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1.
Alkali-metasomatism and/or alkali-metasomatites are commonly recognized in different types of endogenic iron deposit,especially in the contact-metasomatic and porphyrite types in China.Alkali-metasomatites occur at the bottom of the mineralized alteration zone,in the marginal facies of the metallogenetic magmatic masses adiacent to iron ore bodies.They are approximately consistent with the attitudes of the ore bodies.As a result of alkali-metasomatism,great changes have taken place in the source rocks,producing distinet alteration zones with the color becoming lighter and lighter upwards and outwards.The alkali-metesomatic solntion is a kind of pneumato-hydrothermal solution rich in Cl,Si and alkalis.Its main components are alkalis and volatiles(dominantly H2O and Cl).The alkalis are closely related to magmatie source and its subsequent differentiation,while H2O is derived mainly from meteoric waters absorbed by the magma and Cl mainly from magma-mesitized gypsum-salt strata(including ground brines).In essence,alkali-metasomatism is the continuation of magmatic evolution and also an auto-metamorphism within the metallogenetic masses,i.e.,a complex ion-exchange reaction under certain physico-chemical conditions.The whole process of alkali-metasomatism can generally be divided into the Na^ -,Ca^2 -and Na^ -replacement stages.In the Ca^2 -replacement stage iron was largely separated from the source rocks.Alkali-metasomatism and the formation of iron ore deposits are two different forms of expression with respect to the same magmatic process,and both are controlled by and genetically related to magmatism,as is indicated by the facts that some of the oreforming materials are products of the de-iron process during alkali-metasomatism and that alkalis and volatiles have played an active role in the formation of iron and differential fusion of silicate melt.  相似文献   

2.
The Changkeng gold-silver deposits consist of a sediment-hosted, disseminated gold deposit and a replacement-type silver deposit. The mineralizations of gold and silver are zoned and closely related to the silicification of carbonate and clastic rocks, so that siliceous ores dominate in the deposit. The mineralizing temperature ranges mainly from 300 to 170℃, and K+, Na+, Ca2+, Mg2+, and Cl- are the major ions in the ore-forming fluid. Calculations of distribution of metal complexes show that gold is mainly transported by hydrosulphide complexes, but chloride complexes of silver, iron, lead, and zinc, which are transformed into hydroxyl and hydrosulphide complexes under neutral to weak-alkaline circumstances in the late stage, predominate in the ore-forming solutions. Water-rock interaction is confirmed to be the effective mechanism for the formation of silver ores by computer modelling of reaction of hydrothermal solution with carbonate rocks. The solubility analyses demonstrate that the precipitation  相似文献   

3.
One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate-associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides （largely hematite）, which occurred during syn-depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen-enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo-productivity suggests that paleo-productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition.  相似文献   

4.
Eastern Iran has great potential for the discovery of different types of mineralization. The study area encompasses Tertiary magmatism in the northern Lut block located in northern Khur, South Khorasan, eastern Iran and is mostly covered by volcanic rocks, which are intruded by porphyritic subvolcanic intrusions in some places. Application of the spectral angle mapper (SAM) technique to Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images detected sericitic, argillic, and propylitic alterations, silicification, and secondary iron oxides. The alteration is linear and associated within vein-type mineralization. Twelve prospective areas are selected for detailed exploration and based on our processing results, in addition to NW-SE faults, which are associated with Cu mineralization indications, NE-SW faults are also shown to be important. Based on the presence of subvolcanic rocks and numerous Cu ± Pb-Zn vein-type mineralizations, extensive alteration, high anomaly of Cu and Zn (up to 100 ppm), the age (43.6 to 31.4 Ma) and the initial 87Sr/86Sr ratio (0.7047 to 0.7065) of the igneous rocks, and the metallogenic epoch of the Lut block (middle Eocene-lower Oligocene) for the formation of porphyry Cu and epithermal deposits, the studied area shows great potential for porphyry copper deposits.  相似文献   

5.
根据鞍本地区包裹体研究试论弓长岭磁铁富矿的成因   总被引：5，自引：0，他引：5  
Gongchangling high-grade magnetite ores,which constitute one of the major rich from deposits in China,occur in the BIF .of the Anshan-Group in Precambrian metamorphic rocks.But its origin has long been a controversial problem,although most researchers are in favour of the eoncept that it is genetically related to hydrothermal process connected with migmatite.On the basis of field observation,this problem has been dealt with in this paper in the light of fluid inclusion studies.The results show that hydrothermal activity,was widespread in this region,which can be divided into two stages.The late stage hydrothermal activity was intensively developed around rich iron dposits.The formation temperature of the late stage hydrbthermal fluids is in the range of 487- 505℃,and they are slightly alkaline with a salinity of 13.2-28.1 wt%,consisting mainly of Na^ ,Ca^ ,Cl^-,So4^-,etc.As revetled by temperature measurements,the formation temperatures of fluid inclusions are quite uniform from,place to place within the vast areas in this region,and the comparason of these temperatures between rich ores and migmatite and wall rocks indieates that the late hydrothermal fluids are of metamorphie origin.The authors suggest that the rich magnetite ores in the Gongchangling Range seem to be the result of the reworking process(alteration)by metamorphie hydrothermal fluids in response to regional metamorphism on some sedimentary ore deposits that were originally relatively rich in iron.  相似文献   

6.
Abstract: The metamorphosed sedimentary type of iron deposits (BIF) is the most important type of iron deposits in the world, and super-large iron ore clusters of this type include the Quadrilatero Ferrifero district and Carajas in Brazil, Hamersley in Australia, Kursk in Russia, Central Province of India and Anshan-Benxi in China. Subordinated types of iron deposits are magmatic, volcanic-hosted and sedimentary ones. This paper briefly introduces the geological characteristics of major super-large iron ore clusters in the world. The proven reserves of iron ores in China are relatively abundant, but they are mainly low-grade ores. Moreover, a considerate part of iron ores are difficult to utilize for their difficult ore dressing, deep burial or other reasons. Iron ore deposits are relatively concentrated in 11 metallogenic provinces (belts), such as the Anshan-Benxi, eastern Hebei, Xichang-Central Yunnan Province and middle-lower reaches of Yangtze River. The main minerogenetic epoches vary widely from the Archean to Quaternary, and are mainly the Late Archean to Middle Proterozoic, Variscan, and Yanshanian periods. The main 7 genetic types of iron deposits in China are metamorphosed sedimentary type (BIF), magmatic type, volcanic-hosted type, skarn type, hydrothermal type, sedimentary type and weathered leaching type. The iron-rich ores occur predominantly in the skarn and marine volcanic-hosted iron deposits, locally in the metamorphosed sedimentary type (BIF) as hydrothermal reformation products. The theory of minerogenetic series of mineral deposits and minerogenic models has applied in investigation and prospecting of iron ore deposits. A combination of deep analyses of aeromagnetic anomalies and geomagnetic anomalies, with gravity anomalies are an effective method to seeking large and deep-buried iron deposits. China has a relatively great ore-searching potential of iron ores, especially for metamorphosed sedimentary, skarn, and marine volcanic-hosted iron deposits. For the lower guarantee degree of iron and steel industry, China should give a trading and open the foreign mining markets.  相似文献   

7.
The study of Late Cretaceous magmatic rocks, developed as a result of magmatism and related porphyry mineralization in the northern Lhasa block, is of significance for understanding the associated tectonic setting and mineralization. This paper reports zircon chronology, zircon Hf isotope data, whole-rock Sr–Nd isotope data, and geochemistry data of Balazha porphyry ores in the northern Lhasa block. Geochemical features show that Balazha ore-bearing porphyries in the northern Lhasa block belong to high-Mg# adakitic rocks with a formation age of ~90 Ma; this is consistent with the Late Cretaceous magmatic activity that occurred at around 90 Ma in the region. The age of adakitic rocks is similar to the molybdenite Re–Os model age of the ore-bearing porphyries in the northern Lhasa block, indicating that the diagenesis and mineralization of both occurred during the same magmatism event in the Late Cretaceous. The Hf and Sr–Nd isotope data indicate that these magmatic rocks are the product of crust–mantle mixing. Differing proportions of materials involved in such an event form different types of medium-acid rocks, including ore-bearing porphyries. Based on regional studies, it has been proposed that Late Cretaceous magmatism and porphyry mineralization in the northern Lhasa block occurred during collision between the Lhasa and Qiangtang blocks.  相似文献   

8.
Granitic rocks are widespread n Jiangxi, constituting an important part of Nanling granites. It is snggested that they are genetieally related to ore genesis, A great deal of work had been dons by many geologists before and after liberation,but the problem concerning their age division still open to eontrovasy, The authors propose in this paper an age-division ssbeme for Jiangxi granitic rocks in an attempt to shed much light on the following problems,1, The age-divlsion of pro-Caledonian granites; 2: The existence of Varisian granites and their position in the age-division;3, The upper and lower limits of Indosinian Cyele and the distribution patterns of granites belonging to the cycle; and 4. The sub-division of Yenshanian granites.  相似文献   

9.
Sedimentary rock-hosted disseminated gold (SRHDG) deposits in the Youjiang-Nanpanjiang Basin,southwestem Guizhou Province are commonly hosted by the same fold crests that commonly contain a remarkable amount of organic material. The total organic carbon (TOC) contents of the ores and host rocks are usually less than 1%. The reflectance of vitrinite and pyrobitumen in the ores and the host rocks ranges from 1.5% to 4.5%, often in the range of 2% to 3%. In the Lannigou deposit, the reflectance of vitrinite and pyrobitumen in the ores is usually somewhat higher than those within the host rocks, indicating a hydrothermal impact on the organic matter in the altered host rocks. On the contrary, the estimated maximum paleotemperatures of the Getang and Zimudang deposits are higher than the homogenization temperatures of the fluid inclusions in the ores, signifying that the organic matter maturation predated Au mineralization. No correlation between the organic matter contents and Au concentrations were recognized in the ores.However, the most striking observation is that there is a positive correlation between the $2 (a parameter of Rock-Eval analysis), Au and As contents of the ores in the Lannigou deposit. Organic matter maturation and migration is apparent from the TOC vs. HCI diagram. Furthermore, group analysis of the dichloromethane extractable organic component of the ores and host rocks shows that the maturation degree of the organic matter in the ores is slightly higher than that of the host rocks in the Lannigou gold deposit. However, the compositions of their alkanes, steranes and terpenes, which serve as biomarkers, are quite similar; this suggests that the organic matter found in the ores and host rocks has a common marine source. Organic matter probably contributed to the preconcentration of Au in the host rocks. Hydrocarbons in the system,on the other hand, clearly contributed to the emplacement of the gold mineralization through thermal sulfate reduction.Organic matter in the solution might have increased the potential of the hydrothermal solution to transport Au.  相似文献   

10.
刘平 《地球化学》1979,(3):i001-i002
The Fanjingshan group, located in the Mt. Fanjing Region, Guizhou Province, is a flysch formation with a thickness of over 10000 meters. Intrusive basic rocks, varying in thickness, consist mainly of layered gabbrodiabase and diabase. Hornstone, spotted slate and ,albite-quartz-slate are commonly recognized in hanging and foot wall rocks as a result of contact metamorphism. Spilite with pillow structure, averaging about 100 meters in thickness, is also widespread. Ultramafic rocks have relatively limited occurrence, accounting for only 13 percent of the total thickness of the intrusives. Alpine ultrabasic rocks have not been found as separate mass. Ultramafic products resulted from in-situ differentiation are noticed and can be assigned to the iron series of ultrabasie rocks. The intrusive basic rocks are classified as subvolcanics that intruded at shallow depth. They are considered to share a common source, to have emplaced into the same position and to be contemporaneous with the sea floor volcanic-spilite, ,and in accordance with its characters, should be assigned to oohidite suit.  相似文献   

11.
The characters of organic matter in rocks and ores in the Fankou and Dabaoshan deposits are systematically studied with regard to their implications for mineralization.The results show that kerogens in this area faaa mainly into the plutonism field in Van Krevelen‘s diagram.Reflectivity of the organic substance was measured to be 3.06%(Fankou)and 1.67%(Dabaoshan),corresponding to the paleo-geotemperatures of 232℃ and 184℃ respectively.The same types of porphyrins and hydrocarbons were recognized in the rocks and ores and hydrocarbon-bearing inclusions are widespread in quartz and calcite,particularly in Dabaoshan,It is thought that the orgain matter must have played a critical role in diagenesis and metallization in these deposits and that the hydrothermal solution was most likely to be the type of water-oil hot brine.  相似文献   

12.
The mechanism that controls regional mineralization must be governed by a series of geochemical reactions in relation to the source system of magmatism.In this respect,the geological bodies must have been overprinted by various kinds of tracers in terms of either chemical elements or isotopes.For this reason,the problem may be better approached by treating the lithosphere as a whole with due considerations given to the various tracer elements and isotopes and the various media of the magmatism(magmatic as well as sedimentary rocks).Presented in this paper are the results of this attempt based on a great wealth of available data concerning the source system of Mesozoic magmatism in the Middle and Lower Yangtze Valleys and adjacent areas.  相似文献   

13.
Long-standing controversy persists over the presence and role of iron–rich melts in the formation of volcanic rock-hosted iron deposits. Conjugate iron–rich and silica–rich melt inclusions observed in thin-sections are considered as direct evidence for the presence of iron-rich melt, yet unequivocal outcrop-scale evidence of iron-rich melts are still lacking in volcanic rock-hosted iron deposits. Submarine volcanic rock-hosted iron deposits, which are mainly distributed in the western and eastern Tianshan Mountains in Xinjiang, are important resources of iron ores in China, but it remains unclear whether iron-rich melts have played a role in the mineralization of such iron ores. In this study, we observed abundant iron-rich agglomerates in the brecciated andesite lava of the Heijianshan submarine volcanic rock–hosted iron deposit, Eastern Tianshan, China. The iron-rich agglomerates occur as irregular and angular masses filling fractures of the host brecciated andesite lava. They show concentric potassic alteration with silicification or epidotization rims, indicative of their formation after the wall rocks. The iron-rich agglomerates have porphyritic and hyalopilitic textures, and locally display chilled margins in the contact zone with the host rocks. These features cannot be explained by hydrothermal replacement of wall rocks(brecciated andesite lava) which is free of vesicle and amygdale, rather they indicate direct crystallization of the iron-rich agglomerates from iron-rich melts. We propose that the iron-rich agglomerates were formed by open-space filling of volatile-rich iron-rich melt in fractures of the brecciated andesite lava. The iron-rich agglomerates are compositionally similar to the wall-rock brecciated andesite lava, but have much larger variation. Based on mineral assemblages, the iron-rich agglomerates are subdivided into five types, i.e., albite-magnetite type, albite-K-feldsparmagnetite type, K-feldspar–magnetite type, epidote-magnetite type and quartz-magnetite type, representing that products formed at different stages during the evolution of a magmatic-hydrothermal system. The albite-magnetite type represents the earliest crystallization product from a residual ironrich melt; the albite-K-feldspar-magnetite and K-feldspar-magnetite types show features of magmatichydrothermal transition, whereas the epidote-magnetite and quartz-magnetite types represent products of hydrothermal alteration. The occurrence of iron-rich agglomerates provides macroscopic evidence for the presence of iron-rich melts in the mineralization of the Heijianshan iron deposit. It also indicates that iron mineralization of submarine volcanic rock-hosted iron deposits is genetically related to hydrothermal fluids derived from iron-rich melts.  相似文献   

14.
Under and climate conditions the chemical weathering of manganese ores is govermed by the fugacities of O2,CO2 and S2 in the atmosphere and soils.Manganese minerals exhibit solid phase transformations without migration of Fe and Mn.Under tropical and subtropical humid climate condi-tions low-valent Mn is instable and apt to be oxidized into high valency state.High-valent Mn miner-als are stable and easy to form secondary high-grade Mn ores.Secondary concentration is possible for Mn ores in carbonate formations,while those in clastic rocks tend to migrate and may be washed away.Such differences are the main obstacles in prospecting Mn ore deposits.  相似文献   

15.
Recently discovered intermediate-basic volcanic rocks in the Devonian strata at Dachang, Guangxi Zhuang Autonomous Region are dominated by basalts and andesites. Most of them belong to the calc-alkali and alkali series. Petrology and geochemistry data indicate that the volcanic rocks may be formed in a continental rift environment. The volcanic rocks are in conformable contact with the overlying and underlying wall rocks, with such typical sedimentary structures as laminated and striped ones, and the host rocks of the volcanic rocks contain lots of marine fossils such as tentaculite. Many pieces of evidence indicate that the eruption environment of the volcanic rocks is a sea-facies one. The volcanic rocks are of the LREE-enrichment type, with high ratios of light rare-earth elements to heavy rare-earth elements. In addition, they display moderately negative δEu anomalies and moderately negative δCe anomalies with a higher degree of LREE and HREE fractionation. Through the Q-cluster analysis of the REE samples, it is indicated that the ores have a closer relation with the layered volcanic rocks, and also possess a certain inheritance-consistency relationship with the layered volcanic rocks. The source of ore-forming materials may be related with volcanism. It is proposed that the ore deposit in the study area should be genetically explained as the result of marine volcano-sedimentary exhalation of hot water and late superposition-reworking.  相似文献   

16.
论姑山铁矿床的形成条件   总被引：1，自引：0，他引：1  
On the basis of geological characteristics the Gushan iron deposit should be assigned to volcano-hydruthermal type with hematite qusrtz as its principal mineral assemblage.Iron concentration of the ore-forming fluid has been estimated from the ratio of hematite to quartz in the ores. By using experimental and thermodynamic data the soinbilities of iron minerals at elevated temperatures and pressures are calculated in the system FeO-Fe2O3-NaCl-HCl-H2O. The effect of T, P, pH, fe2 and total concentration of chlorine on the solubilities of iron minerals are discussed. Thermodynamic calculations based on presumed physicochemical conditions for the ore-forming solutions are in good agreement with geological observation. The calculation shows that iron minerals were deposited at log fo2=-21--25, log(mKCl mbl^ ) =-2,5--3, P=1-0.75 (or 0.5) Kb,T=400-350℃. It is believed that the original fluid was an acid NaCl-bearing solution of magmatic derivation. However, iron in the solution was enriched with falling temperature by dissolving pre-exist iron minerals in the consolidated rocks rather than extracted directly from the magma. Either decreasing temperature (below 400℃) or pressure is capable of depositing iron minerals from the solution, but the ratio of Fe to Si in the ore is dependent mainly upon the pH. The widespread silica vein at later stages is a reflection of decreasing acidity of the solution. Increase in fo2 will also favor the deposition of iron minerals. The hypabyssal occurrence and the existance of the Huangmaqing shale contribute greatly to the formation of hematite.  相似文献   

17.
The Shazi anatase ore deposit in Qinglong, Guizhou Province, is a large-sized anatase deposit that has been recently explored. The characteristics of major oxides in the ore are similar to those of modem laterite weath- ering crust and laterite in the laterite-type gold deposits in the western part of Guizhou Province. Studies on the REE characteristics of basalts and anatase ores in the study region showed that both of them do have extremely strong affinities. There are two groups of trace elements in the ores, i.e., Au-Ag-As-Sb-Hg-Tl association and Sc-TiO2-Cu-Fe-Mn association, reflecting that the formation of anatase ore is related to the formation of siliceous claystone at the early stage of eruption of the Emeishan basaltic magma. The siliceous claystones are the major country rocks for the formation of laterite-type gold ores and anatase ores. In the region anatase ores are rich in Sc and the basalts enriched in Fe, Mn, Ti and Sc are the material source of metallogenesis.  相似文献   

18.
From the determinations of surface heat flow based on silica geothermometry, residual heat flow,radiogenic heat production of rocks, thermal conductivities of rocks and so on, the temperatures at differentdepths of the lithosphere in Fujian Province are estimated by using a one-dimensional steady-state model. Ac-cording to these and the research on geological structures. the possibility of existence of various geothermalsystems in Fujian is discussed. The authors consider that in Fujian, geothermal systems related to shallow magmatism do not exist andhot dry rock systems can not be exploited for the time being. However, intermediate-and low-temperaturehydrothermal systems are well developed. They are controlled by active faults and distributed widely insoutheastern Fujian. but do not have an anomalous heat source. The groundwater circulates at great depthsand has a temperature usually less than 150℃ with less discharge but good quality. It can be used directly as avaluable geothermal water resource but not suitable to be developed as an energy source.  相似文献   

19.
The Jinding Pb-Zn deposit in Yunnan Province is the representative of a Cd-enriched area and mining activities lead to the release of Cd into the hypergenic ecosystem, resulting in Cd pollution. The concentrations of Cd vary greatly from one type to another type of rocks in the mining district. In the host rock, Cd concentrations range from 50×10^-6 to 650×10^-6 with an average of 310×10^-6. In primary ores, Cd concentrations range from 14×10^-6 to 2800×10^-6 with an average of 767×10^-6. However, in oxidized ores, Cd concentrations are highest, varying within the range of 110×10^-6 to 8200×10^-6 , averaging 1661×10^-6. It is shown that the oxidized ores are the main carder and environmental source of Cd. Leaching test showed that Pb/Zn ores are easy to oxidize and thereafter release Cd and other harmful elements. These leached elements in the leachate may be precipitated rapidly in the order of Zn〉Pb〉Cd. As for the concentration distribution of Cd in the Bijiang River, it is estimated to be 15.7 μg/L Cd in water, 49.3 mg/L in suspended substances, and 203.7 mg/L in sediments. The average value of Cd in soil from the polluted area is 83.0 mg/kg. Natural weathering of Cd-rich rocks and minerals imposes a potential environmental risk on the aquatic ecosystem of the Bijiang catchment.  相似文献   

20.
Anatase and its allomorphic mineral rutile have the most prominent economic significance among titanium mineral resources and constitute one of the badly needed mineral resources currently in China. The Yantizishan-Moshishan anatase deposit was formerly referred to as an iron deposit. Based on recent investigation and exploration the authors believe that it is actually a large metamorphosed sedimentary anatase-dominated deposit belonging to a new genetic type. Ore bodies occur in stratoid and lenticular forms in Mesoproterozoic (1751 Ma) schist, metasandstone (metasiltstone), and amphibolite. Rich ores have perthitic structure comprising chiefly interbedded quartz perthite (with disseminated anatase and rutile) and anatase perthite. Ore minerals are mainly anatase and subordinately rutile and ilmenite (±hematite), while nonmetallic minerals are chiefly quartz with a certain amount of anthophyllite and biotite (±garnet). The grain sizes of anatase, rutile and ilmenite are 0.01–0.1 mm. Rich ores contain 3.14% to 15.46% TiO2, averaging 6.91%, while the low-grade ores have TiO2 content about 1.2%to 2.97%, averaging 1.76%. The ores have relatively high TFe and V contents. Trace elements in anatase and rutile such as Nb and Cr were analyzed by the electron microprobe. According to their relatively low Nb and Cr contents, source anatase and rutile must have come from meta-mafic rocks. Trace elements of the associated ilmenite show relatively high MnO and low MgO contents, just in contrast to those of ilmenite in V-Ti-magnetite ores of magmatic origin. The protoliths of amphibolite wall rocks should be basalt and picrite-basalt. Pertochemical data suggest that the tectonic setting of these rocks belongs to an island arc or a transitional belt between the island arc and oceanic ridge. Silicon isotope study shows that δ30Si values of different anatase ores, quartzite, and schist in this deposit are 0.1‰ to –0.9‰, similar to those of marine hydrothermal exhalative sedimentary deposits. All of these geological and geochemical characteristics of the ore deposit suggest that the anatase ores and amphibolite are products of submarine basic volcanism. The ores had chemical precipitation features, but were later subjected to regional intermediate (or somewhat lower) grade metamorphism (1158 Ma). Rutile was formed mainly in the process of this metamorphism. The ore belt locally underwent hydrothermal modification during the emplacement of Late Yanshanian granite (118?Ma).  相似文献   

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