Apatite Fission Track Thermochronology of Granite from the Xiazhuang Uranium Ore Field,South China:Implications for Exhumation History and Ore Preservation

Xiazhuang uranium ore field,located in the southern part of the Nanling Metallogenic Belt,is considered one of the largest granite-related U regions in South China.In this paper,we contribute new apatite fission track data and thermal history modeling to constrain the exhumation history and evaluate preservation potential of the Xiazhuang Uranium ore field.Nine Triassic outcrop granite samples collected from different locations of Xiazhuang Uranium ore field yield AFT ages ranging from 43 to 24 Ma with similar mean confined fission track lengths ranging from 11.8±2.0 to 12.9±1.9μm and Dpar values between 1.01 and 1.51μm.The robustness time-temperature reconstructions of samples from the hanging wall of Huangpi fault show that the Xiazhuang Uranium ore field experienced a time of monotonous and slow cooling starting from middle Paleocene to middle Miocene(~60-10 Ma),followed by relatively rapid exhumation in the late Miocene(~10-5 Ma)and nearly thermal stability in the Pliocene-Quaternary(~5-0 Ma).The amount of exhumation after U mineralization since the Middle Paleogene was estimated as~4.3±1.8 km according to the integrated thermal history model.Previous studies indicate that the ore-forming ages of U deposits in the Xiazhuang ore field are mainly before Middle Paleocene and the mineralization depths are more than 4.4±1.2 km.Therefore,the exhumation history since middle Paleocene plays important roles in the preservation of the Xiazhuang Uranium ore field.

Robust Timing Constraints for Granitic Magmatism and Hydrothermal Mineralization in the Tieshanlong W-Sn Ore Field,Eastern Nanling Range,South China

The Tieshanlong ore field is an important part of the Nanling Range,which is famous worldwide for its W-Sn mineralization.Notably,the mineralization age of the Tieshanlong ore field is not well constrained,and our field investigation reveals that granitic emplacement occurred at different stages.However,previous studies have not distinguished these multiple stages of magmatism.The Tieshanlong granite complex is closely related to the Huangsha quartz vein-type W-Sn deposit and Tongling skarn-type Cu-W-Sn deposit in this field.Through field investigations and isotopic age analyses,this work studies the relationship between multistage magmatic activity and mineralization in the Tieshanlong ore field.LA-ICP-MS zircon U-Pb isotope analyses revealed that the first-and second-staged granites formed at 154.2±0.6 Ma(MSDW=1.4)and 151.2±0.4 Ma(MSDW=1.5),with zirconε_(Hf)(t)values ranging from-13.1 to-10.5 and from-14.7 to-11.1,respectively.These data suggest that the Tieshanlong granite complex was derived from the partial melting of ancient crustal material.LA-ICP-MS U-Pb dating of wolframite and cassiterite reveals that W-Sn mineralization occurred at 160-150 Ma,which agrees well with the U-Pb dating results of the second-staged granite within analytical errors.The magmatic activity in this ore field can be divided into three stages:175-154 Ma,154-150 Ma and 150-145 Ma.The quartz vein-and skarn-type W-Sn mineralization is closely related to second-staged fine-grained twomica granite,and formed earlier than skarn-type Cu-mineralization.This study establishes a metallogenic model for the Tieshanlong ore field,and this model has important practical significance for identifying concealed W-Sn(-Cu)deposits around other granitic complexes in the Nanling Range.

Geochemistry of intrusive rock in Dachang tin-polymetallic ore field, Guangxi, China: Implications for petrogenesis and geodynamics

The major element, trace element and rare earth element（REE） of the intrusion rock from the Dachang ore field in Guangxi, China, were analyzed. The results show that the phenocryst（about 15%） and matrix（about 85%） mainly consist of quartz, K-feldspar and plagioclase. The rock is composed of low content of Si and high content of Al2O3, low contents of Ca, Fe2O3, Na, TiO2, etc. The intrusion rock has the medium alkali content, attributing to K-rich type rock; and contains medium to low REE contents, of which light rare earth elements（LREEs） and heavy rare earth elements（HREEs） are highly fractionated, showing a weak negative Ce anomaly and a negative Eu anomaly. These rocks are enriched in LREE, and the large ion lithophytes elements（LILE） are rich in Rb, Sr, and U; the high-field-strength elements（Nb, Th, etc） are relatively depleted. The REE chondrite-normalized patterns are consistent with the overall, roughly indicating their similar characteristics, sources and evolution. The intrusion rock mainly formed during the collisional and within-plate periods.

Origin of Ore-Forming Fluids of Mississippi Valley-Type (MVT) Pb-Zn Deposits in Kangdian Area, China

Analyses of fluid\|inclusion leachates from ore deposits show that Na/Br ratios are within the range of 75-358 and Cl/Br 67-394, respectively, and this variation trend coincides with the seawater evaporation trajectory on the basis of the Na/Br and Cl/Br ratios. The average Cl/Br and Na/Br ratios of mineralizing fluids are 185 and 173 respectively, which are very close to the ratios (120 and 233) of the residual evaporated seawater past the point of halite precipitation. It is suggested that the original mineralizing brine was derived from highly evaporated seawater with a high salinity. However, the inclusion fluids have absolute Na values of \{69.9\}-\{2606.2\} mmol kg\+\{-1\} and Cl values of \{106.7\}-\{1995.5\} mmol kg\+\{-1\}. Most of the values are much less than those of seawater: Na, 485 mmol kg\+\{-1\} and Cl, 566 mmol kg\+\{-1\}, respectively; the salinity measured from fluid inclusions of the deposits ranges from \{2.47 wt%\} to \{15.78 wt%\} NaCl equiv. The mineralizing brine has been diluted. The \{δ\{\}\+\{18\}O\} and δD values of ore\|forming fluids vary from \{-8.21‰\} to \{9.51‰\} and from \{-40.3‰\} to \{-94.3‰\}, respectively. The δD values of meteoric water in this region varied from \{-80‰\} to \{-100‰\} during the Jurassic. This evidenced that the ore\|forming fluids are the mixture of seawater and meteoric water. Highly evaporated seawater was responsible for leaching and extracting Pb, Zn and Fe, and mixed with and diluted by descending meteoric water, which resulted in the formation of ores.

REE Geochemistry of Sulfides from the Huize Zn-Pb Ore Field, Yunnan Province: Implication for the Sources of Ore-forming Metals

REE abundances in sulfides from the Huize Zn-Pb ore field were determined with the ICPMS after preconcentration. The REE abundances in 26 sulfide samples （including pyrite, galena and sphalerite） are very low, with the ~REE ranging from 1.6×10^-9 to 166.8×10^-9. Their LREE/HREE ratios range from 7.6 to 98, showing LREE enrichment relatively. The JEu values are below 1, indicating that they were deposited from an Eu-depleted and reducing fluid-system. Similar to the ore-hosting carbonate strata, calcite separates from carbonate veinlets filling in the fractures or faults crosscutting the carbonate strata also show clear Eu-depletion. This indicates that the carbonate veinlets and their parent fluid was possibly sourced from the strata and inherited the REE geochemical features of the strata. Therefore, REE-geochemical characteristics of both the sulfides and calcites, which were deposited from an ore-forming hydrothermal system, are similar to those of carbonate strata, and strongly suggest that the ore metals were mainly sourced from carbonate strata.

Magmatic-Hydrothermal Superlarge Metallogenic Systems——A Case Study of the Nannihu Ore Field

Located in the Qinling （秦岭） molybdenum metallogenic belt on the southern margin of North China craton, the Nannihu （南泥湖） molybdenum （-tungsten） ore field, consisting of the Nannihu, Sandaozhuang （三道幢）, and Shangfang （上房） deposits, represents a superlarge skarn-porphyry molybdenum （-tungsten） accumulation. Outside the ore field, there are some hydrothermal lead-zinc-silver deposits found in recent years, for example, the Lengshuibeigou （冷水北沟）, Yindonggou （银涧沟）, Yangshuwa （杨树凹）, and Yinhegou （银河沟） deposits. Ore-forming fluid geochemistry indicates that these deposits belong to the same metallogenic system. The hydrothermal solutions were mainly derived from primary magmatic water in the early stage and from the mixture of the primary magmatic water and meteoric water in the later stage, with an obvious decreasing tendency in temperature, salinity and gas-liquid ratio of fluid inclusions. Sulfur and lead isotope data show that the ore-forming substances and related porphyries were mainly derived from the lower crust, and a hidden magmatic chamber is indicated by aeromagnetic anomaly and drill hole data indicate that the Nannihu granite body extends to being larger and larger with depth increasing. The large-scale mineralization was the consequence of lithospheric extension during the late stage of the tectonic regime when the main compressional stress changed from NS-trending to EW-trending.

Constraints on granite-related uranium mineralization in the Sanjiu uranium ore field,SE China provided by pyrite mineralogy,major and trace elements,S-He-Ar isotopes

The Sanjiu uranium ore field,located in the central of Zhuguangshan granitic batholith,is a newly discovered granite-related uranium ore field in South China.The main sulfide in the ore field is pyrite,which is closely related to uranium mineralization.The textures major and trace elements,S-He-Ar isotopes compositions of pyrites in ores of different grade were observed and/or analyzed by optical microscope,scanning electron microscope,electron microprobe,laser ablation inductively coupled plasma mass spectrometry,and noble gas mass spectrometer(Helix-SFT).It is observed that these U-related pyrites are generally euhedral-subhedral with dissolution textures,anhedral variety with colloform texture veinlet and fine particles,and the color of the associated minerals is mostly dark hue,such as purple-black fluorite dark-red hematite,and dark-green chlorite,etc.The analytical results show that the average compositions of major elements in pyrite are FeS1.944.Pyrites are characterized by S-deficiency,low content of Co and Th,and Co/Ni>1which indicate that these ores are of low-temperature hydrothermal origin.We found that the higher the grade of ore,the more deficient in S,the more obvious negative δ^34S,and the higher REE content(close to U-rich granitic pluton)of pyrite.The S-He-Ar isotopic compositions of various varieties of pyrites indicate that the ore-forming fluids mainly come from crust-derived fluids and mixed with mantle-derived fluids.

Mineralogy,sulfur isotopes and infrared microthermometric study of the Leishan-Rongjiang antimony ore field,SW China

The Leishan-Rongjiang antimony ore field(LAOF) is in a unique geotectonic location in the uplift between the Youjiang and Xiangzhong basins.This paper focuses on two representative deposits in the LAOF:the Bameng and Peize antimony(Sb) deposits.We analyzed fluid inclusions(FIs) in stibnite and coexisting quartz,as well as the sulfur isotopic composition of stibnite,to better understand the nature of the ore-forming fluid and the metallogenic process.The FIs data from samples of the stibnite and coexisting quartz indicate that the ore-forming fluids were characterized by low-temperature(150-210 ℃),low-salinity(1.5 wt%-6.0 wt%NaCl equiv.),and low-density(0.872-0.961 g/cm^3).The δ^(34)S values of stibnite(-8.21‰ to 3.76‰,average =-6.30‰)fall in between the sulfur isotopic compositions of the mantle and of biogenic sulfur in sedimentary rocks.However,the δ^(34)S_(∑s) values(-4.41 ‰ to +0.04‰,average =-2.49‰) of the ore-forming fluids are generally closer to the sulfur isotopic composition of the mantle source,indicating that the sulfur in the LAOF was mainly sourced from the mantle,but with possible involvement of biogenic sulfur.In addition,FIs petrography and ore deposit geology show that fluid boiling resulted from an abrupt decrease in pressure,which may have triggered the precipitation of stibnite.We conclude that low-temperature,dilute hydrothermal fluids with mixed origins migrated along the regional fault and interacted with the wall rock,extracting the ore-forming materials.Then,the oreforming fluids were injected into the fault fracture zones.

Tectonomagmatic Metallogenic System of Dexing Ore Field, Jiangxi, China

ore deposits and a large number of ore occurrences cluster in Dexing ore field which is 20 km long and 12 km wide. The tectonic evolution, magmatism, as well as the metallogeny are controlled by the Northeast Jiangxi deep seated fracture belt (NJDFB). The source is believed to have been derived from the Meso-Neoproterozoic marine volcanism. The magmatic activity of Mesozoic I type granite could have provided the metal elements, thermal fluid, heat, and the space for ore forming processes. A unified geological model is proposed, which combines the tectonism, magmatism and metallogeny as the basic control of the giant metal mineralizations.

PREDICTION OF LOCATION OF HIDDEN ORE DEPOSITS IN THE AGED ORE FIELDS: AN EXAMPLE FROM FENGHUANGSHAN ORE FIELD, TONGLING, CHINA

This paper discusses the strategy for successfully predicting the location of potential hidden ore bodies in aged ore field, and presents the result of location prediction of hidden ore bodies in Fenghuangshan ore field, Tongling. Innovative conceptual targeting procedures based on a genetic understanding of mineralization systems, carefully geological investigation and correct deduction, together with new geochemical and geophysical technology and integrating of comprehensive information are all very important for the successful prediction. In the aged Fenghuangshan ore field, through researching by application of the metallogenic theory of polygenetic compound ore deposits and triple frequency induced polarization method and exploration tectono geochemical method, we predicted location and quality of hidden ore bodies. According to the prediction, hidden high quality Cu Au ore bodies of skarn type and porphyry type have been discovered.

Genesis of S-type Granites in the Pengshan Sn-polymetallic Ore Field, Northern Jiangxi Province and its Implications

The Pengshan Sn-polymetallic ore field is located in the southeastern part of the Yangtze block,spanning the southeast edge of the MLYDZ and the northern edge of the mid-segment of the Jiangnan Uplift,and on one side of the MLYDZ.The studies of LA-ICP-MS zircon U-Pb chronology and petrogeochemistry for Early Cretaceous acid granites from the Pengshan ore field were carried out in this paper.We report zircon U-Pb geochronology and whole-rock geochemistry for acid granites in the Pengshan ore field.The zircon U-Pb ages of the muscovite-granite,biotite adamellite and granite-porphyry are 127.6±1.7 Ma,126.9±1.6 Ma and 126.6±2.0 Ma,respectively.The granites in Pengshan are characterized by a high silicon content and are rich in alkali.They belong to high-potassium,calc-alkaline,peraluminous granite.The rocks have a relatively high Rb/Ba ratio,and the data points for muscovite-granite and biotite adamellite all fall within the clay-rich sources region,near the pelite-derived end-member,showing that the Pengshan muscovite-granite and biotite adamellite mainly originated from the partial melting of metapelites with high maturity.The transformation of the compressional and extensional tectonics in this region approximately 128 Ma obviously lags behind that in the mid-segment of the Jiangnan Uplift(135 Ma),but occurred earlier than the MLYDZ(126 Ma).The Pengshan ore field extends from the mid-segment of the Jiangnan Uplift to the MLYDZ.Although the tectonic stress field is constrained by the combination of the two secondary tectonic units,the time of tectonic system transformation is closer to the MLYDZ because the spatial orientation of the area is enclosed in the MLYDZ.Relevant geophysical and drilling data confirm the rationality of Pengshan-Ao'xia as a multi-center vertical zoning ore field,and show the scientificity of the prospecting idea of abutting joint between the north-west of Pengshan area and the south-east of Ao'xia area.

Genesis and metallogenic characteristic of Dongnan Cu–Mo deposit associated granitoids:LA-ICP-MS zircon U–Pb dating and isotope constraint from Zijinshan ore field in southeastern China

The Dongnan Cu–Mo deposit,located in the southeast of the Zijinshan ore field(the largest porphyry–epithermal system in Southeast China),represents the complex magmatic and metallogenesis events in the region.The petrogenesis and metallogenesis of granitoids from the deposit are not determined,especially the interactions between ore-bearing(granodiorite porphyry)and barren samples(granodiorite and diorite).In the paper,the whole rock geochemical features shared a similar affinity to the middle-lower content and revealed that they derived from partial melting of the Cathaysian basement with the contribution of mantle materials,even represented that they generated in the plate subduction;LA-ICP-MS zircon U–Pb ages show that these granodiorites,granodioritic porphyry and diorite,were generated during 114–103 Ma.The ore-bearing samples mostly presented ε_(Hf)(t)of negative values(peak value is-4 to-3)with old two-stage Hf model ages(t_(DM)^(2))(peak value is 1.10–1.15 Ga),while the barren sample showed slightly negative ε_(Hf)(t)(peak value is-1 to 0)values with young t_(DM)^(2)(peak value is 1.00–1.05 Ga).The value of zircon Ce^(4+)/Ce^(3+)ratio mostly higher than 450 was first verified for the ore-bearing samples in the Dongnan Cu–Mo deposit,and the values of ore-bearing were found to be higher than those from the barren,which suggests that the ore-bearing formed in more oxidized parental magma with higher oxygen fugacity.Based on the geochemical characteristic of the element and isotope,we concluded that the Early Cretaceous multiphases magmatic activities,low melting temperature and low pressure of pluton,and high oxygen fugacity of zircon,were the favorable conditions for metallogenesis of Dongnan Cu–Mo deposit.

Application of Weights of Evidence to Mineral Potential Mapping of Yujiacun Ore Field in Northwest Yunnan Province, China

The multivariate information comprehensive processing technique is especially important at present to the digital mineral prospecting. However, the GIS-based weights of evidence have provided us with a powerful tool for the quantitative assessment of mineral resource potential. In this paper, the mineralization model is established, based on the achievements made by previous researchers, to mend such deficiencies as few references on ore fields in Yujiacun, Yunnan Province and the shortage of quantitative prediction and assessment of mineral resources. In addition, the weights of evidence are used to make a systematic quantitative prediction and assessment of mineral resources there, so that 2 mineral prospecting target areas of grade Ⅰand 8 mineral prospecting target areas of grade Ⅱ are delineated, providing the further mineral resource exploration with the basis for the selection of mineral deposits.

Timing of formation of the Hongdonggou Pb-Zn polymetallic ore deposit,Henan Province,China:Evidence from Rb-Sr isotopic dating of sphalerites

The Hongdonggou Pb-Zn polymetallic ore deposit, located in the southwestern part of the Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore mineralization in Henan Province, China, is an important part of the East Qinling metallogenic belt. The orebodies in the deposit, which are vein, bedded and lenticular, are mainly hosted in the syenite porphyry, and formed within the carbonate and clastic rocks of the Yuku and Qiumugou formations partially. The genesis of the deposit has previously been argued to be of hydrothermal-vein type or of skarn-hydrothermal type. In this study, we report the results of Rb-Sr isotopic dating based on sphalerites from the main orebody of the Hongdonggou Pb-Zn polymetallic ore deposit, which yield an isochron age of 135.7 ± 3.2 Ma, constraining the timing of mineralization as early Cretaceous. The age is close to those reported for the Pb-Zn deposits in the Luanchuan ore belt. The （87Sr/86Sr）i values of the sphalerites （0.71127± 0.00010） are lower than that of terrigenous silicates （0.720） and higher than the mantle （0.707）, suggesting that the metallogenic components were mainly derived through crust-mantle mixing. Combining the results from this study with those from previous work, we propose that the Hongdonggou Pb-Zn polymetallic ore deposit is a hydrothermal-vein deposit associated with the early Cretaceous tectonothermal event, and the mineralization is controlled by NW- and near EW-trending faults in the Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore concentration belt.

The Mechanism of Structural Control of Ore Formation and Geochemical Characteristics in the Massive Sulfide Deposits of the Wushan Copper Ore Field,Jiangxi

The ore-controlling mechanism of the bedding fault system in the massive sulfide deposits of the Wushancopper orefield may be generalized as the control of ore deposition by optimum surface in an ore-formingstructural trap. The mechanism has three major features: (1) timing of mineralization; (2) positioning of hostformation; and (3) dependence of ore-controlling structure on properties of rocks. The 'optimum surface' is adivisional structural plane which marks obvious difference in physical, chemical and mechanical properties andis favorable for mineralization. It is also a unity of structures. lithofacies and orebodies. The structural and geochemical characteristics of the ore deposits indicate the migration trend of the ma-jor characteristic clements in the ore-controlling fault belt: elements with a small radius (Si, Fe, Mg and Al)moved towards and concentrated at the center of the belt while large-radius ones (Ca, K and Na) were remotefrom the center.

Stable Isotopes and Halogen Geochemistry of the Huayuan Carbonate-hosted Pb-Zn Ore District, South China: Implications for the Salt Source of Ore-forming Fluids

The Huayuan Pb-Zn ore district in China,located in western Hunan Province,is a giant carbonate-hosted Pb-Zn ore district.The source of ore-forming brines in this ore district remains poorly constrained.Whether the highly saline brines are derived from evaporated seawater or dissolved evaporates continues to be intensely debated.Carbonate minerals associated with Pb-Zn mineralization haveδ^(13)CV-PDB andδ^(18)OV-SMOW values ranging from−5.55‰to+1.35‰(mean value of−0.69‰;n=14)and+16.28‰to+25.05‰(mean value of+20.22‰;n=14),respectively.This indicates that carbonate minerals are dominantly formed from dissolved ore-hosted carbonate rocks.Theδ^(34)S values of sulfides range from+20.2‰to+36.8‰,with an average value of+30.0‰(n=27).These results suggest that sulfur is predominantly derived from the thermochemical sulfate reduction of marine sulfate.The crush-leach analyzed solute data of fluid inclusions in sphalerite show the ore-forming fluids have Cl/Br molar ratios range from 118 to 384,and Na/Br molar ratios from 39 to 160(n=8).These Cl/Br ratios of hydrothermal fluid are much lower than those of seawater(657 to 564),but are consistent with bittern brines through early halite precipitation.We propose that ore-forming fluids are mainly derived from evaporitic basin brines,which leached base metals from the basement and/or country rocks.The brine then migrated to the basin margins through clastic rocks of basement and then precipitated sulfides by thermochemical sulfate reduction.

Endogenic Cracking of Rocks at Kolchiktau Gold Deposit in Daugiztau Ore Field

Kolchiktau deposit is located within the Central Kyzylkums in Navoiy region of Uzbekistan.The importance of study of hard-rock deposits is caused by numerous explorations of such deposits in Uzbekistan, which plays a significant role in social-economic aspects of the country.Rational and safe exploration of such deposits requires the study of engineering -geological conditions of territory.The

Characteristics of the ore-forming fluid in the Huayuan Pb-Zn ore filed, Northwest of Hunan Province, China

1 Geological Setting The Huayuan Pb-Zn ore field in Xiangxi is located in the southeastern margin of the Yangtze block and the mid-segment of the West Hunan-West Hubei metallogenic belt.The exposed stratum are the lower

Magnetic Method Surveying and Its Application for the Concealed Ore-Bodies Prospecting of Laba Porphyry Molybdenum Ore Field in Shangri-La, Northwestern Yunnan Province, China

Recently, a number of large molybdenum (-copper) deposits have been discovered successively in the Laba area, Shangri-La county, northwestern Yunnan province. The investigation confirmed that there is a superlarge porphyry-skarn hydrothermal vein type molybdenum-polymetallic- metallogenic system with the total prediction reservoir of more than 150 mt molybdenum. The porphyry intrusions contributed to the mineralization closely, the superficial little vein molybdenum (-copper, lead, silver) ore-bodies are usually located in faults and fractures, and the deep porphyry type ore-bodies occurred in the granodiorite porphyries, the skarn type ore-bodies occurred in the contact zone intrused into Triassic limestone or Permian basalts. Laba ore block is a new exploration area with great prospecting potential. In order to reduce the target area and guide the further exploration work, the magnetic method measurement about 3.3 square kilometres was carried out in the ore field. This paper presents an application of analyzing the horizontal and vertical derivative, using Fast Fourier Transform (FFT) filter (FFT high-pass, low-pass, cosine roll-off, suscepbility), calculated spectra frequency energy to predict the depth and intensity of the apparent remanence magnetization of source (Hilbert). The calculated results and magnetic anomalous show that the remanence anomaly is caused by the intrusions into the Triassic limestone and Permian basalts with small anomalies, and the depth of located source is not great. We have identified a number of positions to the three drilled well, the drilled result specify interpretation with very high accuracy. The magnetic method is helpful to identify porphyry mineralization, and judge the shape and depth of the concealed ore-bearing intrusive bodies under the similar geological condition.

METALLOGENIC SYSTEM OF DACHANG TIN- POLYMETALLIC ORE FIELD

The Dachang tin polymetallic ore field in northern Guangxi, China, lies in a mid late Paleozoic rift that borders up the southern boundary of the Jiangnan Xuefeng Massif. As a giant ore deposit, it deposited in middle of the Nandang Hechi metallogenic zone. The ore hosting strata are of the Devonion, which shows the evident characteristics of polymetallic elements, i.e., Sn, Zn, Pb, Sb, As, Cu, Ag, In, Ge, Cd, et al., and over 1 000 000 t tin reserves.