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This Internet case study is copyrighted (©) 1998 by Kevin A. Morin and Nora M. Hutt. Further details can be found in Environmental Geochemistry of Minesite Drainage: Practical Theory and Case Studies.
When considering surface and ground waters draining from a minesite, some people believe the entire site contributes to the observed concentrations in the drainage. This is incorrect. In reality, a minesite consists of one or more components, and each component can have a unique effect on drainage chemistry.
For instance, 90% of elevated off-site concentrations may originate
from only one component, while all other components contribute the remaining 10%. In this
example, it can be economically foolish to spend equal amounts of money on each component
for drainage-chemistry control (see our Internet case study for
February 1998). It may be
wiser and environmentally more prudent to focus most of the budget on the most problematic
component. Therefore, there are two basic steps to properly and prudently assess, predict,
and control drainage chemistry at a particular minesite:
1) all components must be identified and studied, and
2) the interactions among the components must be defined.
This month's Internet Case Study discusses some of the components that can exist on a minesite. Site photographs will help to illustrate the points (clicking on the thumbnail version of a photograph towards the end of this case study will enlarge it). A list of example components are provided in Table 1.
|Mine: Open Pits (Figures 1, 2, and 6)||Mine: Underground Workings (Figure 3)|
|Waste-Rock Piles (Figures 4 and 6)||Tailings Impoundment (Figure 5)|
The first component is the mine from which ore is extracted and later processed. Some people refer to a minesite (a collection of components) as a "mine", but for the sake of clear terminology this in incorrect. The four basic varieties of mines are: open pit (Figures 1, 2, and 6; see below), underground workings (Figure 3), solution mines, and placer mines. Each of these varieties have types, like a Type 1 Pit (Figures 1, 2, and 6), but there is insufficient space here to describe and explain them. They are described in detail in Environmental Geochemistry of Minesite Drainage: Practical Theory and Case Studies.
In order to better understand minesite components, a discussion of "ore" is warranted here. Within the mine component, ore is the rock, sediment, and/or soil that contains economic levels of one or more metals. Coal is not often called ore, but is considered so here to keep the terminology simple.
The word, "economic", is very important in the definition of ore because, for example, all rock and soil everywhere in the world contains gold, but typically at levels that would not provide a profit or similar benefit. As a result, the difference between ore and waste rock is based on economics and fluctuates with metal/mineral prices as well as production costs at a minesite.
Since the efficiency of extracting and concentrating metals/minerals has improved through the decades and centuries, some older waste rock and tailings have now become ore. In contrast, since gold prices have declined sharply in recent years, some gold ore has now become waste rock. Therefore, other components like waste-rock piles and low-grade-ore stockpiles have some characteristics that may change through time. For example, many "temporary" low-grade-ore stockpiles become "permanent" waste-rock piles towards the end of mine life.
This leads to the next major component, waste-rock piles (Figures 4 and 6; see below). The uneconomic "waste" rock is dumped as close to the mine component as possible, to minimize the cost of hauling this rock. A waste-rock pile is often constructed by dumping the rock in layers, or "lifts". This produces a relatively high pile in contrast to tailings which are often placed in relatively large, low impoundments (Figure 5).
Tailings are often pulverized rock with much of the economic metals/minerals removed in another component, the mill. The tailings are typically sent as a slurry to an impoundment for storage. Due to this semi-liquid form of placement, tailings impoundments often cover the largest land area of all minesite components.
There are many other possible components for minesites, including those in Table 1. For example, roads for access and movement around a site can significantly affect drainage chemistry over a large area. There is one study that suggested the road around a tailings impoundment accounted for elevated concentrations within the impoundment. This highlights the importance of identifying and studying all components at a minesite in order to better understand, predict, and control drainage chemistry.
CLICK ON THE FIGURE TO ENLARGE IT
Figure 1 Figure 2 Figure 3 Figure 4
Fugure 5 Figure 6
© 1998 Kevin A. Morin and Nora M. Hutt
For more details and case studies, see Environmental Geochemistry of Minesite Drainage: Practical Theory and Case Studies.
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Created by K.Morin