Talnachite,a variety of the troctolite type of Noril'sk gabbro-dolerites

Talnakhite is now identified as a basic pegmatoid by its geological, mineralogical, and chemical characteristics. “Talnakhite (troctolite)” should be its proper name, however, because a local variant of chalcopyrite is already known as “talnakhite.” -- V.P. Sokoloff.     

Cu–Fe Bearing Zinc Sulfide from Laloki Stratabound Massive Sulfide Deposit, Papua New Guinea: Chemical Characterization

Abstract: A strange, unidentified, Cu-Fe bearing zinc sulfide occurs in the Laloki massive sulfide deposit, Papua New Guinea. The mineral is optically uniform in texture but is chemically variable and zoned even within a single grain. Copper contents vary from 0.1 up to 8.85 wt%. Iron reaches 18.31 wt% at maximum and decreases as Cu increases. It is remarkable, however, that the total Fe+Cu remains essentially unchanged between roughly 18 and 20 wt%. Zn and S are least variable, giving 45.85–47.84 wt% and 33.48–34.58 wt%, respectively. Other trace elements such as Cd and Mn are in general less than 0.2 wt%. It is strongly suggested that the mineral in question constitutes a unique Fe-Cu substitutional solid solution series belonging essentially to the Zn–Fe–Cu–S system.
The ideal chemical formula of the solid solution series can well be presented as Zn₁₀(Fe, Cu)₅S₁₅ or Zn₂(Fe, Cu)S₃, where Fe is always greater than Cu. It is intriguing that chalcopyrite blebs are recognizable restrictively only in nearby portions of the Cu-rich end member with the ideal composition close to Zn₁₀Fe₃Cu₂S_15. It has been confirmed by vacuum-sealed heating experiments that this mineral is decomposed to produce chalcopyrite and Fe-bearing normal sphalerite at temperatures below 200C. This would provide another evidence for the existence of such distinct phase as suggested here.     

Origin of Bornite Pods in Intrusive Rocks at the Kingking Porphyry Copper-gold Deposit, Southeastern Mindanao, Philippines

At the Kingking porphyry copper-gold deposit, Compostela Valley, south-eastern Mindanao, Philippines, bornite pods occur in the brecciated parts in the biotite diorite porphyry, together with the volcanic rock and diorite fragments without associated stockworks of quartz veinlets. These pods are generally elongated in shape and measure several centimeters across their longest axes. They are composed of bornite and chalcopyrite with traces of calaverite. The δ³⁴S of bornite and subordinate chalcopyrite of bornite pods ranging from −2.2‰ to +0.1‰ are similar to the δ³⁴S of sulfides associated with quartz veinlets such as bornite and chalcopyrite ranging from −4.7‰ to ±0.0‰. This suggests that the ultimate source of sulfur is identical for bornite pods and sulfides associated with quartz veinlets. Bornite pods are associated with volcanic rock and dioritic fragments in the brecciated portion of the biotite diorite porphyry. It was observed that some dioritic fragments contain quartz veinlets, which may indicate an earlier episode of mineralization. Fragments of the earlier dioritic intrusive rocks and the volcanic rocks, together with the sulfides were incorporated into the biotite diorite porphyry magma. A molten sulfide is possible for the composition between bornite and intermediate solid solution at ∼800°C. The sulfides from the earlier dioritic intrusive rocks in the molten state were segregated and then eventually coalesce to form the bornite pods in the brecciated section of the biotite diorite porphyry.     

A second natural occurrence of yoderite

A second example of yoderite has been discovered in whiteschists from the Southern Chewore Hills of northern Zimbabwe. The mineral is pale green in colour and occurs in an equilibrium assemblage with talc+chlorite+kyanite+dravite+hematite. There is no quartz present. Recalculated microprobe analyses give a structural formula of Mg₂Al_5.7Fe_0.3Si₄O₁₈(OH)₂, similar to that obtained for the type locality at Mautia Hill, Tanzania, i.e. Mg₂Al_5.6Fe_0.4Si₄O₁₈(OH)₂. Textural relationships and relative proportions of minerals suggest that the yoderite was formed by reaction between talc, chlorite, kyanite and hematite. Experimental evidence suggests high-water-pressure metamorphic conditions at temperatures exceeding a reaction curve that extends between 13  kbar at 590  °C and 21  kbar at 650  °C. The yoderite-bearing whiteschist is associated with a 1.4  Ga dismembered ophiolite. It is proposed that this yoderite occurrence is associated with a relict subduction/suture zone.     

黄锡矿-似黄锡矿-硫锡铁铜矿组合及其结构特征

黄锡矿-似黄锡矿-硫锡铁铜矿产于湖南大义山花岗岩与石炭、二叠系灰岩接触处的富斑铜矿夕卡岩铜矿床中。硫锡铁铜矿在国内属首次发现。它们的化学成分、物理性质、光学性质和晶体结构与国外相同矿物相似。它们都有两种产状,构成多种结构。     

Control on the emplacement of the andesite lava dome of the Soufriere Hills volcano, Montserrat by degassing-induced crystallization

Lava solidification is controlled by two mechanisms: external cooling and gas exsolution, the latter inducing crystallization due to increasing liquidus temperature. The andesite lava dome of the Soufriere Hills Volcano, Montserrat, is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement. In the magma chamber the magma has an estimated viscosity of 7 × 10⁶ Pa s. During ascent, gas exsolution caused the magma to extrude in a highly crystalline state, with only 5–15% residual melt, viscosities in the range 10¹³–10¹⁴ Pa s and mechanical strength > 1 MPa. Deformation can be heterogeneous with extrusion along shear zones. Rheological stiffening in the upper conduit also causes large overpressures, shallow seismicity, and cyclic patterns of dome extrusion. Gas-rich porphyritic andesites tend to be the least mobile kind of lava, because transition from magma into hot crystalline material was reached during ascent.     

Comparison of Internal Structures of Marine Manganese Deposits of Hydrogenetic, Diagenetic and Hydrothermal Origins

Abstract: Detailed microscopic observation, combined with X-ray diffraction and EPMA analyses of samples from marine manganese deposits of three different origins, suggests that characteristic internal structures are inherent in each manganse mineral; vernadite (δ–MnO₂), buserite (10Å–manganate) and todorokite (10Å–manganate).     

Nickel–bearing Djerfisherite in Gehlenite-Spurrite Skarn at Kushiro, Hiroshima Prefecture, Japan

Abstract: Djerfisherite occurs intimately intergrown with troilite and pentlandite in gehlenite-spurrite skarn at Kushiro, mainly as inclusions in gehlenite and andradite grains. The mode of occurrence indicates that the djerfisherite formed in the culminated stage of the contact metamorphic-metasomatic process. The chemical compositions of the mineral are approximately represented by a formula of K₆Na(Fe, Ni, Cu)₂₄S₂₆Cl with Ni up to 4. 85. It is likely that high temperature condition corresponding to the formation of gehlenite-spurrite skarn as well as low f_O2 and f_S2 conditions are responsible for the formation of djerfisherite in the potassium-rich chemical environments.     

Synchrotron XPS studies of solution exposed chalcopyrite,bornite, and heterogeneous chalcopyrite with bornite

Chalcopyrite, CuFeS₂, is an important source of copper and is recovered from ore by the flotation process. Chalcopyrite is commonly associated with other metal sulfides, e.g. bornite, Cu₅FeS₄. In this study the effect of bornite on the oxidation and leaching of chalcopyrite has been investigated by probing the surface evolution of pure chalcopyrite, bornite, and heterogeneous samples containing both chalcopyrite and bornite using Synchrotron X-ray Photoelectron Spectroscopy (SXPS). Samples were freshly fractured in a N₂ atmosphere and the resulting surfaces were oxidised in pH 9 KOH for 30 min or leached in pH 1 HCl for 2 h before being transferred into vacuum without leaving the N₂ atmosphere. Analysis of the chalcopyrite region of each sample indicates that exposure to pH 9 for 30 min when bornite is present results in a decreased concentration of hydrophobic polysulfide species (from 43% to 36% of the total S 2p spectrum). In addition to this decrease in hydrophobic species, there is an increase in the amount of hydrophilic sulfate on the surface, from trace amounts to 3%. For those samples leached at pH 1 there was a small decrease in the amount of polysulfide species (43% to 39%), but also a slight increase in disulfide species (16% to 19%) indicating an alteration to the oxidation process at low pH in the presence of bornite.     

The evolution of fluorine-rich felsic magmas: source dichotomy, magmatic convergence and the origins of topaz granite

Topaz granite is alkali-feldspar granite that contains essential albite, quartz, K-feldspar, lithium-mica, and topaz. As a group topaz granites are characterized by their extreme enrichment in F (up to 3 wt%) and a wide variety of lithophile elements. They can be subdivided into a 'low-P₂O₅ subtype' (P₂O₅ < 0.1 wt%, Al₂O₃ < 14.5 wt%, SiO₂ > 73 wt%) and a 'high-P₂O₅ subtype' (P₂O₅ > 0.4 wt%, Al₂O₃ > 14.5 wt%, SiO₂ < 73 wt%), the δ¹⁸O values of which indicate a dichotomy of source rock: the low-P₂O₅ subtype (δ¹⁸O < 10‰) having a meta-igneous protolith and the high-P₂O₅ subtype (δ¹⁸O > 10 ‰) a source with a significant component of pelitic material. The unusually high F contents enhance the efficacy of melt segregation and crystal-melt fractionation and so facilitate extreme differentiation in topaz granite magmas. Very low melt volumes restrict the bulk composition of the partial melts regardless of the nature of the source; and extreme fractionation forces them along a path of magmatic convergence, to produce a group of granitic rocks with near-minimum compositions so enriched in a variety of lithophile elements (Li, Nb, Ta, Sn) that economic mineralization often results.     

吉林省东部石炭-二叠系伊利石的成因标志

吉林东部石炭-二叠系主要是一套泥质岩石, 其详细深入的矿物学工作尚不多见。利用JSM-6700F场发射电镜及INCA能谱仪,研究了伊利石的显微形貌和微区成分。采用D/max-2500 X-射线衍射仪,研究了伊利石的结晶度、多型和b₀值。结果表明:研究区伊利石结晶度变化于0.26~0.77,平均值为0.44;伊利石（白云母）多型有3种类型,分别为1M_d型、1M_d+2M₁混合型和2M₁型;伊利石（白云母）b₀值为8.996~9.045,平均值为9.007Å。石炭系伊利石结晶度变化于0.26~0.50,平均值为0.35,主要呈2M₁多型,b₀平均值为9.011Å,主要是低级近变质带的产物;二叠系伊利石结晶度变化于0.26~0.50,平均值为0.42,主要为1M_d+2M₁混合型多型,b₀平均值为9.004Å,主要为晚期成岩带的产物。     

Continuous reactions between biotite, garnet, staurolite, kyanite-sillimanite-andalusite and P-T-time-deformation path in micaschists from the estuary of the river Vilaine, South Brittany, France

Abstract Microprobe analysis of the continuous chemical evolution of coexisting biotite-garnet and biotite-garnet-staurolite has been undertaken from interbedded micaschists of the volcanodetrital group of the Vilaine. A thermobarometric study using pertinent mineralogical equilibria reveals a complex P-T evolution, continuous throughout time, from high pressure, medium temperature (kyanite zone) to medium pressure, high temperature (sillimanite zone), then low pressure, medium temperature (andalusite zone). The T, P, f_H2o and X_H2o variations have been calculated from coexisting biotite-garnet pairs, and from the equilibria: paragonite (in white mica) + quartz ± albite (in plagioclase) + Al silicate + H₂O; and, 3 anorthite ± grossular + 2 Alsilicate + quartz. The P-T evolution is correlated with the continuous change in composition of minerals (using P–X_Mg and T–X_Mg diagrams) and with the evolution of assemblages. This continuous P-T-time evolution, correlated with the successive formation of S₁-S₂ foliations, allows us to propose a P-T-time-deformation path for the micaschists and to relate the growth of its mineral components to tectonic processes.     

Plagioclase relations in pelites, central Menderes Massif, Turkey. I. The peristerite gap with coexisting kyanite

Abstract In pelites of the central Menderes Massif, albite and oligoclase with only slight chemical zoning coexist in apparent textural equilibrium in the garnet zone, staurolite zone, and staurolite + kyanite transition zone. The metamorphic temperature range is estimated as approximately 440–550°C (from the Hodges-Spear calibration of the garnet-biotite geo-thermometer), or 440–500°C (Ganguly-Saxena calibration). While oligoclase composition at the peristerite gap changes from An₂₂ to An₁₄, albite also becomes more sodic (An_1,5–An_0.6). The slope of the albite limb is thus the reverse of that reported in other areas, and may not be a true equilibrium feature. Occurrence of kyanite, at temperatures below the crest of the gap, is due to low water activity in the presence of graphite: a H_2o is estimated at approximately 0.1–0.2 from the Na content of muscovite coexisting with albite + kyanite + quartz.     

Alteration and mineral zonation at the Mt Lyell copper–gold deposit,Tasmania

The Mount Lyell copper deposits are located in the middle Cambrian Mount Read volcanic belt of western Tasmania and consist of more than 24 separate copper–gold–silver orebodies. The dominant copper mineralisation style is disseminated pyrite–chalcopyrite subvertical pipes with subordinate chalcopyrite–bornite ± other copper phases, massive pyrite and base metal sulfides. A zonation in mineralisation style within the pipes is defined from chalcopyrite–magnetite at depth to chalcopyrite–pyrite at intermediate levels, to chalcopyrite–bornite at the shallowest level. Alteration is developed broadly symmetrically around the ore zones and zoned from quartz–chlorite–phengite ± biotite at depth to quartz–muscovite at intermediate levels, and a quartz–muscovite–pyrophyllite–zunyite assemblage at the shallowest levels. This is interpreted to be a result of a fluid that evolved from hot, reduced and neutral conditions at depth to cool, oxidised and acidic conditions at the shallowest level. The chalcopyrite–bornite deposits occur at the top of the hydrothermal system and are associated with intensely silicified rock and muscovite/pyrophyllite alteration. The close relationship of these deposits with the top of the pipes suggests they are part of a single mineralising event. Where the chalcopyrite–bornite deposits are juxtaposed with the Owen Group, rather than a simple chalcopyrite–bornite mineralogy, there are numerous other copper phases, which represent higher oxidation states and collectively suggest variable and fluctuating fluid conditions during deposition. It is proposed that these deposits are formed by an interaction of the reduced hydrothermal fluid with an oxidised fluid generated at very shallow levels within and during deposition of the Owen Group. Mineralisation within the middle Owen Group sandstones and clasts of altered rock within the middle and upper Owen Group sediments marks the end of the hydrothermal system. Around the entire edge of the Mt Lyell field, there is a variation in the white mica composition from proximal muscovite to distal phengite that represents the neutralisation of the hydrothermal fluid by fluid–wall rock interaction.     

Mineral Assemblages as Indicators of the Maturity of Oceanic Hydrothermal Sulfide Mounds

The composition of ore minerals in MAR sulfide occurrences related to ultramafic rocks was studied using methods of mineragraphy, electron microscopy, microprobe analysis, and X-ray analysis. The objects are located at various levels of the maturity of sulfide mounds owing to differences in age, duration, and degree of activity of the following hydrothermal systems: generally inactive Logatchev-1 field (up to 66.5 ka old), inactive Logatchev-2 field (3.9 ka), and generally active Rainbow field (up to 23 ka). Relative to MAR submarine ore occurrences in the basalt substrate, mineralization in the hydrothermal fields mentioned above is characterized by high contents of Au, Cd, Co, and Ni, along with the presence of accessory minerals of Co and Ni. The studied mounds differ in quantitative ratios of major minerals and structural-textural features of ores that suggest their transformation. Ores in the Logatchev-1 field are characterized by the highest Cu content and the development of a wide range of multistage contrast exsolution structures of isocubanite and bornite. In the Logatchev-2 field, sphalerite-chalcopyrite and gold-arsenic exsolution structures are present, but isocubanite exsolution structures are less diverse and contrast. The Rainbow field is marked by the presence of homogenous isocubanite and the subordinate development of exsolution structures. We have identified four new phases in the Cu-Fe-S system. Phases X and Y (close to chalcopyrite and isocubanite, respectively) make up lamellae among isocubanite exsolution products in Logatchev-1 and Logatchev-2. Phase Y includes homogenous zones in zonal chimneys of the Rainbow field. Phases A and B are formed in the orange bornite domain at low-temperature alteration of chalcopyrite in the Logatchev-1 field. Mineral assemblages of the Cu-S system are most abundant and diverse in the Logatchev-1 field, but their development is minimal in the Logatchev-2 field where mainly Cu-poor sulfides of the geerite-covellite series have been identified. Specific features of mineral assemblages mentioned above reflect the maturity grade of sulfide mounds and can serve as indicators of maturity.__________Translated from Litologiya i Poleznye Iskopaemye, No. 4, 2005, pp. 339–367.Original Russian Text Copyright © 2005 by Mozgova, Borodaev, Gablina, Cherkashev, Stepanova.     

Disequilibrium in co-existing clinopyroxene and garnet from blueschist-facies Fe-rich eclogites, Voltri Group, Italy

Abstract Clinopyroxenes and garnets from 11 blueschist-facies Fe-rich eclogite samples from the Voltri Group show a wide range of chemical compositions. Detailed analyses of single pyroxene and garnet grains show wide and scattered chemical inhomogeneity, the K_D(K_D= (Fe₂₊/Mg)^Gt/(Fe²⁺/Mg)^Cpx) ranges from 20 to 87 based on rim analyses only. The data obtained indicate that the mineral pairs never attained equilibrium under uniform P-T conditions and that the compositions of the metamorphic minerals were influenced mainly by the composition of the pre-metamorphic minerals and by topotactical reactions.     

Vanadiferous minerals from the Nereus Deep, Red Sea

The chemical analysis by EMPEDS of 140 samples in cores from six Red Sea troughs and basins has led to the discovery in the Nereus Deep of high vanadium concentrations (up to 1.3% V₂O₃) in several bulk samples, and to the isolation of a major magnetite phase. This vanado-magnetite, remarkable for its high content of vanadium (mean = 1.45% V₂O₃) and its lack of titanium, is frequently zoned, the V-content decreasing toward the outer zones. Oxides with up to 42% V₂O₃, have also been found. Since the origin of the magnetite is clearly authigenic, its high vanadium and low titanium concentrations are traced back to the differential hydrothermal leaching of Fe—Ti-oxides which occur profusely in basic eruptive rock clasts, actually present in some of the overlying seams.     

Two-stage corona growth during Precambrian granulite facies metamorphism of Smitbson Bjerge, north-west Greenland

Abstract Late Archaean orthogneisses and aluminous and iron-rich metasedimentary rocks intruded by anorthosite and a ferrodiorite-granite suite were completely recrystallized during Proterozoic granulite facies metamorphism. Geobarometry and geothermometry indicate P-T conditions of around 7.5kbar. 700°C, with a CO₂-rich fluid phase and logfO₂ at or below -16. A two-stage high-grade history of near isochemical corona growth is preserved in metasediments with the reaction cycle opx + plag + H₂O → hbl+gar+SiO₂→ opx+plag+H₂O. End product compositions resemble those of the initial phases, and the only mobile components were SiO₂ and/or H₂O. The coronas reflect shortlived fluctuations in chemical activity at essentially constant P and T, contrary to simple progressive change in equilibrium parameters recorded by most corona-bearing textures.     

Zinc-rich Pyrite from the TAG Active Mound, the TAG Hydrotherma Field, Mid-Atlantic Ridge

Abstract: Pyrite rich in Zn, up to 3.1 wt%, was found in the TAG active mound of the TAG hydrothermal field, the slow-spreading Mid-Atlantic Ridge at 26°08'N and 44°49'W. The Zn-rich pyrite is characterized by an optical homogeneity, a homogeneous distribution of Zn in the back-scattered electron images, both at a magnification of about 500, a negative correlation between Fe and Zn contents of the pyrite and a rather small unit cell edge (a₀ = 5.4117 ± 0.0008Å), strongly indicating that the detected Zn is present in the pyrite in solid solution. Such Zn concentrations are observed exclusively in dendritic pyrite, suggesting that the Znrich pyrite grew from hydrothermal fluids of a high degree of supersaturation due to quenching on the seafloor.     

Reaction textures in calc-silicate granulites from the Bolingen Islands, Prydz Bay, East Antarctica: implications for the retrograde P–T path

Calc-silicate granulites from the Bolingen Islands, Prydz Bay, East Antarctica, exhibit a sequence of reaction textures that have been used to elucidate their retrograde P–T path. The highest temperature recorded in the calc-silicates is represented by the wollastonite- and scapolite-bearing assemblages which yield at least 760°C at 6 kbar based on experimental results. The calc-silicates have partially re-equilibrated at lower temperatures (down to 450°C) as evidenced by the successive reactions: (1) wollastonite + scapolite + calcite = garnet + CO₂, (2) wollastonite + CO₂= calcite + quartz, (3) wollastonite + plagioclase = garnet + quartz, (4) scapolite = plagioclase + calcite + quartz, (5) garnet + CO₂+ H₂O = epidote + calcite + quartz, and (6) clinopyroxene + CO₂+ H₂O = tremolite + calcite + quartz.
The reaction sequence observed indicates that a CO₂ was relatively low in the wollastonite-bearing rocks during peak metamorphic conditions, and may have been further lowered by local infiltration of H₂O from the surrounding migmatitic gneisses on cooling. Fluid activities in the Bolingen calc-silicates were probably locally variable during the granulite facies metamorphism, and large-scale CO₂ advection did not occur.
A retrograde P–T path, from the sillimanite stability field ( c. 760°C at 6 kbar) into the andalusite stability field ( c. 450°C at <3 kbar), is suggested by the occurrence of secondary andalusite in an adjacent cordierite–sillimanite gneiss in which sillimanite occurs as inclusions in cordierite.