Categories are constructs of our imagination. We define categories to aid our thinking, analysis, and decision-making. It is easier to respond immediately if a stimulus fits a preconceived category, than to analyze afresh. A rustle in the brush fits the definition of the category “Tiger in the woods; the tiger could kill us; therefore flee.” Why analyze the situation to decide that the wind is merely blowing through the trees and making a nasty sound?
So today I cogitated on the question of categories in mining. Keep in mind categories, as metal constructs, are seldom a true reflection of reality. Categories flux, change, blend, intermix, and are subject to confusion and malicious reinterpretation to support preconceived notions.
The categories I thought about today are the conventional ones in mining: pre-feasibility; feasibility; detailed design; construction; operation; closure; and post-closure. I thought about these categories in the context of tailings dams–sometimes called tailings management facilities (TMF); or tailings storage facilities (TSF); or slime dams (SDs). I prefer the simplicity of tailings facility (TF)–although I recognize that TF is weak by comparison with TMF. Somehow a three letter acronym is more powerful than a two letter acronym. So let us settle for TMF. It looks and sounds impressive.
There are many conventional rules for what constitutes a pre-feasibility study of a mine. Similarly what constitutes a feasibility study for a mine. We need not delay on these.
But there are no guidelines that I am aware of that define what is adequate for the pre-feasibility study of a TMF; or of the feasibility study of a TMF. Net alone what is enough for a detailed design of the mine’s TMF.
Obviously for a pre-feasibility study of a TMF you need to demonstrate that the site is correctly selected; that the site is big enough for the mine life; that the environmental impact is minimal; and that it is cost-effective to develop the site.
Obviously for a feasibility study of a TMF, you need to to demonstrate that the embankments can be constructed to be stable; that the tailings can be practically deposited; and that the seepage and discharge waters will not contaminate the surface and groundwater of the site and receiving environment; and that the costs of operation & closure are not excessive.
Obviously for detailed design, you need to compile documents to enable the TMF to be constructed and operated within reasonable cost limits.
Easy, you say? Not necessarily! The ordinary human tendency is to push for more detail, to demand more detail, and to expect a complete & confident conclusion that the TMF will be safe, protective of the environment, and cost-effective. Nobody is normally prepared to suspend final conclusions and to go with the flow of doubt, risk, and uncertainty of the normal sequence of pre-feasibility, feasibility, and detailed design. It is all too risky to delay the demand for detail and finality.
Yet the prudent mine developer will demand this of his consultants: delay expenditure to as late a stage as possible. Do not spend money on site characterization and design now if such data is not needed to make a pre-feasibility decision, or to make a feasibility study decision. Spend the characterization and design money only when and as needed to support the level of detail appropriate to the stage of the overall mining evaluation. This is hard for ordinary civil and tailings engineers to do. We instinctively demand more detail and conclusions of certainty.
It is all well and good to say that the design detail should be sufficient to support a cost estimate that is 50% accurate, or 30% accurate, or 10% accurate. There are too many examples (case histories) of over optimistic cost estimates that bias toward the low side. Too many case histories of cost estimates blowing up by more than 100%. The consultant is biased toward over-optimism and the good-news story. The client, the mine developer, is biased to good-news stories (myths) of low costs and no problems.
I have just lost a job on which we proposed—we were brutally honest that the idea was a bad idea, and that other approaches should be considered at high cost. The mining company obviously did not like our realism and so went with the dreamers, the optimists who negated doubt. Maybe we will be called in when the truth prevails?
This is a vast topic. I am not up to the task this evening. Maybe some day we will establish and write about precise guidelines for what is sufficient for a TMF pre-feasibility study, a feasibility study, and then the detailed design. In the meantime if you have an opinion, ideas, or case histories to help us all in this enquiry, please comment.