THE IMPACT OF FACIES HETEROGENEITY ON FLUID STORAGE AND TRANSPORT IN THE LOWER BURRO CANYON FORMATION, LISBON VALLEY, UTAH

The resource potential of fluvial deposits depends on their fluid storage and transport capacity, which depends on petrophysical heterogeneities caused by stratigraphic and lateral variations. In Lisbon Valley, Utah, Early Cretaceous braided stream deposits of the Lower Burro Canyon Formation (LBCF) form the primary host beds for high-grade copper ore bodies that are potential targets for in-situ leach mining. Variations in the lithology, facies associations, and depositional architecture of the LBCF represent major controls on the porosity and permeability of these ore bodies, and are the focus of this study.

Detailed logging efforts along two perpendicular transects of drill-core reveal the presence of 8 major lithofacies within the LBCF. Lithofacies include green mudstone, siltstone, mud draped siltstone-sandstone, massive to ripple laminated sandstone, planar laminated to cross-bedded sandstone, cross-bedded sandstone with chert pebbles, trough cross-bedded sandstone / pebble conglomerate with rip-up clasts, and crudely bedded gravel with rip-up clasts. Fluid storage and transport capacity were quantified for each lithofacies using mercury injection porosimetry data provided by the mine. Values range from 2-26% for porosity and from 10-350 Md for permeability.

Amalgamation ratio was calculated for each core based on the scheme designed by Zhang et al. (2017); preliminary results suggest that vertical connectivity of sandstone bodies is highest in the middle to upper portions of the LBCF, with overall amalgamation ratios ranging from 0.52 to 0.63.

Measurement of two nearby stratigraphic sections accompanied core-based efforts, and revealed the presence of three different architectural element types within the LBCF. These are, in order of decreasing porosity, permeability, and overall sand body connectivity: amalgamated channel-fill deposits, isolated channel-fill deposits, and floodplain fines.

Modern recovery efforts require more detailed characterizations of the lithologic, stratigraphic, and lateral variability within sedimentary-hosted ore deposits. This study helps to constrain the multiple scales of heterogeneity observed within the Lower Burro Canyon Formation and provides a critical input into the assessment and design of the Lisbon Valley mine expansion.