rich rutile, Cr-spinel and Cr-diopside is a primary exploration tool; (C) Geophysical surveys such as aeromagnetic mothed should be combined with soil sampling for better prospecting results. (6) Work in diamondiferous prospecting target areas in the Tanlu kimberlite zone, Jiangnan lamproite zone and Tarim block should be further strengthened. Illuvial type diamond deposits in China have great potential for mineralization.

Abstract:"Geological interface" is the boundary of various geological units in the earth's crust. It clarifies the contact relationship between geological bodies, and usually also a geological space where the deposit is formed."Metallogenic interface" refers to the place where mineralization occurs and geological interface with the deposit."Marginal metallogenesis" clarifies the occurrence of mineralization at the metallogenic interface and its evolution process, ore-forming material enrichment and post-mineralization preservation process. According to the differences in geological and metallogenic processes, the metallogenic interface can be divided into 9 groups. Metallogenic interfaces are the most easily recognizable and direct indications for prospecting, and constitute one of the theoretical bases of scientific prospecting, and summarize the law of mineralization.

Abstract:Located in the central segment of the Bangong Co-Nujiang Suture Zone, the Dongqiao ophiolite is divided into east and west massifs. The research on the origin and tectonic setting of the ophiolite in the Bangong Co-Nujiang suture zone can provide key clues for revealing the tectonic evolution of the Neo-Tethys and the collision between the Indian plate and the Eurasian plate. The area of the west rock massif is relatively large, consisting of mantle peridotites, pillow-like basalts, gabbros, diabases, etc., while the area of the east massif is small and contains only part of mantle peridotites, with the faults being in contact between different units. Based on petrology, mineralogy and geochemistry of the peridotites in Dongqiao ophiolite, the authors have reached some conclusions:(1) The Dongqiao peridotites are dominated by harzburgites, with minor proportion of dunites (about 15%). The podiform chromitites mainly show banded and disseminated structures, and occur in a thick layer of far-extending dunites. (2) The clinopyroxene content of Dongqiao peridotites is less than 3%. The mineral and the whole-rock geochemistry show that Dongqiao peridotites were formed after 22%-28% degree of partial melting of the spinel-phase mantle source, higher than the partial melting of abyssal peridotites (10%-22%). (3) The Cr^# values of spinels in the Dongqiao peridotites are higher than 60. The chondritenormalized REE patterns of the Dongqiao peridotites display enrichments in LREE. In the primitive mantle-normalized spider diagrams, the Dongqiao peridotites exhibit slightly positive Rb, U, Zr, Sr anomalies and slightly negative Hf, Nb anomalies. These geochemical characteristics jointly indicate the selective enrichments of LREE and some trace elements according to interaction between the residual mantle and the fluid/melt above the subduction zone. Based on the mineral composition and the whole-rock geochemical characteristics of Dongqiao peridotites, the authors hold that the Dongqiao peridotites were formed in the dilated environment of the mid-ocean ridge, and then were influenced by intra-ocean subduction, resulting in highly partially melted peridotites interacting with the fluid/melt above the suprasubduction zone.

Abstract:Most of chromitite ores produced in China are from the Yarlung Zangbo ophiolite belt (YZSZ), which is divided into three parts:the eastern part (Qu Shui to Mo Tuo), the middle part (Ang Ren to Ren Bu) and the western part (Saga to the Sino-Indian border). Furthermore, the western part contains north sub-belt and south sub-belt. For a long time, most of studies have focused on the eastern part and middle part, with very insufficient studies conducted on the western part, especially on the north subbelt, which inhibits mineral exploration along the YZSZ. Cuobuzha ophiolite is located in the north sub-belt, which occurs along a NW-SE trending belt and is mainly composed of harzburgite with diabase dykes. The field investigation discovered several chromite orebodies 0.5-1 m long and 0.2-0.5 m thick within the ophiolite. All of the ores are massive. The analytical results by electron-probe micro-analyzer (EPMA) show that the Cuobuzha chromitite is of typical high-Cr variety with Cr number[Cr^#=100×Cr/(Cr + Al)] ranging from 75 to 78, and Mg number[Mg^#=100×Mg/(Mg + Fe²⁺)] ranging from 66 to 69. Calculated results show that the ratio of FeO/MgO ranges from 0.51 to 0.65, and that the values of Al₂O₃ and TiO₂ are 11.27%-12.1% and 0.19%-0.4%, respectively, revealing that the Cuobuzha chromitite has boninitic affinities. However, the occurrence of clinopyroxene exsolution indicates that it should have experienced a deep process.

Abstract:The Jisong Pb-Zn deposit is one of the newly found deposits in the Tethys Himalaya belt. Orebodies mainly occur as veins in several nearly NE-striking faults. The veins are mainly composed of quartz, calcite, and sulfides. Hydrothermal sericite is genetically associated with zinc and lead mineralization and coexists with quartz, calcite, pyrite, sphalerite and galena. These sericite grains were separated for Ar-Ar isotopes dating. The results yielded a plateau age of (16.61±0.30) Ma at 760-860℃, with the corresponding isochron age being (16.64±0.30) Ma. These two ages are the same within the error, indicating that they can represent the formation age of the Jisong Pb-Zn deposit. Tethys Himalaya developed an Au (Ag) mineralization event in the main collisional orogenic setting, and the Ar-Ar age of the Jisong deposit indicates that Pb-Zn mineralization represented by Jisong in South Tibet occurred at late collisional stage. Combined with close spatial relationships as well as the similarities in time and Pb isotopes between the Jisong deposit and the Cuonadong leucogranite, the authors hold that the leucogranite possibly offered material and heat to the Jisong ore-forming hydrothermal system.

Abstract:An altered syenogranite pluton was found in Fengyu area, southern Taihang Mountain of central-eastern North China Craton, which unconformably underlies the Changcheng System. The rock type is biotite granite, which has undergone obvious Kfeldspar alteration and sericitization. The rocks are characterized by low SiO₂ (SiO₂=67.46%-68.89%) and high K₂O + Na₂O (K₂O + Na₂O=8.09-9.62, K₂O/Na₂O >> 1) content, with aluminum index A/CNK being 1.20-1.57, showing features of peraluminous, calc-alkaline A-type granite. The pluton is also characterized by enrichment of LILE and depletion of Ba, Nb, Ta, Sr, P, Ti, as well as high ∑REE values (192-774 μg/g, 483 ug/g om average). LA-ICP-MS zircon U-Pb dating of Fengyu altered syenogranite pluton yielded an ²⁰⁷Pb/²⁰⁶Pb age of(1790±22) Ma (n=22, MSWD=0.80), which is by far the most direct control of the lower limit age of Changcheng System in southern Taihang Mountain. Petrochemistry, rare earth elements, trace element geochemistry and isotopic geochronology all prove that Fengyu altered syenogranite pluton was formed in an intraplate extensional environment in the Paleoproterozoic period, thus providing an important magmatism evidence for the existence of northeast Xiongerrian trident continental rift; they also show that the Taihang Mountain area where Fengyu altered syenogranite pluton was formed and the western Henan Province where Xiong'er Group volcanic rocks were developed constitute part of the Xiongerrian trident continental rift, which thus provides an important support for the stratigraphic correlation of the Changcheng System between Taihang Mountain area and western Henan Province.

Abstract:The lower Hongshuichuan Formation is mainly distributed around Tuosuo River between Middle Kunlun orogen and South Kunlun orogen in eastern Kunlun Mountains. In this paper, the authors made a comparative study of the conglomerate of Lower Hongshuichuan Formation distributed in Baoriherie area and Kekesha area in components, psephicity and granularity of gravel. The results show that the main components of the gravel are limestone and metamorphic rock in Kekesha area. The main components of gravel in Baoriherie area are granite and metamorphic rock. LA-ICP-MS zircon U-Pb dating of granite yielded magmatic crystallization age of(464.9 ±9.3) Ma(MSWD=2.9) from Baoriherie area. The characteristics of gravel show that the source of the Kekesha area is Halaguole Formation in Qingshuiquan area, whereas the source of the Baoriherie area is Caledonian magmatic rock. These data indicate that the source of Lower Hongshuichuan Formation is Caledonian magmatic rock rather than arc granite of late Hercynian-Indosinian period. Combined with previous data, the authors hold that the Buqingshan-A'nimaqing Ocean began the northward subduction in late Permian, and the Hongshuichuan Formation was a set of sedimentary products in the fore-arc basin. It is held that Buqingshan-A'nimaqing Ocean began its subduction in early Triassic.

Abstract:This paper systematically summarizes the mineralization conditions of the volcanic arc metallogenic belt in southern Lancang River and the geological features of the Hongdoushan ore district. The authors studied the tectonic geochemistry at 1272 and 1220 level. On the basis of the analysis of the data collected from tectonic rock samples and by means of R-type cluster analysis and factor analysis, the authors delineated combinational anomalies of mineralization elements. The authors found that the distribution of anomalies in the altered rock is controlled by NE-trending F₁ fracture and NWW-EW-trending F₃ fracture in the mining area. The zonation of high temperature and low temperature anomalies occur successively from fracture to surrounding rock, indicating the direction of fluid migration as well as the information of orebodies and provided evidence for deep ore prediction. Through the researches on structural ore-controlling regularity and tectonic geochemistry, the authors found the occurrence and deep extension of the NE-trending orebody, delineated the orebodies controlled by NWW-and nearly EW-trending fractures at the 1272 level. Field work demonstrated favorable ore-prospecting areas in the anomaly distribution zone and deep prediction target area, the copper orebody was delineated and predicted, which extends stably to the depth. The authors estimate that the resource reserves are about 50,000 tons. The magmatic hydrothermal orebody controlled by tectonics has the prospect of reaching the medium copper deposit.

Abstract:Paleozoic Carboniferous-Permian strata occur sporadically in the eastern part of the Sanjiang Basin, their total organic carbon and other evaluation indexes of hydrocarbon source rocks are good, but their distribution in the basin has been unknown. In the background of the increasingly high cost of development and the urgent need of new oil and gas replacement area, the authors carried out oil and gas geological survey with gravity-magnetic-electric prospecting engineering in the Sanjiang Basin and established a comprehensive inversion profile through qualitative analysis, integrated information inversion and imaging for the purpose of identifying the developmental characteristics of the Carboniferous-Permian strata in the Sanjiang Basin,. The physical properties of the strata in the study area were systematically studied and summarized, and the distribution characteristics of the Carboniferous-Permian strata was preliminarily characterized by the use of magnetotelluric sounding inversion resistivity for the low-resistance marker layer. Then, the distribution characteristics of the Carboniferous-Permian mudstone were explored by the residual treatment of the two-dimensional inversion resistivity section.

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