1 / 36

Handout MB - 04

Handout MB - 04. Tekstur Mineral Bijih. Tekstur. Kenampakan fisik secara umum atau karakter dari suatu batuan, termasuk aspek geometri, komponen , hubungan antar komponen atau kristal penyusunnya. size, shape, arrangement, crystallinity, granulity, and fabric Secara genetik dibedakan atas :

cili
Télécharger la présentation

Handout MB - 04

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Handout MB - 04 Tekstur Mineral Bijih

  2. Tekstur • Kenampakan fisik secara umum atau karakter dari suatu batuan, termasuk aspek geometri, komponen , hubungan antar komponen atau kristal penyusunnya. • size, shape, arrangement, crystallinity, granulity, and fabric • Secara genetik dibedakan atas : Primary; existing in a rock at a time of its formation  Secondary; resulting from the alteration of primary minerals  Hypogene; formed by precipitation from generally ascending waters  Supergene; formed by generally descending waters includes ores and minerals formed by downward enrichment

  3. Banyak tekstur bila kita mengamati secara umum, kelihatan seperti terbentuk karena suatu proses yang spesifik, tapi bila melihat dalam porsi yang lebih kecil, akan memperlihatkan adanya perbedaan proses yang diperlihatkan oleh teksturnya • Pengamatan tekstur secara megaskopis dan mikroskopis secara umum akan memberikan hasil yang sama, hanya beda pada skala pengamatan saja • Secara mikroskopis akan memperlihatkan pertumbuhan dan asosiasi mineral secara lebih komplek dari pada pengamatan secara megaskopis dari hand specimen. • Pengamatan secara megaskopis (hand specimens) akan sangat membantu sebelum melakukan pengamatan secara mikroskopis secara detail

  4. Tekstur bisa memberikan bukti adanya • Proses awal pengendapan bijih • Kesetimbangan setelah pengendapan bijih • Proses metamorfisma • Proses deformasi • Annealing (penguatan) • Pelapukan karena air meteorik

  5. Pada polimetalik mineral, tekstur merefleksikan urutan pembentukan mineral dan sejarah setelah pembentukan • Morfologi & pola inklusi bisa menunjukkan kondisi temperature tinggi di awal deposisi • Terdapatnya mineral pyrrhotite menunjukkan adanya kesetimbangan ke temperatur menengah saat cooling • Minor sulfosat dan native metals menunjukkan adanya penurunan kesetimbangan ke temperature

  6. Tekstur Primer Tekstur Sekunder Tekstur : Melts Primary Textures : Open Space Deposition Replacements Secondary Textures : Cooling Deformation Annealing/metamorf

  7. Individual grains properties Internal grain properties : • Twinning; dikontrol oleh susunan lattice • Inversion twinning : spindle shaped lamellae (panjang lurus spt gelondongan) • Pressure twinning : umumnya lamellae dgn ketebalan seragam, asosiasi dengan bending, dan tanda awal rekristalisasi • Growth twinning : jalinan dari beberapa lamellae dengan arah berbeda-beda • Inclusions; liquid/gas, solid (primary, exsolutions, replacement • Internal Reflection ; warna internal refleksi eg. Cassiterite, ruby silver, sphalerite, hematite

  8. External grain properties : • Grain shape ; dikontrol oleh struktur kristal itu sendiri atau oleh pengaruh dari kristal disekitarnya • Euhedral : bentuk kristal yang sempurna • Subhedral : bentuk kristal sebagian • Anhedral : tidak mempunyai bentuk kristal

  9. Skeletal kristal : terbentuk karena kristalisasi yang cepat, sehingga menyebabkan berkurangnya supplai atom untuk membentuk kristal, sehingga akan dihasilkan bentuk kristal yang dendritik • Poikiloblasts: Kristal yang besar, dimana bagian tengahnya diisi oleh inklusi dari mineral yang sama dengan ukuran lebih kecil. Mencirikan pembentukan oleh proses metamorfisma • Spheroidal grains : bentuk drop/tetesan • Kasar dan ukuran butir yang sama dapat dihasilkan dari proses deposisi primer atau metamorfisme

  10. Grain bonding Pertumbuhan dari grain yang sederhana terjadi karena adanya deposisi yang terus menerus dan pertumbuhan yang lambat Pada kondisi ekstrim, akan mempunyai permukaan yang halus, batas grain yang membentuk kurva Pertumbuhan grain yang sederhana juga bisa disebabkan oleh adanya proses rekristalisasi Bentuk fabric yang kompleks umumnya dihasilkan oleh deposisi yang cepat atau efek superposisi, khususnya replacement

  11. Filling of voids • Pengisian yang lengkap akan memberikan indikasi yang baik untuk penentuan paragenesisnya • Pada pengisian yang tidak sempurna akan menyebakan porositas, sehingga akan sulit saat membuat polish section dengan kualitas yang baik.

  12. Primary texture formed from Melts • Euhedral ~ Subhedral kristal • Karena sedikit gangguan pada saat pertumbuhan muka kristalnya • Exp. mineral primer chromite, magnetite, ilmenite & platinum • Skeletal kristal • Karena tidak ada gangguan saat pertumbuhan, khususnya pada pendinginan yang cepat dari basalt; bisa seluruhnya atau sebagian merupakan kristalisasi dari silkat • Poikilitik kristal  Pembentukan silicates dalam oxides dan sebaliknya karena adanya kristalisasi yang simultan

  13. Primary texture of open-space deposition • Terbentuk pada rongga (vugs) dan urat yang terbuka (open vein), dicirikan oleh bentuk permukaan kristal yang sempurna • Tidak ada gangguan saat pertumbuhan kristalnya dari fluida yang mengisi rongga • Tekstur yang umum di jumpai: • Zoning • Colloform : karena adanya deposisi koloid

  14. Banding : terjadi karena adanya perubahan physico-chemical env. Saat mineralisasi terjadi sejalan dengan waktu • Comb structures, symetrically & rhythmically crustified : merupakan deposisi dari larutan hydrothermal pada open fissures • Radiating ~ fibrous : mengisi open fracture • Iron, manganese oxide & hydroxides sering terbentuk pada open fracture karena adanya sirkulasi air meteorik (eg. Goethite, lepidocrocite, pyrolusite, cryptomelane). Bisa membentuk concentric, fibrous dan radiating

  15. Secondary textures from replacement • Weathering • Organic material digantikan, oleh mineral sulfida (pyrite, marcasite, chalcocite) atau oxides (hematite, goethite, limonite, uranium minerals • Terbentuk karena proses : • Dissolution ~ reprecipitation • Oxidation • Solid state diffusion • Batas antara mineral yang mengganti dan digantikan biasa tajam atau iregular (corroded)

  16. Fractures, cleavages and grain boundaries • Merupakan hasil dari reaksi kimia pada permukaan kristal • Crystal structure • Replacement pada arah belahan atau arah kristalografinya • Chemical composition  Komposisi kimia bisa mengontrol komposisi dari fasa yang menggantikannya, baik pada proses pelapukan ataupun hidrotermal

  17. Secondary textures from cooling • Recrystalization • Exsolution & Decomposition : diffusion, nucleation, growth  marginal, lamellar, emulsoid, myrmekite • Inversion • Oxidation-Exsolution • Reduction-Exsolution • Thermal stress

  18. Secondary textures from deformation • Twinning • Curvature or offset of linear features • Schlieren • Brecciation, cataclasis & durchbewegung

  19. Special textures • Framboids : berupa agregat dari partikel yang spherical • Oolitic : umum pada karbonat atau iron & manganese ore • Martitization :penggantian magnetit oleh hematit sepanjang bidang belahan (111) • Bird eyes : karakteristikubahan pyrrhotite ke gabungan halus antara pyrit dan marcasite • Flames : exsolution dari pentlandite dalam pyrrhotite • Starts : exsolved sphalerite dalam chalcopyrite

  20. Minute inclusions of chalcopyrite (yellow) in core (a growth zone) of sphalerite (grey). Silver Queen epithermal vein, central B.C. Field width 0.2 mm Vermicular intergrowth of Mathildite (grey) in galena (white). Silver Queen epithermal vein, central B. C. Note 4 micron scale in lower right corner

  21. Electron microscope backscatter image of zoned tetrahedrite. Silver Queen epithermal vein, central B. C. Layers are enriched in Ag relative to Cu. Grain is about 70 microns in diameter Intergrowth of bornite (orange), chalcocite (white), covellite (blue) and hematite (ragged laths in chalcocite-bornite. Discovery zone, White Lake Copper, Kluane Range, Yukon Terr. Ore host is Nikolai basalt. Field width is 1.0 mm.

  22. Granular stibnite, crossed nicols, showing deformation twinning and intense anisotropism. Ferguson Creek, B.C. Field width is 0.8 mm Bireflectance of covellite (dark blue to pale blue). Note kinks across the covellite laths. Location unknown. Field width is 1. 6 mm

  23. Galena (white), tetrahedrite (grey), pyrargyrite (blue) and chalcopyrite (yellow). Note the black triangular cleavage pits in galena. Location unknown. Field width is 0.4 mm Red internal reflection of cinnabar enclosing a twinned crystal of stibnite (blue-grey) under crossed nicols. Red Devil mine, Alaska. Field width is 0.8 mm.

  24. Marcasite stalactite long section showing structure. Note central core of fine granular marcasite and curved platelets surrounding core. Structure is readily visible because of variable tarnish on surface. Pine Point Mines. Field width is 2 cm Margin of a marcasite stalactite under crossed nicols showing anisotropism of marcasite blades and structure at margin of stalactite. Pine Point Mines. Field width is 2mm.

  25. Cross section of sphalerite stalaclite. Contrast of layers is a combination of textural differences and slight variation in the sphalerite composition. Pine Point Mine. Field width is 1. 0 cm Ilmenite exsolution in magnetite. Crystallographic texture

  26. Colloform sphalerite. Contrast of layers is a combination of textural differences and slight variation in the sphalerite composition. Pine Point Mines. Field width is 2 mm Sphalerite (grey) "stars" in chalcopyrite (yellow). Probably an exsolution texture.

  27. Microbrecciated pyrite. Nadina epithermal vein, central B. C. Field width is 1.6 mm. Growth zoning in pyrite. Nadina epithermal vein, central B.C. Field width is 0.4 mm

  28. Specularite (hematite). Echo Bay, N. W. T. Radiating sheets, plane polarized light. Field width is 1. 6 mm Bornite (orange), digenite (blue) and chalcocite (grey). Rainy Hollow, B. C. Digenite forms thin rim between bornite and chalcocite. Field width is 0.4 mm

  29. Relict chalcopyrite (yellow) in network of goethite (blue grey) and malachite (grey-green). Note some malachite rims chalcopyrite. Field width is 1.6 mm. Bornite (orange) partly replaced by covellite (blue) along fractures. Small white grain is galena

  30. Tennantite (grey-green), pyrargyrite (blue) and chalcopyrite (yellow). Note pale grey rim (tetrahedrite) between pyrarg and tennantite, possibly a reaction zone indicating replacement of Tn by pyrarg with Cu and Fe in Tn left as chalcopyrite. Field width is 0.4 mm. Galena (white) fractured along cleavage planes. Small grey blebs are tetrahedrite. Venus vein, Yukon Terr. Field width is 0.4 mm

  31. Illustration open space filling textures Galena (Gn; white) deposited on sphalerite (Sl; grey) in Tri-State lead-zinc ores. The ores exhibit open space filling textures in which sphalerite was deposited first forming euhedral crystals upward into open space, and galena was subsequently deposited on sphalerite with its base taking the shape of the underlying sphalerite.

  32. Pyrite (Py; white) and marcasite (Mc; whitish yellow) deposited on sphalerite (Sl; grey). Pyrite and marcasite have formed euhedral crystals upward into open space, and take the shape of the underlying rotund sphalerite. Pyrite has formed cubes and marcasite formed more elongate prismatic crystals upward into open space. Plastic (P) fills the former open space. Picher field, Tri-State Lead-Zinc District, Missouri, Oklahoma, and Kansas. Ore microscopy, reflected light, medium magnification.

  33. Pyrite (Py; white) deposited on sphalerite (Sl; grey) taking the shape of the earlier deposited sphalerite and forming it own euhedral cubic shape upward into former open space. Chalcopyrite (Cp; deep yellow) was subsequently deposited on the top of pyrite and sphalerite. Picher field, Tri-State Lead-Zinc District, Missouri, Oklahoma, and Kansas. Ore microscopy, reflected light, medium magnification.

  34. Illustration replacement textures Pyrite (Py; yellow) partially replaced by chalcocite (Cc; bluish grey). The Butte, Montana copper ores illustrate typical replacement textures: 1) irregularly shaped replacement remnants ("sea islands") of pyrite being replaced by chalcocite, 2) caries texture in which chalcocite embayments into pyrite are concave with respect to the host pyrite, and 3) vein texture in which chalcocite replacement veins traverse pyrite. Holes in the polished section are black. Ore microscopy, reflected light, low magnification

  35. Bornite (Bo; blue) patches in chalcocite (Cc; grey) in Butte, Montana copper ores. The bornite areas may represent irregularly shaped replacement remnants ("sea islands") of bornite being replaced by chalcocite. However, the smoothly rounded character of the margins of the bornite areas suggests that they more likely have formed by exsolution out of the chalcocite.

  36. Abundant covellite (Cv) and minor chalcocite (Cc) in Butte, Montana ores. Covellite exhibits a variety of colors due to its extreme reflective pleochoism. Depending upon its crystal orientation, covellite may be deep blue, medium blue, or light bluish grey.

More Related