长江中下游成矿带伴生钴资源现状及综合利用潜力评价

钴是中国极度短缺的关键矿产资源,我国矿床中报道的钴资源量大部分以伴生形式产出,因此估算伴生钴资源量及评价其综合利用前景十分必要。长江中下游成矿带铁矿床、铜矿床及硫铁矿床中普遍伴生钴,但不同类型矿床中钴资源特征及差异、钴资源量及可利用性评价等研究尚未开展。目前大部分矿山伴生钴综合利用水平较低,钴资源浪费严重。本文通过全面收集整理近年来长江中下游成矿带相关研究资料,系统总结了成矿带不同类型矿床中钴的赋存状态,阐明钴在各类矿床中的富集特征,并估算了伴生钴资源量,评价了伴生钴的可利用性。研究结果表明,长江中下游成矿带铁矿床和硫铁矿床中主要载钴矿物为黄铁矿,少量为磁黄铁矿、磁铁矿等;铜矿床中载钴矿物以黄铁矿、黄铜矿为主,少量为磁黄铁矿、斑铜矿等;独立钴矿物在各类矿床中均有报道,主要有辉砷钴矿、硫铜钴矿、铁硫砷钴矿、硫镍钴矿、辉钴矿、斜方砷钴矿等。钴在铁、铜和硫铁矿床中发生了不同程度富集,其中矽卡岩型铁矿床中钴较为富集,总体达到了伴生钴边界品位;矽卡岩型铜矿床中的钴多数接近或达到伴生钴边界品位,少数未达到伴生钴边界品位;玢岩型铁矿床、斑岩型铜矿床、矽卡岩型和玢岩型硫铁矿床中钴的富集程度低,普遍未达...     

宁芜玢岩铁矿中伴生磷灰石矿的地质特征和应用前景

宁芜玢岩铁矿中普遍伴生磷灰石，一般含Ｐ２Ｏ５ ０．９９％－２．５％，折合Ｐ２Ｏ５＝３０％的标矿为小一中型规模。本文研究了宁芜地层、火山岩及各类型铁矿伴生的磷矿地质特征、矿物学和形成条件，以期引起重视。在缺磷地区尤应综合利用，提高社会经济效益。     

贵州织金磷矿床中离子吸附型稀土的存在及初步定量

近年来研究表明贵州织金磷块岩矿床中伴生丰富的稀土主要以类质同象形式存在,其主要依据为稀土总量与磷含量的正相关性,而对独立稀土矿物与离子吸附型稀土两种赋存状态的认识目前仍然不清楚。本文通过利用电感耦合等离子体质谱(ICP-MS)稀土元素全分析、磷钼酸喹啉重量法磷分析、岩矿鉴定与实验室选矿试验等方法对该矿床中伴生稀土的赋存规律进行了研究。岩矿鉴定表明矿石中主要矿物成分为胶磷矿并含少量黏土矿物,但未发现独立的稀土矿物;磷与稀土全分析显示稀土总量及各分量都与磷含量呈正相关,从而验证并进一步表明了稀土主要以类质同象形式存在于胶磷矿中。通过研究原矿经选别后稀土与磷在精矿、尾矿和选液(尾矿水)中的分配对比及两者的含量关系来探讨稀土的赋存规律,结果显示磷仅分配于精矿和尾矿中未发生损失,而11.98%的稀土在强电解质硫酸盐的作用下从原矿中解离出来进入了选液,推断这部分稀土在原矿中未进入矿物晶格,而是呈离子态吸附于矿物表面,初步认为漫长时限与潮湿条件下的充分风化作用以及胶磷矿与黏土矿物所充当的吸附载体发挥了作用,表明织金磷矿中稀土总量的11.98%以离子吸附状态存在。综合各分析结果,织金磷矿伴生稀土各赋存状态中类质同象占主导,未发现独立稀土矿物,而离子吸附型稀土占一定的比例,故将稀土的离子吸附形式列为仅次于类质同象的第二大赋存状态。     

辽西勿兰乌苏磷矿床地质特征及控矿因素

勿兰乌苏磷矿是辽宁省西部重要的磷矿床之一,资源储量达到大型规模,同时伴生有益组分（磁铁矿）.磷矿体赋存于新太古界小塔子沟岩组,控矿因素主要为绿岩型含磷磁铁建造.矿石矿物组合为磷灰石+磁铁矿+钛磁铁矿+角闪石+黑云母+斜长石.磷灰石含量与铁钛锰等暗色组分含量呈正相关,显示了磷的亲铁性.矿床成因属于变质型磷灰石矿床.     

应用电子探针-扫描电镜研究陕西华阳川铀稀有多金属矿床稀土矿物特征

陕西华阳川铀稀有多金属矿床伴生大量的稀土资源,其矿石类型独特、组分复杂,系统的稀土矿物学工作将揭示矿石主要稀土矿物类型、稀土元素赋存状态,进而对矿床开发中稀土元素综合利用及选冶技术提供重要参考.本文在岩相学基础上,利用电子探针、扫描电镜对陕西华阳川铀稀有多金属矿床矿石中的稀土独立矿物与含稀土矿物进行系统研究,在矿石中发...     

邹家山铀矿床伴生重稀土元素的赋存特征

初步研究发现,相山矿田邹家山矿床中伴生有较高的重稀土元素,回收这些珍稀的资源和探索其成因具有重要的意义,而查明这些伴生稀土在铀矿床中的赋存特征是前期基础性工作。为此本文采用电子探针和激光剥蚀电感耦合等离子体质谱分析了邹家山铀矿床中稀土元素的赋存状态。结果显示：该矿床稀土矿物主要为独居石、氟碳钙铈矿和磷钇矿;独居石、氟碳钙铈矿的LREE/HREE>1,为轻稀土富集型;而磷钇矿的LREE/HREE<1,为重稀土富集型。沥青铀矿、钛铀矿、铀钍石、铀石、钍石、锆石等铀钍矿物的稀土特征为重稀土富集型;铀钍矿物稀土总量（∑REE+Y）较高,为（3 805.78~65 307.00）×10^-6,LREE/HREE<1,为0.01~0.80,平均为0.29。其他伴生矿物磷灰石、钾长石为轻稀土富集型,萤石为轻、重稀土富集型两类都有,而伊利石、黄铁矿的轻重稀土无明显相对富集。重稀土在磷钇矿和铀钍矿物中以类质同象形式存在,少量赋存于伴生矿物。     

宁芜、庐枞火山岩地区几种表生磷酸盐矿物特征及形成机理

宁芜、庐枞火山岩地区发育有“玢岩”式各种类型的铁矿床。在其氧化带中发现有蓝铁矿、绿松石和银星石等磷酸盐矿物。研究认为它们是磷灰石风化作用形成的表生矿物。     

山东莱芜垂阳矽卡岩型铁矿尾矿中关键金属钴综合利用评价探讨

钴是高温合金、电池材料、防腐材料、磁性材料等重要原料,广泛应用于航空航天、电子电器、机械制造、汽车、化工农业、陶瓷等领域,在国民经济和社会发展中具有特殊的意义。特别是从移动电子设备,到新能源汽车的动力电池,再到电网储能,钴作为锂电池正极材料——钴酸锂的重要组成,都是不可或缺。因此,钴被世界上众多国家列为21世纪重要的关键战略资源(Gulley et al., 2018)。现今我国是世界上最大的钴资源进口国(95%依靠进口)和消费国(US Geological Survey, 2018),而且钴资源紧缺,保障程度低(蒋少涌等,2019;许德如等,2019)。因此,在复杂的国际政治和经济形势下,摸清我国钴资源的家底,增强我国钴矿资源供应保障程度,对我国国民经济发展和国家安全保障具有重要的战略意义。我国钴矿床类型多样,包括岩浆铜镍硫化物型、红土风化型、沉积砂岩型、热液型(如沉积喷流型、矽卡岩型、斑岩型、IOCG型等)(王辉等,2019;许德如等,2019;卢宜冠等,2020)。然而,与世界上钴矿资源相比,我国钴矿规模小、品位低,大部分钴矿为伴生矿,钴多作为副产品回收利用,主要伴生铜、镍金属产出,其次伴生铜铁矿床。其中,矽卡岩型矿床是我国伴生钴矿的一种重要类型,富钴矽卡岩矿床主要发育在东昆仑地区、长江中下游和冈底斯地区。目前,关键金属元素在自然界的矿物和岩石中赋存状态研究已广泛开展,但在矿山尾矿中的赋存状态和可回收利用性研究则相对薄弱。基于山东省新一轮找矿突破战略行动及鲁西地区矽卡岩型铁矿尾矿综合利用程度低等背景,为有效发挥尾矿二次资源的作用,摸清尾矿中伴生的矿产资源的可利用性,本次选取山东省莱芜垂阳铁矿床开展了尾矿中伴生矿产资源的综合利用评价工作,大致查明垂阳铁矿尾矿中可利用伴生资源类型、赋存状态及推荐选矿工艺。通过铁矿尾矿中伴生矿产资源综合利用评价工作,对提高山东矽卡岩型铁矿床中矿产资源综合利用水平,提升战略性矿产资源安全保障能力,助力山东省新一轮找矿突破战略行动具有重要意义。     

安徽庐枞盆地泥河玢岩型铁矿床地质-原生晕地球化学找矿模型

开展长江中下游地区玢岩型铁矿床轴向原生晕地球化学分析及建模,可弥补地球物理勘探结果的多解性及探测精度的局限性,对定位和评价深部盲矿体具有至关重要的作用。文章在以往研究的基础上,开展庐枞盆地泥河玢岩型铁矿床钻孔原生晕的研究工作,采用多元统计分析方法,查明了主要成矿指示元素在不同地质体中的富集和亏损,确定了磁铁矿、硫铁矿和硬石膏矿体的矿中、近矿及远矿指示元素组合,结合矿床成因模型,建立了泥河玢岩型铁矿床地质-原生晕地球化学找矿模型,通过罗河和小包庄玢岩型铁矿床的佐证,认为该模型可以应用于长江中下游成矿带玢岩型铁矿床的勘探工作中。     

宁芜盆地陶村铁矿床磷灰石的LA-ICP-MS研究

宁芜盆地是长江中下游成矿带中的重要矿集区,磷灰石是该区各矿床中的标志性矿物.本文以宁芜玢岩铁矿典型代表的陶村铁矿床为研究对象,利用激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)微区分析新技术和电子探针分析对该矿床中辉石闪长玢岩中的磷灰石(Ap-I)、浸染状磁铁矿矿石中的磷灰石(Ap-D)和脉状磁铁矿矿石中的磷灰石(...     

Implication of Apatite and Anhydrite for Formation of an Iron‐Oxide‐Apatite (IOA) Rare Earth Element Prospect,Benjamin River,Canada

The Benjamin River apatite prospect in northern New Brunswick, Canada, is hosted by the Late Silurian Dickie Brook plutonic complex, which is made up of intrusive units represented by monzogranite, diorite and gabbro. The IOA ores, composed mainly of apatite, augite, and magnetite at Benjamin River form pegmatitic pods and lenses in the host igneous rocks, the largest of which is 100 m long and 10–20 m wide in the diorite and gabbro units. In this study, 28 IOA ore and rock samples were collected from the diorite and gabbro units. Mineralogical observations show that the apatite–augite–magnetite ores are variable in the amounts of apatite, augite, and magnetite and are associated with minor amounts of epidote‐group minerals (allanite, REE‐rich epidote and epidte) and trace amounts of albite, titanite, ilmenite, titanomagnetite, pyrite, chlorite, calcite, and quartz. Apatite and augite grains contain small anhydrite inclusions. This suggests that the magma that crystallized apatite and augite had high oxygen fugacity. In back scattered electron (BSE) images, apatite grains in the ores have two zones of different appearance: (i) primary REE‐rich zone; and (ii) porous REE‐poor zone. The porous REE‐poor zones mainly appear in rims and/or inside of the apatite grains, in addition to the presence of apatite grains which totally consist of a porous REE‐poor apatite. This porous REE‐poor apatite is characterized by low REE (<0.84 wt%), Si (<0.28 wt%), and Cl (<0.17 wt%) contents. Epidote‐group minerals mainly occur in grain boundary between the porous REE‐poor apatite and augite. These indicate that REE leached from primary REE‐rich apatite crystallized as allanite and REE‐rich epidote. Magnetite in the ores often occurs as veinlets that cut apatite grains or as anhedral grains that replace a part of augite. These textures suggest that magnetite crystallized in the late stage. Pyrite veins occur in the ores, including a large amount of quartz and calcite veins. Pyrite veins mainly occur with quartz veins in augite. These textures indicate pyrite veins are the latest phase. Apatite–augite–magnetite ore, gabbro–quartz diorite and feldspar dike collected from the Benjamin River prospect contain dirty pure albite (Ab₉₈Or₂–Ab₁₀₀) under the microscope. The feldspar dikes mainly consist of dirty pure albite. Occurrences of the dirty pure albite suggest remarkable albitization (sodic alteration) of original plagioclase (An_25.3–An₆₀ in Pilote et al., 2012) associating with intrusion of monzogranite into gabbro and diorite. SO₄^2? bearing magma crystallized primary REE‐rich apatite, augite and anhydrite reacted with Fe in the sodic fluids, which result in oxidation of Fe²⁺ and release of S^2? into the sodic fluids. REE, Ca and Fe from primary REE‐rich apatite, augite and plagioclase altered by the sodic fluids were released into the fluids. Then Fe³⁺ in the sodic fluids precipitated as Fe oxides and epidote‐group minerals in apatite–augite–magnetite ores. Finally, residual S^2? in sodic fluids crystallized as latest pyrite veins. In conclusion, mineralization in Benjamin River IOA prospect are divided into four stages: (1) oxidized magmatic stage that crystallized apatite, augite and anhydrite; (2) sodic metasomatic stage accompanying alteration of magmatic minerals; (3) oxidized fluid stage (magnetite–epidote group minerals mineralization); and (4) reduced fluid stage (pyrite mineralization).     

Thorium-poor monazite and columbite-(Fe) mineralization in the Gleibat Lafhouda carbonatite and its associated iron-oxide-apatite deposit of the Ouled Dlim Massif,South Morocco

Recent exploration work in South Morocco revealed the occurrence of several carbonatite bodies, including the Paleoproterozoic Gleibat Lafhouda magnesiocarbonatite and its associated iron oxide mineralization, recognized here as iron-oxide-apatite (IOA) deposit type. The Gleibat Lafhouda intrusion is hosted by Archean gneiss and schist and not visibly associated with alkaline rocks. Metasomatized micaceous rocks occur locally at the margins of the carbonatite outcrop and were identified as glimmerite fenite type. Rare earth element (REE) and Nb mineralization is mainly linked to the associated IOA mineralization and is represented by monazite-(Ce) and columbite-(Fe) as major ore minerals. The IOA mineralization mainly consists of magnetite and hematite that usually contain large apatite crystals, quartz and some dolomite. Monazite-(Ce) is closely associated with fluorapatite and occurs as inclusions within the altered parts of apatite and along cracks or as separate phases near apatite. Monazite shows no zonation patterns and very low Th contents (<0.4 wt%), which would be beneficial for commercial extraction of the REE and which indicates monazite formation from apatite as a result of hydrothermal volatile-rich fluids. Similar monazite-apatite mineralization and chemistry also occurs at depth within the carbonatite, although the outcropping carbonatite is barren, suggesting an irregular REE ore distribution within the carbonatite body. The barren carbonatite contains some tiny unidentified secondary Nb-Ta-U phases, synchysite and monazite. Niobium mineralization is commonly represented by anhedral minerals of columbite-(Fe) which occur closely associated with magnetite-hematite and host up to 78 wt% Nb₂O₅, 7 wt% Ta₂O₅ and 1.6 wt% Sc₂O₃. This association may suggest that columbite-(Fe) precipitated by an interaction of Nb-rich fluids with pre-existing Fe-rich minerals or as pseudomorphs after pre-existing Nb minerals like pyrochlore. Our results most strongly suggest that the studied mineralization is economically important and warrants both, further research and exploration with the ultimate goal of mineral extraction.     

The Sin Quyen Cu–Fe–Au–REE deposit (northern Vietnam): composition and formation conditions

The Sin Quyen Cu–Fe–Au–REE deposit is localized in the Proterozoic deposits of the Phan Xi Pang zone, northern Vietnam. The mineralization is formed by lenticular and sheet-like bodies occurring concordantly with the host rocks. Seventeen orebodies have been recognized in the deposit, which form an ore horizon up to 140 m in total thickness, about 2 km in strike, and up to 350 m in dip. The ores are of simple mineral composition: Au-rich copper and iron sulfides (chalcopyrite, pyrite, pyrrhotite) and iron oxides (magnetite, hematite). Gold and silver are distributed unevenly in the ores: Their contents vary from hundredths and tenths of ppm to 1.8 ppm. Copper sulfide ores are the main concentrator of gold and silver. All ores are characterized by high REE contents, tens and hundreds of times exceeding the element clarkes. The highest contents have been revealed for Ce and La. Orthite is the main carrier of REE. No correlation between REE and ore elements of sulfide-oxide ores has been revealed, which points to the independent formation of the mineralization. Orebodies together with the host rocks underwent metamorphism at 500–600 to 630–685 °C and 3–7 kbar. The spatial association of the mineralization with amphibolites (metamorphosed basites) and the mineral composition of ores suggest that the Sin Quyen deposit is of Cyprian volcanogenic type.     

REE redistribution during hydrothermal alteration of ores of the Kalahari Manganese Deposit

The Kalahari Manganese Deposit (KMD) is the largest land-based manganese deposit, hosting approximately 80% of the world's known, mineable manganese resources. The deposit, located near Kuruman in the Northern Cape Province of South Africa, is one of five erosional relics of the Paleoproterozoic (ca. 2.2 Ga) Hotazel Formation, with sedimentary manganese ores occurring as up to 50 m thick beds interbedded with banded iron-formation (BIF) and hematite lutite.The study focuses on the manganese ores of the Nchwaning–Gloria mining area of the northern KMD. In this area, pronounced mineralogical and major element alteration was imparted on the sedimentary manganese ores by a structurally-controlled hydrothermal fluid flow event. Most notable effects of hydrothermal alteration are the decomposition and leaching of Ca- and Mg-carbonate, and marked residual enrichment of manganese. On the basis of mineral assemblage, grade, texture and geochemical characteristics, three ore types were distinguished in the studied sample set, classified into least altered (LA), partially altered (PA) and advanced altered (AA) types. Advanced altered ores may be further classified into five different types, based on mineral assemblages that contain hausmannite and/or braunite as significant minerals. The rare earth element (REE) geochemistry of these fundamental ore types was studied in detail, to document REE mobility during hydrothermal alteration.Total REE concentrations in LA ores were found to be very low (14–22 ppm) and remarkably uniform, within the range typically observed for BIF. Hydrothermal alteration results in residual enrichment and a much larger scatter in REE contents. A small Ce anomaly observed in the protolith remains similar in magnitude when observed in PAAS-normalised REE plots. The data define, however, a power trend in the (Ce/Ce*) vs (Pr/Pr*) diagram. Such behaviour is interpreted in terms of a conservative system that was predominantly protolith-buffered. Local remobilisation of REE during hydrothermal alteration is attributed to the dissolution of diagenetic apatite and redistribution of hydrothermal trace minerals, including neoformed apatite, monazite and cerianite.     

In-situ LA-ICP-MS trace elemental analyses of magnetite: The Bayan Obo Fe-REE-Nb deposit,North China

The Bayan Obo Fe-REE-Nb deposit in northern China is the world's largest light REE deposit, and also contains considerable amounts of iron and niobium metals. Although there are numerous studies on the REE mineralization, the origin of the Fe mineralization is not well known. Laser ablation (LA) ICP-MS is used to obtain trace elements of Fe oxides in order to better understand the process involved in the formation of magnetite and hematite associated with the formation of the giant REE deposit. There are banded, disseminated and massive Fe ores with variable amounts of magnetite and hematite at Bayan Obo. Magnetite and hematite from the same ores show similar REE patterns and have similar Mg, Ti, V, Mn, Co, Ni, Zn, Ga, Sn, and Ba contents, indicating a similar origin. Magnetite grains from the banded ores have Al + Mn and Ti + V contents similar to those of banded iron formations (BIF), whereas those from the disseminated and massive ores have Al + Mn and Ti + V contents similar to those of skarn deposits and other types of magmatic-hydrothermal deposits. Magnetite grains from the banded ores with a major gangue mineral of barite have the highest REE contents and show slight moderate REE enrichment, whereas those from other types of ores show light REE enrichment, indicating two stages of REE mineralization associated with Fe mineralization. The Bayan Obo deposit had multiple sources for Fe and REEs. It is likely that sedimentary carbonates provided original REEs and were metasomatized by REE-rich hydrothermal fluids to form the giant REE deposit.     

湖北大冶铜绿山尾矿的地球化学特征及其综合利用

对尾矿进行深入细致的研究, 认真分析其物理化学组成将为矿山环境的治理以及尾矿的综合利用提供重要的科学依据.探讨了铜绿山矽卡岩型铜铁矿床尾矿砂的矿物组合特征和地球化学特征, 初步研究了稀硫酸溶液萃取尾矿砂中有价金属元素方法的可行性.研究结果表明: 尾矿砂先后经过化学冶选和长期堆存风化, 矿物组成发生显著改变, 以粘土矿物(高岭石和伊利石)为主; 尾矿中的铜矿物以氧化铜为主, 尾矿砂中金属元素的活动性明显增强, 含量从顶部到第6层逐渐增加, 并在尾砂库的第6层强烈富集, 重金属铜具有回收利用的价值.      

Differentiation of nelsonitic magmas in the formation of the ~1.74 Ga Damiao Fe–Ti–P ore deposit, North China

The ~1.74 Ga Damiao anorthosite complex, North China, is composed of anorthosite and leuconorite with subordinate melanorite, mangerite, oxide-apatite gabbronorite, perthite noritic (i.e., jotunitic) and ferrodioritic dykes. The complex hosts abundant vein-, pod- and lens-like Fe–Ti–P ores containing variable amounts of apatite (10–60 modal%) and Fe–Ti oxides. In addition to Fe–Ti–P ores, there are also abundant Fe–Ti ores which are closely associated with Fe–Ti–P ores in the deposit. Most of Fe–Ti–P ores are dominated by Fe–Ti oxides and apatite, devoid of silicate minerals, mineralogically similar to the common nelsonites elsewhere. In contrast, Fe–Ti ores are dominated by Fe–Ti oxides with minor apatite (<5 modal %). The parental magma of these ores, estimated from olivine and apatite compositions using mineral-melt partition coefficients, has composition similar to the ferrodioritic dykes. Fe–Ti–P ores have variable Fe–Ti oxides and apatite proportions, indicating that they are cumulates. Their simple assemblage of Fe–Ti oxides and apatite and local net-texture suggest that the Fe–Ti–P ores in Damiao have formed from nelsonitic melts immiscibly separated from the ferrodioritic magma during late-stage differentiation. Fe–Ti ores are also cumulates and have mineral compositions similar to Fe–Ti–P ores. The close association between Fe–Ti and Fe–Ti–P ores indicates that the Fe–Ti ores may have also formed from the nelsonitic melts. We proposed that differentiation of nelsonitic melts accompanied by gravity settling is responsible for the formation of Fe–Ti and Fe–Ti–P ores. Such a differentiation process in nelsonitic melts is well supported by variations of Sr, Y, Th, U, REE and Eu/Eu* of apatite in Fe–Ti–P ores. Using oxides/apatite ratio of 2:1 and compositions of apatite and calculated primary oxides, we estimate the composition of the nelsonitic melt as ~52.0 wt% Fe₂O₃t, ~18.5 wt% CaO, ~14.2 wt% P₂O₅, ~8.7 wt% TiO₂, ~4.0 wt% Al₂O₃ and ~1.1 wt% MgO with minor SiO₂, K₂O, Na₂O and F. Such a nelsonitic melt is suggested to be possibly conjugated with Si-rich melts compositionally similar to the Damiao jotunitic dykes (~50 wt% SiO₂ and ~15 wt% Fe₂O₃t) which may subsequently evolve to mangeritic rocks in Damiao. Our modeling also indicates that the onset of immiscibility occurs at a time when the evolved melt has ~44 wt% SiO₂, ~21 wt% Fe₂O₃t, ~3.0 wt% TiO₂ and ~2.6 wt% P₂O₅. High oxygen fugacity and phosphorous content in magmas may play important roles in the immiscibility of nelsonitic magmas, including promoting iron enrichments and widening the two-liquid field.     

Chadormalu Kiruna-type magnetite-apatite deposit,Bafq district,Iran: Insights into hydrothermal alteration and petrogenesis from geochemical,fluid inclusion,and sulfur isotope data

The Chadormalu is one of the largest known iron deposits in the Bafq metallogenic province in the Kashmar-Kerman belt, Central Iran. The deposit is hosted in Precambrian-Cambrian igneous rocks, represented by rhyolite, rhyodacite, granite, diorite, and diabasic dikes, as well as metamorphic rocks consisting of various schists. The host rocks experienced Na (albite), calcic (actinolite), and potassic (K-feldspar and biotite) hydrothermal alteration associated with the formation of magnetite–(apatite) bodies, which are characteristic of iron oxide copper-gold (IOCG) and iron oxide-apatite (IOA) systems. Iron ores, occurring as massive-type and vein-type bodies, consist of three main generations of magnetite, including primary, secondary, and recrystallized, which are chemically different. Apatite occurs as scattered irregular veinlets in various parts of the main massive ore-body, as well as apatite-magnetite veins and disseminated apatite grains in marginal parts of the deposit and in the immediate wall rocks. Minor pyrite occurs as a late phase in the iron ores. Chemical composition of magnetite is representative of an IOA or Kiruna-type deposit, which is consistent with other evidence.Whole rock geochemical data from various host rocks confirm the occurrence of Na, Ca, and K alteration consistent with the formation of albite, actinolite, and K-feldspar, respectively. The geochemical investigation also includes the nature of calc-alkaline igneous rocks, and helps elaborating on the spatial and temporal association, and possible contribution of mafic to felsic magmas to the evolution of ore-bearing hydrothermal fluids.Fluid inclusion studies on apatites from massive- and vein-type ores show a range of homogenization temperatures from 266 to 580 °C and 208–406 °C, and salinities from 0.5 to 10.7 wt.% and 0.3–24.4 wt.% NaCl equiv., respectively. The fluid inclusion data suggest the involvement of evolving fluids, from low salinity-high temperature, to high salinity-low temperature, in the formation of the massive- and vein-type ores, respectively. The δ³⁴S values obtained for pyrite from various parts of the deposit range between +8.9 and +14.4‰ for massive ore and +18.7 to +21.5‰ for vein-type ore. A possible source of sulfur for the ³⁴S-enriched pyrite would be originated from late Precambrian-early Cambrian marine sulfate, or fluids equilibrated with evaporitic sulfates.Field observations, ore mineral and alteration assemblages, coupled with lithogeochemical, fluid inclusion, and sulfur isotopic data suggest that an evolving fluid from magmatic dominated to surficial brine-rich fluid has contributed to the formation of the Chadormalu deposit. In the first stages of mineralization, magmatic derived fluids had a dominant role in the formation of the massive-type ores, whereas a later brine with higher δ³⁴S contributed to the formation of the vein-type ores.     

Uranium–lead ages of apatite from iron oxide ores of the Bafq District,East-Central Iran

Iron oxide–apatite (IOA) deposits, often referred to as Kiruna-type iron ore deposits, are known to have formed from the Proterozoic to the Tertiary. They are commonly associated with calc–alkaline volcanic rocks and regional- to deposit-scale metasomatic alteration. In the Bafq District in east Central Iran, economic iron oxide–apatite deposits occur within felsic volcanic tuffs and volcanosedimentary sequences of Early Cambrian age. In order to constrain the age of formation of these ores and their relationship with the Early Cambrian magmatic event, we have determined the U–Pb apatite age for five occurrences in the Bafq District. In a ²⁰⁶Pb/²³⁸U vs. ²⁰⁷Pb/²³⁵U diagram, apatite free of or poor in inclusions of other minerals plots along the Concordia between 539 and 527 Ma with four out of five samples from one deposit clustering at the upper end of this range. For this deposit, we interpret this cluster to represent the age of apatite formation, whereas the spread towards younger ages may reflect either minor Pb loss or several events of IOA formation. Apatite with inclusions of monazite (±xenotime) yields disturbed systems with inclusions having developed after formation of the iron ore–apatite deposits, possibly as late as 130–140 Ma ago. Obtained apatite ages confirms that (IOA) and the apatite-rich rocks (apatites) of the Bafq district formed coevally with the Early Cambrian magmatic (-metasomatic) events.