J. J. Keet, F. Roelofse, C. Gauert, D. Grobler, M. Butler
The Flatreef, a down-dip, sub-horizontal extension of the Platreef, which underlies the Turfspruit and Macalacaskop farms, represents the future of platinum mining in South Africa. The stratigraphic connection between the Platreef, located at the base of the northern limb of the Bushveld Complex, and the Merensky Reef in the western and eastern limbs of the complex, was disputed for many years due to the heterogeneous nature of the Platreef along strike. However, the discovery of the Flatreef led to a new perspective on the Platreef as the former allowed for the study of a magmatic stratigraphy less affected by footwall interaction. Here, we report whole-rock S isotope (δ34S) compositions across the stratigraphic units of the Flatreef and its footwall and hanging wall as intersected by boreholes UMT-276 and UMT-393, as well as stratigraphic units of the Merensky Reef at Two Rivers Platinum mine in the eastern limb. The units of the Flatreef containing platinum group element mineralization, namely the Main Reef and Upper Reef, have δ34S values that overlap with the range recorded for the Merensky Reef in the western and eastern limbs. In UMT-393, Main Reef δ34S values range between 0.2 and 1.5‰ (with the exception of three outliers, 9.7‰, 11.1‰, and 7.9‰), and 0.52‰ and 11.2‰ for two Upper Reef samples. However, in UMT-276, Main Reef δ34S values range between –0.96 and 2.24‰ and 3.19‰ was recorded for an Upper Reef sample. The S isotope compositions recorded for the Merensky Reef pyroxenite at Two Rivers Platinum mine are relatively higher with δ34S values ranging between 1.24 and 4.83‰. The top unit of the Flatreef, which is a transition zone below the Main Zone, as well as the Footwall Cyclic Unit have heavier S isotope compositions with δ34S values ranging between 6 and 17‰ for the former and 0.7 and 18.6‰ for the latter. At Two Rivers Platinum mine, the hanging-wall anorthosite has a δ34S value of 2.9‰ in contrast to the 5.7‰ measured for the footwall anorthosite and 3.27‰ for the footwall feldspathic pyroxenite. The consistent near-mantle S isotope signature and accompanying metal enrichment in the Main Reef of the Flatreef may be explained by extensive interaction of sulfide minerals in a Lower Zone conduit/pre-Platreef staging chamber with large volumes of uncontaminated magma. The δ34S values of the Merensky Reef at Two Rivers Platinum mine are slightly higher compared to that of the Main Reef at Turfspruit and Macalacaskop possibly due to interaction with underlying carbonate rocks.
{"title":"A Comparative Study of Sulfur Isotope Variations within the Flatreef and Merensky Reef of the Bushveld Complex, South Africa","authors":"J. J. Keet, F. Roelofse, C. Gauert, D. Grobler, M. Butler","doi":"10.3749/canmin.2100028","DOIUrl":"https://doi.org/10.3749/canmin.2100028","url":null,"abstract":"\u0000 The Flatreef, a down-dip, sub-horizontal extension of the Platreef, which underlies the Turfspruit and Macalacaskop farms, represents the future of platinum mining in South Africa. The stratigraphic connection between the Platreef, located at the base of the northern limb of the Bushveld Complex, and the Merensky Reef in the western and eastern limbs of the complex, was disputed for many years due to the heterogeneous nature of the Platreef along strike. However, the discovery of the Flatreef led to a new perspective on the Platreef as the former allowed for the study of a magmatic stratigraphy less affected by footwall interaction. Here, we report whole-rock S isotope (δ34S) compositions across the stratigraphic units of the Flatreef and its footwall and hanging wall as intersected by boreholes UMT-276 and UMT-393, as well as stratigraphic units of the Merensky Reef at Two Rivers Platinum mine in the eastern limb. The units of the Flatreef containing platinum group element mineralization, namely the Main Reef and Upper Reef, have δ34S values that overlap with the range recorded for the Merensky Reef in the western and eastern limbs. In UMT-393, Main Reef δ34S values range between 0.2 and 1.5‰ (with the exception of three outliers, 9.7‰, 11.1‰, and 7.9‰), and 0.52‰ and 11.2‰ for two Upper Reef samples. However, in UMT-276, Main Reef δ34S values range between –0.96 and 2.24‰ and 3.19‰ was recorded for an Upper Reef sample. The S isotope compositions recorded for the Merensky Reef pyroxenite at Two Rivers Platinum mine are relatively higher with δ34S values ranging between 1.24 and 4.83‰. The top unit of the Flatreef, which is a transition zone below the Main Zone, as well as the Footwall Cyclic Unit have heavier S isotope compositions with δ34S values ranging between 6 and 17‰ for the former and 0.7 and 18.6‰ for the latter. At Two Rivers Platinum mine, the hanging-wall anorthosite has a δ34S value of 2.9‰ in contrast to the 5.7‰ measured for the footwall anorthosite and 3.27‰ for the footwall feldspathic pyroxenite. The consistent near-mantle S isotope signature and accompanying metal enrichment in the Main Reef of the Flatreef may be explained by extensive interaction of sulfide minerals in a Lower Zone conduit/pre-Platreef staging chamber with large volumes of uncontaminated magma. The δ34S values of the Merensky Reef at Two Rivers Platinum mine are slightly higher compared to that of the Main Reef at Turfspruit and Macalacaskop possibly due to interaction with underlying carbonate rocks.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127515292","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Milidragovic, G. Nixon, J. Scoates, J. Nott, D. Spence
The Early Jurassic Polaris Alaskan-type intrusion in the Quesnel accreted arc terrane of the North American Cordillera is a zoned, mafic-ultramafic intrusive body that contains two main styles of magmatic mineralization of petrologic and potential economic significance: (1) chromitite-associated platinum group element (PGE) mineralization hosted by dunite (±wehrlite); and (2) sulfide-associated Cu-PGE-Au mineralization hosted by olivine (±magnetite) clinopyroxenite, hornblendite, and gabbro-diorite. Dunite-hosted PGE mineralization is spatially associated with thin discontinuous layers and schlieren of chromitite and chromitiferous dunite and is characterized by marked enrichments in iridium-subgroup PGE (IPGE) relative to palladium-subgroup PGE (PPGE). Discrete grains of platinum group minerals (PGM) are exceedingly rare, and the bulk of the PGE are inferred to reside in solid solution within chromite±olivine. The absence of Pt-Fe alloys in dunite of the Polaris intrusion is atypical, as Pt-enrichment of dunite-hosted chromitite is widely regarded as a characteristic feature of Alaskan-type intrusions. This discrepancy appears to be consistent with the strong positive dependence of Pt solubility on the oxidation state of sulfide-undersaturated magmas. Through comparison with experimentally determined PGE solubilities, we infer that the earliest (highest temperature) olivine-chromite cumulates of the Polaris intrusion crystallized from a strongly oxidized ultramafic parental magma with an estimated log f(O2) > FMQ+2. Parental magmas with oxygen fugacities more typical of volcanic arc settings [log f(O2) ∼ FMQ to ∼ FMQ+2] are, in turn, considered more favorable for co-precipitation of Pt-Fe alloys with olivine and chromite. More evolved clinopyroxene- and hornblende-rich cumulates of the Polaris intrusion contain low abundances of disseminated magmatic sulfides, consisting of pyrrhotite and chalcopyrite with minor pentlandite, pyrite, and rare bornite (≤12 wt.% total sulfides), which occur interstitially or as polyphase inclusions in silicates and oxides. The sulfide-bearing rocks are characterized by strong primitive mantle-normalized depletions in IPGE and enrichments in Cu-PPGE-Au, patterns that resemble those of other Alaskan-type intrusions and primitive arc lavas. The absolute abundances and sulfur-normalized whole-rock concentrations (Ci/S, serving as proxy for sulfide metal tenor) of chalcophile elements, including Cu/S, in sulfide-bearing rocks are highest in olivine clinopyroxenite. Sulfide saturation in the relatively evolved magmas of the Polaris intrusion, and Alaskan-type intrusions in general, appears to be intimately tied to the appearance of magnetite. Fractional crystallization of magnetite during the formation of olivine clinopyroxenite at Polaris resulted in reduction of the residual magma to log f(O2) ≤ FMQ+2, leading to segregation of an immiscible sulfide melt with high Cu/Fe and Cu/S, and high PGE and Au tenors. Continued
{"title":"Redox-controlled chalcophile element geochemistry of the Polaris Alaskan-type mafic-ultramafic complex, British Columbia, Canada","authors":"D. Milidragovic, G. Nixon, J. Scoates, J. Nott, D. Spence","doi":"10.3749/canmin.2100006","DOIUrl":"https://doi.org/10.3749/canmin.2100006","url":null,"abstract":"\u0000 The Early Jurassic Polaris Alaskan-type intrusion in the Quesnel accreted arc terrane of the North American Cordillera is a zoned, mafic-ultramafic intrusive body that contains two main styles of magmatic mineralization of petrologic and potential economic significance: (1) chromitite-associated platinum group element (PGE) mineralization hosted by dunite (±wehrlite); and (2) sulfide-associated Cu-PGE-Au mineralization hosted by olivine (±magnetite) clinopyroxenite, hornblendite, and gabbro-diorite. Dunite-hosted PGE mineralization is spatially associated with thin discontinuous layers and schlieren of chromitite and chromitiferous dunite and is characterized by marked enrichments in iridium-subgroup PGE (IPGE) relative to palladium-subgroup PGE (PPGE). Discrete grains of platinum group minerals (PGM) are exceedingly rare, and the bulk of the PGE are inferred to reside in solid solution within chromite±olivine. The absence of Pt-Fe alloys in dunite of the Polaris intrusion is atypical, as Pt-enrichment of dunite-hosted chromitite is widely regarded as a characteristic feature of Alaskan-type intrusions. This discrepancy appears to be consistent with the strong positive dependence of Pt solubility on the oxidation state of sulfide-undersaturated magmas. Through comparison with experimentally determined PGE solubilities, we infer that the earliest (highest temperature) olivine-chromite cumulates of the Polaris intrusion crystallized from a strongly oxidized ultramafic parental magma with an estimated log f(O2) > FMQ+2. Parental magmas with oxygen fugacities more typical of volcanic arc settings [log f(O2) ∼ FMQ to ∼ FMQ+2] are, in turn, considered more favorable for co-precipitation of Pt-Fe alloys with olivine and chromite. More evolved clinopyroxene- and hornblende-rich cumulates of the Polaris intrusion contain low abundances of disseminated magmatic sulfides, consisting of pyrrhotite and chalcopyrite with minor pentlandite, pyrite, and rare bornite (≤12 wt.% total sulfides), which occur interstitially or as polyphase inclusions in silicates and oxides. The sulfide-bearing rocks are characterized by strong primitive mantle-normalized depletions in IPGE and enrichments in Cu-PPGE-Au, patterns that resemble those of other Alaskan-type intrusions and primitive arc lavas. The absolute abundances and sulfur-normalized whole-rock concentrations (Ci/S, serving as proxy for sulfide metal tenor) of chalcophile elements, including Cu/S, in sulfide-bearing rocks are highest in olivine clinopyroxenite. Sulfide saturation in the relatively evolved magmas of the Polaris intrusion, and Alaskan-type intrusions in general, appears to be intimately tied to the appearance of magnetite. Fractional crystallization of magnetite during the formation of olivine clinopyroxenite at Polaris resulted in reduction of the residual magma to log f(O2) ≤ FMQ+2, leading to segregation of an immiscible sulfide melt with high Cu/Fe and Cu/S, and high PGE and Au tenors. Continued","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"268 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114430682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tatiana L. Grokhovskaya, A. Vymazalová, F. Laufek, C. Stanley, S. Y. Borisovskiy
Palladothallite, Pd3Tl, is a new mineral discovered in the Monchetundra layered intrusion, Kola Peninsula, Russia. Palladothallite occurs in orthopyroxenite with disseminated Ni-Cu-Fe sulfides and in near-surface oxidized ore of an orthopyroxenite unit. In the holotype specimen, the new mineral forms anhedral grains about 1 to 20 μm in size intergrown with bortnikovite (Pt4Cu3Zn). Palladothallite and bortnikovite form a rim around tulameenite (Pt2FeCu), Pt-Pd-Fe-Cu alloys, and Pt-Pd-Fe-Cu “oxides” in a goethite matrix. In plane-polarized light, palladothallite is white, anisotropy was not observed; it exhibits no internal reflections. Reflectance values of palladothallite in air (R' in %) are: 53.9 at 470 nm, 57.1 at 546 nm, 59.4 at 589 nm and 61.7 at 650 nm. Twelve electron probe microanalyses of palladothallite gave an average composition (in wt.%): Pd 59.99, Cu 1.19, Fe 0.35, Ag 1.1, Tl 35.64, Se 0.34, and S 0.09, total 99.67, corresponding to the empirical formula (Pd2.894Cu0.096Fe0.032Ag0.053)∑3.075(Tl0.895Se0.023S0.008)∑0.926 based on four atoms, with the ideal formula Pd3Tl. The density, calculated on the basis of the empirical formula, is 13.04 g/cm3. Palladothallite crystallizes with the same structure as synthetic Pd3Tl, which was solved by Kurtzemann & Kohlmann (2010) from powder neutron diffraction data. Palladothallite is tetragonal, space group I4/mmm, with a 4.10659(9), c 15.3028(4) Å, V 258.07(1) Å3, and Z = 4. Palladothallite crystallizes in the ZrAl3 structure type. The name corresponds to its chemical composition, palladium and thallium.
Palladothallite, Pd3Tl,是在俄罗斯科拉半岛Monchetundra层状侵入岩中发现的一种新矿物。帕拉多辉石产于具有浸染镍铜铁硫化物的正辉石中和近表面氧化的正辉石中。在全模试样中,新矿物形成1 ~ 20 μm大小的四面体晶粒,与硼钛矿(Pt4Cu3Zn)共生。在针铁矿基体中,帕拉多长石和硼钛长石在图拉长石(Pt2FeCu)、Pt-Pd-Fe-Cu合金和Pt-Pd-Fe-Cu“氧化物”周围形成一个边缘。在平面偏振光下,palladothallite呈白色,未观察到各向异性;它没有内部反射。空气中palladothallite的反射率值(R′in %)分别为:470nm处53.9,546nm处57.1,589nm处59.4,650nm处61.7。12个电子探针显微分析得到钯石的平均组成(wt.%)为:Pd 59.99, Cu 1.19, Fe 0.35, Ag 1.1, Tl 35.64, Se 0.34, S 0.09,总计99.67,对应于基于四原子的实验式(Pd2.894Cu0.096Fe0.032Ag0.053)∑3.075(Tl0.895Se0.023S0.008)∑0.926,理想式为Pd3Tl。根据经验公式计算出的密度为13.04 g/cm3。Palladothallite的结晶结构与合成Pd3Tl相同,Kurtzemann & Kohlmann(2010)利用粉末中子衍射数据解决了这一问题。Palladothallite为四边形,空间群为I4/mmm,具有4.10659(9),c 15.3028(4) Å, V 258.07(1) Å3, Z = 4。Palladothallite以ZrAl3结构型结晶。这个名字对应于它的化学成分,钯和铊。
{"title":"Palladothallite, Pd3Tl, a new mineral from the Monchetundra layered intrusion, Kola Peninsula, Russia","authors":"Tatiana L. Grokhovskaya, A. Vymazalová, F. Laufek, C. Stanley, S. Y. Borisovskiy","doi":"10.3749/canmin.2100002","DOIUrl":"https://doi.org/10.3749/canmin.2100002","url":null,"abstract":"\u0000 Palladothallite, Pd3Tl, is a new mineral discovered in the Monchetundra layered intrusion, Kola Peninsula, Russia. Palladothallite occurs in orthopyroxenite with disseminated Ni-Cu-Fe sulfides and in near-surface oxidized ore of an orthopyroxenite unit. In the holotype specimen, the new mineral forms anhedral grains about 1 to 20 μm in size intergrown with bortnikovite (Pt4Cu3Zn). Palladothallite and bortnikovite form a rim around tulameenite (Pt2FeCu), Pt-Pd-Fe-Cu alloys, and Pt-Pd-Fe-Cu “oxides” in a goethite matrix. In plane-polarized light, palladothallite is white, anisotropy was not observed; it exhibits no internal reflections. Reflectance values of palladothallite in air (R' in %) are: 53.9 at 470 nm, 57.1 at 546 nm, 59.4 at 589 nm and 61.7 at 650 nm. Twelve electron probe microanalyses of palladothallite gave an average composition (in wt.%): Pd 59.99, Cu 1.19, Fe 0.35, Ag 1.1, Tl 35.64, Se 0.34, and S 0.09, total 99.67, corresponding to the empirical formula (Pd2.894Cu0.096Fe0.032Ag0.053)∑3.075(Tl0.895Se0.023S0.008)∑0.926 based on four atoms, with the ideal formula Pd3Tl. The density, calculated on the basis of the empirical formula, is 13.04 g/cm3. Palladothallite crystallizes with the same structure as synthetic Pd3Tl, which was solved by Kurtzemann & Kohlmann (2010) from powder neutron diffraction data. Palladothallite is tetragonal, space group I4/mmm, with a 4.10659(9), c 15.3028(4) Å, V 258.07(1) Å3, and Z = 4. Palladothallite crystallizes in the ZrAl3 structure type. The name corresponds to its chemical composition, palladium and thallium.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127002585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Preface part II: Summary of contributions","authors":"M. Junge, F. Ford, A. Mcdonald","doi":"10.3749/canmin.int012","DOIUrl":"https://doi.org/10.3749/canmin.int012","url":null,"abstract":"","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128068486","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Drill-core samples from the basal Cu-Ni-platinum-group element mineralization of the Early Proterozoic Fedorova Tundra intrusion in the Fedorova-Pana layered intrusion, central Kola Peninsula, Russia, were studied in two separate projects in Canada and Russia. In Canada, trace precious metal analyses by laser ablation inductively coupled mass spectrometry of 323 base metal sulfide particles [pentlandite (101), pyrrhotite (98), chalcopyrite (25), and pyrite (99)] show that Pd is highly concentrated in pentlandite. Most of the analyses (71%) were done using two master composite samples of comminuted drill core representative of the West Pit and East Pit mineralization, FWMC and FEMC, respectively. Fewer analyses were made of three other comminuted drill core samples from the West Pit referred to as “lithology” samples: OLFW (olivine-bearing rocks), ANFW (leucocratic rocks), and GNFW (gabbronorite). In Russia, 120 polished sections sliced from drill core from the West and East Pits and from four other Fedorova Tundra intrusion deposits (Kievey, Northern Kamennik, Eastern Chuarvy, and Southern Kievey) were studied mineralogically. Platinum group mineral characterization and trace Pd electron probe microanalyses of pentlandite were done using polished sections from all six locations (n = 95). The trace electron probe microanalysis data for Pd in pentlandite from the West (n = 35) and East (n = 19) Pit samples, though at much higher detection levels, are considered to be comparable to the laser ablation inductively coupled mass spectrometry data. The Eastern Chuarvy samples show particularly high Pd concentrations averaging 0.49 wt.% Pd (n = 11) and as high as 1.64 wt.% Pd. The combined data from these studies guides our estimate that pentlandite accounts for 30 to 50% of the Pd in these ores and that Rh solid solution in sulfides may account for >98% of the total Rh.
{"title":"Trace precious metals in major sulfide minerals from the Federova Tundra platinum group element deposit in the Fedorova-Pana layered intrusion, central Kola Peninsula, Russia","authors":"L. Cabri, V. Subbotin","doi":"10.3749/canmin.2000126","DOIUrl":"https://doi.org/10.3749/canmin.2000126","url":null,"abstract":"\u0000 Drill-core samples from the basal Cu-Ni-platinum-group element mineralization of the Early Proterozoic Fedorova Tundra intrusion in the Fedorova-Pana layered intrusion, central Kola Peninsula, Russia, were studied in two separate projects in Canada and Russia. In Canada, trace precious metal analyses by laser ablation inductively coupled mass spectrometry of 323 base metal sulfide particles [pentlandite (101), pyrrhotite (98), chalcopyrite (25), and pyrite (99)] show that Pd is highly concentrated in pentlandite. Most of the analyses (71%) were done using two master composite samples of comminuted drill core representative of the West Pit and East Pit mineralization, FWMC and FEMC, respectively. Fewer analyses were made of three other comminuted drill core samples from the West Pit referred to as “lithology” samples: OLFW (olivine-bearing rocks), ANFW (leucocratic rocks), and GNFW (gabbronorite). In Russia, 120 polished sections sliced from drill core from the West and East Pits and from four other Fedorova Tundra intrusion deposits (Kievey, Northern Kamennik, Eastern Chuarvy, and Southern Kievey) were studied mineralogically. Platinum group mineral characterization and trace Pd electron probe microanalyses of pentlandite were done using polished sections from all six locations (n = 95). The trace electron probe microanalysis data for Pd in pentlandite from the West (n = 35) and East (n = 19) Pit samples, though at much higher detection levels, are considered to be comparable to the laser ablation inductively coupled mass spectrometry data. The Eastern Chuarvy samples show particularly high Pd concentrations averaging 0.49 wt.% Pd (n = 11) and as high as 1.64 wt.% Pd. The combined data from these studies guides our estimate that pentlandite accounts for 30 to 50% of the Pd in these ores and that Rh solid solution in sulfides may account for >98% of the total Rh.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125754804","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. González-Jiménez, I. Tretiakova, M. Fiorentini, V. Malkovets, L. Martin, Júlia Farré-de-Pablo
This paper focuses on a nanoscale study of nano- and micrometer-size Os-rich mineral particles hosted in a Ni-Fe-Cu sulfide globule found in an olivine megacryst from the Udachnaya pipe (Yakutia, Russia). These platinum-group element mineral particles and their host sulfide matrices were investigated using a combination of techniques, including field emission gun electron probe microanalyzer, field emission scanning electron microscopy, and focused ion beam and high-resolution transmission electron microscopy. The sulfide globule is of mantle origin, as it is hosted in primitive olivine (Fo90–93), very likely derived from the crystallization of Ni-Fe-Cu sulfide melt droplets segregated by liquid immiscibility from a basaltic melt in a volume of depleted subcontinental lithospheric mantle. Microscopic observations by means of field emission scanning electron microscopy and single-spot analysis and mapping by field emission gun electron probe microanalyzer reveal that the sulfide globule comprises a core of pyrrhotite with flame-like exsolutions (usually <10 μm thickness) of pentlandite, which is irregularly surrounded by a rim of granular pentlandite and chalcopyrite. Elemental mapping by energy dispersive spectroscopy (acquired using the high-resolution transmission electron microscopy) of the pyrrhotite (+ pentlandite) core reveals that pentlandite exsolution in pyrrhotite is still observable at the nanoscale as fringes of 100 to 500 nm thicknesses. The sulfide matrices of pyrrhotite, pentlandite, and chalcopyrite contain abundant nano- and micrometer-size platinum group element mineral particles. A careful inspection of eight of these platinum group element particles under focused ion beam and high-resolution transmission electron microscopy showed that they are crystalline erlichmanite (OsS2) with well-developed crystal faces that are distinctively oriented relative to their sulfide host matrices. We propose that the core of the Ni-Fe-Cu sulfide globule studied here was derived from a precursor monosulfide solid solution originally crystallized from a sulfide melt at >1100 °C, which later decomposed into pyrrhotite and the pentlandite flame-like exsolutions upon cooling at <600 °C. Once solidified, the solid monosulfide solid solution reacted with non-equilibrium Cu-and Ni-rich sulfide melt(s), giving rise to the granular pentlandite in equilibrium with chalcopyrite now forming the rim of the sulfide globule. Meanwhile, nano- to micron-sized crystals of erlichmanite crystallized directly from or slightly before monosulfide solid solution from the sulfide melt. Thus, Os, and to a lesser extent Ir and Ru, were physically partitioned by preferential uptake via early formation of nanoparticles at high temperature instead of low-temperature exsolution from solid Ni-Fe-Cu sulfides. The new data provided in this paper highlight the necessity of studying platinum group element mineral particles in Ni-Fe-Cu sulfides using analytical techniques that can
{"title":"Nano- and Micrometer-Sized PGM in Ni-Cu-Fe Sulfides from an Olivine Megacryst in the Udachnaya Pipe, Yakutia, Russia","authors":"J. González-Jiménez, I. Tretiakova, M. Fiorentini, V. Malkovets, L. Martin, Júlia Farré-de-Pablo","doi":"10.3749/canmin.2100017","DOIUrl":"https://doi.org/10.3749/canmin.2100017","url":null,"abstract":"This paper focuses on a nanoscale study of nano- and micrometer-size Os-rich mineral particles hosted in a Ni-Fe-Cu sulfide globule found in an olivine megacryst from the Udachnaya pipe (Yakutia, Russia). These platinum-group element mineral particles and their host sulfide matrices were investigated using a combination of techniques, including field emission gun electron probe microanalyzer, field emission scanning electron microscopy, and focused ion beam and high-resolution transmission electron microscopy. The sulfide globule is of mantle origin, as it is hosted in primitive olivine (Fo90–93), very likely derived from the crystallization of Ni-Fe-Cu sulfide melt droplets segregated by liquid immiscibility from a basaltic melt in a volume of depleted subcontinental lithospheric mantle. Microscopic observations by means of field emission scanning electron microscopy and single-spot analysis and mapping by field emission gun electron probe microanalyzer reveal that the sulfide globule comprises a core of pyrrhotite with flame-like exsolutions (usually <10 μm thickness) of pentlandite, which is irregularly surrounded by a rim of granular pentlandite and chalcopyrite. Elemental mapping by energy dispersive spectroscopy (acquired using the high-resolution transmission electron microscopy) of the pyrrhotite (+ pentlandite) core reveals that pentlandite exsolution in pyrrhotite is still observable at the nanoscale as fringes of 100 to 500 nm thicknesses. The sulfide matrices of pyrrhotite, pentlandite, and chalcopyrite contain abundant nano- and micrometer-size platinum group element mineral particles. A careful inspection of eight of these platinum group element particles under focused ion beam and high-resolution transmission electron microscopy showed that they are crystalline erlichmanite (OsS2) with well-developed crystal faces that are distinctively oriented relative to their sulfide host matrices. We propose that the core of the Ni-Fe-Cu sulfide globule studied here was derived from a precursor monosulfide solid solution originally crystallized from a sulfide melt at >1100 °C, which later decomposed into pyrrhotite and the pentlandite flame-like exsolutions upon cooling at <600 °C. Once solidified, the solid monosulfide solid solution reacted with non-equilibrium Cu-and Ni-rich sulfide melt(s), giving rise to the granular pentlandite in equilibrium with chalcopyrite now forming the rim of the sulfide globule. Meanwhile, nano- to micron-sized crystals of erlichmanite crystallized directly from or slightly before monosulfide solid solution from the sulfide melt. Thus, Os, and to a lesser extent Ir and Ru, were physically partitioned by preferential uptake via early formation of nanoparticles at high temperature instead of low-temperature exsolution from solid Ni-Fe-Cu sulfides. The new data provided in this paper highlight the necessity of studying platinum group element mineral particles in Ni-Fe-Cu sulfides using analytical techniques that can","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116262545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Malose M. Langa, P. Jugo, M. Leybourne, D. Grobler
The UG-2 chromitite layer, with its elevated platinum-group element content, is a key marker horizon in the eastern and western limbs of the Bushveld Igneous Complex and the largest platinum-group element chromite-hosted resource of its kind in the world. In contrast, much less is known about its stratigraphic equivalent in the northern limb, the “UG-2 equivalent” (UG-2E) chromitite. Recent studies on chromite mineral chemistry show similarities between the UG-2 and sections of the UG-2E, but also that the UG-2E was partially contaminated by assimilation of local metasedimentary rocks. Here, we provide a detailed characterization of sulfide minerals and platinum-group minerals in a suite of samples from the UG-2E and compare the results with data obtained from a reference suite of samples from the UG-2. Results from petrographic observations, electron probe microanalysis, laser ablation-inductively coupled plasma-mass spectrometry, quantitative evaluation of materials by scanning electron microscopy, and δ34S isotopes show that: (1) sulfide minerals in the UG-2E and UG-2 consist mainly of pentlandite-chalcopyrite-pyrrhotite, but pyrrhotite is significantly more abundant in the UG-2E and almost absent in the UG-2; (2) iron contents in pentlandite from the UG-2E are significantly higher than in the UG-2; (3) platinum-group element contents within sulfide minerals are different between the two chromitites; (4) UG-2E platinum-group minerals are dominated by arsenides and bismuthotellurides, and by alloys and platinum-group element-sulfide minerals in the UG-2; (5) sulfide mineral chemistry and δ34S values indicate some crustal contamination of the UG-2E; and (6) sulfide mineral and secondary silicate mineral textures in both the UG-2E and UG-2 are indicative of minor, millimeter- to centimeter-scale, hydrothermal alteration. From our observations and results, we consider the UG-2E chromitite in the northern limb to be the equivalent to the UG-2 in the eastern and western limbs that has been contaminated by assimilation of Transvaal Supergroup footwall rocks during emplacement. The contamination resulted in UG-2E sulfide mineral elemental contents and platinum-group mineral types and abundances that are distinct from those of the UG-2 in the rest of the Bushveld.
{"title":"Sulfide mineral chemistry and platinum-group minerals of the UG-2 chromitite in the northern limb of the Bushveld Igneous Complex, South Africa","authors":"Malose M. Langa, P. Jugo, M. Leybourne, D. Grobler","doi":"10.3749/canmin.2100042","DOIUrl":"https://doi.org/10.3749/canmin.2100042","url":null,"abstract":"\u0000 The UG-2 chromitite layer, with its elevated platinum-group element content, is a key marker horizon in the eastern and western limbs of the Bushveld Igneous Complex and the largest platinum-group element chromite-hosted resource of its kind in the world. In contrast, much less is known about its stratigraphic equivalent in the northern limb, the “UG-2 equivalent” (UG-2E) chromitite. Recent studies on chromite mineral chemistry show similarities between the UG-2 and sections of the UG-2E, but also that the UG-2E was partially contaminated by assimilation of local metasedimentary rocks. Here, we provide a detailed characterization of sulfide minerals and platinum-group minerals in a suite of samples from the UG-2E and compare the results with data obtained from a reference suite of samples from the UG-2. Results from petrographic observations, electron probe microanalysis, laser ablation-inductively coupled plasma-mass spectrometry, quantitative evaluation of materials by scanning electron microscopy, and δ34S isotopes show that: (1) sulfide minerals in the UG-2E and UG-2 consist mainly of pentlandite-chalcopyrite-pyrrhotite, but pyrrhotite is significantly more abundant in the UG-2E and almost absent in the UG-2; (2) iron contents in pentlandite from the UG-2E are significantly higher than in the UG-2; (3) platinum-group element contents within sulfide minerals are different between the two chromitites; (4) UG-2E platinum-group minerals are dominated by arsenides and bismuthotellurides, and by alloys and platinum-group element-sulfide minerals in the UG-2; (5) sulfide mineral chemistry and δ34S values indicate some crustal contamination of the UG-2E; and (6) sulfide mineral and secondary silicate mineral textures in both the UG-2E and UG-2 are indicative of minor, millimeter- to centimeter-scale, hydrothermal alteration. From our observations and results, we consider the UG-2E chromitite in the northern limb to be the equivalent to the UG-2 in the eastern and western limbs that has been contaminated by assimilation of Transvaal Supergroup footwall rocks during emplacement. The contamination resulted in UG-2E sulfide mineral elemental contents and platinum-group mineral types and abundances that are distinct from those of the UG-2 in the rest of the Bushveld.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125094508","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Good, R. Linnen, Imran Meghji, I. Samson, J. McBride
The Geordie Lake Cu-Pd deposit is associated with troctolite at the base of the Geordie Lake intrusion, located near the center of the Coldwell Complex (1106.5 + 1.2 Ma). It is the only platinum group element deposit in the Midcontinent Rift associated with alkaline rocks. This study focuses on the long-standing questions regarding genetic relationships among the Geordie Lake gabbros, the Wolfcamp basalt, and the various syenites that make up the east-central portion of the Coldwell Complex. Primitive mantle-normalized trace-element patterns for the Geordie Lake intrusion are nearly flat from Th to Ce and show negative Sr, Eu, and Zr anomalies. Characteristic ratios for the Geordie Lake gabbro and troctolite include Th/Nb (0.12), La/Nb (1.1), La/Lu (150), La/Sm (6.9), Zr/Sm (18), and Gd/Yb (2.8). Trace-element patterns that are useful for determining petrogenesis for gabbros are similar to the Wolfcamp basalt and augite syenite with some key exceptions, notably the middle rare earth element and Zr abundances. Affects due to metasomatism or crustal contamination in Wolfcamp basalt and Geordie Lake gabbros and syenites are negligible. Results of Rayleigh fractionation modeling show (1) the Geordie Lake intrusion and Wolfcamp basalt are very similar but not directly related by crystallization, (2) the gabbros and basalt are not related to the syenites, (3) the lower augite syenite can be related to the upper augite syenite and amphibole quartz syenite by fractionation of a hypothetical crystal cumulate composed of orthoclase (78%), clinopyroxene (15%), olivine (1%), and titanomagnetite (6%). We conclude that the Geordie Lake intrusion, Wolfcamp basalt, and saturated syenites in the Coldwell were derived by separate partial melting events in a common mantle source. The origin of the sulfide mineralization is enigmatic because it exhibits characteristics of both magmatic and hydrothermal processes. The sulfide assemblage changes from disseminated bornite and chalcopyrite in the basal zone to pyrrhotite plus chalcopyrite in the upper zones. Sulfides occur as coarse blebs interstitial to fresh or partly altered silicates, or as very fine grains intergrown with clusters of biotite and actinolite. Primitive mantle-normalized platinum group element patterns exhibit a W-shape for Pd-Pt-Rh-Ir-Ni, indicating a relative depletion of Pt and Ir. The Cu/Pd ratios in the mineralized zones are within the range of mantle values (1000–10,000), Pd/Pt is 14–19, Pd/Rh is 91 + 37, and Pd/Ir >16,000. The Pd/Pt, Pd/Rh, and Pd/Ir are considerably higher than in the Wolfcamp basalt (<1, 17, and 75, respectively). If the sulfides are magmatic in origin, then either the Geordie Lake magma was, unlike the Wolfcamp basalt magma, depleted in Pt, Rh, and Ir, or these elements were selectively removed from the sulfide assemblage. Alternatively, Pd was enriched by late-stage hydrothermal processes. Additional work is recommended to constrain petrogenesis of the sulfides by detail
{"title":"Relationships among the Geordie Lake Cu-Pd deposit, alkaline basalt, and syenites in the Coldwell Complex, Midcontinent Rift, Canada","authors":"D. Good, R. Linnen, Imran Meghji, I. Samson, J. McBride","doi":"10.3749/canmin.2100043","DOIUrl":"https://doi.org/10.3749/canmin.2100043","url":null,"abstract":"\u0000 The Geordie Lake Cu-Pd deposit is associated with troctolite at the base of the Geordie Lake intrusion, located near the center of the Coldwell Complex (1106.5 + 1.2 Ma). It is the only platinum group element deposit in the Midcontinent Rift associated with alkaline rocks. This study focuses on the long-standing questions regarding genetic relationships among the Geordie Lake gabbros, the Wolfcamp basalt, and the various syenites that make up the east-central portion of the Coldwell Complex. Primitive mantle-normalized trace-element patterns for the Geordie Lake intrusion are nearly flat from Th to Ce and show negative Sr, Eu, and Zr anomalies. Characteristic ratios for the Geordie Lake gabbro and troctolite include Th/Nb (0.12), La/Nb (1.1), La/Lu (150), La/Sm (6.9), Zr/Sm (18), and Gd/Yb (2.8). Trace-element patterns that are useful for determining petrogenesis for gabbros are similar to the Wolfcamp basalt and augite syenite with some key exceptions, notably the middle rare earth element and Zr abundances. Affects due to metasomatism or crustal contamination in Wolfcamp basalt and Geordie Lake gabbros and syenites are negligible. Results of Rayleigh fractionation modeling show (1) the Geordie Lake intrusion and Wolfcamp basalt are very similar but not directly related by crystallization, (2) the gabbros and basalt are not related to the syenites, (3) the lower augite syenite can be related to the upper augite syenite and amphibole quartz syenite by fractionation of a hypothetical crystal cumulate composed of orthoclase (78%), clinopyroxene (15%), olivine (1%), and titanomagnetite (6%). We conclude that the Geordie Lake intrusion, Wolfcamp basalt, and saturated syenites in the Coldwell were derived by separate partial melting events in a common mantle source.\u0000 The origin of the sulfide mineralization is enigmatic because it exhibits characteristics of both magmatic and hydrothermal processes. The sulfide assemblage changes from disseminated bornite and chalcopyrite in the basal zone to pyrrhotite plus chalcopyrite in the upper zones. Sulfides occur as coarse blebs interstitial to fresh or partly altered silicates, or as very fine grains intergrown with clusters of biotite and actinolite. Primitive mantle-normalized platinum group element patterns exhibit a W-shape for Pd-Pt-Rh-Ir-Ni, indicating a relative depletion of Pt and Ir. The Cu/Pd ratios in the mineralized zones are within the range of mantle values (1000–10,000), Pd/Pt is 14–19, Pd/Rh is 91 + 37, and Pd/Ir >16,000. The Pd/Pt, Pd/Rh, and Pd/Ir are considerably higher than in the Wolfcamp basalt (<1, 17, and 75, respectively). If the sulfides are magmatic in origin, then either the Geordie Lake magma was, unlike the Wolfcamp basalt magma, depleted in Pt, Rh, and Ir, or these elements were selectively removed from the sulfide assemblage. Alternatively, Pd was enriched by late-stage hydrothermal processes. Additional work is recommended to constrain petrogenesis of the sulfides by detail","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129513447","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dienerite, ideally Ni3As, was discovered in 1919 near Radstadt (Salzburg, Austria) and its description and chemical characterization date back to the 1920s. The paucity of reliable experimental data, as well as the absence of any other documented occurrences of such a mineral in over 80 years, led to the supposition of a typographic error in the transcription of the original chemical analysis, suggesting the mineral might in fact be nickelskutterudite [(Ni,Co,Fe)As3]. As a consequence, the mineral was discredited and deleted in the post-2006 IMA list of valid mineral species. Nonetheless, several minerals having a metal/As ratio close to 3:1 and a description fitting that of dienerite were reported after its discreditation. Here we report the discovery of minute inclusions in a sample of josephinite from Josephine Creek (Oregon, USA) exhibiting high optical and electron reflectance. Structural and chemical investigations unequivocally showed that a mineral having cubic structure [a = 9.6206(9) Å, sp. gr. I3d; R1 = 0.0353] and ideal chemical formula Ni3As does exist, suggesting that dienerite could in fact be a valid species. The proposal to revalidate dienerite has been approved by the Commission on New Minerals, Nomenclature and Classification (IMA-Proposal 19-E). The neotype is deposited in the mineralogical collections of the Natural History Museum, University of Florence, Italy, under catalogue number 3364/I.
{"title":"Structural and chemical characterization of dienerite, Ni3As, and its revalidation as a mineral species","authors":"P. Bonazzi, L. Bindi","doi":"10.3749/canmin.2100012","DOIUrl":"https://doi.org/10.3749/canmin.2100012","url":null,"abstract":"\u0000 Dienerite, ideally Ni3As, was discovered in 1919 near Radstadt (Salzburg, Austria) and its description and chemical characterization date back to the 1920s. The paucity of reliable experimental data, as well as the absence of any other documented occurrences of such a mineral in over 80 years, led to the supposition of a typographic error in the transcription of the original chemical analysis, suggesting the mineral might in fact be nickelskutterudite [(Ni,Co,Fe)As3]. As a consequence, the mineral was discredited and deleted in the post-2006 IMA list of valid mineral species. Nonetheless, several minerals having a metal/As ratio close to 3:1 and a description fitting that of dienerite were reported after its discreditation.\u0000 Here we report the discovery of minute inclusions in a sample of josephinite from Josephine Creek (Oregon, USA) exhibiting high optical and electron reflectance. Structural and chemical investigations unequivocally showed that a mineral having cubic structure [a = 9.6206(9) Å, sp. gr. I3d; R1 = 0.0353] and ideal chemical formula Ni3As does exist, suggesting that dienerite could in fact be a valid species.\u0000 The proposal to revalidate dienerite has been approved by the Commission on New Minerals, Nomenclature and Classification (IMA-Proposal 19-E). The neotype is deposited in the mineralogical collections of the Natural History Museum, University of Florence, Italy, under catalogue number 3364/I.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127220008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fabian Fröhlich, J. Siikaluoma, Inga Osbahr, J. Gutzmer
The Sakatti Ni-Cu-platinum-group element deposit is situated in northern Finland and comprises massive, disseminated, and vein sulfide mineralization. A stockwork is formed by chalcopyrite-rich sulfide veins, which contain exceptionally high platinum-group elements and Au grades. The mineralogy and geochemistry of this stockwork zone ore is documented in this investigation. The results are used to develop the first robust genetic concept and its relationship to massive and disseminated mineralization of the Sakatti deposit. This model is similar to that proposed for many Cu-rich magmatic sulfide ores, most importantly the Cu-rich footwall veins described from the Sudbury Complex in Canada and the Cu-rich ore at Noril'sk-Talnakh in Russia. Detailed petrographic studies using a sample suite from exploration drill core intersecting vein-style mineralization revealed a classic magmatic sulfide assemblage of chalcopyrite ± pyrrhotite, pentlandite, and pyrite. More than 1000 platinum-group mineral grains belonging almost exclusively to the moncheite (PtTe2) – merenskyite (PdTe2) – melonite (NiTe2) solid solution series were identified in the studied samples. Notably, almost two thirds of the platinum-group element-bearing minerals consist of melonite. Some of the platinum-group minerals contain inclusions of Ag-rich gold (AgAu2) and muthmannite (AuAgTe2). Most of the platinum-group minerals occur as inclusions in chalcopyrite, although a few grains are located at base-metal sulfide grain boundaries and in fractures in base-metal sulfides. The whole-rock compositions of the stockwork veins are Cu-rich and are interpreted to represent a fractionated Cu-rich sulfide liquid enriched in Pt, Pd, Au, Ag, As, Bi, Pb, Se, Te, Zn, which separated from a monosulfide solid solution (mss). An intermediate solid solution (iss) solidified from the Cu-rich sulfide liquid, recrystallizing chalcopyrite at <550 °C. Simultaneously, small volumes of intercumulus residual melt contained mainly the precious metals, Bi, and Te due to their incompatibility in iss. Solitary and composite platinum-group minerals as well as Au-minerals crystallized first from the residual melt (<600 °C), followed by a succession of various Bi-, Ag-, and Pb-tellurides (∼540 °C), and finally sphalerite and galena. Melonite crystallized as mostly large, solitary grains exsolved directly from Ni-bearing intermediate solid solution (∼600 °C), shortly after the formation of moncheite and merenskyite from the residual melt. Finally, remobilization of the platinum-group minerals occurred at temperatures of <300 °C, as suggested by the presence of minor amounts of Cl-bearing minerals and ragged grain shapes.
{"title":"Genesis of sulfide vein mineralization at the Sakatti Ni-Cu-PGE deposit, Finland","authors":"Fabian Fröhlich, J. Siikaluoma, Inga Osbahr, J. Gutzmer","doi":"10.3749/canmin.2100020","DOIUrl":"https://doi.org/10.3749/canmin.2100020","url":null,"abstract":"\u0000 The Sakatti Ni-Cu-platinum-group element deposit is situated in northern Finland and comprises massive, disseminated, and vein sulfide mineralization. A stockwork is formed by chalcopyrite-rich sulfide veins, which contain exceptionally high platinum-group elements and Au grades. The mineralogy and geochemistry of this stockwork zone ore is documented in this investigation. The results are used to develop the first robust genetic concept and its relationship to massive and disseminated mineralization of the Sakatti deposit. This model is similar to that proposed for many Cu-rich magmatic sulfide ores, most importantly the Cu-rich footwall veins described from the Sudbury Complex in Canada and the Cu-rich ore at Noril'sk-Talnakh in Russia.\u0000 Detailed petrographic studies using a sample suite from exploration drill core intersecting vein-style mineralization revealed a classic magmatic sulfide assemblage of chalcopyrite ± pyrrhotite, pentlandite, and pyrite. More than 1000 platinum-group mineral grains belonging almost exclusively to the moncheite (PtTe2) – merenskyite (PdTe2) – melonite (NiTe2) solid solution series were identified in the studied samples. Notably, almost two thirds of the platinum-group element-bearing minerals consist of melonite. Some of the platinum-group minerals contain inclusions of Ag-rich gold (AgAu2) and muthmannite (AuAgTe2). Most of the platinum-group minerals occur as inclusions in chalcopyrite, although a few grains are located at base-metal sulfide grain boundaries and in fractures in base-metal sulfides.\u0000 The whole-rock compositions of the stockwork veins are Cu-rich and are interpreted to represent a fractionated Cu-rich sulfide liquid enriched in Pt, Pd, Au, Ag, As, Bi, Pb, Se, Te, Zn, which separated from a monosulfide solid solution (mss). An intermediate solid solution (iss) solidified from the Cu-rich sulfide liquid, recrystallizing chalcopyrite at <550 °C. Simultaneously, small volumes of intercumulus residual melt contained mainly the precious metals, Bi, and Te due to their incompatibility in iss. Solitary and composite platinum-group minerals as well as Au-minerals crystallized first from the residual melt (<600 °C), followed by a succession of various Bi-, Ag-, and Pb-tellurides (∼540 °C), and finally sphalerite and galena. Melonite crystallized as mostly large, solitary grains exsolved directly from Ni-bearing intermediate solid solution (∼600 °C), shortly after the formation of moncheite and merenskyite from the residual melt. Finally, remobilization of the platinum-group minerals occurred at temperatures of <300 °C, as suggested by the presence of minor amounts of Cl-bearing minerals and ragged grain shapes.","PeriodicalId":134244,"journal":{"name":"The Canadian Mineralogist","volume":"154 3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133004872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}