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Edward M. Ripley

Bio: Edward M. Ripley is an academic researcher from Indiana University. The author has contributed to research in topics: Sulfide & Olivine. The author has an hindex of 49, co-authored 188 publications receiving 6792 citations. Previous affiliations of Edward M. Ripley include China University of Geosciences (Beijing) & NASA Astrobiology Institute.
Topics: Sulfide, Olivine, Mafic, Ultramafic rock, Basalt


Papers
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Journal ArticleDOI
TL;DR: The importance of externally derived sulfur in the genesis of sulfide-rich, magmatic Ni-Cu-(platinum group element [PGE]) deposits remains a key, yet unresolved, issue as mentioned in this paper.
Abstract: The importance of externally derived sulfur in the genesis of sulfide-rich, magmatic Ni-Cu-(platinum group element [PGE]) deposits remains a key, yet unresolved, issue Calculations utilizing a variety of mafic magma types indicate that, in general, sulfide saturation by fractional crystallization occurs after Ni has been depleted due to olivine crystallization Cu- and PGE-rich layers may form during relatively later stages of closed-system crystallization, but unless the collection of the cotectic proportion of immiscible sulfide is extremely efficient, the mass of sulfide is too small to produce an economic deposit We show that there are numerous processes that may lead to early sulfide saturation in mafic/ultramafic magmas Contamination of mantle-derived magmas by siliceous country rocks or their partial melts will lower the sulfur content needed to induce sulfide liquid saturation, typically by amounts ranging from 200 to 700 ppm The mixing of magmas, particularly if the result is to lower the liquidus temperature of the mixed magma, may also lower the sulfur content needed to attain sulfide saturation by similar amounts An increase in magma fO2 related to the addition of volatiles such as H2O and CO2 is less effective in decreasing the sulfur concentration needed to achieve sulfide liquid saturation Contamination processes that lead to an increase in the activity of SiO2 in the melt, and hence may promote orthopyroxene rather than olivine crystallization, aid in generating relative Ni enrichment in remaining liquid as a result of the lower DNi (mineral – melt) value of orthopyroxene relative to olivine Although contamination and magma mixing may produce early sulfide saturation without the addition of externally derived sulfur, Ni-rich sulfide deposits can form in such cases only from large-volume, open systems, where the efficiency of sulfide collection is high No matter what the liquidus minerals may be, without the addition of country rock-derived sulfur, the mass of sulfide necessary to generate economic Ni-Cu-(PGE) concentrations requires efficient sulfide collection from large, but not necessarily unrealistic, volumes of magma Small deposits (4–30 Mt of sulfide) may form from the collection of cotectic proportions of sulfide from less than 50 km3 of magma Larger deposits such as those at Noril’sk could involve more than 200 km3 of magma; this volume of magma is not unreasonable, particularly in rift/plume-related settings Despite such possibilities, sulfur isotope data clearly indicate that externally derived sulfur has been involved in the formation of many large deposits, and that collection of mantle-derived sulfide in sufficient quantities to produce orebodies is a rare process We propose that magmatic Ni-Cu-(PGE) sulfide ore formation normally requires significant sulfide supersaturation, and that the addition of sulfur derived from xenoliths is the most viable mechanism for producing sulfide well above the cotectic proportion in mafic/ultramafic magmas

210 citations

Journal ArticleDOI
TL;DR: In this article, the authors developed an analytical model to predict the sulfur content of mafic magma at the time of sulfide saturation based on several sets of published experimental data.
Abstract: Empirical equations to predict the sulfur content of a mafic magma at the time of sulfide saturation have been developed based on several sets of published experimental data. The S content at sulfide saturation (SCSS) can be expressed as: $$\ln \,X_{\text S} = 1.229 - 0.74(10^4/T) - 0.021(P) - 0.311\,\ln \,X_{{\text{FeO}}} - 6.166X_{{\text{SiO}}_{\text{2}}} $$ $$ - 9.153X_{{\text{Na}}_{\text{2}} {\text{O + K}}_{\text{2}} {\text{O}}} - 1.914X_{{\text{MgO}}} + 6.594X_{{\text{FeO}}} $$ where T is in degrees Kelvin, X is mole fraction and P is in kbar. The squared multiple correlation coefficient (r 2) for the equation is 0.88. Application of the equation to data from sulfide-saturated mid-ocean ridge basalts (MORB) samples show that the SCSS is closely predicted for primitive MORBs, but that accuracy decreases for lower T (<1,130°C) and more evolved MORB samples. This suggests that because the calibrations are based on anhydrous experimental runs done at temperatures of 1,200°C and above, it is not possible to extrapolate them to significantly lower temperatures and hydrous conditions. Because the SCSS of a primitive MORB magma increases with decreasing P, sulfide saturation in MORB appears to be a function of the degree of en route assimilation of S from country rocks as well as the degree of fractional crystallization in shallow staging chambers. Application of the equation to the high-T impact melt sheet that produced the Sudbury Igneous Complex and associated Ni–Cu sulfide ores indicates that sulfide-saturation was reached at ~1,500°C, well above the start of orthopyroxene crystallization at ~1,190°C. This would permit ample time for the gravitational settling and collection of immiscible sulfide liquid that produced the high-grade ore bodies. The development of a platinum group element (PGE)-enriched layer in the Sonju Lake Intrusion of the Duluth Complex is thought to be due to the attainment of sulfide saturation in the magma after a period of fractional crystallization. Using the composition of the parent magma of the Sonju Lake Intrusion the presented equation indicates that sulfide saturation would have been reached at ~60% crystallization, when iron oxide was a liquidus mineral; the prediction is in agreement with field evidence which indicates that PGE-enrichment occurs in the oxide-rich gabbro zone. Contamination and mixing processes that may be related to the attainment of sulfide saturation in mafic magmas can also be evaluated. Mixing of a siliceous melt and a liquid of olivine tholeiite composition, similar to that thought to be a reasonable parental composition for many Duluth Complex intrusions, can induce sulfide saturation at mixing ratios in excess of ~0.1. If the contaminant contains low quantities of sulfur the mixing ratio required to promote saturation is reduced. Mixing of mafic magmas at various stages of fractionation is evaluated using magma compositions that are thought to be appropriate for the generation of the Merensky Reef in the Bushveld Complex. Magma mixing is shown to be an effective process for the attainment of sulfide saturation, depending strongly on the sulfur concentrations of the end-member magmas.

207 citations

Journal ArticleDOI
TL;DR: In this paper, an empirical equation for estimating sulfur content in silicate melts at anhydrite saturation based on available experimental results and an updated empirical equation was presented for estimating sulfide-liquid saturation by adding relevant experimental data.
Abstract: We present a new empirical equation for estimating sulfur content in silicate melts at anhydrite saturation based on available experimental results and an updated empirical equation for estimating sulfur content in silicate melts at sulfide-liquid saturation by adding relevant experimental data that were not previously used and excluding controversial experimental data. The fits of our empirical equations to the data used for calibration are within 10 percent error. Only total pressure, temperature, and silicate melt composition, parameters that are often known or can be reasonably assumed for natural magmatic systems, are required for utilization of the equations. The empirical equations are useful for petrologic modeling of natural magmatic systems, including magmatic hydrothermal ore deposits. Several example applications including the effect of decompression on sulfur content at sulfide-liquid saturation in komatiite and high Mg basaltic magmas and the ratio of silicate minerals to immiscible sulfide liquids during fractional crystallization of these magmas are provided.

177 citations

Journal ArticleDOI
01 Sep 2015-Lithos
TL;DR: In this paper, the accuracy of trace element discrimination diagrams for basalts using new datasets from two petrological databases, PetDB and GEOROC, was tested using both binary and ternary diagrams using Zr, Ti, V, Y, Th, Hf, Nb, Ta, Sm, and Sc.

160 citations

Journal ArticleDOI
TL;DR: The chromitite seams of the Nuasahi and Sukinda massifs are part of layered ultramafic bodies which occur within Archaean low-grade metamorphic rocks of the Iron Ore Group (IOG) in the Singhbhum Craton of the Indian Shield.

159 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the authors summarize knowledge of the behavior of elements in the subduction system and highlight the physical and chemical processes that have been invoked as being important in controlling the composition of volcanic arc magmas.
Abstract: Volcanic arc magmas can be defined tectonically as magmas erupting from volcanic edifices above subducting oceanic lithosphere. They form a coherent magma type, characterized compositionally by their enrichment in large ion lithophile (LlL) elements relative to high field strength (HFS) elements. In terms of process, the predominant view is that the vast majority of volcanic arc magmas originate by melting of the underlying mantle wedge, which contains a component of aqueous fluid and/or melt derived from the subducting plate. Recently, opinions have converged over the key aspects of the physical model for magma generation above subduction zones (Davies & Stevenson 1992), namely: 1. that the mantle wedge experiences subduction-induced corner flow (e.g. Spiegelman & MacKenzie 1987); 2. that the subduction component reaches the fusible part of the mantle wedge by the three-stage process of (i) metasomatism of mantle lithosphere, followed by (ii) aqueous fluid release due to breakdown of hydrous minerals at depth (e.g. Wyllie 1983, Tatsumi et al 1983) and (iii) aqueous fluid migration, followed by hydrous melt migration, to the site of melting; 3. that slab-induced flow may be locally reversed beneath the arc itself, allowing mantle decompression to contribute to melt generation (e.g. Ida 1983). The simplified model in Figure 1 highlights the physical and chemical processes that have been invoked as being important in controlling the composition of volcanic arc magmas. Magma compositions (coupled with experimental data on element behavior) can help us gain further understanding of these physical and chemical processes. In this review, we first summarize knowledge of the behavior of elements in the subduction system. We then focus on compositional evidence for the processes illustrated in Figure 1, which we group as follows: 1. derivation of the subduction component, 2. transport of the subduction component to the melting column, 3. depletion and enrichment of the mantle wedge, and 4. processes in the melting column.

2,374 citations

Journal ArticleDOI
TL;DR: The average chemical composition of the upper continental crust (UC) as a function of age is estimated from chemical analyses, geologic maps, stratigraphic sections and isotopic ages as discussed by the authors.

1,916 citations

Journal ArticleDOI
31 Mar 2005-Nature
TL;DR: Modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from a deep olivine-bearing source, and the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plumes edge.
Abstract: More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations.

966 citations

Journal ArticleDOI
TL;DR: In this paper, an up-to-date along-strike synthesis of the Tianshan orogenic collage and a new tectonic model to explain its accretionary evolution is provided.

837 citations

Journal ArticleDOI
TL;DR: Sulfur isotope geochemistry has a long history of application to the study of sulfide-bearing mineral deposits as discussed by the authors, with a particular emphasis on high-temperature processes.
Abstract: Sulfur, the 10th most abundant element in the universe and the 14th most abundant element in the Earth’s crust, is the defining element of sulfide minerals and provides insights into the origins of these minerals through its stable isotopes. The insights come from variations in the isotopic composition of sulfide minerals and related compounds such as sulfate minerals or aqueous sulfur species, caused by preferential partitioning of isotopes among sulfur-bearing phases, known as fractionation. These variations arise from differences in temperature, or more importantly, oxidation and reduction reactions acting upon the sulfur. The oxidation and reduction reactions can occur at high temperature, such as in igneous systems, at intermediate temperatures, such as in hydrothermal systems, and at low temperature during sedimentary diagenesis. At high temperatures, the reactions tend to occur under equilibrium conditions, whereas at low temperatures, disequilibrium is prevalent. In addition, upper atmospheric processes also lead to isotopic fractionations that locally appear in the geologic record. Sulfur isotope geochemistry as a subdiscipline of the geological sciences began in the late 1940s and early 1950s with early publications by Thode et al. (1949) and Szabo et al. (1950) on natural variations of sulfur isotopes, and Macnamara and Thode (1950) on the isotopic composition of terrestrial and meteoritic sulfur. Sakai (1957) presented an early scientific summary of sulfur isotope geochemistry, with a particular emphasis on high-temperature processes. Thode et al. (1961) also presented an early summary, but with an emphasis on low-temperature processes. Both of these summaries outlined salient aspects of the global sulfur cycle. Sulfur isotope geochemistry understandably has had a long history of application to the study of sulfide-bearing mineral deposits. Early noteworthy papers include those by Kulp et al. (1956) and Jensen (1957, 1959). Similarly, there is also a legacy of contributions to understanding …

780 citations