1. PROFESSIONAL CAREER OF MINING
ENGINEERING
Skarn type deposit
COURSE:
DEPOSIT OF MINERALS
TEACHER:
Ing. JOSE SALAS MEDINA
SEMESTER:
2018-1
2. Content
TYPE SKARN FACILITY
1.Definition:............................................................................................................................................................................1
2. Origin: .................................................................................................................................................................................1
3.Mineralization:....................................................................................................................................................................2
4. Metamorphic and metasomatic final members ............................................................................................................2
5. Formation stages:..............................................................................................................................................................3
a) Isochemical metamorphism:............................................................................................................................................3
b) Multiple stages of metasomatism:..................................................................................................................................3
c) Retrograde alteration: .......................................................................................................................................................3
6.Principal types of Skarn structures..................................................................................................................................4
7. Types of Skarn deposits ...................................................................................................................................................4
7.1 Gold Skarns .................................................................................................................................................................4
7.2 Iron Skarns...................................................................................................................................................................5
7.3 Tungsten skarns ..........................................................................................................................................................5
7.4 Copper skarns..............................................................................................................................................................5
7.5 Zinc-Lead Skarns........................................................................................................................................................5
7.6 Tin Skarns ....................................................................................................................................................................6
7.7 Molybdenum Skarns ..................................................................................................................................................6
8.Skarn in Peru:......................................................................................................................................................................6
9.Conclusions:........................................................................................................................................................................7
10. Bibliography:...................................................................................................................................................................7
3. 1
TYPE SKARN FACILITY
1.Definition:
Skarn refers to a rock or metamorphosed zone around an igneous intrusion that is
characterized as consisting of a carbonate rock with minerals product of
metasomatism.
In mining it refers to a bargain of silicates (amphiboles, pyroxenes, garnets, etc.) of
certain deposits of iron and sulfides of Archaic age, particularly those that have
replaced limestones and dolomites with the introduction of large quantities of Si, Al, Fe
and Mg, some use it as a synonym of tactita.
2. Origin:
Skarn deposits refer to an association of calcium silicates and associated
metals, whose origin is the result of processes involving a metasomatic and
hydrothermal replacement, also called pyrometatomics, related in time and
space to the cooling of acidic to intermediate igneous bodies, and the action
of magmatic emanations that react with carbonate box rock.
A condition of the Skarn formation, referred to a magmatic arc where the
intrusives of medium - acid composition come into contact with sedimentary
rocks of the calcareous and dolomite type and from this interaction
metamorphism phenomena of contact occur and that later with the cooling
of the intrusive Fluids are released that react with the limestones and the
phenomenon of metasomatism occurs.
4. 2
3.Mineralization:
The mineralogy of these deposits varies widely, so generalizations should be viewed
with caution. These are the world's leading source of tungsten, large producers of
copper, iron, molybdenum and zinc and a minor source of cobalt, gold, silver, lead,
bismuth, tin, beryllium and boron. They are a source of industrial minerals such as
graphite, asbestos, wollastonite, magnesite, phlogopite, talc and fluorite.
The main minerals of ore (highly variable from one deposit to another) are:
Molybdenite, magnetite, sphalerite, galena, chalcopyrite, bornite, pyrite,
arsenopyrite, marcasite wolframite and scheelite. Among the minors are pyrrhotine,
cassiterite, hematite, gold and sulfur bismuth and silver.
The gangue minerals are represented by garnets, pyroxenes, olivine, pyroxene,
amphiboles, epidote and plagioclase.
4. Metamorphic and metasomatic final members
The skarn, a rock that consists of calc-silicate minerals, can be generated by purely
metamorphic or purely metasomatic processes, skarns can also encompass a range
between the processes of final members.
Metamorphism of volcano-sedimentary rocks group enrichment in additional metals
such as manganese and zinc.
In some cases; The generating environment of mineralizing fluids are metamorphic
and the mineral components were mobilized by some early concentration dissolution
processes. The resulting mineral deposits can be equal in mineralogical and
petrographic terms of the final interaction result of a magmatic hydrothermal fluid with
carbonate rocks. This is because hydrothermal fluids of different origin can, after
5. 3
interaction enough with a given environment to acquire similar chemical
characteristics and produce similar results. The framework of a scheme of two final
members for the genesis of thermometamoric and metasomatic skarn deposits is
based on the source of the components.
It is concluded that hydrothermal fluids include the formation of mineral deposits that
can acquire their dissolution load through different paths, however, the classification
scheme based only on the source of the components is intrinsic properties including
mineralogy, morphology and tectonic origin.
5. Formation stages:
There are three stages in the formation of a skarn type deposit:
a) Isochemical metamorphism: metamorphic recrystallization occurs and
mineralogical changes, which form chalcosilicate minerals. It includes the development
of marble, cornea, quartzite, reaction skarn, skarnoides, talc and wollastonite towards
the periphery.
b) Multiple stages of metasomatism: crystallization of the magma and release of a
fluid phase. Formation of anhydrous minerals at temperatures of 400 ° -800 ° C.
c) Retrograde alteration: cooling of the pluton and circulation of water temperatures
lower than the previous stage. Hydrated minerals are formed from the anhydrous
minerals previously formed, including: epidote, actinolite, chlorite and others. There is
a structural control and a superimposition to the progrado sequence.
6. 4
6.Principal types of Skarn structures
A: Skarn Biometasomático
B: Vein in Exoskarn
C: Vein in Endoskarn
D: Skarn Frontal
1: Intrusive. 2: Limestone
3: Skarn. 4: Shale
7. Types of Skarn deposits
7.1 Gold Skarns
It refers to deposits of minerals that are extracted, exclusively or predominantly gold, and that
exhibit alteration of calcosilicático rocks, usually dominated by garnet and pyroxene, which is
related to mineralization. This excludes the use of deposits that contain gold but are mined
primarily for other commodities such as copper. On the contrary, this definition includes
deposits that contain large amounts of other metals (such as Fe, in the form of magnetite) that
are not mined
7. 5
7.2 Iron Skarns
The largest skarns are iron deposits. Iron Skarns are mined for their magnetite
content and although small amounts of Cu, Co, Ni and Au may be present, iron
is generally the only recoverable commodity. Many of the deposits are very large
(> 500 million tons,> 300 million tons listed as Fe) and consist predominantly of
magnetite with little gangue silicate. Some deposits contain significant amounts
of copper and are more typical of transition to copper skarns.
7.3 Tungsten skarns
Tungsten skarns are found on most continents in associationwith calco-alkaline
plutons in the main orogenic belts. As a group, tungsten skarns are associated
with coarse-grained, equigranular batholiths (with pegmatite and aplite dykes),
surrounded by large, high-temperature metamorphic aureoles. These
characteristics are collectively indicative of a deep environment. Plumes with
endoskarn near the contact areas typically fresh with only small amounts of
mirmakita-plagioclase and pyroxene.
7.4 Copper skarns
Copper skarns are perhaps the most abundant type in the world. They are
especially frequent in areas related to orogenic subduction, both in the
continental and oceanic configuration. Most copper skarns are related to type
I, magnetite series, calco-alkaline, porphyric plutons, many of which are co-
genetic to volcanic rocks, veins in stockwork, and brecciation brittle fracture,
and intense hydrothermal alteration. These are indicative characteristics of a
relatively training environment. Most copper skarns are formed in the vicinity of
contacts with a mineralogy relatively dominated by andradite.
7.5 Zinc-Lead Skarns
Most zinc skarns occur in the continental territory associated with subduction
or rifting zones. They are mines of zinc, lead, silver ore although zinc is usually
dominant. They also cover diverse deep geological environments such as
batholiths to shallow complex dike-sills on the surface of volcanic extrusions.
The common criterion that binds most Skarn minerals to distal zinc is that they
occur in association with igneous rocks. Zinc Skarns can be subdivided
according to several criteria, including the distance of magmatic origin, the
formation temperature, the relative proportion of Skarn and sulfides, and the
geometrical shape of the mineral body.
8. 6
7.6 Tin Skarns
Tin skarns are almost exclusively associated with high silica granites produced
by the melting of the continental crust. Tin skarns can be subdivided according
to several criteria, including proximal versus distal, magnesian versus calcic,
Skarn rich versus poor skarns, rich oxide versus rich sulfur, and greisen versus
Skarn. Unfortunately, some of these categories are mutually exclusive.
Many of the large tin Skarn systems are spatially zoned from rich Skarn to poor
Skarn (or absent).
7.7 Molybdenum Skarns
Most molybdenum skarns are associated with leucocratic granites and the
range of high-rank, relatively small low-grade deposits. Numerous small
deposits are also found in the Precambrian associated with stable cratons of
pegmatite, aplite, rocks and other leucocráticos. Most molybdenum skarns
contain a variety of metals such as W, Cu, Zn, Pb, Bi, Sn, and U, and some are
actually polymetallic in various metals that must be recovered in order to be
mined economically. Mo-W-Cu is the most common association of some
tungsten skarns and copper skarns containing recoverable molybdenum zones.
8.Skarn in Peru:
The Skarn type deposits in Peru are of great importance in the production of metal
mining, much of the polymetallic production (zinc, lead, copper, silver) comes from
these skam-type deposits located in the Mesozoic Sedimentary Belt in the Interandina
Mountain Range, as son: Antamina (Cu, Zn, Ag, Mo), Raura (Zn, Pb, Ag), Morococha
(Cu, Ag, Zn, Pb), Milpo-Atacocha (Zn, Pb, Ag), Tintaya (Cu, Mo ), and a skarn type
deposit in Cobriza in the Eastern Cordillera.
The only iron deposit in real production in Peru is the Marcona skarn deposit. The
future of the iron deposits in Peru is in the Mesozoic Sedimentary Belt of the
Interandina Mountain Range, between Andahuaylas (department of Apurímac) and
Yauri (department of Cusco); These are deposits of iron type skarn.
9. 7
9.Conclusions:
Skarn type deposits are important sources mainly of Copper and Tungsten
throughout the world.
Describing the evolutionary processes of the Skarn is of vital importance, as this
will identify the minerals associated with each type of deposit.
The relationship exists between the different training environments of skarns, and
what defines a rock as skarn, is mineralogy.
The minerals that are very useful for the classification and exploration of skarns
are garnet, pyroxene and amphiboles.
The development of skarn depends on the depth of formation. At shallower levels,
the metasomatic skarn has a wide lateral extension and can surpass the
metamorphic aureole, while in depth it is relatively small compared to the aureole
of metamorphism.
10. Bibliography:
http://www.geovirtual2.cl/depos/02skarn01.htm
BATEMAN, A. (1961): Yacimientos Minerales de Rendimiento Económico. - 975
páginas; Ediciones Omega S.A. Barcelona (España).
http://www.geoaprendo.com/2015/06/resumen-depositos-tipo-skarn.html
