Nish
- 1. WINTERTemplateORE & METAMORPHISM- CAUSES,EFFECT & RELATIONS Presented by, Nishad.B.H 𝑰𝑰 𝒏𝒅semester MSc. Marine Geology
- 2. ORE DEPOSITS FORMED BY METAMORPHISM Metamorphic processes profoundly alter pre-existing mineral deposits and form new ones. The chief agencies involved are heat, pressure, time, and various solutions. The materials acted upon are either earlier formed mineral deposits or rocks. Valuable nonmetallic mineral deposits are formed from rocks chiefly by the crystallization and the combination of rock making minerals
- 4. Role of Temperature and Pressure Metamorphic processes occur to make adjustments between the chemical potential of any system and the changes in temperature and pressure. A particular chemical reaction that cannot occur in one environment may readily do so under different temperature and pressure conditions. An increase in pressure will cause a reaction to move in a direction in which the total volume of the system decreases.
- 5. An increase in temperature normally results in endothermic reactions. eg:conversion of pyroxene to hornblende during the metamorphism of diabase to amphibolite. In short, metamorphic reactions result from the tendency of mineral systems to adjust to their physicochemical environment of high temperatures and pressures in contrast to the low temperatures of weathering processes, both of which processes generally occur in the presence of water.
- 6. Olivine + anorthite → garnet augite +anorthite → garnet +quartz ilmenite + anorthite → sphene + hornblende nepheline + albite → glaucophane or jadeite anorthite + gehlenite + wollastonite → grossularite Andalusite → Sillimanite → Kyanite
- 7. Metamorphism of Earlier Deposits When rocks are metamorphosed, enclosed mineral deposits may also be metamorphosed. Unlike rocks that undergo both textual and mineralogical changes, Ores undergo less mineral re-combinations. Textual changes, however, are pronounced. Schistose or gneissic textures are induced, particularly with sectile minerals, and flow structure is not uncommon. Galena, for example, becomes gneissic. It may also be rendered so fine grained that individual cleavage surfaces cannot be discerned with a hand lens.
- 8. The original textures and structures may be so obscured that it is difficult to determine to which class the originally deposits belonged. Such deposits are then classified as "metamorphosed". The result is that ores may exhibit streaked, banded, smeared appearances with indistinct boundaries between minerals of different color. It "flows" around hard minerals, such as pyrite. Other minerals, such as chalcopyrite, bornite, covellite, or stibnite, behave similarly.
- 10. RECRYSTALIZATION occurs under situations of intense temperature and pressure where grains, atoms or molecules of a rock or mineral are packed closer together, creating a new crystal structure. The basic composition remains the same. It is a physical process. Limestone is a sedimentary rock that undergoes metamorphic recrystallization to form marble, and clays can recrystallize to muscovite mica.
- 11. Contact Metamorphism Heat and chemical reactions with hot fluids from the magma can change the composition of the surrounding rock. This process is called contact metamorphism. It also occurs when hot fluids called hydrothermal solutions move through small cracks in a large mass of rock. Ores, such as copper Cu and zinc Zn, form by contact metamorphism.
- 13. Formation of Mineral Deposits by Metamorphism Several kinds of nonmetallic mineral deposits are formed as a result of regional metamorphism. The source materials are rock constitutions that have undergone recrystallization or re-combination, or both. Rarely, water or carbon dioxide has been added, but other new constitutions are not introduced as they are in contact metasomatism deposits The enclosing rocks are wholly or in part metamorphosed; it is the rock metamorphism that has given rise to the deposits.
- 14. The chief deposits thus formed are asbestos, graphite, talc, soapstone, Andalusite-kyanite- sillimanite, dumortieritea, garnet, and possibly some emery.
- 15. a) Asbestos forms by the metamorphism (hydration) of ultrabasic igneous rocks – peridotites and dunites. b)Graphite forms by regional metamorphism of organic matter, crystallization from igneous rocks, contact metamorphism and hydrothermal solutions. c)Talc, soapstone and pyrophyllite form by a mild hydrothermal metamorphism of magnesium minerals e.g. : tremolite, actinolite, olivine, epidote and mica. Talc also occurs in regionally metamorphosed lime stones, altered ultrabasic igneous rocks, and contact metamorphic zones. d) Andalusite-kyanite-sillimanite – these minerals are high grade refractories. Kyanite is formed by the dynamo thermal metamorphism of aluminous silicate minerals. Andalusite is formed by the pneumatolytic action on aluminous silicates. Sillimanite results from high temperature metamorphism of aluminous crystalline rocks. e) Garnet forms during the regional and contact metamorphism and is consequently found in schist's and gneisses. It is also found as a constituent of igneous rocks. f)Emery is a mixture of corundum and magnetite with hematite or spinel and is a product of contact metamorphism.
- 16. Bedded manganese deposits in parts of Madhya Pradesh and Maharashtra, primarily of sedimentary origin, have been subsequently effected by metamorphism. Braunite, a manganese silicate, is the important ore mineral besides several other oxide minerals.
- 17. TYPES OF METAMORPHIC DEPOSITS METAMORPHIC DEPOSITS LEAD RICH LEAD-ZINC-SILVER-RICHCOPPER RICH
- 18. Copper-Rich Types: associated with very low grade to low grade metamorphism. they form in terrains where mafic or ultramafic basement rocks are overlain up section by organic-rich sedimentary rocks. Richest zones are usually in close proximity to a fault or other structure where fluids migrate.
- 19. EXAMPLES White Pine, Michigan: Ore = chalcocite + bornite + chalcopyrite + minor sphalerite Proterozoic subaerial basalts overlain by sandstone-shale sequence.
- 20. Kennecott, Alaska: Ore = Chalcocite + Bornite. Cross section of Kennecott copper deposit
- 21. Gold-Rich Types Gold rich Metamorphic types Archean iron formation types quartz-carbonate veins
- 22. Archean Iron Formation Types Occur mostly in Precambrian shield areas. Vein morphology Iron-bearing minerals form a mineral zonation The zonation is thought to result from differences in water depth during diagenesis. Gold occurs in quartz veins in the silicate or sulfide facies host rocks.
- 24. Jardine, Montana
- 25. Quartz-Carbonate Types Associated with greenstone belts in shield areas. Serious deformation of host rocks. Ore formed in structural zones/shear zones which are regional in scale. The districts usually contain large scale folding as well. Typically dismembered Associated with green schist facies rocks, namely greenstone.
- 26. EXAMPLES Valdez Creek District, Alaska Conn Mine, Eastern Canada AJ Mine, southeast Alaska
- 27. Lead-Silver-Rich Types Contains galena, sphalerite, and locally tetrahedrite and chalcopyrite as ore minerals. The gangue is typically quartz and siderite (iron carbonate). Mineral zoning is from galena + sphalerite in the lower portion of the veins to galena + siderite in the upper portion of the veins.
- 28. EXAMPLE Coer de Lane district, Idaho