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LITHOEN

Mineral system

Porphyry copper system

Also known as Porphyry Cu system

A magmatic-hydrothermal system in which fluids exsolved from a crystallising granitoid porphyry carry copper, sulfur and other components into the surrounding rock, producing large volumes of weakly mineralised, strongly altered ground. It is the archetype against which other hydrothermal systems are described.

A schematic left-to-right chain of seven linked stages above a separate dashed band labelled observable expressions, with arrows running down from three of the stages into that band.
SchematicThe seven stages Lithoen records for every system: source, mobilisation, transport, pathway, trap, modification, preservation — with the observable expressions drawn as a separate band beneath, because only some stages leave anything to see. The order is the claim; nothing here is to scale in space or time, and the deposit, where there is one, is a very small part of the whole.

Original Lithoen diagram · LITHOEN-ORIGINAL

Classification

system class
magmaticHydrothermal
model provenance
publishedModel

System architecture

The chain from source to what may be observed. A limb is shown only where Lithoen has recorded it from a source; nothing here identifies a place, ranks ground or implies that a deposit exists.

  1. Source

    Where the system draws its components from. Each edge names the component it refers to; source differs between systems and is never generalised.

    • Continental crustinferred

      component
      The host and wall rocks through which the system operates, and which are altered by it.
      precisionNote
      A setting edge, not a metal-source edge: the model attributes the metals to the magma, not to leaching of the crust.

    • Magmatic-hydrothermal fluidinferred

      component
      Metals and the ore-forming fluid, both derived from the associated granitoid porphyry magma.
      model
      USGS Porphyry Copper Deposit Model, which describes the source as magmatic in its generalized model.

  2. Transport

    What moves the components, and under what conditions. What a medium can carry depends on temperature, pressure, salinity and redox state, so every edge states the conditions it holds under.

    • Hypersaline brinemodelled

      conditions
      Below about 1.4 kilobars, where the single-phase fluid separates into a high-salinity brine and a lower-salinity vapour.

    • Magmatic-hydrothermal fluidmodelled

      conditions
      Single supercritical phase of about 3 to 5 weight percent salinity above about 1.4 kilobars, equivalent to depths greater than about 5 kilometres.

  3. Pathway and focusing

    What concentrated the flow. The presence of a structure is never on its own evidence that it focused anything, so each edge states the basis for the claim.

    • Advanced argillic alterationestablished

      method
      Named by the USGS model among the alteration types of the system.

    • Intermediate argillic alterationestablished

      method
      Named by the USGS model as intermediate argillic alteration.

    • Potassic alterationestablished

      method
      Alteration mapping compiled by the USGS model; potassic alteration is directly associated with the quartz-rich stockwork veining that carries the mineralisation.

    • Propylitic alterationestablished

      method
      Named by the USGS model among the alteration types of the system.

    • Sericitic alterationestablished

      method
      Named by the USGS model among the alteration types of the system.

    • Volatile exsolutionmodelled

      precisionNote
      Exsolution from the crystallising magma is what makes a fluid available to the system at all; the edge records the model’s account, not an observation.

  4. Deposition

    Why the components stopped moving. A system may use more than one mechanism, and different mechanisms leave different signatures.

    • Coolinginferred

      precisionNote
      Inferred from the zoned alteration pattern the model describes; the report does not isolate cooling as a single named mechanism as the VMS model does.

    • Fluid phase separationmodelled

  5. Minerals, in their role here

    Mineral role is a property of a mineral in a system, not of the mineral. The same species is an ore mineral in one system and gangue in another.

    • Chalcopyriteestablished

      role
      ore mineral

    • Magnetiteestablished

      role
      accessory mineral

    • Muscoviteinferred

      role
      alteration mineral
      precisionNote
      Sericite in the model’s usage is fine-grained white mica; Lithoen records the IMA species muscovite and marks the identification inferred rather than asserting that all sericite is muscovite.

    • Pyriteestablished

      role
      gangue
      precisionNote
      Pyrite is the sulfur-bearing gangue of the porphyry assemblage; in other systems it is the ore mineral. The role is a property of the mineral in this system, not of pyrite.

    • Quartzestablished

      role
      gangue
      precisionNote
      Quartz forms the stockwork veins that carry the mineralisation and is never itself the ore.

  6. Modification and preservation

    What happened after the system finished. Formation is not preservation, and what is observed today is the sum of both.

    • Erosional removalinferred

      precisionNote
      Preservation depends on erosion having removed enough cover to expose the system but not enough to destroy it. The cited evidence establishes the general principle from the VMS model.

    • Supergene enrichmentinferred

      precisionNote
      Recorded because near-surface oxidation and supergene redistribution overprint what is exposed of these systems. The cited evidence establishes supergene processes generally, not their operation in any named porphyry system.

  7. Commodity association

    A geological association only: a commodity characteristically won from this class of system where one is developed and preserved. No statement about any occurrence, and none about value.

  8. Tectonic and geological context

    The settings in which this system has been DOCUMENTED. Tectonic context is a necessary or common component of some models; it is not proof that mineralisation is present anywhere. Every entry states what else the setting contains.

    • Subductionestablished

      What else the setting contains
      Subduction-related magmatic arcs have existed continuously somewhere on Earth for most of Earth history and are among its most extensive features. The model adds that porphyry systems are localized in time and space within an arc’s evolution, so the arc does not determine the outcome.
      precisionNote
      A documented context, not a prediction. The setting is vastly more extensive than the systems found in it, and this edge asserts only that sources place the system here.

  9. Observable expressions

    Features commonly associated with this system — and, for each, what else produces the same observation. None of these demonstrates that a system operated anywhere, and Lithoen ranks nothing.

    • Hydrothermal alterationinferred

      What else produces this
      Hydrothermal alteration is produced by any hydrothermal system, mineralised or barren; propylitic assemblages in particular are widespread and weakly diagnostic, and infrared mapping detects the mineralogy without distinguishing its cause.

How this record is known

9
Settled consensus
Cited as the accepted position of the discipline.
7
Interpretation
Reached by reasoning from evidence, or produced by a named model.

16 of 16 claims on this page cite at least one registered source. Counts describe how each statement is known, not how likely it is to be true.

What Lithoen records

Each claim states how it is known and cites its evidence.

InferredContext describes where systems have been found. It predicts nothing about a place.

A documented tectonic context is a statement about where a class of system has been found, not a statement about where one exists. Every setting recorded in this corpus is vastly more extensive than the systems found in it, several systems occur across settings with nothing in common, and one — nickel-cobalt laterite — depends more on climate and exposure than on tectonics at all. Lithoen records context and makes no inference from it about any place.

  • method: Follows from comparing the six documented contexts: their extents, their diversity, and the model statements that assignment is uncertain in Archean terranes and that affinity is poorly understood for older porphyry deposits.
  • non uniqueness: This claim is the general form of the nonUniqueness qualifier carried on every individual context claim.

Evidence support: Supported by the cited evidence 3 sources, multiple sources, independence unknown

Evidence: John 2010 Primary authority; Marsh 2013 Primary authority; III 2012 Primary authority

InferredMineralisation → deposit → resource → reserve: each step adds something Lithoen does not assert.

Mineralisation, deposit, resource and reserve are four different things. Mineralisation is the geological presence of concentrated minerals; a deposit is a body of it; a resource and a reserve are classifications that add economic and engineering judgement Lithoen does not make.

  • method: Follows from the cited definition of ore, in which value and recoverability are explicit, combined with the system-versus-deposit distinction.
  • precision note: Lithoen implements no resource or reserve classification framework and makes no statement in either category.

Evidence support: Supported by the cited evidence 2 sources, multiple sources, independence unknown

Evidence: John 2010 Primary authority; Geoscience Australia 2016 Primary authority

EstablishedOre = concentration + value + location + recoverability under stated economic requirements.

Ore is not a purely geological term. The USGS porphyry model defines ore as rock in which the concentration, value, location and recoverability of the metal enable mining under predetermined economic requirements — so value and recoverability are part of the definition, not consequences of it.

  • definition basis: The definition is quoted from a Tier A deposit model, not constructed by Lithoen.
  • precision note: It follows that a mineralised body is not ore merely because it contains a useful element, and that Lithoen — which holds no economic framework — may not call anything ore.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

EstablishedPotassic, sericitic, advanced argillic, intermediate argillic, propylitic, sodic-calcic and sodic, greisen, skarn.

The alteration types recognised in porphyry copper systems are potassic, sericitic, advanced argillic, intermediate argillic, propylitic, sodic-calcic and sodic, greisen, and skarn.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

EstablishedMany features of these systems remain poorly understood as controls of ore formation.

The report states that the regional, deposit-scale and local-scale environments of porphyry copper deposits are diverse and that, despite much scientific study, many features are poorly understood in regard to their relevance as controls of ore formation.

  • precision note: Recorded for the best-studied and most economically important mineral system on Earth, in the words of the model that describes it.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

EstablishedDisseminated and vein-hosted copper through large rock volumes around an altered granitoid porphyry.

Porphyry copper deposits consist of disseminated copper minerals and copper minerals in veins and breccias, relatively evenly distributed through large volumes of rock; host rocks are altered, genetically related granitoid porphyry intrusions and adjacent wall rocks.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

Model output3–5 wt%NaCleq

Fluids derived from porphyry magma at more than 1.4 kilobars have moderate to low salinity of about 3 to 5 weight percent before phase separation.

  • model: USGS Porphyry Copper Deposit Model, which reports the value as a model attribute rather than a single measurement.
  • system context: Single-phase magmatic fluid before separation into brine and vapour, in porphyry copper systems.
  • conditions: Pressures above about 1.4 kilobars, equivalent to more than about 5 kilometres depth.
  • precision note: Salinity is conventionally reported as weight percent NaCl equivalent, a recalculation rather than a direct measurement of NaCl.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

Model output0.3–2 wt%m Copper

The USGS model characterises porphyry copper deposits as low- to moderate-grade, in the range 0.3 to 2.0 percent copper.

  • model: USGS Porphyry Copper Deposit Model, which gives this as a class descriptor.
  • locality: The deposit class as a whole, not any individual occurrence.
  • precision note: A descriptive attribute of the class in a published model. It is not a resource statement, not a reserve statement, and says nothing about any particular place.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

EstablishedUSGS Porphyry Copper Deposit Model (SIR 2010–5070–B), John and others, 2010.

This record represents the USGS Porphyry Copper Deposit Model, chapter B of Mineral Deposit Models for Resource Assessment, edited by David A. John with thirteen contributors and published in 2010. Lithoen represents that model and does not extend it.

  • model: USGS Porphyry Copper Deposit Model, Scientific Investigations Report 2010–5070–B.
  • precision note: A model is an interpretation of many deposits, not an observation of any one.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

EstablishedAlteration mineralogy detectable by infrared remote sensing.

Hydrothermal minerals characteristic of sericitic, intermediate and advanced argillic, and propylitic alteration, together with iron oxides and hydroxides and silica, can be mapped remotely through their distinctive absorption features in the visible near-infrared, short-wave infrared and thermal infrared.

  • non uniqueness: The same alteration minerals are produced by hydrothermal systems that never developed mineralisation, and propylitic assemblages in particular are widespread and weakly diagnostic.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

Model outputMetals and fluids both derived from the associated magma.

The generalized model involves the interplay between magmatic metal sources and hydrothermal fluid systems, in igneous rocks related to one another geographically, temporally and genetically.

  • model: USGS Porphyry Copper Deposit Model.
  • component: Metals and ore-forming fluids.
  • precision note: A generalized model, in the report’s own words; individual systems may differ.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

Established60 percent

Porphyry copper deposits account for more than 60 percent of annual world copper production and about 65 percent of known copper resources.

  • precision note: The value carried is the production share, stated by the source as "more than 60 percent"; the resource share of about 65 percent is given in the statement.
  • method: Reported by the USGS deposit model from published production and resource compilations.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

Model output1.4 kbar

The transition between single-phase supercritical fluid and separated brine plus vapour in porphyry systems occurs near 1.4 kilobars.

  • model: USGS Porphyry Copper Deposit Model.
  • system context: Magmatic fluid exsolving from porphyry plutons.
  • precision note: A model boundary rather than a measured threshold; the report gives it alongside an approximate depth of 5 kilometres.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

EstablishedSubduction-related arcs, mostly — with real variety inside that, and poorer resolution with age.

Most porphyry copper deposits form in subduction-related magmatic arcs along convergent plate margins, in both continental and oceanic settings. Within those arcs deformation can be very complex and the deposits form in a variety of tectonic settings; some form in back-arc or post-subduction settings where, the model says, tectonic affinity is more poorly understood — especially for most Mesozoic and older deposits.

  • non uniqueness: Subduction-related magmatic arcs are among the most extensive tectonic features on Earth and have been for most of Earth history. The setting is where these systems are found; it is not a place where one should be expected.
  • precision note: The model adds that porphyry systems are widespread but seem to be localized in time and space within the evolution of an arc — which is a statement that the setting alone does not determine the outcome.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

Model outputExsolved magmatic fluid, initially supercritical, separating into brine and vapour as pressure declines.

Fluid-phase separation from porphyry magmas fractionates water, metals, sulfur and other volatiles out of the crystallising melt. Fluids leaving magma deeper than about 5 kilometres are a single supercritical phase of moderate to low salinity, around 3 to 5 weight percent, which separates into high-salinity brine and lower-salinity vapour as pressure falls.

  • model: USGS Porphyry Copper Deposit Model.
  • conditions: Above about 1.4 kilobars, equivalent to depths greater than about 5 kilometres, the fluid is a single supercritical phase.
  • component: Water, metals, sulfur and other volatiles.

Evidence support: Supported by the cited evidence one source

Evidence: John 2010 Primary authority

EstablishedThe system is the geosystem; the deposit is a small part of it that may or may not be present.

A mineral deposit is one very small part of a much larger geosystem. The signatures of a mineral system extend well beyond any deposit it may contain, which is why the system is treated as the larger target — Geoscience Australia applies the approach because roughly 80 per cent of Australia is covered by younger basins and regolith that obscure direct signatures. It follows that evidence for part of a system is not evidence that a deposit exists.

  • precision note: Stated by Geoscience Australia in the context of exploration under cover. Lithoen records the scientific relation, not the exploration application.

Evidence support: Supported by the cited evidence one source

Evidence: Geoscience Australia 2016 Primary authority

In the knowledge graph

Figures

A schematic ladder of four boxes — observation, interpretation, system inference, and a dashed deposit-conclusion box above a solid red line labelled Lithoen does not cross this line — with explanatory text at the right.
SchematicFour levels of statement, and the line Lithoen does not cross. An observation is a fact about a rock; an interpretation is a fact about a model; a system inference needs several independent observations to coincide, because each control typically has an unmineralised counterpart; and a deposit conclusion needs spatial data, validation and an economic framework this corpus does not hold.

Original Lithoen diagram · LITHOEN-ORIGINAL

Outcrop of pale mottled rock crossed by wavy brown mineralised veins, with whitish clay-altered zones adjacent to each vein.
Wall rock beside hydrothermal veins in the Butte quartz monzonite, where the original minerals have been altered to clay. Argillic alteration of this kind is one of the assemblages the USGS porphyry model recognises, and it is also, on its own, one of the least diagnostic: alteration marks where hot water was, which is a far larger thing than where metal accumulated. Locality: Orphan Boy Mine, Butte, Montana, United States, as stated by the source.

James St. John, CC BY 2.0 · CC-BY-2.0 · source · Derivative: Downscaled to 1200 px wide by the Wikimedia thumbnail service; no cropping, no colour or content alteration.

Record last updated 2026-09-07. Corrections follow the published corrections policy; superseded claims are retained, never silently edited.