The development of the surface geometry inversion method with applications to modeling seafloor hydrothermal alteration and associated mineralization

Galley, Christopher George (2022) The development of the surface geometry inversion method with applications to modeling seafloor hydrothermal alteration and associated mineralization. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (120MB)

Abstract

As the exploration and exploitation of seafloor polymetallic deposits appears to be the next frontier in mineral exploration, developing and optimizing remote sensing methods to locate and study these deposits is becoming increasingly important for understanding the resource potential and environmental implications of mining from the deep seafloor. One such deposit type is seafloor massive sulfide (SMS) deposits, which form on and below the seafloor at sites of high-temperature hydrothermal fluid venting at a variety of tectonic settings where seafloor extension and magmatism takes place. SMS deposits have promise to offer new sources of Cu, Zn, Pb, Au, and Ag, but the remote environment in which they are located creates difficulties for their discovery and resource estimates. In particular, the proportion of ore found below the seafloor, versus that found within the sulfide mound, has only been estimated from a limited number of collected drillcores. These cores are expensive, with respect to time and money, and unless collected in large numbers, and to sufficient depth, offer limited geometric information of the subseafloor components of the deposit. Alternatively, magnetic voxel-based inverse models can be used to locate SMS deposits as magnetic lows, due to the hydrothermal fluids stripping much of the magnetite from the alteration zone, and the data can be inverted with a surface geometry inverse (SGI) modelling method to resolve subseafloor structures. Additionally gravity inverse models can be used to model the SMS deposits' massive sulfide layer as a density high. The SGI method inverts for the position of nodes in a wireframe mesh rather than physical properties within a fixed mesh. This thesis demonstrates the SGI method to be an excellent tool for modelling the contact surfaces between the sulfide mound, the hydrothermally altered chloritized basalt, and least altered basaltic host rock. The volumes within these surfaces can then be used to calculate an estimated tonnage for the ore located below the seafloor, developing a better resource model for SMS deposits.

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