İfade olarak: Hydrothermal = Hot solution; Alteration= Change; Changes caused by hot solutions

Transcription

1 İfade olarak: Hydrothermal = Hot solution; Alteration= Change; Changes caused by hot solutions Scientically: Chemical, mineralogical and physical changes in a rock caused by the chemical and physical interaction of the hyrothermal fluid with the surrounding rock during its flow through the rock. Genetic Types of Hydrothermal Alteration Supergene alteration Surficial alteration or weathering of surficial rocks caused by the descent of surficial waters through the rock beneath the surface. Occurs near the surface But could reach very deep zones in tropical zones, and may cause Al, Ni and Fe deposits Hypogene alteration Alteration caused by hydrothermal fluids of hypogene environments

2 Vary in width from mm to km; usually m wide zones around 1-2 m thick / wide veins Basalt Ore zone The more the width of hydrothermal alteration zone around a vein, the higher the fluid / rock ratio. i.e. the higher the potential of occurrence of a relatively bigger ore deposit Fluid/rock ratio in hydrothermal systems vary from 0,1 to 4. Basalt Small Fluid/ Rock ratio Ore zone Big Fluid/ Rock ratio Alteration zone is rather wide

3 How Hydrothermal alteration has an affect on rocks? Physical features of wall rock: Porosity and permeability of rocks Chemical features of wall rock : Wheather the wall rock is reactive or not. Whether it contains easily solvable minerals. Eh and ph values of hydrothermal fluids Pressure of hydrothermal fluid Composition of hydrothermal fluid T and P values at which fluid-rock interaction takes place Strength of minerals against hydrothermal alteration Irresistant mineraller: Carbnates, zeolites, feldspatoids, Ca-plagioclase Rather resistant minerals : Pyroxene, amfibole and biotite Resistant mineraller: Na-plagioclase, K-feldspar, muscovite Very resistant minerals: Quartz. Briefly, Bowen s crystallisation sequence refects increasing resistance of minerals

4 Reactions occurring during hydrothermal alteration 1) Hydrolysis Occurs due to addition of H + from fluid to the rock. Unhydrous minerals (feldspars) are converted into hydrous minerals (mica) H + content of fluid increases. i.e. Acidity of fluid (ph) increases Example: Conversion of feldspars into micas 3 KAlSi 3 O H + KAl 3 Si 3 O 10 (OH) SiO K + Ortoclase Muscovite Quartz 3 NaAlSi 3 O 8 + 2H + NaAl 3 Si 3 O 10 (OH) SiO K + Albite Paragonit Quartz

5 Reactions occurring during hydrothermal alteration 2) Hydration / Dehiydration Loss of some of molecular water from fluid to minerals in the rock with which it interacts. 2 Mg 2 SiO H 2 O Mg 3 Si 2 O 5 (OH) 4 + Mg 2+ Olivin Serpantin Dehydration is just the opposite. i.e. Addition of fluid into the fluid following dissoluton of hydrous minerals Al 2 Si 2 O 5 (OH) SiO 2 Kaolen Al 2 Si 4 O 10 (OH) 2 + H 2 O Profillit

6 Reactions occurring during hydrothermal alteration 3) Alkali metasomatism Exchange of cations between fluid and minerals in the rock during interaction. 2 CaCO 3 + Mg 2+ CaMg(CO 3 ) 2 + Ca 2+ Calcite Dolomite KAlSi 3 O 8 + Na + NaAlSi 3 O 8 + K + Ortoclase Albite

7 Reactions occurring during hydrothermal alteration 4) Decarbonation / Carbonation Dissolution of carbonates / Formation of carbonates from noncarbonates CaMg(CO 3 ) SiO 2(sç) (Ca, Mg)Si 2 O CO 2 Dolomite Diyopsite MgCO 3 MgO + CO 2 Magnezite Periklaze

8 Reactions occurring during hydrothermal alteration 5) Silicification Addition of silica from the fluid into rock, inthe from of silicates Example: Precipitatipn of minerals from solution SiO 2 (sç) SiO 2 (K) (Ca, Mg)Si 2 O CO 2 CaMg(CO 3 ) SiO 2 Diyopsite Dolomite Quartz

9 Reactions occurring during hydrothermal alteration 6) Silication Formation of silicates from free silica and other minerals CaMg(CO 3 ) SiO 2(sç) (Ca, Mg)Si 2 O CO 2 Dolomit Diyopsit CaCO 3 + SiO 2 (sç) CaSiO 3 + 2CO 2 Kalsit Vollastonit

10 Reactions occurring during hydrothermal alteration 7) Oxidation / Reduction Conversion of magnetite to hematite Fe 3 O 4 + O 2 + H 2 O 3 Fe 2 O 3 + (OH) 2 Manyetit Hematit

11 1) Alkali metasomatizm or K-silicate alteration Caused by magmatic fluids left after crystalisation of a magmatic body at high temperatures ( o C ) in presence of faults and cracks within and in the immediate vicinity of magmatic body) a) Chemical changes taking place Exchange of Na with K or K with Na (alkali metasomatism) Changes in crystal structure of feldspars Albitisation Microclinisation Formation of new mica minerals

12 Yan Kayaç Alterasyon Çeşitleri 1) Alkali metasomatizm or K-silicate alteration b) Mineral Association K-feldspar- biotite-quartz K-feldspar-chlorite K-feldspar- biotite-magnetite K-feldspar: Red coloured due to hematite content Biotite: Green in colour and rich in iron c) Occurence Occurs in the centre of alteration zone within porphyry type Cu and Mo deposits, epithermal systems. Forms with metasomatism of plagioclase and mafic silicates at C or at higher T. K-feldspar and biotite in porphyry type deposits Adularia in epithermal systems + albite, serisite, anhydrite, apatite, rutile

13 1) Alkali metasomatizm or K-silicate alteration d) Recognition Enclosure of plagioclase remnants by K-feldspar K-feldspar veins in plagioclase Biotite veins (secondary biotites) Albite formation within K- feldspar Albite veinlets

14 1) Alkali metasomatizm or K-silicate alteration d) Recognition Enclosure of plagioclase remnants by K- feldspar K-feldspar veins in plagioclase Biotite veins (secondary biotites) Albite formation within K-feldspar Albite veinlets

15 1) Alkali metasomatizm or K-silicate alteration d) Recognition

16 1) Alkali metasomatizm or K-silicate alteration d) Recognition

17 1) Alkali metasomatizm or K-silicate alteration

18 2) Propylitic Alteration An alteration characterised by destruction of plagioclase and ferromagnesian minerals (such as biotite and amphibole), and formation of epidote, chlorite, carbonates and clay minerals. Result in addition of H 2 O, H +, CO 2 and S to the rock. a) Bulunuş Occurs in the outer zones of alteration profiles and covers large areas, and therefore is an indicator for the presence and location of ore deposits. Towards outer zones of this zone, fresh and unaltered rock is present.

19 2) Propylitic Alteration b) Composition Chlorite, epidote, albnite, pyrite and carbonates Calcite, dolomite, ankerite are dominant carbonates Minor sericite, Kfeldspar and magnetite, and zeolite and montrmorillonite

20 2) Propylitic Alteration b) Composition Chlorite, epidote, albnite, pyrite and carbonates Calcite, dolomite, ankerite are dominant carbonates Minor sericite, Kfeldspar and magnetite, and zeolite and montrmorillonite

21 2) Propylitic Alteration b) Composition Chlorite, epidote, albnite, pyrite and carbonates Calcite, dolomite, ankerite are dominant carbonates Minor sericite, Kfeldspar and magnetite, and zeolite and montrmorillonite

22 3) Phyllic / Sericitic Alteration Al alteration type characterised by the conversion of feldspars to quartz, mica, and additional formation of pyrite and chalcopyrite due to addition of OH-, H+, K+ and S from fluid to the rock. Characteristic in Al-enriched rocks, and recognised by the enrichment of sericite. a) Composition Sericite and quartz dominant. Pyrite abundant. K-feldspar, kaolene, calcite, biotite, rutile, anhydrite, apatite, Fe-oxideshydroxides, chlorite rare. Grades into potassic alteration with the presence of secondary K-feldspar and biotite, and into argillic alteration with the abundance of kaolene S may be as abundant as 20 vol %. Na, Mg, Fe, Ti, K are leached out of the rock during alteration

23 3) Phyllic / Sericitic Alteration b) Oluşum One of the most widesprtead alteration types Present in almost all types of ore deposits

24 3) Phyllic / Sericitic Alteration b) Oluşum One of the most widesprtead alteration types Present in almost all types of ore deposits

25 3) Phyllic / Sericitic Alteration b) Oluşum One of the most widesprtead alteration types Present in almost all types of ore deposits

26 4) Argillic Alteration An alteration type that occurs based on addition of H+ from the hydrothermal solution to the rock through which it penetrates. Characterised by the formation of clay minerals and hence known as clay alteration. a) Mineralogic Composition Kaolene and montmorillonite are dominant Clay mineras areformed from plagioclase, biotite and amphiboles Sericite rare May have an zonation indicated by dominance of kaolene towards seicitic zone, and by montmorillonite towards propilytic zone. Silica may be added to the rock together with argillic alteration

27 4) Argillic Alteration b) Formation In outer zones of prophyry type deposits, and in epithermal systems

28 4) Argillic Alteration 1 cm

29 5) Advanced Argillic Alteration Forms based on complete destruction of feldspars and mafic minerals, and leaching of alkali and alkali earth elements of the rock due to H+ addition from the solution to the rock, which results in the formation of clay minerals a) Mineralogic Composition Dickite and kaolene are dominant. Barite, alunite, sericite, pyrite, topas and tıurmaline aree scarce If sulphur is very high, covellite, digenite and enargite may also accompany pyrite. If T is higher than 300 oc, prophyllite, andalusite, quartz, topaz and pyrite are present. In addition, sericite, diaspore, kaolene, rutile, anhydrite, corundum and chloritoid may be present.

30 5) Advanced Argillic Alteration b) Formation Porphyry systems, Inner zones of hydrothermal tye vein deposits Especially in epithermal systems, characterised by alunite formation.

31 6) Silicification An increase in silica content of the rock due to interaction between hydrothermal solution and the rock through wich it penetrates SiO 2 is added to the rock directly from hydrothermal solution as well as as a consequence of alteration of feldspars and other silicates Siliciification is one of the best indicator in the pursuit of mineralised zones, as it is located in the center of hydrothermal alteration zones Present in almost all hydrothermal mineral deposits. 3 KAlSi 3 O 8 + 2H + KAl 3 Si 3 O 10 (OH) SiO K + K feldspar Muskovite Quartz 2 CaCO 3 + SiO 2(aq) + 4 H + 2Ca 2+ (aq) + 2 CO 2 + SiO 2 (K) + 2 H 2 O

32 6) Silicificat Olucak, Gümüşhane ion Hazine mağara Cerattepe, Artvin

33 Silicification

34 7) Listwenitisation Analteration characterised by enrichment of silica in ultrabasic rocks based on hydrothermal fluidrock interaction. Forms especially as a results of epithermal systems developed in ultrabasic rocks.

35 8) Serpantinisation Forms as a result of transformation of olivine and pyroxenes in ultrabasic rocks to serpantine minerals (crysotile, antigorite and lisardite) with addition of H 2 O and CO 2 to the rock May be related to Au, Ag and Co deposits

36 9) Fenitisation Forms as a result of destruction of silicates in carbonatites and alkaline igneous complexes, addition of Na, K, CO 2, CaO and Al 2 O 3 to the rock and formation of alkaline pyroxene, amphibole and feldspars. Alkalen granit

37 10) Tourmalinisation An alteration formed by transformation of mafic silicates to tourmaline in B- enriched granitic rocks. Found usually in quartztourmaline association. Found in Sn-W deposits, tourmalineüenriched breccia pipes, and some polymetallic vein type base metal deposits.

38 11) Greyzenisation Has a similar composition to advanced argillic and sericitic alterations. But contains more sericite or muscovite. Greyzenleşmiş bir granit. Composed mainly of quartz, muskovite and topaz, and lesser flourite, cassiterite, volframite and magnetite. Found at the marginss of granitic rocks. Characteristic in Sn-W deposits. İleri derecede greyzenleşme. Beyaz mikalar çok yoğun.

39 12) Skarn Alteration Forms by intrusion of graniitic rocks into carbonaceous rocks and fromation of calcsilicate minerals along the contact. Characterised by garnet, epidote, pyroxene, actinolite, quartz. Found in skarn type deposits. Dereli (Giresun) Fe madeninde çok iyi gelişmiş bir skarnlaşma. Garnet, epidot, kuvars, kalsit son derece iyi gelişmiş.

40 Skarn Alteration

41 12) Jaspillitisation Present in Fe and Mn deposits, this type of alteration is formed as result of Si-, Fe- and Mnenrichment of especially carbonaceous rocks.