Os-isotope study of platinum-group minerals in chromitites in Alpine-type ultramafic intrusions and the associated placers in Borneo

1992 ◽  
Vol 56 (383) ◽  
pp. 157-164 ◽  
Author(s):  
Keiko Hattori ◽  
Klaus-Peter Burgath ◽  
Stanley R. Hart
Keyword(s):  
Igneous Rocks ◽  
Chemical Inhomogeneity ◽  
Minor Variation ◽  
Platinum Group Minerals ◽  
Isotope Study ◽  
Platinum Group ◽  
Individual Grains ◽  
A Minor ◽  
Os Isotope

Abstract187Os/186Os ratios were determined for in-situ laurite grains in Alpine-type chromitites and platinumgroup minerals (PGM) in the associated alluvial placers in Borneo, Indonesia/Malaysia. The Osisotope ratios of laurite grains in chromite defne an 187Os/186Os ratio for the 100 Ma mantle source of c. 1.04. Thelow 187Os/186Os ratios in all grains confirm the essential derivation of these platinum-group elements (PGE) from the mantle. A minor variation in 187Os/186Os ratios was detected among PGM from placers, but no variation was found within individual grains, including a grain with chemical inhomogeneity. The values are similar to those for PGM in the associated chromitites. The data are consistent with a detrital origin of PGM in placers: the placer PGM originated in the ultramafic section of ophiolities and the release of these grains from igneous rocks and their deposition in placers was almost entirely by mechanical processes.

scholarly journals Open System Re-Os Isotope Behavior in Platinum-Group Minerals during Laterization?

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1083
Author(s):  
Thomas Aiglsperger ◽  
José M. González-Jiménez ◽  
Joaquín A. Proenza ◽  
Salvador Galí ◽  
Francisco Longo ◽  
...  
Keyword(s):  
Noble Metals ◽  
Dynamic Models ◽  
Isotope Composition ◽  
Small Scale ◽  
Tectonic Processes ◽  
Platinum Group Minerals ◽  
Different Populations ◽  
Platinum Group ◽  
Individual Grains ◽  
Os Isotope

In this short communication, we present preliminary data on the Re-Os isotopic systematics of platinum-group minerals (PGM) recovered from different horizons in the Falcondo Ni-laterite in the Dominican Republic. The results show differences in the Os-isotope composition in different populations of PGM: (i) pre-lateritic PGM yield 187Os/188Os varying from 0.11973 ± 0.00134 to 0.12215 ± 0.00005 (2σ uncertainty) whereas (ii) lateritic PGM are more radiogenic in terms of 187Os/188Os (from 0.12390 ± 0.00001 to 0.12645 ± 0.00005; 2σ uncertainty). We suggest that these differences reflect the opening of the Re-Os system in individual grains of PGM during lateritic weathering. The implications of these results are twofold as they will help to (1) elucidate the small-scale mobility of noble metals in the supergene setting and therefore the possible formation of PGM at these very low temperatures, (2) better refine the Os-isotopic datasets of PGM that are currently being used for defining dynamic models of core–mantle separation, crustal generation, and fundamental plate-tectonic processes such as the opening of oceans.

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

1997 ◽  
Vol 61 (406) ◽  
pp. 367-375 ◽  
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.

Observation of Ag Precipitate in CuAgZr Alloy during In Situ High Temperature TEM

2017 ◽  
Vol 263 ◽  
pp. 50-54
Author(s):  
Waraporn Piyawit ◽  
Panya Buahombura
Keyword(s):  
High Temperature ◽  
Heating Process ◽  
Minor Variation ◽  
Transmission Electron ◽  
Large Lattice ◽  
Dislocation Movement ◽  
Higher Temperature ◽  
Average Size ◽  
A Minor

CuAgZr alloy is a minor variation of CuAg alloy that is remarkably known for good combination of strength and electrical conductivity. Strengthening and conductivity enhancing of CuAgZr alloy is essentially proficient by the precipitation of Ag precipitates. The behavior of Ag precipitates at high temperature was investigated using in-situ transmission electron microscopy. These nanoscale Ag precipitates are formed in CuAgZr alloy during heating process with the average size of 5 nm. Growth of precipitates at higher temperature can be explained by the consumption of solute diffusing from smaller precipitates. Dislocation looping at high temperature would be the effects of a large lattice strain along matrix/precipitate interface that would retard the dislocation movement.

scholarly journals Placer platinum-group minerals in the Shetland ophiolite complex derived from anomalously enriched podiform chromitites

2018 ◽  
Vol 82 (3) ◽  
pp. 491-514
Author(s):  
Hazel M. Prichard ◽  
Saioa Suárez ◽  
Peter C. Fisher ◽  
Robert D. Knight ◽  
John S. Watson
Keyword(s):  
Cold Climate ◽  
Source Rocks ◽  
Ophiolite Complex ◽  
Cu Alloy ◽  
Platinum Group Minerals ◽  
Small Streams ◽  
Podiform Chromitites ◽  
Fe Alloys ◽  
Platinum Group

ABSTRACTHighly anomalous platinum-group element (PGE) concentrations in the podiform chromitites at the Cliff and Harold's Grave localities in the Shetland ophiolite complex have been well documented previously. The focus of this study is alluvial platinum-group minerals (PGM) located in small streams that drain from the PGE-rich chromitites. The placer PGM assemblage at Cliff is dominated by Pt-arsenides (64%) and Pd-antimonides (17%), with less irarsite–hollingworthite (11%) and minor Pd-sulfides, Pt–Pd–Cu and Pt–Fe alloys and laurite. Gold also occurs with the PGM. Alluvial PGM have average sizes of 20 µm × 60 µm, with sperrylite the largest grain identified at 110 µm in diameter, matching the range reported for the primary PGM in the source rocks. The placer assemblage contains more Pt-bearing and less Pd-bearing PGM compared with the rocks. The more resistant sperrylite and irarsite–hollingworthite grains which are often euhedral become more rounded further downstream whereas the less resistant Pd-antimonides which are commonly subhedral may become striated and etched. Less stable phases such as Pt- and Pd-oxides and other Ni-Cu-bearing phases located in the rocks (i.e. Ru-pentlandite, PtCu, Pd–Cu alloy) are absent in the placer assemblage. Also the scarce PGM (PdHg, Rh- and Ir-Sb) and Os in the rocks are absent. At Harold's Grave only three alluvial PGM (laurite, Ir, Os) and Au were recovered reflecting the limited release of IPGM from chromite grains in the rocks. In this cold climate with high rainfall, where erosion dominates over weathering, the PGM appear to have been derived directly from the erosion of the adjacent PGE-rich source rocks and there is little evidence of in situ growth of any newly formed PGM. Only the presence of dendritic pure Au and Pd-, Cu-bearing Au covers on the surface of primary minerals may indicate some local reprecipitation of these metals in the surficial conditions.

scholarly journals Tamuraite, Ir5Fe10S16, a New Species of Platinum-Group Mineral from the Sisim Placer Zone, Eastern Sayans, Russia

Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 545
Author(s):  
Andrei Y. Barkov ◽  
Nadezhda D. Tolstykh ◽  
Robert F. Martin ◽  
Andrew M. McDonald
Keyword(s):  
National Laboratory ◽  
X Ray Diffraction ◽  
Calculated Density ◽  
Cell Parameters ◽  
Reflected Light ◽  
Platinum Group Minerals ◽  
Platinum Group ◽  
Probable Space ◽  
Layered Complex ◽  
Residual Melt

Tamuraite, ideally Ir5Fe10S16, occurs as discrete phases (≤20 μm) in composite inclusions hosted by grains of osmium (≤0.5 mm across) rich in Ir, in association with other platinum-group minerals in the River Ko deposit of the Sisim Placer Zone, southern Krasnoyarskiy Kray, Russia. In droplet-like inclusions, tamuraite is typically intergrown with Rh-rich pentlandite and Ir-bearing members of the laurite–erlichmanite series (up to ~20 mol.% “IrS2”). Tamuraite is gray to brownish gray in reflected light. It is opaque, with a metallic luster. Its bireflectance is very weak to absent. It is nonpleochroic to slightly pleochroic (grayish to light brown tints). It appears to be very weakly anisotropic. The calculated density is 6.30 g·cm−3. The results of six WDS analyses are Ir 29.30 (27.75–30.68), Rh 9.57 (8.46–10.71), Pt 1.85 (1.43–2.10), Ru 0.05 (0.02–0.07), Os 0.06 (0.03–0.13), Fe 13.09 (12.38–13.74), Ni 12.18 (11.78–13.12), Cu 6.30 (6.06–6.56), Co 0.06 (0.04–0.07), S 27.23 (26.14–27.89), for a total of 99.69 wt %. This composition corresponds to (Ir2.87Rh1.75Pt0.18Ru0.01Os0.01)Σ4.82(Fe4.41Ni3.90Cu1.87Co0.02)Σ10.20S15.98, calculated based on a total of 31 atoms per formula unit. The general formula is (Ir,Rh)5(Fe,Ni,Cu)10S16. Results of synchrotron micro-Laue diffraction studies indicate that tamuraite is trigonal. Its probable space group is R–3m (#166), and the unit-cell parameters are a = 7.073(1) Å, c = 34.277(8) Å, V = 1485(1) Å3, and Z = 3. The c:a ratio is 4.8462. The strongest eight peaks in the X-ray diffraction pattern [d in Å(hkl)(I)] are: 3.0106(26)(100), 1.7699(40)(71), 1.7583(2016)(65), 2.7994(205)(56), 2.9963(1010)(50), 5.7740(10)(45), 3.0534(20)(43) and 2.4948(208)(38). The crystal structure is derivative of pentlandite and related to that of oberthürite and torryweiserite. Tamuraite crystallized from a residual melt enriched in S, Fe, Ni, Cu, and Rh; these elements were incompatible in the Os–Ir alloy that nucleated in lode zones of chromitites in the Lysanskiy layered complex, Eastern Sayans, Russia. The name honors Nobumichi Tamura, senior scientist at the Advanced Light Source of the Lawrence Berkeley National Laboratory, Berkeley, California.

scholarly journals Chlorine as a Discriminant Element to Establish the Provenance of Central Mediterranean Obsidians

2020 ◽  
Vol 6 (1) ◽  
pp. 454-476
Author(s):  
Franco Foresta Martin ◽  
Silvio G. Rotolo ◽  
Manuela Nazzari ◽  
Maria Luisa Carapezza
Keyword(s):  
Electron Microprobe ◽  
Minor Element ◽  
Igneous Rocks ◽  
Chlorine Concentration ◽  
Silicate Melts ◽  
Alkali Content ◽  
Central Mediterranean ◽  
A Minor

Abstract Chlorine is a minor element present in obsidians in quantities greater than in average igneous rocks. The chlorine concentration in obsidians is generally low, of the order of tenths of wt %, but it exhibits an appreciable differentiation among geological sources. Despite these characteristics, chlorine has rarely been taken into consideration as a possible indicator of obsidian provenance and it does not appear in the chemical analytical tables accompanying the geochemical characterisation of obsidian samples. In this work, after an overview of chlorine geochemistry and cycle, we present thirty-one new electron microprobe (EPMA) analyses, including Cl, of geologic obsidians sampled from the four sources of the Central Mediterranean, exploited in prehistoric times (Monte Arci, Palmarola, Lipari and Pantelleria). The results are compared with 175 new EPMA analyses, including Cl, of archaeological obsidians already characterised in previous work and of known provenance. As such it was possible to ascertain that each source has a characteristic chlorine concentration, showing the utility of its use in the studies of obsidian provenance. Furthermore, given that the solubility of chlorine in silicate melts is correlated to its alkali content, in particular sodium, we assessed the efficacy of simple binary graphs Cl vs Na2O to better constrain the provenance of the obsidian samples.

A Road Section near Guy's Hill, Jamaica

1942 ◽  
Vol 79 (4) ◽  
pp. 241-252 ◽  
Author(s):  
C. A. Matley ◽  
Frank Raw
Keyword(s):  
Sedimentary Rocks ◽  
Plutonic Rock ◽  
Igneous Rocks ◽  
The Road ◽  
Road Section ◽  
Igneous Intrusions ◽  
Microscope Slides

The rocks exposed along the road between Linstead and Guy's Hill, Jamaica, were described by Dr. C. T. Trechmann in this magazine in 1936 (pp. 259–260). The chief object of his account was to prove that the igneous rocks there were intrusions later than the associated Cretaceous and Tertiary limestones, which, according to him, had been metamorphosed into hornfelses, some of which, he stated later (1937, p. 561), he knew to have an “igneous” appearance under the microscope, “which tends to support my contention that in Jamaica we have sedimentaries altered in situ into rocks that would ordinarily be classified as igneous.” Dissent from his descriptions and interpretations was expressed by C. A. M. (Matley, 1937, pp. 501–3), the criticisms being mainly based on an examination of Trechmann's own microscope slides by F. R. A visit to Jamaica by C. A. M. in 1939 allowed him to study this road and to collect a suite of rocks for petrological examination. The results show that Trechmann's interpretation cannot be sustained. There is no granodiorite or other plutonic rock present, no metamorphism hornfelsing the sedimentary rocks, and no igneous intrusions into the Tertiary limestones.

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