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Secondary Dispersion Halos of Platinum and Palladium in the Shorzha Dunite-Peridotite Massif of the Sevan Ophiolite Belt of Armenia

Authors:
Arshavir Hovhannisyan at National Academy of Sciences of Armenia
Arshavir Hovhannisyan
Shahen Khachatryan at Yerevan State University
Shahen Khachatryan
Yeghis Keheyan at University of Rome "La Sapienza
Yeghis Keheyan
  • University of Rome "La Sapienza
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Schematic geological map of Shorzha ore field with the secondary multiplicative haloes of dispersion of platinoids. Conventions: 1. Modern alluvial-dealluvial deposits; 2. Middle Eocene: lava flows, volcanogenic formations of andesite composition; 3. Upper Cretaceous: Campanian-Maastrichtian, limestones and marls; 4. Middle Jurassic: peridotites (harzburgites and wehrlites); dunnites, serpentinites; 5. Middle Eocene: gabbro, olivine gabbro, tractolites, anorthosites; 6. Carbonatites; 7. Contours of the site and zones of chromite mineralization (1. Southern chromite zone, 2. Northern chromite zone, 3. Site "Zalezh"); 8. Numbers of anomalies; 9, 10, 11. Distribution of platinoids (Pt, Pd) in the secondary haloes (9. 50-70mg/t, 10. 70-90mg/t, 11. 90-385mg/t). Serpentinized dunnites and peridotites are developed within the anomalies. No accumulation of chromite mineralization has been revealed in them. Chromite-bearing dunnites in the form of ingrained mineralization are only delineated on the site "Zalezh". In trench and core samples of basic hyperbasites of central parts of the III and IV anomalies, the contents of chromium oxide -0.37-1.45%, of platinum -0.00012-0.01g/t and palladium -0.0011-0.17g/t have been determined. The accumulation trend of Pt and Pd is observed in the samples, where the content of chromium oxide is within 0.6-1.45% (high-chromium hyperbasites). In chromite clusters the contents of PGM (Platinum Group Metals) rise. In samples taken from chromite zones of the site "Zalezh" (the content of chromium oxide -3.14-8.74%) the contents of 0.002-0.8g/t platinum and 0.0012-1.38g/t palladium were obtained by spectrochemical analyses of 20 samples. The V anomaly in the east also partially covers tractolites, which are embedded in peridotites. In root samples of tractolites the contents of platinoids do not exceed 0.001g/t. The anomaly may be due to the movement of eluvium. Even though sometimes "hurricane" contents of platinum (up to 15g/t) are obtained in rock chip samples, and the presence of platinum minerals was established in chromite ores, it should be noted that, within development of massive chromite bodies in the southern chromite zone of the western part of Shorzha massif, anomalous geochemical sites of PGM are not formed. Absence of
Schematic geological map of Shorzha ore field with the secondary multiplicative haloes of dispersion of platinoids. Conventions: 1. Modern alluvial-dealluvial deposits; 2. Middle Eocene: lava flows, volcanogenic formations of andesite composition; 3. Upper Cretaceous: Campanian-Maastrichtian, limestones and marls; 4. Middle Jurassic: peridotites (harzburgites and wehrlites); dunnites, serpentinites; 5. Middle Eocene: gabbro, olivine gabbro, tractolites, anorthosites; 6. Carbonatites; 7. Contours of the site and zones of chromite mineralization (1. Southern chromite zone, 2. Northern chromite zone, 3. Site "Zalezh"); 8. Numbers of anomalies; 9, 10, 11. Distribution of platinoids (Pt, Pd) in the secondary haloes (9. 50-70mg/t, 10. 70-90mg/t, 11. 90-385mg/t). Serpentinized dunnites and peridotites are developed within the anomalies. No accumulation of chromite mineralization has been revealed in them. Chromite-bearing dunnites in the form of ingrained mineralization are only delineated on the site "Zalezh". In trench and core samples of basic hyperbasites of central parts of the III and IV anomalies, the contents of chromium oxide -0.37-1.45%, of platinum -0.00012-0.01g/t and palladium -0.0011-0.17g/t have been determined. The accumulation trend of Pt and Pd is observed in the samples, where the content of chromium oxide is within 0.6-1.45% (high-chromium hyperbasites). In chromite clusters the contents of PGM (Platinum Group Metals) rise. In samples taken from chromite zones of the site "Zalezh" (the content of chromium oxide -3.14-8.74%) the contents of 0.002-0.8g/t platinum and 0.0012-1.38g/t palladium were obtained by spectrochemical analyses of 20 samples. The V anomaly in the east also partially covers tractolites, which are embedded in peridotites. In root samples of tractolites the contents of platinoids do not exceed 0.001g/t. The anomaly may be due to the movement of eluvium. Even though sometimes "hurricane" contents of platinum (up to 15g/t) are obtained in rock chip samples, and the presence of platinum minerals was established in chromite ores, it should be noted that, within development of massive chromite bodies in the southern chromite zone of the western part of Shorzha massif, anomalous geochemical sites of PGM are not formed. Absence of
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Secondary Dispersion Halos of Platinum and
Palladium in the Shorzha Dunite-Peridotite
Massif of the Sevan Ophiolite Belt of Armenia
Keheyan Y1*, Khachatryan SV2 and Hovhannisyan AE3
1        

2
3
Opinion

  
         
         


Geological structure of NE shore of Lake Sevan


  
      
       
            
  
     




    


Crimson Publishers
Wings to the Research Opinion
*Corresponding author:  -
  

-


Submission: 
Published: 

How to cite this article:  
   
      
    
     

2
Copyright@  
      
    
   
   
     

ISSN: 2578-0255
Aspects in Mining & Mineral Science 984
Aspects Min Miner Sci
Copyright © Yeghis Keheyan
AMMS.MS.ID.000702.9(1).2022 990
Figure 1: Schematic geological map of Shorzha ore eld with the secondary multiplicative haloes of dispersion
of platinoids. Conventions: 1. Modern alluvial-dealluvial deposits; 2. Middle Eocene: lava ows, volcanogenic
formations of andesite composition; 3. Upper Cretaceous: Campanian-Maastrichtian, limestones and marls; 4.
Middle Jurassic: peridotites (harzburgites and wehrlites); dunnites, serpentinites; 5. Middle Eocene: gabbro, olivine
gabbro, tractolites, anorthosites; 6. Carbonatites; 7. Contours of the site and zones of chromite mineralization
(1. Southern chromite zone, 2. Northern chromite zone, 3. Site “Zalezh”); 8. Numbers of anomalies; 9, 10, 11.
Distribution of platinoids (Pt, Pd) in the secondary haloes (9. 50-70mg/t, 10. 70-90mg/t, 11. 90-385mg/t).
     
       
     
       
        

        
    
          
      
        

         
       


          
          

 
        
    

         
         
        
    


        

Refrences
  

       
         

 
          
   

 
         

             
       

   

991
Aspects Min Miner Sci
Copyright © Yeghis Keheyan
AMMS.MS.ID.000702.9(1).2022
           

 ü      
        
          
        

 
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Subductions, obduction and collision in the Lesser Caucasus (Armenia, Azerbaijan, Georgia), new insights
Article
Full-text available
  • Sep 2010
In the Lesser Caucasus three main domains are distinguished from SW to NE: (1) the autochthonous South Armenian Block (SAB), a Gondwana-derived terrane; (2) the ophiolitic Sevan–Akera suture zone; and (3) the Eurasian plate. Based on our field work, new stratigraphical, petrological, geochemical and geochronological data combined with previous data we present new insights on the subduction, obduction and collision processes recorded in the Lesser Caucasus. Two subductions are clearly identified, one related to the Neotethys subduction beneath the Eurasian margin and one intra-oceanic (SSZ) responsible for the opening of a back-arc basin which corresponds to the ophiolites of the Lesser Caucasus. The obduction occurred during the Late Coniacian to Santonian and is responsible for the widespread ophiolitic nappe outcrop in front of the suture zone. Following the subduction of oceanic lithosphere remnants under Eurasia, the collision of the SAB with Eurasia started during the Paleocene, producing 1) folding of ophiolites, arc and Upper Cretaceous formations (Transcaucasus massif to Karabakh); 2) thrusting toward SW; and 3) a foreland basin in front of the belt. Upper–Middle Eocene series unconformably cover the three domains. From Eocene to Miocene as a result of the Arabian plate collision with the SAB to the South, southward propagation of shortening featured by folding and thrusting occurred all along the belt. These deformations are sealed by a thick sequence of unconformable Miocene to Quaternary clastic and volcanic rocks of debated origin.
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Structural position of ophiolites of the Caucasus.
Article
  • Jan 1980
  • OFIOLITI
Two major ophiolite zones occur in Caucasus. The northern Front Range ophiolite in Great Caucasus constitutes a sliced unit as a complex of four major nappes; it includes serpentinized harzburgites, gabbro-norites, diabases, basaltic porphyries and aphyries, with sedimentary slices. Ophiolites are of pre-Silurian age, and are interpreted as the crust of a marginal sea obducted on island arc sequences at the beginning of early Carboniferous. The southern ophiolite belt in Lesser Caucasus includes ultramafics, gabbros, spilites and radiolarian cherts. The Vedi Zone comprises, from bottom to top: the autochthon ending in Lower Coniacian; an ophiolite-bearing melange nappe; an ultramafic-gabbro nappe. The Sevan-Akera zone displays an autochthon topped by Lower Coniacian and a sequence of nappes including, from bottom to top, ultramafics and gabbros, Upper Jurassic-Lower Cretaceous volcano-sedimentary sequences, Cenomanian olistostromes and basalts, and serpentinite melange. In both zones Neo-authochton begins in Upper Coniacian. The Lesser Caucasus ophiolites represent a Mesozoic oceanic crust obducted both N (Sevan-Akera) and S (Vedi) from a suture line (Zangezur), as a consequence of the collision of the African and European plates since Cenomanian. -from Authors
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Geology, geochemistry and 40Ar/39Ar dating of Sevan ophiolites (Lesser Caucasus, Armenia): Evidence for Jurassic Back-arc opening and hot spot event between the South Armenian Block and Eurasia
Article
  • Feb 2009
  • J ASIAN EARTH SCI
In the Lesser Caucausus the Sevan-Akera ophiolites of N Armenia have lithological features of a slow-spreading oceanic lithosphere: serpentinites are frequently exposed and hydrothermalized at sea-floor level, plutonic rocks and dykes are rare. A complete differentiation trend is observed from mafic norites evolving to diorites and plagiogranites. Normal faults have exposed some of the deep magmatic rocks at sea-floor level. Geochemically, two distinct lava flow series have been distinguished: (1) a contaminated Mid-Oceanic Ridge Basalt (MORB) series evolving from gabbros to plagiogranites and from basalts to basaltic andesites, exhibiting slight calc-alkaline features (enrichments in Large Ion Lithophile Elements (LILE); negative anomalies in Nb–Ta and Ti relative to N-MORB); (2) an alkaline series evolving from basanites to trachy-andesites (on anhydrous basis). 40Ar/39Ar age on amphibole-bearing gabbros evidence a Middle Jurassic age (165.3 ± 1.7 Ma, 2σ) for oceanic crust formation. Structural data, including geological cross-sections and logs of the ophiolite along the northern part of Sevan Lake allow discussing the geodynamic evolution of that segment of the Amassia-Sevan-Akera ophiolitic suture zone.
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Shorzha's chromite-bearing peridotite massif (Transcaucasia) and the genesis of chromite iron ore deposits
  • Jan 1937
  • 7-152
  • A G Betekhtin
Betekhtin AG (1937) Shorzha's chromite-bearing peridotite massif (Transcaucasia) and the genesis of chromite iron ore deposits. In: Chromites of the USSR. Russia, pp. 7-152.
Evidence for superposed MORB, oceanic plateau and volcanic arc series in the Lesser Caucasus
  • Jan 2007
  • CR GEOSCI
  • 482-492
  • G Galoyan
  • Y Rolland
  • M Sosson
  • M Corsini
  • R Melkonian
Galoyan G, Rolland Y, Sosson M, Corsini M, Melkonian R (2007) Evidence for superposed MORB, oceanic plateau and volcanic arc series in the Lesser Caucasus (Stepanavan, Armenia). Comptes Rendus Geosciences 339(7): 482-492.
Petrological, geochemical and geochronological studies of the ophiolites of petit Caucasus (Armenia)
  • Jan 2008
  • G Galoyan
Galoyan G 2008) Petrological, geochemical and geochronological studies of the ophiolites of petit Caucasus (Armenia). Doctorate in Sciences, University of Nice-Sophia Antipolis, France.