C1 · Publication Volume 11

Economic Geology, Ore Deposits and Mineral Systems

Introduces ore deposits through mineral-systems processes and the distinction between geological potential and economic value.

Purpose and boundary of this book

Economic geology asks how ordinary geological processes concentrate material, how those concentrations are recognised, and which additional conditions would have to be satisfied before anyone could describe them as economically valuable. Those are related questions, but they are not interchangeable. A mineral occurrence may be scientifically important without being an ore deposit. A large geochemical anomaly may have no coherent mineralised body. A geological resource estimate may describe quantity and grade while leaving modifying factors unresolved. This book keeps those boundaries visible.

The sequence begins with abundance, enrichment, grade and tonnage; defines ore, gangue, mineralisation and deposit; develops the mineral-systems framework; compares major magmatic, hydrothermal, sediment-hosted, gold, iron-oxide, uranium, rare-earth and weathering-related families; then examines the proper use of deposit models and the distinction between geological potential and economic value. Deposit names are used as compact hypotheses about processes and expected evidence, never as substitutes for evidence.

This is a geology tutorial, not an investment guide, valuation, resource report, mine plan or prediction that a synthetic occurrence would be viable. Legal reporting codes, commodity markets, extraction technology, environmental requirements and social decisions change with jurisdiction and context. Any real decision must use current competent work and the applicable rules; the instructional calculations here only expose geological reasoning.

General and institution-neutral scope

This is a general, institution-neutral tutorial. It has no affiliation with, sponsorship by, endorsement from or curriculum relationship to any company or individual. It is not written for a named mine, operator, investor, consultancy, university, government programme, software product or private dataset. Every numerical example and unnamed geological setting is synthetic teaching material unless a published regional example is explicitly identified in a source note.

People, public agencies, standards organisations, journals and repositories named in source notes identify technical sources only. A citation does not make any person or organisation the author, publisher, sponsor, partner, endorser, scientific authority or curriculum subject of this tutorial. The website that hosts this material is only a delivery surface. It is not presented as the textbook's author, publisher, sponsor, scientific authority or curriculum subject.

The same evidence discipline should transfer between jurisdictions, commodities and working environments. Commercial product names are unnecessary. Learners work from observable geology, declared measurements, explicit transformations and falsifiable process models.

The mineral-deposit evidence chain

A defensible mineral-deposit interpretation preserves at least seven linked layers:

  1. Geological object: outcrop, interval, grain, vein, alteration domain, stratigraphic unit, intrusive phase, regolith horizon or interpreted body.
  2. Observation support: location, scale, orientation, sample mass or volume, recovery, compositing rule, detection limits and spatial coverage.
  3. Measured properties: mineralogy, texture, structure, lithology, concentration, density, thickness, continuity, age, isotopic composition or physical response.
  4. Transformation: unit conversion, length or mass weighting, density assignment, compositional normalisation, interpolation, domaining or uncertainty propagation.
  5. Process hypothesis: source, energy or ligand, pathway, trap, precipitation or concentration mechanism, and preservation.
  6. Deposit-model comparison: expected and absent features, scale compatibility, alternative systems and observations capable of refutation.
  7. Decision statement: geological potential, exploration priority, resource classification or economic study, each limited to the evidence and authority actually available.

Skipping a layer creates category errors. A high assay becomes a high-grade body; an alteration mineral becomes proof of a deposit class; a regional analogue becomes proof of local continuity; contained metal becomes recoverable product; or geological potential becomes economic value. The cure is an auditable chain, not a more confident adjective.

Learning outcomes

After completing this book, you should be able to:

  • distinguish background abundance, enrichment, mineralisation, grade, tonnage, geological resource and ore;
  • calculate simple weighted grades, contained quantities and enrichment or mass-balance checks while declaring units and support;
  • describe a mineral system in terms of source, pathway, trap, preservation and the critical processes that connect them;
  • compare major deposit families using predicted architecture, alteration, mineralogy, geochemistry, timing and scale;
  • explain why similar products can arise from different processes and why a single process can produce varied products;
  • use a deposit model as a testable working hypothesis rather than a template to be matched selectively;
  • build two or three competing explanations and identify necessary, supporting, ambiguous and refuting evidence for each;
  • separate geological uncertainty from sampling, analytical, geometrical, metallurgical, market, environmental and social uncertainty; and
  • state whether a conclusion concerns scientific occurrence, geological potential, estimated resources or economic value.

Prerequisites and notation

The book assumes introductory mineralogy, petrology, stratigraphy, structural geology, geochemistry and geological observation. You should be comfortable with ratios, percentages, mass and volume, weighted means, logarithmic plots and the difference between observation and inference. Prior knowledge of mining finance is not required because no economic decision is being made here.

Concentration may be written as a mass fraction, percentage, parts per million or another declared basis. Grade is a concentration attached to a defined sampling or estimation support. Tonnage is mass, not volume. For a body divided into domains, a mass-weighted mean grade is

$\bar G=\frac{\sum_i M_iG_i}{\sum_i M_i}.$

Contained commodity on the same basis is Q=MG. If G is in percent it must first be divided by 100; if it is in grams per tonne, MG yields grams. Neither expression estimates recovery, dilution, losses, saleable product or value. Symbols are defined in each lesson because conventions differ between disciplines.

How to use the diagrams and examples

Each lesson includes one purpose-built schematic. It is a conceptual teaching diagram, not a measured section, a universal vertical sequence or a map of a real district. Arrows mean hypothesised transfer or causal connection; they do not prove timing or continuity. Relative widths, colours and positions carry only the meaning stated in the caption.

Every worked dataset is synthetic. Values are selected so that learners can audit units and reasoning, not to imply a normal grade, expected tonnage, preferred commodity or real discovery. When a synthetic scenario resembles a known deposit family, the resemblance is pedagogical and does not identify a company, property, person or locality.

For each example, write three separate outputs: the calculation; the geological interpretation conditional on assumptions; and the unresolved observation that could change the interpretation. This habit prevents a correct equation from becoming an unsupported geological conclusion.

Reproducibility and evidence records

A reusable record keeps original observations immutable and links every derived field to its inputs, equation, units, method and version. Sample identifiers must connect location, interval, orientation, recovery, preparation, analytical result, qualifiers, quality-control status and geological log. Domain boundaries, excluded data, density assignments and compositing rules must be versioned rather than overwritten.

Process models need an evidence ledger. For each proposed source, pathway, trap and preservation condition, record the observation, scale, reliability, predicted consequence, alternative explanation and test. Absence is informative only if the observation method had a realistic chance of detecting the feature at the relevant scale.

Maps and models should distinguish observed contacts, interpreted contacts and extrapolated volumes. Report detection limits, censored values and uncertainty rather than replacing them with convenient zeros. Preserve rejected interpretations and the reason for rejection so that a later reviewer can reconstruct how the preferred model developed.

Assessment and completion standard

Completion requires a mineral-systems dossier for an unfamiliar synthetic district. The dossier must contain:

  • an object-and-measurement register with units, support and quality status;
  • at least two competing deposit or process models;
  • a source-pathway-trap-preservation diagram for each model;
  • a matrix of necessary, supporting, ambiguous and refuting evidence;
  • at least one checked grade, tonnage or mass-balance calculation;
  • explicit discussion of scale, representativity and negative evidence;
  • a distinction between geological potential and economic value; and
  • a next-test plan chosen for its ability to discriminate between models.

A submission is satisfactory when another reader can reach a different preferred model without changing the recorded facts. A model that survives only because contrary observations were omitted does not meet the standard. No assessment requires a claim of discovery, resource, reserve, profitability or investment merit.

Core sources