Scientific Investigations Report 2013–5091
This descriptive model for magmatic iron-titanium-oxide (Fe-Ti-oxide) deposits hosted by Proterozoic age massif-type anorthosite and related rock types presents their geological, mineralogical, geochemical, and geoenvironmental attributes. Although these Proterozoic rocks are found worldwide, the majority of known deposits are found within exposed rocks of the Grenville Province, stretching from southwestern United States through eastern Canada; its extension into Norway is termed the Rogaland Anorthosite Province. This type of Fe-Ti-oxide deposit dominated by ilmenite rarely contains more than 300 million tons of ore, with between 10- to 45-percent titanium dioxide (TiO2), 32- to 45-percent iron oxide (FeO), and less than 0.2-percent vanadium (V).
The origin of these typically discordant ore deposits remains as enigmatic as the magmatic evolution of their host rocks. The deposits clearly have a magmatic origin, hosted by an age-constrained unique suite of rocks that likely are the consequence of a particular combination of tectonic circumstances, rather than any a priori temporal control. Principal ore minerals are ilmenite and hemo-ilmenite (ilmenite with extensive hematite exsolution lamellae); occurrences of titanomagnetite, magnetite, and apatite that are related to this deposit type are currently of less economic importance. Ore-mineral paragenesis is somewhat obscured by complicated solid solution and oxidation behavior within the Fe-Ti-oxide system. Anorthosite suites hosting these deposits require an extensive history of voluminous plagioclase crystallization to develop plagioclase-melt diapirs with entrained Fe-Ti-rich melt rising from the base of the lithosphere to mid- and upper-crustal levels. Timing and style of oxide mineralization are related to magmatic and dynamic evolution of these diapiric systems and to development and movement of oxide cumulates and related melts.
Active mines have developed large open pits with extensive waste-rock piles, but because of the nature of the ore and waste rock, the major environmental impacts documented at the mine sites are reported to be waste disposal issues and somewhat degraded water quality.
First posted August 22, 2013
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Woodruff, L.G., Nicholson, S.W., and Fey, D.L., 2013, A deposit model for magmatic iron-titanium-oxide deposits related to Proterozoic massif anorthosite plutonic suites: U.S. Geological Survey Scientific Investigations Report 2013–5091, 47 p., http://pubs.usgs.gov/sir/2013/5091/.
Deposit Type and Related Commodities
Historical Evolution of Descriptive and Genetic Knowledge and Concepts
Physical Description of Deposit
Hypogene Ore Characteristics
Gangue Mineral Characteristics
Supergene Ore and Gangue Characteristics
Weathering and Supergene Processes
Petrology of Associated Igneous Rocks
Petrology of Associated Sedimentary Rocks
Petrology of Associated Metamorphic Rocks
Theory of Deposit Formation
Ore Deposit System Affiliation
Sources of Ti-Fe-P-Ore Components
Mechanisms that Concentrate Ore
Summary of the Origin of Magmatic Fe-Ti-Oxide Deposits
Geological Assessment Guides
Attributes Required for Inclusion in Permissive Tract at Various Scales
Geoenvironmental Features and Anthropogenic Mining Effects