Located approximately 60 km northwest of Tom Price, the Nammuldi mine consists of several Lenses (A, B, CD, and EF) that host mineralised banded iron ore within the Mount Newman Member of the Marra Mamba Iron Formation. Several geochemical components of concern exist within these lenses, particularly Lens CD, which has outcrops of potentially acid forming (PAF) Lignite and Siderite material in the proposed pit walls. These lithologies contain pyrite and are therefore likely to produce acid and metalliferous drainage (AMD). The occurrence of AMD is considered a risk with respect to pit lake acidification, metal accumulation, and salinisation, and is the main focus of the modelling carried out and reported in this document.
The objective of this assessment was to construct a detailed water quality model for Lens CD at the Nammuldi mine using associated water balances, post-closure groundwater models (derived from the operational dewatering groundwater model), and geochemistry, including kinetics and geochemical speciation, to evaluate the potential, post-closure water quality for Lens CD. Special attention is given to the assessment of acid and metalliferous drainage (AMD) in the post-closure pit lake.
Aspects of this work included:
- A desktop review of available data necessary for construction of the model.
- Construction of the Nammuldi Water Balance and Water Quality Model.
- Modelling of post-closure pit water balance.
- Assessment of predicted water qualities as a function of closure scenarios.