Management of Acid and Metalliferous Drainage in Tasmania
The Good Practice Guide for Management of Acid and Metalliferous Drainage (AMD) has been developed to provide guidance on how AMD is best managed on sites within Tasmania. Mineral Resources Tasmania (MRT) managed the project, which involved significant stakeholder consultation to ensure that the Good Practice Guide (GPG) is relevant for the large and small mining and quarrying activities around the state. The project is funded by the Mining Sector Innovation Initiative Program (MSIIP), which was released as part of the State Government's 2017/2018 budget. The MSIIP funding has a number of projects which are aimed at helping to keep the mining and mineral processing industry at the cutting edge of technology and best practice.
The intent of the GPG is to abridge the current resources available for management of AMD within Tasmania and provide management solutions which are specific for the Tasmanian climate and geological setting. The GPG will not be an exclusive resource for management of AMD, but instead provide the resources for current and future operators to understand and implement leading practice techniques for management of AMD. The emphasis of the GPG is to prevent AMD forming by managing Potentially Acid Forming (PAF) material in a manner which excludes oxygen as early as practical after blasting or crushing and minimises the water transport pathways.
AMD occurs when sulfide-bearing rocks are exposed to oxygen (the air). Most sulfides in Tasmania are present as pyrite (iron sulfide), and chalcopyrite (copper iron sulfide). Exposure to oxygen results in the oxidation of sulfur leading to the production of acid, which can leach metals and other elements from surrounding rock. Once started this process is difficult to stop. During most forms of mining and quarrying, rocks are routinely blasted or crushed, exposing large areas of fresh rock to oxygen and allowing oxidation to commence. The figure (left) shows Tasmanian geology predisposed to AMD.
The GPG is presented in two sections, the first part provides:
- an overview of what AMD is;
- approaches for detection and testing of potentially acid produce rock; and
- best practice management strategies.
This part of the document provides a technical basis for AMD management and aims to highlight the significant cost savings which an operation can achieve, over the life of the project, by identifying the presence of PAF material and managing the risk of AMD throughout the operating life and into closure.
The Knowledge Base section covers topics which are needed throughout the AMD management cycle, and don't fit neatly into any specific category. This section covers modelling, risk assessment and regulatory requirements. Mangers of AMD should continually assess these topics throughout the mine life from exploration to closure.
Part 2 of the document is a series of technical factsheets, which identify further resources that may be needed at each stage of an operation. The factsheets provide useful technical guidance for qualified practitioners seeking further resources, or for less experienced operators, background knowledge when seeking expert help.
This fact sheet gives a list of references and a glossary of terms which can be used when assessing and managing AMD during all phases of an operation. The list of resources is not exhaustive, but covers the major publications in Australia and worldwide.
This fact sheet discusses the implications of failing to manage AMD throughout the mining lifecycle.
AMD needs to be considered throughout the life cycle of a mine, and long-term management plans, including final closure, need to be developed from the initial states of mine planning.
This fact sheet is designed to help explorers understand why identification and testing for AMD is important during all phases of exploration.
During this phase, explorers are aiming to identify is there is an economic resource. Management of AMD during the life of mine, affects the overall economics of an operation therefore it is prudent to identify the quantity and extent sulfide mineralisation which is present on the site. The quantity and extent of the AMD should be represented in a statistically valid spatial ore and waste model.
This fact sheet is aimed at sites which have discovered economic mineralisation and are planning construction of a project.
The feasibility stage of a new project is where the conceptual designs are generated, these include waste rock dumps, pit shells and tailings storage facilities. To design and cost the designs, the operation must understand how the material will react to exposure to oxygen, how rapidly it might oxidise and form AMD. During these early stages of design, expert assistance is often needed to ensure that the appropriate test work is undertaken and interpreted correctly. Incorrect estimation of AMD management costs can be the difference between profitability and failure of an operation over the life of the project.
This fact sheet covers topics which are pertinent to management of AMD on a site which is operating.
Successful implementation of the AMD management plan requires commitment by mine management and staff and positive collaboration across all relevant sections of the business unit. Management must also commit to ongoing waste characterisation as the mine develops, updating the waste model over the life of the mine Managing water within a site that has sulfide-bearing materials can be one of the biggest reasons for success (or failure) when managing AMD on a site. The primary objective with water management is to allow the least amount of water to become contaminated.
This fact sheet covers handling of PAF materials during operations.
The fact sheet covers both tailings and waste rock as streams of PAF which are managed in separate ways. Tailings represent waste which has been through the process plan (mill) and waste rock is part of the in-pit segregation process.
This fact sheet covers active and passive treatment systems. Treatment systems are used to remove metals from the water and raise pH to improve water quality when AMD leaves the site. Using a treatment system should be a last resort for AMD management.
This fact sheet covers planning for closure, including landform design, stakeholder consultation, and planning for relinquishment.
A 'design for closure' approach should be applied to all parts of the mining cycle from Feasibility and Operations, through to Closure. Plans should be developed as part of mine planning and progressively implemented. Unplanned closure means the risks are increased for both the environment, due to physical and contamination risks, and the community as the landform left may not provide a final landform which can be used and community resources (i.e. water) may be contaminated.