scholarly journals PGE-Enrichment in Magnetite-Bearing Olivine Gabbro: New Observations from the Midcontinent Rift-Related Echo Lake Intrusion in Northern Michigan, USA

Minerals ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 21 ◽  
Author(s):  
Alexander Koerber ◽  
Joyashish Thakurta
Keyword(s):  
Sulfide Minerals ◽  
Group Element ◽  
Olivine Gabbro ◽  
Rock Unit ◽  
Midcontinent Rift ◽  
Upper Peninsula ◽  
Titaniferous Magnetite ◽  
Sulfide Melt ◽  
Sudden Decrease ◽  
Northern Michigan

The Echo Lake intrusion in the Upper Peninsula (UP) of Michigan, USA, was formed during the 1.1 Ga Midcontinent Rift event in North America. Troctolite is the predominant rock unit in the intrusion, with interlayered bands of peridotite, mafic pegmatitic rock, olivine gabbro, magnetite-bearing gabbro, and anorthosite. Exploratory drilling has revealed a platinum group element (PGE)-enriched zone within a 45 m thick magnetite-ilmenite-bearing olivine gabbro unit with grades up to 1.2 g/t Pt + Pd and 0.3 wt. % Cu. Fine, disseminated grains of sulfide minerals such as pyrrhotite and chalcopyrite occur in the mineralized interval. Formation of Cu-PGE-rich sulfide minerals might have been caused by sulfide melt saturation in a crystallizing magma, which was triggered by a sudden decrease in fO2 upon the crystallization and separation of titaniferous magnetite. This PGE-enriched zone is comparable to other well-known reef-like PGE deposits, such as the Sonju Lake deposit in northern Minnesota.

Sulfide mineral chemistry and platinum-group minerals of the UG-2 chromitite in the northern limb of the Bushveld Igneous Complex, South Africa

2021 ◽  
Vol 59 (6) ◽  
pp. 1339-1362
Author(s):  
Malose M. Langa ◽  
Pedro J. Jugo ◽  
Matthew I. Leybourne ◽  
Danie F. Grobler
Keyword(s):  
Platinum Group Element ◽  
Mineral Chemistry ◽  
Sulfide Mineral ◽  
Sulfide Minerals ◽  
Group Element ◽  
Igneous Complex ◽  
Northern Limb ◽  
Platinum Group Minerals ◽  
Platinum Group ◽  
Bushveld Igneous Complex

ABSTRACT 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.

Nano- and Micrometer-Sized PGM in Ni-Cu-Fe Sulfides from an Olivine Megacryst in the Udachnaya Pipe, Yakutia, Russia

2021 ◽  
Vol 59 (6) ◽  
pp. 1755-1773
Author(s):  
José María González-Jiménez ◽  
Irina Tretiakova ◽  
Marco Fiorentini ◽  
Vladimir Malkovets ◽  
Laure Martin ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Field Emission ◽  
Platinum Group Element ◽  
Group Element ◽  
Monosulfide Solid Solution ◽  
Mineral Particles ◽  
Transmission Electron ◽  
Sulfide Melt ◽  
Platinum Group

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 image nanoscale textural features in order to better understand the mechanisms of platinum group element fractionation in magmatic systems. These processes may play a crucial role in controlling the background geochemical budgets for siderophile and chalcophile elements in a wide range of mantle-derived magmas.

Distribution of sulfides and PGE minerals in the picritic and taxitic gabbro-dolerites of the Norilsk 1 intrusion

2021 ◽  
Vol 59 (6) ◽  
pp. 1437-1451
Author(s):  
Nadezhda Tolstykh ◽  
Jonathan Garcia ◽  
Gennadiy Shvedov
Keyword(s):  
Platinum Group Element ◽  
Group Element ◽  
Olivine Gabbro ◽  
Native Copper ◽  
Sulfur Fugacity ◽  
Cu Content ◽  
Geochemical Zoning ◽  
Monoclinic Pyrrhotite ◽  
Low Sulfur ◽  
Reverse Zoning

ABSTRACT Disseminated ores in the Norilsk 1 intrusion were studied to elucidate the typomorphic features of sulfides and noble metal mineralizations in picritic and taxitic (or lower olivine) gabbro-dolerites. The former are characterized by the development of a low-sulfur sulfide association (troilite, Fe-rich pentlandite, talnakhite, chalcocite, native copper) while the latter exhibits a high-sulfur association (monoclinic pyrrhotite, Ni-rich pentlandite, pyrite, heazlewoodite). The contact between these types of rocks is geochemically and mineralogically contrasting. The mineralogical and geochemical zoning directed from the roof to the base of each layer is expressed by an increase in the Cu content (and chalcopyrite) in ores, an increase in the concentration of Ni in pentlandite and S in pyrrhotite in line with a decrease of the crystallization temperature, and an increase in sulfur fugacity in the same direction. Zoning of Pd(Pt) mineralization in picritic and taxitic (olivine) gabbro-dolerites is uniform and characterized by the distribution of Pd-Sn compounds in the upper parts (together with Pd-Pb minerals in picritic rocks) and Pd-As compounds in the lower parts of the sections according to a drop in temperature. Such reverse zoning contradicts the typical mechanism of differentiation by fractional crystallization, and possibly suggests a fluid-magmatic nature. Mineralogical and geochemical features in platinum group element-Cu-Ni-bearing rocks are consistent with the idea that different stages of multi-pulse intrusions of mafic-ultramafic magmas with different compositions formed the picritic and taxitic gabbro-dolerites of the Norilsk region.

The role of magma injection and crystal sorting in the formation of early gabbros at the Coldwell Complex, Ontario, Canada

2019 ◽  
Vol 56 (7) ◽  
pp. 715-737 ◽  
Author(s):  
Yong-hua Cao ◽  
David J. Good ◽  
Robert L. Linnen ◽  
Iain M. Samson
Keyword(s):  
Major Element ◽  
Mineral Chemistry ◽  
Ultramafic Rocks ◽  
Chemical Compositions ◽  
Olivine Gabbro ◽  
Additional Observation ◽  
Midcontinent Rift ◽  
Layered Series ◽  
Incompatible Elements

The Layered Series of the Midcontinent Rift related Coldwell Complex comprises thick sections of gabbro, without any known associated ultramafic rocks. It represents a major early intrusive unit of the Coldwell Complex and consists of thick accumulations of olivine gabbro and oxide augite melatroctolite. This study combines petrography, mineral chemistry, and lithogeochemistry to constrain the magma composition and petrogenesis of the Layered Series. The presence of cumulus orthoclase together with the observation that the Layered Series rocks plot in the alkaline field on a total alkali–silica diagram indicate that the Layered Series magma has an alkaline parentage. The stratigraphy of the Layered Series cannot be fully correlated between different areas using lithogeochemistry and mineral chemistry. This together with observed normal and reverse trends for mineral chemical compositions in different areas suggest that the processes related to magma emplacement and crystallization were different in different locations. The whole-rock concentrations of incompatible elements and the compositions of major minerals of the olivine gabbro and oxide augite melatroctolite units are chemically similar. However, major element lithogeochemistry is variable, dominantly due to differences in the abundances of olivine, clinopyroxene, plagioclase, and magnetite. An additional observation is that olivine and clinopyroxene are not in chemical equilibrium. Together, these observations are interpreted to reflect a combination of multiple injections of magma and crystal sorting in an open system.

Significance of the metasomatized lithospheric mantle in the formation of early basalts and Cu – platinum group element sulfide mineralization in the Coldwell Complex, Midcontinent Rift, Canada

2019 ◽  
Vol 56 (7) ◽  
pp. 693-714 ◽  
Author(s):  
David J. Good ◽  
Peter C. Lightfoot
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Trace Element ◽  
Lithospheric Mantle ◽  
Group Element ◽  
Light Rare Earth ◽  
Midcontinent Rift ◽  
Northern Margin ◽  
Lithospheric Mantle Source ◽  
Light Rare Earth Elements

A diverse suite of tholeiitic to alkaline basalt and gabbroic intrusions located in the Coldwell Complex on the northern margin of the Midcontinent Rift exhibit unusual trace element signatures that show enriched large ion lithophile elements and light rare earth elements with negative Nb and Zr anomalies. These features are not typical of magmas derived by partial melting within or above a rising mantle plume, as might be expected in an early Midcontinent Rift magmatic event. In this paper, we provide a detailed geochemical study of a 500 m thick sequence of metabasalt that represents the earliest stage of magmatism in the Coldwell Complex. We show that contamination or crystallization processes or subsequent metasomatism cannot explain the trace element variations. Instead, we propose partial melting in a metasomatized Subcontinental Lithospheric Mantle source to explain the decoupled behavior of large ion lithophile elements from light rare earth elements and heavy rare earth elements and rare earth elements from high field strength elements and the enriched Nd isotope signature of metabasalt. Similar features occur in unit 5b of the Mamainse Point Volcanic Group located at the northern margin of the Rift. An objective of this paper is to relate Two Duck Lake gabbro, host rock for low-sulfur, high precious metal sulfide mineralization at the Marathon deposit, to the metabasalt sequence. The excellent match of trace element abundances in Two Duck Lake gabbro to metabasalt unit 3 confirms an early Coldwell Complex age for metabasalt and a Subcontinental Lithospheric Mantle source for Cu – platinum group element mineralized gabbros.

Relating jack pine budworm damage to stand inventory variables in northern Michigan

1996 ◽  
Vol 26 (12) ◽  
pp. 2180-2190 ◽  
Author(s):  
Deborah G. McCullough ◽  
Lyle J. Buss ◽  
Larry D. Marshall ◽  
Jari Kouki
Keyword(s):  
Tree Mortality ◽  
Basal Area ◽  
Site Index ◽  
The United States ◽  
Jack Pine ◽  
Inventory Data ◽  
Upper Peninsula ◽  
Jack Pine Budworm ◽  
Lake States ◽  
Northern Michigan

Stand-level mortality and top kill from a 1991–1993 jack pine budworm (Choristoneurapinuspinus Freeman) outbreak were surveyed annually in the Raco Plains area of the Hiawatha National Forest in Michigan's Upper Peninsula from 1992 to 1994. Defoliation was visually estimated and percentage of trees killed or top killed was determined in 104 stands. In 1994, tree mortality attributable to the outbreak averaged 8% and 17% of trees had dead tops. Current stand inventory data, including age, site index, basal area, and size, were acquired from the Hiawatha Forest. Stands were grouped on the basis of inventory variables used for jack pine management in the Lake States region of the United States. Differences in tree mortality and top kill between groups, and associations between tree mortality and inventory variables, were evaluated. Tree mortality was greater in overmature stands and in overstocked stands, but stand size had little effect. Contrary to expectations, mortality was lower on poor sites with low site index values than on better sites with higher site index values. Mortality was not related to abundance of open-grown, full-canopied wolf trees or to abundance of trees infected with pine gall rust (Endocronartiumharknessii (J.P. Moore) Y. Hiratsuka (=Peridermiumharknessii J.P. Moore)). Amount of top kill was related to defoliation severity and was higher in overmature and understocked stands. Top kill was not strongly associated with amount of tree mortality or with inventory variables.

Quartz deformation in the Marquette and Republic troughs, Upper Peninsula of Michigan

1984 ◽  
Vol 21 (7) ◽  
pp. 793-801 ◽  
Author(s):  
Janet Kappmeyer ◽  
David V. Wiltschko
Keyword(s):  
Subgrain Size ◽  
Stress Regime ◽  
Upper Peninsula ◽  
Metamorphic History ◽  
Dislocation Densities ◽  
History Of ◽  
Peak Metamorphism ◽  
Quartz Fabrics ◽  
Upper Peninsula Of Michigan ◽  
Northern Michigan

Quartz fabrics and microstructures in quartzites of the Mesnard and Goodrich formations were examined to better define the deformation and metamorphic history of the Marquette Synclinorium, northern Michigan. Fabric development is very weak in the whole-rock samples and indicates that mica contamination, extensive annealing, and (or) low imposed strains prevented the formation of distinct c-axis fabrics. However, well defined fabrics are preserved in five quartzite pebbles from the Goodrich conglomerate. Double maxima of varying intensities among these pebbles suggest that the northwest section of the district experienced inhomogeneous shear strain. Measured grain sizes yielded differential stresses ranging from 44 to 548 bar (4.4 to 54.8 MPa). Subgrain size data indicate stresses ranging from 151 to 248 bar (15.1 to 24.8 MPa). Dislocation densities determined by observed etch-pit densities using scanning electron microscopy indicate a range of stresses from 330 to 730 bar (33 to 73 MPa). Stress values from dislocation density measurements vary inversely with metamorphic intensity. Cumulatively, these microstructural data indicate that a low-stress regime of deformation preceded a cooler, higher stress pulse. The data also imply that deformation of the Marquette Synclinorium continued after peak metamorphism, contrary to early hypotheses.

The Paleoproterozoic (2.5–1.7 Ga) Midcontinent rift system of the northeastern Fennoscandian Shield

1997 ◽  
Vol 34 (4) ◽  
pp. 426-443 ◽  
Author(s):  
V. F. Smolkin
Keyword(s):  
Tholeiitic Basalt ◽  
Rift System ◽  
Olivine Gabbro ◽  
Midcontinent Rift ◽  
Granulite Belt ◽  
Mantle Sources ◽  
Third Stage ◽  
Midcontinent Rift System ◽  
Archean Crust ◽  
Dyke Swarms

The Karelian epoch of tectono-magmatic activity resulted in an intensive structural–tectonic rearrangement of Archean crustal blocks, origination, development, and orogenesis of the Pechenga – Varzuga belt. Being emplaced on the Archean crust of the continental type, the Pechenga – Varzuga belt is an intracontinental paleorift system formed during four stages: prerifting (2.55–2.30 Ga), early rifting (2.30–2.20 Ga), late rifting (2.20–1.95 Ga), and orogenic (1.95–1.70 Ga). During the stage of 2.55–2.30 Ga, as a result of formation of an extensive asthenolens whose projection to the surface covered most of the Kola – Lapland – Karelian province, there appeared paleoaulacogen depressions and mantle and crustal magma associations with normal alkalinity: gabbronorite dykes (2.55–2.40 Ga), low-Ti picrite–basalt (2.45–2.41 Ga), basalt, andesite–basalt (initial 87Sr/86Sr = 0.7042) and dacite volcanics, peridotite–pyroxenite–gabbronorite (2.50–2.43 Ga, εNd = −1, −2), lherzolite–gabbronorite (or drusite) (2.45 Ga), and gabbro–anorthosite (2.45 Ga) layered intrusions characterized by chromite, platinum, and titanomagnetite mineralization. As the rocks of Archean blocks were generally warmed up, intracrustal chambers of granitoid magmas were common. During the stage of 2.30–2.20 Ga, the asthenolens broke up and differentiation of its fragments significantly increased. Over the most heated fragments, the paleorift system (Pechenga–Varzuga belt) appeared, accompanied by generation of mantle melts with higher alkalinity (volcanic series of picrite – trachybasalt – trachyandesitic basalts, 87Sr/86Sr = 0.7035). During the third stage (2.20–1.95 Ga), rifting reached its maximum owing to intense sinistral fault-rifting, and mantle sources of deep ferropicritic (87Sr/86Sr = 0.7032; εNd = +1.6) and shallow tholeiitic basalt (87Sr/86Sr = 0.7021) melts formed at different depths; eruption of these magmas gave rise to thick volcanic sequences (1.98 Ga), Ni – Cu-bearing differentiated gabbro–wehrlite intrusions (1.98–1.90 Ga, 87Sr/86Sr = 0.7029; εNd = +1.5), and cogenetic, peridotite – olivine gabbro dyke swarms (1.96 Ga, εNd = +1.4), which are characterized by the elevated Fe, Ti, P, and light rare earth element contents. Intrusions of sulfide-bearing gabbronorite and websterite formed in the Lapland–Kolvitsa granulite belt, which experienced collision and high-grade (6–10 kbar (1 kbar = 100 MPa)) metamorphism. During the final stage (1.95–1.70 Ga), enclosure and orogenesis of the paleorift system took place; these events were accompanied by extensive development of mixed mantle–crustal and crustal sources, the formation of calc-alkaline volcanic and sedimentary orogenic associations, and the emplacement of P–Ti-bearing alkaline gabbro – nepheline syenite and U – Mo-bearing monzonite–granodiorite intrusions.

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