Journal articles: 'Mafic–ultramafic intrusions'

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Hart, Thomas Robert, and Carole Anne MacDonald. "Proterozoic and Archean geology of the Nipigon Embayment: implications for emplacement of the Mesoproterozoic Nipigon diabase sills and mafic to ultramafic intrusions." Canadian Journal of Earth Sciences 44, no. 8 (August 1, 2007): 1021–40. http://dx.doi.org/10.1139/e07-026.

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The Nipigon Embayment is underlain by Archean rocks of the English River, Wabigoon, and Quetico subprovinces, and intruded along the west side by late- to post-tectonic mafic to ultramafic intrusions. The early Mesoproterozoic ultramafic to felsic Badwater intrusion and felsic English Bay Complex are located in the northwest corner of the Nipigon Embayment. Three mafic to ultramafic intrusions, the Disraeli, Seagull, and Hele intrusions, are located south of Lake Nipigon, and the Kitto intrusion is located east of the lake. A number of mafic to ultramafic bodies (Jackfish (Island), Shillabeer, Kama Hill, Nipigon Bay) have only limited outcrops. The gabbroic Nipigon diabase sills intrude all other rocks in the Nipigon Embayment and generally have a consistent mineralogy and geochemistry, except for the Inspiration sill(s) and the McIntyre Sill. Geological and geophysical data suggest emplacement of the ultramafic intrusions by mechanisms similar to those controlling emplacement of the saucer-shaped diabase sills. These mechanisms are partially dependent on a series of pre-existing north-, northwest-, and northeast-trending faults formed prior to Keweenawan magmatism. The presence of sills, rather than dykes, indicates that the Nipigon Embayment was not extensional during the Keweenawan Midcontinent Rift, suggesting that the Nipigon Embayment is not a classic failed arm.

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Zi, Jian-Wei, Birger Rasmussen, Janet R. Muhling, Wolfgang D. Maier, and Ian R. Fletcher. "U-Pb monazite ages of the Kabanga mafic-ultramafic intrusions and contact aureoles, central Africa: Geochronological and tectonic implications." GSA Bulletin 131, no. 11-12 (April 15, 2019): 1857–70. http://dx.doi.org/10.1130/b35142.1.

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AbstractMafic-ultramafic rocks of the Kabanga-Musongati alignment in the East African nickel belt occur as Bushveld-type layered intrusions emplaced in metasedimentary sequences. The age of the mafic-ultramafic intrusions remains poorly constrained, though they are regarded to be part of ca. 1375 Ma bimodal magmatism dominated by voluminous S-type granites. In this study, we investigated igneous monazite and zircon from a differentiated layered intrusion and metamorphic monazite from the contact aureole. The monazite shows contrasting crystal morphology, chemical composition, and U-Pb ages. Monazite that formed by contact metamorphism in response to emplacement of mafic-ultramafic melts is characterized by extremely high Th and U and yielded a weighted mean 207Pb/206Pb age of 1402 ± 9 Ma, which is in agreement with dates from the igneous monazite and zircon. The ages indicate that the intrusion of ultramafic melts was substantially earlier (by ∼25 m.y., 95% confidence) than the prevailing S-type granites, calling for a reappraisal of the previously suggested model of coeval, bimodal magmatism. Monazite in the metapelitic rocks also records two younger growth events at ca. 1375 Ma and ca. 990 Ma, coeval with metamorphism during emplacement of S-type granites and tin-bearing granites, respectively. In conjunction with available geologic evidence, we propose that the Kabanga-Musongati mafic-ultramafic intrusions likely heralded a structurally controlled thermal anomaly related to Nuna breakup, which culminated during the ca. 1375 Ma Kibaran event, manifested as extensive intracrustal melting in the adjoining Karagwe-Ankole belt, producing voluminous S-type granites. The Grenvillian-aged (ca. 990 Ma) tin-bearing granite and related Sn mineralization appear to be the far-field record of tectonothermal events associated with collision along the Irumide belt during Rodinia assembly. Since monazite is a ubiquitous trace phase in pelitic sedimentary rocks, in contact aureoles of mafic-ultramafic intrusions, and in regional metamorphic belts, our study highlights the potential of using metamorphic monazite to determine ages of mafic-ultramafic intrusions, and to reconstruct postemplacement metamorphic history of the host terranes.

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Li, Ai, Jian Wang, and Yue Song. "Petrology, mineral chemistry, and geochemistry of Late Triassic Ni–Cu ore-bearing mafic–ultramafic intrusions, Hongqiling, northeastern China: petrogenesis and tectonic implications." Canadian Journal of Earth Sciences 56, no. 2 (February 2019): 111–28. http://dx.doi.org/10.1139/cjes-2018-0014.

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The Hongqiling magmatic Ni–Cu sulfide deposit, situated on the southern margin of the eastern Central Asian Orogenic Belt (CAOB), is composed of over 30 mafic–ultramafic intrusions. These ore-bearing intrusions are composed mainly of harzburgite, lherzolite, websterite, orthopyroxenite, and norite (gabbro). The constituent minerals are olivine, diopside, bronzite, calcic-hornblende, plagioclase, and spinel with orthopyroxene as a dominant mineral in these intrusions. These ore-bearing intrusions are not Alaskan-type complexes. Spinel and clinopyroxene both exhibit different chemical compositions from those in the Alaskan-type complexes. The rocks that make up the intrusions have high contents of MgO (average value = 25.20 wt.%) and low TiO2 (average value = 0.58 wt.%). The high MgO contents of the minerals and the high Mg# (71) of the calculated melt in equilibrium with olivine demonstrate that the parental magma of the Hongqiling mafic–ultramafic intrusions was a high-Mg tholeiitic magma. The Hongqiling ore-bearing mafic–ultramafic intrusions and the calculated “trapped liquids” for the olivine-orthopyroxene cumulate rocks are all enriched in large-ion lithophile elements and depleted in high field strength elements. The Ce/Pb, Ta/La, Th/Yb, and (La/Sm)PM values and the depletion of Nb and Ta suggest that the magma experienced crustal contamination. The Hongqiling ore-bearing intrusions display many similarities with mafic–ultramafic intrusions that formed in a post-collisional extensional environment in the western CAOB (e.g., Huangshanxi). Common features include their whole-rock compositions and mineral chemistry. Combined with the evolutionary history of the eastern segment of the CAOB, we believe that the Late Triassic Hongqiling mafic–ultramafic intrusions formed in a post-collisional extensional environment.

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Zhao, Xinyun, Libo Hao, Qiaoqiao Wei, Qingqing Liu, Jian Zhou, Xueqiu Wang, Jilong Lu, Yuyan Zhao, and Chengyou Ma. "Origin of Late Triassic mafic–ultramafic intrusions in the Hongqiling Ni–Cu sulfide deposit, Northeast China: evidence from trace element and Sr–Nd isotope geochemistry." Canadian Journal of Earth Sciences 55, no. 12 (December 2018): 1312–23. http://dx.doi.org/10.1139/cjes-2018-0041.

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There are many Late Triassic mafic–ultramafic intrusions in the Hongqiling magmatic Ni–Cu sulfide deposit, Northeast China. Research on magma evolution leading to formation of these mafic–ultramafic intrusions is of great significance for understanding the mantle beneath Northeast China and associated Ni–Cu mineralization. A trace element study of the No. 1, 3, and 7 intrusions in the Hongqiling deposit reveals that these mafic–ultramafic intrusions are characterized by enrichment of incompatible elements, which however cannot be interpreted by subduction modification. Furthermore, model of batch partial melting of depleted mantle accompanied by upper crustal contamination can simulate the trace element patterns of these mafic–ultramafic intrusions, but partial melting of depleted mantle accompanied by lower crustal contamination model cannot work. In addition, Sr–Nd isotopic compositions of the Hongqiling No. 1, 3, and 7 intrusions also indicate that crustal contamination could have occurred mainly during the magma ascent. Consequently, a possible scenario for the magma evolution is that the primary mafic–ultramafic magma was derived from batch partial melting of a depleted mantle, and then contaminated by Cambrian–Ordovician metamorphic rocks of the Hulan Group during ascent. We conclude that the mantle source contained no significant crustal component in the Late Triassic and was also independent of substantial contribution from subducted material, and therefore the Mesozoic large-scale lithospheric delamination beneath eastern China may happen after a period of time of the Late Triassic.

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Guice, George L., Michael R. Ackerson, Robert M. Holder, Freya R. George, Joseph F. Browning-Hanson, Jerry L. Burgess, Dionysis I. Foustoukos, Naomi A. Becker, Wendy R. Nelson, and Daniel R. Viete. "Suprasubduction zone ophiolite fragments in the central Appalachian orogen: Evidence for mantle and Moho in the Baltimore Mafic Complex (Maryland, USA)." Geosphere 17, no. 2 (February 5, 2021): 561–81. http://dx.doi.org/10.1130/ges02289.1.

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Abstract Suprasubduction zone (SSZ) ophiolites of the northern Appalachians (eastern North America) have provided key constraints on the fundamental tectonic processes responsible for the evolution of the Appalachian orogen. The central and southern Appalachians, which extend from southern New York to Alabama (USA), also contain numerous ultramafic-mafic bodies that have been interpreted as ophiolite fragments; however, this interpretation is a matter of debate, with the origin(s) of such occurrences also attributed to layered intrusions. These disparate proposed origins, alongside the range of possible magmatic affinities, have varied potential implications for the magmatic and tectonic evolution of the central and southern Appalachian orogen and its relationship with the northern Appalachian orogen. We present the results of field observations, petrography, bulk-rock geochemistry, and spinel mineral chemistry for ultramafic portions of the Baltimore Mafic Complex, which refers to a series of ultramafic-mafic bodies that are discontinuously exposed in Maryland and southern Pennsylvania (USA). Our data indicate that the Baltimore Mafic Complex comprises SSZ ophiolite fragments. The Soldiers Delight Ultramafite displays geochemical characteristics—including highly depleted bulk-rock trace element patterns and high Cr# of spinel—characteristic of subduction-related mantle peridotites and serpentinites. The Hollofield Ultramafite likely represents the “layered ultramafics” that form the Moho. Interpretation of the Baltimore Mafic Complex as an Iapetus Ocean–derived SSZ ophiolite in the central Appalachian orogen raises the possibility that a broadly coeval suite of ophiolites is preserved along thousands of kilometers of orogenic strike.

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Hart, Thomas, Adam Richardson, Carole Anne MacDonald, and Pete Hollings. "Geochemistry of the Mesoproterozoic intrusive rocks of the Nipigon Embayment, northwestern Ontario: evaluating the earliest phases of rift development." Canadian Journal of Earth Sciences 44, no. 8 (August 1, 2007): 1087–110. http://dx.doi.org/10.1139/e06-127.

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The intrusive rocks of the Nipigon Embayment comprise a series of four mafic to ultramafic intrusions and a number of laterally extensive diabase sills that are among the oldest expression of the ~1.1 Ga Mesoproterozoic Mid-continent Rift. New geochemical data indicate that the sills can be subdivided into five distinct groups: three mafic sills (Nipigon, Inspiration, and McIntyre diabase sills), with the Nipigon sills forming the bulk of the outcrop, and two spatially restricted ultramafic to mafic sills (Jackfish and Shillabeer sills). The latter mafic sills are typically massive, medium-grained, intergranular textured gabbros ranging in thickness from a few metres to more than 250 m. Two of the ultramafic intrusions included in this study (Disraeli and Hele) consist of a core of pyroxene peridotite with olivine gabbro along the margins. The geochemical characteristics of the ultramafic intrusions and diabase sills are consistent with plume-derived melts that have undergone subsequent fractionation and been contaminated by continental crust, likely at depth, but a few samples from the Hele and Disraeli intrusions have the characteristics of primary, uncontaminated melts that have been rapidly transported through the lithosphere with little interaction with wall rocks. The field and geochemical characteristics of the intrusions and sills are consistent with the ultramafic intrusions having been emplaced before the diabase sills and indicate that the history of the Midcontinent Rift is more complex and protracted than previously recognized.

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Blanchard, J. A., R. E. Ernst, and C. Samson. "Gravity and magnetic modelling of layered mafic–ultramafic intrusions in large igneous province plume centre regions: case studies from the 1.27 Ga Mackenzie, 1.38 Ga Kunene–Kibaran, 0.06 Ga Deccan, and 0.13–0.08 Ga High Arctic events." Canadian Journal of Earth Sciences 54, no. 3 (March 2017): 290–310. http://dx.doi.org/10.1139/cjes-2016-0132.

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Gravity and magnetic data from the global EGM2008 and EMAG2 datasets are used to identify geophysical anomalies in large igneous province (LIP) plume centre regions with the goal of characterizing mafic–ultramafic intrusions linked to those LIPs. Geophysical anomalies within 18 LIPs distributed globally are investigated. Four of these LIPs are selected for detailed modelling: the 1.27 Ga Mackenzie, 1.38 Ga Kunene–Kibaran, 0.06 Ga Deccan, and 0.13–0.08 Ga High Arctic LIPs. We recognize three spatial distribution types for intrusions in plume centre regions. These are (1) intrusions emplaced along a circular fault system that circumscribes the plume centre, (2) intrusions emplaced along linear rifts that, in some cases, converge towards the plume centre, and (3) single or unclassified intrusions. Modelling supports that the geophysical anomalies associated with these LIPs tend to be produced by large (radius >30 km) and deep-seated crustal intrusions, with densities consistent with mafic–ultramafic rock and magnetic susceptibilities consistent with serpentinized ultramafic rock, except within the Deccan where intrusions are smaller, mainly mafic in composition, and positioned at shallower depths in the crust.

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Smyk, Mark C., and James M. Franklin. "A synopsis of mineral deposits in the Archean and Proterozoic rocks of the Lake Nipigon Region, Thunder Bay District, Ontario." Canadian Journal of Earth Sciences 44, no. 8 (August 1, 2007): 1041–53. http://dx.doi.org/10.1139/e07-013.

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A variety of metallic and non-metallic mineral deposit types occur within Archean and Proterozoic rocks in the area encompassing the Lake Nipigon Region Geoscience Initiative. Archean deposit types include Algoma-type banded iron formation-hosted iron (e.g., Lake Nipigon iron range); volcanogenic massive sulphide copper–zinc (e.g., Onaman–Tashota belt); ultramafic intrusion-hosted chromium (e.g., Puddy–Chrome lakes); mafic to ultramafic intrusion-hosted copper–nickel – platinum group element (PGE) (e.g., Lac des Iles); and pegmatite-hosted deposits of rare metals (Li, Ta, Be), uranium, and molybdenum (e.g., Georgia Lake field, Black Sturgeon Lake, and Anderson Lake, respectively). Mesothermal lode gold deposits are prominent in the Beardmore–Geraldton camp. Superior-type iron formation occurs in Paleoproterozoic Gunflint Formation. "Red-bed" copper occurs in Mesoproterozoic Midcontinent Rift-related Osler Group volcanic and interflow sedimentary rocks. Native copper and copper sulphides occur in Mesoproterozoic Sibley Group sedimentary rocks, adjacent to ultramafic intrusions. These mafic to ultramafic intrusions, associated with Midcontinent Rift magmatism, host copper–nickel–PGE deposits (e.g., Seagull, Great Lakes Nickel). Silver-bearing veins occur in Paleoproterozoic Animikie Group sedimentary rocks in proximity to Midcontinent Rift-related mafic intrusions (e.g., Silver Islet, Silver Mountain). Lead–zinc–barite veins, uranium-bearing veins, and amethyst vein and replacement-type deposits may be cogenetic and formed at or near the unconformity between Sibley Group basal sandstone and underlying Archean granitic basement (e.g., Dorion, Black Sturgeon Lake, McTavish Township). The hydrothermal systems that produced all of these veins were probably driven by heat associated with Midcontinent rifting. Many occur in structures related to rift-bounding faults. Iron oxide – copper–gold deposits may occur near the English Bay intrusion.

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Makkonen, Hannu V., and Pekka Tuisku. "Geology and crystallization conditions of the Särkiniemiintrusion and related nickel-copper ore, central Finland – implications for depth of emplacement of 1.88 Ga nickel-bearing intrusions." Bulletin of the Geological Society of Finland 92, no. 2 (December 15, 2020): 111–30. http://dx.doi.org/10.17741/bgsf/92.2.003.

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Several Ni-Cu deposits occur within the Kotalahti area, central Finland, in proximity to an Archaean gneiss dome surrounded by a Palaeoproterozoic craton-margin supracrustal sequence comprising quartzites, limestones, calc-silicate rocks, black schists and banded diopside amphibolites. The geology of the area and age of the Ni-bearing intrusions (1.88 Ga) are similar to the Thompson Ni belt in the Canadian Trans-Hudson Orogen. The small mafic-ultramafic and Ni-Cu -bearing Särkiniemi intrusion, closely associated with the Archaean basement core of the Kotalahti Dome, is composed of a western peridotite and eastern gabbro body, both of which are mineralized. The eastern gabbro has a contact aureole several meters thick, consisting of orthopyroxene +/- cordierite bearing hornfels between the intrusion and the migmatites. Geochemically, the Särkiniemi intrusion shares many features in common with other Svecofennian mafic-ultramafic intrusions, including crustal contamination and nickel depletion. The related Ni-Cu deposit has a low Ni/Co value (15) and low nickel content in the sulphide fraction (2.8 wt.%), together with a low estimated magma/sulphide ratio of around 170. Svecofennian 1.88 Ga mafic-ultramafic intrusions occur in terrains of variable metamorphic grade (from low-amphibolite to granulite facies) and are likely to represent emplacement at different crustal depths. Multi-equilibrium thermobarometry indicates that the contact aureole at Särkiniemi reached equilibrium at pressures of 4.5–6 kbar (15–20 km depth) and temperatures of 600–670 °C. Combined with the results of earlier research on the Svecofennian intrusions, this study indicates that a depth of 15–20 km crustal level was favourable, along with other critical factors, for nickel sulfide deposition at 1.88 Ga.

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Cao, Yonghua, Christina Yan Wang, and Bo Wei. "Magma oxygen fugacity of mafic-ultramafic intrusions in convergent margin settings: Insights for the role of magma oxidation states on magmatic Ni-Cu sulfide mineralization." American Mineralogist 105, no. 12 (December 1, 2020): 1841–56. http://dx.doi.org/10.2138/am-2020-7351.

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Abstract Oxygen fugacities (fO2) of mantle-derived mafic magmas have important controls on the sulfur status and solubility of the magmas, which are key factors to the formation of magmatic Ni-Cu sulfide deposits, particularly those in convergent margin settings. To investigate the fO2 of mafic magmas related to Ni-Cu sulfide deposits in convergent margin settings, we obtained the magma fO2 of several Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the Central Asian Orogenic Belt (CAOB), North China, based on the olivine-spinel oxygen barometer and the modeling of V partitioning between olivine and melt. We also calculated the mantle fO2 on the basis of V/Sc ratios of primary magmas of these intrusions. Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the CAOB include arc-related Silurian-Carboniferous ones and post-collisional Permian-Triassic ones. Arc-related intrusions formed before the closure of the paleo-Asian ocean and include the Jinbulake, Heishan, Kuwei, and Erbutu intrusions. Post-collisional intrusions were emplaced in extensional settings after the closure of the paleo-Asian ocean and include the Kalatongke, Baixintan, Huangshandong, Huangshan, Poyi, Poshi, Tulaergen, and Hongqiling No. 7 intrusions. It is clear that the magma fO2 values of all these intrusions in both settings range mostly from FMQ+0.5 (FMQ means fayalite-magnetite-quartz oxygen buffer) to FMQ+3 and are generally elevated with the fractionation of magmas, much higher than that of MORBs (FMQ-1 to FMQ+0.5). However, the mantle fO2 values of these intrusions vary from ~FMQ to ~FMQ+1.0, just slightly higher than that of mid-ocean ridge basalts (MORBs) (≤FMQ). This slight difference is interpreted as the intrusions in the CAOB may have been derived from the metasomatized mantle wedges where only minor slab-derived, oxidized components were involved. Therefore, the high-magma fO2 values of most Ni-Cu sulfide-bearing mafic-ultramafic intrusions in the CAOB were attributed to the fractionation of magmas derived from the slightly oxidized metasomatized mantle. In addition, the intrusions that host economic Ni-Cu sulfide deposits in the CAOB usually have magma fO2 of >FMQ+1.0 and sulfides with mantle-like δ34S values (–1.0 to +1.1‰), indicating that the oxidized mafic magmas may be able to dissolve enough mantle-derived sulfur to form economic Ni-Cu sulfide deposits. Oxidized mafic magmas derived from metasomatized mantle sources may be an important feature of major orogenic belts.

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You, Minxin, Wenyuan Li, Houmin Li, Zhaowei Zhang, and Xin Li. "Petrogenesis and Tectonic Significance of the ~276 Ma Baixintan Ni-Cu Ore-Bearing Mafic-Ultramafic Intrusion in the Eastern Tianshan Orogenic Belt, NW China." Minerals 11, no. 4 (March 26, 2021): 348. http://dx.doi.org/10.3390/min11040348.

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The Baixintan mafic-ultramafic intrusion in the Dananhu-Tousuquan arc of the Eastern Tianshan orogenic belt is composed of lherzolite, olivine gabbro, and gabbro. Olivine gabbros contain zircon grains with a U-Pb age of 276.8 ± 1.1 Ma, similar to the ages of other Early Permian Ni-Cu ore-bearing intrusions in the region. The alkaline-silica diagrams, AFM diagram, together with the Ni/Cu-Pd/Ir diagram, indicate that the parental magmas for the Baixintan intrusion were likely high-Mg tholeiitic basaltic in composition. The Cu/Pd ratios, the relatively depleted PGEs and the correlations between them demonstrate that the parental magmas had already experienced sulfide segregation. The lower CaO content in pyroxenites compared with the Duke Island Alaskan-type intrusion and the composition of spinels imply that Baixintan is not an Alaskan-type intrusion. By comparing the Baixintan intrusion with other specific mafic-ultramafic intrusions, this paper considers that the mantle source of the Baixintan intrusion is metasomatized by subduction slab-derived fluids’ components, which gives rise to the negative anomalies of Nb, Ti, and Ta elements. Nb/Yb-Th/Yb, Nb/Yb-TiO2/Yb, and ThN-NbN plots show that the Baixintan intrusion was emplaced in a back-arc spreading environment and may be related to a mantle plume.

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Järvinen, Ville, Tapio Halkoaho, Jukka Konnunaho, Jussi S. Heinonen, and O. Tapani Rämö. "Parental magma, magmatic stratigraphy, and reef-type PGE enrichment of the 2.44-Ga mafic-ultramafic Näränkävaara layered intrusion, Northern Finland." Mineralium Deposita 55, no. 8 (December 31, 2019): 1535–60. http://dx.doi.org/10.1007/s00126-019-00934-z.

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AbstractAbout 20 mafic-ultramafic layered intrusions in the northern Fennoscandian shield were emplaced during a widespread magmatic event at 2.5–2.4 Ga. The intrusions host orthomagmatic Ni-Cu-PGE and Cr-V-Ti-Fe deposits. We update the magmatic stratigraphy of the 2.44-Ga Näränkävaara mafic-ultramafic body, northeastern Finland, on the basis of new drill core and outcrop observations. The Näränkävaara body consists of an extensive basal dunite (1700 m thick), and a layered series comprising a peridotitic–pyroxenitic ultramafic zone (600 m thick) and a gabbronoritic–dioritic mafic zone (700 m thick). Two reversals are found in the layered series. The composition of the layered series parental magma was approximated using a previously unidentified marginal series gabbronorite. The parental magma was siliceous high-Mg basalt with high MgO, Ni, and Cr, but also high SiO2 and Zr, which suggests primary magma contamination by felsic crust. Cu/Pd ratio below that of primitive mantle implies PGE-fertility. The structural position of the marginal series indicates that the thick basal dunite represents an older wallrock for the layered intrusion. A subeconomic reef-type PGE-enriched zone is found in the border zone between the ultramafic and mafic zones and has an average thickness of 25 m with 150–250 ppb of Pt + Pd + Au. Offset-type metal distribution and high sulfide tenor (50–300 ppm Pd) and R-factor (105) suggest reef formation by sulfide saturation induced by fractional crystallization. The reef-forming process was probably interrupted by influx of magma related to the first reversal. Metal ratios suggest that this replenishing magma was PGE-depleted before emplacement.

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Fan, Dongxu, Shucheng Tan, Xia Wang, Zeli Qin, Junfang Zhao, Le Yang, Wanhui Zhang, et al. "Geochronology, Petrogenesis and Geodynamic Setting of the Kaimuqi Mafic–Ultramafic and Dioritic Intrusions in the Eastern Kunlun Orogen, NW China." Minerals 13, no. 1 (January 2, 2023): 73. http://dx.doi.org/10.3390/min13010073.

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The Kaimuqi area in the Eastern Kunlun Orogen (EKO) contains many lherzolite, olivine websterite, gabbro and diorite intrusions, and new zircon U‒Pb dating, Lu‒Hf isotope and whole-rock geochemical data are presented herein to further confirm the Late Triassic mafic–ultramafic magmatism with Cu–Ni mineralization and to discuss the petrogenesis and geodynamic setting. Zircon U‒Pb dating shows that the Late Triassic ages, corresponding to 220 Ma and 222 Ma, reveal the mafic–ultramafic and dioritic magmatism in Kaimuqi, respectively. Zircon from gabbro has εHf(t) values of −3.4 to −0.2, with corresponding TDM1 ages of 994–863 Ma. The mafic–ultramafic rocks generally have low SiO2, (Na2O+K2O) and TiO2 contents and high MgO contents and Mg# values. They are relatively enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy REEs (HREEs) and high-field-strength elements (HFSEs), indicating that the primary magma was derived from the metasomatized lithospheric mantle. The diorites show sanukitic high-Mg andesite properties (e.g., MgO = 2.78%–3.54%, Mg# = 50–55, Cr = 49.6–60.0 ppm, Sr = 488–512 ppm, Y = 19.6–21.8 ppm, Ba = 583–722 ppm, Sr/Y = 23.5–25.4, K/Rb = 190–202 and Eu/Eu* = 0.73–0.79), with LREEs and LILEs enrichments and HREEs and HFSEs depletions. We suggest that the primary Kaimuqi diorite magma originated from enriched lithospheric mantle that was metasomatized by subduction-derived fluids and sediments. The Kaimuqi mafic–ultramafic and dioritic intrusions, with many other mafic–ultramafic and K-rich granitic/rhyolitic rocks in the EKO, formed in a dynamic extensional setting after the Palaeo-Tethys Ocean closure.

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Ernst, R. E., S. M. Jowitt, J. A. Blanchard, and D. A. Liikane. "Large Igneous Provinces and Their Mafic-Ultramafic Intrusions." IOP Conference Series: Earth and Environmental Science 110 (December 2017): 012005. http://dx.doi.org/10.1088/1755-1315/110/1/012005.

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Fedortchouk, Yana, and William LeBarge. "Sources of placer platinum in Yukon: provenance study from detrital minerals." Canadian Journal of Earth Sciences 45, no. 8 (August 2008): 879–96. http://dx.doi.org/10.1139/e08-032.

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Source rocks for the platinum group minerals (PGM), historically reported in a number of Yukon placers, remain either unknown or poorly understood. A study of heavy-mineral samples from five creeks draining bedrock in west and central Yukon was undertaken to confirm the presence of placer platinum, to determine which mafic–ultramafic rock is the source of PGM in Kluane area, southern Yukon, and to explain platinum occurrences in Canadian and Florence creeks, central Yukon, where no known mafic–ultramafic rocks are present. Diverse composition of chromian spinel and clinopyroxenes from three creeks in the Kluane area indicate several sources of ultramafic rocks, including fragments of Alpine-type peridotites formed in back-arc basin and mid-ocean-ridge settings, and a source rock for zoned zinc-rich chromites of unknown origin. The Kluane ultramafic sills are the most likely source of PGM in this area. The heavy-mineral sample from Canadian Creek returned one PGM grain, no chromite, and abundant ilmenite and titanomagnetite. A group of chromium-rich magnesian ilmenites (∼4 wt.% MgO) closely match the composition of ilmenites from continental mafic intrusions produced during continental rift magmatism. This supports the continental rifting event recently proposed for this part of Yukon and indicates the economic potential of the Canadian Creek platinum occurrence. Composition of spinel from Florence Creek sample indicates an Alaskan-type intrusion as the source of PGM.

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Boneschans, R. B., M. S. Coetzee, and S. J. Siebert. "A geobotanical investigation of the Koedoesfontein Complex, Vredefort Dome, South Africa." Australian Journal of Botany 63, no. 4 (2015): 324. http://dx.doi.org/10.1071/bt14267.

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The Vredefort Dome (impact structure) in South-Africa hosts several unique peralkaline to ultramafic intrusive bodies that were emplaced into its core and collar. Because of the broad difference in mineral composition, between the intrusions as well as the abundant siliciclastic country rocks, abrupt transitions in soil chemical characteristics are produced that can ultimately affect the floristic and physiognomic characteristics of the associated vegetation in the dome. Despite various efforts to study the ultramafic-adapted vegetation of southern Africa, little is known about the effect these particular intrusions have on the soil and floristical components of the dome. The aim of the present study was to investigate the geobotany of one of the ultramafic-peralkaline complexes in the dome, namely the Koedoesfontein Complex. The complex hosts several different intrusions that collectively form a mineralogical gradient ranging from mafic- to felsic-dominant silicates. Three primary components (geology, soil and woody vegetation) were sampled along this gradient and analysed to determine the effect of these intrusions on the residual soil chemistry, and the floristics and physiognomy of the supported vegetation type. Weathering of the peralkaline to ultramafic lithologies greatly affected the soil’s chemical properties and related species composition and physiognomy. Major chemical variation in the soil, including the total chromium and nickel content, is correlated with the difference in abundance of sodium-, calcium-, iron- and magnesium-rich silicate minerals. Significant variations in woody species composition (particularly across Senegalia and Vachellia genera) have been established between soils originating from ultramafic–mafic, intermediate and felsic rock types and can be utilised as indicators for different geological substrates within the dome.

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Hunt, Emma J., Brian O'Driscoll, and James M. D. Day. "Sintering as a key process in the textural evolution of chromitite seams in layered mafic-ultramafic intrusions." Canadian Mineralogist 59, no. 6 (November 1, 2021): 1661–92. http://dx.doi.org/10.3749/canmin.2100021.

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ABSTRACT Nearly monomineralic stratiform chromitite seams of variable thickness (millimeters to meters) occur in many of the world's layered mafic-ultramafic intrusions. These seams are often associated with economically significant quantities of platinum group metals, yet the petrogenesis of these societally important materials remains enigmatic. Here we evaluate processes associated with late-magmatic (postcumulus) textural maturation of chromitite seams from four layered mafic-ultramafic intrusions of different ages and sizes. From largest to smallest, these intrusions are the ∼2060 Ma Bushveld Complex (South Africa), the ∼2710 Ma Stillwater Complex (USA), the ∼1270 Ma Muskox Intrusion (Canada), and the ∼60 Ma Rum Eastern Layered Intrusion (Scotland). Three endmember chromitite textures are described, based on chromite grain size and degree of textural equilibration: (1) coarse-grained chromite crystals (>0.40 mm) that occur in the central portions of seams and exhibit high degrees of solid-state textural equilibration; (2) fine-grained chromite crystals (0.11–0.44 mm) at the margins of seams in contact with and disseminated throughout host anorthosite or pyroxenite; and (3) fine-grained chromite crystals (0.005–0.28 mm) hosted within intra-seam orthopyroxene, clinopyroxene, and olivine oikocrysts. Crystal size distribution and spatial distribution pattern analyses are consistent with coarsening occurring through processes of textural maturation, including the sintering of grains by coalescence. We propose that textural maturation initially occurred in the supra-solidus state followed by an important stage of solid-state textural maturation and that these equilibration processes played a major role in the eventual microstructural and compositional homogeneity of the chromitite seams.

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Keep, Myra, and J. K. Russell. "Mesozoic alkaline rocks of the Averill plutonic complex." Canadian Journal of Earth Sciences 29, no. 11 (November 1, 1992): 2508–20. http://dx.doi.org/10.1139/e92-197.

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The 150 Ma Averill alkaline plutonic complex is situated in southern British Columbia within the Intermontane Belt of the Canadian Cordillera. It comprises concentrically arranged phases of pyroxenite, monzogabbro, monzodiorite, monzonite, and syenite. Gradational changes in the modal composition of the phases contrast with an abrupt change in crystallinity from euhedral mafic minerals in the ultramafic–mafic phases to an anhedral, interstitial habit for mafic minerals in the syenite. Whole-rock compositions have clear alkaline affinities (e.g., feldspathoid normative) and indicate a chemical discontinuity between the ultramafic–mafic phases and the late syenite phases. Melanite garnet is an important accessory mineral of the syenite and is characteristic of silica-undersaturated alkaline intrusions. Clinopyroxene, feldspar, amphibole, biotite, melanite, and titanite compositions compare closely with those of other alkaline complexes in the western Cordillera.

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Heaman, L. M., R. M. Easton, T. R. Hart, P. Hollings, C. A. MacDonald, and M. Smyk. "Further refinement to the timing of Mesoproterozoic magmatism, Lake Nipigon region, Ontario." Canadian Journal of Earth Sciences 44, no. 8 (August 1, 2007): 1055–86. http://dx.doi.org/10.1139/e06-117.

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The Midcontinent Rift in the Lake Superior region of North America is one of the best preserved examples of an aborted Precambrian intercontinental rift, one that hosts a diverse suite of rock types in addition to the well-studied and voluminous rift-fill flood basalts. Although there is a growing database of high-precision age information for the main volcanic packages and the largest mafic intrusions, there is relatively little information available on the absolute timing of mafic-ultramafic intrusions, dyke swarms, and alkaline complexes, especially in the Ontario portion of the rift. We report new high-precision U–Pb ages for 29 samples, primarily collected in the Lake Nipigon area, Ontario. From these new age results, it is now possible to expand the known distribution of Geon 15 magmatism in the region, confirm an early stage of Midcontinent Rift mafic magmatism between 1150 and 1130 Ma, provide evidence that significant mafic–ultramafic magmatism occurred in the Lake Nipigon region slightly earlier (~1115–1110 Ma) than the main stage of rift magmatism (1108–1094 Ma), and further document synchronous ~1110–1100 Ma tholeiitic and alkaline magmatism.

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SARLUS, ZMAR, ULF B. ANDERSSON, TOBIAS E. BAUER, CHRISTINA WANHAINEN, OLOF MARTINSSON, ROGER NORDIN, and JOEL B. H. ANDERSSON. "Timing of plutonism in the Gällivare area: implications for Proterozoic crustal development in the northern Norrbotten ore district, Sweden." Geological Magazine 155, no. 6 (April 27, 2017): 1351–76. http://dx.doi.org/10.1017/s0016756817000280.

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AbstractZircon ion probe (secondary-ion mass spectrometry or SIMS) data from a set of intrusive rocks emplaced in the vicinity of major ore bodies, as well as from large igneous intrusions in the Gällivare area, gave the following results: (1) the Dundret ultramafic–mafic layered complex (1883±5 Ma), the Aitik granite (1883±5 Ma), the Nautanen diorite (1870±12 Ma), the Vassaravaara ultramafic–mafic layered complex (1798±4 Ma), the Aitik dolerite (1813±9 Ma), the Bergmästergruvan and Sikträsk syenites (1795±4 Ma and 1801±3 Ma, respectively) and the Naalojärvi granite (1782±5 Ma). These data broadly fall within the ranges 1.89–1.87 Ga (early Svecofennian) and 1.80–1.78 Ga (late Svecofennian), but geochronologically allow further subdivision into pulses at 1885–1880, 1875–1870, 1800 and 1780 Ma. During these events, large layered ultramafic–mafic and felsic plutonic rocks were generated with distinct overlap in time suggesting coeval felsic–mafic magmatism. Results also indicate the presence of inheritedc.1.87 Ga zircon crystals in the plutonic rocks at 1.78 Ga, supporting reworking of the previous crust. These data indicate the importance of mantle-derived mafic underplating in the process of crustal magma generation in the region. Thec.1.88 Ga event that generated ultramafic–mafic layered complexes is tentatively suggested to have played an important role in the formation of the Aitik Cu–Au porphyry system. The later event atc.1.80 Ga, generating voluminous mafic–felsic units, is suggested to be coupled to the regional iron-oxide-copper-gold (IOCG) overprint.

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Barkov, Andrew Yu, Yakov A. Pakhomovskii, and Yurii P. Men'shikov. "Baddeleyite: new occurrences from two mafic-ultramafic layered intrusions, Russia." Mineralogical Magazine 59, no. 395 (June 1995): 349–53. http://dx.doi.org/10.1180/minmag.1995.059.395.18.

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22

Dung, Pham Thi, Tran Tuan Anh, Tran Quoc Hung, Tran Trong Hoa, R. A. Shelepaev, Nguyen Hoang, and Tran Quoc Cong. "Petrographic and geochemical characteristics of the Nui Chua pegmatoid mafic-ultramafic series, Northern Vietnam: Significance in petrogenesis and Fe-Ti-V metallogenesis." VIETNAM JOURNAL OF EARTH SCIENCES 43, no. 1 (December 4, 2020): 80–94. http://dx.doi.org/10.15625/0866-7187/15720.

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The pegmatoid intrusions of the Nui Chua complex are one of the important mafic-ultramafic intrusive series associated with Fe-Ti-V ores in northern Vietnam. These intrusions consist of plagiowebsterite, clinopyroxenite, melanogabbronorite, mesogabbro, gabbronorite, and leucogabbronorite. The Fe-Ti oxide ores being massive or disseminated appear layered or veined in pegmatoid rocks. The geochemical characteristics of pegmatoid rocks are rich in Fe, Ti, V and poor Mg; their HREE are higher than LREE, with [La/Yb]N of 0.49 to 0.91 (average: 0.67), showing negative anomalies at Nb, Ta, Th, U, Sr, Zr and positive anomalies at Cs, Ti, and K. The chemical composition and distribution characteristics of trace and rare earth elements of mafic and ultramafic rocks show that they share the same magma source. Having the same geochemical tendency of intrusive formations, Fe-Ti oxide ores are magmatic origin associated with intrusive pegmatoid rocks. The pegmatoid rocks of the Nui Chua complex and Fe-Ti oxide ores are formed as a product of the fractional crystallization of Fe-Ti-rich residual melts after crystallization of the layered rocks.

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23

Venturi, Chantal M., John D. Greenough, Chad Ulansky, and Charles Fipke. "Stratigraphy, thickness, tectonic environment, and economic implications of the giant Suwar – Wadi Qutabah layered mafic complex in northwestern Yemen." Canadian Journal of Earth Sciences 52, no. 2 (February 2015): 134–46. http://dx.doi.org/10.1139/cjes-2014-0141.

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The Wadi Qutabah layered mafic intrusion in northwestern Yemen, considered part of a giant (>250 km2), Neoproterozoic (∼638.5 Ma) intrusion referred to as the Suwar – Wadi Qutabah Complex, has significant potential for economic platinum-group element and Ni–Cu–Co mineralization. A search for platinum-group element mineralization at Wadi Qutabah yielded cores from 14 drillholes along two east and west lines. Stratigraphically, they reveal ∼500 m of interlayered norites with subordinate gabbros, anorthosites, pyroxenites, and massive sulphide layers showing modal and cryptic layering that can be correlated between individual holes and between the east and west areas. Energy dispersive spectrometry major element analyses on mineral phases show gradual upward changes in plagioclase composition from An52 (lowest level drilled) to An44, and En61 to En57 in orthopyroxene, up to a distinctive, ilmenite-rich unit termed 5a (augite norite). Above 5a, minerals show a dramatic shift to more primitive An57 and En69 compositions. The gradual changes are typical of layered mafic intrusions and reflect progressive crystallization of magma upward. The dramatic changes, such as above 5a, are also common and reflect magma chamber recharge. In addition to the 500 m reported here, mineral exploration data from more-mafic rocks at Suwar suggest 400 m of layered rocks below those at Wadi Qutabah (total 900 m). A regression analysis plot of the cumulus mineral (plagioclase and orthopyroxene) compositional change versus thickness for seven well-known, giant, layered mafic intrusions suggests that the Suwar – Wadi Qutabah Complex is >2 km thick and one of the largest (thickness and area) intrusions on Earth. Comparison of the stratigraphy and mineral compositions at Wadi Qutabah with intrusions bearing PGE deposits suggests prospective areas for mineral exploration to the north and south of the study area. Recent reviews identify many similar-aged, mafic–ultramafic intrusive complexes across the Arabian–Nubian Shield. The large size of the Suwar – Wadi Qutabah Complex, its noritic composition, and subcontinental lithospheric mantle signature are characteristics typical of mafic rocks formed in extension-related, continental rift settings. Thus, the Suwar – Wadi Qutabah Complex may be part of a previously unrecognized large igneous province associated with a late Proterozoic magmatic event and preserved in what is today, the Arabian Shield.

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Dyer, Richard D., and Peter J. Barnett. "Multimedia exploration strategies for PGEs: insights from the Surficial Geochemistry Case Studies Project, Lake Nipigon Region Geoscience Initiative, northwestern Ontario." Canadian Journal of Earth Sciences 44, no. 8 (August 1, 2007): 1169–202. http://dx.doi.org/10.1139/e07-031.

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The Surficial Geochemistry Case Studies Project in the Lake Nipigon region involved detailed Quaternary mapping and multimedia geochemical sampling within five case study areas. Two of these areas, Lac des Iles and Tib Lake, contain known platinum group element (PGE) mineralization. The other three case study areas feature drainage catchments with lakes that contain anomalous levels of PGEs in bottom sediment. Surficial media sampled included till, soils, stream sediment, lake sediment, peat, surface water, and groundwater. Over Archean terrain, such as at Lac des Iles and Tib Lake, there is excellent geochemical contrast between the PGE prospective rock type (mafic to ultramafic intrusive) and the surrounding rock type (e.g., granitoid rocks). This geochemical contrast is mirrored in the geochemistry of most surficial media sampled during this project. Over the Nipigon Embayment, the geochemical contrast between mafic and ultramafic rocks (e.g., Seagull-type intrusions) and the surrounding diabase sill rocks is inherently weaker due to the relatively high background levels for copper, palladium, and gold in the Nipigon diabase sills. However, the results of stream-water geochemistry over the Seagull and Disraeli ultramafic intrusions highlight their unique geochemical footprint on the surficial landscape, in particular with respect to Cr, Mg, and Ni, compared with the surrounding Nipigon diabase. In addition, lake sediments underlain by the Seagull, Disraeli, and Hele intrusions have distinctly elevated Cr concentrations and Gd/Yb ratios compared with the surrounding areas underlain by Nipigon diabase sills or Sibley Group rocks. Therefore, exploration value can be maximized over the Nipigon Embayment by exploiting these geochemical contrasts in surficial media to discriminate between ultramafic rocks and the surrounding Nipigon diabase sills. The results of this study highlight the importance of chromium concentrations in surficial media as a diagnostic feature for the presence of ultramafic rocks, regardless of their age or location. In general, a cost-effective exploration strategy for PGE mineralization includes targeting the associated metals (Cr, Ni) within drift deposits (C-horizon till) and drainage media (stream sediment, lake sediment) to vector to prospective mafic–ultramafic intrusive rocks, prior to detailed (property scale) follow-up, involving the determination of base metals and PGEs within soil, till, stream sediment, and peat samples. Relative to the metals copper, nickel, and chromium (ppm levels), the PGEs have significantly lower initial concentrations (ppb levels), are less mobile in the surficial environment, have significantly shorter glacial dispersion trains, and are less reliably determined at the laboratory.

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Bayanova, Tamara, Aleksey Korchagin, Alexander Mitrofanov, Pavel Serov, Nadezhda Ekimova, Elena Nitkina, Igor Kamensky, Dmitry Elizarov, and Milosh Huber. "Long-Lived Mantle Plume and Polyphase Evolution of Palaeoproterozoic PGE Intrusions in the Fennoscandian Shield." Minerals 9, no. 1 (January 18, 2019): 59. http://dx.doi.org/10.3390/min9010059.

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The NE Fennoscandian Shield comprises the Northern Belt in Finland and the Southern Belt in Karelia. They host mafic-ultramafic layered Cu-Ni-Cr and Pt-Pd-bearing intrusions. Precise U-Pb and Sm-Nd analyses indicate the 130-Ma evolution of these intrusions, with major events at 2.53, 2.50, 2.45, and 2.40 Ga. Barren phases were dated at 2.53 Ga for orthopyroxenites and olivine gabbro in the Fedorovo-Pansky massif. PGE-bearing phases of gabbronorites (Pechenga, Fedorovo-Pansky, Monchetundra massifs) and norites (Monchepluton) are 2.50 Ga old. Anorthosites of Mt. Generalskaya (Pechenga), the Fedorovo-Pansky, and Monchetundra massifs occurred at 2.45 Ga. This event produced layered PGE-bearing intrusions in Finland (Penikat, Kemi, Koitelainen) and mafic intrusions in Karelia. The Imandra lopolith dikes occurred at the final phase (2.40 Ga). Slightly negative εNd and ISr values (0.703–0.704) suggest that intrusions originated from an enriched mantle reservoir. Low 3He/4He ratios in accessory minerals (ilmenite and magnetite) indicate an upper mantle source. Large-scale correlations link the Fennoscandian Shield with the Superior and Wyoming cratons.

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Kissin, Stephen A., Geoffrey J. Heggie, James M. Franklin, and Alireza Karimzadeh Somarin. "Sulfide saturation mechanisms in gabbroic intrusions in the Nipigon Embayment." Canadian Journal of Earth Sciences 44, no. 8 (August 1, 2007): 1203–14. http://dx.doi.org/10.1139/e07-030.

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The Seagull and Kitto intrusions in the Nipigon Embayment of northwestern Ontario were studied to gain an understanding of the processes involved in sulfur saturation of the mafic to ultramafic magmas leading to the formation of platinum group element (PGE) concentrations. Profiles of sulfur, copper, nickel, gold, palladium, and platinum concentrations as a function of depth revealed that sulfur saturation occurred at the base of the Seagull intrusion. A higher grade horizon occurs well above the base of the intrusion, suggesting that a reef-type of process was significant here and possibly in the Kitto intrusion, as well. Olivine compositions indicate that, in both cases, the parental magmas were undersaturated with respect to sulfur. Sulfur, neodymium–samarium, and rubidium–strontium isotopic data suggest that assimilation of country rock and sulfide played a role, especially in the formation of basal concentrations of PGEs.

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Milidragovic, Dejan, Graham T. Nixon, James S. Scoates, James A. Nott, and Dylan W. Spence. "Redox-controlled chalcophile element geochemistry of the Polaris Alaskan-type mafic-ultramafic complex, British Columbia, Canada." Canadian Mineralogist 59, no. 6 (November 1, 2021): 1627–60. http://dx.doi.org/10.3749/canmin.2100006.

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ABSTRACT 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 fractionation resulted in sulfide melts that were progressively more depleted in precious and base chalcophile metals. The two styles of PGE mineralization in the Polaris Alaskan-type intrusion are interpreted to reflect the evolution of strongly oxidized, hydrous ultramafic parental magma(s) through intrinsic magmatic fractionation processes that potentially promote sulfide saturation in the absence of wallrock assimilation.

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Roman, Alberto, and Claude Jaupart. "The fate of mafic and ultramafic intrusions in the continental crust." Earth and Planetary Science Letters 453 (November 2016): 131–40. http://dx.doi.org/10.1016/j.epsl.2016.07.048.

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Boyd, R., and W. A. Ashcroft. "Significance of the cumulate mineralogy of the Belhelvie mafic-ultramafic intrusion—comments on: Silicate mineralogy of the Belhelvie cumulates, NE Scotland, by W. J. Wadsworth." Mineralogical Magazine 56, no. 384 (September 1992): 329–33. http://dx.doi.org/10.1180/minmag.1992.056.384.04.

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AbstractNew data on the composition of cumulus phases in the Belhelvie intrusion presented by Wadsworth (1991) are discussed in the light of existing data and of knowledge on the form and internal structure of the intrusion. The relevance of the Rustenburg Layered suite of the Bushveld Complex as a model for the 'single intrusion' hypothesis for the layered basic intrusions in NE Scotland is examined: current knowledge of the Rustenburg Layered Suite and related intrusions suggests that similar crystallisation sequences of cumulus phases and ranges of cryptic variation do not give any case for a single intrusion hypothesis.

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30

Hofmann, A., C. R. Anhaeusser, and X.-H. Li. "Layered ultramafic complexes of the Barberton Greenstone Belt – age constraints and tectonic implications." South African Journal of Geology 124, no. 1 (March 1, 2021): 7–16. http://dx.doi.org/10.25131/sajg.124.0002.

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Abstract Layered ultramafic–mafic complexes are a common component of the stratigraphically uppermost part of the Onverwacht Group of the Barberton Greenstone Belt. Associated with the Mendon Formation in the south and the Weltevreden Formation in the north, they represent an assemblage of thick differentiated flows and shallow synvolcanic intrusions ranging in composition from dunite to gabbro. U-Pb zircon dating of gabbro from the Sawmill and the Mundt’s Concession ultramafic complexes from the northern part of the Barberton Greenstone Belt yielded ages of 3 258 ± 8 Ma and 3 244 ± 11 Ma, respectively. The ultramafic complexes are thus regarded to have been emplaced during a magmatic flare-up in the final stage of Weltevreden Formation volcanism, post-dating ultramafic magmatism in the southern part of the belt by several millions of years and thus suggesting diachronous evolution of the Onverwacht Group in the Barberton Greenstone Belt.

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31

Chen, Bao-Yun, Jin-Jie Yu, and Shuai-Jie Liu. "Source characteristics and tectonic setting of mafic–ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic–ultramafic intrusion." Lithos 308-309 (May 2018): 329–45. http://dx.doi.org/10.1016/j.lithos.2018.03.016.

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32

Shellnutt, J. Gregory, and Jaroslav Dostal. "Derivation of the Early Carboniferous Wedgeport pluton by crystal fractionation of a mafic parental magma: a rare case of an A-type granite within the Meguma terrane (Nova Scotia, Canada)." Geological Magazine 157, no. 2 (August 13, 2019): 248–62. http://dx.doi.org/10.1017/s0016756819000694.

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AbstractThe Cambrian–Ordovician metasedimentary rocks of the Meguma terrane (Canadian Appalachians) were extensively intruded by silicic plutons during Middle Devonian to Early Carboniferous times. Syn-plutonic but volumetrically minor mafic-ultramafic intrusions were also emplaced. In most localities, the silicic plutons and mafic-ultramafic intrusions do not appear to be petrogenetically related and are likely derived from different sources. The Attwoods Brook gabbronorite of SW Nova Scotia yielded an in situ zircon weighted-mean 206Pb–238U age of 357.9 ± 3.3 Ma that is within the uncertainty of the age of the neighbouring Wedgeport pluton (357 ± 1 Ma). The Wedgeport pluton is a rare example of a mantle-derived, peraluminous A-type granite within the Meguma terrane. The similar ages and Nd isotopes of the Attwoods Brook gabbronorite (εNd(t) = +1.1 to +4.0) and Wedgeport pluton (εNd(t) = +2.1 to +3.3) suggest the two intrusions are petrogenetically related. Fractional crystallization modelling demonstrates that a parental magma similar to the Attwoods Brook gabbronorite can produce residual silicic liquids that resemble the granites of the Wedgeport pluton, indicating that they could be members of the same intrusive complex. The emplacement of the gabbronorite and Wedgeport pluton occurred during a period of tensional plate stress that was contemporaneous with rifting of the Maritimes Basin that produced the Fountain Lake continental flood basalts and A-type granites of the Cobequid Highlands within the Avalon terrane. It is possible that the Early Carboniferous rocks of SW Nova Scotia are related to the rifted-related magmatism within the Maritimes Basin.

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Nie, Yonghong, and Shuguang Li. "Sm-Nd age of syncollisional mafic-ultramafic intrusions in the Dabie Mountains." Chinese Science Bulletin 43, no. 2 (January 1998): 160–63. http://dx.doi.org/10.1007/bf02883934.

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34

ROBERTS, R. J., F. CORFU, T. H. TORSVIK, L. D. ASHWAL, and D. M. RAMSAY. "Short-lived mafic magmatism at 560–570 Ma in the northern Norwegian Caledonides: U–Pb zircon ages from the Seiland Igneous Province." Geological Magazine 143, no. 6 (September 18, 2006): 887–903. http://dx.doi.org/10.1017/s0016756806002512.

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The Seiland Igneous Province (SIP) of northern Norway comprises a suite of mainly gabbroic plutons, with subordinate ultramafic, syenitic and felsic intrusions. Several intrusions from the Seiland Igneous Province have been dated by ID-TIMS U–Pb zircon and monazite analyses. The Hasvik Gabbro on the island of Sørøy, previously assigned an age of 700±33 Ma by Sm–Nd, yields a U–Pb zircon age of 562±6 Ma, within error of the Storelv Gabbro (569±5 Ma) and a diorite associated with the Breivikbotn Gabbro (571±4 Ma). Various intrusions on the Øksfjord peninsula give nearly identical ages of 565±9 Ma (gabbro), 566±4 Ma (monzonite), 565±5 Ma (monzodiorite), 570±9 Ma (norite), and 566±1 Ma (orthopyroxenite). These ages overlap with those from Sørøy, and define a single and short-lived period of gabbroic (to felsic) magmatism for the region between 570 and 560 Ma, pre-dating a subordinate episode of alkalic magmatism at 530–520 Ma. The U–Pb ages contradict the previous geochronological interpretation for the Finnmark area, which implied a period of 250 m.y. for the emplacement of the SIP intrusions. The new age data also clearly distinguish the Seiland intrusions, emplaced into the Sørøy Group metasediments of the Kalak Nappe Complex, from several older granitic intrusions (c. 850 to 600 Ma) that cut the Sørøy Group farther east and south. The coincident ages of the different Seiland intrusive bodies also contradict the previous structural model for the area, which posits that the different gabbro bodies were emplaced at intervals, with compressional deformation affecting the gabbros between periods of intrusion. The short time span between the main plutonic phases strongly suggests that the mechanism for the emplacement of mafic magma operated in a single, probably extensional, tectonic regime. The mafic intrusions were later deformed and metamorphosed to at least amphibolite facies, most likely by the Scandian (420 Ma) phase of the Caledonian Orogeny.

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SU, YUPING, JIANPING ZHENG, LILI LIANG, HONGKUN DAI, JUNHONG ZHAO, MING CHEN, XIANQUAN PING, ZIQI LIU, and JIAN WANG. "Derivation of A1-type granites by partial melting of newly underplated rocks related with the Tarim mantle plume." Geological Magazine 156, no. 3 (November 20, 2017): 409–29. http://dx.doi.org/10.1017/s0016756817000838.

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AbstractThe granitic rocks of the Tarim large igneous province (LIP) are temporally and spatially related to mafic intrusions. However, their tectonic setting and genetic relationship are debated. Here, we report geochemical, and zircon U–Pb–Hf isotopic results for three alkali feldspar granitic plutons in the Halajun area, western margin of the Tarim Block. Zircon U–Pb ages suggest these plutons were emplaced at 268–275 Ma, coeval with the neighbouring mafic–ultramafic complexes and syenitic rocks. These granitic rocks have high contents of SiO2, alkalis, Rb, Th, Zr and REE (except Eu), and high ratios of FeO*/MgO and Ga/Al, and show strong depletions in Ba, Sr, Eu, which are commonly observed in the A1-type granites. Zircon Hf isotopes reveal a limited range ofεHf(t) values from −1.0 to +3.5 for different samples from three granitic plutons, obviously higher than those (mostly <0) of the mafic rocks. This distinct difference, along with a Daly gap and small volume of mafic rocks, argues against extreme fractionation of mafic magma as the main origin of the A1-type granites. Instead the A1-type granites were most likely derived from partial melting of newly underplated rocks triggered by the upwelling asthenosphere, followed by extensive fractionation. These A1-type granites were emplaced within an anorogenic setting during the late stage of the Tarim LIP, which possibly lasts for more than 30 Ma. The Piqiang mafic–ultramafic complex directly stemmed from asthenospheric mantle and Halajun A1-type granites represent two manners of vertical crustal growth.

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Kudrin, Konstantin Yu. "The geological structure of the left part of Big Polya river (Prepolar Urals) on the results of geological training surveying practice in 2015." Yugra State University Bulletin 11, no. 3 (November 15, 2015): 62–66. http://dx.doi.org/10.17816/byusu201511362-66.

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Largescale geological mapping of the left part of the valleys of the Big Polya river of (downstream) and Polya river (upstream) on the Eastern slope of the Prepolar Urals is performed. Most (north-western) part of the territory represents a fragment of a large heterogeneous Shchekurinskiy massif, which is the most northern representative in the chain of mafic-ultramafic intrusions of the Uralian platinum belt. The south-eastern part of the area is composed of basalts and dolerites of the complex of parallel dikes.

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Gouedji, Franck, Christian Picard, Marc Antoine Audet, Thierry Augé, and Jorge Spangenberg. "Ni-Cu sulfide mineralization and PGM from the Samapleu mafic-ultramafic intrusion, Yacouba complex, western Ivory Coast." Canadian Mineralogist 59, no. 4 (July 1, 2021): 631–65. http://dx.doi.org/10.3749/canmin.1900030.

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ABSTRACT The mafic-ultramafic Samapleu deposits of the Yacouba complex, which host nickel, copper sulfides, and platinum-group minerals, are located in the Biankouma-Silipou region, western Ivory Coast. These intrusions originate from the mantle and would have been established during the Proterozoic (2.09 Ga) around 22 km deep within the Archean granulites (3.6–2.7 Ga) which at least partially contaminated them. Platinum-group and sulfide minerals from the Samapleu deposits were studied using optical microscopy, scanning electron microscopy, the electronic microprobe, X-ray fluorescence, fire assay, and a Thermo Fisher Scientific Delta S isotope ratio mass spectrometer system. The sulfide mineralization (mainly pyrrhotite, pentlandite, chalcopyrite ± pyrite) is mainly disseminated with, in places, semi-massive to massive sulfide veins. It is especially abundant in pyroxenite horizons with net or breccia textures. The isotopic ratios of sulfur measured from the sulfides (an average of 0.1‰), the R factor (between 1500 and 10,000), and the Cu/Pd ratios indicate a mantle source. Thus, the sulfides would have formed from sulfide liquids produced by immiscibility from the silicate mantle magma under mafic-ultramafic intrusion emplacement conditions and with possible geochemical modification of the magmas by assimilation of the surrounding continental crust. The platinum-group minerals (michenerite, merenskyite, moncheite, Co-rich gersdorffite, irarsite, and hollingworthite) are mainly associated with the sulfide phases. The nature of the platinum-group minerals is indicative of the probable role of late-magmatic hydrothermal fluids during the mineralizing process.

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Pettigrew, Neil T., and Kéiko H. Hattori. "The Quetico Intrusions of Western Superior Province: Neo-Archean examples of Alaskan/Ural-type mafic–ultramafic intrusions." Precambrian Research 149, no. 1-2 (September 2006): 21–42. http://dx.doi.org/10.1016/j.precamres.2006.06.004.

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GRENNE, T., R. B. PEDERSEN, T. BJERKGÅRD, A. BRAATHEN, M. G. SELASSIE, and T. WORKU. "Neoproterozoic evolution of Western Ethiopia: igneous geochemistry, isotope systematics and U–Pb ages." Geological Magazine 140, no. 4 (July 2003): 373–95. http://dx.doi.org/10.1017/s001675680300801x.

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New geochemical, isotopic and age data from igneous rocks complement earlier models of a long-lived and complex accretionary history for East African Orogen lithologies north of the Blue Nile in western Ethiopia, but throw doubt on the paradigm that ultramafic complexes of the region represent ophiolites and suture zones. Early magmatism is represented by a metavolcanic sequence dominated by pyroclastic deposits of predominantly basaltic andesite composition, which give a Rb–Sr whole-rock errorchron of 873±82 Ma. Steep REE patterns and strong enrichments of highly incompatible trace elements are similar to Andean-type, high-K to medium-K calc-alkaline rocks; εNd values between 4.0 and 6.8 reflect a young, thin continental edge. Interlayered basaltic flows are transitional to MORB and compare with mafic rocks formed in extensional, back-arc or inter-arc regimes. The data point to the significance of continental margin magmatism already at the earliest stages of plate convergence, in contrast with previous models for the East African Orogen. The metavolcanites overlap compositionally with the Kilaj intrusive complex dated at 866±20 Ma (U–Pb zircon) and a related suite of dykes that intrude thick carbonate-psammite sequences of supposedly pre-arc, continental shelf origin. Ultramafic complexes are akin to the Kilaj intrusion and the sediment-hosted dykes, and probably represent solitary intrusions formed in response to arc extension. Synkinematic composite plutons give crystallization ages of 699±2 Ma (Duksi, U–Pb zircon) and 651±5 Ma (Dogi, U–Pb titanite) and testify to a prolonged period of major (D1) contractional deformation during continental collision and closure of the ‘Mozambique Ocean’. The plutons are characterized by moderately peraluminous granodiorites and granites with εNd values of 1.0–2.0. They were coeval with shoshonitic, latitic, trachytic and rare trachybasaltic intrusions with very strong enrichments of highly incompatible trace elements and εNd of 0.4–8.0. The mafic end-member is ascribed to partial melting of enriched sub-continental mantle that carried a subduction component inherited from pre-collision subduction. Contemporaneous granodiorite and granite formation was related to crustal underplating of the mafic magmas and consequent melting of lower crustal material derived from the previously accreted, juvenile arc terranes of the East African Orogen.

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Maier, Wolfgang D., and Eero J. Hanski. "Layered Mafic–Ultramafic Intrusions of Fennoscandia: Europe's Treasure Chest of Magmatic Metal Deposits." Elements 13, no. 6 (December 1, 2017): 415–20. http://dx.doi.org/10.2138/gselements.13.6.415.

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Maier, W. D., H. M. Howard, R. H. Smithies, S. H. Yang, S. J. Barnes, H. O'Brien, H. Huhma, and S. Gardoll. "Magmatic ore deposits in mafic–ultramafic intrusions of the Giles Event, Western Australia." Ore Geology Reviews 71 (December 2015): 405–36. http://dx.doi.org/10.1016/j.oregeorev.2015.06.010.

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Rundkvist, Tatiana, and Pavel Pripachkin. "Accessory Cr-Spinels in the Section of the Nude-Poaz Massif in the Monchegorsk (2.5 Ga) Mafic-Ultramafic Layered Complex (Kola Peninsula, Russia): Comparison with Ore-Forming Chromites." Minerals 11, no. 6 (June 3, 2021): 602. http://dx.doi.org/10.3390/min11060602.

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The paper studies accessory Cr-spinels from deep drill holes crossing the Nude-Poaz massif, which is a part of the Monchegorsk mafic-ultramafic layered complex (2.5 Ga, Kola Peninsula, Russia). Cr-spinels occur as two morphological types that differ in their chemical composition, i.e., Cr-spinels of the first type are more aluminous, while Cr-spinels of the second type are more ferruginous and titaniferous. Cr-spinels of the Nude-Poaz massif are characterized by a Fe-Ti trend known for layered intrusions in the world. Cr-spinels of the Nude-Poaz massif quite clearly differ in composition from chromites of the Sopcheozero deposit: they are more ferruginous and less chromous. The specific composition of Cr-spinels in rocks of the Nude-Poaz massif can be correlated with the sequence of the magmatic phases intrusion.

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Pripachkin, P. V. "Major deposits and occurrences of platinum ores of the Kola belt layered intrusions (Kola Peninsula, Russia)." LITHOSPHERE (Russia) 19, no. 5 (November 23, 2019): 731–51. http://dx.doi.org/10.24930/1681-9004-2019-19-5-731-751.

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Research subject. This paper presents data characterizing major occurrences and deposits of platinum group elements (PGE) of Kola belt layered mafic-ultramafic intrusions (Kola Peninsula).Materials and methods. The study was based on extensive experimental data collected by the author over a long-term period and a comprehensive analysis of published and archive literature pertaining to this field.Results. Certificates (so-called passports) were compiled for all major PGE objects in theKola Peninsula, which include diverse characterization parameters (geological, structural, isotope-geochemical, mineralogical). The formation of PGE mineralization was compared with both the age characteristics of large layered complexes and the sequence of intrusion of individual magmatic phases.Conclusion. The proposed parameters can be used to determine specific features of PGE objects, thus allowing identification of objects promising in terms of industrial development. The obtained results demonstrate the importance of taking into account these specific features during mineral deposit exploitation.

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BLADES, MORGAN L., JOHN FODEN, ALAN S. COLLINS, TADESSE ALEMU, and GIRMA WOLDETINSAE. "The origin of the ultramafic rocks of the Tulu Dimtu Belt, western Ethiopia – do they represent remnants of the Mozambique Ocean?" Geological Magazine 156, no. 1 (October 30, 2017): 62–82. http://dx.doi.org/10.1017/s0016756817000802.

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AbstractThe East African Orogen contains a series of high-strain zones that formed as Gondwana amalgamated. The Tulu Dimtu shear belt is one of these N–S structures within the Barka–Tulu Dimtu zone in western Ethiopia, and contains ultramafic bodies of equivocal origin. Identifying the petrogenetic origin of these enigmatic rocks provides evidence for the geodynamic significance of these shear zones. Owing to their altered state, these ultramafic rocks’ well-preserved chrome spinels provide the only reliable evidence for their source and tectonic affiliation. Chrome spinels have high Cr2O3 (30.04–68.76 wt %), while recalculated Fe2O3 (< 2 %) and TiO2 (0.01–0.51 %) values are low. The Cr# (molar Cr3+/Cr3+ + Al2+) and Mg# (Mg2+/Mg2+ + Fe2+) have averages of 0.88 and 0.22, respectively. Based on olivine–spinel equilibria, the calculated fO2 values (FMQ +3.03) for the dunites reveal a highly oxidized environment. This spinel chemistry (high Cr# > 0.6 and low Ti) supports a supra-subduction origin, with an oxidized mantle source more refractory than depleted MORB mantle (DMM). These spinel compositions indicate that some ultramafic bodies in western Ethiopia, including those from Daleti, Tulu and Dimtu, are serpentinized peridotites emplaced as obducted ophiolite complexes. By contrast, the ultramafic rocks from the Yubdo locality have a different spinel chemistry, with strong affiliation with igneous spinels formed in Alaskan-style mafic intrusions. These collective results suggest that regardless of their origin as supra-subduction ophiolites or as Alaskan-type intrusions, these spinels were formed on a convergent-subduction margin.

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Ibrahim, Mohammed, Alexander Kotelnikov, Pavel Podolko, and Elena Kotelnikova. "Remote sensing data for Geological mapping and gold prospecting of Inteet area, northern Sudan." E3S Web of Conferences 258 (2021): 03009. http://dx.doi.org/10.1051/e3sconf/202125803009.

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The mineral exploration has improved in the last decades, today there are different methods of remote exploration, that are applied in mining industry worldwide, helping to discover ore minerals deposits in zones that have not access to them. The study area of this article is located about 400 km from Khartoum, characterized by low reliefs covered by sand and gravely sand. The study wants to carry out the geological mapping and the prospective zones using remote sensing and GIS techniques. Sudan is characterized by geological formations over inaccessible areas, in that way the remote sensing technique has a great value in these conditions, saving time and money. The used methodology has been divided into three phases: Pre-field office work, field work and post-field work. The processing of the satellite images includes color band composites, in order to obtain the lithological and geological features, the different types of rocks were defined by a different color. Obtaining the following rock types: High-grade gneisses and migmatites described to comprise the basement complex, ophiolitic mafic-ultramafic rocks that appear in the northern and southern sides of the area, metasediments that cover most of the study area, syn-orogenic intrusions that cut the older mafic-ultramafic units and the metavolcanosedimentary sequences, post-orogenic intrusions and gold mineralization. Based on the image analysis results of Landsat 8 OLI, 32 ore samples were collected to analysis gold and pathfinder elements obtaining high anomalies results for Au, Ag, Cu, Zn, Pb and Fe.

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Xing, Chang-Ming, Christina Yan Wang, and Wei Tan. "Disequilibrium growth of olivine in mafic magmas revealed by phosphorus zoning patterns of olivine from mafic–ultramafic intrusions." Earth and Planetary Science Letters 479 (December 2017): 108–19. http://dx.doi.org/10.1016/j.epsl.2017.09.005.

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Okrugin, A. V., O. V. Yakubovich, R. E. Ernst, and Zh Yu Druzhinina. "PLATINUM-BEARING PLACERS: MINERAL ASSOCIATIONS AND THEIR 190Pt-4He AND Re-Os AGES, AND POTENTIAL LINKS WITH LARGE IGNEOUS PROVINCES IN THE SIBERIAN CRATON." Economic Geology 115, no. 8 (October 26, 2020): 1835–53. http://dx.doi.org/10.5382/econgeo.4773.

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Abstract Placer deposits in the Siberian platform are closely associated with well-known platiniferous intrusions (Kondyor, Inagli, Noril’sk, Chiney, and Guli) but there are also abundant platinum-group mineral (PGM) placers of large areal extent in the river basins of Siberia (Vilyui, Lena, Aldan, Anabar, and Olenek) for which the primary sources are unknown. The 190Pt-4He dating method is introduced, compared with existing Re-Os isotope dating of PGMs, and applied to Pt-bearing placers of Siberia. Correlations between the 190Pt-4He and Re-Os isotope ages of the PGMs and with ages of major magmatic events in the Siberian craton show that the potential sources for some of the placers are likely buried Precambrian mafic-ultramafic intrusions of Large Igneous Provinces (LIP). The approach of this paper can be applied to other cratonic areas with alluvial PGMs of unknown origin.

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Badanina, I. Yu, K. N. Malitch, and A. P. Romanov. "Isotopic-geochemical characteristics of the ore-bearing ultramafic-mafic intrusions of western Taimyr, Russia." Doklady Earth Sciences 458, no. 1 (September 2014): 1165–67. http://dx.doi.org/10.1134/s1028334x14090256.

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Essawy, M. A. "Pan African Mafic-Ultramafic Cumulate Intrusions SW Sinai Massif: Mineralogy, Geochemistry and Crustal Growth." Mineralogical Magazine 58A, no. 1 (1994): 257–58. http://dx.doi.org/10.1180/minmag.1994.58a.1.135.

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Scherstén, Anders, Hans Årebäck, David Cornell, Paul Hoskin, Anton Åberg, and Richard Armstrong. "Dating mafic-ultramafic intrusions by ion-microprobing contact-melt zircon: examples from SW Sweden." Contributions to Mineralogy and Petrology 139, no. 1 (May 12, 2000): 115–25. http://dx.doi.org/10.1007/s004100050577.

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Journal articles on the topic 'Mafic–ultramafic intrusions'

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