Ultramafic and Mafic Rock Distributions in Central Alaska and Implications for CO2 Sequestration

Abstract

Understanding the distribution of mafic and ultramafic rocks in Interior Alaska provides important constraints on potential economic uses of these igneous rocks, such as future sites for CO2 sequestration. However, poor surface exposure limits understanding of the subsurface geometry and extent of these rocks. In this study, regional aeromagnetic and gravity surveys, geologic maps, drill hole data, physical rock properties, and magnetic data from surface samples were used to build an integrated potential field model that provides a model of the distribution and volume of two of the most significant of these bodies, the mafic and ultramafic rocks of the Tozitna and Livengood Terranes. Although solutions to theoretically calculated geophysical models are non-unique and consequently subject to unquantified uncertainties, our highly integrated model provides a first-order approximation of the distribution of these rocks. Modeling results indicate that mafic and ultramafic rocks in both Terranes are sheet-like, probably thrust-bounded, and continue to significant depths. First approximation volume estimates suggest that there is up to 3,300 billion m3 of mafic and ultramafic rocks between the surface and 3,000 m depth within 10 km of the existing transportation corridor. The maximum carbonation potential of Mg-bearing minerals via a combination of surface and subsurface CO2 injection techniques in these two Terranes is 722 gigatons of CO2. Assuming an actual CO2 uptake capacity of these rocks of only 1 %, this study indicates there is a sufficient quantity of mafic and ultramafic rocks adjacent to existing transportation corridors to meet foreseeable CO2 sequestration needs in Interior Alaska.