North-Central Section - 49th Annual Meeting (19-20 May 2015)

Paper No. 5
Presentation Time: 9:25 AM


FLOYD, Corrie, WELNA, Sara, CONSIDINE, Ellen J., JOHNSON, Leif A. and AIKEN, James S., Barr Engineering Company, 4700 W 77th St, Suite 200, Edina, MN 55435,

Over the last five years, Wisconsin and Minnesota have seen intense interest in developing Cambrian-aged sandstone deposits for industrial sand. Exploration drilling and logging of these industrial sand resources is often focused on finding “good sand” and neglects to collect the field data which is required for a complete resource evaluation and thorough financial analysis. Often times, there is relatively little attention paid to localized differences in geologic lithology and/or depositional environments that can radically alter the quality of the deposit. Frequently, investment of millions of dollars is made with very little accurate site-specific drilling or testing data, and go/no-go decisions turn on tonnages that are within a resource evaluation’s margin of error. Lack of a more complete characterization of the site’s geology could therefore put the investment at risk if the deposit or overburden turns out to be substantially different than originally thought.

Our work conducted at several prospective mines in the region indicates that documentation of seemingly incidental observations during the early phases of site exploration can later save thousands to millions of dollars as a site enters the permitting process. These oft-neglected data include: precise location and elevation data for boreholes, thorough geologic descriptions of overburden materials, depth-to-water measurements in boreholes, detailed descriptions of cemented intervals, and collection of assay samples through the full thickness of a deposit. These data can help to identify and locate faults, assign value to overburden previously assumed to be valueless, determine which areas must be blasted prior to removal, determine whether a site can be dry-mined or must be dewatered, and estimate proportions of various sand products (e.g. 20/40, 40/70).

Case studies demonstrating the effect of quality field data, or lack thereof, on the results of resource evaluations will be presented. The case studies will emphasize the importance of an unbiased characterization of the site specific lithology and depositional environment to assessing the operational and economic viability of mine development.