The geochemical properties of Kaiata Mudstone and Brunner Coal Measures are
evaluated in order to determine their suitability for placement at the proposed
Cypress and existing Stockton mines. Correct scheduling of this waste material
is needed in order to prevent sulfide oxidation and the generation of acid rock
drainage. The Kaiata Mudstone has both acid generating and acid neutralizing
properties. Results from this study and previous research from Kingett Mitchell
Ltd (2003), indicate that within the Kaiata Mudstone sulphur content decreases
with distance away from the Brunner Coal Measure/Kaiata Mudstone contact, while
calcium carbonate content increases; sulphur values range from 0.33 to 4.23 wt
%; and the acid neutralizing capacity ranges from 0 to 10.4 wt %. The Brunner
Coal Measures have a low capacity to neutralize acid and sulphur content is
variable ranging from 0.25 to 3.5 wt %. Appropriate control measures are
therefore needed for the Brunner Coal Measures and any Kaiata Mudstone within
close proximity to its contact.
Tests have been undertaken to develop a rapid field or laboratory procedure
to define the potentially acid-forming from the non-acid-forming Kaiata
material. Results indicate that paste pH, Net Acid Generation (NAG) and
Carbonate Bomb tests are suitable. Results from the Carbonate Bomb Test show a
strong relationship with the Acid Neutralizing Capacity (ANC) and the Net Acid
Production Potential (NAPP), indicating that this method may efficiently
determine non-acid forming material in the field within fifteen minutes. Ongoing
research includes kinetic column and shake extraction tests. These tests will
quantify what trace elements could be leached from the waste rock and provide
information on the usefulness of alkaline producing products such as Bauxsol,
Limestone and Cement Kiln Dust.