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Papers by Sarah Dare
Economic Geology
Seven major and numerous lesser Fe oxide occurrences within the 1.47 Ga St. Francois Mountains te... more Seven major and numerous lesser Fe oxide occurrences within the 1.47 Ga St. Francois Mountains terrane in Missouri (USA) have previously been described as iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG) deposits. Researchers speculate that these contain significant amounts of critical minerals, most notably rare earth elements and cobalt. One of the less-studied deposits in the region is the 1.455 Ga Kratz Spring deposit. The deposit consists of two steeply dipping magnetite bodies beneath 450 m of sedimentary cover. The genesis of the Kratz Spring deposit and its relationship to nearby IOA-IOCG deposits remains poorly constrained. To better understand the formation of the Kratz Spring deposit, the authors integrated stratigraphic, petrographic, and bulk rock studies with in situ trace element and Fe isotope chemistry of magnetite and hematite. These data show that the Kratz Spring deposit is hydrothermal in origin but is divided into two subdeposits according to differen...
Geochimica et Cosmochimica Acta
Mineralium Deposita
Chalcopyrite from 13 worldwide representative Ni-Cu sulfide and Reef-type PGE deposits were inves... more Chalcopyrite from 13 worldwide representative Ni-Cu sulfide and Reef-type PGE deposits were investigated using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to evaluate its potential as an indicator mineral for exploration. Trace element data were investigated with PLS-DA (partial least square-discriminant analysis) which, combined with discriminant binary diagrams, allows identification of geochemical criteria for discrimination of deposit type (Ni-Cu sulfide vs. Reef-type PGE) and ore type (Cu-rich vs. Fe-rich). A first PLS-DA model (using Bi, In, Se Sn and Te ) discriminates chalcopyrite by deposit type; those from Reef-type PGE have higher Se relative to Ni-Cu sulfide deposits, as a result of higher R factors, whereas chalcopyrite from Ni-Cu sulfide deposits is higher in Te, Bi and Sb. Platinum Group Mineral (PGM) crystallization in Reef-type PGE deposits typically deplete Te, Bi and Sb in co-existing chalcopyrite, enhancing the differences between these two deposit types. The second PLS-DA model (based on Sb, Se, Sn, Tl and Zn) discriminates by ore type, showing that chalcopyrite from Cu-rich samples is enriched in Sn, Se and Zn relative to Fe-rich/unzoned samples, mainly as a result of sulfide fractionation. Complementary discriminant diagrams Se/(Te+Bi) vs. Se and 2Zn/(3Se+5Sn) vs. Se are proposed to discriminate chalcopyrite by deposit type and ore type, respectively. This study demonstrates that the trace element composition of chalcopyrite enables its use as an indicator mineral for exploration.
Ore Geology Reviews, 2022
Knowledge of the trace element compositions of Fe-oxides will help to develop indicator minerals ... more Knowledge of the trace element compositions of Fe-oxides will help to develop indicator minerals for exploration in addition to improving our understanding of the petrogenesis of the deposit. This study has characterized Fe-oxides, using laser ablation ICP-MS, from the upper part of Sept-Iles layered intrusion (Quebec, Canada), which hosts an Fe-Ti-P deposit, rich in magnetite, ilmenite and apatite. The Fe-oxides record a sequence of fractional crystallization that evolves from the bottom to the top of the deposit. Trace elements in both magnetite and ilmenite vary as a function of their stratigraphic position (Fig. 1). Aluminium, Co, Cr, Mg and V decrease in the Fe-oxides up sequence whereas Ga, Ge, Hf, Mn, Mo, Nb, W, Sc, Sn, Ta, Zr and Zn increase. These geochemical variations appear to be controlled by the partition coefficients of compatible (e.g., V) and incompatible (e.g., Mo) elements into the cocrystallizing phases (olivine, plagioclase, magnetite, ilmenite and apatite) and ...
Magnetite forms under a wide variety of conditions, crystallizing at high temperature from silica... more Magnetite forms under a wide variety of conditions, crystallizing at high temperature from silicate magmas or precipitating at low temperature from hydrothermal fluids or seawater. Trace element content of magnetite may reflect the differences in these conditions. Therefore as part of a larger project examining the trace element content of magnetite, by laser ablation ICP-MS, we have characterized magnetite in magmatic massive Fe-oxide deposits (magnetite-ilmenite, ± apatite) from layered intrusions (Bushveld and Sept Iles Complexes) and a massif anorthosite (Lac St. Jean) in order to study how magmatic processes affect the trace element compositions. We have also collected trace element data from the enigmatic “magnetite lava flows” from El Laco, Chile, in order to consider whether these magnetites are indeed of igneous origin. Magnetite from the layered intrusions record the evolution of the fractionating silicate liquid (Fig. 1a), with those found lower in the sequence (more prim...
Economic Geology, 2020
Mineralogical and chemical zonations observed in massive sulfide ores from Ni-Cu-platinum group e... more Mineralogical and chemical zonations observed in massive sulfide ores from Ni-Cu-platinum group element (PGE) deposits are commonly ascribed to the fractional crystallization of monosulfide solid solution (MSS) and intermediate solid solution (ISS) from sulfide liquid. Recent studies of classic examples of zoned orebodies at Sudbury and Voisey’s Bay (Canada) demonstrated that the chemistry of magnetite crystallized from sulfide liquid was varying in response to sulfide fractional crystallization. Other classic examples of zoned Ni-Cu-PGE sulfide deposits occur in the Norilsk-Talnakh mining district (Russia), yet magnetite in these orebodies has received little attention. In this contribution, we document the chemistry of magnetite in samples from Norilsk-Talnakh, spanning the classic range of sulfide composition, from Cu poor (MSS) to Cu rich (ISS). Based on textural features and mineral associations, four types of magnetite with distinct chemical composition are identified: (1) MSS...
Goldschmidt2021 abstracts, 2021
Goldschmidt2021 abstracts, 2021
Goldschmidt2021 abstracts, 2021
Goldschmidt2021 abstracts, 2021
Economic Geology, 2020
Pentlandite is the dominant Ni-hosting ore mineral in most magmatic sulfide deposits and has conv... more Pentlandite is the dominant Ni-hosting ore mineral in most magmatic sulfide deposits and has conventionally been interpreted as being entirely generated by solid-state exsolution from the high-temperature monosulfide solid solution (MSS) (Fe,Ni)1–xS. This process gives rise to the development of loops of pentlandite surrounding pyrrhotite grains. Recently it has been recognized that not all pentlandite forms by exsolution. Some may form as the result of peritectic reaction between early formed MSS and residual Ni-Cu–rich sulfide liquid during differentiation of the sulfide melt, such that at least some loop textures may be genuinely magmatic in origin. Testing this hypothesis involved microbeam X-ray fluorescence mapping to image pentlandite-pyrrhotite-chalcopyrite intergrowths from a range of different deposits. These deposits exemplify slowly cooled magmatic environments (Nova, Western Australia; Sudbury, Canada), globular ores from shallow-level intrusions (Norilsk, Siberia), ext...
Journal of Sedimentary Research, 2016
Conventional provenance studies of high grade (e.g., amphibolite facies) metamorphic sandstone ar... more Conventional provenance studies of high grade (e.g., amphibolite facies) metamorphic sandstone are limited due to intense recrystallization, destruction of original minerals, and growth of new minerals. Magnetite is a heavy mineral common in a wide range of sedimentary rocks. It can originate from a wide range of rock sources from high-temperature to low-temperature magmatic, metamorphic, or hydrothermal environments. Laser ablation (LA)-ICP-MS and electron microprobe analytical techniques allowed determination of a wide range of trace elements at sub ppm levels in magnetite to identify the provenance of two Archean sedimentary formations in Eeyou Istchee Baie-James, Québec, Canada. Results were plotted on multi-element diagrams. The most compatible elements in magnetite were identified as the most discriminant elements to differentiate four potential different rock sources for the Magin Formation. Overlap between the spectra of the Magin and Keyano formations substantiate the existence of a common source. Interbedded conglomerate magnetite-bearing clasts were examined to determine potential source-rocks. Mafic clasts apparently do not contain magnetite. Detrital magnetites analyzed have low Ti values that would support either felsic (to intermediate) plutonic or a hydrothermal source. The trace-element spectra of detrital magnetite from the sandstone beds were compared to magnetite spectra from conglomerate clasts of banded iron formation and felsic to intermediate plutonic rocks. Only magnetites from felsic plutonic rocks have a signature similar to those from the sandstone. To further substantiate a felsic plutonic source, a detailed study of magnetite chemistry from ten felsic and intermediate regional plutons from a regional databank allowed us to recognize that each of these plutons has a particular signature on the basis of wide variations in Ni and Cr. From this data base, four individual plutons were identified as potential sources for the Magin Formation. Recently published magnetite discrimination diagrams proposed for mineral deposits can be applied to sedimentary magnetite provenance. However, our database shows the importance of identifying low-Ti magnetite from felsic rocks since these could be misidentified as low-Ti magnetite from hydrothermal mineral deposits. Thus, we propose improvement to these diagrams by differentiating magnetite from felsic magmatic (low Ni/Cr) and hydrothermal (high Ni/Cr) sources before applying the mineral-deposit discrimination diagrams.
ABSTRACT It is now possible to determine the platinum-group element (PGE) and chalcophile element... more ABSTRACT It is now possible to determine the platinum-group element (PGE) and chalcophile element contents of pyrrhotite (Po), pentlandite (Pn) and chalcopyrite (Ccp). This information may be used to: a) Improve recovery of important economic elements from ore; b) Consider the petrogenesis of the rocks. We have determined the PGE and other chalcophile element contents of Po, Pn and Ccp from a meteorite, a subvolcanic sill, the Merensky Reef Bushveld, Great Dyke, JM Reef Stillwater, AP and PV Reefs Penikat and Creighton Mine at Sudbury. The aims of these studies are to determine which phases host the elements and what implications the host phases have for the petrogenesis of the rocks involved. Sulfides from the meteorite and the subvolcanic sill have been chilled fairly rapidly and experienced very little subsolidus re-equilibration. The Bushveld and Great Dyke sulfides cooled slowly and thus had longer to exsolve. The Stillwater and Penikat sulfides were metamorphosed post-intrusion thus these sulfides have been reheated. The Sudbury sulfides have been deformed and metamorphosed and are the major phases whereas in all other cases the sulfides were minor phases in the rocks. In all cases Pt and Au are not present in the sulfides. Platinum is generally found as Pt-arsenides, Pt-bismuth- tellurides or Pt-alloys as inclusions in the sulfides. Palladium is generally hosted principally by Pn. Osmium and Ru are present in Po and Pn. In the meteorite, the subvolcanic sill and the unmetamorphosed intrusions Re, Ir and Rh are also present in Po and Pn. However in the metamorphosed and deformed sulfides Ir and Rh are present largely as sulfarsenides and as various Re minerals included in the sulfides. Thus in the least metamorphosed and deformed rocks all the PGE except Pt are present in the sulfides. In the metamorphosed rocks Re, Ir and Rh tend to form inclusions in the sulfides. We suggest that this is the result of exsolution during reworking of the sulfides. The concentration of Re, Os, Ir, Ru and Rh in Po and Pn is consistent with the formation of Po and Pn from monosulfide solid solution. However the mechanism for the concentration of Pd in pentlandite is not understood.
In order to use trace element composition of magnetite as an indication of its origin it is neces... more In order to use trace element composition of magnetite as an indication of its origin it is necessary to understand the processes that control the trace element concentrations in magnetite. We have characterised trace element distribution in magnetite, using laser ablation ICP-MS, from magmatic ore deposits (Fe-Ti-V-P and Ni-Cu-PGE) where the paragenetic sequences are well constrained. Changes in composition of the liquid, driven by crystal fractionation, are recorded by magnetite in both silicate and sulfide melts. The composition of magnetite is sensitive to co-crystallizing phases, with marked depletion in Ti when ilmenite crystallizes before magnetite and in Cu when a sulfide liquid segregates. Multi-element variation diagrams show that magmatic magnetites have chemical signatures distinct from hydrothermal magnetite due to differences in fluid composition and different conditions of formation (e.g., competing phases, redox and temperature). Chemical fingerprinting of magnetite from the magnetite 'lava flows' of El Laco, northern Chile, provides new evidence to support the hydrothermal alteration model rather than a magmatic origin.
J'aimerais d'abord remercier Sarah Dare, co-directrice du projet, qui semaines après semaines éta... more J'aimerais d'abord remercier Sarah Dare, co-directrice du projet, qui semaines après semaines était là pour me soutenir, me conseiller, me diriger et surtout de m'encourager. Merci beaucoup j'ai adoré travailler avec vous. Merci à Sarah-Jane Barnes, directrice du projet et titulaire de la Chaire de Recherche du Canada en Métallogénie Magmatique, qui a initié le projet et qui m'a orienté dans la bonne direction pour la présentation. Merci de vos conseils. Merci à Danny Savard et Sadia Mehdi du laboratoire LabMaTer pour leur patience et de leur aide pour l'utilisation et l'interprétation avec le LA-ICP-MS. Merci à Paul Bédard, second lecteur, pour les conseils lors de la rédaction de cet ouvrage. Merci à Hugues Guérin Tremblay de la compagnie Ressources d'Arianne qui ma ouvert ses portes pour répondre à mes questions.
ABSTRACT Oxide minerals such as magnetite and chromite are becoming popular in the field of geoch... more ABSTRACT Oxide minerals such as magnetite and chromite are becoming popular in the field of geochemical exploration because the wide variety of trace elements present could potentially be used in provenance studies [1]. The method of analysis used is commonly LA-ICP-MS because it provides limits of detections down to ng/g levels when the analytical parameters can be optimized. No matrixmatched reference materials (RM) are available at the moment for in-situ calibration. Artificial glasses could be used to calibrate but only Fe can be used as an internal standard because of the inhomogeneous distribution of most of the other elements in magnetite. [2] proposed using NIST-610 to calibrate. However, the Fe content in NIST-610 is low at c.a. 0.05% while Fe in magnetite is c.a. 72%, thus limiting the use of NIST-610 to a beam >25m, with a maximum precision of R2<0.85 when results are compared to EMPA analysis of natural magnetite. [3] proposed the combination of 5 iron-rich RM to cover the elements of interest. Based on the elements for which EMPA results are available this calibration is satisfactory. However, this technique is time consuming and reduces the space available in the ablation cell.
Mineralium Deposita, 2014
Gondwana Research, 2015
Various combinations of zircon, quartz, corundum, K-feldspar, plagioclase, apatite, amphibole, ru... more Various combinations of zircon, quartz, corundum, K-feldspar, plagioclase, apatite, amphibole, rutile, titanite, almandine garnet, kyanite, andalusite, and coesite have been recovered from podiform chromitites of the Luobusa and Dongqiao ophiolites in Tibet, the Oman ophiolite and the Ray-Iz ophiolite in the Polar Urals, Russia. Chromitites in all four ophiolites also contain moissanite and the Luobusa and Ray-Iz ophiolites contain in-situ diamonds. Most of the recovered zircons are sub-rounded grains with complex internal structures indicating polyphase growth. Trace element contents and a low-pressure inclusion assemblage (quartz, muscovite, K-feldspar, apatite, ilmenite, rutile) indicate a continental crustal origin for the zircons. They have SIMS U-Pb ages that are generally much older than the host body (total range: 90 to 2500 Ma). The presence of numerous crustal minerals, particularly zircon, suggests derivation from metasedimentary rocks subducted into the mantle. Their preservation in chromitites and peridotites implies effective isolation from the mafic melts that formed the ophiolites. We suggest that most of these minerals were derived from the crustal parts of subducted slabs and were encapsulated into chromite grains precipitated from rising asthenospheric and suprasubduction magmas. The chromite grains were carried in melt channels to shallow levels in suprasubduction mantle wedges and then deposited as podiform chromitites near the Moho. The rise of asthenospheric peridotites into suprasubduction zones was facilitated by subduction initiation and possibly by slab tear allowing mixing of the UHP, highly reduced minerals and crustal minerals now found in ophiolitic chromitites and peridotites.
Economic Geology
Seven major and numerous lesser Fe oxide occurrences within the 1.47 Ga St. Francois Mountains te... more Seven major and numerous lesser Fe oxide occurrences within the 1.47 Ga St. Francois Mountains terrane in Missouri (USA) have previously been described as iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG) deposits. Researchers speculate that these contain significant amounts of critical minerals, most notably rare earth elements and cobalt. One of the less-studied deposits in the region is the 1.455 Ga Kratz Spring deposit. The deposit consists of two steeply dipping magnetite bodies beneath 450 m of sedimentary cover. The genesis of the Kratz Spring deposit and its relationship to nearby IOA-IOCG deposits remains poorly constrained. To better understand the formation of the Kratz Spring deposit, the authors integrated stratigraphic, petrographic, and bulk rock studies with in situ trace element and Fe isotope chemistry of magnetite and hematite. These data show that the Kratz Spring deposit is hydrothermal in origin but is divided into two subdeposits according to differen...
Geochimica et Cosmochimica Acta
Mineralium Deposita
Chalcopyrite from 13 worldwide representative Ni-Cu sulfide and Reef-type PGE deposits were inves... more Chalcopyrite from 13 worldwide representative Ni-Cu sulfide and Reef-type PGE deposits were investigated using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to evaluate its potential as an indicator mineral for exploration. Trace element data were investigated with PLS-DA (partial least square-discriminant analysis) which, combined with discriminant binary diagrams, allows identification of geochemical criteria for discrimination of deposit type (Ni-Cu sulfide vs. Reef-type PGE) and ore type (Cu-rich vs. Fe-rich). A first PLS-DA model (using Bi, In, Se Sn and Te ) discriminates chalcopyrite by deposit type; those from Reef-type PGE have higher Se relative to Ni-Cu sulfide deposits, as a result of higher R factors, whereas chalcopyrite from Ni-Cu sulfide deposits is higher in Te, Bi and Sb. Platinum Group Mineral (PGM) crystallization in Reef-type PGE deposits typically deplete Te, Bi and Sb in co-existing chalcopyrite, enhancing the differences between these two deposit types. The second PLS-DA model (based on Sb, Se, Sn, Tl and Zn) discriminates by ore type, showing that chalcopyrite from Cu-rich samples is enriched in Sn, Se and Zn relative to Fe-rich/unzoned samples, mainly as a result of sulfide fractionation. Complementary discriminant diagrams Se/(Te+Bi) vs. Se and 2Zn/(3Se+5Sn) vs. Se are proposed to discriminate chalcopyrite by deposit type and ore type, respectively. This study demonstrates that the trace element composition of chalcopyrite enables its use as an indicator mineral for exploration.
Ore Geology Reviews, 2022
Knowledge of the trace element compositions of Fe-oxides will help to develop indicator minerals ... more Knowledge of the trace element compositions of Fe-oxides will help to develop indicator minerals for exploration in addition to improving our understanding of the petrogenesis of the deposit. This study has characterized Fe-oxides, using laser ablation ICP-MS, from the upper part of Sept-Iles layered intrusion (Quebec, Canada), which hosts an Fe-Ti-P deposit, rich in magnetite, ilmenite and apatite. The Fe-oxides record a sequence of fractional crystallization that evolves from the bottom to the top of the deposit. Trace elements in both magnetite and ilmenite vary as a function of their stratigraphic position (Fig. 1). Aluminium, Co, Cr, Mg and V decrease in the Fe-oxides up sequence whereas Ga, Ge, Hf, Mn, Mo, Nb, W, Sc, Sn, Ta, Zr and Zn increase. These geochemical variations appear to be controlled by the partition coefficients of compatible (e.g., V) and incompatible (e.g., Mo) elements into the cocrystallizing phases (olivine, plagioclase, magnetite, ilmenite and apatite) and ...
Magnetite forms under a wide variety of conditions, crystallizing at high temperature from silica... more Magnetite forms under a wide variety of conditions, crystallizing at high temperature from silicate magmas or precipitating at low temperature from hydrothermal fluids or seawater. Trace element content of magnetite may reflect the differences in these conditions. Therefore as part of a larger project examining the trace element content of magnetite, by laser ablation ICP-MS, we have characterized magnetite in magmatic massive Fe-oxide deposits (magnetite-ilmenite, ± apatite) from layered intrusions (Bushveld and Sept Iles Complexes) and a massif anorthosite (Lac St. Jean) in order to study how magmatic processes affect the trace element compositions. We have also collected trace element data from the enigmatic “magnetite lava flows” from El Laco, Chile, in order to consider whether these magnetites are indeed of igneous origin. Magnetite from the layered intrusions record the evolution of the fractionating silicate liquid (Fig. 1a), with those found lower in the sequence (more prim...
Economic Geology, 2020
Mineralogical and chemical zonations observed in massive sulfide ores from Ni-Cu-platinum group e... more Mineralogical and chemical zonations observed in massive sulfide ores from Ni-Cu-platinum group element (PGE) deposits are commonly ascribed to the fractional crystallization of monosulfide solid solution (MSS) and intermediate solid solution (ISS) from sulfide liquid. Recent studies of classic examples of zoned orebodies at Sudbury and Voisey’s Bay (Canada) demonstrated that the chemistry of magnetite crystallized from sulfide liquid was varying in response to sulfide fractional crystallization. Other classic examples of zoned Ni-Cu-PGE sulfide deposits occur in the Norilsk-Talnakh mining district (Russia), yet magnetite in these orebodies has received little attention. In this contribution, we document the chemistry of magnetite in samples from Norilsk-Talnakh, spanning the classic range of sulfide composition, from Cu poor (MSS) to Cu rich (ISS). Based on textural features and mineral associations, four types of magnetite with distinct chemical composition are identified: (1) MSS...
Goldschmidt2021 abstracts, 2021
Goldschmidt2021 abstracts, 2021
Goldschmidt2021 abstracts, 2021
Goldschmidt2021 abstracts, 2021
Economic Geology, 2020
Pentlandite is the dominant Ni-hosting ore mineral in most magmatic sulfide deposits and has conv... more Pentlandite is the dominant Ni-hosting ore mineral in most magmatic sulfide deposits and has conventionally been interpreted as being entirely generated by solid-state exsolution from the high-temperature monosulfide solid solution (MSS) (Fe,Ni)1–xS. This process gives rise to the development of loops of pentlandite surrounding pyrrhotite grains. Recently it has been recognized that not all pentlandite forms by exsolution. Some may form as the result of peritectic reaction between early formed MSS and residual Ni-Cu–rich sulfide liquid during differentiation of the sulfide melt, such that at least some loop textures may be genuinely magmatic in origin. Testing this hypothesis involved microbeam X-ray fluorescence mapping to image pentlandite-pyrrhotite-chalcopyrite intergrowths from a range of different deposits. These deposits exemplify slowly cooled magmatic environments (Nova, Western Australia; Sudbury, Canada), globular ores from shallow-level intrusions (Norilsk, Siberia), ext...
Journal of Sedimentary Research, 2016
Conventional provenance studies of high grade (e.g., amphibolite facies) metamorphic sandstone ar... more Conventional provenance studies of high grade (e.g., amphibolite facies) metamorphic sandstone are limited due to intense recrystallization, destruction of original minerals, and growth of new minerals. Magnetite is a heavy mineral common in a wide range of sedimentary rocks. It can originate from a wide range of rock sources from high-temperature to low-temperature magmatic, metamorphic, or hydrothermal environments. Laser ablation (LA)-ICP-MS and electron microprobe analytical techniques allowed determination of a wide range of trace elements at sub ppm levels in magnetite to identify the provenance of two Archean sedimentary formations in Eeyou Istchee Baie-James, Québec, Canada. Results were plotted on multi-element diagrams. The most compatible elements in magnetite were identified as the most discriminant elements to differentiate four potential different rock sources for the Magin Formation. Overlap between the spectra of the Magin and Keyano formations substantiate the existence of a common source. Interbedded conglomerate magnetite-bearing clasts were examined to determine potential source-rocks. Mafic clasts apparently do not contain magnetite. Detrital magnetites analyzed have low Ti values that would support either felsic (to intermediate) plutonic or a hydrothermal source. The trace-element spectra of detrital magnetite from the sandstone beds were compared to magnetite spectra from conglomerate clasts of banded iron formation and felsic to intermediate plutonic rocks. Only magnetites from felsic plutonic rocks have a signature similar to those from the sandstone. To further substantiate a felsic plutonic source, a detailed study of magnetite chemistry from ten felsic and intermediate regional plutons from a regional databank allowed us to recognize that each of these plutons has a particular signature on the basis of wide variations in Ni and Cr. From this data base, four individual plutons were identified as potential sources for the Magin Formation. Recently published magnetite discrimination diagrams proposed for mineral deposits can be applied to sedimentary magnetite provenance. However, our database shows the importance of identifying low-Ti magnetite from felsic rocks since these could be misidentified as low-Ti magnetite from hydrothermal mineral deposits. Thus, we propose improvement to these diagrams by differentiating magnetite from felsic magmatic (low Ni/Cr) and hydrothermal (high Ni/Cr) sources before applying the mineral-deposit discrimination diagrams.
ABSTRACT It is now possible to determine the platinum-group element (PGE) and chalcophile element... more ABSTRACT It is now possible to determine the platinum-group element (PGE) and chalcophile element contents of pyrrhotite (Po), pentlandite (Pn) and chalcopyrite (Ccp). This information may be used to: a) Improve recovery of important economic elements from ore; b) Consider the petrogenesis of the rocks. We have determined the PGE and other chalcophile element contents of Po, Pn and Ccp from a meteorite, a subvolcanic sill, the Merensky Reef Bushveld, Great Dyke, JM Reef Stillwater, AP and PV Reefs Penikat and Creighton Mine at Sudbury. The aims of these studies are to determine which phases host the elements and what implications the host phases have for the petrogenesis of the rocks involved. Sulfides from the meteorite and the subvolcanic sill have been chilled fairly rapidly and experienced very little subsolidus re-equilibration. The Bushveld and Great Dyke sulfides cooled slowly and thus had longer to exsolve. The Stillwater and Penikat sulfides were metamorphosed post-intrusion thus these sulfides have been reheated. The Sudbury sulfides have been deformed and metamorphosed and are the major phases whereas in all other cases the sulfides were minor phases in the rocks. In all cases Pt and Au are not present in the sulfides. Platinum is generally found as Pt-arsenides, Pt-bismuth- tellurides or Pt-alloys as inclusions in the sulfides. Palladium is generally hosted principally by Pn. Osmium and Ru are present in Po and Pn. In the meteorite, the subvolcanic sill and the unmetamorphosed intrusions Re, Ir and Rh are also present in Po and Pn. However in the metamorphosed and deformed sulfides Ir and Rh are present largely as sulfarsenides and as various Re minerals included in the sulfides. Thus in the least metamorphosed and deformed rocks all the PGE except Pt are present in the sulfides. In the metamorphosed rocks Re, Ir and Rh tend to form inclusions in the sulfides. We suggest that this is the result of exsolution during reworking of the sulfides. The concentration of Re, Os, Ir, Ru and Rh in Po and Pn is consistent with the formation of Po and Pn from monosulfide solid solution. However the mechanism for the concentration of Pd in pentlandite is not understood.
In order to use trace element composition of magnetite as an indication of its origin it is neces... more In order to use trace element composition of magnetite as an indication of its origin it is necessary to understand the processes that control the trace element concentrations in magnetite. We have characterised trace element distribution in magnetite, using laser ablation ICP-MS, from magmatic ore deposits (Fe-Ti-V-P and Ni-Cu-PGE) where the paragenetic sequences are well constrained. Changes in composition of the liquid, driven by crystal fractionation, are recorded by magnetite in both silicate and sulfide melts. The composition of magnetite is sensitive to co-crystallizing phases, with marked depletion in Ti when ilmenite crystallizes before magnetite and in Cu when a sulfide liquid segregates. Multi-element variation diagrams show that magmatic magnetites have chemical signatures distinct from hydrothermal magnetite due to differences in fluid composition and different conditions of formation (e.g., competing phases, redox and temperature). Chemical fingerprinting of magnetite from the magnetite 'lava flows' of El Laco, northern Chile, provides new evidence to support the hydrothermal alteration model rather than a magmatic origin.
J'aimerais d'abord remercier Sarah Dare, co-directrice du projet, qui semaines après semaines éta... more J'aimerais d'abord remercier Sarah Dare, co-directrice du projet, qui semaines après semaines était là pour me soutenir, me conseiller, me diriger et surtout de m'encourager. Merci beaucoup j'ai adoré travailler avec vous. Merci à Sarah-Jane Barnes, directrice du projet et titulaire de la Chaire de Recherche du Canada en Métallogénie Magmatique, qui a initié le projet et qui m'a orienté dans la bonne direction pour la présentation. Merci de vos conseils. Merci à Danny Savard et Sadia Mehdi du laboratoire LabMaTer pour leur patience et de leur aide pour l'utilisation et l'interprétation avec le LA-ICP-MS. Merci à Paul Bédard, second lecteur, pour les conseils lors de la rédaction de cet ouvrage. Merci à Hugues Guérin Tremblay de la compagnie Ressources d'Arianne qui ma ouvert ses portes pour répondre à mes questions.
ABSTRACT Oxide minerals such as magnetite and chromite are becoming popular in the field of geoch... more ABSTRACT Oxide minerals such as magnetite and chromite are becoming popular in the field of geochemical exploration because the wide variety of trace elements present could potentially be used in provenance studies [1]. The method of analysis used is commonly LA-ICP-MS because it provides limits of detections down to ng/g levels when the analytical parameters can be optimized. No matrixmatched reference materials (RM) are available at the moment for in-situ calibration. Artificial glasses could be used to calibrate but only Fe can be used as an internal standard because of the inhomogeneous distribution of most of the other elements in magnetite. [2] proposed using NIST-610 to calibrate. However, the Fe content in NIST-610 is low at c.a. 0.05% while Fe in magnetite is c.a. 72%, thus limiting the use of NIST-610 to a beam >25m, with a maximum precision of R2<0.85 when results are compared to EMPA analysis of natural magnetite. [3] proposed the combination of 5 iron-rich RM to cover the elements of interest. Based on the elements for which EMPA results are available this calibration is satisfactory. However, this technique is time consuming and reduces the space available in the ablation cell.
Mineralium Deposita, 2014
Gondwana Research, 2015
Various combinations of zircon, quartz, corundum, K-feldspar, plagioclase, apatite, amphibole, ru... more Various combinations of zircon, quartz, corundum, K-feldspar, plagioclase, apatite, amphibole, rutile, titanite, almandine garnet, kyanite, andalusite, and coesite have been recovered from podiform chromitites of the Luobusa and Dongqiao ophiolites in Tibet, the Oman ophiolite and the Ray-Iz ophiolite in the Polar Urals, Russia. Chromitites in all four ophiolites also contain moissanite and the Luobusa and Ray-Iz ophiolites contain in-situ diamonds. Most of the recovered zircons are sub-rounded grains with complex internal structures indicating polyphase growth. Trace element contents and a low-pressure inclusion assemblage (quartz, muscovite, K-feldspar, apatite, ilmenite, rutile) indicate a continental crustal origin for the zircons. They have SIMS U-Pb ages that are generally much older than the host body (total range: 90 to 2500 Ma). The presence of numerous crustal minerals, particularly zircon, suggests derivation from metasedimentary rocks subducted into the mantle. Their preservation in chromitites and peridotites implies effective isolation from the mafic melts that formed the ophiolites. We suggest that most of these minerals were derived from the crustal parts of subducted slabs and were encapsulated into chromite grains precipitated from rising asthenospheric and suprasubduction magmas. The chromite grains were carried in melt channels to shallow levels in suprasubduction mantle wedges and then deposited as podiform chromitites near the Moho. The rise of asthenospheric peridotites into suprasubduction zones was facilitated by subduction initiation and possibly by slab tear allowing mixing of the UHP, highly reduced minerals and crustal minerals now found in ophiolitic chromitites and peridotites.