Noble metals in Thetford Mines ophiolites, Quebec, Canada; Part I, Distribution of gold, iridium, platinum, and palladium in the ultramafic and gabbroic rocks

Oshin, I. O.; Crocket, J. H.

doi:10.2113/gsecongeo.77.6.1556

Cited by 72 publications

(27 citation statements)

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“…Agiorgitis and Wolf (1978) noted that Os, Ir, and Ru correlate with Cr in Greek chromites, implying that the metals substitute for Cr 3 + . Oshin and Crocket (1982) concluded that Ir alloys in some chromitites formed through exsolution during cooling. Other workers (Prichard et al, 1981;Stockman and Hlava, 1984) found alloys and PGE-rich sulfides in ophiolitic chromites and hypothesized that both inclusions were engulfed during chromite growth.…”

Section: Fractionation Of Chromitementioning

confidence: 99%

“…However, various studies have shown that olivine-rich rocks contain high Ir values (Gijbels et al, 1976;Oshin and Crocket, 1982;Crocket and MacRae, 1986), and Ross and Keays (1979) reported high Ir contents (5.7 ppb) for cumulus olivine from an Australian komatiite flow. These data appear at odds with the low Ir contents of olivine from spinel and garnet Iherzolites (0.07-0.5 ppb; Mitchell and Keays, 1981), but the lherzolite olivine probably equilibrated with sulfides that would scavenge most of the Ir (Brugmann et al, 1987).…”

Section: Fractionation Of Silicate Mineralsmentioning

confidence: 99%

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Distribution of Gold, Palladium, Platinum, Rhodium, Ruthenium, and Iridium in Leg 115 Hotspot Basalts: Implications for Magmatic Processes

Greenough¹,

Fryer²

1990

Proceedings of the Ocean Drilling Program

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A comparison of 50 basalts recovered at Sites 706, 707, 713, and 715 along the Reunion hotspot trace during Ocean Drilling Program Leg 115 in the Indian Ocean shows that seafloor alteration had little effect on noble metal concentrations (Au, Pd, Pt, Rh, Ru, and Ir), determined by inductively coupled plasma-mass spectrometry (ICP-MS), which generally tend to decrease with magma evolution. Their compatible-element behavior may be related to the precipitation of Ir-Os-based alloys, chromite, sulfides, and/or olivine and clinopyroxene in some combination. The simplest explanation indicates silicate control of concentrations during differentiation.Basalts from the different sites show varying degrees of alkalinity. Noble metal abundances tend to increase with decreasing basalt alkalinity (i.e., with increasing percentages of mantle melting), indicating that the metals behave as compatible elements during mantle melting. The retention of low-melting-point Au, Pd, and Rh in mantle sulfides, which mostly dissolve before significant proportions of Ir-Os-based alloys melt, explains increasing Pd/Ir ratios with decreasing alkalinity (increasing melting percentages) in oceanic basalts. High noble metal concentrations in Indian Ocean basalts (weighted averages of Au, Pd, Rh, Pt, Ru, and Ir in Leg 115 basalts are 3.2, 8.1, 0.31, 7.3, 0.22, and 0.11 ppb, respectively), compared with basalts from some other ocean basins, may reflect fundamental primary variations in upper-mantle noble metal abundances.

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Section: Fractionation Of Chromitementioning

confidence: 99%

Section: Fractionation Of Silicate Mineralsmentioning

confidence: 99%

Distribution of Gold, Palladium, Platinum, Rhodium, Ruthenium, and Iridium in Leg 115 Hotspot Basalts: Implications for Magmatic Processes

Greenough¹,

Fryer²

1990

Proceedings of the Ocean Drilling Program

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“…Very little is known about the distribution of PGE within a single ophiolite. In the extensive literature on ophiolite, information about the noble metals is fragmentary, except a few works like this of Oshin and Crocket (1982) on the Thetford ophiolite. The more abundant data concern the podiform chromitites.…”

Section: Introductionmentioning

confidence: 99%

Platinum-Group Elements and Gold in Ophiolitic Complexes: Distribution and Fractionation from Mantle to Oceanic Floor

Leblanc

1991

Petrology and Structural Geology

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This review paper attempts to discuss the distribution of noble metals in ophiolitic complexes and suggests new targets for exploration.Platinum-Group Elements (PGE) are nearly unfractionated in the less depleted mantle rocks (lherzolites). Residual dunites are clearly empoverished in Pt, Pd, and Au which were collected by silicate melts during partial melting. The chromite grains of the podiform chromitites, which crystallized early in magmatic conduits in the mantle, include Os-Ir-Ru minerals. Podiform chromitites are PGE-poor (100-500 ppb) or PGE-rich (up to 1 ppm), the highest PGE contents (>ppm) are often related to the presence of interstitial sulphides. In the crustal section PGE are fractionated among the magmatic rocks (Pd/Ir ratio increases from dunite to gabbro). The very low PGE content of the basaltic lavas involves a PGE segregation in a magmatic sulphide phase before emplacement at surface. PGE-rich sulphides are locally present at the base of the crustal section (in chromite-rich dunite or in pyroxenite) or among the upper gabbros. Hydrothermal processes related to serpentinization concentrate mainly gold (1-10 ppm) in sulphide-rich serpentinites, or in carbonatized (listwaenite) or silicified serpentinites where the noble metals are in sulphides and/or arsenides. Convective hydrothermal systems strongly leached the magmatic pile, then precipitated on the ocean floor (i) Massive Sulphide Deposits (Cyprus-type MSD) which may be goldrich (> 1ppm); and (ii) metalliferous sediments displaying slight enrichments in Pt-Pd and Au. Up to 1 ppm Pt may be found in oceanic Mn-nodules. Lastly, weathering and erosion should concentrate PGE in laterites and placers.PGE are an economically important group of elements and new targets should be explored in ophiolites: (1) chromitite pods (Os-Ir-Ru) which may be also Ru-Pt-Pd-rich when sulphides are present; (2) sulphide-rich serpentinites or carbonatized-serpentinites (listwaenites) mainly for gold; (3) sulphidebearing magmatic rocks (Ru-Pt-Pd); (4) exhalative metalliferous sediments; and (5) laterites and placers.

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“…For example, Watkinson and Dunning (1979) and Oshin and Crocket (1982) concluded that intense serpentinization of various mafic and ultramafic rocks in central Canada resulted in little (or only local) centimeter-scale Pt, Pd, or Ir mobility. Nevertheless, recognizing that some platinum-group-element (PGE) ore deposits dominated by Pt, Pd, and Rh are of hydrothermal or diagenetic/epithermal origin (e.g., New Rambler deposit, Wyoming [McCallum et al, 1976] and Rathbun Lake, Ontario [Dressier, 1982]) and that highly saline fluids played an important role in the formation of some deposits (e.g., Pt-rich dunite pipes, Bushveld Intrusion [Schiffries, 1982;Stumpfl and Rucklidge, 1982]), it is now apparent that PGE are highly soluble in some fluids.…”

Section: Discussionmentioning

confidence: 99%

Geochemical Effects of Alteration on Mafic Rocks from Indian Ocean Site 706

Greenough¹,

Fryer²,

Robinson³

1990

Proceedings of the Ocean Drilling Program, 115 Scientific Results

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Highly vesicular and glassy pillow basalts from the sunken oceanic island at Ocean Drilling Program Site 706 in the Indian Ocean show variable alteration and the addition of secondary zeolite facies clay minerals. The mineralogical changes reflect chemical additions of K, Rb, Cs, Li, Si, Sc, Fe, and possibly Sr, Pb, Tl, Au, Pt, and Rh. The elements Ca, Mg, Mn, Ni, and possibly Na, Ba, U, and Ir were removed, but the rare earth elements as well as the elements Zr, Nb, Y, Ti, Al, V, Th, and probably P and Hf were immobile. The data for Cr, Cu, Zn, Bi, Pd, and Ru show large variations, indicating that they were probably mobile; whether they were generally added or removed could not be ascertained, however.The chemical additions and removals are similar to the low-temperature changes observed in ocean-floor basalts near the seawater-seafloor interface. The large, though nonpervasive, chemical changes reflect the effects of alteration caused by seawater percolating down through easily altered glass-rich basalts. They imply that a low-temperature alteration zone similar to the zone in the recharge portion of the ocean-floor (ridge) hydrothermal system also occurs on oceanic islands.

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Noble metals in Thetford Mines ophiolites, Quebec, Canada; Part I, Distribution of gold, iridium, platinum, and palladium in the ultramafic and gabbroic rocks

Cited by 72 publications

References 0 publications

Distribution of Gold, Palladium, Platinum, Rhodium, Ruthenium, and Iridium in Leg 115 Hotspot Basalts: Implications for Magmatic Processes

Distribution of Gold, Palladium, Platinum, Rhodium, Ruthenium, and Iridium in Leg 115 Hotspot Basalts: Implications for Magmatic Processes

Platinum-Group Elements and Gold in Ophiolitic Complexes: Distribution and Fractionation from Mantle to Oceanic Floor

Geochemical Effects of Alteration on Mafic Rocks from Indian Ocean Site 706

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