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1.
The products of the activity of the Late Quaternary Kazbek neovolcanic center in the Greater Caucasus are studied by isotopic-geochronological methods. It is found that the youngest magmatism evolved during the last 400–450 k.y. over four discrete phases: 395–435, 200–250, 90–120, and less than 50 ka. The petrological-geochemical and published isotopic data point to the mixed mantle-crustal origin of the Kazbek lavas with the leading role of crystallization differentiation of deep magmas and assimilation of the crustal material. We recorded two episodes (～100 and less than 50 ka) of replenishment of the subsurface magmatic chamber under the Kazbek center by the main mantle melt and its mixing with the relict dacite magma that led to the formation of highly mobile hybrid andesite lavas and served as a trigger of the renewal of volcanic activity. Reactivation of the mantle source of the Kazbek center at the end of the Neopleistocene and the Holocene age of the last eruptions indicate the potential danger of this region because of the renewal of the volcanic activity. The medium Devdoraki copper deposit is located in the vicinity of the Kazbek volcano. It represents a unique polychronous, currently evolved ore-magmatic system that originated in the Jurassic.  相似文献   

2.
The results of geochronological, petrological–mineralogical, and isotope-geochemical studies of the Tanadon gold deposit in the Greater Caucasus (Republic of North Ossetia–Alania) have made it possible to determine the age of ore veins and identify ore matter sources of sulfide mineralization. The Tanadon deposit is localized in Paleozoic synmetamorphic granitic rocks at the southern margin of the epi-Hercynian Scythian Plate, which is included in the tectonic zone of the Main Caucasus Range. The orebodies are represented by quartz veins varying in thickness and containing complex sulfide mineralization (pyrite, arsenopyrite, chalcopyrite, pyrrhotite, galena, sphalerite, stannite, cobaltite, and bismuthinite). Arsenopyrite is the main repository of invisible gold. Mineralogical data provide evidence for hydrothermal ore formation, which proceeded at least in two stages, giving rise to earlier pyrite + arsenopyrite and later galena + sphalerite + chalcopyrite mineral assemblages. The Tanadon deposit is a zone of intense young magmatic activity. Neointrusions widespread therein are related to the Early Pliocene Tsana Complex (trachyandesitic dikes, ~4.7 Ma in age) and to the Late Pliocene–Early Pleistocene Tepli Complex (dacitic necks, ~1.4 Ma). According to K–Ar dating of sericite from ore-bearing veins, the Tanadon deposit formed synchronously with Early Pliocene dikes of the Tsana Complex. The total duration of the hydrothermal process likely did not exceed hundreds of thousands of years. As follows from Pb-isotope-geochemical data, hydrothermal processes coeval with Early Pliocene magmatic activity, as well as geological relationships between ore-bearing veins and trachyandesitic dikes, show that the sulfide mineralization of the Tanadon deposit is genetically related to the intrusive Tsana Complex. The main source of ore components is represented by hydrothermal solutions produced in an Early Pliocene melt spot localized beneath the considered part of Greater Caucasus. In the adjacent territory of Georgia, a number of ore objects similar in structure and mineral composition to the Tanadon deposit are also genetically and spatially related to the intrusions of the Tsana Complex. Therefore, the Tsana Complex should be regarded as productive and the areas occupied by Early Pliocene intrusive bodies as promising for Au-bearing arsenopyrite and base-metal mineralization.  相似文献   

3.
Wulaga epithermal gold deposit is located in northeast China. Gold mineralization mainly occurs within the crypto‐explosive breccia belt of subvolcanic intrusion. Constraints on the precise timing of mineralization are of fundamental importance for understanding the ore genesis of the Wulaga gold deposit and its mineralization potential. Three hydrothermal stages have been identified: the early veiny quartz–euhedral pyrite stage; the fine pyrite–marcasite–gray or black chalcedony stage; and the late carbonate–pyrite stage. The Rb–Sr dating of gold‐bearing pyrites from the fine pyrite–marcasite–gray or black chalcedony stage is 113.8 ± 4.4 Ma with an initial 87Sr/86Sr ratio of 0.706346 ± 0.000019. The age of the gold deposit is consistent with the age of ore‐bearing volcanic (109–113 Ma) and subvolcanic intrusion (103–112 Ma) within the error limits, and the pyrite initial ratio has an identical value of 87Sr/86Sr to subvolcanic intrusion (0.705547 ± 0.000012). These indicate that crystallization of the wall rock and epithermal gold mineralization was coeval and likely cogenetic. Moreover, a lot of epithermal gold deposits that formed in Early Cretaceous volcanic and subvolcanic intrusions have been discovered in recent years in Heilongjiang province. Combined with the studies of tectonic and magmatic activities, we propose that the formation of the Wulaga gold deposit might be caused by the heated circum‐flow water related to the volcanic–subvolcanic intrusive hydrothermal event triggered by the ancient subduction of the Izanagi plate in the Early Cretaceous.  相似文献   

4.
《Ore Geology Reviews》2003,22(1-2):61-90
Quantitative laser ablation (LA)-ICP-MS analyses of fluid inclusions, trace element chemistry of sulfides, stable isotope (S), and Pb isotopes have been used to discriminate the formation of two contrasting mineralization styles and to evaluate the origin of the Cu and Au at Mt Morgan.The Mt Morgan Au–Cu deposit is hosted by Devonian felsic volcanic rocks that have been intruded by multiple phases of the Mt Morgan Tonalite, a low-K, low-Al2O3 tonalite–trondhjemite–dacite (TTD) complex. An early, barren massive sulfide mineralization with stringer veins is conforming to VHMS sub-seafloor replacement processes, whereas the high-grade Au–Cu ore is associated with a later quartz–chalcopyrite–pyrite stockwork mineralization that is related to intrusive phases of the Tonalite complex. LA-ICP-MS fluid inclusion analyses reveal high As (avg. 8850 ppm) and Sb (avg. 140 ppm) for the Au–Cu mineralization and 5 to 10 times higher Cu concentration than in the fluids associated with the massive pyrite mineralization. Overall, the hydrothermal system of Mt Morgan is characterized by low average fluid salinities in both mineralization styles (45–80% seawater salinity) and temperatures of 210 to 270 °C estimated from fluid inclusions. Laser Raman Spectroscopic analysis indicates a consistent and uniform array of CO2-bearing fluids. Comparison with active submarine hydrothermal vents shows an enrichment of the Mt Morgan fluids in base metals. Therefore, a seawater-dominated fluid is assumed for the barren massive sulfide mineralization, whereas magmatic volatile contributions are implied for the intrusive related mineralization. Condensation of magmatic vapor into a seawater-dominated environment explains the CO2 occurrence, the low salinities, and the enriched base and precious metal fluid composition that is associated with the Au–Cu mineralization. The sulfur isotope signature of pyrite and chalcopyrite is composed of fractionated Devonian seawater and oxidized magmatic fluids or remobilized sulfur from existing sulfides. Pb isotopes indicate that Au and Cu originated from the Mt Morgan intrusions and a particular volcanic strata that shows elevated Cu background.  相似文献   

5.
文章在矿床地质、地球化学及同位素年代学研究的基础上,总结了菲莫铜钼多金属矿床的成因及理想模式。矿床中岩、矿石S、Pb同位素组成显示,矿床成矿物质主要来源于深部地幔或下地壳古老基底,后混入部分上地壳物质;H、O同位素特征显示,矿床成矿热液以上升的岩浆热液为主,结合部分变质热液及渗透淋滤的大气降水形成混合热液;Re-Os同位素测年得出矿床形成时间为(47·81±0·71)Ma,矿化主要发生于大皮甲岩体岩浆侵位晚期的期后热液阶段。矿床成因类型属沉积-变质-岩浆热液叠加改造型铜钼多金属矿床。成矿作用具长期性、多期次、多来源、多阶段、多成因的特征,大致经历了古元古代的沉积定位阶段→中新元古代的区域变质改造富集阶段→喜马拉雅期的颠覆性改造叠加富集成矿阶段。  相似文献   

6.
江西银山铅锌铜矿化机制的讨论   总被引：8，自引：2，他引：8  
华仁民 《矿床地质》1987,6(2):90-96
本文分析了银山矿区所处的火山盆地边缘这一特定地质构造环境,火山活动的多阶段性以及蚀变矿化的基本特征,指出在银山发生过两期矿化作用,分别对应于两个阶段的火山-次火山活动。第一阶段的流纹英安质次火山活动产生铅锌银矿化,第二阶段英安质次火山活动则伴随铜(铅锌)矿化。因此,作者认为银山铅锌铜矿床是典型的次火山热液矿床,是两期矿化叠加的结果,从而对前人关于银山矿的成因模式和归类提出了异议。本文还对银山矿与德兴斑岩铜(钼)矿田的成因联系问题提出了独特的看法,并指出了银山式铅锌(铜)矿化的找矿方向。  相似文献   

7.
The paper presents detailed isotope-geochronological, geological, and petrologic–mineralogical data on lavas of one of the greatest Quaternary magmatic area in the Greater Caucasus, the Kazbek neovolcanic center, including polygenetic Kazbek stratovolcano and a number of subordinate volcanic cones in its vicinities. The research was conducted based on a representative collection of more than 150 geological samples that characterize most of the volcanic cones and lava flows of different age, some of which were known previously, and other were discovered by the authors. The high-precision K–Ar data obtained on these materials make it possible to reproduce the evolutionary history of youngest magmatism at the Kazbek center and evaluate the total duration of this evolution at ~450 ka. The magmatic activity was subdivided into four phases (at 460–380, 310–200, 130–90, and <50 ka) with long-lasting interludes in between. Because the latest eruptions occurred in the Kazbek vicinity in the Holocene, this volcano is regarded as potentially active. The volcanic rocks of the Kazbek center make up a continuous compositional succession of basaltic (trachy)andesite–(trachy)andesite–dacite and mostly belong to the calc–alkaline series. The principal petrographic characteristics of the rocks and the composition of their phenocryst minerals are determined, mineral assemblages of these minerals are distinguished in the lavas of different type, and the temperature of the magmatic melts is evaluated. A principally important role in the petrogenesis of the Kazbek youngest magmas is proved to have been played by fractional crystallization and replenishment of mafic melts in the magmatic chambers beneath the volcano, which resulted in their mixing and mingling with the residual dacite melt and the origin of high-temperature hybrid andesite lavas. The comprehensive geological studies, involving interpretation of high-resolution satellite images, allowed the authors to compile the first detailed (1: 25 000) volcanologic map of the Kazbek center and a geochronologic chart supplemented with a stratigraphic column, which illustrate the origin sequence of the volcanic vents and their lava flows, geological relations between them, as seen in reference geological sections, and variations in the composition of the magmatic products with time.  相似文献   

8.
罗文铁矿位于柬埔寨北部柏威夏省罗文县境内,区域上位于罗文真基底穹窿中部,是柬埔寨铁矿产资源的重要产地。该矿区燕山期中酸性岩浆喷发-侵入活动强烈,原生矿体主要呈似层状、透镜状、脉状、囊状产于安山岩、闪长玢岩、凝灰岩等火山岩中,大部分赋矿围岩蚀变发育,主要有矽卡岩化、绿泥石化、绿帘石化、硅化、黑云母化、碳酸盐化等。通过对矿石组构、矿物共生组合、围岩蚀变特征分析,该矿床形成划分为岩浆期和热液期2个成矿期,进一步分为3个成矿阶段:透辉石-石榴子石-磁铁矿阶段、透辉石-石榴子石-透闪石-绿泥石-磁铁矿阶段、黄铁矿(黄铜矿)-镜铁矿-碳酸盐矿物阶段。笔者在野外地质调查和室内分析研究的基础上,认为罗文铁矿矿床成因与火山-次火山岩及其热液活动有关,成矿主要受火山机构尤其是火山口、火山颈相控制,属火山-次火山岩型铁矿床。  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.
粤北大宝山多金属矿床成矿流体的He-Ar-Pb-S同位素示踪   总被引：3，自引：0，他引：3  
大宝山多金属矿床是粤北地区典型的巨厚型及细脉带型矿化的多金属硫化物矿床.层状和脉状黄铁矿的氦氩同位素表明:3He/4He的R/Ra值为0.60～4.13,40Ar/86Ar=327～411,反映该成矿流体是大气饱和水(海水)与地幔流体混合作用的结果.铅和硫同位素都揭示了层状(块状)和脉状矿体可能来自不同时期的成矿流体.其中层状矿体为泥盆纪海底火山喷发沉积作用所致,脉状矿体可能来自燕山期岩浆热液充填叠加形成,古大陆碎屑物质和部分有机质的还原对后期成矿流体具有较大的影响作用.  相似文献   

11.
长江中下游成矿带存在一套产于泥盆系五通组砂岩和石炭系黄龙组白云质灰岩层间的层状含铜硫化物矿体,对其成因存在很大争议。本文以产出典型层状矿体的武山铜矿为解剖重点,结合区域控矿地质要素、矿石结构构造特征及矿石中黄铁矿的稀土元素地球化学,提出层状矿体是海底喷流同生沉积与岩浆热液叠加成矿作用的产物。对武山铜矿层状矿体中的胶黄铁矿和黄铁矿、矽卡岩矿体中黄铁矿和脉状矿体中黄铁矿进行的稀土元素含量分析发现,从层状矿体胶黄铁矿、层状矿体黄铁矿、到矽卡岩和脉状矿体黄铁矿,稀土总量和稀土配分曲线显示递变规律,即层状矿体胶黄铁矿具有较低的稀土总量和轻重稀土分异不明显的较平坦型配分曲线;而矽卡岩和脉状矿体黄铁矿具有较高的稀土总量和轻重稀土分异较明显的右倾型配分曲线。层状矿体黄铁矿的稀土特征则介于两者之间,反映了岩浆热液的叠加作用。根据矿物组合共生关系及矿石结构构造的研究,可将武山铜矿黄铁矿分为3个期次:I期为微球粒、草莓状、条带状、纹层状沉积型黄铁矿; II期为半自形、自形粒状和港湾状黄铁矿,可见与长英质斑晶、岩屑或晶屑凝灰岩伴生或共生, 说明黄铁矿形成与同沉积期火山凝灰岩的密切关系。III期为块状、粗晶状、碎裂状黄铁矿。黄铜矿的形成晚于I、II期黄铁矿,成微粒状、脉状交错穿插或包裹早期球粒状、粒状黄铁矿及长英质矿物。对新发现的灰泥丘构造的详细研究表明,武山铜矿中含矿的灰泥丘与武山外围乌石街出露的不含矿的灰泥丘具有不同的特征,其中前者具有封闭的孔洞系统,而后者为开放的孔洞系统。总之,武山铜矿控矿地质条件、矿石结构构造及不同类型矿石黄铁矿的稀土元素证据表明矿床存在两期成矿事件,即海西期海底喷流同生沉积成矿期和燕山期岩浆热液叠加成矿期。  相似文献   

12.
《International Geology Review》2012,54(13):1616-1625
We report new zircon U–Pb and pyrite Re–Os geochronological studies of the Yinjiagou poly-metallic deposit, sited along the southern margin of the North China Craton (SMNCC). In this deposit, pyrite, the most important economic mineral, is intergrown/associated with Mo, Cu, Au, Pb, Zn, and Ag. Prior to our new work, the age of chalcopyrite–pyrite mineralization was known only from its spatial relationship with molybdenite mineralization and with intrusions of known ages. The U–Pb and Re–Os isotope systems provide an excellent means of dating the mineralization itself and additionally place constraints on the ore genesis and metal source. Zircons separated from the quartz–chalcopyrite–pyrite veins include both detrital and magmatic groups. The magmatic zircons confine the maximum age of chalcopyrite–pyrite mineralization to 142.0 ± 1.5 Ma. The Re–Os results yield an age of 141.1 ± 1.1 Ma, which represents the age of the chalcopyrite–pyrite mineralization quite well. The common Os contents are notably low (0.5–20.1 ppt) in all samples. In contrast, the Re contents vary considerably (3.0–199.2 ppb), most likely depending on intensive boiling, which resulted in an increase of Re within the pyrite. This study demonstrates that the main chalcopyrite–pyrite mineralization occurred late in the magmatic history and was linked to a deeper intrusion involving dominant mantle-derived materials. This mineralization event might be related to the Early Cretaceous lithospheric destruction and thinning of the SMNCC.  相似文献   

13.
The world-class Imiter silver deposit, in the Anti-Atlas Mountains of Morocco, is a Neoproterozoic epithermal vein deposit genetically associated with a felsic volcanic event, and formed within a regional extensional tectonic regime. Rhyolitic volcanism related to ore formation has been dated at 550Dž Ma by ion-probe U/Pb on zircons. The economic silver mineralization is superimposed on an older, discrete base-metal assemblage associated with calc-alkaline granodioritic magmatism. The magmatism is dated at 572LJ Ma by ion-probe U/Pb dating on zircons, and by 40Ar/39Ar dating on hydrothermal muscovites. In the Anti-Atlas Mountains, the Precambrian-Cambrian transition appears as an important period for the formation of major, productive precious-metal deposits associated with volcanic events and extensional tectonics. The Imiter silver deposit constitutes a Precambrian analogue to modern epithermal deposits.  相似文献   

14.
The Xinlu Sn‐polymetallic ore field is located in the western Nanling Polymetallic Belt in northeastern Guangxi, South China, where a number of typical skarn‐, hydrothermal vein‐type tin deposits have developed. There are two types of Sn deposits: skarn‐type and sulfide‐quartz vein‐type. The tin mineralizations mainly occur on the south side of the Guposhan granitic complex pluton and within its outer contact zone. To constrain the Sn mineralization age and further understand its genetic links to the Guposhan granitic complex, a series of geochronological works has been conducted at the Liuheao deposit of the ore field using high‐precision zircon SHRIMP U‐Pb, molybdenite Re‐Os, and muscovite Ar‐Ar dating methods. The results show that the biotite‐monzogranite, which is part of the Xinlu intrusive unit of the Guposhan complex pluton, has a SHRIMP U‐Pb zircon age of 161.0 ± 1.5 Ma. The skarn‐type ore has a 40Ar‐39Ar muscovite plateau age of 160 ± 2 Ma (same as its isochron age), and the sulfide‐quartz vein‐type ore yields an Re‐Os molybdenite isochron age of 154.4 ± 3.5 Ma. The magmatic‐hydrothermal geochronological sequence demonstrated that the hydrothermal mineralization took place immediately following the emplacement of the monzogranite, with the skarn metasomatic mineralization stage predating the sulfide mineralization stage. Geochronologically, we have compared this ore field with 26 typical Sn deposits distributed along the Nanling Polymetallic Belt, leading to the suggestion of the magmatic‐metallogenic processes in the Xinlu ore field (ca. 161–154 Ma) as a component of the Early Yanshanian large‐scale Sn‐polymetallic mineralization event (peaked at 160–150 Ma) in the Nanling Range of South China. Petrogenesis of Sn‐producing granite and Sn‐polymetallic mineralization were probably caused by crust–mantle interaction as a result of significant lithospheric extension and thinning in South China in the Late Jurassic.  相似文献   

15.
Abstract

A newly discovered, shoshonitic lava-hosted Pb deposit at Nariniya in central Tibet provides an excellent example to help improve our understanding of the linkage between post-collisional potassic magmatism and ore formation in Tibet. The Pb ores exist as veins or veinlets in NWW-striking fracture zones within the potassic lava (trachyte). The veins contain quartz, galena, pyrite, and sericite (muscovite) as well as minor chalcopyrite, sphalerite, calcite, and dolomite with sericitization, pyritization, and minor silicification. The 40Ar–39Ar plateau age of the hydrothermal muscovite is 37.95 ± 0.30 Ma, which represents the Pb mineralization age. This obtained age is indistinguishable, within analytical error, from the zircon U–Pb age of 37.88 ± 0.22 Ma for potassic lava. Therefore, the ore formation can be genetically linked to potassic magmatism. Galena has similar Pb isotopic composition to magmatic feldspar from the host lava, suggesting the derivation of Pb from the magmatic system. Previous studies have suggested that S- and ore-forming fluids are of magmatic origin. Published data show that the Nariniya volcanic rocks are acidic, shoshonitic, akakitic, peraluminous, and enriched in Sr–Nd–Pb isotopes. Thus, they are geochemically different from other potassic volcanic rocks (no adakitic affinity) in the North Qiangtang terrane, but similar to the 46–38 Ma high-K calc-alkaline peraluminous adakitic rocks in this terrane and the late Eocene Cu-generating potassic porphyries from the Sanjiang region of eastern Tibet. As such, the Nariniya potassic magma likely originated from melting of subducted continental crust, with or without interaction with the overlying enriched mantle. Such post-collisional potassic rocks in Tibet are thought to be potential targets for prospecting of both Pb–Zn and porphyry Cu ores. Note that other ore styles (in addition to the Nariniya ore style) may exist in the potassic volcanic districts of Tibet.  相似文献   

16.
The Kalaxiange’er porphyry copper ore belt is situated in the eastern part of the southern Altai of the Central Asian Orogenic Belt and forms part of a broad zone of Cu porphyry mineralization in southern Mongolia, which includes the Oyu Tolgoi ore district and other copper–gold deposits. The copper ore bodies are spatially associated with porphyry intrusions of granodiorite, quartz diorite, quartz syenite, and quartz monzonite and have a polygenetic (polychromous) origin (magmatic porphyry, hydrothermal, and supergene). The mineralized porphyries are characterized by almost identical REE and trace element patterns. The Zr/Hf and Nb/Ta ratios are similar to those of normal granite produced through the evolution of mantle magma. The low initial Sr isotope ratio ISr, varying within a narrow range of values (0.703790–0.704218), corresponds to that of primitive mantle, whereas the εNd(T) value of porphyry varies from 5.8 to 8.4 and is similar to that of MORB. These data testify to the upper-mantle genesis of the parental magmas of ore-bearing porphyry, which were then contaminated with crustal material in an island-arc environment. The isotopic composition of sulfur (unimodal distribution of δ34S with peak values of − 2 to − 4‰) evidences its deep magmatic origin; the few lower negative δ34S values suggest that part of S was extracted from volcanic deposits later. The isotopic characteristics of Pb testify to its mixed crust–upper-mantle origin. According to SHRIMP U–Pb geochronological data for zircon from granite porphyry and granodiorite porphyry, mineralization at the Xiletekehalasu porphyry Cu deposit formed in two stages: (1) Hercynian “porphyry” stage (375.2 ± 8.7 Ma), expressed as the formation of porphyry with disseminated and vein–disseminated mineralization, and (2) Indosinian stage (217.9 ± 4.2 Ma), expressed as superposed hydrothermal mineralization. The Re–Os isotope data on molybdenite (376.9 ± 2.2 Ma) are the most consistent with the age of primary mineralization at the Xiletekehalasu porphyry Cu deposit, whereas the Ar–Ar isotopic age (230 ± 5 Ma) of K-feldspar–quartz vein corresponds to the stage of hydrothermal mineralization. The results show that mineralization at the Xiletekehalasu porphyry Cu deposit was a multistage process which resulted in the superposition of the Indosinian hydrothermal mineralization on the Hercynian porphyry Cu mineralization.  相似文献   

17.
Geological and structural conditions of localization, hydrothermal metasomatic alteration, and mineralization of the Petropavlovskoe gold deposit (Novogodnenskoe ore field) situated in the northern part of the Lesser Ural volcanic–plutonic belt, which is a constituent of the Middle Paleozoic island-arc system of the Polar Urals, are discussed. The porphyritic diorite bodies pertaining to the late phase of the intrusive Sob Complex play an ore-controlling role. The large-volume orebodies are related to the upper parts of these intrusions. Two types of stringer–disseminated ores have been revealed: (1) predominant gold-sulfide and (2) superimposed low-sulfide–gold–quartz ore markedly enriched in Au. Taken together, they make up complicated flattened isometric orebodies transitory to linear stockworks. The gold potential of the deposit is controlled by pyrite–(chlorite)–albite metasomatic rock of the main productive stage, which mainly develops in a volcanic–sedimentary sequence especially close to the contacts with porphyritic diorite. The relationships between intrusive and subvolcanic bodies and dating of individual zircon crystals corroborate a multistage evolution of the ore field, which predetermines its complex hydrothermal history. Magmatic activity of mature island-arc plagiogranite of the Sob Complex and monzonite of the Kongor Complex initiated development of skarn and beresite alterations accompanied by crystallization of hydrothermal sulfides. In the Early Devonian, due to emplacement of the Sob Complex at a depth of approximately 2 km, skarn magnetite ore with subordinate sulfides was formed. At the onset of the Middle Devonian, the large-volume gold porphyry Au–Ag–Te–W ± Mo,Cu stockworks related to quartz diorite porphyry—the final phase of the Sob Complex— were formed. In the Late Devonian, a part of sulfide mineralization was redistributed with the formation of linear low-sulfide quartz vein zones. Isotopic geochemical study has shown that the ore is deposited from reduced, substantially magmatic fluid, which is characterized by close to mantle values δ34S = 0 ± 1‰, δ13C =–6 to–7‰, and δ18O = +5‰ as the temperature decreases from 420–300°C (gold–sulfide ore) to 250–130°C (gold–(sulfide)–quartz ore) and pressure decreases from 0.8 to 0.3 kbar. According to the data of microanalysis (EPMA and LA-ICP-MS), the main trace elements in pyrite of gold orebodies are represented by Co (up to 2.52 wt %), As (up to 0.70 wt %), and Ni (up to 0.38 wt %); Te, Se, Ag, Au, Bi, Sb, and Sn also occur. Pyrite of the early assemblages is characterized by high Co, Te, Au, and Bi contents, whereas the late pyrite is distinguished by elevated concentrations of As (up to 0.7 wt %), Ni (up to 0.38 wt %), Se (223 ppm), Ag (up to 111 ppm), and Sn (4.4 ppm). The minimal Au content in pyrite of the late quartz–carbonate assemblage is up to 1.7 ppm and geometric average is 0.3 ppm. The significant correlation between Au and As (furthermore, negative–0.6) in pyrite from ore of the Petropavlovskoe deposit is recorded only for the gold–sulfide assemblage, whereas it is not established for other assemblages. Pyrite with higher As concentration (up to 0.7 wt %) is distinguished only for the Au–Te mineral assemblage. Taking into account structural–morphological and mineralogical–geochemical features, the ore–magmatic system of the Petropavlovskoe deposit is referred to as gold porphyry style. Among the main criteria of such typification are the spatial association of orebodies with bodies of subvolcanic porphyry-like intrusive phases at the roof of large multiphase pluton; the stockwork-like morphology of gold orebodies; 3D character of ore–alteration zoning and distribution of ore components; geochemical association of gold with Ag, W, Mo, Cu, As, Te, and Bi; and predominant finely dispersed submicroscopic gold in ore.  相似文献   

18.
吴如灼  胡伦积 《地质论评》1992,38(3):279-288
笔者应用岩石学、构造学、矿床学、地球化学等手段和方法研究了该区金矿床的特点和形成条件,结果表明青龙河金矿的容矿岩石是一套成分以火山(碎屑)岩岩屑为主的浊积岩,其含金量高达2.87g/t,且金主要与硫化物共生,浊积岩是金的矿源层。矿区内有细脉浸染型和含金石英脉型矿床。金矿的形成受浊流作用、火山作用和后生热液作用的控制。  相似文献   

19.
The Elna Cu(Au)–porphyry deposit is one of the typical ore objects in the northeastern margin of the Argun superterrane facing the Mongolia–Okhotsk foldbelt. Mineralization includes zones of argillization with fine quartz veins in granodiorite of the Elna massif. The geochronological 40Ar/39Ar studies of hydrothermal near-ore metasomatites and magmatic rocks of the deposit show that the age of host granitoids is 126 ± 2 Ma, which corresponds to the upper age boundary of granitoids from the Burinda Complex, whereas the age of overprinted hydrothermal processes is 122–117 Ma. The age of mineralization correlates well with the age of the thermal event in East Asia. An intense stage of magmatism including both volcanic and intrusive forms occurred in this period.  相似文献   

20.
The Xiaohongshilazi deposit located in central Jilin Province, Northeast China, is a newly discovered and medium‐scale Pb–Zn–(Ag) deposit with ore reserves of 34,968 t Pb, 100,150 t Zn, and 158 t Ag. Two‐stage mineralization has been identified in this deposit. Stratiform volcanic‐associated massive sulfide (VMS) Pb–Zn mineralization interbedding with the marine volcanic rocks of the Late Carboniferous–Early Permian Daheshen Formation was controlled by the premineralization E–W‐trending faults. Vein‐type Pb–Zn–(Ag) mineralization occurs within or parallel to the granodiorite and diorite porphyries controlled by the major‐mineralization N–S‐trending faults that cut the stratiform mineralization and volcanic rocks. To constrain the age of vein‐type Pb–Zn–(Ag) mineralization and determine the relationship between mineralization and magmatism, we conducted LA–ICP–MS U–Pb dating on zircon from the ore‐bearing granodiorite and diorite porphyries and Rb–Sr dating on metal sulfide. Granodiorite and diorite porphyries yield zircon U–Pb weighted‐mean 206Pb/238U ages of 203.6 ± 1.8 Ma (Mean Standard Weighted Deviation [MSWD] = 1.8) and 225.6 ± 5.1 Ma (MSWD = 2.3), respectively. Sulfides from four vein‐type ore samples yield a Rb–Sr isochron age of 195 ± 17 Ma (MSWD = 4.0). These results indicate a temporal relationship between the granodiorite porphyry and vein‐type Pb–Zn–(Ag) mineralization. The granodiorite associated with vein‐type mineralization has high SiO2 (68.99–70.49 wt.%) and Na2O (3.9–4.2 wt.%; Na2O/K2O = 1.07–1.10) concentrations, and A/CNK values of 0.95–1.04; consequently, the intrusion is classified as a high‐K, calc‐alkaline, metaluminous I‐type granite. The granodiorite porphyry is enriched in large‐ion lithophile elements (e.g. Rb, Th, U, and K) and light REE and is depleted in high‐field‐strength elements (e.g. Nb, Ta, P, and Ti) and heavy REE, indicating that it represents a subduction‐related rock that formed at an active continental margin. Furthermore, the granodiorite porphyry has Mg# values of 31–34, indicating a lower crustal source. Based on petrological and geochemical features, we infer that the ore‐bearing granodiorite porphyry was derived from the partial melting of the lower crust. In summary, mineralization characteristics, cross‐cutting relationships, geochronological data, and regional tectonic evolution indicate that the region was the site of VMS Pb–Zn mineralization that produced stratiform orebodies within the Late Carboniferous–Early Permian marine volcanic rocks of the Daheshen Formation, followed by mesothermal magmatic hydrothermal vein‐type Pb–Zn–(Ag) mineralization associated with granodiorite porphyry induced by the initial subduction of the Paleo‐Pacific Plate beneath the Eurasia Plate during the Late Triassic–Early Jurassic.  相似文献   

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