earth science

Greisen

Greisen 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 Greisen rather than just read about it. In short: Greisen is a highly altered granitic rock or pegmatite, usually composed predominantly of quartz and micas (mostly muscovite). Greisen is formed by self-generated alteration of a granite and is a class of moderate- to high-temperature magmatic-hydrothermal alteration related to the late-stage release of volatiles dissolved in a magma during the solidification of that magma.

Key takeaways

Greisen 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 Greisen to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Greisen from memory before moving on to harder problems.

Reference excerpt

Greisen is a highly altered granitic rock or pegmatite, usually composed predominantly of quartz and micas (mostly muscovite). Greisen is formed by self-generated alteration of a granite and is a class of moderate- to high-temperature magmatic-hydrothermal alteration related to the late-stage release of volatiles dissolved in a magma during the solidification of that magma. Greisens are usually variably altered rocks, grading from coarse, crystalline granite, commonly vuggy with miarolitic cavities, through to quartz and muscovite rich rocks, which may be locally rich in topaz, tourmaline, cassiterite, fluorite, beryl, wolframite, siderite, molybdenite and other sulfide minerals, and other accessory minerals. They may occur as small to large veins, or large zones in the roof of some granites. The rocks can sometimes be mined as ores of tin and other minerals.

Petrogenesis Greisens are formed by endogenous alteration of granite during the cooling stages of emplacement. Greisen fluids are formed by granites as the last highly gas- and water-rich phases of complete crystallisation of granite melts. This fluid is forced through the interstitial spaces of the granite into veins and pools at the upper margins, where boiling and rock alteration occur.

Alteration facies Incipient greisen (granite): addition of muscovite ± chlorite, topaz, tourmaline, and fluorite (original texture of granites retained). Greisenized granite: quartz-muscovite-topaz-fluorite, ± tourmaline (some original texture of granites retained). Massive greisen: quartz-muscovite ± topaz ± fluorite ± tourmaline (typically no original texture preserved). Tourmaline can be ubiquitous as disseminations, concentrated or diffuse clots, or late fracture fillings. Greisen may form in any wallrock environment, but typically in granites and metamorphic rocks.

Greisen environments Greisens appear to be restricted to intrusions which are emplaced high in the crust, generally at a depth between 0.5 and 5 km, as the hydrous fluid separation from granite to produce greisenation cannot occur deeper than about 5 kilometres. The roof or upper aureole is mostly sealed shut to prevent most fluids escaping. This sealing is largely due to hornfelsing and silicification of the overlying rocks, and fracturing of these rock typically forms greisen veins. They are generally associated mostly with potassic plutonic rocks; Alkali feldspar granite, and are rare in less potassic rocks like granodiorite or diorite. Greisens are prospective for mineralisation because the last fluids of granite crystallization tend to concentrate incompatible metals such as tin, tungsten, molybdenum and beryllium, and in places other metals such as tantalum, gold, silver, and copper. Tectonically, greisen granites are generally associated with generation of S-type suites of granites in thick arc and back-arc fold belts where subducted sedimentary and felsic rock is melted.

Distribution

Examples of greisen are:

Tin and tungsten deposits of Cornwall Ardlethan, New South Wales, Australia (tin-antimony greisen) Timbarra gold mine, New South Wales, Australia (gold greisen deposit) Anchor Mine, Lottah, Tasmania, Australia (tin copper topaz greisen) Pitinga topaz granite, Brazil (tin, topaz, beryl) Lost River, Alaska, US (tin greisen) Sisson Brook, Burnt Hill and other deposits, New Brunswick, Canada (tin-tungsten-molybdenum greisen) Ore Mountains, Czech Republic (tin greisen) Panasqueira Mine, Portugal Tin and Tungsten deposit The Tin Range Tungsten-Tin deposit, Stewart Island/Rakiura, New Zealand

See also Granite – Type of igneous rock; specifically for S-type and I-type distinction List of rock textures – List of rock textural and morphological terms Metasomatism – Chemical alteration of a rock by hydrothermal and other fluids Ore genesis – How the various types of mineral deposits form within the Earth's crust Quartzolite – Extremely rare igneous rock made mostly of quartz

References

Evans, A.M., 1993. Ore Geology and Industrial Minerals, An Introduction., Blackwell Science, ISBN 0-632-02953-6 Reed, B.L., 1986, Descriptive model of Sn greisen deposits, in Dennis P. Cox and Donald A. Singer, eds, Characteristics of mineral deposit occurrences: U.S. Geological Survey Bulletin 1693, https://pubs.usgs.gov/bul/b1693/html/bull217y.htm Taylor, R.G., 1979, Geology of tin deposits: Elsevier, Amsterdam, 543 p. ISBN 0-444-41805-9 Mustard, R. 2004. Textural, mineralogical and geochemical variation in the zoned Timbarra Tablelands pluton, New South Wales. Australian Journal of Earth Sciences, 51. Richardson, G.C. (2016) Lottah and the Anchor: the history of a tin mine and a dependent town: North East Tasmania. Tasmania Forty South Publishing Pty Ltd, Hobart, 265 pages and maps.

External links Lenharo, S.L.R., Pollard P.J., Born H., Matrix rock texture in the Pitinga Topaz Granite, Amazonas, Brazil, Brazilian Geoscience Reviews, vol 30, 2000 (pdf)

Illustrations

Worked examples

Example 1 — a first encounter with Greisen

Start with the simplest possible case. Write down what Greisen 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 Greisen 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 Greisen 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 Greisen

In research: Greisen 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 Greisen 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: Greisen is common in secondary-school and first-year university syllabi. It links to neighbouring topics Economic geology, Igneous rocks, so understanding it makes those chapters shorter.
In everyday life: Look for Greisen 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 Greisen in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Greisen 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 Greisen out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Greisen in simple terms?

Why does Greisen 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 Greisen?

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 Greisen.