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1.
Lead isotope analyses of 25 sulfide samples (galenas, iron sulfides, and sulfosalts) from five different mines of the Skellefte district, northern Sweden, demonstrate that the Pb-isotopic composition of galenas and other sulfides rich in lead varies between individual deposits within the district. This contrasts with many other base-metal districts, where ore lead is isotopically homogeneous on a regional basis. Although all of the Skellefte leads are depleted in 207Pb relative to average global lead evolution models, thus suggesting a large mantle-derived component in their sources, the Nasliden deposit lying at the contact of the host volcanic rocks and the overlying metasediments contains a significant component of crustal lead. It is concluded that while the Pb-isotope data are consistent with a volcanic exhalative origin of the ores of the Skellefte district, they also demonstrate that older crustal lead was incorporated into the sulfides during their emplacement and the subsequent period of magmatic and metamorphic activity which followed their deposition.  相似文献   

2.
The lead isotope composition of three Cu-Zn-Pb sulfide deposits and one Au deposit in the Early Proterozoic Svecofennian of central Sweden reveals the existence of two distinct lead sources in the region. Rockliden and Enstern contain lead of upper crustal affinity and are isotopically homogeneous. Lead in these deposits probably originates from Archean-derived detritus which was well homogenized by sedimentary processes and deposited over large areas as a component in Early Proterozoic sedimentary and tuffaceous rocks. Lead isotopic homogeneity within the Tjärnberget and Enåsen deposits is less pronounced, and the less radiogenic character of the lead suggests a source of mantle affinity. In areas where metasedimentary rocks are absent or contain very little Archean-derived material the isotopic signature of mantle-derived volcanic rocks is reflected in the ore lead. This approach is also applicable to other Svecofennian deposits. Together with deposits in west-central Finland the Rockliden deposit constitutes the northern boundary for lead of upper-crustal affinity, i.e., Archean-derived lead, in Svecofennian sulfide deposits.Despite these differences the isotope ratios of the four deposits indicate that they formed roughly contemporaneously with other Svecofennian deposits in Sweden and Finland.  相似文献   

3.
拜仁达坝和维拉斯托是近年来在内蒙古东部地区发现的2个大型银多金属矿床,文章对其开展了硫和铅同位素研究。结果表明,拜仁达坝矿床矿石中硫化物的δ34S值为-4.0‰～+1.6‰,维拉斯托矿床矿石中硫化物的δ34S值为-0.8‰～+2.0‰,与岩浆热液型矿床的硫同位素值接近,表明这2个矿床中的硫主要来自岩浆。拜仁达坝矿区43件金属硫化物的206Pb/204Pb值为18.333～18.515,207Pb/204Pb值为15.532～15.656,208Pb/204Pb值为38.057～38.610;维拉斯托矿区20件金属硫化物的206Pb/204Pb值为18.304～18.377,207Pb/204Pb值为15.520～15.610,208Pb/204Pb值为38.112～38.435。拜仁达坝东矿区矿石中的铅同位素组成与维拉斯托矿区相似,变化范围小,相对贫放射性铅同位素,并且均为混合铅。矿石中的铅可能来自围岩地层及深源岩浆。  相似文献   

4.
Isotopic ratios of Pb in sulfide minerals (primarily pyrrhotite, chalcopyrite, and pentlandite) from a suite of samples from the platiniferous J-M Reef of the Stillwater Complex were measured to elucidate the temporal and genetic relationship between sulfides and host silicate minerals. Results indicate that sulfides and coexisting plagioclases are generally not in isotopic equilibrium, that both sulfides and feldspars record highly radiogenic initial ratios at 2.7 Ga, and that a component of “post-emplacement” radiogenic Pb has mixed with common Pb in the sulfides. A model involving introduction of radiogenic Pb carried by fluids derived from sources external to the complex is favored. Analyses of the lead isotopic composition of sulfides in veins which cut the complex indicate that a significant fraction of the radiogenic lead which was added to the sulfides was externally derived during an extensive hydrothermal episode, associated with Proterozoic regional metamorphism around 1.7 Ga. The possibility that some fractions of the radiogenic Pb may have been derived from primary minerals altered during the low-grade metamorphism cannot be discounted. The amount of radiogenic lead added is variable and in some cases negligible. There is a good correlation between the lead isotope composition and the nature of the secondary mineral assemblage. Sulfides and plagioclases in samples that show little or no alteration of the primary minerals are generally in isotopic equilibrium and preserve isotope ratios consistent with magmatic crystallization at 2.7 Ga. Samples with the most radiogenic sulfides contain abundant secondary minerals (serpentine, talc, actinolite, chlorite and zoisite) associated with greenschist facies metamorphism. Some of the radiogenic Pb in the sulfides can be removed by progressive stepwise leaching. However, in most samples recrystallization of sulfides during metamorphism has mixed common Pb and radiogenic Pb throughout the crystal structure such that, in these samples, stepwise leaching does not recover initial Pb isotopic ratios. Plagioclases are much more resistant to low temperature recrystallization and in almost all cases, stepwise leaching reveals the initial lead isotopic composition. The reactivity of sulfides over a wide temperature range enhances their utility in understanding not only the processes involved in their formation at the time of magmatic emplacement but also postmagmatic processes which were important in the redistribution and enrichment of platinum group elements (PGE) within the ore zone. Received: 30 December 1998 / Accepted: 16 June 1999  相似文献   

5.
The Cangyuan Pb-Zn-Ag polymetallic deposit is located in the Baoshan Block, southern Sanjiang Orogen. The orebodies are hosted in low-grade metamorphic rocks and skarn in contact with Cenozoic granitic rocks. Studies on fluid inclusions (FIs) of the deposit indicate that the ore-forming fluids are CO2-bearing, NaCl-H2O. The initial fluids evolved from high temperatures (462–498 °C) and high salinities (54.5–58.4 wt% NaCl equiv) during the skarn stage into mesothermal (260–397 °C) and low salinities (1.2–9.5 wt% NaCl equiv) during the sulfide stage. The oxygen and hydrogen isotopic compositions (δ18OH2O: 2.7–8.8‰; δD: −82 to −120‰) suggest that the ore-forming fluids are mixture of magmatic fluids and meteoric water. Sulfur isotopic compositions of the sulfides yield δ34S values of −2.3 to 3.2‰; lead isotopic compositions of ore sulfides are similar to those of granitic rocks, indicating that the sulfur and ore-metals are derived from the granitic magma. We propose that the Cangyuan Pb-Zn-Ag deposit formed from magmatic hydrothermal fluids. These Cenozoic deposits situated in the west of Lanping-Changdu Basin share many similarities with the Cangyuan in isotopic compositions, including the Laochang, Lanuoma and Jinman deposits. This reveals that the Cenozoic granites could have contributed to Pb-Zn-Cu mineralization in the Sanjiang region despite the abundance of Cenozoic Pb-Zn deposits in the region, such as the Jingding Pb-Zn deposit, that is thought to be of basin brine origin.  相似文献   

6.
How to utilize sulfur isotope for many domestic and foreign researchers to trace the sulfur source of metallic sulfide deposit has been explored for many years. Fruitful results have been gained now. Based on summing up the characteristics of sulfur isotopic composition of hydrothermal mineral from metallic sulfide deposits, this paper illuminated the total sulfur isotopic composition of ore-forming fluids is the key factor in estimating the sulfur source. This paper also summarized three approaches about how to obtain the total sulfur isotopic composition (δ34S∑S) of ore-forming fluids. They are physical-chemical equilibrium analysis, mineral paragenetic association analysis and Pinckey-Rafter, respectively. We gave some applied examples and made a brief comment of them as well. There are three points worth noting. Firstly, choosing appropriate approach is a critical factor to acquire the δ34S∑S successfully according to the characteristics of different types of metallic sulfide deposit. Secondly, currently, these above mentioned approaches and applications are effective after the establishment of equilibrium state of sulfur isotope. As to the sulfur isotopic disequilibrium condition in metallic sulfide deposits probably resulted from lower temperature or rapid emplacement, there are quite some problems in theory and technique. Therefore, an in-depth study should also be continued. Thirdly, it is a new development trend to study isotope composition of different forms of sulfur and to discuss their source, forming environment and process respectively, which is probably more effective and significant for tracing sulfur sources of metallic sulfide deposits.  相似文献   

7.
The Huangshaping Pb–Zn–W–Mo polymetallic deposit, located in southern Hunan Province, China, is one of the largest deposits in the region and is unique for its metals combination of Pb–Zn–W–Mo and the occurrence of significant reserves of all these metals. The deposit contains disseminated scheelite and molybdenite within a skarn zone located between Jurassic granitoids and Carboniferous sedimentary carbonate, and sulfide ores located within distal carbonate-hosted stratiform orebodies. The metals and fluids that formed the W–Mo mineralization were derived from granitoids, as indicated by their close spatial and temporal relationships. However, the source of the Pb–Zn mineralization in this deposit remains controversial.Here, we present new sulfur, lead, and strontium isotope data of sulfide minerals (pyrrhotite, sphalerite, galena, and pyrite) from the Pb–Zn mineralization within the deposit, and these data are compared with those of granitoids and sedimentary carbonate in the Huangshaping deposit, thereby providing insights into the genesis of the Pb–Zn mineralization. These data indicate that the sulfide ores from deep levels in the Huangshaping deposit have lower and more consistent δ34S values (− 96 m level: + 4.4‰ to + 6.6‰, n = 13) than sulfides within the shallow part of the deposit (20 m level: + 8.3‰ to + 16.3‰, n = 19). The δ34S values of deep sulfides are compositionally similar to those of magmatic sulfur within southern Hunan Province, whereas the shallower sulfides most likely contain reduced sulfur derived from evaporite sediments. The sulfide ores in the Huangshaping deposit have initial 87Sr/86Sr ratios (0.707662–0.709846) that lie between the values of granitoids (0.709654–0.718271) and sedimentary carbonate (0.707484–0.708034) in the Huangshaping deposit, but the ratios decreased with time, indicating that the ore-forming fluids were a combination of magmatic and formation-derived fluids, with the influence of the latter increasing over time. The lead isotopic compositions of sulfide ores do not correlate with sulfide type and define a linear trend in a 207Pb/204Pb vs. 206Pb/204Pb diagram that is distinct from the composition of the disseminated pyrite within sedimentary carbonates and granitoids in the Huangshaping deposit, but is similar to the lead isotopic composition of sulfides within coeval skarn Pb–Zn deposits in southern Hunan Province. In addition, the sulfide ores have old signatures with relative high 207Pb/206Pb ratios, suggesting that the underlying Paleoproterozoic basement within southern Hunan Province may be the source of metals within the Huangshaping deposit.The isotope geochemistry of sulfide ores in the Huangshaping deposit shows a remarkable mixed source of sulfur and ore-forming fluids, and the metals were derived from the basement. These features are not found in representative skarn-type Pb–Zn mineralization located elsewhere. The ore-forming elements (S, Pb, and Zn) from the granitoids made an insignificant contribution to sulfide precipitation in this deposit. However, the emplacement of granitoids did provide large amounts of heat and fluids to the hydrothermal system in this area and extracted metals from the basement rocks, indicating that the Jurassic magmatism associated with the Huangshaping deposit was crucial to the Pb–Zn mineralization.  相似文献   

8.
Summary The Dachang Sn-polymetallic ore district is one of the largest tin producing districts in China. Its origin has long been in dispute between magmatic-hydrothermal replacement and submarine exhalative-hydrothermal origin. The Dachang ore district comprises several types of ore deposits, including the Lamo magmatogenic skarn deposit near a granite intrusion, the Changpo-Tongkeng bedded and vein-type sulfide deposit, and the Gaofeng massive sulfide deposit. Sulfide minerals from the Lamo skarn ores show δ34S values in the range between −3 and +4‰ with a mean close to zero, suggesting a major magmatic sulfur source that likely was the intrusive Longxianggai granite. Sulfide minerals from the Gaofeng massive ores show higher δ34S values between +5 and +12‰, whereas sulfide minerals from the Changpo-Tongkeng bedded ores display lighter δ34S values between −7 and −0.2‰. The difference in the sulfur isotope ranges in the two deposits can be interpreted by different degrees of inorganic thermochemcial reduction of marine sulfate using a one-step batch separation fractionation model. Sulfur isotopic compositions from the vein-type ores at Changpo-Tongkeng vary widely from −8 to +4‰, but most of the data cluster around −2.9‰, which is close to that of bedded ores (−3.6‰). The sulfur in vein-type ores might be derived from bedded ores or it represents a mixture of magmatic- and sedimentary-derived sulfur. Pb isotopic compositions of sulfide minerals in the Dachang ore district reveal a difference between massive and bedded ores, with the massive ores displaying more radiogenic Pb isotope ratios. Correlations of 206Pb/204Pb and 207Pb/204Pb or 208Pb/204Pb for the massive and bedded ores are interpreted as two-component mixing of Pb leached from sedimentary host rocks and from deep-seated Precambrian basement rocks composed of metamorphosed volcano-sedimentary rocks. Pb isotopic compositions of sulfide minerals from vein-type ores overlap with those of bedded sulfides. Similar to the sulfur, the lead in vein-type ores might be derived from bedded ores. Skarn ores at Lamo show very limited variations in Pb isotopic compositions, which may reflect a major magmatic-hydrothermal lead source. Helium isotope data of fluid inclusions trapped in sulfides indicate that He in the massive and bedded ores has a different origin than He in fluorite of granite-related veins. The 3He/4He ratios of 1.2–2.9 Ra of fluid inclusions from sulfides at Gaofeng and Changpo-Tongkeng imply a contribution of mantle-derived fluids. Overall our data support a submarine exhalative-hydrothermal origin for the massive and bedded ore types at Dachang. Supplementary material to this paper is available in electronic form at Appendix available as electronic supplementary material  相似文献   

9.
吴胜华  孙冬阳  李军 《岩石学报》2020,36(1):245-256
华南包括两个世界级的W矿带,分别是南岭和江南造山带W成矿带。柿竹园W多金属矿床位于南岭地区,香炉山W矿床位于江南造山带东北部。两个矽卡岩W矿床都发育硫化物成矿阶段。但硫化物和成矿元素组成存在显著的差异。前者由含Pb、Zn、Ag硫化物和黝铜矿、银黝铜矿、含Ag斜方辉铅铋矿和铁硫锡铜矿硫盐组成;后者主要为磁黄铁矿。柿竹园远接触带Pb-Zn-Ag矿脉中硫化物(闪锌矿、黄铜矿、方铅矿和磁黄铁矿)较富集B、Mn、Cr、Sb、Sn和Hg,香炉山似层状矽卡岩和硫化物-白钨矿矿体中硫化物(磁黄铁矿、黄铜矿和闪锌矿)较富集W、Se和Bi。两个矿床中黄铜矿、闪锌矿和方铅矿较富集Ag,黄铜矿、闪锌矿富集In和Sn,闪锌矿还富集Cd。两个矿床中的硫化物微量元素分析表明与矽卡岩W矿成矿相关的硫化物可载有多种微量元素。这些元素参与到硫化物中程度由多种因素控制。具体如下,硫化物中B含量高低与成矿相关岩体中B含量相关;在相对高温和还原条件下,硫化物中W含量较高;闪锌矿中Mn和Cd与Zn发生取代作用; Cr可以一定程度进入到硫化物中,并受成矿流体中Cr含量影响; Se与S发生了一定程度的取代进入硫化物,并受流体中它的含量控制; Bi在闪锌矿与黄铜矿易形成固溶体;硫化物中Sb含量受初始流体中它的含量影响,方铅矿中易包裹一定的辉锑矿(Sb_2S_3)或含Sb的硫盐矿物; Ag是否形成独立的矿物相和进入哪些硫化物中,取决于流体中Ag的初始含量和硫化物的沉淀次序;硫化物中Hg的含量受温度影响。  相似文献   

10.
云南兰坪盆地西缘脉状铜多金属矿床主要赋存于由砂岩、粉砂岩和页岩组成的碎屑岩建造中.为了查明兰坪盆地西缘脉状铜多金属矿床成矿物质来源,对盆地西缘四个典型脉状铜多金属矿床(科登涧、连城、金满和水泄)的硫、铅同位素的组成进行了分析和对比研究.结果表明,这些矿床的铅同位素组成总体变化较小,且大部分落在盆地沉积地层铅范围内,金满、连城铜矿床可能有部分深源铅的加入.硫同位素特征表明,兰坪盆地西缘脉状铜多金属矿床的硫主要来源于地层硫酸盐的还原作用,其中金满铜矿床和连城铜钼多金属矿床可能有深源硫的混入.各矿床硫同位素不同的特点,除反映各矿床源区硫同位素组成的差异外,可能还与各矿床成矿时不同的物理化学条件(温度、氧逸度、pH 值和离子强度等)差异有关  相似文献   

11.
Lead isotope determinations were made on galenas from three strata-bound sulfide ores in the early Proterozoic (Svecokarelian) Bergslagen district of central Sweden and four epigenetic deposits in the Älvdalen and Vansbro districts in the early to middle Proterozoic post-Svecokarelian belt. The leads from the strata-bound Bergslagen deposits show exceptional isotopic homogeneity over large areas. Their isotopic composition suggests the existence of a pre-Svecokarelian crust in the district and is consistent with exhalative-sedimentary ore formation in an active continental margin environment. The Vansbro and Älvdalen leads display constant compositions within each district, but marked divergence between the districts. Their compositions preclude derivation exclusively from recycled Svecokarelian lead and suggest a substantial lead contribution from a mantle-like source. The difference between model ages and geologic ages for many of the deposits, with a small but significant excess of radiogenic lead, suggests a significant deviation of the Fennoscandian Shield from conventional global lead evolution models.  相似文献   

12.
The Huogeqi orefield located on the northern side of Mt. Langshan, Inner Mongolia occurs in the Middle Proterozoic Langshan Group metamorphic rocks, and the orebodies arc stratiform. In the past twenty years, many Chinese geologists have conducted researches on the Huogeqi Cu-Pb-Zn deposit, but there has been still a controversy on its origin. Some advocate that the deposit is of sedimentary-metamorphic rcworking origin, some hold that it is of sea-floor SEDEX origin, and others have a preference for magmatic superimposition origin. The crux of the controversy is that there is no common understanding about the source of ore-forming materials. In this paper, the Pb isotopic compositions of regional Achaean-Early Proterozoic basement rocks, various types of sedimentary- metamorphic rocks and volcanic rocks in the mining district, Late Proterozoic and Hercynian magmatic rocks arc introduced and compared with the orc-lead composition, so as to constrain the source of the ore lead. The result indicates that （1） sulfides in the ores have homogeneous Pb isotopic compositions, showing a narrow variation range. Their ^206pb/^204pb ratios arc within a range of 17.027- 17.317; ^207Pb/^204pb ratios, 15.451-15.786 and ^208Pb/^204pb ratios, 36.747-37.669; （2） the Pb isotopic compositions of the regional Achaean-Early Proterozoic basement rocks arc characteristic of the old Pb isotopic composition at the early-stage evolution of the Earth, which varies over a wider range, reflecting significant differences in Pb isotopic compositions of the ores. All this indicates that the source of ore lead has no bearing on the basement rocks; （3） the sedimentary-metamorphic rocks in the mining district arc characterized by highly variable and more radiogenic Pb isotopic compositions and their Pb isotopic ratios arc obviously higher than those of ores, demonstrating that ore lead did not result from metamorphic rcworking of these rocks; （4） Pb isotopic compositions of Late Proterozoic diorite-gabbro and Hercynian granite are higher than those of ores. Meanwhile, the Pb isotopic compositions of sulfides in the small-sized strata-penetrating mineralized veinlets formed at later stages arc completely consistent with that of sulfides in stratiform-banded ores, suggesting that these veiniets arc the product of autochthonous rcworking of the stratiform-banded ores during the period of metamorphism and the late magmatic superimposition-mineralization can be excluded; （5） amphibolite, whose protolith is basic volcanic rocks, has the same Pb isotopic compositions as ores, implying that ore lead was derived probably from basic volcanism. So, the source of ore-forming materials for the Huogeqi deposit is like that of the volcanic massive sulfide （VMS） deposits. However, the orebodies do not occur directly within the volcanic rocks, and instead they overlie the volcanic rocks, showing some differences from those typical VMS-type deposits.  相似文献   

13.
We have studied Pb isotopic systems of K-feldspar, pyrite, and pyrrhotine from gabbroids and ore of the Velimyaki Early Proterozoic massif in the northern Ladoga region in the southeastern part of the Fennoscandian Shield. The isochronous Pb–Pb age of sulfides has been determined as ～450 Ma, which corresponds to intersection of the regression line with the lead accumulation curve with μ = 10.4–10.8; the model Pb age of sulfides is close to isochronous under the condition that the composition of lead evolved from a geochemical reservoir with an age of 1.9 Ga. The isotopic parameters of the lead in sulfides and K-feldspar indicate their formation in upper crust conditions (μ = 238U/204Pb > 10). From the obtained data, it follows that the isotopic composition of lead in K-feldspar corresponds to a Proterozoic age (1890 Ma) of magmatic crystallization of the rocks in the massif, and strongly radiogenic lead sulfides testify, with the greatest probability, to the later (Caledonian) formation of sulfide ores.  相似文献   

14.
This article presents the new mineralogical, fluid inclusion, and isotopic data for ores of the Novoshirokinsky base metal–gold deposit. Mineralogical sequence is supplemented and specified. The mineral assemblages containing native gold are studied. Morphology, grain size and chemical composition of native gold are described. Major parameters and composition of mineralizing fluids of the main ore stages at the deposit are estimated: main base metal (mid-temperature conditions, fluid salinity 3.1–13.1 wt % equiv NaCl) and carbonate–base metal (low-temperature conditions, fluid salinity 1.0–12.9 wt % equiv. NaCl). Sulfur isotopic composition of sulfides from commercial mineral assemblages has been studied. The δ34S value (+10.5 ± 1‰) of mineralizing fluid has been calculated. The Novoshirokinsky deposit is similar to epithermal deposits and is spatially related to the Late Jurassic porphyry system. Evidence is provided on carbonate rocks of basement involved in the ore-forming process.  相似文献   

15.
内蒙古柳坝沟一哈达门沟金矿田是华北地台北缘成矿带上的一处以广泛发育钾长石化为特色的超大型金矿田。本文在成矿地质条件分析的基础上,系统研究了柳坝沟、哈达门沟金矿床的氢、氧、碳和硫同位素组成特征,探讨了成矿热液类型和成矿物质来源。研究表明,成矿热液早期以岩浆水或初始岩浆水为主,后期有部分大气降水的加入,且柳坝沟金矿床中大气降水的参与程度更高。热液中碳主要为深源岩浆来源。矿石中硫化物的硫同位素组成特征反映了硫具有地层和岩浆的混合硫特征。柳坝沟金矿床的δ34S值低于哈达门沟金矿床;哈达门沟金矿床东段的δ34S值低于西段,可能反映了柳坝沟金矿床较哈达门沟金矿床剥蚀程度小,哈达门沟会矿床东段较西段剥蚀程度小。  相似文献   

16.
《Resource Geology》2018,68(3):227-243
As a newly discovered medium‐sized deposit (proven Pb + Zn resources of 0.23 Mt, 9.43% Pb and 8.73% Zn), the Dongzhongla skarn Pb–Zn deposit is located in the northern margin of the eastern Gangdese, central Lhasa block. Based on the geological conditions in this deposit of ore‐forming fluids, H, O, C, S, Pb, Sr, and noble gas isotopic compositions were analyzed. Results show that δ18OSMOW of quartz and calcite ranged from −9.85 to 4.17‰, and δDSMOW ranged from −124.7 to −99.6‰ (where SMOW is the standard mean ocean water), indicating magma fluids mixed with meteoric water in ore‐forming fluids. The δ13CPDB and δ18OSMOW values of calcite range from −1.4 to −1.1‰ and from 5.3 to 15.90‰, respectively, show compositions consistent with the carbonate limestone in the surrounding rocks, implying that the carbon was primarily sourced from the dissolution of carbonate strata in the Luobadui Formation. The ore δ34S composition varied in a narrow range of 2.8 to 5.7‰, mostly between 4‰ and 5‰. The total sulfur isotopic value δ34S was 4.7‰ with characteristics of magmatic sulfur. The 3He/4He values of pyrite and galena ranged from 0.101 to 5.7 Ra, lower than those of mantle‐derived fluids (6 ± 1 Ra), but higher than those of the crust (0.01–0.05 Ra), and therefore classified as a crust–mantle mixed source. The Pb isotopic composition for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the ores were in the ranges of 18.628–18.746, 15.698–15.802, and 39.077–39.430, respectively, consistent with the Pb isotopic composition of magmatic rocks in the deposit, classified as upper‐crust lead. The ore lead was likely sourced partially from the crustal basement of the Lhasa Terrane. The initial (87Sr/86Sr)i value from five sulfide samples ranged from 0.71732 to 0.72767, and associated ore‐forming fluids were mainly sourced from the partial melting of the upper‐crust materials. Pb isotopic compositions of ore sulfides from the Dongzhongla deposit are similar to that of the Yuiguila and Mengya'a deposit, indicating that they have similar sources of metal‐rich ore‐forming solution. According to basic skarn mineralogy, the economic metals, and the origin of the ore‐forming fluids, the Dongzhongla deposit was classified as a skarn‐type Pb–Zn deposit.  相似文献   

17.
In order to discuss the source of ore-forming materials of the Bingdongshan lead-zinc deposit, Rb-Sr isotopes of the main ore-stage sphalerites have been analyzed by using the full dissolution method and fluid inclusions leaching method in this paper, with yielded isochion ages of 507. 7-507. 8 Ma, initial 87Sr/86Sr values of 0. 709193-0. 709220.These isoch-ron ages, representing the age of the main mineralization stage of the deposit, indicate that the deposit was formed in Early Ordovician, or the mineralization occurred in the middle Caledonian. The characteristics of initial strontium isotopic ratios of sphaleritess how that the ore-forming materials or the ore-forming fluid were provided by both of basement rocks and the Sinian carbonates. Combining with geological characteristics of the deposit and regional Pb-Zn metallogenic geological background, it is believed that the Caledonian tectonic movement played important role for the formation of lead-zinc deposits in the northern margin of the Yangtze Block. The Bingdongshan lead-zinc deposit was probably formed under the Caledonian extensional environment, through the precipitation of sulfides, in certain physic-chemical condition, from the ore-forming hydrothermal fluids which were associated with dome structure activities.  相似文献   

18.
谭文娟  魏俊浩  郭大招  谭俊 《地质与资源》2005,14(3):227-230,237
石英脉型金矿是常见的金矿床类型.金主要以粒间金、裂隙金和包裹金3种形式赋存于石英、黄铁矿等金属硫化物中.目前了解此类金矿的成矿流体组成主要是通过石英中的流体包裹体成分的定量和定性分析结果,揭示矿床成因.但是野外和室内镜下的综合研究已证实,金矿的形成经历了若干个成矿阶段.每个阶段都有石英和金属硫化物形成,而石英要明显早于金属硫化物的结晶,同时金在硫化物中的存在形式多为包裹金和裂隙金,这至少说明金和硫化物同时结晶沉淀或金比硫化物更晚沉淀.因此,金运移沉淀结晶时的流体和石英结晶时的流体存在着明显的时间差,金矿化与黄铁矿等金属硫化物有着密切的联系.研究金属硫化物中的流体包裹体来反映主成矿阶段的成矿流体物质来源,比研究石英中的流体包裹体更具有实际的意义.  相似文献   

19.
Integrated studies of seven Proterozoic sediment-hosted, Pb-Zn-Ag sulfide deposits of Brazil, permit the estimation of the age of the hosting sequence and the mineralization, the nature of the sulfur and metal sources, the temperature range of sulfide formation and the environment of deposition. These deposits can be classified into three groups, according to their ages. (a) Archean to Paleoproterozoic: the Boquira deposit, in Bahia state, consists of stratiform massive and disseminated sulfides hosted by parametamorphic sequences of grunnerite-cummingtonite+magnetite that represent a silicate facies of the Boquira Formation (BF). Lead isotope data of galena samples indicate a time span between 2.7 and 2.5 Ga for ore formation, in agreement with the stratigraphic position of the BF. The relatively heavy sulfur isotope compositions for the disseminated and stratiform sulfides (+8.3 to +12.8 ‰ CDT)suggest a sedimentary source for the sulfur. (b) Paleo to Mesoproterozoic: stratiform and stratabound sulfides in association with growth faults are present in the Canoas mine (Ribeira, in Paraná state) and in the Caboclo mineralization (Bahia state). They are hosted by calcsilicates and amphibolites in the Canoas deposit, whereas in the Caboclo area the mineralization is associated with hydrothermally altered dolarenites at the base of the 1.2 Ga Caboclo Formation. The interpreted Pb-Pb age of the Canoas mineralization is coeval with the 1.7 Ga host rocks. Sulfur isotopic data for Canoas sulfides (+1.2 to +16 ‰ CDT) suggest a sea water source for the sulfur. The range between −21.1 and +8.8 ‰ CDT for the Caboclo sulfides could suggest the action of bacterial reduction of seawater sulfates, but this interpretation is not conclusive. (c) Neoproterozoic: stratiform and stratabound sulfide deposits formed during the complex diagenetic history of the host carbonate rocks from the Morro Agudo (Bambui Group), Irecê and Nova Redenção (Una Group), yield heavy sulfur isotope values (+18.9 to +39.4 ‰ CDT). The uniform heavy isotope composition of the barites from these deposits (+25.1 to +40.9 ‰) reflect their origin from Neoproterozoic seawater sulfates. The late-stage, and most important, metallic concentrations represent sulfur scavenged from pre-existing sulfides or from direct reduction of evaporitic sulfate minerals. Lead isotope data from the Bambui Group suggest focused fluid circulation from diverse Proterozoic sediment sources, that probably was responsible for metal transport to the site of sulfide precipitation. (d) Late Proterozoic to Early Paleozoic: lead-zinc sulfides (+pyrite and chalcopyrite) of Santa Maria deposits, in Rio Grande do Sul, form the matrix of arkosic sandstones and conglomerates, and are closely associated with regional faults forming graben structures. Intermediate volcanic rocks are intercalated with the basal siliciclastic members. Lead isotope age of the mineralization (0.59 Ga) is coeval with the host rocks. Sulfur isotopic values between −3.6 and +4.1 are compatible with a deep source for the sulfur.Geological, petrographic and isotopic data of the deposits studied suggest that they were formed during periods of extensional tectonics. Growth faults or reactivated basement structures probably were responsible for localized circulation of metal-bearing fluids within the sedimentary sequences. Sulfides were formed by the reduction of sedimentary sulfates in most cases. Linear structures are important controls for sulfide concentration in these Proterozoic basins.  相似文献   

20.
Zn- and Cu-rich massive sulfide ores of volcanogenic origin [volcanogenic massive sulfide (VMS) deposits] occur as stratiform/stratabound lenses of variable size hosted by gneisses, amphibolites, and schists of the Areachap Group, in the Northern Cape Province of South Africa. The Areachap Group represents the highly deformed and metamorphosed remnants of a Mesoproterozoic volcanic arc that was accreted onto the western margin of the Kaapvaal Craton during the ∼1.0–1.2 Ga Namaquan Orogeny. Sulfur isotope data (δ34S) are presented for 57 sulfide separates and one barite sample from five massive sulfide occurrences in the Areachap Group. Although sulfides from each site have distinct sulfur isotope values, all δ34S values fall within a very limited range (3.0‰ to 8.5‰). Barite has a δ34S value of 18.5‰, very different from that of associated sulfides. At one of the studied sites (Kantienpan), a distinct increase in δ34S of sulfides is observed from the massive sulfide lens into the disseminated sulfides associated with a distinct footwall alteration zone. Sulfide–sulfide and sulfide–barite mineral pairs which recrystallized together during amphibolite- and lower granulite facies metamorphism are not in isotopic equilibrium. Sulfur isotope characteristics of sulfides and sulfates of the Zn–Cu ores in the Areachap Group are, however, very similar to base metal sulfide accumulations associated with modern volcanic arcs and unsedimented mid-ocean ridges. It is thus concluded that profound recrystallization and textural reconstitution associated with high-grade regional metamorphism of the massive sulfide ores of the Areachap Group did not result in extensive sulfur isotopic homogenization. This is similar to observations in other metamorphosed VMS deposit districts and confirms that massive sulfide ores remain effectively a closed system for sulfur isotopes for both sulfides and sulfates during metamorphism.  相似文献   

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