Hard Rock Miner’s Handbook
Rules of Thumb
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Introduction
This document contains a list of over 680 Rules of Thumb gathered over 30 years of hard rock mining service provided by Jack de la Vergne, Stantec - Mining and predecessor firms. We have endeavored to provide Rules of Thumb for every applicable area in the industry. The list is an excerpt from the Hard Rock Miner’s Handbook, Edition 3, published June 2003. To facilitate usefulness, the attached compilation is sorted by topic.
Our objective in producing the Rules is to present a gift of value to the industry in return for providing our main source of revenue for many years, sustaining our business, and providing gainful employment for members of our team.
History
Rules of Thumb constituted the sole body of mining knowledge until the disciplines of science and engineering first evolved.
Agricola first introduced methodology to the mining industry in the sixteenth century, exemplified in his book entitled De Re Metalica. In this huge volume, he set out principles, standards, and provided Rules of Thumb for mining, concentration, and smelting. The following excerpt provides an example of how mining depended on Rules of Thumb at that time:
"Now when a miner finds a vena profunda, he begins sinking a shaft two fathoms in breadth, two-thirds of a fathom wide, and thirteen fathoms deep."
More than three hundred years later, in 1891, the Royal Commission on Mineral Resources in Ontario, Canada stated that we had been "mining by rule of thumb for long enough." They probably never imagined that over one hundred years later we not only continue to employ these Rules, but they retain a fundamental role in the mining sector.
Definition
What is a Rule of Thumb? A definition is necessary that offers good application in the Hard Rock Mining Industry. Webster’s defines a "Rule of Thumb" as follows:
- "A general or approximate principal, procedure or rule based on experience or practice, as opposed to a specific, scientific calculation or estimate;"
- "A rough practical method of procedure."
As we compiled the attached list of Hard Rock Mining Rules of Thumb, we struggled with the subjectivity surrounding many of the Rules. Is a statement a "Rule of Thumb," or is it simply an arguable opinion? We ultimately decided, somewhat subjectively, that a Rule of Thumb could be whatever we wanted it to be and so have provided our own definition of Hard Rock Mining Rules of Thumb.
Rules of Thumb – Mining Industry Definition
For the mining industry, a Rule of Thumb is an empirical standard. It can be further defined as a pragmatic guideline or "norm" related more to the art than the science of mining. A Rule’s main roles are to provide the perspective required to ensure practical concepts and designs, and to facilitate finding pragmatic solutions for operating problems.
Mining Industry Rules of Thumb – Distinguishing Features
Based on the above definition, and to separate Rules of Thumb from other interesting facts and opinions, we determined that Rules of Thumb generally contain certain distinguishing features. We then developed those features into a set of test questions that can be used as a sieve to qualify a Rule of Thumb.
- Does the Rule contain specific value quantities, such as time, cost, weight, temperature, distance, speed, etc.?
- Can the Rule be used in a practical application?
- Is the Rule based on identifiable, repeatable experience?
- Is the Rule procedural in nature and relatively independent of other variables or conditions?
- Is the Rule put forward and defended by the experience of a qualified practitioner in the mining industry?
- Can the Rule be checked by other practitioners through review of historical examples supporting the principle under consideration?
Current Use
In today’s mining industry, problems with design, build, and operations arise every day. Most must be solved promptly. Usually, an approximate answer to a particular question is all that is required in determining an acceptable solution.
Often the participants may not even realize they have employed Rules of Thumb to develop a design concept or trouble shoot a problem. This is one reason that we do not attribute as much value to Rules of Thumb as we should.
The conceptual design of a new mine is an example of an iterative process. Using trial and error assumptions will eventually provide results, but this procedure is slow and cumbersome. A more efficient and effective method is to break the circle by employing Rules of Thumb for key assumptions. Thus, Rules of Thumb are employed to great advantage in preparing mine feasibility studies and due diligence reports, and in other areas such as setting range limits for controls in PLC programs.
When the time arrives for final design and actual construction, Rules of Thumb are no substitute for sound engineering practices. For example, one Rule of Thumb states, "A shaft should not be located less than 200 feet (60 m) from the crest of an open pit." At least three case histories exist where this Rule was applied to a major shaft installation only to find later that the shaft was too close to the pit. In two cases, circular concrete lined shafts were damaged by ground movement and eventually abandoned for hoisting service but retained for ventilation airways. In the third case, the overburden moved damaging the structures around the shaft collar. The surface plant was saved from eventual collapse by very expensive remedial measures.
As noted in the example above, critical pitfalls must be avoided when using Rules of Thumb. Although most of Rules of Thumb used in mining are sound, some are controversial, ambivalent, or even contradictory. A significant effort has been made to delete unsound Rules from the attached list, but we cannot guarantee the absolute accuracy of any Rule presented.
Future Application
An indisputable future role of the Rules is to develop knowledge-based or "expert" computer models. An example is the simulation of a design process that mimics the decisions of a seasoned engineer or designer with the aim of reliable and consistent performance at lightning speed by a non-specialist. The complex decisions made by designers must be broken down into a set of Rules. The format will be used in conjunction with a database to devise algorithms with which the computer can work. The necessary compilation of the Rules of Thumb and the programming effort will provide the beneficial side effect of forcing consideration of the validity and range of accuracy for each Rule of Thumb employed.
Disclaimer
As stated above, the primary usage of Rules of Thumb should be in the development of conceptual designs and feasibility studies or, when a quick decision is required in the solution of an operating problem. Although an approximated answer, derived from a Rule of Thumb may solve an immediate problem, Rules of Thumb are not a substitute for the application of sound engineering and design methodologies. Although we firmly believe that the presented Rules of Thumb provide great continuing value to our industry, McIntosh Engineering does not guarantee their validity, nor do we (or the referenced individual sources) accept responsibility for application of the Rules of Thumb by others. Where possible, direct quotes have been provided from individual references. However, it is possible that referenced sources may not have directly stated the Rule of Thumb for which they are assigned credit. Although we have endeavored to accurately quote all individual references contained in the Rules of Thumb compilation, we apologize in advance for any misquotes that may be attributed to individual sources. We will provide updates to the Rules of Thumb compilation, as we become aware of corrections that may be necessary.
Questions or comments about the Hard Rock Miners Handbook or the Rule of Thumb, please contact us.
Scott McIntosh
Stantec - Mining
scott.mcintosh@mcintoshengineering.com