Alternatives to Acid-Base Accounting for Waste Management at the Stibnite Gold Project, Idaho

Acid-Base Accounting (ABA) is an industry-recognized laboratory assessment of the acid generation or acid neutralization potential of rock materials. The
goals of the method are to determine the material’s acid generation potential (AP)
and neutralization potential (NP). The collection of ABA data is typically limited
to the development stage geochemical studies of a mining project and is not routinely collected during either the exploration or operating mining activities. In
addition, the turnaround time between sample collection and receipt of the results
is typically a minimum of two to six weeks. For these reasons, an alternative ABA
method was developed for the Stibnite, Idaho advanced exploration/feasibility
stage gold project to correlate ABA data to more routinely collected data including the multi-element exploration database.
The Stibnite Gold Project is located in the Stibnite Mining District in Valley
County, Idaho. The main ore body is intrusion-hosted precious metals (gold and
silver) which occur in association with very fine-grained, disseminated, arsenical
pyrite and, to a lesser extent, arsenopyrite. Antimony is primarily associated with
stibnite deposited after gold. Probable mineral reserves are estimated at 4.6 million ounces gold and 137 million pounds antimony.
Baseline geochemical data (including ABA) was collected to understand the
characteristics of the waste material of the Stibnite deposit. Results were then
compared to the existing exploration database to establish correlations between
the two datasets. This comparison included principal component analysis (PCA)
to first assess trends by lithotype and alteration before calculating correction factors to be applied to the exploration database. Acid potential and neutralization
potential calculated using the correction factors were then applied to the block
model to assess acid generation on a deposit scale thereby enabling improved
waste management.
Keywords: Acid-Base Accounting, Stibnite, Geochemistry, Waste Rock, Surrogate Methods