SRK provided Geological Modeling and Mineral Resource Estimation updates in support of a Feasibility Study on SRA’s Black Butte Copper Project.
The Black Butte Copper Project is located 27 km north of White Sulphur Springs, Montana, USA. The Johnny Lee and Lowry copper deposits that comprise the Black Butte Project are considered hybrid sedimentary exhalative (SEDEX) - sediment-hosted stratabound copper (SCC) sulfide deposits.
In 1985, the Johnny Lee deposit was discovered by a joint venture between Broken Hill Proprietary Ltd. (BHP) and Cominco American Inc. (CAI), followed by the CAI discovery of Lowry in 1990. In 2010, Tintina Resources Inc. (Tintina) acquired the mineral rights and completed resource definition drilling and a Preliminary Economic Assessment study. In 2013, Sandfire Resources NL acquired a majority shareholding in Tintina and the company name was changed to Sandfire Resources America, Inc. (SRA).
Copper mineralization at the Johnny Lee deposit is hosted by two massive sulfide units that occur at different stratigraphic levels within the sedimentary succession, referred to as the Upper Sulfide Zone and Lower Sulfide Zone. At the Lowry deposit, copper mineralization is hosted by a succession of sub-parallel, ferruginous sediment with interbedded shale and conglomerate lithofacies.
Economically significant copper mineralization is further domained in discrete bedding-parallel areas and lower-grade halos within the main zones.
SRK worked collaboratively with SRA teams in Montana and Australia to prepare the Mineral Resource estimation and played a central role in the project’s Feasibility Study, as summarized below:
- Acted as the NI 43-101 Qualified Person (QP) for Mineral Resources;
- Performed a site visit for verification and audits of supporting data and methodologies;
- Reviewed and validated the drilling database, geological logging, sampling procedures, laboratory analytical results, and QA/QC protocols and results;
- Exploratory data analysis of domained analytical data (e.g. capping, compositing);
- Revised 3D models for geological, geometallurgical, and estimation domains;
- Developed a block model with estimated resources for economic variables and validated the model and supporting assumptions, such as density measurements;
- Classified the resources to reflect the relative confidence of the geological interpretation and modeling, analytical data quality, grade estimates, and mineralization continuity;
- Reviewed metallurgical data to derive metal recovery estimates;
- Evaluated underground optimization and other modifying factors to determine “reasonable prospects for eventual economic extraction” and commented on cutoff grade assumptions and variability.
The project culminated in a Feasibility Study Technical Report following the Canadian National Instrument 43-101 disclosure format. SRK completed the FS reporting with a multi-disciplinary team of independent consultants selected by SRA.
