GoldSim is a computer code that enables you to model systems consisting of units (elements) into, through, and out of which things flow. Obviously it works well for dams, ponds, reservoirs, and all the other parts of the water circuit of a mine.

A GoldSim model was used at the Marillana Creek (Yandi) mine in Australia. There is a good technical paper on this mine in Mine Closure 2006: Integration of groundwater modelling with mine planning to optimize mine closure plans- the Marillana Creek (Yandi) mine story. Seems the story is this: The ore deposit is a channel iron deposit that also forms the major aquifer of the region. Mining over the next 30 years will create a series of open pits upto 90-m deep, extending over more than 20-km in length. The stripping ratio is less than one (actually 0.35:1), so there is not enough waste left over to backfill the many long and narrow pits resulting from mining. Pit lakes will develop in unfilled open pits, and this could compromise water quality.

The objective for mine closure is a "walk away solution for the decommissioned mine site."

To achieve this they will use available waste rock to partially backfill pits; allow groundwater to seep on through the backfill pits; divert Marillana Creek away from the workings; divert some upstream tributaries into the mine to "enhance groundwater system attributes"; and allow some pit lakes to develop. (You will have to see the full paper for the details, I am afraid.) They say that this approach will result in no reduction of downgradient surface water flows or quality, and maintenance of adequate downstream groundwater throughflow to support groundwater dependant ecosystems.

While you cannot get the paper I have just described free on the web, you can look at the GoldSim site for more details. Here is a copy of what they tell us of the use of the GoldSim models at this project:

From Flow and salt balance modelling in a mine with palaeochannel aquifer by Rob Garnham: As part of a continuing closure study into BHP Iron Ore's operations in the Pilbara Region of north-western Australia, Golder Associates Pty Ltd was commissioned to develop a dynamic model to simulate the mining activities at the Marillana Creek operation. The model was to be capable of capturing all the major processes relating to the asset value of the operation and the liabilities (from mining through to post-closure) generated as a result of extraction of ore, including:

  • revenue generated from ore sales through to the end of mining
  • costs attributable to mining
  • costs associated with amelioration of environmental impacts, both during and after closure.

Earlier studies had identified that the main potential environmental impacts will be from evaporation from the pit void lakes, causing salinisation and lowered groundwater levels, and the subsequent impacts upon groundwater and, to a lesser extent, surface water systems. A conjunctive GoldSim model was developed, comprising three sub-models relating financial, water balance (pre-dominantly an advective groundwater flow model) and salt flux aspects of the mining operation. The mining schedule (details of material movements) was provided by the client and formed the primary input to the model. The three sub-models were used to simulate the mining operations and impacts upon groundwater salinities during mining and after closure. In areas where unacceptable salinities were predicted, additional costs were applied to the operation to manage these impacts. The model results were used to illustrate how GoldSim can provide a management tool that facilitates financial planning for closure. The financial predictions provide the opportunity for optimisation of current mining practises to minimise closure impacts and costs, an assessment of the true value of the minable resource and planning for future expenditure during mine closure.

Thanks to the internet you can get a lot more detailed information on this mine and its surface water and groundwater management. The best is the water management plan for the mine at this link - but be aware that it is a very large file that take a long time to download. But it is worth the wait. Similarly for the environmental management plan.