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1.
The Dongmozhazhua deposit, the largest Pb–Zn deposit in south Qinghai, China, is stratabound, carbonate‐hosted and associated with epigenetic dolomitization and silicification of Lower–Middle Permian—Upper Triassic limestones in the hanging walls of a Cenozoic thrust fault system. The mineralization is localized in a Cenozoic thrust‐folded belt along the northeastern edge of the Tibetan plateau, which was formed due to the India–Asia plate collision during the early Tertiary. The deposit comprises 16 orebodies with variable thicknesses (1.5–26.3 m) and lengths (160–1820 m). The ores occur as dissemination, vein, and breccia cement. The main sulfide assemblage is sphalerite + galena + pyrite + marcasite ± chalcopyrite ± tetrahedrite, and gangue minerals consist mainly of calcite, dolomite, barite, and quartz. Samples of pre‐ to post‐ore stages calcite yielded δ13C and δ18O values that are, respectively, similar to and lower than those yielded by the host limestones, suggesting that the calcite formed from fluids derived from carbonate dissolution. Fluid inclusions in calcite and sphalerite in the polymetallic sulfidization stage mostly comprise liquid and gas phases at room temperature, with moderate homogenization temperatures (100–140°C) and high salinities (21–28 wt% NaCl eq.). Micro‐thermometric fluid inclusion data point to polysaline brines as ore‐forming fluids. The δD and δ18O values of ore fluids, cation compositions of fluid inclusions, and geological information suggest two main possible fluid sources, namely basinal brines and evaporated seawater. The fluid inclusion data and regional geology suggest that basinal brines derived from Tertiary basins located southeast of the Dongmozhazhua deposit migrated along deep detachment zones of the regional thrust system, leached substantial base metals from country rocks, and finally ascended along thrust faults at Dongmozhazhua. There, the base‐metal‐rich basinal brines mixed with bacterially‐reduced H2S‐bearing fluids derived from evaporated seawater preserved in the Permo–Triassic carbonate strata. The mixing of the two fluids resulted in Pb–Zn mineralization. The Dongmozhazhua Pb–Zn deposit has many characteristics that are similar to MVT Pb–Zn deposits worldwide.  相似文献   

2.
甘肃代家庄铅锌矿的地质特征与找矿意义   总被引：5，自引：1，他引：4  
位于甘肃宕昌县的代家庄矿床曾被认为是西成矿田铅锌找矿的重大进展,矿床产于秦岭西成盆地西北端泥盆系浅海相的富含生物化石的细碎屑岩—灰岩中。矿体不规则受NW向断裂的控制,呈角砾状分布于下部碎屑岩与上部厚层灰岩界面附近灰岩一侧。矿石的矿物共生组合为闪锌矿 方铅矿 少量黄铁矿 少量白铁矿 方解石,不含石英。硫化物发育大量的胶状、球粒状、草霉状微晶结构,部分显现出微生物化石结构特点。对代家庄与西成主要类型铅锌矿床地质地球化学特征的对比发现,二者在容矿围岩沉积环境、矿石形态、结构构造以及同位素地球化学等多方面存在明显的差异,代家庄矿床成因属于碳酸盐岩容矿的低温热液矿床,不同于西成矿田的主要SEDEX类型。主要控矿因素为灰岩—碎屑界面附近、NW向断裂等。  相似文献   

3.
云南昭通铅锌矿床是铅锌多金属矿集区的典型代表之一。该矿床严格受NE向毛坪冲断褶皱构造控制,矿体分布于毛坪逆断层上盘的猫猫山倒转背斜西翼层间断裂带中,呈大脉状陡倾斜产出,其延深远远大于走向延长。主要矿石矿物由闪锌矿、方铅矿、黄铁矿组成,脉石矿物主要为铁白云石、方解石、石英和重晶石。本文针对成矿流体研究的薄弱环节,进行了闪锌矿、脉石矿物(方解石、石英)流体包裹体成分研究,研究认为流体包裹体类型主要呈纯液相和液相,成矿热液属Na+-K+-Ca2+-Cl--F-型,与典型MVT矿床存在明显差异,为深化"会泽型"铅锌矿床"构造–流体‘贯入’成矿"模型提供了重要证据,而且该研究无疑对矿床深部及外围找矿具有指导意义。  相似文献   

4.
The Tres Marias carbonate-hosted Zn–Ge deposit in Chihuahua, Mexico contains sphalerite with the highest average Ge (960 ppm) and willemite with the highest reported Ge contents of Mississippi-Valley-type (MVT) deposits worldwide. This has prompted current exploration efforts to focus on the deposit as a high-grade source of germanium. The sulfide-rich ore type (>125,000 t at 20% Zn and 250 g/t Ge) contains Fe-rich botryoidal sphalerite (type I) associated with solid hydrocarbons. This type exhibits distinctive intimately intergrown lamellar texture of high-Fe sphalerite (average 9.9 wt.% Fe and 800 ppm Ge) and a somewhat less Fe-rich sphalerite phase (average 5.5 wt.% Fe and 470 ppm Ge). Reddish-brown banded sphalerite (type II, average 5.7 wt.% Fe and 1,320 ppm Ge) is subordinately followed by galena and pyrite. The sulfide-poor “oxidized” zinc ore (up to 50 wt.% Zn; 250 to 300 ppm Ge) is a fine-grained, often friable, alteration product of the sulfide ore and associated limestone and breccia host. While some areas are dominated by carbonates and sulfates, others are enriched in silicates such as hemimorphite and willemite. The gangue assemblage includes goethite, hematite, and amorphous silica or quartz. Minor wulfenite, greenockite, cinnabar, and descloizite also occur. Willemite occurs as interstitial replacement of sphalerite and fracture fillings in the oxidized ore and can be unusually rich in Pb (up to 2.0 wt.%) and Ge (up to 4,000 ppm). Oscillatory zonation reflects trace element incorporation into willemite from the oxidation of primary Ge-bearing sphalerite and galena by siliceous aqueous fluids. The Tres Marias deposit has hybrid characteristics consisting of a primary low-temperature MVT Ge-rich Zn–Pb sulfide ore body, overprinted by Ge-rich hemimorphite, willemite, and Fe oxide mineralization.  相似文献   

5.
High-salinity, Na–Ca–Cl-rich fluids (˜20 wt% salts) in inclusions in gangue and ore minerals from Mesozoic Mississippi Valley-type (MVT) deposits in the Verviers Synclinorium (eastern Belgium) and in Cretaceous vein calcites at the Variscan front were investigated by microthermometric and crush-leach analysis. The MVT deposits formed at temperatures of ˜110 °C while the Cretaceous vein calcites were precipitated at temperatures <50 °C. Their Cl–Br content (Cl/Br ratio between 246 and 458) suggests that the fluids probably originated by the evaporation of seawater during basin development at the southern margin of the Caledonian Brabant Massif in the Late Palaeozoic. The Na–Ca–K content (Na: 29,700–49,600 ppm, Ca: 25,700–46,200 ppm, K: 1,000–5,620 ppm) is similar to that of the mineralising fluids in other Pb–Zn districts, interpreted to be of evaporative origin (e.g. Newfoundland, East Tennessee, Polaris). Furthermore, comparison of the Na–Ca–K content of the fluids with that of an evolved evaporitic brine enables the recognition of major water–rock interactions that modified the fluid composition. It indicates that the ambient fluids participated in the early diagenetic dolomitisation of Upper Palaeozoic carbonates and also in the albitisation of plagioclase in Lower Palaeozoic siliciclastics of the Caledonian basement. Illitisation of smectites or dissolution of K-feldspar probably controlled the K-content of the fluids. A model is proposed where the bittern brines migrated down into the deep subsurface because of their density during extension. After the Variscan orogeny, these fluids were finally expelled along extensional faults, resulting in the formation of Zn–Pb deposits. Received: 26 April 2000 / Accepted: 22 November 2000  相似文献   

6.
Two Mississippi Valley-type (MVT) ore deposits, Kicking Horse and Monarch, have been studied with the aim of comparing the ores at the two localities and to characterize the origin of the mineralizing fluids and the ore formation process(es). Both deposits are hosted by the Middle Cambrian Cathedral Formation carbonate host rocks, Kicking Horse on the north and Monarch on the south flank of the Kicking Horse valley near Field (SE British Columbia). The ore bodies are situated at the transition of (western) basinal to (eastern) shallow-water strata of the paleo-Pacific passive margin succession in the Cordilleran Foreland Province of the Western Canada Sedimentary Basin. Both deposits are related spatially to normal faults. In both localities, the ore minerals are dominated by pyrite, sphalerite, and galena. Dolomite, minor quartz, and calcite are also present in close association with the ores. The salinity (21–30 wt% NaCl eq.) and homogenization temperatures (63–182°C) measured in fluid inclusions in carbonate, quartz, and sphalerite lie within the typical range of MVT fluid conditions. The good stoichiometry (50–53 mol% CaCO3), low δ18O values (−21 to −14‰ Vienna Peedee belemnite) and relatively high homogenization temperatures (>95°C) of the dolomite suggest the dolomites were formed under burial diagenesis. The ore-forming fluids probably interacted with siliciclastic units, based on elevated Li contents and 87Sr/86Sr ratios, which are highest in the dolomite type after the main ore stage. We propose that the ores formed from the mixing of a downward-infiltrating, sulfur-bearing halite-dissolution fluid with an upward-migrating, metal-rich evaporated seawater fluid, which had already undergone minor mixing with a dilute fluid.  相似文献   

7.
The chief host of cadmium in zinc deposits is sphalerite, the cadmium content of which depends on the type of deposit. Sphalerite from Mississippi Valley-type (MVT) deposits has high cadmium concentrations whereas sphalerite from exhalative deposits has low cadmium concentrations. The Cd content of sphalerite depends on the Cd/Zn ratio, ligand activities, and temperature of the ore-forming fluids. The combined effect of variation of temperature, pH, total activity of reduced sulfur, and activity of Cl- cannot by itself account for either Cd depletion (exhalative deposits) or Cd enrichment (MVT deposits). Variations in the Cd/Zn ratio of the fluid have a significant effect in determining that of sphalerite. Basinal brines, which can considered to be the recent equivalents of MVT fluids, have high Cd/Zn ratios, and active exhalative systems are characterized by low Cd/Zn ratios. Probably the differences in sphalerite composition between the different deposit types are less a function of temperature and ligand activities than Cd/Zn ratio of the ore-forming fluids. In the hydrothermal environment, the Cd/Zn ratio is generally not high enough to allow crystallization of cadmium sulfides (greenockite or hawleyite). The abundance of greenockite in the supergene alteration zone of hydrothermal zinc deposits can be explained on the basis of Zn scavenging by crystallizing smithsonite.  相似文献   

8.
The Mount Black Pb‐Zn deposit is a quartz‐galena‐sphalerite replacement body in the Silurian Cooleman Limestone. Fluid inclusion homogenisation temperatures range from 120° to 170°C for paragenetically early sphalerite, to 210° to 315°C for late quartz, and 245° to 320°C for calcite from contiguous recrystallised limestone. Fluid salinities increased with rising temperature, during deposition of the minerals, and the fluid composition changed from NaCl‐rich to possibly CaCl2‐NaCl (‐?MgCl2)‐rich brines.

δ34S values of sphalerite and galena range from —8.1 to —2.7 per mil, and —13,5 to —4.4 per mil respectively. Although a magmatic source for sulphur is not excluded, it is suggested that most probably the sulphur was derived by biogenic reduction of sea‐water sulphate during diagenesis. Carbon and oxygen isotope data for the Cooleman Limestone range from compositions typical of Silurian marine carbonate in samples distant from the deposit, to fluctuating, but 12C‐ and 16O‐enriched in recrystallised material adjacent to the quartz‐sulphide rocks. 12C‐enrichment probably reflects organic carbon oxidation during karst formation, continuing later during limestone recrystallisation and accompanied by 16O‐enrichment during the action of saline formation waters.

The process of formation of the Mount Black deposit may have been analogous to that of Mississippi Valley‐type deposits, but modified by and/or resulting from, an increasing geothermal gradient caused by nearby synchronous intrusions.  相似文献   

9.
The Polaris deposit is one of the largest Mississippi Valley-type deposits in the world, with 22 million tonnes of ore at 14% Zn and 4% Pb contained in a single, compact orebody surrounded by dolomitized host rocks. Using detailed sampling of carbonates in the orebody and the dolostone halo, this paper aims to characterize the temporal and spatial evolution of the mineralizing system, and to understand the mechanisms that controlled the accumulation of this large, compact Zn–Pb deposit. Five types of dolomite have been distinguished, including three replacement (RD) and two pore-filling dolomites (PD). The paragenetic order is RD1, RD2, RD3, PD1, and PD2. Pore-filling calcite (PC) postdates all other minerals. In most cases, sulfides and dolomite did not co-precipitate, but sphalerite and galena largely overlap with RD3 and PD1. Various dolomites are dissolved or replaced by sulfide-precipitating fluids; sulfides in turn can be overgrown by dolomites. Colloform texture in sphalerite is widespread. Fluid inclusions were studied in RD3, PD1, PD2, sphalerite, and PC. The overall ranges of homogenization temperatures (T h) and last ice-melting temperatures (T m-ice) for fluid inclusions in dolomites and sphalerite are from 67 to 141 °C and from −46.7 to −27.0 °C, respectively, consistent with warm basinal brines with high salinities and Ca/Na ratios. Gas chromatographic analysis of these fluid inclusions indicates low concentrations of hydrocarbons (<0.06 mol%). C, O, and Sr isotopes were analyzed for all dolomites and PC, as well as for the fine-grained host limestone and early diagenetic calcite (SC–RC). The isotopic values of RD2, RD3, PD1, and PD2 cluster tightly and form largely overlapping domains. With respect to the host limestone, they are depleted in 18O, similar in δ13C, and slightly enriched in 87Sr. There are no regular spatial variations for fluid inclusion and isotope data, indicating an overall geochemical homogeneity in the hydrothermal system. However, certain samples close to the fracture zones in the orebody with slightly elevated T h and 87Sr/86Sr values and depleted δ18O values suggest that the fracture zone was the conduit for the hot brines. Based on the geological and geochemical characteristics of the deposit, we propose that sulfide precipitation at Polaris was caused by mixing of a reduced, metal-rich, sulfur-poor fluid with a reduced, metal-poor, sulfur-rich fluid at the site of mineralization. The metal-carrying fluid ascended along fractures from below the deposit and was hotter than the host rocks, whereas the reduced sulfur-carrying fluid was delivered to the site of mineralization laterally and was in thermal equilibrium with the host rocks. This model can readily explain the dissolution of dolomite during sulfide precipitation and the abundance of colloform sphalerite, as well as the low concentrations of hydrocarbons in fluid inclusions. Accepted: 20 December 1999  相似文献   

10.
The Emarat deposit, with a total proved reserve of 10 Mt ore grading 6% Zn and 2.26% Pb, is one of the largest Zn–Pb deposits in the Malayer–Esfahan belt. The mineralization is stratabound and restricted to Early Cretaceous limestones and dolomites. The ore consists mainly of sphalerite and galena with small amounts of pyrite, chalcopyrite, calcite, quartz, and dolomite. Textural evidence shows that the ore has replaced the host rocks and thus is epigenetic.Sulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from Cretaceous seawater through thermochemical sulfate reduction. Sulfur isotope compositions of four apparently coprecipitated sphalerite–galena pairs suggest their precipitation was under equilibrium conditions. The sulfur isotopic fractionation observed for the sphalerite–galena pairs corresponds to formation temperatures between 77 °C and 168 °C, which agree with homogenization temperatures of fluid inclusions.Lead-isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high 238U/204Pb and 232Th/204Pb ratios. Ages derived from the Pb-isotope model give meaningless ages, ranging from Early Carboniferous to future. It is probable that the Pb-isotope model ages that point to an earlier origin than the Early Cretaceous host rocks are derived from older reservoirs in the underlying Carboniferous or Jurassic units, either from the host rocks or from earlier-formed ore deposits within these units.This research and other available data show that the Emarat Zn–Pb deposit has many important features of Mississippi Valley-type (MVT) lead–zinc deposits and thus we argue that it is an MVT-type ore deposit.  相似文献   

11.
The Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province, located in southwestern margin of the Yangtze Block, is an important part of the large-scale low-temperature metallogenic domain in southwestern China. The Maliping Pb-Zn deposit, situated in the central part of Zhaotong-Qujing metallogenic belt, was found in northeastern Yunnan Province recently. The orebody is hosted in Late Cambrian Yuhucun Formation, occurring as stratabound, tense and venis. The mineral assemblage of the Maliping deposit is relatively simple. The main sulfide minerals are sphalerite and galena with minor pyrite. Gangue minerals include mainly dolomite, calcite, quartz and barite. LA-ICPMS spots and mapping analysis for the different sulfides from Maliping Pb-Zn deposit, and the distribution and existing forms of germanium, cadmium, indium and other trace elements were investigated. The results show that different sulfides are characterized by different contents of trace elements. Mn, Cu, Sn, Cd, In and Ge are mainly enriched in sphalerite, while galena from this deposit is enrichment of Ag, Sb and Se, and pyrite is characterized by enrichment of As, Co and Ni. Comparing with the content of dispersed elements in different sulfides, the results indicate that sphalerite is the primary carrier mineral of Ge, In and Cd. Cd, Ge, In, Mn, As, Sb and Ag occur as isomorphous substitution in the sphalerite, and Cu mostly exists in sphalerite as isomorphism but part of Cu occurs as micro-inclusions (chalcopyrite) in sphalerite. Considered the distinct positive relationship between Cu and Ge, the results imply that the substitution mechanism of Ge and Cu is possibly 3Zn(2+) <-> Ge4+ + 2Cu(+). Additionally, sphalerite from Maliping Pb-Zn deposit is characterized by enrichment of Cd, Ge and depleted in Mn, Fe, Co and Sn which coincides with the feature of MVT Pb-Zn deposit and differs from the sedimentary-exhalative deposit and magmatic-hydrothermal deposit. On account of the geological features, other geochemical researches and its ore-forming temperature belonging to low temperature, it is suggested that the Maliping deposit belongs to an MVT Pb-Zn deposit. Notably, we imply that ore-forming fluid extracted indium of magmatic and volcaniclastic rocks from the metamorphic basement, resulting in the enrichment of indium in sphalerite from the deposit.  相似文献   

12.
The Mount Black lead‐zinc deposit at Cooleman Plains, southern New South Wales, occurs in the uppermost part of the moderately folded, weakly metamorphosed, Upper Silurian Cooleman Limestone. A joint‐controlled collapse‐breccia zone interpreted as a palaeokarst structure has been partly replaced by quartz, sphalerite, galena, and a little chalcopyrite, pyrite, marcasite, tetrahedrite, arseno‐pyrite, and mackinawite. These minerals show evidence of having encrusted and replaced limestone fragments in the breccia. Oxidic Zn, Pb, Cu, and Fe minerals have formed by the near‐surface oxidation of the sulphides.

Petrographic and field evidence indicates that the quartz and sulphides were deposited mainly by encrustation and precipitation from saline solutions (possibly diagenetically expelled connate brines) in cavities, probably at low temperature at shallow depth. The deposit has many similarities to Mississippi Valley‐type lead‐zinc deposits.  相似文献   

13.
陕西几类重要铅锌矿床的矿物微量元素和稀土元素特征   总被引：13，自引：6，他引：7  
文章将陕西铅锌矿分为海底喷气沉积型(即SEDEX型)、与海底喷气沉积-改造作用有关的类SEDEX型和MVT型3类.对马元(MVT型)、南沙沟和江坡(类SEDEX型)、铅硐山和二里河(SEDEX型)铅锌矿床中的闪锌矿等矿物进行的微量元素和稀土元素测定结果表明,3类矿床各具特点:马元铅锌矿床闪锌矿的Co、Ni、Th、Y含量较低,而Mo、Cs、Sr、Ba、T1含量较高;南沙沟和江坡铅锌矿床闪锌矿的Sn、Sb、W含量较低,而Mn、Y、Zr、In含量较高;铅硐山和二里河铅锌矿床闪锌矿的Li、Zr、CB、Ba含量较低,而W含量较高;在闪锌矿Li-Cs、Zr-In、W-Sn、∑REE-δEu、δEu-δCe散点图上,5个矿床的投点按上述3类分别集中.但铅硐山和二里河铅锌矿床与南沙沟和江坡铅锌矿床具有更多的相似性,而与马元铅锌矿床差异较大:在闪锌矿Sr-Ba、Co-Ni、Th-Y、Mo-T1散点图上,马元的投点集中于一处,而其他4个矿床的投点集中于另一处;马元闪锌矿具有十分明显的铕正异常,而南沙沟、江坡、铅硐山和二里河闪锌矿铕异常不明显,或具有负铕异常;5元素矿床闪锌矿稀土元素配分曲线均为轻稀土元素稍富集的右倾型,但马元的稀土元素总量明显低于其他4个矿床.  相似文献   

14.
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   

15.
The newly discovered Chaqupacha Mississippi Valley-type (MVT) Pb–Zn deposit in central Tibet has been found to be helpful for understanding MVT ore formation relative to tectonic evolution of a foreland fold and thrust belt. The deposit lies in the Tuotuohe area of the western Fenghuo Shan-Nangqian fold and thrust belt of the India–Asia continental collision zone. It contains NNW-striking and folded Late Permian strata including an upper clastic unit and an underlying limestone unit. The strata overlie late Oligocene clastic rocks through a south-dipping reverse fault that is associated with regional northward thrusting during the Paleogene. The Late Permian and late Oligocene strata are unconformably overlain by flat-lying early Miocene marl and mudstone of the Wudaoliang Formation. Lead and zinc ores are mainly hosted by pre-ore dissolution and collapse breccias in the Late Permian limestone. The style of mineralization is epigenetic, as shown by replacement of the pre-ore dissolution breccia matrix and open-space-fill by galena, sphalerite, calcite, and minor barite and pyrite. δ34S values of the main sulfide galena range from − 27.5‰ to + 12.6‰. These features, together with the lack of magmatic activity during the mineralization, suggest that Chaqupacha is an MVT deposit. Subordinate mineralization is also present in the early Miocene Wudaoliang Formation marl and the paleokarst breccia which contains matrix compositionally equivalent to strata of the Wudaoliang Formation. The mineralization shares similar mineral associations and textures with the pre-ore dissolution breccia-hosted mineralization. Thus, the Pb and Zn mineralization in the entire deposit probably resulted from the same mineralizing event, which is younger than the youngest ore-hosting rocks (i.e., the early Miocene Wudaoliang Formation). Considering that thrusting in the Tuotuohe area had ceased prior to deposition of the Wudaoliang Formation host rocks, the mineralization at Chaqupacha post-dated the regional deformation. The Chaqupacha deposit thus provides a good example of MVT mineralization in a foreland fold and thrust belt that post-dates regional thrusting.  相似文献   

16.
李荣清 《湖南地质》1992,11(4):305-310
湘南地区存在钨锡多金属和铅锌铜多金属两类岩控矿床,它们的矿物组合,黄铁矿、闪锌矿、方铅矿、石榴石和方解石的某些特征,以及矿床分带性等方面均存在差异,本文作了初步对比研究。  相似文献   

17.
A multidisciplinary study including geology, petrography and reconnaissance isotope analyses has been carried out on the Reza-Abad, Reza-Barak and Heydar-Abad Pb–Zn deposits, hosted by different types of Cretaceous dolostone and limestone in northeast of the city of Shahmirzad in the central Alborz region of Iran. Dolostones are dominated by replacement dolomite with minor dolomite cements. The studied deposits are strata-bound vein and breccia type and are associated with tensional faults and fractures. Mineralisation occurs in veins and in karstic and tectonic breccias. Hypogene minerals include galena with minor sphalerite and pyrite. Supergene minerals comprise Fe-oxide, cerussite, anglesite, plattnerite, minimum and mimetite. Calcite, quartz and dolomite form gangue minerals. The δ18O and δ13C values of dolomites vary between –5.8 and +2.1‰ VPDB and between 0.0 and +2.9‰ VPDB, respectively. Isotopic and previous fluid inclusion studies suggest that deposits formed from brines (15–25 wt.% NaCl equiv.) at temperatures of 70 to 110°C. Lead isotope data are homogeneous and represent upper crust source. This study provides an insight into the ore-forming processes of MVT deposits in the northeast Shahmirzad region.  相似文献   

18.
The Tianbaoshan deposit, located in the southwestern part of the Yangtze Block, is a representative Pb–Zn deposit in the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province. The Pb–Zn orebodies are hosted in the upper Sinian Dengying Formation dolostone. The predominant minerals are sphalerite, galena, pyrite, chalcopyrite, quartz, and calcite with minor arsenopyrite, fahlore, and dolomite. The deposit is characterized by relatively strong Cu mineralization. However, the relationship between Pb–Zn and Cu mineralization is unknown. We analyzed the mineralogy and composition of fahlore, chalcopyrite, arsenopyrite, sphalerite, and galena using scanning electron microscopy–energy dispersive spectroscopy, with the aim of providing new evidence for the genesis of the Pb–Zn–(Cu) ore. The results show that the Cu ore in the deposit is dominated by chalcopyrite and fahlore, both of which formed before or during the Pb–Zn ore-forming stage. The fahlore showed dramatic compositional variation and was characterized by negative correlations between Ag and Cu, and between As and Sb, suggesting substitution of Ag for Cu, and that As and Sb substitute in the same site in the fahlore lattice. Based on backscattered electron images and composition, the fahlore was divided into two types. Type I fahlore crystallized early and is characterized by enrichment of Cu and depletion in Ag and Sb. Type II fahlore formed after Type I, and is rich in Ag and poor in Cu and As. Moreover, galena and fahlore are the host minerals of Ag. The variation of valence state with As host mineral—from fahlore to arsenopyrite—indicates the metallogenic environment changed from relatively oxidizing to reducing with a high pH. In the light of Gibbs energies of reciprocal reactions and isotherms for cation exchange, the composition of the fahlore implies its ore-forming temperature was lower than 220 °C, corresponding with typical Mississippi Valley-type (MVT) deposits. Based on the geologic character and geochemical data of this deposit, we suggest that the Tianbaoshan deposit belongs to the MVT deposit category.  相似文献   

19.
会泽超大型铅锌矿是滇东北铅锌多金属成矿域中典型的密西西比河谷型(MVT)或会泽型(HZT)矿床,因其独特的成矿系统以及矿床中富锗而被地质学者熟知,由于该类型矿床成矿温度较低且缺少合适的定年矿物,其成矿时代一直存在较大的争议。本文在会泽铅锌矿麒麟厂矿区1584中段0-11号穿脉坑道块状铅锌硫化物矿石中挑选了9件硫化物样品(黄铁矿、方铅矿和闪锌矿),采用负离子热表面电离质谱法进行Re-Os同位素分析,获得Re-Os等时线年龄为40.7±2.6 Ma(n=9),与模式年龄加权平均值40.0±2.6Ma(n=8)在误差内完全一致,闪锌矿和方铅矿模式年龄分别为38.24±0.41 Ma和36.57±0.40 Ma。上述同位素年龄揭示了会泽超大型铅锌矿的成矿时代可能为始新世。结合滇东北铅锌矿集区NE向逆冲断层和冲断褶皱控矿构造区域构造解析以及断裂、矿体构造-岩相蚀变特征,提出会泽超大型铅锌矿经历了燕山期、喜山期两阶段构造-流体贯入的成矿作用模型。  相似文献   

20.
Located adjacent to the Banded Gneissic Complex, Rampura–Agucha is the only sulfide ore deposit discovered to date within the Precambrian basement gneisses of Rajasthan. The massive Zn–(Pb) sulfide orebody occurs within graphite–biotite–sillimanite schist along with garnet–biotite–sillimanite gneiss, calc–silicate gneisses, amphibolites, and garnet-bearing leucosomes. Plagioclase–hornblende thermometry in amphibolites yielded a peak metamorphic temperature of 720–780°C, whereas temperatures obtained from Fe–Mg exchange between garnet and biotite (580–610°C) in the pelites correspond to postpeak resetting. Thermodynamic considerations of pertinent silicate equilibria, coupled with sphalerite geobarometry, furnished part of a clockwise P–T–t path with peak P–T of ∼6.2 kbar and 780°C, attained during granulite grade metamorphism of the major Zn-rich stratiform sedimentary exhalative deposits orebody and its host rocks. Arsenopyrite composition in the metamorphosed ore yielded a temperature [and log f(S 2)] range of 352°C (−8.2) to 490°C (−4.64), thus indicating its retrograde nature. Contrary to earlier research on the retrogressed nature of graphite, Raman spectroscopic studies on graphite in the metamorphosed ore reveal variable degree of preservation of prograde graphite crystals (490 ± 43°C with a maximum at 593°C). The main orebody is mineralogically simple (sphalerite, pyrite, pyrrhotite, arsenopyrite, galena), deformed and metamorphosed while the Pb–Ag-rich sulfosalt-bearing veins and pods that are irregularly distributed within the hanging wall calc–silicate gneisses show no evidence of deformation and metamorphism. The sulfosalt minerals identified include freibergite, boulangerite, pyrargyrite, stephanite, diaphorite, Mn–jamesonite, Cu-free meneghinite, and semseyite; the last three are reported from Agucha for the first time. Stability relations of Cu-free meneghinite and semseyite in the Pb–Ag-rich ores constrain temperatures at >550°C and <300°C, respectively. Features such as (1) low galena–sphalerite interfacial angles, (2) presence of multiphase sulfide–sulfosalt inclusions, (3) microcracks filled with galena (±pyrargyrite) without any hydrothermal alteration, and (4) high contents of Zn, Ag (and Sb) in galena, indicate partial melting in the PbS–Fe0.96S–ZnS–(1% Ag2S ± CuFeS2) system, which was critical for metamorphic remobilization of the Rampura–Agucha deposit.  相似文献   

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