Pyrite commonly incorporates a wide range of trace and minor elements, which in turn may modify s... more Pyrite commonly incorporates a wide range of trace and minor elements, which in turn may modify some of the mineral’s physical and chemical properties. Published band position data for the Raman spectra of pyrite show a wide variation, and the relationship between band position and the trace/minor element incorporation in pyrite is poorly constrained until now. This prompted a case study on pyrite with varying As content from the Shizilishan Sr-(Pb-Zn) deposit, eastern China, combining electron probe microanalysis with Raman spectroscopy. Results show a significant correlation, with a major downshift (~10 cm–1) of the positions of all three Raman bands with increase of As content from below 0.05 to 4.89 wt % in pyrite. This phenomenon is attributed to increased bond lengths and local distortions within an expanded pyrite crystal structure. Results highlight the potential that Raman spectroscopy offers to estimate the contents of trace/minor elements—especially As—in pyrite. Given th...
Our compilation of ~900 published results of analyses for minerals of the tetradymite series (tel... more Our compilation of ~900 published results of analyses for minerals of the tetradymite series (tellurobismuthite, tetradymite, guanajuatite, paraguanajuatite, kawazulite, skippenite, tsumoite, hedleyite, pilsenite, laitakarite, ikunolite, joséite-A, joséite-B) allows compositional fields among naturally occurring Bi–Te–Se–S compounds to be established. New compositional data for ingodite, laitakarite, pilsenite, kawazulite and tellurobismuthite extend previously known compositional limits. Recognized minerals can, for the most part, be satisfactorily and conveniently classified according to the ratio Bi(+ Pb)/(Te + Se + S), into the subsystems (isoseries) Bi2Te3–Bi2Se3–Bi2S3, Bi4Te3–Bi4Se3–Bi4S3 and BiTe–BiSe–BiS. Most minerals show limited compo-sitional variation, but this is generally more extensive in the Se-bearing phases (e.g., laitakarite) and in certain members of the system Bi–Te, such as hedleyite and tsumoite. Substitution of minor Pb for Bi is widespread throughout the gr...
Trace element concentrations, particularly rare earth elements and yttrium (REY) in feldspars and... more Trace element concentrations, particularly rare earth elements and yttrium (REY) in feldspars and accessory minerals have been determined in a suite of albitized igneous, metasedimentary and metasomatite rocks from the Moonta-Wallaroo district, Olympic Cu-Au Province, South Australia. Results show that changes in REY-fractionation trends and concentrations in feldspars and common accessories are associated with key textures in albite-bearing associations from different lithologies. In granitic rocks, pseudomorphic replacement of pre-existing feldspars is typified by porous albite with cleavage-oriented intergrowths of sericite and pore-attached hematite. These observations are comparable with albitization features of granitic terranes elsewhere. A mineral association (albite-sericite ± chlorite), similar to that from granitoids, is observed as pervasive spots in limestone, inferring prograde skarnoid reactions at low fluid/rock ratio in an impure carbonate. In metasedimentary and me...
ABSTRACT Sphalerite is a common sulphide and is the dominant ore mineral in Zn-Pb sulphide deposi... more ABSTRACT Sphalerite is a common sulphide and is the dominant ore mineral in Zn-Pb sulphide deposits. Precise determination of minor and trace element concentrations in sulphides, including sphalerite, by Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry (LA-ICP-MS) is a potentially valuable petrogenetic tool. In this study, LA-ICP-MS is used to analyse 19 sphalerite samples from metamorphosed, sphalerite-bearing volcanic-associated and sedimentary exhalative massive sulphide deposits in Norway and Australia. The distributions of Mn, Fe, Co, Cu, Ga, Se, Ag, Cd, In, Sn, Sb, Hg, Tl, Pb and Bi are addressed with emphasis on how concentrations of these elements vary with metamorphic grade of the deposit and the extent of sulphide recrystallization. Results show that the concentrations of a group of trace elements which are believed to be present in sphalerite as micro- to nano-scale inclusions (Pb, Bi, and to some degree Cu and Ag) diminish with increasing metamorphic grade. This is interpreted as due to release of these elements during sphalerite recrystallization and subsequent remobilization to form discrete minerals elsewhere. The concentrations of lattice-bound elements (Mn, Fe, Cd, In and Hg) show no correlation with metamorphic grade. Primary metal sources, physico-chemical conditions during initial deposition, and element partitioning between sphalerite and co-existing sulphides are dominant in defining the concentrations of these elements and they appear to be readily re-incorporated into recrystallized sphalerite, offering potential insights into ore genesis. Given that sphalerite accommodates a variety of trace elements that can be precisely determined by contemporary microanalytical techniques, the mineral has considerable potential as a geothermometer, providing that element partitioning between sphalerite and coexisting minerals (galena, chalcopyrite etc.) can be quantified in samples for which the crystallization temperature can be independently constrained.
ABSTRACT The Basil Cu–Co deposit, Harts Range, central Australia, is hosted by the Riddock Amphib... more ABSTRACT The Basil Cu–Co deposit, Harts Range, central Australia, is hosted by the Riddock Amphibolite, a sequence that has been metamorphosed at upper-amphibolite- to granulite-facies conditions at 480–460 Ma (Larapinta Event), and subsequently reworked at amphibolite-facies conditions (450–300 Ma). As a result, many of the primary mineralization textures and other features that could characterise ore genesis have been obliterated. However, preserved textures and mineral relationships in the mineralized zone, allow some constraints to be placed on the genetic history of the deposit using mineralogical, petrographic and geochemical studies of host rocks and sulphides. Results of this study permit at least two geneticmodels to be ruled out. Firstly,whole rock geochemistry and garnet compositions suggest that the deposit is not a skarn system. Secondly, the lack of any significant Ni-signature, and the presence of abundant zircons in the host amphibolite (indicating that not all host rocks are mafic incomposition and/or magmatic in character), make an orthomagmatic Ni–Cu–(PGE) system unlikely. Alternatively, Basil is assigned to a volcanic-hosted massive sulphide (VHMS)-style of mineralization, formed on the seafloor, within basaltic and sedimentary host rocks, typical of deposits occurring in such settings. The lack of a recognisable hydrothermal alteration zone is consistent with either destruction of the alteration zone during metamorphism or detachment of the ore from alteration during later deformation. The occurrence of sulphide inclusions within garnet and amphibole indicates that the sulphides must be synmetamorphic or earlier. Partitioning of trace elements between pyrite and co-existing pyrrhotite suggests that (re)crystallization occurred under equilibrium conditions. The composition of sphalerite coexisting with pyrite and pyrrhotite indicates crystallization at pressures of at least 10 kbar, consistent with peak metamorphism during the Early Ordovician Larapinta Event. Zr-in-titanite geothermometry indicates peak temperatures of 730–745 °C.
ABSTRACT ‘Green energy futures’ are driving unprecedented demand for Rare Earth Elements (REE), u... more ABSTRACT ‘Green energy futures’ are driving unprecedented demand for Rare Earth Elements (REE), underpinning significant exploration activity worldwide. Understanding how economic REE concentrations form is critical for development of exploration models. REE mineralisation in the Browns Ranges, Gordon Downs Region, Western Australia, comprises xenotime-dominant mineralisation hosted within Archaean to Palaeoproterozoic metasedimentary units (Browns Range Metamorphics). Mineralogical, petrographic and mineral-chemical investigation, including trace element analysis by Laser-Ablation Inductively-Coupled Plasma Mass Spectroscopy, gives insights into the mineralogical distribution and partitioning of REE, and also provides evidence for the genetic evolution of the Browns Range REE mineralisation via a succession of hydrothermal processes.
ABSTRACT The common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at ... more ABSTRACT The common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at Pepegoona, Pepegoona West and Pannikan, Lake Eyre Basin, South Australia. Combined chemical, isotopic and microstructural analysis of pyrite indicates variation in fluid composition, sulfur source and precipitation conditions during a protracted mineralization event. The results show the significant role played by pyrite as a metal scavenger and monitor of fluid changes in low-temperature hydrothermal systems.
Zirconium is an element of considerable petrogenetic significance but is rarely found in hematite... more Zirconium is an element of considerable petrogenetic significance but is rarely found in hematite at concentrations higher than a few parts-per-million (ppm). Coarse-grained hematite ore from the metamorphosed Peculiar Knob iron deposit, South Australia, contains anomalous concentrations of Zr and has been investigated using microanalytical techniques that can bridge the micron- to nanoscales to understand the distribution of Zr in the ore. Hematite displays textures attributable to annealing under conditions of high-grade metamorphism, deformation twins (r~85˚ to hematite elongation), relict magnetite and fields of sub-micron-wide inclusions of baddeleyite as conjugate needles with orientation at ~110˚/70˚. Skeletal and granoblastic zircon, containing only a few ppm U, are both present interstitial to hematite. Using laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) spot analysis and mapping, the concentration of Zr in hematite is determined to be ~260 ppm on ...
The accelerated pace of transition to green energy technologies has led to increased demand for r... more The accelerated pace of transition to green energy technologies has led to increased demand for rare-earth elements (REEs). Fluorocarbonates from the bastnäsite [REE(CO3)F]—synchysite [CaREE(CO3)2F] group are abundant in nature and the dominant REE minerals in the >10 billion ton Olympic Dam Cu–U–Au–Ag deposit, South Australia. Intergrowths of bastnäsite and synchysite slabs at the nanometer to micron scales are the rule rather than the exception and account for structural and compositional changes between the two endmembers. This article reviews REE-fluorocarbonate mineralogy at Olympic Dam with emphasis on the significance of intergrowths among bastnäsite and synchysite for achievement of thermodynamic equilibrium. Imaging by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) allows visualization of atomic-scale periodicity and structural modularity in REE fluorocarbonates and, in turn, determination of domain compositions, which are otherwise ...
The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias ... more The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm-to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled
The new mineral graţianite, MnBi 2 S 4, is described from the Bǎiţa Bihor skarn deposit, Bihor Co... more The new mineral graţianite, MnBi 2 S 4, is described from the Bǎiţa Bihor skarn deposit, Bihor County, Romania. Graţianite occurs as thin lamellae, intimately intergrown with cosalite and bismuthinite, or as flower-shaped blebs within chalcopyrite, where it is associated with cosalite and tetradymite. Graţianite displays weak to modest bireflectance in air and oil, respectively, and strong anisotropy. The mean empirical composition based on 20 electron probe microanalyses is: (Mn 0.541 Fe 0.319 Pb 0.070 Cu 0.040 Cd 0.009 Ag 0.001) Σ0.980 (Bi 1.975 Sb 0.018) Σ1.993 (S 4.008 Se 0.012 Te 0.007) Σ4.027 , corresponding to the ideal formula MnBi 2 S 4. Graţianite crystallizes in the monoclinic system (space group C2/m). Single crystal X-ray studies of material extracted by the Focused Ion Beam-Scanning This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Cite as Authors (Year) Title. American Mineralogist, in press. (DOI will not work until issue is live.
Mineralization at Maldon, Victorian goldfields, Australia, is part of the Western Lachlan Foldbel... more Mineralization at Maldon, Victorian goldfields, Australia, is part of the Western Lachlan Foldbelt and is hosted by deformed Lower Ordovician metasediments intruded by the Late Devonian Harcourt Granite. Gold-BiTe -S associations in the deposit include four gold-bearing minerals (maldonite, native gold, jonassonite, and aurostibite) and a range of sulphotellurides from the tetradymite group, all of which are paragenetically tied to native bismuth. The simpler phase associations, involving bismuth, maldonite and one or the other Bi-(sulpho)tellurides, resemble the equivalents of eutectics in the system Au-BiTe and hint at crystallisation from melts. The complex associations include symplectites of gold and bismuth resulting from replacement of maldonite and are dominated by co-existing, sulphur-bearing species (joséite-A, joséite-B, an unnamed phase with bulk composition approximating to Bi 3 (Te,S) 2 and jonassonite). The complexity of such assemblages is also underpinned by chemical-structural inhomogeneity within the unnamed phase, i.e. nanoscale domains of Bi 14 (Te,S) 9 and Bi 5 (Te,S) 3 , as documented from electron diffractions obtained from a FIB-TEM foil. Although such lattice-scale intergrowths reveal polysomatic disorder that can be associated with replacement of one telluride by another, the structural modules in the overall stacking sequence indicate formation under local equilibrium conditions. The mineralogical complexity of all Au-BiTe -S associations can be modelled in terms of interaction between simpler assemblages and sulphur-bearing fluids. Three stages-all involving gold minerals-are recognised: (1) bismuth+ maldonite ± hedleyite; (2) Bi-sulphotellurides + jonassonite, and decomposition of maldonite (gold + bismuth); and (3) bismuthinite + gold from decomposition of maldonite or jonassonite. The last stage is coincident with chloritisation and occurs during or following granite emplacement. Thermodynamic modelling of maldonite replacement by bismuthinite and gold indicates conditions to overlap with the pyrite-hematite buffer at 258°C if neutral fluids are involved. The general replacement model for the deposit shows that local-scale reworking of maldonite and resultant gold remobilisation contributed to the apparent abundance of native gold. This interpretation is consistent with the protracted geological history at Maldon where granite intrusion postdates an orogenic event. Initial sulphur-poor assemblages crystallised from melts predating granite emplacement. The latest sulphidation event is attributed to retrograde fluids in the contact aureole, whereas the earlier one could also have been produced during the multi-stage deformation. Although observed assemblages and textures are the product of a complex sequence of overprinting, there is no need to invoke input of gold from more than a single fluid generation.
ABSTRACT Uranium-bearing hematite (containing up to several wt.% U), also containing Al, Mo, W an... more ABSTRACT Uranium-bearing hematite (containing up to several wt.% U), also containing Al, Mo, W and radiogenic Pb, is described from Olympic Dam, South Australia. These elements are present in grains that display both oscillatory zonation and porous structures. Laser-ablation inductively coupled mass spectrometry (LA-ICP-MS) element mapping confirms oscillatory and sectorial zoned domains in hematite grains are enriched in 238U- and 206Pb, and are distinct from those of W and Mo. The crystal structure and absence of inclusions within zoned hematite was assessed by transmission electron microscopy on foils obtained by in situ slicing across zonation patterns using the scanning electron microscope-focused ion beam technique. Satellite reflections on the electron diffraction patterns obtained from banded zones in hematite are attributable to long-range superstructure ordering, that is inferred to assist metal incorporation via the substitution 2Fe3+ ↔ Me6+ + vacancy, where Me = U, W, Mo. The suitability of U-bearing hematite for Pb–Pb geochronology as a first pass was tested on both zoned and porous hematite grains via LA-ICP-MS, using the GJ-1 zircon as the primary external standard. Only Pb–Pb ages were considered and resulted in 207Pb–206Pb ages of 1590 ± 8 Ma and 1577 ± 5 Ma for oscillatory and sector zoned hematite from two samples. Although reconnaissance in nature, these ages potentially support the supposition that mineralization is coeval with emplacement of the Gawler Range Volcanics and associated Hiltaba Intrusive Suite. The geochronological application utilizing an abundant refractory mineral represents a new tool for dating iron-bearing ores.
Pyrite commonly incorporates a wide range of trace and minor elements, which in turn may modify s... more Pyrite commonly incorporates a wide range of trace and minor elements, which in turn may modify some of the mineral’s physical and chemical properties. Published band position data for the Raman spectra of pyrite show a wide variation, and the relationship between band position and the trace/minor element incorporation in pyrite is poorly constrained until now. This prompted a case study on pyrite with varying As content from the Shizilishan Sr-(Pb-Zn) deposit, eastern China, combining electron probe microanalysis with Raman spectroscopy. Results show a significant correlation, with a major downshift (~10 cm–1) of the positions of all three Raman bands with increase of As content from below 0.05 to 4.89 wt % in pyrite. This phenomenon is attributed to increased bond lengths and local distortions within an expanded pyrite crystal structure. Results highlight the potential that Raman spectroscopy offers to estimate the contents of trace/minor elements—especially As—in pyrite. Given th...
Our compilation of ~900 published results of analyses for minerals of the tetradymite series (tel... more Our compilation of ~900 published results of analyses for minerals of the tetradymite series (tellurobismuthite, tetradymite, guanajuatite, paraguanajuatite, kawazulite, skippenite, tsumoite, hedleyite, pilsenite, laitakarite, ikunolite, joséite-A, joséite-B) allows compositional fields among naturally occurring Bi–Te–Se–S compounds to be established. New compositional data for ingodite, laitakarite, pilsenite, kawazulite and tellurobismuthite extend previously known compositional limits. Recognized minerals can, for the most part, be satisfactorily and conveniently classified according to the ratio Bi(+ Pb)/(Te + Se + S), into the subsystems (isoseries) Bi2Te3–Bi2Se3–Bi2S3, Bi4Te3–Bi4Se3–Bi4S3 and BiTe–BiSe–BiS. Most minerals show limited compo-sitional variation, but this is generally more extensive in the Se-bearing phases (e.g., laitakarite) and in certain members of the system Bi–Te, such as hedleyite and tsumoite. Substitution of minor Pb for Bi is widespread throughout the gr...
Trace element concentrations, particularly rare earth elements and yttrium (REY) in feldspars and... more Trace element concentrations, particularly rare earth elements and yttrium (REY) in feldspars and accessory minerals have been determined in a suite of albitized igneous, metasedimentary and metasomatite rocks from the Moonta-Wallaroo district, Olympic Cu-Au Province, South Australia. Results show that changes in REY-fractionation trends and concentrations in feldspars and common accessories are associated with key textures in albite-bearing associations from different lithologies. In granitic rocks, pseudomorphic replacement of pre-existing feldspars is typified by porous albite with cleavage-oriented intergrowths of sericite and pore-attached hematite. These observations are comparable with albitization features of granitic terranes elsewhere. A mineral association (albite-sericite ± chlorite), similar to that from granitoids, is observed as pervasive spots in limestone, inferring prograde skarnoid reactions at low fluid/rock ratio in an impure carbonate. In metasedimentary and me...
ABSTRACT Sphalerite is a common sulphide and is the dominant ore mineral in Zn-Pb sulphide deposi... more ABSTRACT Sphalerite is a common sulphide and is the dominant ore mineral in Zn-Pb sulphide deposits. Precise determination of minor and trace element concentrations in sulphides, including sphalerite, by Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry (LA-ICP-MS) is a potentially valuable petrogenetic tool. In this study, LA-ICP-MS is used to analyse 19 sphalerite samples from metamorphosed, sphalerite-bearing volcanic-associated and sedimentary exhalative massive sulphide deposits in Norway and Australia. The distributions of Mn, Fe, Co, Cu, Ga, Se, Ag, Cd, In, Sn, Sb, Hg, Tl, Pb and Bi are addressed with emphasis on how concentrations of these elements vary with metamorphic grade of the deposit and the extent of sulphide recrystallization. Results show that the concentrations of a group of trace elements which are believed to be present in sphalerite as micro- to nano-scale inclusions (Pb, Bi, and to some degree Cu and Ag) diminish with increasing metamorphic grade. This is interpreted as due to release of these elements during sphalerite recrystallization and subsequent remobilization to form discrete minerals elsewhere. The concentrations of lattice-bound elements (Mn, Fe, Cd, In and Hg) show no correlation with metamorphic grade. Primary metal sources, physico-chemical conditions during initial deposition, and element partitioning between sphalerite and co-existing sulphides are dominant in defining the concentrations of these elements and they appear to be readily re-incorporated into recrystallized sphalerite, offering potential insights into ore genesis. Given that sphalerite accommodates a variety of trace elements that can be precisely determined by contemporary microanalytical techniques, the mineral has considerable potential as a geothermometer, providing that element partitioning between sphalerite and coexisting minerals (galena, chalcopyrite etc.) can be quantified in samples for which the crystallization temperature can be independently constrained.
ABSTRACT The Basil Cu–Co deposit, Harts Range, central Australia, is hosted by the Riddock Amphib... more ABSTRACT The Basil Cu–Co deposit, Harts Range, central Australia, is hosted by the Riddock Amphibolite, a sequence that has been metamorphosed at upper-amphibolite- to granulite-facies conditions at 480–460 Ma (Larapinta Event), and subsequently reworked at amphibolite-facies conditions (450–300 Ma). As a result, many of the primary mineralization textures and other features that could characterise ore genesis have been obliterated. However, preserved textures and mineral relationships in the mineralized zone, allow some constraints to be placed on the genetic history of the deposit using mineralogical, petrographic and geochemical studies of host rocks and sulphides. Results of this study permit at least two geneticmodels to be ruled out. Firstly,whole rock geochemistry and garnet compositions suggest that the deposit is not a skarn system. Secondly, the lack of any significant Ni-signature, and the presence of abundant zircons in the host amphibolite (indicating that not all host rocks are mafic incomposition and/or magmatic in character), make an orthomagmatic Ni–Cu–(PGE) system unlikely. Alternatively, Basil is assigned to a volcanic-hosted massive sulphide (VHMS)-style of mineralization, formed on the seafloor, within basaltic and sedimentary host rocks, typical of deposits occurring in such settings. The lack of a recognisable hydrothermal alteration zone is consistent with either destruction of the alteration zone during metamorphism or detachment of the ore from alteration during later deformation. The occurrence of sulphide inclusions within garnet and amphibole indicates that the sulphides must be synmetamorphic or earlier. Partitioning of trace elements between pyrite and co-existing pyrrhotite suggests that (re)crystallization occurred under equilibrium conditions. The composition of sphalerite coexisting with pyrite and pyrrhotite indicates crystallization at pressures of at least 10 kbar, consistent with peak metamorphism during the Early Ordovician Larapinta Event. Zr-in-titanite geothermometry indicates peak temperatures of 730–745 °C.
ABSTRACT ‘Green energy futures’ are driving unprecedented demand for Rare Earth Elements (REE), u... more ABSTRACT ‘Green energy futures’ are driving unprecedented demand for Rare Earth Elements (REE), underpinning significant exploration activity worldwide. Understanding how economic REE concentrations form is critical for development of exploration models. REE mineralisation in the Browns Ranges, Gordon Downs Region, Western Australia, comprises xenotime-dominant mineralisation hosted within Archaean to Palaeoproterozoic metasedimentary units (Browns Range Metamorphics). Mineralogical, petrographic and mineral-chemical investigation, including trace element analysis by Laser-Ablation Inductively-Coupled Plasma Mass Spectroscopy, gives insights into the mineralogical distribution and partitioning of REE, and also provides evidence for the genetic evolution of the Browns Range REE mineralisation via a succession of hydrothermal processes.
ABSTRACT The common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at ... more ABSTRACT The common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at Pepegoona, Pepegoona West and Pannikan, Lake Eyre Basin, South Australia. Combined chemical, isotopic and microstructural analysis of pyrite indicates variation in fluid composition, sulfur source and precipitation conditions during a protracted mineralization event. The results show the significant role played by pyrite as a metal scavenger and monitor of fluid changes in low-temperature hydrothermal systems.
Zirconium is an element of considerable petrogenetic significance but is rarely found in hematite... more Zirconium is an element of considerable petrogenetic significance but is rarely found in hematite at concentrations higher than a few parts-per-million (ppm). Coarse-grained hematite ore from the metamorphosed Peculiar Knob iron deposit, South Australia, contains anomalous concentrations of Zr and has been investigated using microanalytical techniques that can bridge the micron- to nanoscales to understand the distribution of Zr in the ore. Hematite displays textures attributable to annealing under conditions of high-grade metamorphism, deformation twins (r~85˚ to hematite elongation), relict magnetite and fields of sub-micron-wide inclusions of baddeleyite as conjugate needles with orientation at ~110˚/70˚. Skeletal and granoblastic zircon, containing only a few ppm U, are both present interstitial to hematite. Using laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) spot analysis and mapping, the concentration of Zr in hematite is determined to be ~260 ppm on ...
The accelerated pace of transition to green energy technologies has led to increased demand for r... more The accelerated pace of transition to green energy technologies has led to increased demand for rare-earth elements (REEs). Fluorocarbonates from the bastnäsite [REE(CO3)F]—synchysite [CaREE(CO3)2F] group are abundant in nature and the dominant REE minerals in the >10 billion ton Olympic Dam Cu–U–Au–Ag deposit, South Australia. Intergrowths of bastnäsite and synchysite slabs at the nanometer to micron scales are the rule rather than the exception and account for structural and compositional changes between the two endmembers. This article reviews REE-fluorocarbonate mineralogy at Olympic Dam with emphasis on the significance of intergrowths among bastnäsite and synchysite for achievement of thermodynamic equilibrium. Imaging by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) allows visualization of atomic-scale periodicity and structural modularity in REE fluorocarbonates and, in turn, determination of domain compositions, which are otherwise ...
The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias ... more The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm-to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled
The new mineral graţianite, MnBi 2 S 4, is described from the Bǎiţa Bihor skarn deposit, Bihor Co... more The new mineral graţianite, MnBi 2 S 4, is described from the Bǎiţa Bihor skarn deposit, Bihor County, Romania. Graţianite occurs as thin lamellae, intimately intergrown with cosalite and bismuthinite, or as flower-shaped blebs within chalcopyrite, where it is associated with cosalite and tetradymite. Graţianite displays weak to modest bireflectance in air and oil, respectively, and strong anisotropy. The mean empirical composition based on 20 electron probe microanalyses is: (Mn 0.541 Fe 0.319 Pb 0.070 Cu 0.040 Cd 0.009 Ag 0.001) Σ0.980 (Bi 1.975 Sb 0.018) Σ1.993 (S 4.008 Se 0.012 Te 0.007) Σ4.027 , corresponding to the ideal formula MnBi 2 S 4. Graţianite crystallizes in the monoclinic system (space group C2/m). Single crystal X-ray studies of material extracted by the Focused Ion Beam-Scanning This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Cite as Authors (Year) Title. American Mineralogist, in press. (DOI will not work until issue is live.
Mineralization at Maldon, Victorian goldfields, Australia, is part of the Western Lachlan Foldbel... more Mineralization at Maldon, Victorian goldfields, Australia, is part of the Western Lachlan Foldbelt and is hosted by deformed Lower Ordovician metasediments intruded by the Late Devonian Harcourt Granite. Gold-BiTe -S associations in the deposit include four gold-bearing minerals (maldonite, native gold, jonassonite, and aurostibite) and a range of sulphotellurides from the tetradymite group, all of which are paragenetically tied to native bismuth. The simpler phase associations, involving bismuth, maldonite and one or the other Bi-(sulpho)tellurides, resemble the equivalents of eutectics in the system Au-BiTe and hint at crystallisation from melts. The complex associations include symplectites of gold and bismuth resulting from replacement of maldonite and are dominated by co-existing, sulphur-bearing species (joséite-A, joséite-B, an unnamed phase with bulk composition approximating to Bi 3 (Te,S) 2 and jonassonite). The complexity of such assemblages is also underpinned by chemical-structural inhomogeneity within the unnamed phase, i.e. nanoscale domains of Bi 14 (Te,S) 9 and Bi 5 (Te,S) 3 , as documented from electron diffractions obtained from a FIB-TEM foil. Although such lattice-scale intergrowths reveal polysomatic disorder that can be associated with replacement of one telluride by another, the structural modules in the overall stacking sequence indicate formation under local equilibrium conditions. The mineralogical complexity of all Au-BiTe -S associations can be modelled in terms of interaction between simpler assemblages and sulphur-bearing fluids. Three stages-all involving gold minerals-are recognised: (1) bismuth+ maldonite ± hedleyite; (2) Bi-sulphotellurides + jonassonite, and decomposition of maldonite (gold + bismuth); and (3) bismuthinite + gold from decomposition of maldonite or jonassonite. The last stage is coincident with chloritisation and occurs during or following granite emplacement. Thermodynamic modelling of maldonite replacement by bismuthinite and gold indicates conditions to overlap with the pyrite-hematite buffer at 258°C if neutral fluids are involved. The general replacement model for the deposit shows that local-scale reworking of maldonite and resultant gold remobilisation contributed to the apparent abundance of native gold. This interpretation is consistent with the protracted geological history at Maldon where granite intrusion postdates an orogenic event. Initial sulphur-poor assemblages crystallised from melts predating granite emplacement. The latest sulphidation event is attributed to retrograde fluids in the contact aureole, whereas the earlier one could also have been produced during the multi-stage deformation. Although observed assemblages and textures are the product of a complex sequence of overprinting, there is no need to invoke input of gold from more than a single fluid generation.
ABSTRACT Uranium-bearing hematite (containing up to several wt.% U), also containing Al, Mo, W an... more ABSTRACT Uranium-bearing hematite (containing up to several wt.% U), also containing Al, Mo, W and radiogenic Pb, is described from Olympic Dam, South Australia. These elements are present in grains that display both oscillatory zonation and porous structures. Laser-ablation inductively coupled mass spectrometry (LA-ICP-MS) element mapping confirms oscillatory and sectorial zoned domains in hematite grains are enriched in 238U- and 206Pb, and are distinct from those of W and Mo. The crystal structure and absence of inclusions within zoned hematite was assessed by transmission electron microscopy on foils obtained by in situ slicing across zonation patterns using the scanning electron microscope-focused ion beam technique. Satellite reflections on the electron diffraction patterns obtained from banded zones in hematite are attributable to long-range superstructure ordering, that is inferred to assist metal incorporation via the substitution 2Fe3+ ↔ Me6+ + vacancy, where Me = U, W, Mo. The suitability of U-bearing hematite for Pb–Pb geochronology as a first pass was tested on both zoned and porous hematite grains via LA-ICP-MS, using the GJ-1 zircon as the primary external standard. Only Pb–Pb ages were considered and resulted in 207Pb–206Pb ages of 1590 ± 8 Ma and 1577 ± 5 Ma for oscillatory and sector zoned hematite from two samples. Although reconnaissance in nature, these ages potentially support the supposition that mineralization is coeval with emplacement of the Gawler Range Volcanics and associated Hiltaba Intrusive Suite. The geochronological application utilizing an abundant refractory mineral represents a new tool for dating iron-bearing ores.
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