Different mineralization styles in a volcanic-hosted ore deposit: the fluid and isotopic signatures of the Mt Morgan Au–Cu deposit,Australia

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

滇西姚安金矿床磷灰石化学特征及指示意义

姚安金矿床位于金沙江-哀牢山富碱斑岩带中段,大地构造位置处于扬子板块西缘与三江特提斯造山带结合部位,其成矿与新生代富碱岩浆-岩浆热液密切相关.野外调查发现矿化仅存在于黑云母正长斑岩体内,而与黑云母正长斑岩空间关系密切的石英正长斑岩却未发现矿化.为探讨黑云母正长斑岩与石英正长斑岩岩体含矿性差异,运用电子探针、LA-ICP...     

The magmatic-hydrothermal evolution of two barren granites: a melt and fluid inclusion study of the Rito del Medio and Cañada Pinabete plutons in northern New Mexico (USA)

The magmatic-hydrothermal evolution of two barren granites associated with the Tertiary Questa Caldera in northern New Mexico was reconstructed on the basis of microthermometric and laser-ablation inductively coupled plasma mass spectrometry analysis of fluid and melt inclusions in quartz of magmatic and hydrothermal origin. During progressive crystallization and fluid exsolution, the Cs content of the residual melt increased from 1 ppm to values as high as 5500 ppm, which requires an increase in crystallinity by at least 99.98%. In conjunction with a Rayleigh fractionation model simulating the melt evolution at fluid-saturated vs. fluid-undersaturated conditions, the melt inclusion data can be used to determine the crystallinity at which fluid saturation was reached. Our results suggest that both plutons attained fluid saturation before 30% crystallization and that evolved residual melts accumulated in their roof zones. At ∼90% crystallization, the exsolving fluids were of low salinity (∼5 wt.% NaCl_equiv) and in the one-phase field, in accordance with phase relations at the reconstructed P and T conditions (∼1.1 to 1.3 kbar, 700 to 720°C). Fluid-melt partition coefficients for a range of metals determined on assemblages of coeval melt and fluid inclusions were generally too low to allow efficient metal extraction from the melt (D_{X, fluid-melt} < 22). As a result, the metal concentrations in both the residual melt and the coexisting fluid increased with progressive crystallization. Absolute metal contents in the fluids exsolving from barren systems appear low, however, when compared with mineralized systems. It is concluded that the absence of mineralization in the Rito del Medio and Cañada Pinabete plutons primarily stems from a low salinity of the exsolving fluids, resulting in a less efficient metal extraction from the melt.     

Geochemical characteristics of biotite from felsic intrusive rocks around the Sisson Brook W–Mo–Cu deposit,west-central New Brunswick: An indicator of halogen and oxygen fugacity of magmatic systems

The Sisson Brook W–Mo–Cu deposit was formed by hydrothermal fluids likely related to the Nashwaak Granites (muscovite–biotite granite, Group I; and biotite granite, Group II) and related dykes (biotite granitic dykes, Group III; and a feldspar–biotite–quartz porphyry dyke, Group IV). Chemical data obtained using EPMA and LA-ICP-MS data of primary magmatic biotites were used to investigate magmatic processes and associated hydrothermal fluids.Trace element features of biotite in the Group I two-mica granite suggest other magmatic processes along with a simple fractional crystallization. The K/Rb ratios and compatible elements (Cr, Ti, Co, V, and Ba) in biotite from Groups II, III, and IV decrease, whereas incompatible elements including Ta, Tl, Ga, Cs, Li, and Sn increase with magma fractionation. No correlation of Cu, W and Mo with K/Rb ratios is evident, suggesting that partitioning of Cu, W, and Mo into biotite may not be entirely controlled by magma fractionation.Halogen fugacity of the parental magma of the Nashwaak Granites and related dykes, calculated from zircon saturation temperature shows that Group I has high fHF/fCl ratios (broadly higher than 0), similar to the plutons at the Henderson porphyry Mo deposit. The fHF/fCl ratios of the other groups are generally lower than 0, comparable to the Santa Rita porphyry Cu deposit. The fH₂O/fHCl and fH₂O/fHF ratios inferred from biotite in the Nashwaak Granites and related dykes range from 3 to 5 and from 4 to 5, respectively. The inferred oxygen fugacity shows that the dyke phases (Groups III and IV) have the oxygen fugacity around the nickel–nickel oxide buffer. The plutonic phases (Groups I and II) have the oxygen fugacity around the quartz–fayalite–magnetite (QFM) buffer at high temperatures and oxidized to nickel–nickel oxide buffer at lower temperatures. This oxidation process in the plutonic phases (Groups I and II) could be caused by H₂ release at or near H₂O vapor saturation at high H₂O/Fe^2 +. The magma associated with the biotite dykes (Group III) is more likely the source of the hydrothermal fluids at the Sisson Brook deposit since it has the highest differentiation degree and seems to have formed in an oxidized setting, necessary for Mo to concentrate in the late stage fluids.     

Metasomatic silicate chemistry at the Bayan Obo Fe–REE–Nb deposit,Inner Mongolia,China: Contrasting chemistry and evolution of fenitising and mineralising fluids

Fenite aureoles around carbonatite dykes, and alteration associated with Fe–REE–Nb ore bodies at Bayan Obo, Inner Mongolia, China, show alkali silicate assemblages containing aegirine–augite, (magnesio-)riebeckite, (magnesio-)arfvedsonite, and phlogopite, accompanied by varying amounts of apatite, albite and quartz. In both fenites and orebodies simple thermodynamic constraints indicate mineral parageneses are consistent with rock buffered cooling accompanied by the infiltration of a range of externally buffered hydrothermal fluids. Statistical analysis of amphibole chemistry indicates that even in apparently texturally well constrained paragenetic stages wide variations in chemistry occur in both the ore bodies and fenites. Much of this variation is attributable to the Mg and F content of amphibole, and is therefore interpreted as a result of variation in externally controlled variables (P, T, initial fluid composition) rather than internally controlled variables such as protolith composition. Similarities in chemistry exist between fenite and some ore body amphiboles. Thermodynamic analysis of the composition of biotite and apatite allows constraints to be placed on the F-content of hydrothermal fluids, and indicates relatively consistent compositions in fenites and orebodies (log a_HF/a_H2O = − 3.8 to − 3.6 at 300 °C and 1 kbar). Amphibole and biotite associated with niobate mineralization are both enriched in fluorine relative to the rest of the paragenesis, and biotite compositions indicate significantly higher HF activities in the hydrothermal fluid (log a_HF/a_H2O = − 2.6 at 300 °C and 1 kbar). The data presented here reinforce previous interpretations of the complex, multistage nature of mineralisation at Bayan Obo, but are still consistent with a direct involvement of carbonatite derived fluids during ore genesis.     

Fluid infiltration and regional metamorphism of the Waits River Formation, north-east Vermont, USA

Abstract The Siluro-Devonian Waits River Formation of north-east Vermont was deformed, intruded by plutons and regionally metamorphosed during the Devonian Acadian Orogeny. Five metamorphic zones were mapped based on the mineralogy of carbonate rocks. From low to high grade, these are: (1) ankerite-albite, (2) ankerite-oligoclase, (3) biotite, (4) amphibole and (5) diopside zones. Pressure was near 4.5kbar and temperature varied from c. 450° C in the ankerite-albite zone to c. 525° C in the diopside zone. Fluid composition for all metamorphic zones was estimated from mineral equilibria. Average calculated χ_co2[= CO₂/(CO₂+ H₂O)] of fluid in equilibrium with the marls increases with increasing grade from 0.05 in the ankerite-oligoclase zone, to 0.25 in the biotite zone and to 0.44 in the amphibole zone. In the diopside zone, χ_CO2 decreases to 0.06. Model prograde metamorphic reactions were derived from measured modes, mineral chemistry, and whole-rock chemistry. Prograde reactions involved decarbonation with an evolved volatile mixture of χ_CO2 > 0.50. The χ_CO2 of fluid in equilibrium with rocks from all zones, however, was generally <0.40. This difference attests to the infiltration of a reactive H₂O-rich fluid during metamorphism. Metamorphosed carbonate rocks from the formation suggests that both heat flow and pervasive infiltration of a reactive H₂O-rich fluid drove mineral reactions during metamorphism. Average time-integrated volume fluxes (cm³ fluid/cm² rock), calculated from the standard equation for coupled fluid flow and reaction in porous media, are (1) ankerite-oligoclase zone: c. 1 × 10⁴; (2) biotite zone: c. 3 × 10⁴; (3) amphibole zone: c. 10 × 10⁴; and diopside zone: c. 60 × 10⁴. The increase in calculated flux with increasing grade is at least in part the result of internal production of volatiles from prograde reactions in pelitic schists and metacarbonate rocks within the Waits River Formation. The mapped pattern of time-integrated fluxes indicates that the Strafford-Willoughby Arch and the numerous igneous intrusions in the field area focused fluid flow during metamorphism. Many rock specimens in the diopside zone experienced extreme alkali depletion and also record low χ_CO2. Metamorphic fluids in equilibrium with diopside zone rocks may therefore represent a mixture of acid, H₂O-rich fluids given off by the crystallizing magmas, and CO₂-H₂O fluids produced by devolatilization reactions in the host marls. Higher fluxes and different fluid compositions recorded near the plutons suggest that pluton-driven hydrothermal cells were local highs in the larger regional metamorphic hydrothermal system.     

新疆阿尔泰巴斯铁列克钨多金属矿区花岗岩黑云母特征及成岩成矿意义

黑云母是花岗质岩石中常见的造岩矿物,其成分可以有效指示花岗岩形成的物理化学条件和岩石成因。巴斯铁列克矿床是近年来在新疆阿尔泰造山带南缘发现的首例二叠纪矽卡岩型钨多金属矿床。矿区出露多种类型二叠纪含钨花岗岩。为理清花岗质岩体之间、岩体与钨多金属矿化之间的关系,文章采用电子探针测定了黑云母花岗岩、二长花岗岩、二云母花岗岩和钾长花岗岩中的黑云母成分。结果表明,所有黑云母具有富铁、高铝、贫镁特征,含铁指数(Fe²⁺/(Mg+Fe²⁺))为0.66~0.80,二云母花岗岩属铁质黑云母而黑云母花岗岩、二长花岗岩和钾长花岗岩属铁叶黑云母。所有岩石是具有A型特征的I型花岗岩。不同类型岩石中黑云母的成分差异与岩浆来源、分异演化程度有关。二云母花岗岩中黑云母的w(MgO)与结晶温度最高,与黑云母平衡流体的log(fHF/fHCl)值（-1.13~-1.25）最低,log(fH₂O/fHF)值（4.64~4.96）最高,母岩浆相对富Cl;黑云母花岗岩中log(fHF/fHCl)值最高,log(fH₂O/fHF)最低,与二长花岗岩是同一岩浆房不同演化阶段的产物,与二云母花岗岩和钾长花岗岩属不同的岩浆体系,母岩浆相对富F元素。黑云母花岗岩与W矿化关系更密切。     

Compositions of biotite,amphibole, apatite and silicate melt inclusions from the Tongchang mine,Dexing porphyry deposit,SE China: Implications for the behavior of halogens in mineralized porphyry systems

The Dexing deposit, located in the Circum-Pacific ore belt, is the largest porphyry copper deposit in eastern China. It is composed of 3 separate plutons, which host three mines: Tongchang, Fujiawu and Zhushahong mines. The porphyritic granodiorite samples studied in this investigation were collected from the Tongchang ore-forming pluton of this giant deposit. This paper presents electron microprobe analyses of biotite, apatite, amphibole, plagioclase, potassium feldspar and rehomogenized glassy melt inclusions from the Tongchang porphyritic granodiorites. Petrographic observations of the samples are consistent with portions of the granodioritic magma represented by our samples being overprinted by potassic hydrothermal fluid which variably altered these minerals.All of the studied micas are Mg-rich biotites. The biotites are separated into altered magmatic and secondary types based on their petrographic and geochemical characteristics. The phlogopite components of the secondary biotites are typically higher than those of the altered magmatic biotites, and the X_Mg values of all biotites correlate negatively with Cl contents, consistent with the Mg–Cl avoidance principle. The X_Mg values also correlate negatively with (K₂O + Na₂O + BaO), FeO and TiO₂ for both generations of biotites. The calculated log (fH₂O/fHCl) values (for 690 K) of the coexisting potassic fluids, which are determined from the altered magmatic biotite compositions, range from 4.43 to 4.67, and are very similar to those of other major porphyry deposits. However, the log(fH₂O/fHF) and log(fHF/fHCl) values for the same batch of hydrothermal fluids are significant higher and lower than those of these other porphyry deposits, respectively.The Cl concentrations of amphiboles and melt inclusions range from 0.18 to 0.32 wt.% and 0.15 to 0.44 wt.%, respectively. Most apatites trapped in biotite and plagioclase phenocrysts display a bimodal Cl distribution: 0.19 to 1.35 wt.% and 1.48 to 3.73 wt.%. Similarly, the S contents of the apatite also show a distinct bimodal distribution reflecting the effects of variable anhydrite saturation during evolution of the Tongchang melt and variable dissolution of anhydrite by saline aqueous fluids. The Cl contents of the apatites from the Tongchang system are typically higher than those of other studied porphyry deposits. Furthermore, the Cl contents of the melt inclusions are at or very near the Cl saturation levels (0.36 to 0.46 wt.% at 850 °C and 50 MPa and 0.42 to 0.54 wt.% at 850 °C and 200 MPa) for these melt compositions at shallow crustal pressures. These findings suggest that the area of the granodioritic magma represented by our samples, and perhaps the bulk of the Tongchang granodioritic magma was rich in Cl. The melt inclusion compositions are consistent with a high-salinity, hydrosaline liquid being exsolved directly from the granodioritic melt directly. This high-salinity hydrosaline liquid was likely very efficient at dissolving, transporting and precipitating ore metals in the mineralizing magmatic–hydrothermal system.     

Ore Genesis and Tectonic Significance of the Xiaojiashan Tungsten Deposit,Eastern Tianshan,Xinjiang, China: Evidence from Geology,Fluid Inclusions,and Stable Isotope Geochemistry

The Xiaojiashan tungsten deposit is located about 200 km northwest of Hami City, the Eastern Tianshan orogenic belt, Xinjiang, northwestern China, and is a quartz vein‐type tungsten deposit. Combined fluid inclusion microthermometry, host rock geochemistry, and H–O isotopic compositions are used to constrain the ore genesis and tectonic setting of the Xiaojiashan tungsten deposit. The orebodies occur in granite intrusions adjacent to the metamorphic crystal tuff, which consists of the second lithological section of the first Sub‐Formation of the Dananhu Formation (D₂d ₁²). Biotite granite is the most widely distributed intrusive bodies in the Xiaojiashan tungsten deposit. Altered diorite and metamorphic crystal tuff are the main surrounding rocks. The granite belongs to peraluminous A‐type granite with high potassic calc‐alkaline series, and all rocks show light Rare Earth Element (REE)‐enriched patterns. The trace element characters suggest that crystallization differentiation might even occur in the diagenetic process. The granite belongs to postcollisional extension granite, and the rocks formed in an extensional tectonic environment, which might result from magma activity in such an extensional tectonic environment. Tungsten‐bearing quartz veins are divided into gray quartz vein and white quartz veins. Based on petrography observation, fluid inclusions in both kinds of vein quartz are mainly aqueous inclusions. Microthermometry shows that gray quartz veins have 143–354°C of T_h, and white quartz veins have 154–312°C of T_h. The laser‐Raman test shows that CO₂ is found in fluid inclusions of the tungsten‐bearing quartz veins. Quadrupole mass spectrometry reveals that fluid inclusions contain major vapor‐phase contents of CO₂, H₂O. Meanwhile, fluid inclusions contain major liquid‐phase contents of Cl^?, Na⁺. It can be speculated that the ore‐forming fluid of the Xiaojiashan tungsten deposit is characterized by an H₂O–CO₂, low salinity, and H₂O–CO₂–NaCl system. The range of hydrogen and oxygen isotope compositions indicated that the ore‐forming fluids of the tungsten deposit were mainly magmatic water. The ore‐forming age of the Xiaojiashan deposit should to be ~227 Ma. During the ore‐forming process, the magmatic water had separated from magmatic intrusions, and the ore‐bearing complex was taken to a portion where tungsten‐bearing ores could be mineralized. The magmatic fluid was mixed by meteoric water in the late stage.     

Mineralogical evidence for crystallization conditions and petrogenesis of ilmenite-series I-type granitoids at the Baogutu reduced porphyry Cu deposit (Western Junggar,NW China): Mössbauer spectroscopy,EPM and LA-(MC)-ICPMS analyses

Primary ore-forming minerals retain geochemical signatures of magmatic crystallization information and can reveal the petrochemical conditions prevalent at the time of their formation. The Baogutu deposit is a typical reduced porphyry Cu deposit. Amphibole and biotite Fe³⁺/ΣFe ratios, minerals (feldspar, biotite, amphibole, zircon and apatite), in situ elemental and apatite Nd isotopic compositions were determined by Mössbauer spectroscopy, electron probe microanalysis, and laser ablation multiple-collection inductively coupled plasma mass spectrometry, respectively, to investigate the magma oxidation state, petrogenesis, source features, and to constrain the carbon species at magmatic stages for the intrusive phases. The results show that the primary plagioclase and amphibole in the mineralized diorite to granodiorite porphyry and post ore hornblende diorite porphyry are distinct (An_26-55 versus An_60-69; Mg-hornblende versus tschermakite). In particular, the amphibole shows distinct major and trace element compositions with light rare earth element enrichments and negative Eu anomalies in Mg-hornblende and light rare earth element depletions and no Eu anomalies in tschermakite. All the analyzed biotites are primary igneous phases with a biotite phenocryst profile showing significant variations of Zn, Cr, Sc and Sr from core to rim. These results may indicate the occurrence of mixing between two distinct magmas during mineral formation. Titanium in zircon and Si¹ in amphibole thermometries indicate that magma crystallized at >900 °C and continued to ∼650 °C. In situ apatite Nd isotope (εNd(t) = 5.6–7.6, T_DM2 = 620–460 Ma), indicate absence of significant reduced sedimentary contamination and the source of juvenile lower crust. Slightly decreasing Fe³⁺/ΣFe ratios from biotite and amphibole to whole rock indicate decreasing oxygen fugacity during magma crystallization. Recalculated biotite compositions according to Fe³⁺/ΣFe ratios indicate fO₂ values of less than Ni-NiO buffer (NNO) which show slightly lower values than that estimated according to zircon/melt distribution coefficients Ce anomalies (∼ΔNNO + 0.6). These values are consistent with the features of reduced porphyry Cu deposits. Crystallization of other mineral phases significantly affects the reliability of oxybarometer of zircon/melt distribution coefficients Eu anomalies and Mn contents in apatite. This oxidation state suggests that only CO₂ was present at the magmatic stage, and implies that CH₄ formed during CO₂ reduction occurring later hydrothermal alteration. The alteration of primary amphibole to actinolite released Ti, Al, Fe, Mn, Na and K to the fluid with later precipitation of titanite, albite and minor ilmenite and magnetite during actinolite alteration.     

西南三江甭哥金矿床磷灰石地球化学特征及地质意义

甭哥金矿床位于西南三江造山带北段的义敦弧南缘,属于与富碱侵入岩有关的金矿床。目前,对其成矿机理认识仍较为薄弱,制约了资源评价和找矿勘查进展。本文选取甭哥金矿床强矿化的正长斑岩和弱矿化的黑云辉石正长岩中的磷灰石作为研究对象,详细剖析磷灰石的地球化学特征,探讨其记录的成岩成矿信息。结果表明,磷灰石的稀土元素含量特征及配分模式显示富碱岩浆主要来自于壳幔混合的源区,黑云辉石正长岩中磷灰石的(La/Sm)N、(La/Yb)N、(Sm/Yb)N值和Sr含量呈正相关,说明长石结晶对岩浆结晶分异有重要的影响;正长斑岩中磷灰石具有高Sr/Y、Ce/Pb值,而Th/U、(Sm/Yb)N值较低,指示强烈的流体活动参与了岩浆结晶过程;磷灰石挥发分(F、Cl)含量及比值特征指示金矿成矿流体主要来自地幔源区,成矿与富碱、高氯的成矿流体有关。磷灰石Mn氧逸度计估算结果显示,甭哥富碱侵入岩具有高氧逸度特性,但两种不同岩性岩石的氧逸度具有差异性。其中,正长斑岩的logf_(O_2)值为-12～-10. 3,黑云辉石正长岩的logf_(O_2)值为-15. 5～-11. 1,磷灰石中SO_3含量及Ga含量也暗示正长斑岩的氧逸度高于黑云辉石正长岩的特征;结合磷灰石低Mn、Ga含量和高的Cl、SO_3含量,反映甭哥金矿床金的成矿是在高氧逸度条件下金氯络合物迁移、富集而沉淀的结果。因而,磷灰石的地球化学特征对金矿床成矿过程示踪和勘查评价具有重要的指示意义。     

Chemical composition of rock-forming minerals in granitoids associated with Au–Bi–Cu,Cu–Mo,and Au–Ag mineralization at the Freegold Mountain,Yukon, Canada: magmatic and hydrothermal fluid chemistry and petrogenetic implications

The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au–Bi–Cu–As deposit, Revenue Au ± Cu and Stoddart Cu–Mo ± W mineral occurrences, and Laforma Au–Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4–91% Or), whereas plagioclase spans a wide range (4.4–70.07% An). In all of the investigated samples, T _Ab = T _An = T _Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu–Mo ± W, Laforma Au–Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au–Bi–Cu–As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O₂) values between 10–13 and 10–11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X _Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X _Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8–7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6–2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520–780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X _Mg biotite associated with the mineralized (Cu–Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X _Mg. In both Nucleus and Revenue Au–Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization.     

Stable (C,O) and radiogenic (Sr,Nd) isotopes of carbonates as indicators of magmatic and post-magmatic processes of phoscorite-series rocks and carbonatites from Catalão I,central Brazil

The Late-Cretaceous Catalão I contains stockworks of thin dykes of phoscorite-series rocks, which can be subdivided into P1 (olivine-bearing, phoscorites) and P2/P3 (olivine-lacking, nelsonites). Dolomite carbonatites (DC) are intimately associated with nelsonites, as pockets and dykes. The P2 apatite nelsonite, the P3 magnetite nelsonite, and, to a lesser extent DC, host the Catalão I niobium mineralization. C–O isotopes signatures in carbonates reveal several distinct magmatic and post-magmatic processes. Limpid carbonates with stable isotopic mantle-like composition show Rayleigh fractionation and are interpreted as primary, while those with brittle-turbid aspect, and higher oxygen isotope composition, probably underwent recrystallization by interaction with H₂O-rich fluids. A group of samples shows higher oxygen compositions and lower carbon values, which could be explained by degassing of carbonatite magma during cooling. A degassing pattern, parallel to magmatic degassing but at higher oxygen and lower carbon compositions, observed in carbonate veins, may indicate degassing of fracture filling fluids. Furthermore, C–O isotopes of carbonate from monazite-bearing carbonatite have a positive correlation, indicating a distinct, late-stage carbo-hydrothermal event. Though the Catalão I nelsonites and phoscorites are of igneous origin, they underwent several post-magmatic events, which sometimes overprinted partially or entirely the magmatic isotope signature.     

赣东北朱溪矿床深部似层状钨(铜)矿体白钨矿、磷灰石原位U-Pb年代学及微量元素研究

钨和铜由于地球化学行为存在明显差异,导致二者通常很难同时发生大规模的成矿作用.然而,江南钨矿带却出现了以石门寺和朱溪为代表的钨(铜)矿床.本文对朱溪钨(铜)矿床中最为重要的铜矿化作用开展了研究,即对形成于新元古代浅变质岩与古生代碳酸盐岩不整合界面附近的似层状钨(铜)矿体进行了精细的矿物学微区原位测试分析.厘定了朱溪矿床...     

富挥发分岩浆补给对斑岩型铜-钼矿床形成的关键作用:以西藏尼木岗讲矿床为例

西藏冈底斯带中段的岗讲斑岩铜-钼矿床发育多期次侵入体,而成矿作用主要与其中一期岩体(流纹英安斑岩)密切相关。为探究其原因,本文对岗讲斑岩铜-钼矿床中发育的各期次侵入体进行了全岩主、微量元素分析,并重点研究各期次侵入体内部新鲜斑晶(黑云母、斜长石)和副矿物(锆石、磷灰石)的化学成分和结构特征。结果表明,矿区各期次侵入岩均属于高钾钙碱性系列,具有相近的锆石饱和温度,都来自较为氧化的岩浆。此外,相比其他期次侵入岩,主成矿期的流纹英安斑岩中的磷灰石具有较高的SO_3、Cl含量,较低的F含量;黑云母含有较高的Cl含量和较低的F含量;同时,斜长石发育反环带。这些证据表明,在主成矿期岩浆就位之前,存在富S、Cl的偏基性岩浆注入了深部岩浆房,并发生岩浆混合作用,这不仅导致了主成矿期斑岩体的就位,同时还诱发流体出溶进入浅部岩浆房,并最终形成岗讲斑岩铜-钼矿床。     

江西阳储岭两期岩浆活动与钨成矿作用的关系：来自黑云母地球化学的证据

阳储岭斑岩型W-Mo矿床位于江南造山带中部,是华南地区最早发现的斑岩型钨钼矿床。已探明WO₃资源储量6.13万吨(平均品位0.2%),Mo资源储量1.69万吨(平均品位0.03%～0.06%),其成矿作用与中生代花岗质岩浆活动密切相关。区内发育早期花岗闪长岩和晚期二长花岗斑岩,钨矿体以细脉状和浸染状产于二长花岗斑岩体内,而花岗闪长岩内未见矿化。两期岩浆活动与钨成矿的关系尚不明确,制约其含矿差异性的因素尚不清楚。本文以花岗闪长岩和二长花岗斑岩中的黑云母为研究对象,对比研究两类岩浆结晶分异程度、氧逸度、岩浆流体卤素浓度,探讨其对钨成矿的制约。黑云母主量元素分析结果显示,阳储岭两类岩浆岩均为壳源,但显著不同于S型花岗岩的Mg/(Fe+Mg)和Al^VI值,指示其具有I型花岗岩的特征。黑云母的微量元素信息显示,相对于花岗闪长岩中的黑云母(类型一),二长花岗斑岩中的黑云母(类型二)显示低的K/Rb、Nb/Ta比值,高的Rb、Cs、Nb和Ta含量,表明其分异程度较花岗闪长岩更高,更有利于钨的富集。两类黑云母所指示的岩浆氧逸度均在NNO缓冲线附近,表明其母岩...     

Alkaline granites and Be (Phenakite-bertrandite) mineralization: An example of the Orot and Ermakovka deposits

The Orot (Or) and Ermakovka (Er) intrusions of aegirine granites with various resources of accompanying Be mineralization in Transbaikalia were studied to reproduce Be behavior during the crystallization and degassing of alkaline granite magma. Data on the petrography and geochemistry of the rocks and the microthermomety and microprobe analysis of fluid and melt inclusions in them indicate that the intrusions were formed by discrete magma portions derived from a single magmatic source during successive stages of its differentiation. The intrusions crystallized at temperatures higher than 1030–1070°C (Or) and 840–640°C (Er), and the melts contained elevated concentrations of H₂O and F: from 2.1 to 3.5% F and from <1 to 1% H₂O for the former intrusion and from 3.9 to 6.7% F and from <2.6 to 4.1% H₂O for the latter. Fluids were released from the magma during a late crystallization stage for the Orot intrusion and an intermediate stage for the Ermakovka intrusion. Early in the course of this process, the fluids were halide-sulfate brines with the Cl: F ratio higher for the Orot intrusion and lower for the Ermakovka intrusion. A temperature decrease resulted in the exsolution of the fluids into two immiscible phases, one of which contained low and the other high concentrations of salts. The magmatic brines and low-salinity solutions of both intrusions were enriched in Be (up to 1.1 g/kg), which is comparable with the concentration of this element in the emanations of Be-bearing pegmatites in the Pamirs and is manyfold higher than C _Be in magmatic fluids related to granite intrusions with W-Sn mineralization. The Be ore mineralization of the Orot and Ermakovka deposits was produced by solutions whose composition and Be concentrations were analogous to those in the low-salinity phase of the corresponding magmatic fluids. The brines of the Ermakovka intrusion were enriched in Mo (up to 17 g/kg) and, to a lesser extent, Mn, Ce, and La and produced uneconomic monazite-molybdenite ore mineralization. Based on available data and results of our calculations, we arrived at the conclusion that the very high alkali concentrations in the melts of both intrusions (ASI < 1), their high F concentrations (up to 4.1%), and the absence of magmatic Be-bearing minerals facilitated Be selective extraction by the separated fluids in the form of its most soluble F-complexes. The high oxidation of the melt predetermined the predominance of hexavalent S and Mo compounds, which could be efficiently extracted by the fluid phase in the form of sulfates and molybdates of alkali metals. The differences in the ore potentials of the Orot and Ermakovka intrusions were caused by the different H₂O, F, and perhaps, also Be concentrations in the parental melts, which was, in turn, caused by their different degrees of differentiation during the preintrusive stages of their magmatic evolution.     

The Fe–C–O–H–N system at 6.3–7.8 GPa and 1200–1400 °C: implications for deep carbon and nitrogen cycles

Interactions in a Fe–C–O–H–N system that controls the mobility of siderophile nitrogen and carbon in the Fe⁰-saturated upper mantle are investigated in experiments at 6.3–7.8 GPa and 1200–1400 °C. The results show that the γ-Fe and metal melt phases equilibrated with the fluid in a system unsaturated with carbon and nitrogen are stable at 1300 °C. The interactions of Fe₃C with an N-rich fluid in a graphite-saturated system produce the ε-Fe₃N phase (space group P6₃/mmc or P6₃22) at subsolidus conditions of 1200–1300 °C, while N-rich melts form at 1400 °C. At IW- and MMO-buffered hydrogen fugacity (fH₂), fluids vary from NH₃- to H₂O-rich compositions (NH₃/N₂?>?1 in all cases) with relatively high contents of alkanes. The fluid derived from N-poor samples contains less H₂O and more carbon which mainly reside in oxygenated hydrocarbons, i.e., alcohols and esters at MMO-buffered fH₂ and carboxylic acids at unbuffered fH₂ conditions. In unbuffered conditions, N₂ is the principal nitrogen host (NH₃/N₂?≤?0.1) in the fluid equilibrated with the metal phase. Relatively C- and N-rich fluids in equilibrium with the metal phase (γ-Fe, melt, or Fe₃N) are stable at the upper mantle pressures and temperatures. According to our estimates, the metal/fluid partition coefficient of nitrogen is higher than that of carbon. Thus, nitrogen has a greater affinity for iron than carbon. The general inference is that reduced fluids can successfully transport volatiles from the metal-saturated mantle to metal-free shallow mantle domains. However, nitrogen has a higher affinity for iron and selectively accumulates in the metal phase, while highly mobile carbon resides in the fluid phase. This may be a controlling mechanism of the deep carbon and nitrogen cycles.     

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.     

<Emphasis Type="Italic">P</Emphasis>–<Emphasis Type="Italic">T</Emphasis> and fluid evolution of barren and lithium pegmatites from Vlastějovice,Bohemian Massif,Czech Republic

Fluid inclusions, mineral thermometry and stable isotope data from two types of mineralogically and texturally contrasting pegmatites, barren ones and lithium ones, from the Moldanubian Zone of the Bohemian Massif were studied in order to constrain P–T conditions of their emplacement, subsolidus hydrothermal evolution and to estimate composition of the early exsolved fluid and that of the parental melt. Despite the fact that the lithium pegmatites are abundant throughout the crystalline units of the Bohemian Massif, data similar to this paper have not been published yet. The studied pegmatites are hosted by iron-rich calcic skarn bodies. This specific setting allowed scavenging of calcium, fluorine and some other elements from the host rocks into the pegmatitic melts and post-magmatic fluids. Such contamination process was important namely in the case of barren pegmatites, as can be deduced from the variation in anorthite contents in plagioclase and from the presence of fluorite, hornblende (with F content) or garnet in the contact zones of pegmatite dykes. Fluid inclusions were studied mostly in quartz, but also in fluorite, titanite and apatite. Early aqueous–carbonic and late aqueous fluids were identified in both pegmatite types. The P–T conditions of crystallization as well as the detailed composition of exsolved magmatic fluid, however, particularly differ. The magmatic fluids associated with barren pegmatites correspond to H₂O–CO₂ low salinity fluids, composition of which evolved from 20 to 23 to <5 mol% CO₂, and from 2 to 4–6 mol% NaCl eq. Sudden decrease in the CO₂ content of the post-magmatic fluids (<5 mol% CO₂) seems to coincide with the enrichment of the fluid in calcium (from the contamination process) and resulted in precipitation of calcites (frequently found as trapped solid phases in fluid inclusions). The fluids associated with lithium pegmatites are more complex (H₂O–CO₂/N₂–H₃BO₃–NaCl). The CO₂ content of early exsolved fluid is 26–20 mol% CO₂ and remains the same in the next fluid generation. The main difference between the magmatic and the first post-magmatic fluids is the presence of 7–9 wt% of H₃BO₃ (identified as daughter mineral sassolite) in the former. The second post-magmatic fluids are again CO₂-poor (∼4 mol%) and more saline (∼4 mol% NaCl eq.). The composition of exsolved fluid was further used to constrain volatile composition and content of the parental melts. Finally, P–T conditions of pegmatite crystallization are constrained: 600–640°C and 420–580 MPa for the barren pegmatites and 500–570°C and 310–430 MPa for the lithium pegmatite. While the emplacement of the former occurred in thermal equilibrium with the Moldanubian host rock environment, the emplacement of the later suggests substantial thermal disequilibrium.