earth science

McKelvey diagram

McKelvey diagram is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand McKelvey diagram rather than just read about it. In short: A McKelvey diagram or McKelvey box is a visual representation used to describe a natural resource such as a mineral or fossil fuel, based on the geologic certainty of its presence and its economic potential for recovery. The diagram is used to estimate the uncertainty and risk associated with availability of a natural resource.

Key takeaways

McKelvey diagram belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect McKelvey diagram to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of McKelvey diagram from memory before moving on to harder problems.

Reference excerpt

A McKelvey diagram or McKelvey box is a visual representation used to describe a natural resource such as a mineral or fossil fuel, based on the geologic certainty of its presence and its economic potential for recovery. The diagram is used to estimate the uncertainty and risk associated with availability of a natural resource. As geological assurance of a resource's occurrence decreases, risk increases. As economic recoverability of a resource decreases, risk also increases.

Meaning of the diagram The terminology used may vary somewhat, but resources in a McKelvey diagram fall into three main areas:

Reserves, which are already discovered and commercially-viable mineral deposits, Contingent or conditional resources, whose existence is known but which are not commercially viable at present, Prospective or undiscovered resources that might exist but have not been found. Natural resources are classified in two dimensions, with geologic certainty shown horizontally and economic viability shown vertically. As described by McKelvey in 1976, geological certainty may be categorized as Demonstrated (directly measured), Inferred (based on strong indirect evidence such as seismic data and detailed knowledge of the local geology) or Hypothetical & Speculative (based on limited or very general geological knowledge). Financially, recovery of a resource is categorized as either profitable or Economic to recover at today's price with today's technology, or not profitable and Subeconomic. The conditions represented by a McKelvey diagram are dynamic in nature: geological and technological knowledge and economic conditions are all subject to change over time. They are also inter-related: for example, lower availability of a natural resource may increase prices, which in turn may mean that a previously unprofitable technology is now considered viable.

History

The diagram was introduced in 1972 by American geologist Vincent Ellis McKelvey, the 9th Director of the United States Geological Survey. It was jointly adopted for use by the Geological Survey and the United States Bureau of Mines in 1973.

Impact Most current classification systems are based on the McKelvey diagram with its distinction between reserves and resources. The basic diagram has been adopted, modified and expanded by a various groups in multiple ways. An even more minimalist version than the original, referred to as the Total Resource Box, has been "simplified and modified to make it more understandable to politicians and laypersons."

SPE The Society of Petroleum Engineers (SPE) has built upon the McKelvey diagram for use in the fossil fuels industry. SPE has worked with the World Petroleum Congress and the American Association of Petroleum Geologists to further develop the SPE/WPC/AAPG Petroleum Resource Classification System. First SPE added levels of field project status relating to possible levels of risk. Other modifications introduced a further subcategory, dividing reserves into proved (P1), probable (P2) and possible (P3) reserves. A number of recommendations have been made towards standardizing and improving petroleum reporting. However, as recently as 2012, the use of terms in reports from different oil companies and countries has been noted to be "inconsistent", with identical terms used to refer "to entirely different aspects."

CRIRSCO Another system that draws on the McKelvey diagram is the CRIRSCO Template or International Template for Reporting of Exploration Results, Mineral Resources and Mineral Reserves, developed by the international Committee for Mineral Reserves International Reporting Standards (CRIRSCO). The CRIRSCO Template attempts to standardize terms both internationally and between fields, particularly the mining and petroleum industries.

UNFC The United Nations Framework Classification for Resources (UNFC) incorporates elements from the McKelvey diagram and other systems. UNFC explicitly identifies three dimensions for assessing projects, each containing multiple levels. The UNFC dimensions are: (E) Economic and commercial viability, (F) Field project status and feasibility, and (G) Geological knowledge. The G-E dimensions of UNFC and the McKelvey diagram correspond. Each point in the 3-dimensional classification is described by a numeric code. The sequence used is always EFG, with “1” indicating the highest quality in a given dimension. The highest quality level would be "1:1:1", indicating that something is economically and commercially recoverable (E1), justified to be technically recoverable (F1) and has a reasonably assured geology (G1). The UNFC approach can be used to compare and harmonize different systems of classification. An updated version of UNFC was released in 2019. It is compatible with sustainable management practices and the 2030 Agenda for Sustainable Development.

References

Illustrations

Worked examples

Example 1 — a first encounter with McKelvey diagram

Start with the simplest possible case. Write down what McKelvey diagram claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to McKelvey diagram before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about McKelvey diagram ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of McKelvey diagram

In research: McKelvey diagram appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses McKelvey diagram in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: McKelvey diagram is common in secondary-school and first-year university syllabi. It links to neighbouring topics Diagrams, Economic geology, Mineral economics, so understanding it makes those chapters shorter.
In everyday life: Look for McKelvey diagram outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study McKelvey diagram in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what McKelvey diagram means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain McKelvey diagram out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is McKelvey diagram in simple terms?

Why does McKelvey diagram matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study McKelvey diagram?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on McKelvey diagram.