Problems of Siderite Formation and Iron Ore Epochs: Communication 1. Types of Siderite-Bearing Iron Ore Deposits

It is shown that siderite is unstable during sedimentation, diagenesis, and metamorphism of sedimentary and volcanosedimentary rocks. Regularities in the distribution of siderite in Precambrian jaspilites (iron formations), metasomatic ores of the Bakal type, continental–marine coaliferous formations, and oolitic iron ores are discussed. The genesis of the Precambrian iron formations and Riphean–Lower Paleozoic elisional–hydrothermal deposits is considered. The genetic relation of nodular siderites from coaliferous formations and oolitic iron ores with lowmoor coal-forming peat deposits is noted.     

Siderite formation and evolution of sedimentary iron ore deposition in the Earth’s history

The role of siderite in Phanerozoic and Precambrian iron formations is discussed. Various types of iron formations are characterized, and their place in the evolution of sedimentary iron ore deposition is outlined. In Precambrian iron ore deposition, siderite is a primary mineral, whereas in Phanerozoic iron formations it becomes a secondary mineral and is commonly related to diagenetic and catagenetic processes.     

安徽新桥矿床矿相学与Fe同位素特征及其对矿床成因的制约

对安徽新桥矿床进行系统的野外地质调查和矿相学研究发现,层状矿体中的胶状黄铁矿交代矽卡岩磁铁矿矿体,为探讨层状硫化物矿床是早期沉积成因还是岩浆热液成因提供了新的地质约束。对铜陵矿集区内的新桥矿床层状菱铁矿矿体和凤凰山矽卡岩型矿体中的菱铁矿开展了Fe同位素组成的对比研究,结果显示：新桥矿床菱铁矿与典型低温热液脉型矿床和沉积铁矿中的菱铁矿在Fe同位素组成特征上有所不同,而与凤凰山矽卡岩型矿床中的菱铁矿更为接近;新桥矿床中胶状黄铁矿和菱铁矿相对于磁铁矿富集Fe的轻同位素,表明磁铁矿不是过去认为的由胶状黄铁矿和菱铁矿矿胚层经热液改造形成,而是与典型的岩浆热液有关。新桥矿区层状硫化物矿体和矽卡岩型矿体中,近岩体矽卡岩和最早形成的金属矿物磁铁矿比岩体更为富集Fe的轻同位素,而赋矿围岩比岩体更为富集Fe的重同位素。同时,不同矿化阶段形成的含铁矿物和不同空间位置的硫化物中的Fe同位素组成呈现出时空分带现象,Fe同位素组成的时空演化特征与流体出溶、流体演化非常一致,并且符合同位素分馏的基本理论,表明层状硫化物矿体和矽卡岩型矿体具有相同的成矿物质来源,为同一流体体系演化的产物。新桥矿区岩相学的研究结果和Fe同位素组成特征均表明,新桥层状硫化物矿床不是海西期喷流沉积成矿作用的产物,而是燕山期热液成矿作用的产物,为一个典型的热液成因矿床。     

Organic and inorganic geochemistry of Ljubija siderite deposits,NW Bosnia and Herzegovina

The Ljubija siderite deposits, hosted by a Carboniferous sedimentary complex within the Inner Dinarides, occur as stratabound replacement-type ore bodies in limestone blocks and as siderite–sulfides veins in shale. Three principal types of ore textures have been recognized including massive dark siderite and ankerite, siderite with zebra texture, and siderite veins. The ore and host rocks have been investigated by a combination of inorganic (major, trace, and rare earth element concentrations), organic (characterization of hydrocarbons including biomarkers), and stable isotope geochemical methods (isotope ratios of carbonates, sulfides, sulfates, kerogen, and individual hydrocarbons). New results indicate a marine origin of the host carbonates and a hydrothermal–metasomatic origin of the Fe mineralization. The differences in ore textures (e.g., massive siderite, zebra siderite) are attributed to physicochemical variations (e.g., changes in acidity, temperature, and/or salinity) of the mineralizing fluids and to the succession and intensity of replacement of host limestone. Vein siderite was formed by precipitation from hydrothermal fluids in the late stage of mineralization. The equilibrium fractionation of stable isotopes reveals higher formation temperatures for zebra siderites (around 245°C) then for siderite vein (around 185°C). Sulfur isotope ratios suggest Permian seawater or Permian evaporites as the main sulfur source. Fluid inclusion composition confirms a contribution of the Permian seawater to the mineralizing fluids and accord with a Permian mineralization age. Organic geochemistry data reflect mixing of hydrocarbons at the ore site and support the hydrothermal–metasomatic origin of the Ljubija iron deposits.     

Lithogeochemical halos and geochemical vectors to stratiform sediment hosted Zn–Pb–Ag deposits, 1. Lady Loretta Deposit, Queensland

Stratiform sediment hosted Zn–Pb–Ag deposits, often referred to as SEDEX deposits, represent an economically important class of ore, that have received relatively little attention in terms of defining lithochemical halos and geochemical vectors useful to exploration. This study concentrates on the Lady Loretta deposit which is a typical example of the class of Proterozoic SEDEX deposits in northern Australia. We examined the major and trace element chemistry of carbonate-bearing sediments surrounding the deposit and defined a series of halos which extend for several hundred metres across strike and up to 1.5 km along strike. The stratiform ore lens is surrounded by an inner sideritic halo [Carr, G.R., 1984. Primary geochemical and mineralogical dispersion in the vicinity of the Lady Loretta Zn–Pb–Ag deposit, North Queensland. J. Geochem. Expl. 22, 217–238], followed by an outer ankerite/ferroan dolomite halo which merges with low iron dolomitic sediments representative of the regional background compositions. Carbonate within the inner siderite halo varies in composition from siderite to pistomesite (Fe_0.6Mg_0.4CO₃), whereas carbonate in the outer ankerite halo varies from ferroan dolomite to ankerite (Ca_0.5Mg_0.3Fe_0.2CO₃). Element dispersion around the stratiform ore lens is variable with Pb, Cu, Ba and Sr showing very little dispersion (<50 m across strike), Zn and Fe showing moderate dispersion (<100 m) and Mn and Tl showing broad dispersion (<200 m). Within the siderite halo Cu, Mg and Na show marked depletion compared to the surrounding sediments. The magnitude of element dispersion and change in carbonate chemistry around the Lady Loretta orebody has enabled the development of three geochemical vectors applicable to exploration. Whole rock analyses are used to calculate the three vector quantities as follows: (1) SEDEX metal index = Zn + 100Pb + 100Tl; (2) SEDEX alteration index = (FeO + 10MnO)100/(FeO + 10MnO + MgO); (3) manganese content of dolomite: MnO_d = (MnO × 30.41)/CaO. All three vectors increase to ore both across strike and along strike. The manganese content of dolomite (MnO_d) exhibits the most systematic pattern increasing from background values of about 0.2 wt% to a maximum of around 0.6 wt% at the boundary between the ankerite and siderite halos. Siderite within the inner halo contains considerably more Mn with MnO values of 0.4 to 4.0 wt%. It is suggested here that the basket of indices defined at Lady Loretta (Zn, Tl, metal index, alteration index, MnO_d and MnO_s) is applicable in the exploration for stratiform Zn–Pb–Ag deposits in dolomite-rich sedimentary basins generally. The indices defined can firstly assist in the identification of sedimentary units favourable for SEDEX mineralisation, and secondly provide vectors along these units to ore. The alteration index and MnO_d, however, should only be used for exploration dolomitic sequences; they are not recommended for exploration in clastic sequences devoid of carbonates.     

山西袁家村矿区前寒武纪铁矿的形成条件

山西省吕梁山地区早元古宙袁家村铁矿以变质程度浅、地层剖面完整和地质构造简单为特征。厚约1200m 的袁家村组含铁岩系可以分成三个段,它们分别代表了三个沉积-成矿旋回。其中每一个旋回都是以粗碎屑岩开始,经过粉砂岩和泥质岩逐渐过渡为较纯的胶体化学沉积物即硅质岩。矿区出现的铁矿物相沿剖面自下而上依次为黄铁矿、菱铁矿、铁硅酸盐(包括铁绿泥石、铁滑石和黑硬绿泥石)、磁铁矿和赤铁矿。这些铁矿物相是沉积阶段、成岩阶段至初级变质阶段的产物。它们在地层剖面上的空间分布,反映各旋回铁矿物相的形成环境,在时间上自早至晚,空间上自下而上,其氧逸度逐渐增高。控制铁矿物相类型和其中铁价态形式的主要因素,是沉积时泥砂质碎屑组分和铁硅质胶体化学组分的性质和相对比例,以及其中有机质的存在与否及其多寡。     

运用高分遥感技术圈定西昆仑黑恰铁多金属矿化带

为了在西昆仑地区圈定黑恰铁多金属矿化带,主要运用高分遥感解译和矿化遥感异常信息增强与提取技术,配合适量的野外调查验证及采样测试工作,建立遥感综合找矿模型,为后续区域地质矿产工作规划部署和矿产勘查提供依据。调查结果表明,在黑恰一带圈定了1条找矿潜力巨大的含铜铅锌的菱铁-赤铁矿化带,延伸长度约60 km,宽度200~500 m。矿化带内含多个铁多金属矿化体。矿化体位于温泉沟群d段偏顶部碎屑岩向碳酸盐岩的过渡部位,呈层状、似层状、透镜状产出,产状一般为40°~50°∠68°~81°,与区域地层产状一致。单矿化体长度数百~9 500余m,地表出露厚度2~50 m,一般厚约15 m。地表矿石矿物以赤铁矿和褐铁矿为主,次为镜铁矿,含少量菱铁矿。铁矿化体顶板碎裂化的碳酸盐岩中普遍见Pb-Zn-Cu矿化,部分铁矿化体上部也可见Pb-Zn(少量Cu)矿化。高分遥感技术在西昆仑地区矿产地质综合调查中作用显著,可为实现找矿工作的快速突破创造条件,并为高分遥感技术在相同或类似地区开展找矿工作提供依据和借鉴。     

Geochemistry and Metallogeny of Phosphorus in the Russian Platform during the Jurassic–Cretaceous

The composition and metallogeny of igneous rocks and relevant weathering crusts of Jurassic–Cretaceous provenances of the Russian Platform are considered. It is shown that the association of metals that accumulated in the process of weathering and erosion of ancient substratum includes P, Fe, Ti, V, and Cr. This process is reflected in the formation of nodular phosphorites, Ti and Zr placers, and iron ore deposits in the Jurassic–Cretaceous seas of the platform.     

Diagenesis of Carbonate and Siderite Deposits of the Lower Riphean Bakal Formation,the Southern Urals: Sr Isotopic Characteristics and Pb-Pb Age

The Rb-Sr and U-Pb systematics were studied for carbonate rocks of the Lower Riphean Bakal Formation of the southern Urals and related siderite ores of the Bakal iron deposit. The least-altered limestones taken at a significant distance from the Bakal ore field satisfy the strict geochemical criteria of retentivity: Mn/Sr < 0.2, Fe/Sr < 0.5, and ⁸⁷Sr/⁸⁶Sr (difference between the measured ⁸⁷Sr/⁸⁶Sr values in secondary and primary carbonate phases) < 0.001. The least-altered carbonate phases were extracted by the stepwise dissolution in 0.5 N HBr. The Pb-Pb date of limestones (1430 ± 30 Ma) defines the age of early diagenesis of carbonate sediments of the Bakal Formation. The ⁸⁷Sr/⁸⁶Sr ratio in the sedimentary environment of the Bakal carbonates (0.70457–0.70481) yields isotopic signature for the Early Riphean seawater. The Pb-Pb age of metasomatic siderites (1010 ± 100 Ma), which formed at the end of the main ore formation stage and did not undergo late epigenesis, corresponds to the final phases of the Grenville tectonogenesis. Siderites of the main ore formation stage are confined to central parts of the thickest carbonate units and have high ratios of ⁸⁷Sr/⁸⁶Sr (0.73482–0.73876) and ²⁰⁸Pb/²⁰⁴Pb (41.4–42.9). Iron-bearing solutions formed during the diagenesis of mainly Lower Riphean clayey rocks and migrated along low-density zones and faults. The solutions discharged at the interformational unconformity between the Bakal and Zigalga formations. At the contact with shales, carbonate rocks and siderites experienced the later epigenetic dolomitization (partial desideritization) caused by the circulation of solutions enriched in radiogenic ⁸⁷Sr and low-radiogenic ²⁰⁶Pb. This dolomitization occurred simultaneously with the Cadomian tectonothermal activation of the region.__________Translated from Litologiya i Poleznye Iskopaemye, No. 3, 2005, pp. 227–249.Original Russian Text Copyright © 2005 by Kuznetsov, Krupenin, Ovchinnikova, Gorokhov, Maslov, Kaurova, Ellmies.     

吉林省小栗子铁矿地质特征及成因探讨

小栗子铁矿是矿体赋存一定层位;矿体与围岩整合接触;围岩蚀变微弱或无蚀变;组成矿石矿物的成分简单;铁矿石是在胶体溶液中化学沉积形成;铁矿石是由菱铁矿、赤铁矿受后期变质、迭加改造作用的中元古时期形成的沉积变质矿床,即＂大栗子式铁矿＂。     

Problems of Iron and Phosphorus Geochemistry in the Precambrian

The localization of economic sedimentary iron ore and phosphorite resources is discussed in comparative aspects. It is shown that the major economic resources of iron ore are hosted in Precambrian rocks, whereas the phosphorites are related to Upper Phanerozoic. High-temperature hydrothermal solutions served as an important source of iron for jaspilite ores. The low P₂O₅content therein indicates that the phosphorus deposition was only weakly related to the hydrothermal activity. Thus, the hydrothermal origin of phosphorite is denied from the geochemical standpoint.     

Ore-Clastic Olistostromes, Ore Clasts, and Allochthonous Antimony–Mercury Deposits in the Alay Range, Southern Tien Shan

Based on the detailed study of outcrops, two generations of ore clasts were recognized in clastic haloes around allochthonous antimony–mercury deposits: (1) early generation composed of in situ fragments of older autochthonous deposits (ore clasts) and (2) late generation of fragments related to the destruction of ore-bearing allochthons and found as exotic inclusions in flysch and olistostromes. Ore clasts reside in the terrigenous (pre-flysch) sequence that makes up the upper part of terrigenous–carbonate nappes and olistoplaques in the lower flysch–olistostrome sequence. Thus, they belong to allochthonous units. The terrigenous sequence differs from the younger flysch sediments by a relatively small thickness, predominantly clayey composition, and absence of rhythmic bedding and large erratic blocks. It is also characterized by the synsedimentary volcanic activity with the eruption of intermediate and acid igneous rocks, silicification, and ore mineralization in the lower part of the sequence, the maximal mineralization being confined to the boundary with underlying limestones. Relative to the terrigenous sequence the flysch–olistostrome sequence, which hosts ore-bearing allochthons, is distinguished by the primary attitude, greater abundance of ore clasts, and higher extent of ore disintegration. Some genetic features of autochthonous and allochtonous jasperoid deposits are considered. Their differences in age, host environment, formation depth, vertical extent of ore deposition, and zoning are also outlined.     

Pyritic shales and microbial mats: Significant factors in the genesis of stratiform Pb-Zn deposits of the Proterozoic?

Extensive horizons of pyritic shale occur in Mid-Proterozoic sediments of the eastern Belt basin, Montana, U.S.A. These pyritic shales are of striped appearance. Laminated pyrite beds alternate with nonpyritic shale beds. Laminated pyrite beds have wavycrinkly internal laminae and are interpreted as mineralized microbial mats. Pyrite is essentially the only sulfide mineral in these shales. Pyritic shale horizons occur along the basin margins, and it is feasible that colloidal iron was introduced by rivers into basin marginal lagoons and then incorporated into microbial mats and reduced to pyrite. The pyritic shales in the Newland Formation show great similarity to those that host the Pb-Zn deposits of Mt. Isa and McArthur River. It is suggested that pyritic shales of this kind are relatively common in Mid-Proterozoic shales, and that the processes that led to the occasional formation of Pb-Zn ore bodies in these shales are not related to those that formed the pyritic shales themselves.     

Sulfide geochemistry and genesis of Chouichia and Ain el Bey copper deposits in northwestern Tunisia

The Chouichia and Ain el Bey copper veins that occur in the Eastern Atlas fold belt in northwestern Tunisia, are hosted in Upper Cretaceous-Paleogene sedimentary sequences in a regional transcurrent shear zone. Paragenetic assemblages were formed during four distinct stages all of which are separated by fracturing and brecciation: Stage 1 consists of low temperature siderite (160–180 °C) formation in association with pyrite, including framboidal pyrite and marcasite. Stage 2 includes pseudomorphing of marcasite by As-rich pyrite and arsenopyrite, and formation of chalcopyrite at higher temperatures (200–300 °C) from S-rich, Fe-Cu-bearing fluids; As contents in individual pyrite and arsenopyrite crystals increase markedly in the rims relative to the centers, thus indicating non-equilibrium conditions. Stage 3 involves fracturing and brecciation predating deposition of enargite, luzonite and tennantite at Ain el Bey, and famatinite and tetrahedrite at Chouichia, from As-Sb-Bi-bearing oreforming fluids; tennantite-tetrahedrite series exhibit iron and copper-excess replacements in tetrahedral sites interrelated with Cu-Fe interactions (electron transfer). In Stage 4 fracturing was followed by calcite formation in voids. Comprehensive data was obtained from scanning electron microprobe (SEM) and microprobe chemical analyses of minerals, geothermometry using sulfur isotopes, As contents in arsenopyrite crystals and fluid inclusions in siderite and calcite, support an input of magmatic hydrothermal ore-forming fluids, although contamination by sedimentary sulfur were also identified.     

庐枞盆地龙桥铁矿床中菱铁矿的地质特征和成因意义

龙桥铁矿床是庐枞火山岩盆地中的一个大型的铁矿床,多年来对其矿床成因的认识存在较大的争论.文章在野外地质研究工作的基础上,通过对矿床中菱铁矿的岩矿分析鉴定和电子探针测试,确定了矿床纹层状矿石中的菱铁矿为沉积成因.通过对菱铁矿的产出特征分析,并结合龙桥铁矿床的部分地质地球化学研究成果,认为在该矿床形成过程中,早期沉积形成了纹层状的菱铁矿层,在燕山期的岩浆热事件中,部分沉积菱铁矿被交代形成了磁铁矿和具有残余骸晶结构等一系列矿石交代组构特征的矿物.纹层状矿石既具有沉积特征,也具有热液改造特征,证实了矿床的形成存在早期(三叠纪)的沉积成矿(菱铁矿)作用和晚期(燕山期)的热液成矿(磁铁矿)作用.菱铁矿的研究为进一步确定龙桥铁矿床的成因提供了新的佐证.     

Iron isotope fractionation during hydrothermal ore deposition and alteration

Iron isotopes fractionate during hydrothermal processes. Therefore, the Fe isotope composition of ore-forming minerals characterizes either iron sources or fluid histories. The former potentially serves to distinguish between sedimentary, magmatic or metamorphic iron sources, and the latter allows the reconstruction of precipitation and redox processes. These processes take place during ore formation or alteration. The aim of this contribution is to investigate the suitability of this new isotope method as a probe of ore-related processes. For this purpose 51 samples of iron ores and iron mineral separates from the Schwarzwald region, southwest Germany, were analyzed for their iron isotope composition using multicollector ICP-MS. Further, the ore-forming and ore-altering processes were quantitatively modeled using reaction path calculations. The Schwarzwald mining district hosts mineralizations that formed discontinuously over almost 300 Ma of hydrothermal activity. Primary hematite, siderite and sulfides formed from mixing of meteoric fluids with deeper crustal brines. Later, these minerals were partly dissolved and oxidized, and secondary hematite, goethite and iron arsenates were precipitated. Two types of alteration products formed: (1) primary and high-temperature secondary Fe minerals formed between 120 and 300 °C, and (2) low-temperature secondary Fe minerals formed under supergene conditions (<100 °C). Measured iron isotope compositions are variable and cover a range in δ⁵⁶Fe between −2.3‰ and +1.3‰. Primary hematite (δ⁵⁶Fe: −0.5‰ to +0.5‰) precipitated by mixing oxidizing surface waters with a hydrothermal fluid that contained moderately light Fe (δ⁵⁶Fe: −0.5‰) leached from the crystalline basement. Occasional input of CO₂-rich waters resulted in precipitation of isotopically light siderite (δ⁵⁶Fe: −1.4 to −0.7‰). The difference between hematite and siderite is compatible with published Fe isotope fractionation factors. The observed range in isotopic compositions can be accounted for by variable fractions of Fe precipitating from the fluid. Therefore, both fluid processes and mass balance can be inferred from Fe isotopes. Supergene weathering of siderite by oxidizing surface waters led to replacement of isotopically light primary siderite by similarly light secondary hematite and goethite, respectively. Because this replacement entails quantitative transfer of iron from precursor mineral to product, no significant isotope fractionation is produced. Hence, Fe isotopes potentially serve to identify precursors in ore alteration products. Goethites from oolitic sedimentary iron ores were also analyzed. Their compositional range appears to indicate oxidative precipitation from relatively uniform Fe dissolved in coastal water. This comprehensive iron isotope study illustrates the potential of the new technique in deciphering ore formation and alteration processes. Isotope ratios are strongly dependent on and highly characteristic of fluid and precipitation histories. Therefore, they are less suitable to provide information on Fe sources. However, it will be possible to unravel the physico-chemical processes leading to the formation, dissolution and redeposition of ores in great detail.     

History of the Formation of the Tsentral'noe Titanium–Zirconium Sand Deposit in the European Part of Russia

Based on the study of the Tsentral'noe deposit, specific features of the formation of mineral assemblages of complex titanium–zirconium placers are considered. The placers formed during the multiple redeposition of clastogenic minerals from source rocks and younger sedimentary rocks (intermediate collectors of titanium–zirconium minerals). The location of erosion and sedimentation zones significantly varied in the Phanerozoic in the adjacent region, resulting in the development of intricate relationships between different-aged terrigenous rocks (possible intermediate collectors) that provided the formation of new mineral assemblages of clastogenic ore minerals. In addition, erosional processes during the continental evolution of the study region could promote the exposure of more ancient rock complexes, the local washout of crystalline basement rocks, and the delivery of ore minerals from the latter rocks to the coastal zone of sedimentary basins. The aim of this communication is to attract the attention of researchers to the issue of the formation of mineral assemblages of complex placers of heavy minerals with similar hydraulic grain dimension and migration capacity for concentration in a rather narrow grain size range. Such mineral assemblages only slightly inherit the primary compositional features of provenances and primarily reflect changes in the sedimentation environment.     

繁昌桃冲铁矿成因探讨

The problems of the formation conditions for stratiform skarns and the genesis of the Taochong iron deposits are dealt with in this paper. Following is a summary of this discussion: 1. Stratiform skarns in this area occur in carbonate rocks of the Upper and Middle Carboniferous Period and the lower part of the Permian Qixia Group. No outcropping or concealed igneous bodies have ever been found, let alone any indications of an igneous contact zone or a corresponding zonality from "dry" skarn to "wet" skarn. The mineral facies and zonation of the skarns depend predominantly on the properties of the initial host rocks, and the development of skarns seems to have had much to do with chemical potential of silicon in these host rocks. As a result of the reaction of iron-bearing carbonates with siliceous materials in the rocks, iron-bearing silicates were formed, which in turn were transformed by pneumato-hydrothermal processes of the later stage. The stratiform skarns of this area, therefore, probably fall into the category of stratabound skarns subjected to transformation of thermometamorphism. 2. The iron deposits bear undisputable stratabound characteristics. The positions of ore-bearing beds and the petrological features as well as the mineral associations all point to a sedimentary ore-forming process of iron-carbonate (siderite). The presumption of siderite ore source is supported by the following facts: (l) Remnants of sedimentary siderite which survived the metamorphism have recently been observed in magnetite ore from neighbouring Xinqiao mining area. Siderite can have as many as 12.07% Fe⁺⁺ and, after corrosion, shows oolitic texture. (2) The ore is mainly of calcite/ dolomite- magnetite type. Mineral associations are quite simple and sulfides are rarely seen. (3) A comparison of the analytical data suggests that the content of organic carbon in iron ore decreases due to oxidation caused by metamorphism but is still higher than that in magnetite of contact- metasomatic skarn. (4) The paleogeographic reconstruction shows that this area was once an ancient underwater uplift favorable for the precipitation of iron carbonates. After its formation, the siderate bed underwent thermodynamic metamorphism and was hence decomposed into magnetite, which was then subjected to the superimposed transformation by subsequent hydrothermal fluids, leading to the partial activation and migration of iron matter and thus the formation of such ore as hematite (specularite) at shallow depth of the Changlongshan mining area. In brief, this deposit has a complex genesis: it experienced sedimentation, thermal metamorphism and transformation by hydrothermal fluids.     

鲁西地区绿岩带型金矿及其矿源层探讨

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繁昌桃冲铁矿成因探讨

桃冲铁矿,开采历史悠久,由于其品位富,以平炉富矿为主要矿石类型,受到了重视。有关矿床的成因也一直被人们所注意。自三十年代提出火成接触变质——热液成因的观点以来(谢家荣、程裕淇1935),人们习惯于将矿床划归于矽卡岩型。作者通过野外调查和初步研究之后,对本区铁矿的成因产生了疑问。本文就现有资料的分析,对层状矽卡岩的形成条件和铁矿的成因,做如下讨论。