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Alan E. Boudreau

Alan E. Boudreau

Professor Emeritus of Geology
Earth and Climate Sciences
Box 90328, Durham, NC 27708
9 Circuit Drive, 3101 Grainger Hall, Durham, NC 27708

Selected Publications

The role of hydrothermal processes and the formation of the J-M reef and associated rocks of olivine-bearing zone I of the Stillwater Complex, Montana

Journal Article Mineralium Deposita · March 1, 2025 Several lines of evidence, including hydrous melt inclusions and unusually Cl-rich apatite, have been used to suggest that the reappearance of olivine and PGE-sulfide of the J-M Reef in the Stillwater Complex, Montana, is due to fluid infiltration and hydr ... Full text Cite

Investigating the Influence of Crustal Contamination on the Stillwater Complex, Montana Using Sr, Nd, and Pb Isotopes

Journal Article Journal of Petrology · April 1, 2024 The presence of pegmatoid bodies in the Stillwater Complex is poorly understood, but they have been suggested to have resulted from the presence of fluids in the complex. To better understand the origin of the pegmatoids and to trace the possible influence ... Full text Cite

Testing the hypothesis that simulated melting can identify evolving liquid compositions and crystallization models at the Stillwater Complex, Montana, USA

Journal Article Contributions to Mineralogy and Petrology · March 1, 2023 Layered intrusions present a number of problems in understanding how they crystallized, including identification of parental magma and the effect of trapped liquid on modifying the original mineral assemblage. This work explores how simulated remelting of ... Full text Cite

Magmatic volatiles and platinum-group element mineralization in the Stillwater layered intrusion, U.S.A

Journal Article American Mineralogist · May 1, 2022 The activity of volatile-rich fluids may be important in the evolution of basaltic magmatic systems and associated precious metal ore formation. There is evidence for Cl-rich fluids within the Stillwater Complex (Montana, U.S.A.), which have been linked to ... Full text Cite

Formation of Chromitite Seams and Associated Anorthosites in Layered Intrusion by Reactive Volatile-rich Fluid Infiltration

Journal Article Journal of Petrology · February 1, 2021 Drilling related to development of the platinum-group element deposit of the J-M Reef of the Stillwater Complex returned samples of a rare chromitite seam between anorthosite and norite in a discordant anorthositic body. Plagioclase core An concentrations ... Full text Cite

Crustal fluid contamination in the Bushveld Complex, South Africa: An analogue for subduction zone fluid migration

Journal Article International Geology Review · January 1, 2021 Crystallization of the 2.06 Ga Bushveld magma formed a 9 km (maximum) sequence of ultramafic and mafic rocks that generated a large volume of country fluid as it thermally metamorphosed a 3+ km section of previously unaltered underlying sedimentary rocks o ... Full text Cite

Reply to discussion of ‘Crustal fluid contamination in the Bushveld Complex, South Africa: an analogue for subduction zone fluid migration’ by Roger Scoon and Andrew Mitchell (2020)

Journal Article International Geology Review · January 1, 2021 In their discussion of our recent publication, Scoon and Mitchell (2020) put forward a number of arguments against the hydromagmatic model of Bushveld Complex formation that we present. Their criticisms of our model focus primarily on the formation mechani ... Full text Cite

Sulfides, native metals, and associated trace minerals of the Skaergaard intrusion, Greenland: evidence for late hydrothermal fluids

Journal Article Mineralium Deposita · August 1, 2020 Sulfide assemblages, precious metals, transition metal alloys, and associated accessory phases were characterized throughout the Skaergaard intrusion to better constrain the sulfide saturation history of the intrusion and the role of late magmatic volatile ... Full text Cite

The influence of the thick banded series anorthosites on the crystallization of the surrounding rock of the Stillwater Complex, Montana

Journal Article Contributions to Mineralogy and Petrology · December 1, 2019 The Banded Series of the Archean-aged Stillwater Complex contains three thick anorthosites overlain by olivine-bearing rocks with apparently different crystallization sequence in that orthopyroxene appears late, if at all, as compared with that of the Ultr ... Full text Cite

Silica accumulation rates for siliceous sinter at Orakei Korako geothermal field, Taupo Volcanic Zone, New Zealand

Journal Article Geothermics · March 1, 2019 The rate of silica accumulation on glass slides over 895 days (2 years 5 months and 12 days) was determined using in-situ experiments in the discharge channel of Map of Australia hot pool, located at Orakei Korako, Taupo Volcanic Zone (TVZ), New Zealand. T ... Full text Cite

Vapor transport of silver and gold in basaltic lava flows

Journal Article Geology · January 1, 2019 We documented occurrences of native copper (Cu), silver (Ag), and gold (Au) in a pāhoehoe flow from Kīlauea volcano (Hawaii, USA), an ā flow from Mauna Loa volcano (Hawaii), and a mid-oceanic-ridge basalt (MORB) from the Chile Ridge (southeastern Pacific O ... Full text Cite

Hydromagmatic processes and platinum-group element deposits in layered intrusions

Book · January 1, 2019 The role of hydrothermal fluids during the crystallization of layered intrusions and the ore deposits they contain has long been debated. This book summarizes the evidence for fluid-crystal-liquid (hydromagmatic) interactions and their importance for the u ... Full text Cite

The origin of high-Cu/S sulfides by shallow-level degassing in the Skaergaard intrusion, East Greenland

Journal Article Geology · December 1, 2017 The Skaergaard intrusion of East Greenland is characterized by unusually low sulfur (S) and high metal/S ratios. Explanations range from S lost during cooling to suggestions that low S was characteristic of the original magma. A nonequilibrium thermodynami ... Full text Cite

A PERSONAL PERSPECTIVE ON LAYERED INTRUSIONS

Journal Article Elements · December 1, 2017 Full text Cite

A study of the trace sulfide mineral assemblages in the Stillwater Complex, Montana, USA

Journal Article Mineralium Deposita · March 1, 2017 The sulfide assemblages of the Stillwater Complex away from the well-studied ore zones are composed mainly of variable proportions of pyrrhotite, chalcopyrite, pentlandite, and ±pyrite. Excluding vein assemblages and those affected by greenschist and lower ... Full text Cite

The Stillwater Complex, Montana - Overview and the significance of volatiles

Journal Article Mineralogical Magazine · June 1, 2016 The geology of the 2.7 Ga Stillwater Complex in South-Central Montana is reviewed with a focus on the role of volatiles in locally modifying both the crystallization sequence of the evolving parent magma and the initially precipitated solid assemblages to ... Full text Cite

Bubble migration in a compacting crystal-liquid mush

Journal Article Contributions to Mineralogy and Petrology · April 1, 2016 Recent theoretical models have suggested that bubbles are unlikely to undergo significant migration in a compaction crystal mush by capillary invasion while the system remains partly molten. To test this, experiments of bubble migration during compaction i ... Full text Cite

The Lac Des Iles Palladium Deposit, Ontario, Canada. Part II. Halogen variations in apatite

Journal Article Mineralium Deposita · March 1, 2015 Analysis of apatite from the Mine Block Intrusion (MBI) of the Lac des Iles Igneous Complex shows two pronounced trends in the halogens. Apatite from relatively fresh norite and melanorites from the Pd-sulfide zone contain up to 57 mol% chlorapatite endmem ... Full text Cite

Igneous Layering in Basaltic Magma Chambers

Chapter · January 1, 2015 Layering is a common feature in mafic and ultramafic layered intrusions and generally consists of a succession of layers characterized by contrasted mineral modes and/or mineral textures, including grain size and orientation and, locally, changing mineral ... Full text Cite

The Lac Des Iles Palladium Deposit, Ontario, Canada part I. The effect of variable alteration on the Offset Zone

Journal Article Mineralium Deposita · January 1, 2014 The recently discovered Offset Zone of the Mine Block Intrusion of the Lac des Iles Complex hosts palladium mineralization with unusually high Pd/Pt and Pd/Ir ratios in rocks that range from relatively unaltered norite to amphibolites and chlorite-actinoli ... Full text Cite

High-temperature carbonate minerals in the Stillwater Complex, Montana, USA

Journal Article Contributions to Mineralogy and Petrology · October 1, 2013 High-temperature carbonate minerals have been observed in association with sulfide minerals below the platiniferous Johns-Manville (J-M) reef of the Stillwater Complex in a stratigraphic section that has been previously shown to be characterized by unusual ... Full text Cite

Sulfide-associated mineral assemblages in the Bushveld Complex, South Africa: Platinum-group element enrichment by vapor refining by chloride-carbonate fluids

Journal Article Mineralium Deposita · February 1, 2013 The petrology of base metal sulfides and associated accessory minerals in rocks away from economically significant ore zones such as the Merensky Reef of the Bushveld Complex has previously received only scant attention, yet this information is critical in ... Full text Cite

The growth of siliceous sinter deposits around high-temperature eruptive hot springs

Journal Article Journal of Volcanology and Geothermal Research · December 1, 2012 Siliceous hot spring deposits (sinter) are of interest as they are indicative of hydrothermal resources at depth and may provide evidence for early life on Earth and possibly Mars. Numeric models of concurrent evaporation and opal-A precipitation around hi ... Full text Cite

Sr and Pb isotopic disequilibrium between coexisting plagioclase and orthopyroxene in the Bushveld Complex, South Africa: Microdrilling and progressive leaching evidence for sub-liquidus contamination within a crystal mush

Journal Article Contributions to Mineralogy and Petrology · April 1, 2012 Progressive leaching of plagioclase for Sr isotopes and microdrilling for Sr and Pb isotopes from grains of plagioclase and orthopyroxene from the Critical Zone and the Lower Zone indicates that these minerals are not in isotopic equilibrium. Leaching sugg ... Full text Cite

Metamorphism of thought about igneous rock textures

Journal Article International Geology Review · February 1, 2011 Full text Cite

The evolution of texture and layering in layered intrusions

Journal Article International Geology Review · February 1, 2011 Mineral segregation in igneous systems, and igneous layering in particular, can occur during ageing of crystal assemblages because areas composed of nominally larger grains or texturally favoured regions grow at the expense of adjacent unfavoured regions o ... Full text Cite

Sulfide minerals in the Bushveld Complex, South Africa

Journal Article Mineralium Deposita · 2010 Cite

Chemical and isotopic fractionation of wet andesite in a temperature gradient: Experiments and models suggesting a new mechanism of magma differentiation

Journal Article Geochimica et Cosmochimica Acta · February 1, 2009 Piston-cylinder experiments were conducted to investigate the behavior of partially molten wet andesite held within an imposed temperature gradient at 0.5 GPa. In one experiment, homogenous andesite powder (USGS rock standard AGV-1) with 4 wt.% H2O was sea ... Full text Cite

Modeling the merensky reef, bushveld complex, republic of South Africa

Journal Article Contributions to Mineralogy and Petrology · March 18, 2008 The Merensky pegmatoid (normal reef) in the western Bushveld Complex is commonly characterized as a pyroxene-rich pegmatoidal unit with a base that is enriched in chromite and platinum-group element-bearing sulfides overlying a leuconorite footwall. Models ... Full text Cite

Modeling mass transport in the Merensky Reef, Bushveld Complex, South Africa

Journal Article Contributions to Mineralogy and Petrology · 2008 The Merensky pegmatoid (normal reef) in the western Bushveld Complex is commonly characterized as a pyroxene-rich pegmatoidal unit with a base that is enriched in chromite and platinum-group element–bearing sulfides overlying a leuconorite footwall. Model ... Cite

Crystallization and Degassing in the Basement Sill, McMurdo Dry Valleys, Antarctica

Journal Article Journal of Petrology · July 1, 2007 The Basement Sill is part of the Ferrar Large Igneous Province exposed in the McMurdo Dry Valleys, Antarctica. The sill is ∼330 m thick in the Bull Pass area and 450 + m thick in the Dais area, ∼12 km to the west, and is characterized by phenocryst-free lo ... Full text Cite

Textures of orthopyroxenites from the Burgersfort bulge of the eastern Bushveld Complex, Republic of South Africa

Journal Article Contributions to Mineralogy and Petrology · April 1, 2006 A suite of 30 samples was collected from the Burgersfort bulge area of the eastern Bushveld Complex for a detailed quantitative textural study. The studied section represents a stratigraphic column approximately 1,000 m thick, of mainly orthopyroxenites fr ... Full text Cite

Diffusion-reaction in a thermal gradient: Implications for the genesis of anorthitic plagioclase, high alumina basalt and igneous mineral layering

Journal Article Earth and Planetary Science Letters · September 15, 2005 Piston-cylinder experiments investigating the interaction between basaltic andesite melt and partially molten gabbro in a thermal gradient provide insight into melt-rock reaction processes occurring during magma differentiation in the crust. In two experim ... Full text Cite

Modeling C-O-H-S fluids and sulfides in igneous systems

Conference GEOCHIMICA ET COSMOCHIMICA ACTA · May 1, 2005 Link to item Cite

Halogen variations in the Paleoproterozoic layered mafic-ultramafic intrusions of East Kimberley, Western Australia: Implications for platinum group element mineralization

Journal Article Economic Geology · August 1, 2004 A number of Paleoproterozoic layered mafic-ultramafic intrusions in the central part of the Halls Creek orogen of East Kimberley, Western Australia, have been explored for platinum group elements, chromium, nickel, copper, cobalt, and gold. Here we report ... Full text Cite

The Lower Zone-Critical Zone transition of the Bushveld Complex: A quantitative textural study

Journal Article Journal of Petrology · June 1, 2004 The Lower Zone-Critical Zone boundary of the Bushveld Complex is an intrusion-wide, major stratigraphic transition from ultramafic harzburgite and pyroxenite in the Lower Zone to increasingly phagioclase-rich pyroxenites and norites in the Critical Zone. Q ... Full text Cite

PALLADIUM, a program to model the chromatographic separation of the platinum-group elements, base metals and sulfur in a solidifying pile of igneous crystals

Journal Article Canadian Mineralogist · January 1, 2004 The formation of platinum-group-element (PGE) deposits in layered intrusions involves an interplay of sulfide saturation and modifications that might be caused by migrating silicate liquida and volatile fluid. The program PALLADIUM has been written to illu ... Full text Cite

IRIDIUM - A program to model reaction of silicate liquid infiltrating a porous solid assemblage

Journal Article Computers and Geosciences · May 1, 2003 The migration of silicate liquid through porous rock can give rise to compositional changes in both the liquid and the host solid assemblage that are important in a number of fields of igneous petrology. Ongoing studies in numerical models of crystallizati ... Full text Cite

Fluid overpressure in layered intrusions: Formation of a breccia pipe in the Eastern Bushveld Complex, Republic of South Africa

Journal Article Mineralium Deposita · January 1, 2003 Fluids and volatile fluid overpressures in layered intrusions are becoming recognized as having important functions in magma chamber processes for the formation of magmatic structures and for the movement and concentration of economically important ore ele ... Full text Cite

Halogens of Bushveld Complex, South Africa: δ37Cl and Cl/F evidence for hydration melting of the source region in a back-arc setting

Journal Article Chemical Geology · March 21, 2002 The Bushveld Complex is one of only a few layered intrusions anomalously enriched in chlorine. This study presents the first chlorine stable isotope analyses of Bushveld and associated rocks designed to constrain the source of Bushveld Cl. Most samples ove ... Full text Cite

Quantitative modeling of compaction in the Holyoke flood basalt flow, Hartford Basin, Connecticut

Journal Article Contributions to Mineralogy and Petrology · January 1, 2002 Compaction in the Holyoke flood-basalt flow is modeled using a quantitative phase equilibrium routine based on the MELTS algorithm that is coupled with compaction-driven heat and mass transport equations. For a crystal-liquid mush that is cooling from both ... Full text Cite

The halogen geochemistry of the Bushveld Complex, Republic of South Africa: Implications for chalcophile element distribution in the Lower and Critical Zones

Journal Article Journal of Petrology · January 1, 2000 Halogen-bearing minerals, especially apatite, are minor but ubiquitous phases throughout the Bushveld Complex. Interstitial apatite is near end-member chlorapatite below the Merensky reef (Lower and Critical Zones) and has increasingly fluorian composition ... Full text Cite

Metal redistribution during fluid exsolution and migration in the middle banded series of the Stillwater Complex, Montana

Journal Article Lithos · June 1, 1999 Olivine-bearing zones III and IV (OB-III and -IV) of the Stillwater Complex, MT preserve evidence of fluid migration particularly in the variation of apatite compositions. This feature, coupled with the lack of evidence of the addition of substantial amoun ... Full text Cite

PELE - A version of the MELTS software program for the PC platform

Journal Article Computers and Geosciences · 1999 Cite

Fluid fluxing of cumulates: The J-M reef and associated rocks of the stillwater complex, Montana

Journal Article Journal of Petrology · January 1, 1999 Olivine-Bearing zone I (OB I) is host to the principal platinum-group element deposit of the Stillwater complex, the J-M reef. OB I is characterized by a lower Troctolite subzone composed of troctolite, dunite, gabbronorite and anorthosite, and an overlyin ... Full text Cite

Chromatographic separation of the platinum-group elements, gold, base metals and sulfur during degassing of a compacting and solidifying igneous crystal pile

Journal Article Contributions to Mineralogy and Petrology · January 1, 1999 The major platinum-group elements (PGE) concentrations in layered intrusions are typically associated with zones in which the sulfide abundance begins to increase. In a number of layered intrusions, there is also a distinct stratigraphic separation in the ... Full text Cite

PELE-a version of the MELTS software program for the PC platform

Journal Article Computers and Geosciences · January 1, 1999 Full text Cite

Compaction of igneous cumulates part I: Geochemical consequences for cumulates and liquid fractionation trends1

Journal Article Journal of Geology · January 1, 1998 The importance of crystallization during compaction of an 800 m section of cumulates in Olivine-bearing zones III and IV of the Stillwater complex is assessed using whole-rock and mineral compositions. Two sets of calculations provide estimates for the liq ... Full text Cite

Compaction of igneous cumulates part II: Compaction and the development of igneous foliations1

Journal Article Journal of Geology · January 1, 1998 Quantitative petrofabric analysis of 66 samples from olivine-bearing zones III and IV of the Middle Banded series of the Stillwater complex, Montana, was conducted to allow direct comparison among textural and chemical variations. Systematic variations in ... Full text Cite

Discordant bodies from olivine-bearing zones III and IV of the Stillwater Complex, Montana - evidence for postcumulus fluid migration and reaction in layered intrusions

Journal Article Contributions to Mineralogy and Petrology · December 1, 1997 Mineralogically zoned and unzoned discordant bodies composed predominantly of plagioclase with up to 35% olivine, occur at three different levels in Olivine-Bearing zones III and IV of the Middle Banded series of the Stillwater complex. The discordant bodi ... Full text Cite

Stable Cl isotopes and origin of high-Cl magmas of the Stillwater Complex, Montana

Journal Article Geology · September 1, 1997 The first Cl isotopic determinations on biotite from the Ultramafic series and from the J-M reef of the Lower Banded series of the Stillwater Complex, Montana, have δ 37 Cl values (normalized to seawater, 95% confidence limit error is 0.2‰) ranging from 0. ... Full text Cite

Stable Cl isotopes and origin of high-Cl magmas of the Stillwater Complex, Montana

Journal Article Geology · January 1, 1997 The first Cl isotopic determinations on biotite from the Ultramafic series and from the J-M reef of the Lower Banded series of the Stillwater Complex, Montana, have δ37Cl values (normalized to seawater, 95% confidence limit error is 0.2‰) ranging from 0.27 ... Full text Cite

The Skaergaard layered series. Part III. Non-dynamic layering

Journal Article Journal of Petrology · January 1, 1997 Layering in the Skaergaard Intrusion has been divided into two general types, one produced by magmatic flow and another by processes resulting from variations of rates of nucleation and crystallization, and, in the case of the Layered Sereis, by compaction ... Full text Cite

Petrology and mineral compositions of the Middle Banded series of the Stillwater Complex, Montana

Journal Article Journal of Petrology · January 1, 1996 The two olivine-bearing zones of the Middle Banded series of the Stillwater Complex are characterized by an increase in the number of cumulus minerals with height. In each, anorthosite and anorthositic troctolite dominate the lower part whereas olishy; vin ... Full text Cite

A reevaluation of crystal-size distributions in chromite cumulates

Journal Article American Mineralogist · January 1, 1996 Although studies have shown that igneous cumulates can form by in situ crystallization without requiring crystal settling, it has not been demonstrated that crystal-size distributions (CSDs) are consistent with such a process. Plots of crystal-size fractio ... Full text Cite

An evaluation of models of apatite compositional variability using apatite from the Middle Banded series of the Stillwater Complex, Montana

Journal Article Contributions to Mineralogy and Petrology · January 1, 1996 Apatite is a relatively common accessory mineral in the olivine-bearing zones (OB-III and OB-IV) of the Middle Banded series of the Stillwater complex, occurring interstitial to cumulus grains, as monomineralic inclusions in cumulus grains, and in polymine ... Full text Cite

Compaction of density-stratified cumulates: Effect on trapped-liquid distribution

Journal Article Journal of Geology · January 1, 1996 Igneous rocks formed by the accumulation of crystals from a cooling magma body compose a significant fraction of both the terrestrial oceanic crust and the lunar crust and mantle. Here we report the results of numerical simulations of compaction of accumul ... Full text Cite

Halogen geochemistry of the Great Dyke, Zimbabwe

Journal Article Contributions to Mineralogy and Petrology · December 1, 1995 Apatite from the Great Dyke of Zimbabwe is relatively rich in the hydroxy-fluorapatite end-members. The mole fraction of fluorapatite increases from approximately 40% in cumulates of the Ultramafic Sequence to over 60% in a sample near the top of the expos ... Full text Cite

Crystal aging and the formation of fine-scale igneous layering

Journal Article Mineralogy and Petrology · March 1, 1995 Fine-scale layering in igneous intrusions shows parallels with experimentally produced banding observed in crystallizing salt solutions in which recent advances have demonstrated the importance of crystal aging on the development of banding. These experime ... Full text Cite

Some geochemical considerations for platinum-group-element exploration in layered intrusions

Journal Article Exploration & Mining Geology · January 1, 1995 It has long been recognized that platinum-group-element (PGE) deposits in layered intrusions preferentially occur in intrusions that crystallized from high-Mg parent magmas. Recent studies suggest that evaluation of any given intrusion for economic PGE pot ... Cite

Compositions of pegmatoids beneath the J-M Reef of the Stillwater Complex, Montana, U.S.A.

Journal Article Chemical Geology · April 1, 1994 Pegmatoids sporadically occur in the cumulates of the Ultramafic series and Norite zone I and Gabbronorite zone I the Lower Banded series below the level of the platiniferous J-M Reef of the Stillwater Complex, but are less common in Norite zone II and Gab ... Full text Cite

Mineral segregation during crystal aging in two-crystal, two- component systems

Journal Article South African Journal of Geology · January 1, 1994 Mineral segregation can occur during aging of crystal assemblages as areas composed of nominally larger grains grow at the expense of nearby, smaller grains owing to solution concentration variations that arise from surface energy effects. The "competitive ... Cite

Variation in the composition of apatite in the Munni Munni Complex and associated intrusions of the West Pilbara Block, Western Australia

Journal Article Geochimica et Cosmochimica Acta · January 1, 1993 Apatite is a ubiquitous intercumulus mineral in the Archean Munni Munni, Radio Hill, and Mount Sholl layered igneous complexes of the west Pilbara Block in Western Australia. Apatite compositions from the three intrusions are relatively rich in the fluorap ... Full text Cite

Chlorine as an exploration guide for the platinum-group elements in layered intrusions

Journal Article Journal of Geochemical Exploration · January 1, 1993 Recent theoretical and experimental work has suggested that Cl may be important for the transport of the platinum-group elements (PGE). A survey of the halogen geochemistry of apatite in layered intrusions, including new data from four intrusions from the ... Full text Cite

Concentration of platinum-group elements by magmatic fluids in layered intrusions

Journal Article Economic Geology · January 1, 1992 Evidence leading to a model which supports the formation of Pt-Pd reefs in a layered intrusion by the action of magmatic fluids is presented, as well as some of the constraints imposed on such a model. The Stillwater Complex is used as an example of this m ... Full text Cite

Infiltration metasomatism in layered intrusions - An example from the Stillwater Complex, Montana

Journal Article Journal of Volcanology and Geothermal Research · January 1, 1992 The contact between Anorthosite zone II (AN II) and the overlying troctolite of Olivine-Bearing zone V (OB V) of the Stillwater Complex is characterized by a 5-m-thick, adcumulate anorthosite. This adcumulate anorthosite separates rocks of AN II, character ... Full text Cite

Volatile fluid overpressure in layered intrusions and the formation of potholes

Journal Article Australian Journal of Earth Sciences · January 1, 1992 Potholes that develop in layered intrusions show morphologic similarities with sedimentary features known as pockmarks. By analogy with pockmark formation theory, it is suggested that the cumulate section below the pothole region develops significant overp ... Full text Cite

Spontaneous development of concentric layering in a solidified siliceous dike, East Greenland

Journal Article Earth Science Reviews · January 1, 1990 A meter-wide rhyolitic dike near the eastern margin of the Skaergaard Intrusion developed fine concentric layering in a small section where a fault appears to have fractured the dike and enhanced its interaction with meteoric water. Layers two or three mil ... Full text Cite

Low temperature alteration of REE-rich chlorapatite from the Stillwater Complex, Montana

Journal Article American Mineralogist · January 1, 1990 Chlorapatite is associated with coarse-grained olivine-rich rocks that host platinum-group element-bearing sulfide mineralization of the J-M Reef of the Stillwater Complex. The chlorapatite may contain in excess of 2 wt% of rare-earth elements (REE). The h ... Cite

Variation in the composition of apatite through the Merensky cyclic unit in the western Bushveld Complex

Journal Article Economic Geology · January 1, 1990 Microprobe analysis of interstitial apatite from a 100-m section through the Merensky reef of the Bushveld Complex reveals that this stratigraphic section marks a transition from Cl-rich to more F-rich compositions in the Critical and Main zones, respectiv ... Full text Cite

Investigations of the Stillwater Complex: Part V. Apatites as indicators of evolving fluid composition

Journal Article Contributions to Mineralogy and Petrology · June 1, 1989 Variations in the F, Cl and OH contents of apatite are not constrained by crystal-chemical factors (in contrast to micas and amphiboles), and thus changes in the abundance of these components provide an indicator of halogen fugacity variations and insights ... Full text Cite

Carbon distribution in the stiliwater complex and evolution of vapor during crystallization of stillwater and bushveld magmas

Journal Article Journal of Petrology · February 1, 1989 The occurrence and distribution of carbon in the Stillwater Complex have been investigated. In mineralized troctolite and associated rocks of olivine-bearing zone I (OB I), carbon is present as graphitic material and calcite. The assemblage forsterite-anti ... Full text Cite

Investigations of the Stillwater Complex: III. The Picket Pin Pt/Pd deposit ( Montana, USA).

Journal Article Economic Geology · December 1, 1986 The Picket Pin Pt/Pd deposit is a zone of disseminated, Pt-group element-bearing sulfide which occurs in the upper 150 m of Anorthosite subzone II (AN II), the thickest anorthosite member (c 600 m) of the Stillwater Complex. The sulfide zone is strata boun ... Full text Cite

Halogen geochemistry of the stillwater and bushveld complexes: Evidence for transport of the platinum-group elements by Cl-rich fluids

Journal Article Journal of Petrology · August 1, 1986 Compositional data on apatite, phlogopite, and amphibole indicate that the high-temperature hydrothermal fluids which affected the lower portions of the Stillwater and Bushveld Complexes were Cl-rich. Apatites from the platinum-group element (PGE) ore zone ... Full text Cite

Pattern formation during crystallization and the formation of fine-scale layering.

Journal Article Origins of igneous layering · January 1, 1986 Fine-scale layering is characterized by the laminar segregation of mineral phases on a mm to cm scale. Where best developed, it is found in specific associations within the Stillwater Complex. In the Banded series, layer spacing is proportional to crystal ... Cite

Investigations of the Howland reef of the Stillwater complex, Minneapolis Adit area: stratigraphy, structure and mineralization.

Journal Article Economic Geology · January 1, 1982 The zone of Pt concentration in the layered Archaean tholeiitic intrusion coincides with the reappearance of olivine. Variable proportions of olivine, bronzite, plagioclase and augite occur, along with phlogopite, hornblende, apatite, sulphides and chrome ... Full text Cite