scholarly journals Adakites, High-Nb Basalts and Copper–Gold Deposits in Magmatic Arcs and Collisional Orogens: An Overview

Geosciences ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 29
Author(s):  
Pavel Kepezhinskas ◽  
Nikolai Berdnikov ◽  
Nikita Kepezhinskas ◽  
Natalia Konovalova
Keyword(s):  
Subduction Zones ◽  
Far East ◽  
Gold Deposits ◽  
Type I ◽  
Isotopic Signatures ◽  
Epithermal Mineralization ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
East Russia ◽  
Collisional Orogens

Adakites are Y- and Yb-depleted, SiO2- and Sr-enriched rocks with elevated Sr/Y and La/Yb ratios originally thought to represent partial melts of subducted metabasalt, based on their association with the subduction of young (<25 Ma) and hot oceanic crust. Later, adakites were found in arc segments associated with oblique, slow and flat subduction, arc–transform intersections, collision zones and post-collisional extensional environments. New models of adakite petrogenesis include the melting of thickened and delaminated mafic lower crust, basalt underplating of the continental crust and high-pressure fractionation (amphibole ± garnet) of mantle-derived, hydrous mafic melts. In some cases, adakites are associated with Nb-enriched (10 ppm < Nb < 20 ppm) and high-Nb (Nb > 20 ppm) arc basalts in ancient and modern subduction zones (HNBs). Two types of HNBs are recognized on the basis of their geochemistry. Type I HNBs (Kamchatka, Honduras) share N-MORB-like isotopic and OIB-like trace element characteristics and most probably originate from adakite-contaminated mantle sources. Type II HNBs (Sulu arc, Jamaica) display high-field strength element enrichments in respect to island-arc basalts coupled with enriched, OIB-like isotopic signatures, suggesting derivation from asthenospheric mantle sources in arcs. Adakites and, to a lesser extent, HNBs are associated with Cu–Au porphyry and epithermal deposits in Cenozoic magmatic arcs (Kamchatka, Phlippines, Indonesia, Andean margin) and Paleozoic-Mesozoic (Central Asian and Tethyan) collisional orogens. This association is believed to be not just temporal and structural but also genetic due to the hydrous (common presence of amphibole and biotite), highly oxidized (>ΔFMQ > +2) and S-rich (anhydrite in modern Pinatubo and El Chichon adakite eruptions) nature of adakite magmas. Cretaceous adakites from the Stanovoy Suture Zone in Far East Russia contain Cu–Ag–Au and Cu–Zn–Mo–Ag alloys, native Au and Pt, cupriferous Ag in association witn barite and Ag-chloride. Stanovoy adakites also have systematically higher Au contents in comparison with volcanic arc magmas, suggesting that ore-forming hydrothermal fluids responsible for Cu–Au(Mo–Ag) porphyry and epithermal mineralization in upper crustal environments could have been exsolved from metal-saturated, H2O–S–Cl-rich adakite magmas. The interaction between depleted mantle peridotites and metal-rich adakites appears to be capable of producing (under a certain set of conditions) fertile sources for HNB melts connected with some epithermal Au (Porgera) and porphyry Cu–Au–Mo (Tibet, Iran) mineralized systems in modern and ancient subduction zones.

Sub-lithospheric mantle sources for overlapping southern African Large Igneous Provinces

2021 ◽  
Author(s):  
L.D. Ashwal
Keyword(s):  
Lithospheric Mantle ◽  
Isotopic Data ◽  
Isotopic Signatures ◽  
Large Igneous Provinces ◽  
Igneous Provinces ◽  
Depleted Mantle ◽  
Heating Event ◽  
Mantle Sources ◽  
Short Time ◽  
Melt Composition

Abstract At least four spatially overlapping Large Igneous Provinces, each of which generated ∼1 x 106 km3 or more of basaltic magmas over short time intervals (&lt;5 m.y.), were emplaced onto and into the Kaapvaal Craton between 2.7 and 0.18 Ga: Ventersdorp (2 720 Ma, ∼0.7 x 106 km3), Bushveld (2 056 Ma, ∼1.5 x 106 km3), Umkondo (1 105 Ma, ∼2 x 106 km3) and Karoo (182 Ma, ∼3 x 106 km3). Each of these has been suggested to have been derived from melting of sub-continental lithospheric mantle (SCLM) sources, but this is precluded because: (1) each widespread heating event sufficient to generate 1 to 2 x 106 km3 of basalt from the Kaapvaal SCLM (volume = 122 to 152 x 106 km3) would increase residual Mg# by 0.5 to 2 units, depending on degree of melting, and source and melt composition, causing significant depletion in already-depleted mantle, (2) repeated refertilization of the Kaapvaal SCLM would necessarily increase its bulk density, compromising its long-term buoyancy and stability, and (3) raising SCLM temperatures to the peridotite solidus would also have repeatedly destroyed lithospheric diamonds by heating and oxidation, which clearly did not happen. It is far more likely, therefore, that the Kaapvaal LIPs were generated from sub-lithospheric sources, and that their diverse geochemical and isotopic signatures represent variable assimilation of continental crustal components. Combined Sr and Nd isotopic data (n = 641) for the vast volumetric majority of Karoo low-Ti tholeiitic magmatic products can be successfully modelled as an AFC mixing array between a plume-derived parental basalt, with &lt;10% of a granitic component derived from 1.1 Ga Namaqua-Natal crust. Archaean crustal materials are far too evolved (εNd ∼ -35) to represent viable contaminants. However, a very minor volume of geographically-restricted (and over-analysed) Karoo magmas, including picrites, nephelinites, meimechites and other unusual rocks may represent low-degree melting products of small, ancient, enriched domains in the Kaapvaal SCLM, generated locally during the ascent of large-volume, plume-derived melts. The SCLM-derived rocks comprise the well-known high-Ti (&gt;2 to 3 wt.% TiO2) magma group, have εNd, 182 values between +10.5 and -20.9, and are characteristically enriched in Sr (up to 1 500 ppm), suggesting a possible connection to kimberlite, lamproite and carbonatite magmatism. These arguments may apply to continental LIPs in general, although at present, there are insufficient combined Sr + Nd isotopic data with which to robustly assess the genesis of other southern African LIPs, including Ventersdorp (n = 0), Bushveld (n = 55) and Umkondo (n = 18).

Gold deposits and gold metallogeny of Far East Russia

2014 ◽  
Vol 59 ◽  
pp. 123-151 ◽  
Author(s):  
Nikolay A. Goryachev ◽  
Franco Pirajno
Keyword(s):  
Far East ◽  
Gold Deposits ◽  
East Russia

scholarly journals Sr-Nd-Pb-Ca Isotopes of Holocene Basalts from Jingpohu, NE China: Implications for the Origin of Their Enriched Mantle Signatures

Minerals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 790
Author(s):  
Feixiang Wei ◽  
Bo Pan ◽  
Jiandong Xu
Keyword(s):  
Volcanic Field ◽  
Magma Chambers ◽  
Ne China ◽  
Isotopic Signatures ◽  
Enriched Mantle ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
Heavy Rare Earth Elements ◽  
Oceanic Island Basalts ◽  
Back Arc

The geochemistry on Holocene lavas from the Jingpohu volcanic field in NE China are compared with other Cenozoic lavas from across the back-arc rift of NE China, in order to constrain their enriched mantle sources. Holocene lavas within Jingpohu volcanic field comprise two separate “Crater Forest” (CF) and “Frog Pool” (FP) volcanic areas. FP lavas have lower MgO, CaO, and heavy rare earth elements and higher Al2O3, Na2O, K2O, and large-ion lithophile elements than CF lavas. Yet, both CF and FP lavas share similar isotopic signatures, with depleted Sr and Nd isotopes (87Sr/86Sr = 0.703915–0.704556, 143Nd/144Nd = 0.512656–0.512849) and unradiogenic Pb isotopes (208Pb/204Pb = 37.79–38.06, 207Pb/204Pb = 15.45–15.54, 206Pb/204Pb = 17.49–18.15), similar to oceanic island basalts. An important new constraint for the Jingpohu lavas lies in their Ca isotopes of δ44/40Ca from 0.63 to 0.77‰, which are lower than that of the bulk silicate earth (0.94 ± 0.05‰). By comparing the isotopic signatures of sodic lavas with that of the potassic lavas across NE China, we propose a three-component mixing model as the source for the sodic lavas. In consistence with geophysical results, we propose that subducting Pacific plate induces asthenospheric mantle upwelling of an upper depleted mantle (DM), including subducted ancient sediments (EM I), which partially melted upon ascent. These primary melts further interacted with the lithospheric mantle (EM II), before differentiating within crustal magma chambers and erupting.

scholarly journals Gold in Mineralized Volcanic Systems from the Lesser Khingan Range (Russian Far East): Textural Types, Composition and Possible Origins

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 103
Author(s):  
Nikolai Berdnikov ◽  
Victor Nevstruev ◽  
Pavel Kepezhinskas ◽  
Ivan Astapov ◽  
Natalia Konovalova
Keyword(s):  
Iron Oxide ◽  
Subduction Zones ◽  
Gold Mineralization ◽  
Russian Far East ◽  
Far East ◽  
Volcanic Rocks ◽  
Liquid Immiscibility ◽  
Explosive Volcanism ◽  
Deep Roots ◽  
Scientific Debate

While gold partitioning into hydrothermal fluids responsible for the formation of porphyry and epithermal deposits is currently well understood, its behavior during the differentiation of metal-rich silicate melts is still subject of an intense scientific debate. Typically, gold is scavenged into sulfides during crustal fractionation of sulfur-rich mafic to intermediate magmas and development of native forms and alloys of this important precious metal in igneous rocks and associated ores are still poorly documented. We present new data on gold (Cu-Ag-Au, Ni-Cu-Zn-Ag-Au, Ti-Cu-Ag-Au, Ag-Au) alloys from iron oxide deposits in the Lesser Khingan Range (LKR) of the Russian Far East. Gold alloy particles are from 10 to 100 µm in size and irregular to spherical in shape. Gold spherules were formed through silicate-metal liquid immiscibility and then injected into fissures surrounding the ascending melt column, or emplaced through a volcanic eruption. Presence of globular (occasionally with meniscus-like textures) Cu-O micro-inclusions in Cu-Ag-Au spherules confirms their crystallization from a metal melt via extremely fast cooling. Irregularly shaped Cu-Ag-Au particles were formed through hydrothermal alteration of gold-bearing volcanic rocks and ores. Association of primarily liquid Cu-Ag-Au spherules with iron-oxide mineralization in the LKR indicates possible involvement of silicate-metallic immiscibility and explosive volcanism in the formation of the Andean-type iron oxide gold-copper (IOCG) and related copper-gold porphyry deposits in the deeper parts of sub-volcanic epithermal systems. Thus, formation of gold alloys in deep roots of arc volcanoes may serve as a precursor and an exploration guide for high-grade epithermal gold mineralization at shallow structural levels of hydrothermal-volcanic environments in subduction zones.

Le terrane de Slide Mountain (Cordillères canadiennes) : une lithosphère océanique marquée par des points chauds

2003 ◽  
Vol 40 (6) ◽  
pp. 833-852 ◽  
Author(s):  
M Tardy ◽  
H Lapierre ◽  
D Bosch ◽  
A Cadoux ◽  
A Narros ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Island ◽  
Light Rare Earth ◽  
Isotopic Compositions ◽  
Incompatible Elements ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
British Colombia ◽  
Ultramafic Cumulates ◽  
Back Arc

The Slide Mountain Terrane consists of Devonian to Permian siliceous and detrital sediments in which are interbedded basalts and dolerites. Locally, ultramafic cumulates intrude these sediments. The Slide Mountain Terrane is considered to represent a back-arc basin related to the Quesnellia Paleozoic arc-terrane. However, the Slide Mountain mafic volcanic rocks exposed in central British Colombia do not exhibit features of back-arc basin basalts (BABB) but those of mid-oceanic ridge (MORB) and oceanic island (OIB) basalts. The N-MORB-type volcanic rocks are characterized by light rare-earth element (LREE)-depleted patterns, La/Nb ratios ranging between 1 and 2. Moreover, their Nd and Pb isotopic compositions suggest that they derived from a depleted mantle source. The within-plate basalts differ from those of MORB affinity by LREE-enriched patterns; higher TiO2, Nb, Ta, and Th abundances; lower εNd values; and correlatively higher isotopic Pb ratios. The Nd and Pb isotopic compositions of the ultramafic cumulates are similar to those of MORB-type volcanic rocks. The correlations between εNd and incompatible elements suggest that part of the Slide Mountain volcanic rocks derive from the mixing of two mantle sources: a depleted N-MORB type and an enriched OIB type. This indicates that some volcanic rocks of the Slide Mountain basin likely developed from a ridge-centered or near-ridge hotspot. The activity of this hotspot is probably related to the worldwide important mantle plume activity that occurred at the end of Permian times, notably in Siberia.

scholarly journals Ore and Geochemical Specialization and Substance Sources of the Ural and Timan Carbonatite Complexes (Russia): Insights from Trace Element, Rb–Sr, and Sm–Nd Isotope Data

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 711
Author(s):  
Irina Nedosekova ◽  
Nikolay Vladykin ◽  
Oksana Udoratina ◽  
Boris Belyatsky
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Crustal Evolution ◽  
Trace Element Data ◽  
The Urals ◽  
Nd Isotope ◽  
Enriched Mantle ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
Geochemical Specialization

The Ilmeno–Vishnevogorsk (IVC), Buldym, and Chetlassky carbonatite complexes are localized in the folded regions of the Urals and Timan. These complexes differ in geochemical signatures and ore specialization: Nb-deposits of pyrochlore carbonatites are associated with the IVC, while Nb–REE-deposits with the Buldym complex and REE-deposits of bastnäsite carbonatites with the Chetlassky complex. A comparative study of these carbonatite complexes has been conducted in order to establish the reasons for their ore specialization and their sources. The IVC is characterized by low 87Sr/86Sri (0.70336–0.70399) and εNd (+2 to +6), suggesting a single moderately depleted mantle source for rocks and pyrochlore mineralization. The Buldym complex has a higher 87Sr/86Sri (0.70440–0.70513) with negative εNd (−0.2 to −3), which corresponds to enriched mantle source EMI-type. The REE carbonatites of the Chetlassky сomplex show low 87Sr/86Sri (0.70336–0.70369) and a high εNd (+5–+6), which is close to the DM mantle source with ~5% marine sedimentary component. Based on Sr–Nd isotope signatures, major, and trace element data, we assume that the different ore specialization of Urals and Timan carbonatites may be caused not only by crustal evolution of alkaline-carbonatite magmas, but also by the heterogeneity of their mantle sources associated with different degrees of enrichment in recycled components.

PERMIAN RADIOLARIAN FAUNAS FROM CHERT IN THE KHABAROVSK COMPLEX, FAR EAST RUSSIA, AND THE AGE OF EACH LITHOLOGIC UNIT OF THE KHABAROVSK COMPLEX

2005 ◽  
Vol 79 (4) ◽  
pp. 687-701 ◽  
Author(s):  
NORITOSHI SUZUKI ◽  
SATORU KOJIMA ◽  
HARUMASA KANO ◽  
SATOSHI YAMAKITA ◽  
AKIHIRO MISAKI ◽  
...  
Keyword(s):  
Far East ◽  
East Russia ◽  
Lithologic Unit
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