Sedimentary Environment and Mineralization of the Black Shale Polymetallic Layer in the Early Cambrian,SW China:Constraints from in situ LA-ICP-MS Analysis of Pyrite

A polymetallic layer is usually developed at the bottom of the early Cambrian black shale in Guizhou Province.The mineral that makes up the polymetallic layer is related to the sedimentary facies.To analyze the differentiation mechanism between polymetallic deposits(Ni-Mo and V),the Zhijin Gezhongwu profile located in the outer shelf and the Sansui Haishan V deposit located in the lower slope are selected to study the in situ sulfur isotopes and trace elements of pyrite.The results show that δ^(34)S values of pyrite vary widely from−7.8‰to 28‰in the Gezhongwu profile,while the δ^(34)S values are relatively uniform(from 27.8‰to 38.4‰)in the Haishan profile.The isotopic S composition is consistent with the transition that occurs in the sedimentary phase from the shelf to the deep sea on the transgressive Yangtze platform;this indicates that the δ^(34)SO_(4)^(2−)values in seawater must be differently distributed in depositional environments.The sulfur in the Ni-Mo layer is produced after the mixing of seawater and hydrothermal fluid,while the V layer mainly originates from seawater.Overall,the Ni-Mo and V deposits have been differentiated primarily on the basis of the combined effect of continental weathering and hydrothermal fluid.

Deep-seated structure and metallogenic dynamics of the Ailaoshan polymetallic mineralization concentration area, Yunnan Province, China

The Ailaoshan poly-metallic mineralization concentrated area (MCA) consists of the well known Ailaoshan metallogenic belt and adjacent mineral districts and/or deposits. Located in an area of several complex and intersecting tectonic units, the Ailaoshan poly-metallic MCA is controlled by deep crustal and mantle tectonism. Through interpretation of remote sensing images, we identified a large ring structure system that surrounds the MCA. This ring structure encloses regional deep-crustal faults, ductile shear zones, geothermal anomalies, magmatic rocks, and the major mineral deposits, all of which are the reflections of deep tectonic geodynamics that have been long active in this area. Geophysical data indicate that the crust is comprised of relatively stable two or three layers, with some irregular lower-velocity belts. The Moho in the ring sutures occurs as an area of local uplift. There exists an obvious transitional zone between the crust and mantle boundaries. Asthenopheric mantle shows multi-layer upwelling, which indicates multiple events during different geological epochs. It is believed that these mantle events or pulses were responsible for the formation of the regional shear zones, magmatic rocks, and polymetallic orebodies. Furthermore, an integrated metallogenic dynamics model related to the asthenopheric upwelling pulses in the MCA is established, defining events as old as Late Paleozoic.

The effect of Fe-Mn minerals and seawater interface and enrich-ment mechanism of ore-forming elements of polymetallic crusts and nodules from the South China Sea

Ferromanganese crusts and nodules are important submarine mineral resources that contain various metal elements with significant economic value. In this study, polymetallic crusts and nodules obtained from the South China Sea(SCS) were determined by using X-ray power diffraction(XRD), Raman spectroscopy(RS), Fourier transform infrared spectroscopy(FTIR), and X-ray photoelectron spectroscopy(XPS) to systematically investigate and analyze the mineralogical and spectral characteristics of the Fe-Mn minerals. XRD measurements revealed that the SCS polymetallic crusts and nodules were composed of vernadite, quartz, and plagioclase. The nodules also contained todorokite. The Fe-phase minerals of the SCS crusts and nodules were composed of amorphous Fe oxide/hydroxide, and the Mn-and Fe-phases minerals exhibited relatively poor degrees of crystallization. FTIR results showed that the Fe-Mn minerals in the crusts and nodules included a large number of surface hydroxyl groups. These surface hydroxyl groups contained protons that could provide reactive sites for complexation of ore-forming elements in seawater. XPS results indicated that the surfaces of the Fe-Mn minerals mainly contained Fe, Mn, and O. Fe was present in the trivalent oxidation state, while Mn, which may contain several bivalent oxidation state, was present in the tetravalent and trivalent oxidation states. The SCS polymetallic crusts and nodules were compared with Pacific seamount crusts, and results showed that the surface hydroxyl(-OH) groups of the SCS crusts and nodules numbered more than the lattice oxygen(O^(2-)). But the lattice oxygen of Pacific seamount crusts numbered more than the surface hydroxyl groups. This characteristic indicated that the degree of crystallization of Fe-Mn minerals from the Pacific Ocean was higher than that of minerals from the South China Sea. Comprehensive studies showed that ore-forming elements in the interface between seawater and the Fe-Mn minerals in the submarine ferromanganese crusts and nodules employed the following enrichment mechanisms:(1) the metal ion complexed with the surface hydroxyl of Fe-Mn minerals to form hydroxyl complexes, which were connected by coordination bonds or stable inner-sphere complexes that exchanged protons on the mineral surfaces;(2) the charged surfaces of the minerals and metal cations formed outer-sphere complexes, which made up the electrostatic double layer, through electrostatic adsorption; and(3) the metal cations isomorphously exchanged the Mn and Fe ions of the mineral lattice structure.

Application of Singular Value Decomposition(SVD)to the Extraction of Gravity Anomalies Associated with Ag-Pb-Zn-W Polymetallic Mineralization in the Bozhushan Ore Field,Southwestern China

The Bozhushan Ore Field,located at the western margin of the South China Block,is an important area for Ag-Pb-Zn-W polymetallic mineralization which may be associated with the Late Cretaceous granitic magmaism.In this paper,the singular value decomposition(SVD)was effectively applied to decompose gravity data at scale of 1:50000 within the Bozhushan Ore Field to extract deep ore-finding information.Two gravity anomaly images displaying different scales of the ore-controlling factors were obtained.(1)The low-pass filtered image may reflect the deeply buried geological structures,hidden intrusions and concealed ore bodies.The negative gravity anomaly may reflect the overall distribution of granite bodies in the Bozhushan Ore Field.One negative gravity anomaly area may correspond to the exposed part of the Baozhushan granitic intrusion and the other corresponds to the concealed part of the granitic intrusion.The granitic intrusions are the main ore-controlling factors in this ore district.(2)The band-pass filtered image depicts the shallow concealed geological structures and geological bodies within this study area.There are two obvious negative gravity anomalies,which may be created by the hidden granites at different depths at both northwestern and southeastern sides of the exposed granitic intrusion.Thus the two negative gravity anomalies are favorable prospecting areas for various type of polymetallic ore deposits at depth.The gravity anomalies extracted by using the SVD exactly reflect the distribution of the ore deposits,structures and intrusions,which will give new insights for further mineral exploration in the study area.

Application of BEMD in Extraction of Magnetic Anomaly Components Associated with Sn-W Polymetallic Mineralization in SE Yunnan,SW China

The tin(Sn)-tungsten(W)polymetallic ore concentrated district in SE Yunnan is distributed at the junction region of the Yangtze Block,the Cathaysian Block and the Indosinian Block,where there are several giant deposits of tin,tungsten,copper,silver,lead,zinc and indium closely associated with a large scale Late Cretaceous magmatism.Bi-dimensional empirical mode decomposition(BEMD)is used to extract aeromagnetic anomalous components at the survey scale of 1:200000 from the original aeromagnetic data of SE Yunnan.Four intrinsic mode functions(IMFs)and a residues component are obtained,which may reflect the geological structures and geological bodies at different spatial scales from high frequency to low frequency.The results are shown as follows:(1)Two different types of Precambrian basement in the study area were recognized:one is the Yangtze Block basement characterized by a strong positive magnetic anomaly,the other is the Cathaysian Block basement with a weak negative magnetic anomaly.The former consists of high grade metamorphic rocks including metamorphosed basic igneous rocks,while the latter consists of low grade metamorphosed sedimentary rocks.(2)The aeromagnetic anomalies associated with Sn-W polymetallic mineralization and related to granites in the study area illustrate a pattern of a skarnized alteration-mineralization zone with a positive ring magnetic anomaly enclosing a granitic intrusion with negative magnetic anomaly;(3)The ring positive magnetic anomaly zones enclosing the negative magnetic anomaly are defined as the SnW polymetallic ore-searching targets in the study area.

Mechanism and Modes of Microbial Minerogenesis of Polymetallic Nodules on the Ocean Floor

This paper presents a quantitative analysis of the relations of the occurrence of polymetallic nodules with the geochemical actions of microbes in the seawater, pore water and sediments at the bottom of the eastern Pacific Ocean basin. Emphasis is laid on the relations of the activity intensity and biochemical transformation rate of aerobic bacteria (iron bacteria, Thiobacillus thioparus, halobacteria and manganese-oxidizing bacteria) and anaerobic bacteria (sulphate-reducing bacteria, denitrifying bacteria, Thiobacillus denitrificans) with mineralization. The experimental research on the migration and accumulation of ore-forming elements caused by microbial and chemical actions shows that the microbes have changed the conditions of oxidation and reduction in the system, and their effect on the element precipitation is much stronger than the chemical actions and accelerates the enrichment of Fe and Mn. It demonstrates that the microbes can change the environment to promote the accumulation of

Electron Microscopic Study of Manganese Minerals in the Polymetallic Nodules from the Central Pacific Ocean

Manganese minerals in the polymetallic nodules from the Central Pacific Ocean were studied using electron microscopy. The principal Mn minerals, being vernadite and todorokite, exhibit different electron diffraction patterns and morphological features. According to its morphological feature, todorokite shows three phases: fibrous, lamellar and lath-shaped. Both vernadite and todorokite are authigenic minerals. While vernadite was mainly precipitated directly from the relevant solution by microbiological oxidation, todorokite was separated from the solution chemically without the help of microbe. Hence, these two minerals show a close genetic relation.

Genetic links of porphyry Mo-epithermal Pb–Zn–Ag mineralization system:a case study of the Shipingchuan polymetallic deposit,South China

Compared with the porphyry Cu-epithermal Au mineralization system,detailed studies on the porphyry Mo-epithermal Pb–Zn–Ag–Au mineralization are rare due to limited exposures.The Shipingchuan polymetallic deposit,located in the South China Mo Province(SCMP)represents a typical example containing both porphyry Mo and epithermal Pb–Zn–Ag mineralization.The Mo mineralization mainly occurs as molybdenite-quartz veins in veinlets or as disseminated molybdenite within the potassic,silicic,and sericitic syenogranite.The Pb–Zn–Ag mineralization is characterized by veinlet-type sphalerite–galena–pyrite–quartz–calcite vein within the volcanic rocks accompanied with silicifi cation and propylitization.Five molybdenite samples yield a Re–Os isochron age of 104.7±0.7 Ma that is consistent with the zircon age(107.5±2.1 Ma)of the ore-bearing syenogranite within errors.Together with previous reported Ar–Ar ages(106.6–121.8 Ma)of Pb–Zn–Ag related volcanic rocks,the Mo and Pb–Zn–Ag mineralization belong to a magmatic-hydrothermal event in the Early Cretaceous.Meanwhile,the total Re contents of molybednite range from 1.28 to 45.55 ppm,indicating the ore-forming materials were from a mixture between the mantle and crustal material.Moreover,previous sulfur isotopic values(3.7–4.3‰)of the pyrites from the porphyry Mo mineralization were consistent with the reported range of 4.0–6.1‰of the sphalerites from the Pb–Zn–Ag mineralization,implying that the sulfur of two-types of mineralization was derived from magma.The above-mentioned spatial,temporal,and isotopic lines of evidence suggest that the Mo and Pb–Zn–Ag mineralization of the Shipingchuan deposit was formed from the same metallogenic system.In consideration of regional tectonic evolution history,we propose that the porphyry Mo-epithermal Pb–Zn–Ag mineralization formed in an extensional tectonic setting caused by the continued rollback and the eventual slab break-off of the subducting PaleoPacifi c plate.

Study on the occurrence state of indium in sphalerite of Dulong Sn–Zn–In polymetallic deposit,Southwest China

The Dulong deposit,located in the Laojunshan area of southeastern Yunnan,China,is an important polymetallic deposit due to its high reserves of tin,zinc,and indium.The occurrence state of indium is critical for understanding its supernormal enrichment mechanism.Previous studies investigated the occurrence state of indium(including the valence state)based on the indium content in sphalerite and the correlation between metal concentrations.However,more evidence is needed to better constrain indium occurrence at the micro-,nano-,or even atomic scale.In this study,EPMA-FIB-SEM-TEM and XPS techniques were employed to investigate the indium distribution characteristics and occurrence state in sphalerite from the Dulong Sn–Zn–In polymetallic deposit.The maximum concentration of indium in the indium-rich sphalerite samples is 0.37%,and the results of the EPMA analysis showed a relatively homogeneous distribution of indium in sphalerite.The FIB-SEM-TEM results demonstrated that the lattice stripes of sphalerite were periodically and continuously distributed at the nanoscale,confirming that sphalerite in the deposit was an excellent single crystal structure,and the peak heights of the various characteristic peaks of indium in the EDX spectra were relatively close to each other,with no distinct peaks of high indium content.In addition,the XPS results indicate that the element valence state of indium in sphalerite is In^(3+),and it combines with S^(2-)to form a bond.These results indicate that indium in sphalerite of the Dulong deposit is uniformly distributed at both the micro-and nanoscale,and there is no indium-independent mineral.In^(3+)enters the crystal lattice of sphalerite by replacing Zn2+in the form of isomorphic substitution.

Experimental investigation of the inhibition of deep-sea mining sediment plumes by polyaluminum chloride

Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological environment.This study aims to investigate the potential solution of using polyaluminum chloride(PAC)in the water jet.The effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining area.The experimental results showed that the optimal PAC dose was found to be 0.75 g/L.Compared with the test conditions without the addition of PAC,the presence of PAC leads to a reduction in volume,lower characteristic turbidity,smaller diffusion velocity,and shorter settling time of the plume.This indicates that PAC inhibits the entire development process of the plume.The addition of PAC leads to the flocculation of mm-sized particles,resulting in the formation of cm-sized flocs.The flocculation of particles decreases the rate of erosion on the seabed by around 30%.This reduction in erosion helps to decrease the formation of plumes.Additionally,when the size of suspended particles increases,it reduces the scale at which they diffuse.Furthermore,the settling velocity of flocs(around 10^(-2) m/s)is much higher that of compared to sediment particles(around 10^(-5) m/s),which effectively reduces the amount of time the plume remains in suspension.

New Zircon U-Pb Age of the Super-Large Lijiagou Spodumene Deposit in Songpan Garze Fold Belt, Eastern Tibet： Implications for Early Jurassic Rare-Metal Polymetallic Event

The Songpan-Garze Fold Belt （SGFB）, located in theeastern part of the Tibet Plateau and west of the SichuanBasin, is an important pegmatite province in China. Somefamous pegmatite type deposits occur in the SGFB,including the Xuebaoding, Jiajika, Keeryin rare metaldeposits and Danba muscovite deposit （Li Jiankang et al.,2015）.

Genetic Types and Metallogenic Model for the Polymetallic Copper–Gold Deposits in the Tongling Ore District, Anhui Province, Eastern China

The Tongling ore district is one of the most economically important ore areas in the Middle–Lower Yangtze River Metallogenic Belt, eastern China. It contains hundreds of polymetallic copper–gold deposits and occurrences. Those deposits are mainly clustered(from west to east) within the Tongguanshan, Shizishan, Xinqiao, Fenghuangshan, and Shatanjiao orefields. Until recently, the majority of these deposits were thought to be skarn-or porphyry–skarn-type deposits; however there have been recent discoveries of numerous vein-type Au, Ag, and Pb-Zn deposits that do not fall into either of these categories. This indicates that there is some uncertainty over this classification. Here, we present the results of several systematic geological studies of representative deposits in the Tongling ore district. From investigation of the ore-controlling structures, lithology of the host rock, mineral assemblages, and the characteristics of the mineralization and alteration within these deposits, three genetic types of deposits(skarn-, porphyry-, and vein-type deposits) have been identified. The spatial and temporal relationships between the orebodies and Yanshanian intrusions combined with the sources of the ore-forming fluids and metals, as well as the geodynamic setting of this ore district, indicate that all three deposit types are genetically related each other and constitute a magmatic–hydrothermal system. This study outlines a model that relates the polymetallic copper–gold porphyry-, skarn-, and vein-type deposits within the Tongling ore district. This model provides a theoretical basis to guide exploration for deep-seated and concealed porphyry-type Cu(–Mo, –Au) deposits as well as shallow vein-type Au, Ag, and Pb–Zn deposits in this area and elsewhere.

Ore Genesis for Stratiform Ore Bodies of the Dongfengnanshan Copper Polymetallic Deposit in the Yanbian Area, NE China:Constraints from LA-ICP-MS in situ Trace Elements and Sulfide S–Pb Isotopes

The Dongfengnanshan Cu polymetallic deposit is one representative deposit of the Tianbaoshan ore district in the Yanbian area, northeast(NE) China. There occur two types of ore bodies in this deposit, the stratiform ore bodies and veintype ones, controlled by the Early Permian strata and the Late Hercynian diorite intrusion, respectively. Due to the ambiguous genetic type of the stratiform ore bodies, there has been controversy on the relationship between them and veintype ore bodies. To determine the genetic type of stratiform ore bodies, laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) in situ trace elements and S–Pb isotope analysis have been carried on the sulfides in the stratiform ore bodies. Compared with that in skarn, Mississippi Valley-type(MVT), and epithermal deposits, sphalerite samples in the stratiform ore bodies of the Dongfengnanshan deposit are significantly enriched in Fe, Mn, and In, while depleted in Ga, Ge, and Cd, which is similar to the sphalerite in volcanic-associated massive sulfide(VMS) deposits. Co/Ni ratio of pyrrhotites in the stratiform ore bodies is similar to that in VMS-type deposits. The concentrations of Zn and Cd of chalcopyrites are similar to those of recrystallized VMS-type deposits. These characteristics also reflect the intermediate ore-forming temperature of the stratiform ore bodies in this deposit. Sulfur isotope compositions of sulfides are similar to those of VMS-type deposits, reflecting that sulfur originated from the Permian Miaoling Formation. Lead isotope compositions indicate mixed-source for lead. Moreover, the comparison of the Dongfengnanshan stratiform ore bodies with some VMStype deposits in China and abroad, on the trace elements and S–Pb isotope characteristics of the sulfides reveals that the stratiform ore bodies of the Dongfengnanshan deposit belong to the VMS-type, and have closely genetic relationship with the early Permian marine volcanic sedimentary rocks.

Constraints of molybdenite Re-Os and scheelite Sm-Nd ages on mineralization time of the Kukaazi Pb-Zn-Cu-W deposit, Western Kunlun, NW China

The Kukaazi Pb-Zn-Cu-W polymetallic deposit, located in the Western Kunlun orogenic belt, is a newly discovered skarn-type deposit. Ore bodies mainly occur in the forms of lenses and veins along beddings of the Mesoproterozoic metamorphic rocks. Three ore blocks, KⅠ,KⅡ, and KⅢ, have been outlined in different parts of the Kukaazi deposit in terms of mineral assemblages. The KⅠ ore block is mainly composed of chalcopyrite, scheelite,pyrrhotite, sphalerite, galena and minor pyrite, arsenopyrite,and molybdenite, whereas the other two ore blocks are made up of galena, sphalerite, magnetite and minor arsenopyrite and pyrite. In this study, we obtained a molybdenite isochron Re–Os age of 450.5 ± 6.4 Ma(2σ,MSWD = 0.057) and a scheelite Sm–Nd isochron age of 426 ± 59 Ma(2σ, MSWD = 0.49) for the KⅠ ore block.They are broadly comparable to the ages of granitoid in the region. Scheelite grains from the KⅠ ore block contain high abundances of rare earth elements(REE, 42.0–95.7 ppm)and are enriched in light REE compared to heavy REE, with negative Eu anomalies(δEu = 0.13–0.55). They display similar REE patterns and Sm/Nd ratios to those of the coeval granitoids in the region. Moreover, they also have similar Sr and Nd isotopes [ ^(87)Sr/ ^(86)Sr = 0.7107–0.7118;ε_(Nd)(t) =-4.1 to-4.0] to those of such granitoids, implying that the tungsten-bearing fluids in the Kukaazi deposit probably originate from the granitic magmas. Our results first defined that the Early Paleozoic granitoids could lead to economic Mo–W–(Cu) mineralization at some favorable districts in the Western Kunlun orogenic belt and could be prospecting exploration targets.

Geochemical characteristics of platinum-group elements in polymetallic nodules from the Northwest Pacific Ocean

Polymetallic nodules and cobalt (Co)-rich crusts are enriched in platinum-group elements (PGEs),especially platinum (Pt) and may be important sinks of PGEs.At present,little information is available on PGEs in polymetallic nodules,and their geochemical characteristics and the causes of PGEs enrichment are unclear.Here PGEs of polymetallic nodules from abyssal basin in the Marcus-Wake Seamount area of the Northwest Pacific Ocean are reported and compared with the published PGEs data of polymetallic nodules and Co-rich crusts in the Pacific.The total PGEs (ΣPGE) content of polymetallic nodules in study area is 258×10^–9) in average,markedly higher than that of Clarion-Clipperton Zone (CCZ) nodules (ΣPGE=127×10^–9) and lower than that of Co-rich crusts in the Marcus-Wake Seamount (ΣPGE=653×10^–9),similar to that of Co-rich crusts in the South China Sea(ΣPGE=252×10^~–9).The CI chondrite-normalized PGEs patterns in different regions of polymetallic nodules and cobalt-rich crusts are highly consistent,with all being characterized by positive Pt and negative Pd anomalies These results,together with those of previous studies,indicate that PGEs in polymetallic nodules and Co-rich crusts are mainly derived directly from seawater.Pt contents of polymetallic nodules from the study area are negatively correlated with water depth,and Pt/ΣPGE ratios in nodules there are also lower than those of the Corich crusts in the adjacent area,indicating that sedimentary water depth and oxygen fugacity of ambient seawater are the possible important controlling factors for Pt accumulation in crusts and nodules.

3D Geological Modeling with Multi-source Data Integration in Polymetallic Region:A Case Study of Luanchuan,Henan Province,China

The development of 3D geological models involves the integration of large amounts of geological data,as well as additional accessible proprietary lithological, structural,geochemical,geophysical,and borehole data.Luanchuan,the case study area,southwestern Henan Province,is an important molybdenum-tungsten -lead-zinc polymetallic belt in China.

Analysis of prospecting polymetallic metallogenic belts by comprehensive geophysical method

This paper is based on the analysis and research on the silver-lead-zinc polymetallic ore in New Ballyhoo Banner in southern Manzhouli of Inner Mongolia.Because metal mineralization brings rock formations,the geophysical features such as low resistivity,high polarization rate and uneven distribution of magnetization,the comprehensive geophysical methods are adopted including high-precision magnetic measurement,high-power induced polarization,IP field middle gradient and controlled source audio-frequency magnetotellurics.In the survey work of multi-metal ore deposits,from surface sweeping to single point measurement,and from single point to section going deeper layer by layer,the resolution of measurement is continuously improved,and various geophysical methods support and complement each other,so explorers can successfully predict the direction,scale and volume of the metallogenic belts in conjunction with geochemical exploration,geological survey and drilling.It has provided a strong basis for completing the exploration task of predicting the reserve volume of ore bodies.The research conclusions of this exploration case have thus a high reference value in the same type of exploration work.

EVOLUTION OF ORE-FORMING FLUIDS AND Ag-Cu POLYMETAL MINERALIZATION IN THE LANPING BASIN, YUNNAN

The Lanping Mesozoic—Cenozoic sedimentary basin, situated in the Middle section of the “Sanjiang" (Nujiang—Lancangjiang—Jinshajiang) area in the east margin of the Tibet plateau, is well known for its large production of base\|metal sulphide deposits. The worldwide famous super\|large Jinding Pb\|Zn deposit is located in the middle of the basin. The evolution history of the Lanping basin since Mesozoic can be divided into six stages, i.e., ①active continental marginal basin (T 1—T 2); ②back\|arc rift basin (T 3—J 1); ③intracontinental depressive basin (J 2—J 3); ④foreland basin (K); ⑤strike\|slipping and mutual thrusting (E 1—E 3); and ⑥strike\|slipping and pull\|apart basin (N 1\|present). Three main types of Ag\|Cu polymetal deposits are recognized in the basin. Deposits of sedimentary exhalation\|hydrothermal reworking origin (type Ⅰ) are hosted chiefly in limestones, dolomitic limestones, and siliceous rocks of the Upper Triassic Sanhedong Formation (T 3 s ) in Sanshan area. Deposits formed through normal chemical sedimentation in closed to semi\|closed environments (type Ⅱ; e.g., Jinman and Baiyangchang) during the depressive and foreland basin stages occur in various horizons of Jurassic and Cretaceous ages. Hydrothermal reworking on deposits of this type during the Himalayan period are locally pronounced, especially in the west margin of the basin near the Lancangjiang thrust fault. The third deposit type in the basin (type Ⅲ; e.g., Baiyangping and Fulongchang) is the Ag\|bearing tetrahedrite vein deposits occurring almost in all Mesozoic—Cenozoic strata, especially in the Cretaceous. Ore minerals formed during synsedimentary periods of types Ⅰ and Ⅱ are relatively simple and dominated by chalcopyrite and bornite, though sphalerite, galena, pyrite, tetrahedrite and pyrite are also present. In the deposits of type Ⅲ as well as in the ores formed during the hydrothermal reworking period in deposits of type Ⅰ and Ⅱ, ore minerals are extremely complicated and characterized by predominant Ag\|bearing tetrahedrite and other complex sulfosalts of Cu\|Ni\|Co\|Fe\|As\|S and Cu\|Bi\|S series. The associated gangue minerals are mainly quartz, siderite, Fe\|dolomite, barite, and celestite.

Geochronology and geochemistry of the Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit(73240 t) in Heilongjiang Province, China

The Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit(20000 t Sn at 0.27%,236 t Ag at 122.89 g/t,15000 t Pb at 0.84%,and 38000 t Zn at 1.43%)is located in the Wandashan Terrane of the easternmost segment of the Central Asian Orogenic Belt.The timing of Sn-Pb-Zn-Ag polymetallic mineralization remains unclear due to a lack of precise isotope dating directly conducted on ore minerals.The authors herein report that the LA-ICP-MS U-Pb ages of cassiterite and zircon from the granite porphyry in the Hekoulinchang Sn-Pb-Zn-Ag polymetallic deposit are 101.4±7.9 Ma and 115.4±1.0 Ma,respectively,indicating that Sn mineralization and magmatism occurred during the Early Cretaceous.The granite porphyry belongs to the subalkaline series peraluminous I-type granites that are depleted in Nb,Ta,and Ti and enriched in Rb,Th,U,and Pb.TheεHf(t)values of the granite porphyry range from 0.9 to 7.4,with an average of about 5.6 and two-stage model ages(T_(DM2))of 705–1116 Ma,with an average age of 819 Ma.The ε_(Nd)(t)values of the apatites are–1.60–0.45,with an average of–0.9,and two-stage model ages(T_(DM2))of 872–1040 Ma,with an average age of 983 Ma.The Nd-Hf isotope data indicate that the magma may have been derived from the partial melting of juvenile crustal material.

ANALYSIS OF TECTONIC EVOLUTION AND MAJOR Cu (Au) POLYMETALLIC METALLOGENIC SERIES IN NORTHEAST JIANGXI PROVINCE

Northeast Jiangxi Province is an important area in China with closely packed Cu (Au) polymetallic metallization. The tectonic action of this area is complex and violent, and three stages of geotectonic development of the Earth’s crust have taken place there since the Jingning Movement.Every stage formed a distinctive ore-bearing formation, and the three stages formed three suits of Cu(Au) polymetallic metallogenic series with different features. They are the Proterozoic dynamometamorphic metallogenic series, the Paleozoic exhalation-sediment metallogenic series and the Meso-Cenozoic volcano-subvolcanic metallogenic series.