depositos Skarns

7/27/2019 depositos Skarns

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Skarn Deposits

The Power of Fluids

Skarns

Deposits formed at elevated temperatures by the additionand subtraction of material (metasomatism)

Most often developed at the contact of intrusive plutonsand carbonate country rocks. The latter are converted to

marbles, calc-silicate hornfels and/orskarns by contact

metamorphic effects.

Skarn is an old Swedish mining term for silicate gangue Skarns have been termed tactites, hydrothermal

metamorphic, igneous metamorphic, contact metamorphic,

and pyrometasomatic (Lindgren)


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Generalizations

rough temperature of initial skarn formation400-650C

pressures variable, form at depths of 1 to 10+ km some classic skarns are associated with porphyry

copper deposits, indicating a relatively shallowdepth of emplacement

clinopyroxene, garnet and wollastonite commoncalc-silicate minerals

Definitions

skarns can be classified according to therocks they replace, and the terms exoskarn

and endoskarn are applied to replaced oraltered carbonate metasediments and

intrusive rocks, respectively

both endo- and exoskarns may contain ore However in a couplet where the exoskarn is a

converted marble then it usually contains

most or all the economic mineralization

Classification

Exoskarns may be classified accordingto the dominant mineralogy:

magnesium - Mg - forsteritecalcic - Ca - andradite, diopside

Majority of the worlds economic skarndeposits occur in calcic exoskarns


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Classification

Skarn deposits described according to thedominant economic metal or mineral present:

e.g. copper, iron, tungsten, zinc-lead,molybdenum, tin, talc etc.

Generally skarns are smaller than many otherdeposit types such as porphyries, lead-zinc,

sediment-hosted sulfide deposits

Types of Skarn Deposits

Copper skarn deposits, especially those withby-product Au and/or Ag, have been worked

in many parts of the world.

Large deposits may occur associated withporphyry copper deposits, e.g. Twin Buttes,

Arizona and Bingham Canyon, Utah.

Zn-Pb skarn deposits common but small Mo and Sn skarns of little importance

Skarn Zonation

Exoskarns show zoning of both silicate and oreminerals

Endoskarn also displays zonation resulting from theprogressive addition (back flushing) of calcium into

the igneous protolith.

A common zonation outwards towards the marblehost is biotite - amphibole - cpx - garnet. K-feldspar

may disappear but plagioclase commonly survives.


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Gain-loss: Santa Rita stock, NM

limestone

Gain-loss: Santa Rita stock, NM

shale

Evolution of Skarns


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Average Composition of Plutons Tectonic Settings

Tectonic Settings


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Copper Skarn Zinc Skarn

Copper Canyon, Nevada Cu-Ag-Au: Copper Canyon NV


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Gold SkarnGold Skarn X-section

Iron Skarn - Russia Linchberg Mine, NM


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Pine Creek - W Skarn

As a specific example, Pine Creek, CAwas a world class tungsten source for

many years.

Interesting upside-down mine Interesting underground weather Spectacular scenery


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Igneous Rx

Plagioclase Quartz K-feldspar Biotite

Endoskarn

Plagioclase Quartz K-feldspar Diopside Sphene (titanite) Scapolite

Skarn

Garnet Pyroxene Scheelite

Marble

Calcite Diopside Graphite? Vesuvianite? Grossular?


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Documents

depositos Skarns