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Noble and base metal distribution and processes affecting ore tenors in the disrupted lower stratigraphy of the Stillwater Complex, USA.

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Title: Noble and base metal distribution and processes affecting ore tenors in the disrupted lower stratigraphy of the Stillwater Complex, USA.
Authors: Andersen, Allen K.1 (AUTHOR) akandersen@usgs.gov, Jenkins, M. Christopher1 (AUTHOR)
Source: Mineralium Deposita. Mar2026, Vol. 61 Issue 3, p747-774. 28p.
Subject Terms: *Platinum group, *Sulfide minerals, *Metals, *Industrial metals, *Igneous intrusions, *Precious metals, *Hydrothermal alteration
Abstract: Exploration continues for contact-style Ni-Cu sulfide and chromitite-associated PGE mineralization in ultramafic rocks of the Stillwater Complex. At the Iron and Chrome Mountain areas, massive sulfides occur along the complex's footwall contact and anomalous concentrations of PGE+Au are associated with the three lowermost chromitite seams. Southeast of Chrome Mountain, magmatic layering is highly disrupted by the presence of faults, magmatic breccias, serpentinized discordant dunites, pyroxenite pegmatoids, and disaggregated chromitite seams. The bulk rock chemistry, sulfide chemistry, and noble metal mineralogy of samples from this area were examined to determine the deportment of PGE and processes that led to enrichments in PGE, Au, Cu, Co and Ni. Results show that a sulfide liquid was the principal collector of PGE. If sulfide liquid was initially deposited with chromite, it was disaggregated or redistributed by subsequent melt or fluid infiltration, which may have resulted in the offset of peak PGE(+Cu, Ni) from peak Cr2O3 concentrations, and upgraded PGE tenors. Upon cooling, PGE exsolved from sulfides to form discrete bismuth tellurides, arsenides, arsenic sulfides, antimonides, and alloys, commonly along the margins of sulfide globules. Calculated metal tenors are highest in the disseminated sulfides southwest of Chrome Mountain, whereas massive and net-textured sulfides near the Iron Mountain-Camp zone represent monosulfide solid solution cumulates. At progressively shallower levels, higher metal tenors combined with lower S/Se ratios are consistent with increasing R-factors from 100 to 100,000. Serpentinization and talc-tremolite alteration resulted in S loss through partial replacement of sulfides by secondary silicate+carbonate+magnetite+sulfide assemblages, further upgrading Ni-Cu-PGE tenors. The present work shows that processes responsible for the disruption of magmatic layering and post-magmatic fluid alteration along the intrusion's lower contact led to noble and base metal enrichments. [ABSTRACT FROM AUTHOR]
Database: Energy & Power Source
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Header DbId: enr
DbLabel: Energy & Power Source
An: 191694289
AccessLevel: 6
PubType: Academic Journal
PubTypeId: academicJournal
PreciseRelevancyScore: 0
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  Label: Title
  Group: Ti
  Data: Noble and base metal distribution and processes affecting ore tenors in the disrupted lower stratigraphy of the Stillwater Complex, USA.
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  Data: <searchLink fieldCode="AR" term="%22Andersen%2C+Allen+K%2E%22">Andersen, Allen K.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> akandersen@usgs.gov</i><br /><searchLink fieldCode="AR" term="%22Jenkins%2C+M%2E+Christopher%22">Jenkins, M. Christopher</searchLink><relatesTo>1</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Mineralium+Deposita%22">Mineralium Deposita</searchLink>. Mar2026, Vol. 61 Issue 3, p747-774. 28p.
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  Label: Subject Terms
  Group: Su
  Data: *<searchLink fieldCode="DE" term="%22Platinum+group%22">Platinum group</searchLink><br />*<searchLink fieldCode="DE" term="%22Sulfide+minerals%22">Sulfide minerals</searchLink><br />*<searchLink fieldCode="DE" term="%22Metals%22">Metals</searchLink><br />*<searchLink fieldCode="DE" term="%22Industrial+metals%22">Industrial metals</searchLink><br />*<searchLink fieldCode="DE" term="%22Igneous+intrusions%22">Igneous intrusions</searchLink><br />*<searchLink fieldCode="DE" term="%22Precious+metals%22">Precious metals</searchLink><br />*<searchLink fieldCode="DE" term="%22Hydrothermal+alteration%22">Hydrothermal alteration</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Exploration continues for contact-style Ni-Cu sulfide and chromitite-associated PGE mineralization in ultramafic rocks of the Stillwater Complex. At the Iron and Chrome Mountain areas, massive sulfides occur along the complex's footwall contact and anomalous concentrations of PGE+Au are associated with the three lowermost chromitite seams. Southeast of Chrome Mountain, magmatic layering is highly disrupted by the presence of faults, magmatic breccias, serpentinized discordant dunites, pyroxenite pegmatoids, and disaggregated chromitite seams. The bulk rock chemistry, sulfide chemistry, and noble metal mineralogy of samples from this area were examined to determine the deportment of PGE and processes that led to enrichments in PGE, Au, Cu, Co and Ni. Results show that a sulfide liquid was the principal collector of PGE. If sulfide liquid was initially deposited with chromite, it was disaggregated or redistributed by subsequent melt or fluid infiltration, which may have resulted in the offset of peak PGE(+Cu, Ni) from peak Cr2O3 concentrations, and upgraded PGE tenors. Upon cooling, PGE exsolved from sulfides to form discrete bismuth tellurides, arsenides, arsenic sulfides, antimonides, and alloys, commonly along the margins of sulfide globules. Calculated metal tenors are highest in the disseminated sulfides southwest of Chrome Mountain, whereas massive and net-textured sulfides near the Iron Mountain-Camp zone represent monosulfide solid solution cumulates. At progressively shallower levels, higher metal tenors combined with lower S/Se ratios are consistent with increasing R-factors from 100 to 100,000. Serpentinization and talc-tremolite alteration resulted in S loss through partial replacement of sulfides by secondary silicate+carbonate+magnetite+sulfide assemblages, further upgrading Ni-Cu-PGE tenors. The present work shows that processes responsible for the disruption of magmatic layering and post-magmatic fluid alteration along the intrusion's lower contact led to noble and base metal enrichments. [ABSTRACT FROM AUTHOR]
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RecordInfo BibRecord:
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      – Type: doi
        Value: 10.1007/s00126-025-01413-4
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      – Code: eng
        Text: English
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        PageCount: 28
        StartPage: 747
    Subjects:
      – SubjectFull: Platinum group
        Type: general
      – SubjectFull: Sulfide minerals
        Type: general
      – SubjectFull: Metals
        Type: general
      – SubjectFull: Industrial metals
        Type: general
      – SubjectFull: Igneous intrusions
        Type: general
      – SubjectFull: Precious metals
        Type: general
      – SubjectFull: Hydrothermal alteration
        Type: general
    Titles:
      – TitleFull: Noble and base metal distribution and processes affecting ore tenors in the disrupted lower stratigraphy of the Stillwater Complex, USA.
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            NameFull: Andersen, Allen K.
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            NameFull: Jenkins, M. Christopher
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            – D: 01
              M: 03
              Text: Mar2026
              Type: published
              Y: 2026
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