Ore Morphology and Textures Flashcards
Regular Deposits
Beds
Veins
Irregular Deposits
Stocks
Replacement
layers/beds parallel to bedding or magmatic layering
Bed-Stratiform Deposits
zones parallel or sub-parallel to bedding or schistosity
Bed-Stratabound
formed by deposition along faults or fractures
Vein
wide at the center and tapered at the sides
Lens
cylindrical or tube-shaped enrichment zones with oval cross-sections
Pipes or mantos
develop along intersection zones of faults or dikes
Pipes or Mantos
ore occurrence that can be followed along a strike
Regular Deposits
no geometric shape
variable and abruptly changing boundaries
Stocks
ore with no geometric shape and variable directions and dimensions
Irregular Deposits
ore minerals are found along cross-cutting veinlets
Stockwork
ore minerals are scattered as individual or small clusters of inclusions
Dissemination
ore minerals are disseminated in the matrix
Breccia
ores which have undergone deformation following its formation, giving riseto brecciation of rock as well as minerals
Brecciated texture
broken rock fragments
Clasts
fill spaces between clasts
Matrix
Importance of studying ore textures
- Determine time relationships of mineral assemblages
- Environment of Formation
- Manner of Deposition
Categories of Ore textures
Magmatic Deposition Exsolution textures Replacement textures Open Fill Textures Weathering
may result from direct crystallization, fractionation, crystal settling, filter pressing, and other magmatic ore forming processes
Magmatic Ore Textures
ores in which samples have rather homogeneous character and feature, and usually made up of one or few minerals
Massive Texture
texture in which dissemination of minerals accumulate through the sample
Disseminated Texture
ore in which ore minerals or disseminations of ore minerals accumulate as bands of mm to cm in thickness
Bands or Laminated Texture
ore in which minerals are formed at the surface and have the kidney-like shape
Nodular Texture
Under Nodular texture
mm size
Oolitic texture
Under Nodular texture
cm size
Pisolitic texture
simultaneous capillary solution and deposition by which a new mineral of partly or wholly differing chemical composition may grow in the body of an old mineral
Replacement/Metasomatism
Rules for Replacement
- Sulfides/Arsenides/Tellurides/Sulfosalts can replace any rock, gangue or ore minerals
- Oxides replace all rock and gangue but are rarely replaced by gangue
- Gangue minerals replace rock and other gangue but do not commonly replace sulfides/arsenides/tellurides/sulfosalts
- Oxides rarely replace sulfides/arsenides/tellurides/sulfosalts
a mineral or mineral aggregate retaining the outward form proper to a pre-existing mineral or mineral aggregate which it has replaced
pseudomorphs
widening of a fracture filling to an irregular mass where a fracture crosses a chemically reactive mineral grain or rock
Replacement textures
leading edge of front of replacement which has not completed
Vermicular Intergrowths
varying diffusion rates of ions at the replacement front
Cusp and Caries texture
