含锡磁铁矿-矽卡岩的地球化学特征

Geological and geochemical features of tin-bearing magnetite-skarns are reviewed in this paper together with the author‘s opinion with respect to the mechanism of transportation of tin in this environment. In addition to cassiterite, the commonest mode of occurrence of tin in nature, three other occurrences are also of interest in tin-bearing magnetite-skarns: (1) Tin is present in extremely fine eassiterite as exsolution colloform in magnetite; (2) Being Found in some tin-bearing minerals such as malayaite,stokesite,nordenskioldine,Snpaigeite,Sn-lundwigite and hulsite in a variety of skarns;(3)Occurring in a numbor of skarn minerals such as garnet,pyroxene,spinel,amphibole,epidote,wollastonite and axinite,which become tinrich as a results of the substitution of Sn^4 for Fe^3 or Ti^4 rather than for Fe^2 ,Ca^2 or Si^4 ,When Mg^2 -,Fe^2 -bearing minerals and in some eases even sulfides or other mineralizer-containing minerals replace tin-bearing,Fe^3 -,Ti^4 -skarn minerals during the late stages of skarn alteration,tin in the pre-exsiting silicates may be extracted and remobilized thus contributing to the formation of the associated tindeposits.     

Newly Discovered Native Gold and Bismuth in the Cihai Iron-Cobalt Deposit, Eastern Tianshan, Northwest China

The Cihai iron-cobalt deposit is located in the southern part of the eastern Tianshan ironpolymetallic metallogenic belt. Anomalous native gold and bismuth have been newly identified in Cinan mining section of the Cihai deposit. Ore formation in the deposit can be divided into three stages based on geological and petrographical observations:(I) skarn, with the main mineral assemblage being garnet-pyroxene-magnetite;(II) retrograde alteration, forming the main iron ores and including massive magnetite, native gold, native bismuth, and cobalt-bearing minerals, with the main mineral assemblage being ilvaite-magnetite-native gold-native bismuth; and(III) quartz-calcitesulfide assemblage that contains quartz, calcite, pyrrhotite, cobaltite, and safflorite. Native gold mainly coexists with native bismuth, and they are paragenetically related. The temperature of initial skarn formation was higher than 340℃, and then subsequently decreased to ~312℃ and ~266℃. The temperature of the hydrothermal fluid during the iron ore depositional event was higher than the melting point of native bismuth(271℃), and native bismuth melt scavenged gold in the hydrothermal fluid, forming a Bi-Au melt. As the temperature decreased, the Bi-Au melt was decomposed into native gold and native bismuth. The native gold and native bismuth identified during this study can provide a scientific basis for prospecting and exploration for both gold- and bismuth-bearing deposits in the Cihai mining area. The gold mineralization in Cihai is a part of the Early Permian Cu-Ni-Au-Fe polymetallic ore-forming event, and its discovery has implications for the resource potential of other iron skarn deposits in the eastern Tianshan.     

Geological Characteristics and Zircon U‐Pb Dating of Volcanic Rocks from the Beizhan Iron Deposit in Western Tianshan Mountains,Xinjiang, NW China

The Beizhan large iron deposit located in the east part of the Awulale metallogenic belt in the western Tianshan Mountains is hosted in the Unit 2 of the Dahalajunshan Formation as lens, veinlets and stratoid, and both of the hanging wall and footwall are quartz-monzonite; the dip is to the north with thick and high-grade ore bodies downwards. Ore minerals are mainly magnetite with minor sulfides, such as pyrite, pyrrhotite, chalcopyrite and sphalerite. Skarnization is widespread around the ore bodies, and garnet, diopside, wollastonite, actinolite, epidote, uralite, tourmaline sericite and calcite are ubiquitous as gangues. Radiating outwards from the center of the ore body the deposit can be classified into skarn, calcite, serpentinite and marble zones. LA-ICP-MS zircon U-Pb dating of the rhyolite and dacite from the Dahalajunshan Formation indicates that they were formed at 301.3±0.8 Ma and 303.7±0.9 Ma, respectively, which might have been related to the continental arc magmatism during the late stage of subduction in the western Tianshan Mountains. Iron formation is genetically related with volcanic eruption during this interval. The Dahalajunshan Formation and the quartz-monzonite intrusion jointly control the distribution of ore bodies. Both ore textures and wall rock alteration indicate that the Beizhan iron deposit is probably skarn type.     

个旧某硼氟交代型矽卡岩锡矿的成矿作用

Recently, a, new type of skarn Sn ore formed bY B-F-metasomatism has been found in the central part of the Malage ore field at Gejiu, Yunnan Province, which contains 1--7% Sn. The principal Sn minerals are nordenkioeldine hydromagno-cassitcrite, hydro eassiterite, etc., accounting for about 4%. Cassiterite is rarely seen (less than 0.2%).Outward from the interior of skarns are distinguished four alteration zones. Ore solutions were rich in AL and Si in the early stage of skarnization, and became enriched in Fe, Mg, Sn, B, F, H2O, etc. in the late stage. Two episodes of hydrothermal metasomatism of B and F took place during post-skarnization, and the different alteration zones may be due to reaction between B-and F-bearing hydrothermal solutions and country reeks (calcareous carbonates). The stability of the metasomatic minerals in controlled by the volatile components μB2O3, μCO2, μF2O-1 and μF(OH)-1. It has been concluded from the discussion in terms of the system CaO-SnO2-SiO2-H2O-B2O3-CO2 Fo-1 F2 o-1 proposed by Burr (1978) and the topological diagrams on chemical composition constructed by the author that nordeuskioeldine was formed in the exhaustion of Si at about 400℃ in the skarn environment, where metallogenetic conditions are characterized by rich oxygen but poor sulfur, and high boron hut low fluorine, while hydromagno-cassiterite and hydro-cassiterite were formed at the lower temperature (about 150℃) by hydrothermal metasomatism of fluorine. In comparison with the metallogenetic conditions for adjacont inner-skarn Sn ores and other Sn ore deposits at Gejiu, the role of the characteristic elemental association Sn-B-F is emphasized in this paper.     

Major and Trace Elements of Magnetite from the Qimantag Metallogenic Belt: Insights into Evolution of Ore–forming Fluids

Magnetite, as a genetic indicator of ores, has been studied in various deposits in the world. In this paper, we present textural and compositional data of magnetite from the Qimantag metallogenic belt of the Kunlun Orogenic Belt in China, to provide a better understanding of the formation mechanism and genesis of the metallogenic belt and to shed light on analytical protocols for the in situ chemical analysis of magnetite. Magnetite samples from various occurrences, including the ore–related granitoid pluton, mineralised endoskarn and vein–type iron ores hosted in marine carbonate intruded by the pluton, were examined using scanning electron microscopy and analysed for major and trace elements using electron microprobe and laser ablation–inductively coupled plasma–mass spectrometry. The field and microscope observation reveals that early–stage magnetite from the Hutouya and Kendekeke deposits occurs as massive or banded assemblages, whereas late–stage magnetite is disseminated or scattered in the ores. Early–stage magnetite contains high contents of Ti, V, Ga, Al and low in Mg and Mn. In contrast, late–stage magnetite is high in Mg, Mn and low in Ti, V, Ga, Al. Most magnetite grains from the Qimantag metallogenic belt deposits except the Kendekeke deposit plot in the " Skarn " field in the Ca+Al+Mn vs Ti+V diagram, far from typical magmatic Fe deposits such as the Damiao and Panzhihua deposits. According to the(Mg O+Mn O)–Ti O2–Al2O3 diagram, magnetite grains from the Kaerqueka and Galingge deposits and the No.7 ore body of the Hutouya deposit show typical characteristics of skarn magnetite, whereas magnetite grains from the Kendekeke deposit and the No.2 ore body of the Hutouya deposit show continuous elemental variation from magmatic type to skarn type. This compositional contrast indicates that chemical composition of magnetite is largely controlled by the compositions of magmatic fluids and host rocks of the ores that have reacted with the fluids. Moreover, a combination of petrography and magnetite geochemistry indicates that the formation of those ore deposits in the Qimantag metallogenic belt involved a magmatic–hydrothermal process.     

Evolution of the magmatic–hydrothermal system and formation of the giant Zhuxi W–Cu deposit in South China

The Zhuxi deposit is a recently discovered W–Cu deposit located in the Jiangnan porphyry–skarn W belt in South China. The deposit has a resource of 3.44 million tonnes of WO3, making it the largest on Earth,however its origin and the evolution of its magmatic–hydrothermal system remain unclear, largely because alteration–mineralization types in this giant deposit have been less well-studied, apart from a study of the calcic skarn orebodies. The different types of mineralization can be classified into magnesian skarn, calcic skarn, and scheelite–quartz–muscovite(SQM) vein types. Field investigations and mineralogical analyses show that the magnesian skarn hosted by dolomitic limestone is characterized by garnet of the grossular–pyralspite(pyrope, almandine, and spessartine) series, diopside, serpentine,and Mg-rich chlorite. The calcic skarn hosted by limestone is characterized by garnet of the grossular–andradite series, hedenbergite, wollastonite, epidote, and Fe-rich chlorite. The SQM veins host highgrade W–Cu mineralization and have overprinted the magnesian and calcic skarn orebodies. Scheelite is intergrown with hydrous silicates in the retrograde skarn, or occurs with quartz, chalcopyrite, sulfide minerals, fluorite, and muscovite in the SQM veins.Fluid inclusion investigations of the gangue and ore minerals revealed the evolution of the ore-forming fluids, which involved:(1) melt and coexisting high–moderate-salinity, high-temperature, high-pressure(>450 ℃and >1.68 kbar), methane-bearing aqueous fluids that were trapped in prograde skarn minerals;(2) moderate–low-salinity, moderate-temperature, moderate-pressure(~210–300 ℃and ~0.64 kbar),methane-rich aqueous fluids that formed the retrograde skarn-type W orebodies;(3) low-salinity,moderate–low-temperature, moderate-pressure(~150–240 ℃and ~0.56 kbar), methane-rich aqueous fluids that formed the quartz–sulfide Cu(–W) orebodies in skarn;(4) moderate–low-salinity,moderate-temperature, low-pressure(~150–250 ℃and ~0.34 kbar) alkanes-dominated aqueous fluids in the SQM vein stage, which led to the formation of high-grade W–Cu orebodies. The S–Pb isotopic compositions of the sulfides suggest that the ore-forming materials were mainly derived from magma generated by crustal anatexis, with minor addition of a mantle component. The H–O isotopic compositions of quartz and scheelite indicate that the ore-forming fluids originated mainly from magmatic water with later addition of meteoric water. The C–O isotopic compositions of calcite indicate that the ore-forming fluid was originally derived from granitic magma, and then mixed with reduced fluid exsolved from local carbonate strata. Depressurization and resultant fluid boiling were key to precipitation of W in the retrograde skarn stage. Mixing of residual fluid with meteoric water led to a decrease in fluid salinity and Cu(–W) mineralization in the quartz–sulfide stage in skarn. The high-grade W–Cu mineralization in the SQM veins formed by multiple mechanisms, including fracturing, and fluid immiscibility, boiling, and mixing.     

Sources and Evolution of the Ore-forming Materials in the Anqing Cu-Fe Deposit in Anhui Province-Geological and S,C, O Isotopic ConstraintsEI北大核心CSCD

The Anqing Cu-Fe deposit is one of the representative large Cu-Fe deposits along the Yangtze River in Anhui province, with controversial metallogenic mechanism. Based on the ore-forming geological characteristics, this paper focus on the sulfur, carbon and oxygen isotopic compositions of the ores and surrounding rocks, and discuss the sources and evolution processes of the ore-forming materials. The Cu-Fe deposit occurs in the contact zone between the early Yanshanian Yueshan diorite and Triassic marble, with clear horizontal zonings in the skarns and ore bodies. The garnet skarn and thick massive magnetite ore body commonly occur within the external contact zone, which have clear boundaries with the surrounding rocks; whereas the diopside skarns with disseminated copper sulfide commonly occur within the internal contact zone and show gradual and transitional relations with the diorite. The δ34S values of the ores range from -6.5‰ to 10.6‰, and show a V-shaped trend from the diorite to the outer marble. This compositional variation indicates that most of the sulfur may come from magma, with involvement of some pre-Triassic clastic strata sulfur and Triassic marine sulfates in the later stage. The δ13C values of the gangue minerals range from -5.5‰ to 2.0‰, which decrease from the external contact zone to internal contact zone, indicating that the carbons of the ore-forming fluids may be mainly derived from magma, with some Triassic carbonate stratigraphic carbon involved. The marbles nearby the orebody show δ18O values lower than those of the Triassic strata, indicating that they have been remolded by the low δ18O magmatic hydrothermal fluids. The magnetite have some magma filling geological features and extremely low δ18O value, may be the result from the filling of the high temperature iron-rich fluids along the contact zone and fault. This study shows that the ore-magma filling type and hydrothermal-metasomatic type ore bodies coexist in the Anqing Fe-Cu deposit. The immiscibility between iron oxide and silicate melt occurred in magma chamber, which resulted in the formation of iron-rich fluid. The fluid migrated upward and eventually precipitated in a favorable tectonic area or contact zone, and the magnetite ore bodies were formed in the outer contact zone. By the later fluid mixing, filling metasomasis, and water-rock reaction between the differentiated hydrothermal solutions and diorite, the copper ore bodies and the copper-bearing altered diorite were formed in the internal contact zone. © 2018, Science Press. All right reserved.     

Study on Composition of Inclusions in Minerals and Simulation Experiment on Hydrothermal Metasomatic Process of the Bayan Obo Iron Deposit

On the basis of the mechanism of formation of mineral inclusions, it may be assumed that a certain relation exists between the compositions of fluid inclusions in various minerals formed at the same stage of hydrothermal activity. In order to study the genetic relationships between different minerals in the Bayan Obo iron deposit, the compositions(K~+, Na~+, Ca~+, Mg~+, F~+, Cl~+, CO_2~(2-), ΣSO_4~(2-) and pH) of inclusions in fluorite(23), hematite(13), magnetite(3), sodium pyroxene(2) and dolomite(5) from the main mine and the eastern mine were determined by using the vacuum decrepitation and leaching methods, and cluster analyses of the data on the compostions were made. The Q-mode cluster analysis indicates that some iron oxide minerals in the deposit are related to dolomite of sedimentary origin, while others are related to fluorite and sodium pyroxene--products of hydrothermal activity. The R-mode cluster analysis shows that the components of the leaching solution may be divided into two groups: one includes CO_2~(2-), Mg~(2+) and H~+(pH), which are obviously associated with dolomite; the other comprises Na~+, K~+, Ca~+, F~+, Cl~+ and SO_4~(2-), which may possibly represent the composition of hydrothermal solutions.The reaction of the Na-F-Cl solution(pH 4.72) with hematite dolomite at 300℃ and 5 × 10~7 Pa and under alternately"static and dynamic" conditions produced large amounts of hematite and fluorite and small amounts of smectite and Na(Fe) silicates, and the hematite-fluorite assemblage accords with the actual geological conditions in the deposit. From a comparison between the compositions of"static" and"dynamic" solution samples, it may be known that the flow reaction facilitates the migration of Fe, F, Ca and other components as well as Na-metasomatism(Na and Si are fixed in a solid phase).The study of the compositions of mineral inclusions and simulation experiments on hydrothermal metasomatism have provided new evidence for the hypothesis of metamorphosed-sedimentary and hydrothermal-remoulding origin of the Bayan Obo deposit, and pointed out emphatically that hydrothermal metasomatism plays an important role in the formation of the mineral deposit, particularly in the main and the east mine.     

Origin of trondhjemite and albitite at the expense of A-type granite,Aravalli orogen,India:Evidence from new metasomatic replacement fronts

The A-type Harsora-Dadikar granites in the Alwar complex of northern Aravalli orogen,NW India provide evidence for subsolidus-requilibration of feldspars.They record three new discrete stages of albitisation,producing trondhjemite and albitite sequentially at the expense of original granite.Stage-Ⅰ metasomatism deanorthised the magmatic oligoclase and transformed the grey least-albitised granite to pinkish grey microcline-oligoclase granite.Stage-II converted the latter to trondhjemite by replacement of microcline to oligoclase.Stage-Ⅲ metasomatism led to the formation of albitite/albite granite from trondhjemite,where the metasomatically formed oligoclase was replaced by albite.This stage of metasomatism resulted in nearly complete disappearance of amphibole and biotite,producing a monomineralic rock(albitite),which is consistent with Korzhinskii theory of infiltration metasomatism.The reaction fronts delineating the Stage-Ⅱ and Stage-Ⅲ are sharp and easily discernible by their prominent color differences in Harsora on the outcrop scale.Chemically,the mineral transformations during three stages are manifested by the differential gains/losses in Na,K,Ca,Rb,Ba,Sr,Fe and Mg.The formation of albite,Cl-rich marialitic scapolite and Cl-rich amphibole in the albitised granites are suggestive of Naand Cl-brines as the metasomatising fluids.The fluid-rock interactions,which can significantly transform the pristine mineralogy of granitoids,should be carefully considered to avoid any misinterpretations about their petrological history.     

Fluid Inclusion Studies of the Skarn—type Tin Mineralization at Red—A—ven,Northwest Dartmoor,England

Two principal hydrothermal events have been recognized ,which resulted in the tin-bearing skarns at Red-A-ven ,Northwest Dartmoor.Tin was enriched during both the early (occurring as tin-bearing andradite) and late hydrothermal events (mainly as malayaite stannite and cassiterite,accompanied by boron silicates and minor tungsten).Thermometric measurements of fluid inclusions in diopside,garnet,malayaite,tourmaline-quartz and axinite were carried out,suggesting that the early skarns were formed at the temperature above 600℃and the salinities ranging from 10 to 20 wt.% NaCl eq.while the late skarns at the temperatures of 350-460℃ and the salinities ranging from 30 to 50wt.% NaCl eq.The estimated minimum depths are 2856m(850 bar) for the early event and 2526m(185 bar) for the late event.The birefringence of the andradite might be related with the superimposition of late hydrothermal fluids.     

Composition, mineral assemblages, and genesis of titanite and malayaite in skarns

The composition of minerals of the titanite-malayaite series and their mineral assemblages and genesis were examined at the Bol’shoi Kan’on deposit in Magadan oblast and at other deposits. These minerals were demonstrated to be typomorphic Sn-bearing silicates in postmagmatic bimetasomatic hypabyssal calc skarns and skarnoids in tin-bearing provinces. The series of these minerals with similar crystal structures has a miscibility gap, and the minerals are characterized by notably different Sn concentrations. Moreover, titanite may contain Al, Fe, F, and OH, whose concentrations decrease in the Sn-bearing members of the series (malayaite). These silicates were formed at many deposits after the successive transforms of skarn mineral assemblages. The early assemblages include wollastonite in calcic carbonate rocks and diopside and salite in skarnoids. The latter minerals are replaced first by hedenbergite with subordinate amounts of vesuvianite and garnet first of grossular and then andradite composition. This process was syngenetic with the formation of borosilicates (danburite, axinite, and tourmaline). Ti thereby may be accommodated in grossular and Sn in Fe-bearing silicates, mostly, in andradite. Skarns often contain both titanite and malayaite, which were produced in these rocks earlier than cassiterite. The isomorphic series of these minerals has a miscibility gap. The oreforming processes ended with the crystallization of quartz, fluorite, and rare sulfides, including stannite. The late Sn-bearing minerals at some deposits are stokesite and Mg, Fe, and Ca stannates, which crystallized during malayaite replacement by newly formed calcite-quartz aggregates. The Sn-bearing sulfides are replaced by varlamoffite during supergene processes.     

湖南黄沙坪矽卡岩矿物学特征及地质意义

湘南黄沙坪多金属矿床位于南岭构造带中段北缘,属于矽卡岩型矿床。根据矽卡岩产出状态、矿物共生组合及岩相学特征,从早期到晚期可划分为矽卡岩阶段、退化蚀变阶段、早期硫化物阶段和晚期硫化物阶段。矽卡岩矿物主要为石榴石、辉石、符山石等;金属矿物主要为白钨矿、辉钼矿、磁铁矿、方铅矿、闪锌矿等。电子探针分析结果表明,石榴石为钙铝-钙铁榴石系列,从早期到晚期,石榴石具有由钙铝榴石逐渐向钙铁榴石演化的规律。且钙铁榴石普遍发育震荡环带,而环带结构可持续记录钙铁榴石物理化学条件演化的过程。同时两种石榴石中均含Sn的成分,但钙铁榴石中Sn的含量明显高于钙铝榴石。辉石为透辉石-钙铁辉石系列,而且由内接触带向外接触带,辉石中Fe和Mn的含量有逐渐升高的趋势。矽卡岩矿物学特征及矿物成分的变化表明,成矿流体至少经历了两次氧化还原性质的转变。矽卡岩矿物学特征,对W(Sn) Mo Bi等多金属的矿化具有重要的地质指示意义。     

江西朱溪铜钨多金属矿床矽卡岩矿物学特征及其地质意义

朱溪铜钨多金属矿床位于赣东北深大断裂北西侧。矿体主要产于燕山期侵入岩与碳酸盐岩接触带的矽卡岩或矽卡岩化大理岩中,代表性矽卡岩矿物有石榴子石、透辉石、透闪石、硅灰石、蛇纹石、金云母、符山石、绿泥石等。根据矿物共生组合及交代关系推断流体经历了5个阶段,分别为矽卡岩阶段、退化蚀变阶段、石英硫化物阶段、石英碳酸盐阶段和表生氧化阶段。特征矿物的电子探针分析结果表明,石榴子石主要为钙铝榴石—钙铁榴石;辉石以透辉石—钙铁辉石系列为主;角闪石属钙角闪石系列;绿泥石主要是密绿泥石和斜绿泥石。推测岩浆侵入后,在矽卡岩阶段为中酸性弱氧化条件,在退化蚀变阶段氧逸度和pH值升高,氧化物析出,随着氧逸度的又一次降低,金属硫化物沉淀。最后,通过其矿物成分特征推测该矿床金属矿化的种类。     

内蒙古黄岗锡铁矿床夕卡岩矿物学特征及其成矿指示意义

为进一步查明黄岗锡铁矿矿床成因、夕卡岩矿物成分与金属矿化类型之间的联系,利用电子探针对研究区主要夕卡岩矿物的化学成分进行了详细的分析。测试结果表明,成矿早期石榴石的端员组分以钙铁榴石为主,主成矿期石榴石的端员组分以钙铝榴石为主;辉石端员组分变化较大,主要为透辉石和钙铁辉石。石榴石和辉石的矿物组分分别为Adr28.69～96.44Grs2.00～67.38(Prp+Sps)0.67～5.69和Di11.8～94.12Hd4.08～81.28Jo1.79～20.02,其较大的成分变化特征反映出夕卡岩不是在一个完全封闭的平衡条件下形成的。角闪石大多为镁铁钙角闪石,个别属于铁角闪石,成分变化较大的原因可能是由于氧化还原条件改变导致不同程度的AlⅥSi←→(Na,K)的置换作用,属于一种固相线下的转变。角闪石中四次配位的Si、Al及六次配位的Al、Ti和A位置的阳离子数变化范围很大,可能是由于接触交代作用过程中岩浆的成分差异或结晶时的物理化学条件改变所引起的。富锰的辉石夕卡岩是岩浆流体顺层间破碎带渗滤交代形成的,富锰辉石可作为本区寻找Sn、Cu、Zn等多金属的找矿标志,外接触带夕卡岩和其附近的大理岩中是多金属成矿的有利部位。     

Geochemical characteristics of tin-bearing magnetite-skarns

Geological and geochemical characteristics of tin-bearing magnetite-skarns are reviewed in this paper, together with the author’s opinion with respect to the mechanism of transport of tin in this environment. In addition to cassiterite, the most common form of occurrence of tin in nature, three other forms of occurrence are also of interest in tin-bearing magnetite-skarns: (1) tin present in the form of fine exsolution colloidal grains of cassiterite; (2) tin found as independent tin-bearing minerals, such as malayaite, stokesite, nordenskiöldine, Sn-paigeite, Sn-ludwigite and hulsite in a variety of skarns; (3) tin occurring in the lattice of some skarn minerals, such as garnet, pyroxene, spinel, amphibole, epidote, wollastonite and axinite in the manner of ionic replacement. When Mg²⁺ and Fe²⁺ bearing minerals, in some cases even Sulfides or other mineralizer-containing minerals, replace tin-bearing Fe³⁺ and Ti⁴⁺ skarn minerals during the late stage of skarn alteration, tin in the pre-existing silicates maybe extracted and remobilized, thus contributing to the formation of associated tin deposits.     

大兴安岭南段黄岗矽卡岩型铁锡多金属矿床蚀变矿化特征及其成因

大兴安岭南段黄岗铁锡多金属矿床具有明显的蚀变-矿化特征,对于研究矽卡岩型矿床的成矿过程具有重要的意义.因此对该矿床中具有代表性的蚀变矿物以及金属矿物开展电子探针研究,结果指示研究区的热液演化经历了4个阶段:在进变质矽卡岩阶段（Ⅰ）,矿物以含有钙铁榴石GrtⅠ核的钙铝榴石GrtⅡ和钙铁辉石为主;在退变质矽卡岩阶段（Ⅱ）,矿物以富铁榴石GrtⅢ、浸染状磁铁矿以及含水矿物为代表;氧化物阶段（Ⅲ）的矿物以大量磁铁矿、锡石以及少量钙铁榴石GrtⅣ和透辉石为主;在硫化物阶段（Ⅳ）,磁铁矿逐渐被硫化物交代,最后形成毒砂、黄铁矿、黄铜矿、铁闪锌矿、浅色闪锌矿-黄铜矿-方黝锡矿固溶体、锑黝铜矿等,表明黄岗铁多金属矿床的流体来源从岩浆水、交代流体最后演化为大气降水的加入,流体成分变化复杂,流体演化具体表现为温度逐渐降低,水岩比值逐渐升高,具有还原性→氧化性→还原性等特点.      

Metallogenesis of a B-F-metasomatic skarn tin deposit,Gejiu, Yunnan Province

Recently, a new type of skarn tin ore formed by B-F-metasomatism has been found in the central part of the Malage ore field at Gejiu, Yunnan Province, which contains 1–7% Sn. The principal tin minerals are nordenskiöl dine, schoenfliesite, varlamoffite, etc., accounting for about 4%. Cassiterite is rarely seen (less than 0.2%). Outward from endoskarns are distinguished four alteration zones, ore fluids were rich in Al and Si in the early stage of skarnization, and became enriched in Fe, Mg, Sn, B, F, H₂O, etc. in the later stages. Two episodes of hydrothermal metasomatism of B and F took place during post-skarnization, and the different alteration zones may be due to reaction between B-and F-bearing hydrothermal solutions and country rocks (calcareous carbonates). The stability of tin minerals is controlled by μB₂O₃, μCO₂,μF₂O_-1 and μF(OH)_-1. It has been concluded from the discussion in terms of the system CaO-SnO₂-SiO₂-H₂O-B₂O₃-CO₂-F₂O_-1 proposed by Burt (1978) and the topological diagrams constructed by the author that nordenskiöldine was formed in the depletion of Si at about 400°C in the skarn environment, where metallogenetic conditions are characterized by rich oxygen but poor sulfur, and high boron but low fluorine, while schoenfliesite and varlamoffite were formed at the lower temperature (about 150°C) in response to hydrothermal metasomatism of fluorine. In comparison with the metallogenetic conditions for adjacent endoskarn tin ores and other tin ore deposits at Gejiu, the role of the characteristic elemental association Sn-B-F is emphasized in this paper.     

Malayaite and tin‐bearing silicates from a skarn at Doradilla via Bourke,New South Wales

An extensive complex zoned skarn is developed at the contact of a leucoadamellite intrusive at Doradilla, NW New South Wales. The skarn is a disequilibrium assemblage resulting from a progressive sequence of replacement of a carbonate precursor. Early grossular‐clinopyroxene rocks are replaced by andradite with 0.5–3.5 wt.% SnO₂ clinopyroxene and quartz. Later alteration along fractures and bedding planes of the garnet‐clinopyroxene quartz assemblage has produced calcite‐malayaite (CaSn0.95Ti0.05SiO₅) veins. The final replacement stage was the overprinting of the silicate phases by assemblages containing sulphides, cassiterite, magnetite, titanite, fluorite, biotite and chlorite. The tin content of garent increases with increasing andradite component suggesting replacement of Fe³⁺ by Sn⁴⁺. Associated clinopyroxenes contain 0.1% SnO₂. The coexistence of titanite and its tin isomorph malayaite with extremely limited solid solution indicates late stage skarn temperatures of less than 400°C.     

Mineralogy, Geochemistry, and Age Constraints on the Beni Bou Ifrour Skarn Type Magnetite Deposit, Northeastern Morocco

Abstract: The Beni Bou Ifrour deposit of northeastern Morocco is a skarn type magnetite deposit. K-Ar age determination suggests that the mineralization occurred at 7.040.47 Ma. The spatial relationship between skarn and dikes of microgran-odiorite derived from the batholith of Wiksane Granodiorite, and the similarity of age (8.020.22 Ma), confirms that the Wiksane Granodiorite is the igneous rock most probably related to mineralization. The skarn is distributed asymmetrically in the limestone, and magnetite ore was developed just below the calc-silicate skarn as two parallel beds separated by 100 m of barren limestone and schist.
The mineralization can be divided into three stages. The early stage is characterized by the formation of calc-silicate minerals, mainly clinopyroxene (80–70 % diopside) and garnet (early almost pure andradite to the late 60 % andradite). The main stage is characterized by the formation of a large amount of magnetite. Epidote and quartz formed simultaneously with magnetite. Fluid temperatures exceeded 500 C during the early to main stages. Fluid with very high salinity (50–75 wt% NaCl equiv.) was responsible for the formation of the magnetite ore. The oxygen isotope composition, together with the fluid inclusion data, suggests that magmatic fluid was significant for the formation of calc-silicate skarn minerals and magnetite. Low temperature (-230C) and low salinity (-10 % NaCl equiv.) hydrothermal fluids dominated by meteoric water were responsible for the late stage quartz and calcite formation.     

江西永平铜矿矽卡岩矿物特征及其地质意义

永平铜矿含矿岩石主要为绿帘石透辉石石榴石矽卡岩,这种岩石类型是与斑岩体有关的矽卡岩铜矿的典型赋矿岩石。通过对这一主要赋矿矽卡岩的研究,我们发现石榴石生长分为两个阶段:(1)早期石榴石:主要分布在石榴石颗粒核部,XAdr=1.0,主要以钙铁榴石为主,说明早期流体中可能含有较多的铁,是在较氧化条件下形成的;(2)晚期石榴石,沿石榴石裂隙重新成核或者在靠近流体通道的早期石榴石表面生长,出现震荡环带,XAdr=0.46~0.99,为钙铁-钙铝石榴石系列。石榴石发生变化的期间也形成新的矿物,如绿帘石、萤石、方解石和石英等。共存石榴石和绿帘石矿物中存在Fe3+-Al3+之间的替代,说明流体的氧逸度、组分浓度或aFe3+/aAl3+可能发生了变化。金属矿物也可能是在这一阶段形成的。永平铜矿矽卡岩从接触带到大理岩空间上有分带现象。从岩体到围岩的变化趋势为:石榴石含量减少,颜色存在红棕色-棕色-棕绿色-黄绿色-浅黄色的变化趋势;矿石品位降低,这与石榴石中Al2O3含量的变化较一致。我们认为这种变化是含矿热液对早期矽卡岩进行再交代改造的结果,表现为石榴石和绿帘石中Fe3+-Al3+含量的变化,并将Cu等金属沉淀下来。根据矽卡岩矿物的这些特征,在矿床勘探时,可依据棕色石榴石来追踪主矿体的位置。