Sources of placer platinum in Yukon: provenance study from detrital minerals

2008 ◽  
Vol 45 (8) ◽  
pp. 879-896 ◽  
Author(s):  
Yana Fedortchouk ◽  
William LeBarge
Keyword(s):  
Unknown Origin ◽  
Heavy Mineral ◽  
Source Rocks ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Mafic Intrusions ◽  
Platinum Group Minerals ◽  
Mineral Sample ◽  
Back Arc ◽  
Ocean Ridge

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.

On the provenance of mid-Cretaceous turbidites of the Pindos zone (Greece): implications from heavy mineral distribution, detrital zircon ages and chrome spinel chemistry

2006 ◽  
Vol 143 (3) ◽  
pp. 329-342 ◽  
Author(s):  
P. FAUPL ◽  
A. PAVLOPOULOS ◽  
U. KLÖTZLI ◽  
K. PETRAKAKIS
Keyword(s):  
Detrital Zircon ◽  
Heavy Mineral ◽  
Heavy Minerals ◽  
Chrome Spinel ◽  
Internal Source ◽  
Suprasubduction Zone ◽  
Mid Ocean Ridge ◽  
Detrital Zircon Ages ◽  
Back Arc ◽  
Ocean Ridge

Two heavy mineral populations characterize the siliciclastic material of the mid-Cretaceous turbidites of the Katafito Formation (‘First Flysch’) of the Pindos zone: a stable, zircon-rich group and an ophiolite-derived, chrome spinel-rich one. U/Pb and Pb/Pb dating on magmatic zircons from the stable heavy mineral group clearly illustrate the existence of Variscan magmatic complexes in the source terrain, but also provide evidence for magmatism as old as Precambrian. Based on microprobe analyses, the chrome spinel detritus was predominantly supplied from peridotites of mid-ocean ridge as well as suprasubduction zone origin. A small volcanic spinel population was mainly derived from MORB and back-arc basin basalts. The lithological variability of the mid-Cretaceous ophiolite bodies, based on spinel chemistry, is much broader than that of ophiolite complexes presently exposed in the Hellenides. The chrome spinel detritus compares closely with that from the Outer and Inner Dinarides. The source terrain of the ophiolite-derived heavy minerals was situated in a more internal palaeogeographic position than that of the Pindos zone. The zircon-rich heavy mineral group could have had either an external and/or an internal source, but the chrome spinel constantly accompanying the stable mineral detritus seems to be more indicative of an internal source terrain.

scholarly journals Cr-spinel records metasomatism not petrogenesis of mantle rocks

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Hamed Gamal El Dien ◽  
Shoji Arai ◽  
Luc-Serge Doucet ◽  
Zheng-Xiang Li ◽  
Youngwoo Kil ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Plate Tectonics ◽  
Mantle Metasomatism ◽  
Mantle Melting ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Core Composition ◽  
Mid Ocean Ridge ◽  
Ocean Ridge ◽  
Petrogenetic Indicator

Abstract Mantle melts provide a window on processes related to global plate tectonics. The composition of chromian spinel (Cr-spinel) from mafic-ultramafic rocks has been widely used for tracing the geotectonic environments, the degree of mantle melting and the rate of mid-ocean ridge spreading. The assumption is that Cr-spinel’s core composition (Cr# = Cr/(Cr + Al)) is homogenous, insensitive to post-formation modification and therefore a robust petrogenetic indicator. However, we demonstrate that the composition of Cr-spinel can be modified by fluid/melt-rock interactions in both sub-arc and sub-mid oceanic mantle. Metasomatism can produce Al-Cr heterogeneity in Cr-spinel that lowers the Cr/Al ratio, and therefore modifies the Cr#, making Cr# ineffective as a geotectonic and mantle melting indicator. Our analysis also demonstrates that Cr-spinel is a potential sink for fluid-mobile elements, especially in subduction zone environments. The heterogeneity of Cr# in Cr-spinel can, therefore, be used as an excellent tracer for metasomatic processes.

scholarly journals Decoding of Mantle Processes in the Mersin Ophiolite, Turkey, of End-Member Arc Type: Location of the Boninite Magma Generation

Minerals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 464 ◽  
Author(s):  
Satoko Ishimaru ◽  
Yuji Saikawa ◽  
Makoto Miura ◽  
Osman Parlak ◽  
Shoji Arai
Keyword(s):  
Atomic Ratio ◽  
Mantle Melting ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Crustal Rocks ◽  
Mantle Peridotites ◽  
Mid Ocean Ridge ◽  
Mantle Processes ◽  
Ocean Ridge ◽  
High Degree

The Mersin ophiolite, Turkey, is of typical arc type based on geochemistry of crustal rocks without any signs of mid-ocean ridge (MOR) affinity. We examined its ultramafic rocks to reveal sub-arc mantle processes. Mantle peridotites, poor in clinopyroxene (<1.0 vol.%), show high Fo content of olivine (90–92) and Cr# [=Cr/(Cr + Al) atomic ratio] (=0.62–0.77) of chromian spinel. NiO content of olivine is occasionally high (up to 0.5 wt.%) in the harzburgite. Moho-transition zone (MTZ) dunite is also highly depleted, i.e., spinel is high Cr# (0.78–0.89), clinopyroxene is poor in HREE, and olivine is high Fo (up to 92), but relatively low in NiO (0.1–0.4 wt.%). The harzburgite is residue after high-degree mantle melting, possibly assisted by slab-derived fluid. The high-Ni character of olivine suggests secondary metasomatic formation of olivine-replacing orthopyroxene although replacement textures are unclear. The MTZ dunite is of replacive origin, resulted from interaction between Mg-rich melt released from harzburgite diapir and another harzburgite at the diapir roof. The MTZ dunite is the very place that produced the boninitic and replacive dunite. The MTZ is thicker (>1 km) in Mersin than in MOR-related ophiolite (mostly < 500 m), and this is one of the features of arc-type ophiolite.

scholarly journals Geochemical Variation of Miocene Basalts within Shikoku Basin: Magma Source Compositions and Geodynamic Implications

Minerals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 25
Author(s):  
Shuang-Shuang Chen ◽  
Tong Hou ◽  
Jia-Qi Liu ◽  
Zhao-Chong Zhang
Keyword(s):  
Japan Sea ◽  
Isotopic Signature ◽  
Magma Source ◽  
Isotopic Compositions ◽  
Enriched Mantle ◽  
Shikoku Basin ◽  
Depleted Mantle ◽  
Parece Vela Basin ◽  
Back Arc ◽  
Ocean Ridge

Shikoku Basin is unique as being located within a trench-ridge-trench triple junction. Here, we report mineral compositions, major, trace-element, and Sr-Nd-Pb isotopic compositions of bulk-rocks from Sites C0012 (>18.9 Ma) and 1173 (13–15 Ma) of the Shikoku Basin. Samples from Sites C0012 and 1173 are tholeiitic in composition and display relative depletion in light rare earth elements (REEs) and enrichment in heavy REEs, generally similar to normal mid-ocean ridge basalts (N-MORB). Specifically, Site C0012 samples display more pronounced positive anomalies in Rb, Ba, K, Pb and Sr, and negative anomalies in Th, U, Nb, and Ta, as well as negative Nb relative to La and Th. Site 1173 basalts have relatively uniform Sr-Nd-Pb isotopic compositions, close to the end member of depleted mantle, while Site C0012 samples show slightly enriched Sr-Nd-Pb isotopic signature, indicating a possible involvement of enriched mantle 1 (EM1) and EM2 sources, which could be attributed to the metasomatism of the fluids released from the dehydrated subduction slab, but with the little involvement of subducted slab-derived sedimentary component. Additionally, the Shikoku Basin record the formation of the back-arc basin was a mantle conversion process from an island arc to a typical MORB. The formation of the Shikoku Basin is different from that of the adjacent Japan Sea and Parece Vela Basin, mainly in terms of the metasomatized subduction-related components, the nature of mantle source, and partial melting processes.

scholarly journals A subduction influence on ocean ridge basalts outside the Pacific subduction shield

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Y. Yang ◽  
C. H. Langmuir ◽  
Y. Cai ◽  
P. Michael ◽  
S. L. Goldstein ◽  
...  
Keyword(s):  
Upper Mantle ◽  
The Arctic ◽  
Mantle Flow ◽  
Mantle Heterogeneity ◽  
Gakkel Ridge ◽  
The Pacific ◽  
Mid Ocean Ridge ◽  
The Pacific Ocean ◽  
Back Arc ◽  
Ocean Ridge

AbstractThe plate tectonic cycle produces chemically distinct mid-ocean ridge basalts and arc volcanics, with the latter enriched in elements such as Ba, Rb, Th, Sr and Pb and depleted in Nb owing to the water-rich flux from the subducted slab. Basalts from back-arc basins, with intermediate compositions, show that such a slab flux can be transported behind the volcanic front of the arc and incorporated into mantle flow. Hence it is puzzling why melts of subduction-modified mantle have rarely been recognized in mid-ocean ridge basalts. Here we report the first mid-ocean ridge basalt samples with distinct arc signatures, akin to back-arc basin basalts, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence in this region. This influence can also be identified in Atlantic and Indian mid-ocean ridge basalts but is nearly absent in Pacific mid-ocean ridge basalts. Such a hemispheric-scale upper mantle heterogeneity reflects subduction modification of the asthenospheric mantle which is incorporated into mantle flow, and whose geographical distribution is controlled dominantly by a “subduction shield” that has surrounded the Pacific Ocean for 180 Myr. Simple modeling suggests that a slab flux equivalent to ~13% of the output at arcs is incorporated into the convecting upper mantle.

Platinum-group minerals from alluvial placers of the Kitoy river (south-east part of East Sayan, Russia)

2021 ◽  
Author(s):  
Olga Kiseleva ◽  
Yuriy Ochirov ◽  
Sergey Zhmodik ◽  
Brian Nharara
Keyword(s):  
Publishing House ◽  
Primary Source ◽  
Platinum Metal ◽  
Mineral Chemistry ◽  
Source Rocks ◽  
Tectonic Deformation ◽  
Platinum Group Minerals ◽  
Placer Deposits ◽  
Platinum Group ◽  
Eastern Sayan

&lt;p&gt;The studied area is in the southeastern region of Eastern Sayan. Several tectonically dissected ophiolite complexes were exposed along the margin of the Gargan block and tectonically thrust over this block. Placer nuggets of PGE alloys from the Kitoy river were examined using a scanning electron microscope. Platinum-group minerals (PGM's) in placer deposits provide vital information about the types of their primary source rocks and ores as well as the conditions of formation and alteration. The primary PGM's are Os-Ir-Ru alloys, (Os, Ru)S&lt;sub&gt;2&lt;/sub&gt;, and (Os, Ir, Ru)AsS. (Os, Ru)S&lt;sub&gt;2&lt;/sub&gt; form overgrowth around the Os-Ir-Ru alloys. The secondary, remobilized PGM's are native osmium, (Ir-Ru) alloys, garutite (Ir, Ni, Fe), zaccarinite (RhNiAs), selenides, tellurides (Os, Ir, Ru), and non-stoichiometric (Pd, Pt, Fe, Te, Bi) phases (Fig.1). Secondary PGM's (garutite and RhNiAs) form rims around Os-Ir-Ru alloys, intergrowth with them, or form polyphase aggregates. Such PGM's (identical in composition and microstructure) are also found in chromitites from Neoproterozoic ophiolite massifs of Eastern Sayan (Kiseleva et al., 2014; 2020). Platinum-metal minerals, exotic for ophiolites, are found among secondary PGM's such as selenides and tellurides (Os, Ir, Ru), (Pt, Pd)&lt;sub&gt;3&lt;/sub&gt;Fe, Pd&lt;sub&gt;3&lt;/sub&gt;(Te, Bi), (Au, Ag), and non-stoichiometric (Pd, Pt, Fe, Te, Bi) phases. They occur as inclusions in the Os-Ir-Ru alloys or fill cracks in crushed grains of primary PGM's. PGM's in placer deposits of the Kitoy river are similar to the mineral composition of PGE in chromitites of the Ospa-Kitoy ophiolitic massif, which contain Pt-Pd minerals and Pt impurities in Os-Ir-Ru alloys (Kiseleva et al., 2014). Selenides (Os-Ir-Ru) are rare within PGM's from ophiolite chromitites (Barkov et al., 2017; Airiyants et al., 2020) and also occur in chromitites of the Dunzhugur ophiolite massif (Kiseleva et al., 2016). Features of selenides and tellurides (Os, Ir, Ru) indicate their late formation as a result of the influence of magmatic and metamorphic fluids on primary PGE alloys. The filling of cracks in crushed (Os-Ir-Ru) alloys indicates that selenides and tellurides formed during tectonic deformation processes. The source of platinum-group minerals from the Kitoy river placer is the Ospa-Kitoy ophiolite massif, and primarily chromitites.&lt;/p&gt;&lt;p&gt;&lt;img src=&quot;https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.eb9553e3c70065361211161/sdaolpUECMynit/12UGE&amp;app=m&amp;a=0&amp;c=f3ccc1c7cf7d06094d2afaa34fe9d9a1&amp;ct=x&amp;pn=gepj.elif&amp;d=1&quot; alt=&quot;&quot;&gt;&lt;/p&gt;&lt;p&gt;Figure 1. BSE microphotographs of PGM from from alluvial placers of the Kitoy river&lt;/p&gt;&lt;p&gt;Mineral chemistry was determined at the Analytical Centre for multi-elemental and isotope research SB RAS. This work supported by RFBR grants: No. 16-05-00737a,&amp;#160; 19-05-00764&amp;#1072;, 19-05-00464a and the Russian Ministry of Education and Science&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Airiyants E.V., Belyanin D.K., Zhmodik S.M., Agafonov L.V., Romashkin P.A.&amp;#160; // Ore Geology Reviews. 2020. V. 120. P.&amp;#160; 103453&lt;/p&gt;&lt;p&gt;Barkov A.Y., Nikiforov A.A., Tolstykh N.D., Shvedov G.I., Korolyuk V.N. // European J. Mineralogy. 2017. V.29(9). P.613-621.&lt;/p&gt;&lt;p&gt;Kiseleva O.N., Zhmodik S.M., Damdinov B.B., Agafonov L.V., Belyanin D.K. // Russian Geology and Geophysics. &lt;strong&gt;2014&lt;/strong&gt;. V. 55. P. 259-272.&lt;/p&gt;&lt;p&gt;Kiseleva O.N., Airiyants E.V., Belyanin D.K., Zhmodik S.M., Ashchepkov I.V., Kovalev S.A. // Minerals. 2020. V. 10. N 141. P. 1-30.&lt;/p&gt;&lt;p&gt;Kiseleva O.N., Airiyants E.V., Zhmodik S.M., Belyanin D.K / Russian and international conference proceedings &amp;#8220;The problems of geology and exploitation of platinum metal deposits&amp;#8221; &amp;#8211; St.Petersburg: Publishing house of St.Petersburg State University. 2016. 184 P.&lt;/p&gt;

Tholeiitic volcanic rocks of the late Archean Blake River Group, southern Abitibi greenstone belt: origin and geodynamic implications

1992 ◽  
Vol 29 (7) ◽  
pp. 1448-1458 ◽  
Author(s):  
M. R. Laflèche ◽  
C. Dupuy ◽  
J. Dostal
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Incompatible Trace Element ◽  
Progressive Change ◽  
Abitibi Greenstone Belt ◽  
Mid Ocean Ridge ◽  
Compositional Variations ◽  
Arc Setting ◽  
Back Arc ◽  
Ocean Ridge

The late Archean Blake River Group volcanic sequence forms the uppermost part of the southern Abitibi greenstone belt in Quebec. The group is mainly composed of mid-ocean-ridge basalt (MORB)-like tholeiites that show a progressive change of several incompatible trace element ratios (e.g., Nb/Th, Nb/Ta, La/Yb, and Zr/Y) during differentiation. The compositional variations are inferred to be the result of fractional crystallization coupled with mixing–contamination of tholeiites by calc-alkaline magma which produced the mafic–intermediate lavas intercalated with the tholeiites in the uppermost part of the sequence. The MORB-like tholeiites were probably emplaced in a back-arc setting.

scholarly journals Exsolution Lamellae in Orthopyroxene of Lherzolite from the Pauza Ultramafic Rocks, Ne Iraq: Evidence of Deep Mantle Signature in the Zagros Suture Zone

2013 ◽  
Vol 2 (9) ◽  
pp. 102-115
Author(s):  
Yousif Osman Mohammad ◽  
Nabaz Rashid Hama Aziz
Keyword(s):  
High Pressure ◽  
Upper Cretaceous ◽  
Suture Zone ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Spinel Peridotite ◽  
Incongruent Melting ◽  
Fine Grained ◽  
Ultra High Pressure ◽  
Deep Mantle

The Pauza ultramafic body is part of Upper Cretaceous Ophiolitic massifs of the Zagros Suture Zone, NE Iraq. The present study reveals evidence of Ultra-high pressure (UHP), and deep mantle signature of these peridotites in the Zagros Suture Zone throughout the observation of backscattered images and micro analyses which have been performed on orthopyroxen crystals in lherzolite of Pauza ultramafic rocks.Theorthopyroxen shows abundant exsolution lamellae of coarse unevenly distributed clinopyroxene coupled with the submicron uniformly distributed needles of Cr-spinel. The observed clusters of Opx–Cpx–Spl represent the decompression products of pyrope-rich garnet produced as a result of the transition from ultra-high pressure garnet peridotite to low-pressure spinel peridotite (LP). Neoblastic olivine (Fo92 – 93) with abundant multi-form Cr- spinel inclusions occurs as a fine-grained aggregate around orthopyroxene, whereas coarse olivine (Fo90-91) free from chromian-spinel is found in matrix. The similarity of the Cr-spinel lamellae orientations in both olivine and orthopyroxene, moreover, the enrichments of both Cr and Fe3+ in the Cr-spinel inclusions in neoblastic olivine relative to Cr-spinel lamellae in orthopyroxene, suggest that spinel inclusions in olivine have been derived from former Cr-spinel lamellae in orthopyroxene. Neoblastic olivine is formed by reaction of silica-poor ascending melt and orthopyroxene. It is inferred that the olivines with multi-form spinel inclusions has been formed by incongruent melting of pre-existing spinel lamellae-rich orthopyroxene.

The Ferguson Lake deposit: an example of Ni–Cu–Co–PGE mineralization emplaced in a back-arc basin setting?

2018 ◽  
Vol 55 (8) ◽  
pp. 958-979 ◽  
Author(s):  
P. Acosta-Góngora ◽  
S.J. Pehrsson ◽  
H. Sandeman ◽  
E. Martel ◽  
T. Peterson
Keyword(s):  
Mineral Exploration ◽  
Ultramafic Rocks ◽  
Geodynamic Setting ◽  
Ocean Ridges ◽  
Tectonic Environment ◽  
Pge Mineralization ◽  
Extensional Tectonic ◽  
Basaltic Composition ◽  
Greenstone Belts ◽  
Back Arc

The world’s largest Ni–Cu–Platinum group element (PGE) deposits are dominantly hosted by ultramafic rocks within continental extensional settings (e.g., Raglan, Voisey’s Bay), resulting in a focus on exploration in similar geodynamic settings. Consequently, the economic potential of other extensional tectonic environments, such as ocean ridges and back-arc basins, may be underestimated. In the northeastern portion of the ca. 2.7 Ga Yathkyed greenstone belt of the Chesterfield block (western Churchill Province, Canada), the Ni–Cu–Co–PGE Ferguson Lake deposit is hosted by >2.6 Ga hornblenditic to gabbroic rocks of the Ferguson Lake Igneous Complex (FLIC), which is metamorphosed up to amphibolitic facies. The FLIC has a basaltic composition (Mg# = 31–72), flat to slightly negatively sloped normalized trace element patterns (La/YbPM = 0.7–3.5), and negative Zr, Ti, and Nb anomalies. The FLIC rocks are geochemically similar to the 2.7 Ga back-arc basin tholeiitic basalts from the adjacent Yathkyed and MacQuoid greenstone belts (Mg# = 30–67; La/YbPM = 0.3–3.0), but the Ferguson Lake intrusions appear to be more crustally contaminated. We interpret the FLIC to have formed in an equivalent back-arc basin setting. This geodynamic setting is rare for the formation of Ni–Cu–PGE occurrences, and only few examples of this tectonic environment (or variations of it, e.g., rifted back-arc) are found in other Proterozoic and Archean sequences (e.g., Lorraine deposit, Quebec). We suggest that back-arc basin-derived mafic rocks within the Yathkyed and other Neoarchean greenstone belts of the Chesterfield block (MacQuoid and Angikuni) could represent important targets for future mineral exploration.

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