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1.
The origin and age of the hydrothermal fluids related to the precipitation of fluorite, barite and calcite in the Villabona, La Collada and Berbes localities (Asturias fluorspar district, N Spain) have been evaluated from Sr and Nd radiogenic isotopes. Sr isotope data (87Sr / 86Sr = 0.7081 to 0.7096) are compatible with mixing between seawater and a more evolved groundwater that interacted with the basement. From Nd isotopes in fluorite, an isochron age of 185 ± 29 Ma (Lower Jurassic) was obtained, consistent with other hydrothermal events in the Iberian Peninsula and Europe. These constraints are essential to proceed with a quantitative model for the genesis of the mineralization that includes fluid and heat flow together with reactive transport of solutes.  相似文献   

2.
Absolute ages of granite magmatism, as well as of tungsten mineralization, are poorly constrained in the Mongolian Altai and adjacent areas. There are no reports focusing on special isotopic investigations of the tungsten deposits. For the deposits in the Achit nuur and the Zagaan-Shibetin tectonic zones, two concepts that are discussed in the literature assume Paleozoic or Mesozoic ages for mineralization and related granite magmatism. We report the first results of a combined Sm-Nd and Rb-Sr isotope investigation of rocks and vein minerals of the Ulaan uul tungsten deposit at Kyzyltau; the results suggest Paleozoic ages for vein mineralization and for albitization of the host granite. The Sm-Nd isotope system, and the structure of vein minerals used for isotopic dating, were only slightly affected by late alteration processes. Sm-Nd mineral isochrons for wolframite and fluorite from the veins define an age of 303 ± 17 Ma (MSWD = 1.8, εNd = +0.9 ± 0.2). The Rb-Sr isotope system of the vein-hosting granite was strongly influenced by alteration processes. The Rb-Sr whole-rock isochron (282.2 ± 2.4 Ma, Sri = 0.70667 ± 0.00032, MSWD = 0.53) is interpreted as a mixing line and the age so defined has no direct geological meaning. Nevertheless, using Rb-Sr model ages and data on the degree of alteration of the samples, an age somewhat below 316 Ma can be estimated for albitization of the vein-hosting granite. This age estimation is in good agreement with the Sm-Nd isochron age for the vein mineralization. High εNd values obtained for wolframite and fluorite from the ore veins indicate an important role for material derived from the upper mantle in the ore formation processes.  相似文献   

3.
The fluorite of Santa Catarina that occurs in veins cutting Precambrian granitic rocks of coastal Brazil has been difficult to date by Rb/Sr, K/Ar and Sm/Nd methods. New fission track dating of apatite in granites next to the veins yields ages of 144–76 Ma, which are related to the opening of the South Atlantic Ocean. Four groups of fission track ages were identified: the ca 145 Ma group is a hydrothermal event that preceded fluorite mineralization; the second group of ages, 131–107 Ma, records the first hydrothermal mineralizing event; the third group, 98–93 Ma, represents the second hydrothermal mineralizing event; and the fourth group, 89–76 Ma, dates the last hydrothermal mineralizing event. As shown by previous studies, the temperatures of these events varied from 170° to 70°C, but the last hydrothermal event occurred during a gradual cooling. The smaller lengths of the confined fission tracks from the fourth event support this interpretation. These results are based on sixteen carefully selected samples from four veins ranging from 1 to 4 m in thickness. The ages of these samples were established using the standard methods of fission track dating. Our study clearly demonstrates the value of apatite fission track dating for deposits whose mineralization occurred over a long time span at a wide range of temperatures.  相似文献   

4.
The Niujuan breccia-type silver deposit forms part of the North Hebei metallogenic belt along the northern margin of the North China Craton. The Hercynian Baiyingou coarse-grained granite and the Yanshanian Er’daogou fine-grained granite are the major Mesozoic intrusions exposed in this region. Here we investigate the salient characteristics of the mineralization and evaluate its genesis through zircon U-Pb and fluorite Sm-Nd age data, and Pb, S, O, H, He and Ar isotope data. The orebodies of the Niujuan silver deposit are hosted in breccias, which contain angular fragments of the Baiyingou and Er’daogou granitoids. The δ34S values of pyrite from the silver mineralized veins range from 2.4‰ to 5.3‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the sulfide minerals show ranges of 16.837–16.932, 15.420–15.501 and 37.599–37.950, respectively. The 3He/4He and 40Ar/36Ar ratios of the fluids trapped in pyrite are 0.921–4.81Ra and 299.34–303.84, respectively. The δ18O and δ18Dw values of the ore-forming fluids range from 0.6‰ to −4.15‰ and from −119.4‰ to −98.7‰, respectively. Our isotopic data suggest that the ore-forming fluids were originally derived from the subvolcanic plutons and evolved into a mixture of magmatic and meteoric water during the main hydrothermal stage. The ore-forming materials were primarily derived from the lower crust with limited incorporation of mantle materials. The emplacement time of the Er’daogou granite is constrained by LA-ICP-MS zircon U-Pb geochronology at 145.5 ± 2.1 Ma. Five fluorite samples from the last hydrothermal stage yielded a Sm-Nd isochron age of 139.2 ± 3.8 Ma, indicating the upper age limit for the silver mineralization. These ages correlate with the formation of the Niujuan deposit in an extensional setting associated with the closure of the Mongol-Okhotsk Ocean and the subduction of the Paleo-Pacific oceanic plate beneath the North China Craton.  相似文献   

5.
El Hammam is the only fluorite mine in Morocco (production 100,000 t/year). The fluorite mineralization is in an array of fluorite–calcite veins and is characterized by unusually high REE content in carbonate minerals (1,400 ppm in calcite; up to 2,000 ppm in siderite) and in fluorite (about 600 ppm). Since the 1960s, the genesis of the deposit has been attributed to a mesothermal hydrothermal event connected with late-Variscan granitic intrusions. Precise 40Ar/39Ar dating of hydrothermal K-feldspar yields an age of formation of the El Hammam deposit at 205 ± 1 Ma. Its genesis is therefore associated in time and space with the development of the Triassic–Jurassic basins and the associated anorogenic continental flood basalts of the Moroccan Mesetian Middle Atlas. The source of the hydrothermal mineralization (magmatic and/or metamorphic) is discussed.  相似文献   

6.
The possibility of using hydrothermal fluorite as an Sm–Nd geochronometer is based on the results of an REE pattern study of this mineral (Chernyshev et al., 1986). As a result of REE fractionation, in many cases, the Sm/Nd ratio achieves a multifold increase compared with its level in terrestrial rocks, and the radiogenic shift of the 143Nd/144Nd isotope ratio reaches 10–20 εNd units over a short time interval (as soon as tens of Ma). This is a necessary prerequisite for Sm–Nd isochron dating of fluorite. Zonal polychrome fluorite from a vein referred to the final stage of large-scale uranium mineralization at the Sterl’tsovka deposit in the ore field of the same name located in the eastern Transbaikal region has been dated using the 143Nd/144Nd method. To optimize isochron construction, local probes with high and contrasting Sm/Nd ratios have been sampled from the polished surfaces of two samples, taking into account the REE pattern of zonal fluorite. Sm–Nd isochron dating has been carried out separately for each sample. The 147Sm/144Nd и 143Nd/144Nd ratios vary within the intervals 0.5359–2.037 and 0.512799–0.514105, respectively. Two isochrons, each based on six fluorite probes, have been obtained with the following parameters, which coincide within 2σ uncertainty limits: (1) t = 134.8 ± 1.3 Ma, (143Nd/144Nd)0 = 0.512310 ± 13, MWSD = 0.43 and (2) t = 135.8 ± 1.6 Ma, (143Nd/144Nd)0 = 0.512318 ± 10, MWSD = 1.5. The mean age of fluorite based on two isochron datings is 135.3 ± 1 Ma. Comparison of this value with the most precise dating of pitchblende related to the ore stage in the Strel’tsovka ore field (135.5 ± 1 Ma) shows that four mineralization stages, distinguished by geological and mineralogical data, that were completed with the formation of polychrome fluorite veins 135.3 ± 1 Ma ago, represent a single and indivisible hydrothermal process whose duration does not exceed 1 Ma.  相似文献   

7.
朱桂田  徐文忻  李蘅  朱文风 《地球学报》2005,26(Z1):156-159
古袍矿区的花岗斑岩出露于古袍复向斜西部扬起部位。围岩地层主要为寒武系水口群浅变质砂岩、粉砂岩、硅质岩及板岩、千脉岩和破质页岩。花岗斑岩和花岗斑岩内的石英脉体中石英样品的40Ar/39Ar年龄数据表明户，40Ar/39Ar坪年龄值在187.87±1.53 Ma至244.88±2.48 Ma之间，是加里东期花岗斑岩成岩作用之后，海西、印支或者燕山早期多期构造热液作用的产物。金矿化与花岗斑岩成岩后的多期次构造热液作用有关。主要受控于断层破碎带及其中充填的石英脉和黄铁矿化。  相似文献   

8.
Fluorite mineralization at the La Nueva and Bubu mines yields Sm-Nd ages of 131 ± 22 and 117 ± 26 Ma, respectively. Thus, the mineralization most probably is related to a late Gondwanian (Lower Cretaceous) extensional and magmatic event that affected the Sierras Pampeanas basement during the opening of the Atlantic Ocean. Hydrothermal fluids involved in the formation of the fluorite probably were of meteoric origin, their isotopic composition (Sr and Nd) resulting largely from the incongruent dissolution of feldspars in the host porphyritic granites.  相似文献   

9.
Abstract: The Kanggur gold deposit lies in East Tianshan mountains, eastern section of Central Asia orogenic belt. The gold mineralization occurs on the northern margin of the Aqishan‐Yamansu Paleozoic island arc in the Tarim Plate. It was hosted mainly in Middle‐Lower Carboniferous calc‐alkaline volcanic rocks, and controlled by the distributions of syn‐tectonic intrusions and ductile shear zones. In order to determine ore‐forming age of the Kanggur deposit, samples were collected from ores, wall rocks, altered rocks and intrusions. The dating methods include Rb‐Sr isochron and Sm‐Nd isochron, and secondly 40Ar/39Ar age spectrum, U‐Pb and Pb‐Pb methods. Based on the mineral assemblage and crosscutting relationship of ore veins, five mineralization stages are identified. This result is confirmed by isotope geochronologic data. The first stage featuring formation of pyrite‐bearing phyllic rock, is mineralogically represented by pyrite, sericite and quartz with poor native gold. The Rb‐Sr isochron age of this stage is 2905 Ma. The second stage represents the main ore‐forming stage and is characterized by native gold–quartz–pyrite–magnetite–chlorite assemblage. Magnetite and pyrite of this stage are dated by Sm‐Nd isochron at 290.47.2 Ma and fluid inclusion in quartz is dated by Rb‐Sr isochron at 282.35 Ma. The third mineralization stage features native gold–quartz–pyrite vein. In the fourth stage, Au‐bearing polymetallic sulfide‐quartz veins formed. Fluid inclusions in quartz are dated by Rb‐Sr isochron method at 25821 Ma. The fifth stage is composed of sulfide‐free quartz–carbonate veins with Rb‐Sr age of 2547 Ma. The first and second stages are related to ductile‐brittle deformation of shear zones, and are named dynamo‐metamorphic hydrothermal period. The third to fifth stages related to intrusive processes of tonalite and brittle fracturing of the shear zones, are called magmato‐hydrothermal mineralization period. The Rb‐Sr isochron age of 2905 Ma of the altered andesite in the Kanggur mine area may reflect timing of regional ductile shear zone. The Rb‐Sr isochron age of 28216 Ma of the quartz‐syenite porphyry and the zircon U‐Pb age of 2757 Ma of tonalite in the north of Kanggur gold mine area are consistent with the age of gold mineralization (290‐254 Ma). This correspondence indicates that the tonalite and subvolcanic rocks may have been related to gold mineralization. The Rb–Sr, Sm‐Nd and U‐Pb ages and regional geology support the hypothesis that the Kanggur gold deposit was formed during collisional orogenesis process in Late Variscan.  相似文献   

10.
Associated with the Cretaceous Okorusu carbonatite complex (Namibia) is a hydrothermal fluorite mineralization hosted in Pan-African country rock marbles, which resulted from fluid-rock reaction between the marbles and orthomagmatic, carbonatitic fluids expelled from the carbonatite. Yellow fluorite I was deposited in veins up to 5 cm away from the wallrock contact, followed by purple and colorless fluorite II, smoky quartz and barite, a Mn-rich crust on early calcite, and pure calcite. This clear-cut sequence of mineral growth allows an investigation into fluid-rock interaction processes between the marble and the migrating carbonatitic fluid, and element fractionation patterns between the fluid and subsequent hydrothermal precipitates.Fluorite I shows a progressive change in color from dark yellow to colorless with purple laminations over time of deposition. Subsequent fluorite I precipitates show an increase in Ca, and a continuous decrease in F, Sr, REE, Y, Th, U and Pb contents. The ratios (Eu/Eu*)cn, Th/Pb and U/Pb increase whereas Y/Ho, Th/U and (La/Yb)cn decrease. The Sr-isotopic composition remains constant at 87Sr/86Sr = 0.70456-0.70459, but with varying, highly radiogenic Pb (206Pb/204Pb = 32-190, 238U/204Pb = 7-63). Fluorite II has 87Sr/86Sr = 0.70454-0.70459, 206Pb/204Pb = 18.349, and 207Pb/204Pb = 15.600, and a chemical composition similar to youngest fluorite I. The Mn-rich crust on early calcite accumulated REE, Ba, Pb, Zr, Cs, Th and U, developing into pure calcite with a prominent negative Ce anomaly and successively more radiogenic Sr. The calculated degrees of fluid-rock interaction, f = weight fraction of fluid/(fluid + marble), decrease from fluorite I and most fluorite II (f = 0.5) to calcite (f = 0.2-0.3) and hydrothermal quartz (f ? 0.1). A crush-leach experiment for fluid inclusions in the hydrothermal quartz yielded a Rb-Sr isochron age of 103 ± 12 Ma. Crush-leach analysis for the carbonatitic fluid trapped in the wallrock yielded a trend from the fluid leachate to the host quartz (206Pb/204Pb = 18.224 and 18.602, 207Pb/204Pb = 15.616 and 15.636, respectively) extending from carbonatite towards crustal rocks.Calculated trace element distribution coefficients fluorite/fluid are below unity throughout, and increase from La to Yb. Elements largely excluded from fluorite (Ba, Pb, LREE relative to HREE) were incorporated later into the Mn-rich crust on calcite. The trace element patterns of the hydrothermal minerals are related to changing aCO2 and aF− in the fluid during continued fluid-marble reaction. A predominance of carbonate over fluoride complexing in the fluid as reactions proceeded controlled the Y/Ho, Th/U and REE patterns in the fluid and the crystallizing phases. Deviations from these trends indicate discontinuous processes of fluid-rock reaction.  相似文献   

11.
The Yingchengzi gold deposit, located 10 km west of Shalan at the eastern margin of the Zhangguangcai Range, is the only high commercially valuable gold deposit in southern Heilongjiang Province, NE China. This study investigates the chronology and geodynamic mechanisms of igneous activity and metallogenesis within the Yingchengzi gold deposit. New zircon U–Pb data, fluid inclusion 40Ar/39Ar dating, whole‐rock geochemistry and Sr–Nd isotopic analysis is presented for the Yingchengzi deposit to constrain its petrogenesis and mineralization. Zircon U–Pb dating of the granite and diabase–porphyrite rocks of the igneous complex yields mean ages of 471.7 ± 5.5 and 434 ± 15 Ma respectively. All samples are high‐K calc‐alkaline or shoshonite rocks, are enriched in light rare earth elements and large ion lithophile elements, and are depleted in high field strength elements, consistent with the geochemical characteristics of arc‐type magmas. The Sr–Nd isotope characteristics indicate that the granite formed by partial melting of the lower crust, including interaction with slab‐derived fluids from an underplated basaltic magma. The primary magma of the diabase–porphyrite was likely derived from the metasomatized mantle wedge by subducted slab‐derived fluids. Both types of intrusive rocks were closely related to subduction of the ocean plate located between the Songnen–Zhangguangcai Range and Jiamusi massifs. However, fluid inclusion 40Ar/39Ar dating indicates that the Yingchengzi gold deposit formed at ~249 Ma, implying that the mineralization is unrelated to both the granite (~472 Ma) and diabase–porphyrite (~434 Ma) intrusions. Considering the tectonic evolution of the study area and adjacent regions, we propose that the Yingchengzi gold deposit was formed in a late Palaeozoic–Early Triassic continental collision regime following the closure of the Paleo‐Asian Ocean. In addition, the Yingchengzi deposit could be classified as a typical orogenic‐type gold deposit occuring in convergent plate margins in collisional orogens, and unlikely an intrusion‐related gold deposit as reported by previous studies. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

12.
Precious-metal mineralization in the southern Apuseni Mountains of western Romania is hosted by mid-Miocene (∼14 Ma) andesitic stocks and lava flows. The mineralized veins are surrounded by aureoles of hydrothermal alteration, consisting of quartz, sericite, K-feldspar, pyrite and calcite. The alteration process caused a total homogenization of initial 87Sr/86Sr in the rocks. Ages determined for the hydrothermal alteration are 13.7–15.7 Ma, indicating that hydrothermal alteration immediately followed igneous activity. Furthermore, a large influx of radiogenic Sr took place during alteration, this Sr probably being derived from the hydrothermal leaching of continental meta-sedimentary rocks in the basement. Received: 5 December 1997 / Accepted: 26 February 1998  相似文献   

13.
The Baiyanghe Be–U–Mo deposit is located in the Late Paleozoic Xuemisitan–Kulankazi island arc of the northwestern margin of the Junggar plate, Northwest China. It is the largest Be deposit (2.2 M tons of ore with grades ranging from 0.2% to 1.4%) in Asia. Orebodies in the deposit occur as fractures along contact zones between the Yangzhuang granite porphyry intrusion and Devonian pyroclastic country rocks and within the porphyry itself. Muscovite–fluorite veins are closely associated with the Be–U–Mo mineralization. A new Ar–Ar dating of the muscovite in this study yields a plateau age of 303.0 ± 1.6 Ma, which constrains the timing of the Be–U–Mo mineralization of the deposit. Three stages of fluorite of different colors have been identified at the deposit, with the earliest dark-purple fluorite more closely associated with the mineralization. Microthermometry of fluid inclusions obtained from the three stages of fluorite suggests that the fluorites were precipitated as veins from low temperature (120–150 °C) hydrothermal fluids with salinity ranging from 4.7 to 19.7 wt.% NaCl eqv. Based on the trace elemental concentrations and REE patterns of the fluorite, the style of veining, and the low salinity and low temperature characters of the fluid inclusions, it is suggested that Be and U were most likely transported as fluoride complexes and Mo as hydroxyl complexes. Pb isotopic compositions of the ores and country rocks, as well as O and H isotopic characters of the ore-related muscovite, indicate mixing between magmatic and meteoric waters; both contributed to formation of the ore-forming fluids. Metallic Be, U, and Mo were most likely leached out from the granite porphyry by the fluids. The fluid mixing led to the reduction of U, Mo, and Be and their precipitation at the deposit.  相似文献   

14.
The fluorite-bearing hydrothermal mineralization in Sardinia mainly occurs within Paleozoic volcanic and metasedimentary rocks. Only 3 occurrences are located in volcanic and siliciclastic Cenozoic rocks. Most Sardinian fluorites exhibit relatively high rare earth and Y (REY) contents, strong positive Y anomalies, slightly negative Ce and generally positive Eu anomalies. These features indicate that the REY were mobilized mainly from non-carbonate rocks. Neither Sr nor Nd isotopes can be used to date radiometrically the Sardinian fluorites. However, the measured Sr-isotope ratios of the fluorites hosted by Paleozoic rocks fit mixing lines in the 1000/Sr versus 87Sr/86Sr plot once recalculated at 280 Ma, suggesting that the age inferred for the correction probably represents that of the formation of the fluorite mineralization. Mixing likely occurred between diluted surficial waters and brines circulating mainly through the Lower Paleozoic metasedimentary basement. The Cenozoic fluorites exhibit chemical and isotopic features similar to those of the Paleozoic fluorites, except the Nuraghe Onigu fluorite displaying a possible contribution of Sr from Cenozoic magmatic rocks. The initial εNd values of the Paleozoic fluorites fit the age proposed for the formation of the deposits. Moreover, the values suggest that radiogenic Nd was provided to the fluids from the Ordovician siliciclastic basement, except for 3 deposits where the potential source rocks of Nd were mainly Ordovician acidic magmatic rocks. The initial εNd values of the Cenozoic fluorites suggest a provenance of Nd essentially from the leaching of Variscan granitoids.  相似文献   

15.
通过成矿期方解石的C、O、Sr和含硫矿物的S、Pb同位素,成矿期方解石Sm-Nd测年研究,探讨白秧坪矿集区东矿带矿床成因。测试结果表明,白秧坪矿集区东矿带方解石δ13CPDB值变化范围-4.0‰~2.3‰,平均值-0.2‰,δ18OPDB值范围-27.2‰~20.4‰,平均值-14.1‰,δ18OSMOW值范围2.9‰~24.4‰,平均值16.4‰;方解石Sr同位素值变化范围0.707669~0.710115,平均值0.709320;硫化物δ34SV-CDT值分布范围-20.2‰~1.3‰,平均值约-8.8‰,天青石δ34SV-CDT值分布范围为17.1‰~19.4‰,平均值约18.0‰;Pb同位素测试结果中,206Pb/204Pb的变化范围为18.553~18.857,207Pb/204Pb变化范围为15.501~15.826,208Pb/204Pb变化范围为38.54~39.456;成矿阶段方解石Sm-Nd等时线年龄为29.5±1.7 Ma。对测试结果的研究表明,白秧坪矿集区东矿带碳质的来源较为均一,矿石中热液方解石碳质源自地层中碳酸盐岩溶解,成矿流体来自地层水和大气降水,属于盆地卤水流体系统;成矿物质硫来自海水硫酸盐的还原作用,成矿早期以有机质还原硫为主,成矿后期以生物还原硫为主;金属成矿物质来自沉积地层和盆地基底;测定白秧坪矿集区东矿带铅锌成矿年龄为29.5±1.7 Ma,与地质年龄限定的较为吻合。   相似文献   

16.
Vein fluorite deposits (Tebarray, Lanuza, Bielsa-Parzán, Bizielle and Yenefrito) as well as one MVT-style fluorite mineralization (Portalet) in the Central Pyrenees are the focus in this contribution. These deposits are made up of fluorite, barite, base metal sulphides, calcite, and quartz and are hosted in sedimentary rocks and granites of Palaeozoic age. Generally, these mineral occurrences, typically associated with Late Palaeozoic steeply dipping faults are similar with respect to geologic setting, mineralogy and geochemical trends to other fluorite and base metal veins located in the Central Pyrenees. Veins occurring along such faults most likely represent channelways used by mineralizing solutions that were expelled from the basement. Previous work argued for genetic processes involving circulation of mineralising fluids during the Triassic–Lower Cretaceous period, which is often considered to represent a period of heat, fluid, and mass transfers related to rifting events in the western European basins, which is related to the opening of the Atlantic.A major goal of this study was to decipher the timing of fluid flow and ore formation on the basis of Nd–Sm dating of fluorite sampled from a number of deposits sharing a similar geological framework. No precise age(s) could be obtained due to a scatter in data, but results from the Portalet MVT-style deposit point to a mid-Triassic age (around 220 Ma) for this mineralization. The model that best explains the diagenetic stratabound mineralization at Portalet is gravity-driven fluid flow involving basinal brines during a rifting stage. Indeed, the formation of horst and graben structures during Early Alpine extensional tectonics favoured the infiltration of meteoric water into uplifted blocks, followed by fluid migration through the deeper parts of the basins whereby heat and dissolved components were acquired. This model also explains diagenetic changes recorded in the host limestone at Portalet. Also, overall Pb, Sr and Nd isotopic ratios measured in galena and fluorite suggest that differences in host rock and in the lithology of the basement seem to have exerted control on the chemistry of mineralizing fluids providing each deposit with distinctive characteristics.  相似文献   

17.
《International Geology Review》2012,54(11):1054-1067
China is one of the richest countries in the world in terms of fluorite resources. On the basis of host rocks and mineralization patterns, the fluorite deposits in China have been classified into three types: (1) those occurring in Mesozoic volcanic regions, mainly consisting of veinfilling deposits of the quartz-fluorite association (Type I); (2) those occurring in granite areas, chiefly belonging to veinfilling deposits of the quartz-fluorite association or veinfilling or altered-rock deposits associated with Pb, Zn, W, Sn, etc. (Type II); and (3) those occurring in carbonate rocks as bedded deposits of quartz-fluorite, sulfide-fluorite, and quartz-barite-calcite-fluorite assemblages (Type III).

This paper summarizes the characteristics of fluorite deposits in China on the basis of strontium-, hydrogen-, and oxygen-isotopic and geochronological data, as well as geological investigations of deposits from 22 mining districts. δ18O and δD values of ore-forming fluids are ?10.2 to +3.7‰ and ?77.9 to 41.0‰, respectively, for Type-I deposits, ?13.1 to ?4.9‰ and ?65.5 to ?41.7‰ for Type-II deposits, and -5.6 to +4.3‰ and ?80 to ?29‰ for Type-Ill deposits. Study of the isotopic water-rock exchange indicates that the mineralizing fluids for these types of deposits have been derived mostly from circulating geothermal water that originated from Mesozoic meteoric water. The differences in the isotopic characteristics of hydrothermal systems for various types of deposits depend mainly on isotopic exchange between water and rocks, the water/rock values being 0.05 to 2.0 for Type-I deposits, generally more than 2.0 for Type-II deposits, and 0.5 to 3.0 for Type-Ill deposits.

The ore-forming ages for Type-I and Type-II deposits are roughly separated into three groups—230 to 180 Ma, 120 Ma, and 90 to 60 Ma. These ages successively decrease from northwestern China to southeastern coastal areas.

87Sr/86Sr values of 0.7306 to 0.7710 (mean 0.7513) from fluorite in the early stage (main mineralization) for Type-I deposits are higher than those from host rocks (0.7081 to 0.7260) during the mineralizing event, and mostly fall in the range of 87Sr/86Sr values from basement metamorphic rocks (from 0.7455 to 0.9094) during the epoch of mineralization. But the 87Sr/86Sr values of 0.7102 to 0.7137 (mean 0.7122) for late-stage fluorite and calcite are similar to those of surrounding host rocks. This indicates that the mineralizing materials of early stages in the formation of deposits (Type-I) originated mostly from Precambrian basement metamorphic rocks; those of later stages (Type II) were derived chiefly from host rocks. Type-II and Type-Ill deposits from different mining areas exhibit great variations in 87Sr/86Sr values, but are quite similar to their host rocks, indicating that the mineralizing materials in Type-II and Type-Ill deposits were derived chiefly from their host rocks.  相似文献   

18.
油气成藏和有机质参与金属成矿的内在联系是近年来国内外地学界关注的热点问题.根据流体包裹体岩相学观察和激光拉曼光谱分析,在鄂西宜昌地区震旦系陡山沱组和下寒武统牛蹄塘组页岩储层及震旦系灯影组MVT（Mississippi Valley type）铅锌矿床中发现了高密度甲烷包裹体,并利用甲烷包裹体的甲烷拉曼散射峰v1计算了甲烷包裹体的密度;同时采用Rb-Sr、Sm-Nd同位素定年确定了MVT铅锌矿成矿年代.鄂阳页1井陡山沱组页岩石英脉和何家坪MVT铅锌矿方解石样品中甲烷包裹体密度分别为0.237~0.278 g/cm3和0.213~0.271 g/cm3,属于高密度甲烷包裹体.何家坪铅锌矿共生矿物闪锌矿和方铅矿的Rb-Sr等时线年龄为189.1±1.8 Ma,方解石的Sm-Nd等时线年龄为189.9±2.0 Ma,指示铅锌矿形成于燕山早期的构造挤压运动;共生矿物的初始87Sr/86Sr值（0.711 92）和方解石的初始87Sr/86Sr值（0.712 03~0.712 27）指示何家坪铅锌矿成矿流体的Sr同位素主要来源于页岩层.何家坪铅锌矿中捕获的以流体包裹体形式存在的高密度甲烷流体最有可能来源于陡山沱组页岩和/或牛蹄塘组页岩内高密度超压甲烷流体.页岩气层和MVT铅锌矿中高密度甲烷包裹体的发现及MVT铅锌矿成矿时间的确定为探讨有机质参与MVT铅锌矿成矿提供了新证据.   相似文献   

19.
黔东北(沿河)-渝东南(酉阳)一带广泛发育萤石、重晶石及铅锌(汞)矿化,关于其成矿时代,一直缺少直接的同位素年龄证据。黔东北大竹园萤石矿床位于上扬子地块东南缘,矿体赋存于下奥陶统桐梓组和红花园组碳酸盐岩内,受NW向断裂控制,是本区热液脉型萤石矿床的代表。本文以该矿床为研究对象,利用单矿物Sm-Nd等时线方法进行了成矿年龄测定,获得萤石Sm-Nd等时线年龄为436±15 Ma(MSWD=0. 85),萤石与共生方解石Sm-Nd等时线年龄为430±13 Ma(MSWD=1. 02),两者在误差范围内一致,表明矿床形成于加里东期,该年龄与湘西-黔东MVT铅锌矿床成矿时代(477～410 Ma)一致。本区萤石-重晶石矿床与区内产出的主要铅锌(汞)矿床关系密切,推测它们有相近的物质来源,是在同一构造运动时期形成的一个有亲缘关系的成矿系列。研究结果指示加里东期是区内重要的萤石-重晶石-铅锌(汞)中低温热液成矿期。  相似文献   

20.
Abstract This paper discusses the relationships between granitic magmatism and gold mineralization and the exhumation history of the Dapinggou gold deposit in northern Altun, NW China based on the geochronological data, including zircon U‐Pb ages, Rb‐Sr isochron age and 40Ar‐39Ar dating and MDD modeling data. The main granitic magmatism age in this area is attained from the ID TIMS U‐Pb geochronology of zircons from the Kuoshibulak granite, the biggest granite in the northern Altun area, which gives a concordant age of 443±5 Ma in the Late Ordovician. Zircon ID TIMS U‐Pb geochronology of the West Dapinggou biotite granite west of the Dapinggou gold deposit gives concordant ages around 485±10 Ma, representing the early stage of Ordovician magmatism. The Rb‐Sr isochron age (487±21 Ma) of 6 quartz inclusion samples from quartz veins in this gold deposit is very close to that of the West Dapinggou granite. MDD modeling of step heating 40Ar‐39Ar data of K‐feldspar from the same West Dapinggou biotite granite gives a rapid cooling history from 300°C to 150°C during 200–185 Ma. According to the age data and the geological setting of this area, we conclude that the Dapinggou gold deposit was formed at the early stage of the Early Paleozoic granitic magmatism in northern Altun, and exhumed in the Early Jurassic due to the normal faulting of the Lapeiquan detachment. The Early Paleozoic magmatism may provide heat source and produce geological fluids, which are very important for gold mineralization. Exhumation in the Mesozoic caused the uplift of the deposit towards the ground surface.  相似文献   

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