| Abstract: | Concentrations of tourmaline in Early Proterozoic metasedirnentary rocks of the Cuyuna iron range, east-central Minnesota, provide a basis for redefinition of the evolutionary history of the area. Manganiferous iron ore forms beds within the Early Proterozoic Trommald Formation, between thick-bedded granular iron-formation having shallow-water depositional attributes and thin-bedded, nongranular iron-formation having deeper water attributes. These manganese-rich units were previously assumed to be sedimentary in origin. However, a revaluation of drill core and mine samples from the Cuyuna North range has identified strata-bound tourmaline and tourmalinite, which has led to a rethinking of genetic models for the geology of the North range. We interpret the tourmaline-rich rocks of the area to be a product of submarine-hydrothermal solutions flowing along and beneath the sedirnent-seawater interface. This model for the depositional environment of the tourmaline is supported by previously reported mineral assemblages within the Trommald Formation that comprise aegirine; barium feldspar; manganese silicates, carbonates, and oxides; and Sr-rich barite veins. In many places, tourmaline-rich metasedimentary rocks and tourmalinites are associated locally with strata-bound sulfide deposits. At those localities, the tourmaline-rich strata are thought to be lateral equivalents of exhalative sulfide zones or genetically related subsea-floor replacements. On the basis of the occurrence of the tourmaline-rich rocks and tourmalinites, and on the associated minerals, we suggest that there is a previously unrecognized potential for sediment-hosted sulfide deposits in the Cuyuna North range. |
| Genre: | Article |
| ProdID: | 70018052 |
| Citation Author: | Cleland, J. M.; Morey, G. B.; McSwiggen, P. L. |
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| Citation End Page: | 1291 |
| Citation Issue: | 7 |
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| Citation Language: | English |
| Citation Larger Work Title: | Economic Geology |
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| Citation Number Of Pages: | 10 |
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| Citation Search Results Text: | Significance of tourmaline-rich rocks in the north range group of the cuyuna iron range, East-Central Minnesota; 1996; Article; Journal; Economic Geology; Cleland, J. M.; Morey, G. B.; McSwiggen, P. L. |
| Citation Start Page: | 1282 |
| Citation Volume: | 91 |
| Citation Year: | 1996 |
| Type: | citation/reference |
| Text: | Significance of tourmaline-rich rocks in the north range group of the cuyuna iron range, East-Central Minnesota; 1996; Article; Journal; Economic Geology; Cleland, J. M.; Morey, G. B.; McSwiggen, P. L. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Mon, 1 Jan 1996 00:00 -0600 |
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