The chromitites of the Stillwater Complex, Montana; an editorial review

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Authors:Anonymous
Volume Title:Chromium Review
Source:Chromium Review, Vol.4, p.5-13. Publisher: Mintek, Randburg, South Africa. ISSN: 0256-0038
Publication Date:1985
Note:In English; illus. incl. 7 tables, geol. sketch maps
Summary:In this Precambrian layered intrusion, 13 chromitite seams occur in the peridotite subzone (915 m thick) just above the base of the complex, but a single layer occurs at the top of the bronzitite subzone (305 m thick) stratigraphically above. Some 400 m above the base of the lower banded zone in the main part of the complex, the J-M or Howland reef is a major potential source of the Pt-group elements. The sequence of chromitite layers (A-K) contains only five layers of commercial interest; the best (G) averages 1.5 m thick, has chromite >50% and can be traced 40 km along strike. The chromitites are geochemically anomalous in that the Cr/Fe ratio increases sequentially upwards to a maximum at the H layer and then decreases sharply to K; within the G layer itself the Cr/Fe behaviour is normal. Under present economic circumstances these Stillwater veins of highly faulted chromitites are not viable. Sulphide mineralization is common at the base of the complex (105 million t of ore at Ni and Cu grades of 0.25% each); the Howland reef contains precious metals at an average conc. of 18.38 ppm over a width of approx 2 m, but the grade is variable and erratic. [R.A.H.]
Subjects:Archean; Chemical composition; Chromite ores; Chromitite; Economic geology; Igneous rocks; Intrusions; J-M Reef; Layered intrusions; Metal ores; Metals; Peridotites; Platinum group; Platinum ores; Plutonic rocks; Precambrian; Stillwater Complex; Ultramafics; Absaroka Range; Beartooth Mountains; Montana; North America; Park County Montana; Rocky Mountains; Stillwater County Montana; Sweet Grass County Montana; U. S. Rocky Mountains; United States; Howland Reef; Southwestern Montana
Coordinates:N450000 N451500 W1095000 W1101000
Abstract Numbers:86M/1613
Record ID:1986004346
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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