Micro-PIXE analysis of platinum group minerals from placer deposits

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)S2, and (Os, Ir, Ru)AsS. (Os, Ru)S2 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)3Fe, Pd3(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.<img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.eb9553e3c70065361211161/sdaolpUECMynit/12UGE&app=m&a=0&c=f3ccc1c7cf7d06094d2afaa34fe9d9a1&ct=x&pn=gepj.elif&d=1" alt="">Figure 1. BSE microphotographs of PGM from from alluvial placers of the Kitoy riverMineral 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,&#160; 19-05-00764&#1072;, 19-05-00464a and the Russian Ministry of Education and ScienceReferencesAiriyants E.V., Belyanin D.K., Zhmodik S.M., Agafonov L.V., Romashkin P.A.&#160; // Ore Geology Reviews. 2020. V. 120. P.&#160; 103453Barkov A.Y., Nikiforov A.A., Tolstykh N.D., Shvedov G.I., Korolyuk V.N. // European J. Mineralogy. 2017. V.29(9). P.613-621.Kiseleva O.N., Zhmodik S.M., Damdinov B.B., Agafonov L.V., Belyanin D.K. // Russian Geology and Geophysics. 2014. V. 55. P. 259-272.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.Kiseleva O.N., Airiyants E.V., Zhmodik S.M., Belyanin D.K / Russian and international conference proceedings &#8220;The problems of geology and exploitation of platinum metal deposits&#8221; &#8211; St.Petersburg: Publishing house of St.Petersburg State University. 2016. 184 P.

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Techniques and methodology used in a mineralogical and osmium isotope study of platinum group minerals from alluvial deposits in Colombia, California, Oregon and Alaska

Mineralogical Magazine ◽

10.1180/minmag.1997.061.406.04 ◽

1997 ◽

Vol 61 (406) ◽

pp. 367-375 ◽

Cited By ~ 1

Author(s):

I. C. Lyon ◽

H. Tamana ◽

D. J. Vaughan ◽

A. J. Criddle ◽

J. M. Saxton ◽

...

Keyword(s):

Trace Element ◽

Alluvial Deposits ◽

Ion Probe ◽

Platinum Group Minerals ◽

Placer Deposits ◽

Trace Element Contents ◽

Isotope Study ◽

Platinum Group ◽

Textural Evidence ◽

Rhenium Content

AbstractPlatinum-group minerals (PGM) from placer deposits in Colombia, California, Oregon and Alaska were investigated with the electron microprobe, proton microprobe (μ-PIXE) and ion probe to analyse their major and trace element contents and 187Os/186Os isotopic ratios. Most of the grains in the samples investigated proved to be essentially homogeneous alloys of Pt-Fe and Os-Ir-Ru although a few of them contained inclusions of other PGM such as cooperite and laurite. Detailed analyses were undertaken on the Os-Ir-Ru alloy phases.The 187Os/186Os isotope ratios fell into a range from 1.005 to 1.156 and are consistent with data published on PGM from other placer deposits from these regions. The ratios, together with the trace element data (and in particular the low rhenium content) determined by ion probe and μ-PIXE, indicate that crustal osmium was not incorporated in the grains and that no significant evolution of the 187Os/186Os ratios occurred during their history. These data, along with mineralogical and textural evidence, are consistent with a mantle origin for the grains through ultramafic intrusions, although the data do not entirely rule out alternative interpretations.

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Platinum mineralization in the Alaskan-type intrusive complexes near Fifield, N.S.W., Australia. Part 2. Platinum-group minerals in placer deposits at Fifield

Mineralogy and Petrology ◽

10.1007/bf01166889 ◽

1991 ◽

Vol 43 (3) ◽

pp. 161-180 ◽

Cited By ~ 28

Author(s):

E. Slansky ◽

L. M. Barron ◽

D. Suppel ◽

Z. Johan ◽

M. Ohnenstetter

Keyword(s):

Platinum Group Minerals ◽

Placer Deposits ◽

Platinum Group ◽

Platinum Mineralization

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PLATINUM-GROUP MINERALS FROM FIVE PLACER DEPOSITS IN BRITISH COLUMBIA, CANADA

The Canadian Mineralogist ◽

10.2113/gscanmin.43.5.1687 ◽

2005 ◽

Vol 43 (5) ◽

pp. 1687-1710 ◽

Cited By ~ 17

Author(s):

A. Y. Barkov ◽

M. E. Fleet ◽

G. T. Nixon ◽

V. M. Levson

Keyword(s):

British Columbia ◽

Platinum Group Minerals ◽

Placer Deposits ◽

Platinum Group

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Platinum-Group Minerals in the Placer of the Kitoy River, East Sayan, Russia

Minerals ◽

10.3390/min12010021 ◽

2021 ◽

Vol 12 (1) ◽

pp. 21

Author(s):

Evgenia V. Airiyants ◽

Olga N. Kiseleva ◽

Sergey M. Zhmodik ◽

Dmitriy K. Belyanin ◽

Yuriy C. Ochirov

Keyword(s):

Primary Source ◽

Source Rocks ◽

Southeastern Part ◽

Reducing Conditions ◽

Platinum Group Minerals ◽

Magmatic Stage ◽

Oxide Phases ◽

Placer Deposits ◽

Platinum Group ◽

Eastern Sayan

The platinum-group minerals (PGM) in placer deposits provide important information on the types of their primary source rocks and ores and formation and alteration conditions. The article shows for the first time the results of a study of placer platinum mineralization found in the upper reaches of the Kitoy River (the southeastern part of the Eastern Sayan (SEPES)). Using modern methods of analysis (scanning electron microscopy), the authors studied the microtextural features of platinum-group minerals (PGM), their composition, texture, morphology and composition of microinclusions, rims, and other types of changes. The PGM are Os‑Ir‑Ru alloys with a pronounced ruthenium trend. Many of the Os‑Ir‑Ru grains have porous, fractured, or altered rims that contain secondary PGE sulfides, arsenides, sulfarsenides, Ir-Ni-Fe alloys, and rarer selenides, arsenoselenides, and tellurides of the PGE. The data obtained made it possible to identify the root sources of PGM in the placer and to make assumptions about the stages of transformation of primary igneous Os-Ir-Ru alloys from bedrock to placer. We assume that there are several stages of alteration of high-temperature Os-Ir-Ru alloys. The late magmatic stage is associated with the effect of fluid-saturated residual melt enriched with S, As. The post-magmatic hydrothermal stage (under conditions of changing reducing conditions to oxidative ones) is associated with the formation of telluro-selenides and oxide phases of PGE. The preservation of poorly rounded and unrounded PGM grains in the placer suggests a short transport from their primary source. The source of the platinum-group minerals from the Kitoy River placer is the rocks of the Southern ophiolite branch of SEPES and, in particular, the southern plate of the Ospa-Kitoy ophiolite complex, and primarily chromitites.

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New mineralogical data on platinum-group minerals from the Río Santiago alluvial placer, Esmeraldas province, Ecuador

Boletín de la Sociedad Geológica Mexicana ◽

10.18268/bsgm2020v72n3a090720 ◽

2020 ◽

Vol 72 (3) ◽

pp. A090720

Author(s):

Gladys G. López-Males ◽

Thomas Aiglsperger ◽

Núria Pujol-Solà ◽

Joaquín A. Proenza

Keyword(s):

Coastal Region ◽

Primary Source ◽

Primary Sources ◽

Ultramafic Rocks ◽

Oceanic Plateau ◽

Western Cordillera ◽

Type Complex ◽

Platinum Group Minerals ◽

Placer Deposits ◽

Platinum Group

Mineralogical studies on platinum-group minerals found in placer deposits from the Río Santiago (Ecuador) are scarce. In this investigation, one sample collected from the Río Santiago alluvial placer was studied via a multi-disciplinary approach, including optical microscopy, scanning electron microscopy, electron microprobe, and Raman spectroscopy. Whole-rock geochemistry data of the sample confirms elevated Au and platinum-group elements contents and the chondrite-normalized pattern reveals pronounced positive Ir and Pt anomalies. Free grains of platinum-group minerals were separated via hydroseparation techniques and identified as: i) Pt-Fe alloy (Pt3Fe), ii) tulameenite (Pt2FeCu) and iii) hongshiite (PtCu). The most abundant platinum-group mineral is Pt-Fe alloy (85%) that occasionally hosts cuprorhodsite (CuRh2S4) inclusions. Although the primary source remains unknown, the geochemical and mineralogical data suggests that the source of platinum-group minerals in the Río Santiago alluvial placer is a mafic-ultramafic Ural-Alaska type complex. Possible primary sources are the mafic and ultramafic rocks found in the mafic basement of the coastal region and the Western Cordillera (Piñón, San Juan and Pallatanga units), which derive from the Late Cretaceous Caribbean Colombia Oceanic Plateau (CCOP).

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Platinum-Group Minerals of Pt-Placer Deposits Associated with the Svetloborsky Ural-Alaskan Type Massif, Middle Urals, Russia

Minerals ◽

10.3390/min9020077 ◽

2019 ◽

Vol 9 (2) ◽

pp. 77 ◽

Cited By ~ 4

Author(s):

Sergey Stepanov ◽

Roman Palamarchuk ◽

Aleksandr Kozlov ◽

Dmitry Khanin ◽

Dmitry Varlamov ◽

...

Keyword(s):

Morphological Features ◽

Middle Urals ◽

Transport Distance ◽

Mechanical Attrition ◽

Platinum Group Minerals ◽

Placer Deposits ◽

Fe Alloys ◽

Platinum Group ◽

Ore Zones

The alteration of platinum group minerals (PGM) of eluval, proximal, and distal placers associated with the Ural-Alaskan type clinopyroxenite-dunite massifs were studied. The Isovsko-Turinskaya placer system is unique regarding its size, and was chosen as research object as it is PGM-bearing for more than 70 km from its lode source, the Ural-Alaskan type Svetloborsky massif, Middle Urals. Lode chromite-platinum ore zones located in the Southern part of the dunite “core” of the Svetloborsky massif are considered as the PGM lode source. For the studies, PGM concentrates were prepared from the heavy concentrates which were sampled at different distances from the lode source. Eluvial placers are situated directly above the ore zones, and the PGM transport distance does not exceed 10 m. Travyanistyi proximal placer is considered as an example of alluvial ravine placer with the PGM transport distance from 0.5 to 2.5 km. The Glubokinskoe distal placer located in the vicinity of the Is settlement are chosen as the object with the longest PGM transport distance (30–35 km from the lode source). Pt-Fe alloys, and in particular, isoferroplatinum prevail in the lode ores and placers with different PGM transport distance. In some cases, isoferroplatinum is substituted by tetraferroplatinum and tulameenite in the grain marginal parts. Os-Ir-(Ru) alloys, erlichmanite, laurite, kashinite, bowieite, and Ir-Rh thiospinels are found as inclusions in Pt-Fe minerals. As a result of the study, it was found that the greatest contribution to the formation of the placer objects is made by the erosion of chromite-platinum mineralized zones in dunites. At a distance of more than 10 km, the degree of PGM mechanical attrition becomes significant, and the morphological features, characteristic of lode platinum, are practically not preserved. One of the signs of the significant PGM transport distance in the placers is the absence of rims composed of the tetraferroplatinum group minerals around primary Pt-Fez alloys. The sie of the nuggets decreases with the increasing transport distance. The composition of isoferroplatinum from the placers and lode chromite-platinum ore zones are geochemically similar.

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