User:Lukaszquinn/sandbox

Rough Draft: Week 7 - Skarn


 * Just a note, the only recent papers associated with skarn or skarn deposits are only summaries. There might be papers talking about specific skarn or skarn deposits but they all cite the papers below.

1. Summary Section

I wish to remove the "or tactites" part because I am unable to find publications that even mention this. Therefore, it will be changed to: Skarns are hard, coarse-grained metamorphic rocks that form by a process called Metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate minerals (Einaudi & Burt, 1982; Ray & Webster, 1990; Meinert, 1992; Hammarstrom et al., 1995). These minerals form as a result of alteration which occurs when hydrothermal fluids interact with a protolith of either igneous or sedimentary origin. In many cases, skarns are associated with the intrusion of a grainitic pluton found in and around faults or Shear zones that intrude into a carbonate layer such as a dolomite or limestone. Skarns can form by regional, or contact metamorphism and therefore form in relatively high temperature environments (Einaudi & Burt, 1982; Ray & Webster, 1990; Meinert, 1992; Hammarstrom et al., 1995). The hydrothermal fluids associated with the metasomatic processes can originate from either magmatic, metamorphic, meteoric, marine, or even a mix of these (Meinert, 1992). The resulting skarn may consist of a variety of different minerals which are highly dependent on the original composition of both the hydrothermal fluid and the original composition of the protolith (Meinert, 1992).

If a skarn has a respectable amount of ore mineralization that can be mined for a profit, it can therefore be classified as a skarn deposit (Einaudi & Burt, 1982; Ray & Burt, 1990; Meinert, 1992)

2. Petrology

Skarns are, in their broadest sense, formed by mass and chemical transport and reactions between adjacent rock units. They need not be igneous in origin; two adjacent sedimentary layers such as a banded iron formation and a limestone may react to exchange metals and fluids during metamorphism, creating a skarn.-> this paragraph will be re-written.

However, the widest use of the word is in describing the metasomatised zones of wall rock adjacent to granites. Skarns which are created by reaction between metamorphic-sedimentary layers are also known as chemical skarns or skarnoids. Skarns must also be distinguished from calc-silicate hornfels, usually by field relationships. -> This paragraph will be removed as it is explained in the formation section.

Skarns of igneous origin are classified as exoskarns or endoskarns. Exoskarns occur at and outside the granite which produced them and are alterations of wall rocks. Endoskarns, including greisens, form within the granite mass itself, usually late in the intrusive emplacement and consist of cross-cutting stockworks, cooling joints and around the margins and uppermost sections of the granite itself. -> This paragraph will be removed from the original page as it is explained in the classification section.

Skarn deposits can be classified based on their dominant economic element, such as W-skarn, or Fe-skarn. -> This sentence is also explained in the classification section.

Skarns are composed of calcium-iron-magnesium-manganese-aluminum silicate minerals. Skarn deposits are economically valuable as sources of metals such as tin, tungsten, manganese, copper, gold, zinc, lead, nickel, molbdenum and iron (Hammarstrom et al., 1995).

Skarn is formed by a variety of metasomatic processes during metamorphism between two adjacent lithologic units. Skarn can form in almost any lithology type such as shale, granite and basalt but the majority of skarns are found in lithology containing a limestone or a dolostone. It is common to find skarns near plutons, along faults and major shear zones, in shallow geothermal systems, and on the bottom of the sea floor (Meinert, 1992). The mineralogy of skarn is highly related to the protolith.

Skarn minerals are mainly garnets and pyroxene with a wide variety of calc-silicate and associated minerals. Typical skarn minerals include pyroxene, garnet, idocrase, wollastonite, actinolite, magnetite or hematite, epidote and scapolite. Because skarns are formed from incompatible-element rich, siliceous aqueous fluids a variety of uncommon mineral types are found in the skarn environment, such as: tourmaline, topaz, beryl, corundum, fluorite, apatite, barite, strontianite, tantalite, anglesite, and others.

3. Classification (Decided to make Classification as its own Section because there is a substantial amount of information)

Skarns can be subdivided depending on specific criteria:

One way to classify a skarn, is by its Protolith. If the protolith is of sedimentary origin, it can be referred to as an exoskarn and if the protolith is igneous, it can be called an endoskarn (Ray and Webster, 1990; Meinert, 1992).

Further classification can be made based on the protolith by observing the skarns dominant composition and the resulting alteration assemblage. If the skarn contains minerals such as Olivine, Serpentine, Phlogopite, magnesium Clinopyroxene, Orthopyroxene, Spinel, Pargasite, and minerals from the Humite group, are characteristic of a dolomitic protolith and can be classed as a magnesian skarn. The other class, called calcic skarns, are the replacement products of a limestone protolith with dominant mineral assemblages containing Garnet, Clinopyroxene, and Wollastonite (Ray & Webster, 1990).

Rocks that contain garnet or pyroxene as major phases, are fine-grained, lack iron, and have skarn-like appearances, are generally given the term skarnoid. Skarnoid therefore is the intermediate stage of a fine-grained Hornfel and a coarse-grained skarn(Ray & Webster, 1990; Meinert, 1992).

Skarn deposits have typical skarn Gangue minerals but also contain ore minerals in abundance which are of economic importance. Skarn deposits are therefore classified by their dominant economic element, such as copper (Cu) skarn deposit, or molybdenum (Mo) skarn deposit to name a few (Einaudi & Burt, 1982; Ray & Webster, 1990; Hammarstrom et al., 1995).

Fe (Cu, Ag, Au) skarn deposits

The tectonic setting for calcic Fe skarns tends to be the oceanic island arcs. The host rocks tend to be gabbros to syenite associated with intruding limestone. The tectonic setting for magnesium Fe skarns tends to be the continental margin. The host rocks tend to be granodiorite to granite associated with intruding dolomite and dolomitic sedimentary rocks. Magnetite is the principal ore in these types of skarn deposits which its grade yields from 40 to 60 %. Chalcopyrite, bornite and pyrite are the minor ores. (Nadoll et al., 2014 and Soloviev & Kryazhev, 2017)

Cu (Au, Ag, Mo, W) skarn deposits

The tectonic setting for Cu deposits tends to be the Andean-type plutons intruding older continental-margin carbonate layers. The host rocks tend to be quartz diorite and granodiorite. Pyrite, chalcopyrite and magnetite are typically found in higher abundances. (Nadoll et al., 2014 and Soloviev & Kryazhev, 2017)

Types (After creating the Classification section, it appears that having a Types section is a little redundant. Therefore, since endo- and exoskarn are basically formation "Types", we will elaboration on their formation in the Formation section.)

4. Formation

Exoskarns are more common and form on the outside of an intrusive body that comes into contact with a carbonate unit.[3] They are formed when fluids left over from the crystallisation of the intrusion are ejected from the mass at the waning stages of emplacement. When these fluids come into contact with reactive rocks, usually carbonates such as limestone or dolostone, the fluids react with them, producing alteration (infiltration metasomatism).

Endoskarns form within the intrusive body where fracturing, cooling joints, and stockworks have been produced, which results in a permeable area. The permeable area can incorporate material from the carbonate layer. The magmatic hydrothermal fluids that were transported or created by the intrusion interacts with the carbonate material and forms the endoskarn. Endoskarns are considered to be rare.

Reaction skarn is formed from isochemical metamorphism occurring on thinly interlayered sedimentary lithology units that involves a small scale (perhaps centimetres) metasomatic transfer of components between adjacent units (Zarayskiy et al., 1987; Meinert, 1992).

Skarnoid is a calc-silicate rock that is fine-grained and iron poor. It lies in between a hornfel and a coarse-grained skarn (Korzkinskii, 1948; Zharikov, 1970; Meinert, 1992). Skarnoid tends to reflect the composition of the protolith (Meinert, 1992).

Most large skarn deposits experience a transition from early metamorphism which forms hornfels, reaction skarns, and skarnoids to late metamorphism which forms relatively coarser grained, ore-bearing skarns. The magma intrusion triggers contact metamorphism in the region where sedimentary rocks are present and forms hornfels as a result. The recrystallization and phase change of a hornfel reflect the composition of the protolith. After the formation of a hornfel, a process called metasomatism occurs which involves hydrothermal fluids associated with magmatic, metamorphic, marine, meteoric or even a mix of these. This process is called isochemical metamorphism and can result in the production of a wide range of calc-silicate minerals that form in impure lithology units and along fluid boundaries where small-scale metasomatism occurs (argillite and limestone, and banded iron formation).

The skarn deposits that are considered economically important contains valuable metals, are a result of large-scale metasomatism that the composition of fluid controls the skarn and its ore mineralogy. They are relatively coarser grained and do not reflect the composition of protolith or surrounding rocks. (Ray & Webster, 1990; Meinert, 1992)

Uncommon types of skarns are formed in contact with sulfidic or carbonaceous rocks such as black shales, graphite shales, banded iron formations and, occasionally, salt or evaporites. Here, fluids react less via chemical exchange of ions, but because of the redox-oxidation potential of the wall rocks.

Both the composition and the textures of protolith strongly play a role in the formation of the resulting skarn.

5. Ore Deposits --- (Shall we add the quantities of the ore that is associated with the examples that we have provided?)

The major dominant economic metals that make up skarn deposits are Copper, Tungsten, Iron, Tin, Molybdenum, Zinc-Lead, and Gold (Einaudi & Burt, 1982; Ray & Webster; Meinert, 1992; Hammarstrom 1995). Other minor economic minerals include Uranium, Silver, Boron, Fluorine, and Rare-earth elements (Meinert, 1992).

Some examples of the major economic skarn deposits are *(Note; some of these are currently being mined or have been mined in the past):


 * Iron skarns: Dashkesan Mine, Russia


 * Copper skarns: Bingham Canyon Mine, Utah, U.S.A


 * Tungsten skarns: Sangdong mine, South Korea


 * Gold-bearing skarns: Hedley Mascot Mine, British Columbia, Canada


 * Zinc-lead skarns: Santa Eulalia, Chihuahua, Mexico


 * Nickel skarns: Avebury Mine, Zeehan, Tasmania (Australia)


 * Molybdenum skarns: Yangchiachangtze mine, China

Additional Sources or Sources Used:

- Hammarstrom, J.M., Kotlyar, B.B., Theodore, T.G., Elliott, J.E., John, D.A., Doebrich, J.L., Nash, J.T., Carlson, R.R., Lee, G.K., Livo, K.E., Klein, D.P., 1995. Cu, Au, and Zn-Pb Skarn Deposits, Chapter 12; United States Geological Survey: Preliminary Compilation of Descriptive Geoenvironmental Mineral Deposit Models: https://pubs.usgs.gov/of/1995/ofr-95-0831/CHAP12.pdf.

- Meinert, L.D., 1992. Skarns and Skarn Deposits; Geoscience Canada, Vol. 19, No. 4, p. 145-162.

- Einaudi M.T., & Burt D.M., 1982. Introduction, terminology, classification and composition of skarn deposits. Economic Geology, 77, pp. 745–754.

- Einaudi, M.T., and Burt, D.M., 1982. Introduction – Terminology, classification, and composition of skarn deposits; Econ. Geol., Vol. 77, p. 745-754.

-Korzhinskii, D.S., 1948, Petrology of the Tur'insk skarn deposits of copper: Academy nauk SSSR, Institute of Geology Nauk Trudy, vvp. 68, Ser. Rundnykh Mestorozhdenii, No. 10, 147p.

-Zarayskiy, G.P., Zharikov, V.A., Stoyanovskaya, F.M., and Balashov, V.N., 1987, The Experimental Study Of Bimetasomatic Skarn Formation: International Geology Review, v. 29, p. 761-858

- Nadoll, P., Mauk, J. L., Leveille, R. A., & Koenig, A. E. (2014). Geochemistry of magnetite from porphyry Cu and skarn deposits in the southwestern United States. Mineralium Deposita, 50(4), 493-515. doi:10.1007/s00126-014-0539-y

- Soloviev, S. G., & Kryazhev, S. (2017). Geology, mineralization, and fluid inclusion characteristics of the Chorukh-Dairon W–Mo–Cu skarn deposit in the Middle Tien Shan, Northern Tajikistan. Ore Geology Reviews, 80, 79-102. doi:10.1016/j.oregeorev.2016.06.021

- Ray, G.E., and Webster, I.C.L. (1991): An Overview of Skarn Deposits; in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera; McMillan, W.J., compiler, B. C. Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, pages 213-252.

-Burt, D. M., (19770. Mineralogy and Petrology of Skarn Deposits: Societa Italiana di Mineralogia e Petrologia, 33 (2), 859-873.

Comments from Sarah Looks like you have a well thought out plan. Your references look good but they're old. Is there anything more recent you could add?

Skarn Improvement - February 15, 2018

The improvements we can make on Skarn.

1. The summary section will be edited so that it will flow a bit better. For example, this section has no sources cited and therefore we will be putting sources where applicable; information will therefore be added or removed based on the source material.

2. We hope to split the Petrology and Types into two parts. In the Petrology section, we would like to add any texture(s) associated with an average skarn. The minerals are very broad and hope to make them more specific for the major types of skarn.

3. For types, because the explanation of endo- and exo-skarn are repeated in both the Types section and Formation section, we will be adding a “Classification” section. There is more than one way to classify a skarn and therefore, we will be clarifying them accordingly.

4. A “Formation” section will be under the “Classification” section. Here, we will go into how endo- and exo-skarn form.

5. We likely add more ore deposit examples. Possibly one example per element. Hopefully find links for those examples via Wikipedia.

6. Possibly add a diagram or two. Maybe even a photo.

(Both of us worked on this together*)

View sandbox talk page for Alexander's Peer review of skarns

Sources:

-Tenney, D., 1981. The Whitehorse Copper Belt: Mining, exploration, and geology (1967-1980): Dept. Indian and Northern Affairs, Geology Section, Yukon, Bulletin 1, p. 29.

-Einaudi, M.T., and Burt, D.M., 1982. Introduction – Terminology, classification, and composition of skarn deposits; Econ. Geol., Vol. 77, p. 745-754.

-Einaudi, M.T., Meinert L.D., and Newberry, R.I., 1981. Skarn deposits; Econ. Geol. 75th Anniv. Vol:317-391.

-Einaudi, M.T., 1982. Descriptions of skarns associated with porphyry copper plutons, southwestern North America, in Titley, S.R. (ed.), Advances in geology of the porphyry copper deposits, southwestern North America; Univ. Arizona Press, p. 139-184.

-Grabher, D.E., 1974. Skarn ore relationships in a contact metasomatic Cu-Fe deposit Little Chief Mine, Whitehorse, Yukon Territory; unpublished PhD thesis, Univ. Western Ontario, London, p. 306.

-Harris, N.B., and Einaudi, M.T., 1982, Skarn deposits in the Yeringtond district, Nevada: Metasomatic skarn evolution near Ludwig; ECON. GEOL., v. 77, p. 877-898.

-Meinert, L.D. 1982. Skarn, manto, and breccia pipe formation in sedimentary rocks of the Cananea mining district, Sonora, Mexico; Econ. Geol., v. 77, p. 919-949.

-Ray, G.E., and Webster, I.C.L., 1990. An overview of skarn deposits; B.C. Ministry of Energy, Mines, and Petroleum Resources, p. 213-252.

Article Evaluation

The article that I will be evaluating is Magnetite.

Everything shown in this article topic does appear to have relevance to the article. Nothing appears to be too distracting.

I would say that the article is fairly neutral. It takes on a biological side and a geological one. However, it can be noted that the biological part seems to have the most written for it. Who ever wrote the biological part also must have known a great deal of magnetite and its biological significance; compared to the rest of the article it has probably the most cited information. The article mentions more than once that magnetite is a iron ore: twice in the beginning paragraph and again in the applications section. Also, in the distribution of deposits section, the only deposits that are mentioned are beach sands and sand dunes even though you can find them in many deposit types.

I believe that the distribution of deposits is underrepresented. It only mentions that it can be found in beach sand and sand dunes. This part could use some work.

After checking all the links, all of them work fine. Most of the sources for this article are journal articles. One of the sources that I noticed however, was a blog that talked about the president of some gold company and how you should invest in their find in Peru; the reference specifically was number 14. It was found in the topic of distribution of deposits and talking about how there was a large portion of magnetite found in the sandstone.

From what I noticed, there was a lack of sources for certain sections and paragraphs. For example, in the very first paragraph, there is a part that talks about how ancient people discovered magnetite and its magnetic properties. There is no source associated with this, and for all I know someone just made that up. Another example is the subsection of Reactions. There is not a single reference there for the information that is being provide; a statement such as "Commonly, igneous rocks contain solid solutions of both titanomagnetite and hemoilmentite or titanohematite." This is simply not common knowledge and therefore if it is being stated as such it must have been taken elsewhere. As mentioned above, most of the information that is sourced is coming from a journal article.

There are tons of things that could be added that can be considered missing. But that is up to interpretation on how much information should be presented on a Wikipedia page. As mentioned earlier, more information regarding the deposits should be added. I am sure sand dunes and sand beaches are not the only localities in which they can be found in. A section on how magnetite can be used as an indicator mineral could possibly be added. Mineral properties are there, however there is nothing on reflected light; could even added photos reflected magnetite?

There is talk about previous mentions of the chemical formula being Fe2O2 and that it should be changed to Fe3O4. There is also a huge discussion from multiple editors on the naming of magnetite; using Ferro-Ferri or Ferrous-ferric magnetite. People seem to be confused and why it is being discussed here when it is supposed to be an article for the mineral rather than the chemical. Lastly, a few more applications were talked about being added.

This article is part of the WikiProject Geology and the WikiProject Rocks and Minerals. It has a C-Class on the project's quality scale and is rated as High-importance.

In the class, magnetite was only briefly talked about; more specifically was only really mentioned how it can be found in layered intrusions such as the Bushveld Complex. This page goes into the chemistry of magnetite (formula, chemical structure, properties, etc.), what types of rock it is found in (igneous, metamorphic, and sedimentary), biological occurrences and so on.

Regarding the optional point, I want to at least address the lack of deposit information (the information regard the distribution of deposits). It is very lacking and could have some better information on the different types and so on. Maybe even better deposits that beach sands and sand dunes. Bushveld Complex is a much better topic. In my talk I added:

As per information that has been underrepresented, I believe that the section regarding the distribution of deposits is lacking in information. The only deposit(s) mentioned in this section are banded iron formation and sand dunes. Instead of sticking to sand dunes, why not continue talking about the banded iron formation and how for example in the Bushveld Complex magnetite is mined for its vanadium content. There is also mention of localities but no information on the type of deposits found. There are also links to those localities but no where do they mention magnetite. Magnetite can be found in Iron-Oxide-Copper-Gold (IOCG) deposits, porphyry, Fe-Ti deposits; they can be found in minor to trace amounts in deposits such as, Zn-Pb SEDEX deposits, Ni-Cu-PGE massive sulphides and so on. The last sentence in this section talks about how a cubic magnetite can be found in one locality; should this not be in the crystal habit section since this is not a deposit and merely an interesting fact. Hopefully this helps in making the Magnetite page better.