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criterion. The fracture criterion defines both the stress required for fracturing and the fracture orientation, as it is possible to construct on a Mohr diagram the shear fracture envelope that separates stable from unstable states of stresses. The shear fracture envelope is approximated by a pair of lines that are symmetric across the σ
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axis. As soon as the Mohr circle touches the lines of the fracture envelope that represent a critical state of stress, a fracture will be generated. The point of the circle that first touches the envelope represents the plane along which a fracture forms. A newly formed fracture leads to changes in
326:
On the macroscopic scale, the formation of veins is controlled by fracture mechanics, providing the space for minerals to precipitate. Failure modes are classified as (1) shear fractures, (2) extensional fractures, and (3) hybrid fractures, and can be described by the Mohr-Griffith-Coulomb fracture
472:
The difference between 19th-century and 21st-century mining techniques and the type of ore sought is based on the grade of material being mined and the methods of mining which are used. Historically, hand-mining of gold ores permitted the miners to pick out the lode quartz or reef quartz, allowing
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However, today's mining and assaying allows the delineation of lower-grade bulk tonnage mineralisation, within which the gold is invisible to the naked eye. In these cases, veining is the subordinate host to mineralisation and may only be an indicator of the presence of
332:
the stress field and tensile strength of the fractured rock and causes a drop in stress magnitude. If a stress increases again, a new fracture will most likely be generated along the same fracture plane. This process is known as the crack-seal mechanism
499:
For this reason, veins within hydrothermal gold deposits are no longer the exclusive target of mining, and in some cases gold mineralisation is restricted entirely to the altered wall rocks within which entirely barren quartz veins are hosted.
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Veins are common features in rocks and are evidence of fluid flow in fracture systems. Veins provide information on stress, strain, pressure, temperature, fluid origin and fluid composition during their formation. Typical examples include
371:
In all cases except brecciation, therefore, a vein measures the plane of extension within the rock mass, give or take a sizeable bit of error. Measurement of enough veins will statistically form a plane of principal extension.
343:
of minerals within incipient fractures. This happens swiftly by geologic standards, because pressures and deformation mean that large open spaces cannot be maintained; generally the space is in the order of millimeters or
465:
of the 19th century, vein material alone was typically sought as ore material. In most of today's mines, ore material is primarily composed of the veins and some component of the
476:
Today's mining, which uses larger machinery and equipment, forces the miners to take low-grade waste rock in with the ore material, resulting in dilution of the grade.
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Ores related to hydrothermal mineralisation, which are associated with vein material, may be composed of vein material and/or the rock in which the vein is hosted.
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to the walls of the cavity, and the crystal protruding into open space. This certainly is the method for the formation of some veins. However, it is rare in
368:(to form hydraulic fractures or hydrofracture breccias) or they need open spaces or fractures, which requires a plane of extension within the rock mass.
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mineralisation. Hydrofracture breccias are classic targets for ore exploration as there is plenty of fluid flow and open space to deposit ore minerals.
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active at the time of vein formation. In extensionally deforming regimes, the veins occur roughly normal to the axis of extension.
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which is filled with vein material. Such breccia vein systems may be quite extensive, and can form the shape of tabular
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on the vein walls and appear to fill up the available open space. Often evidence of fluid boiling is present.
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the highest-grade portions of the lodes to be worked, without dilution from the unmineralised wall rocks.
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below the surface. Thus, there are two main mechanisms considered likely for the formation of veins:
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754:"Crack-seal patterns: records of uncorrelated stress release variations in crustal rocks"
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In ductilely deforming compressional regimes, this can in turn give information on the
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for significant open space to remain open in large volumes of rock, especially several
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vein, prominent from the surrounding weathered rock at Cape Jervis, South
Australia
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Renard, Francois; Andréani, Muriel; Boullier, Anne-Marie; Labaume, Pierre.
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570:"A review of the formation of tectonic veins and their microstructures"
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Bons, Paul D.; Elburg, Marlina A.; Gomez-Rivas, Enrique (2012-10-01).
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of minerals on the growth surface as well as being decomposable .
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of the wall-rocks which contains the low-grade mineralisation.
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Veins generally need either hydraulic pressure in excess of
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Crack-seal veins are thought to form quite quickly during
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environments. For open space filling to take effect, the
621:(3 ed.). Cambridge: Cambridge University Press.
159:. Veins form when mineral constituents carried by an
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Sheetlike body of crystallized minerals within a rock
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are all examples of open-space filling phenomena in
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60:. Unsourced material may be challenged and removed.
352:by reopening of the vein fracture and progressive
776:"A historical review of metamorphic fluid flow"
699:"The crack–seal mechanism of rock deformation"
885:
8:
780:Journal of Geophysical Research: Solid Earth
449:In situ gold-bearing vein (in brown) at the
185:in rocks, with the crystal growth occurring
163:within the rock mass are deposited through
892:
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178:Veins are classically thought of as being
136:White veins in dark rock at Imperia, Italy
644:"Hydraulic fracturing and mineralization"
618:The Mechanics of Earthquakes and Faulting
120:Learn how and when to remove this message
461:In many gold mines exploited during the
245:is generally considered to be below 0.5
531:
225:Open space filling is the hallmark of
642:Phillips, William John (1972-08-01).
7:
563:
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58:adding citations to reliable sources
1135:List of tectonic plate interactions
261:of minerals which radiate out from
397:vein (with strain fringe) showing
25:
648:Journal of the Geological Society
300:controlled by boundaries such as
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148:is a distinct sheetlike body of
34:
615:Scholz, Christopher H. (2019).
45:needs additional citations for
823:"California Gold Quartz Veins"
697:Ramsay, John G. (March 1980).
1:
574:Journal of Structural Geology
763:. Université Joseph Fourier.
491:Gold-bearing quartz veins,
469:which surrounds the veins.
257:-like habit, of sequential
171:involved is usually due to
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383:Mineralization and veining
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1220:Thick-skinned deformation
761:hal.archives-ouvertes.fr/
594:10.1016/j.jsg.2012.07.005
1225:Thin-skinned deformation
1001:Stereographic projection
668:10.1144/gsjgs.128.4.0337
229:vein systems, such as a
173:hydrothermal circulation
991:Orthographic projection
974:Measurement conventions
920:Lamé's stress ellipsoid
774:Ferry, John M. (1994).
296:or laterally extensive
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413:
404:sense. Starlight Pit,
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1502:Paleostress inversion
1195:Strike-slip tectonics
1065:Extensional tectonics
1045:Continental collision
915:Deformation mechanism
849:"Elements of Geology"
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360:Tectonic implications
216:
135:
1080:Fold and thrust belt
366:hydrostatic pressure
282:hydraulic fracturing
54:improve this article
1512:Section restoration
1388:Rock microstructure
1050:Convergent boundary
950:Strain partitioning
935:Overburden pressure
925:Mohr–Coulomb theory
827:Nevada Outback Gems
792:1994JGR....9915487F
786:(B8): 15487–15498.
715:1980Natur.284..135R
660:1972JGSoc.128..337P
586:2012JSG....43...33B
69:"Vein" geology
1594:Structural geology
1489:Kinematic analysis
1145:Mountain formation
1060:Divergent boundary
1025:Accretionary wedge
901:Structural geology
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441:Quartz reef mining
435:Gold-bearing veins
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243:confining pressure
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209:Open space filling
199:open-space filling
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1497:3D fold evolution
1383:Pressure solution
1378:Oblique foliation
1258:Exfoliation joint
1248:Columnar jointing
908:Underlying theory
800:10.1029/94JB01147
709:(5752): 135–139.
628:978-1-107-16348-5
410:Western Australia
406:Fortnum Gold Mine
263:nucleation points
203:crack-seal growth
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16:(Redirected from
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1579:Economic geology
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1301:Detachment fault
1296:Cataclastic rock
1230:Thrust tectonics
1200:Structural basin
1175:Pull-apart basin
1115:Horst and graben
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539:Schroeter, Tom.
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348:. Veins grow in
322:Crack-seal veins
161:aqueous solution
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654:(4): 337–359.
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439:Main article:
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110:November 2013
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71: –
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65:Find sources:
59:
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49:
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43:This article
41:
37:
32:
31:
19:
1326:Thrust fault
1272:
1015:Large-scale
986:Inclinometer
960:Stress field
856:. Retrieved
852:
842:
830:. Retrieved
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548:. Retrieved
545:earthsci.org
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482:metasomatism
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275:hydrothermal
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150:crystallized
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52:Please help
47:verification
44:
1507:Paleostress
1393:Slickenside
1368:Crenulation
1321:Fault trace
1316:Fault scarp
1306:Disturbance
1291:Cataclasite
1180:Rift valley
1100:Half-graben
1070:Fault block
1055:Décollement
853:geology.com
515:Ore genesis
463:gold rushes
346:micrometers
337:deformation
309:sedimentary
18:Quartz vein
1573:Categories
1535:Pure shear
1522:Shear zone
1479:Competence
1363:Compaction
1240:Fracturing
1035:Autochthon
1030:Allochthon
858:1 November
832:1 November
550:1 November
526:References
467:wall rocks
392:Boudinaged
354:deposition
227:epithermal
195:kilometers
80:newspapers
1589:Petrology
1471:Boudinage
1451:Monocline
1446:Homocline
1426:Anticline
1408:Tectonite
1398:Stylolite
1373:Fissility
1350:lineation
1346:Foliation
1210:Syneclise
1155:Obduction
1125:Inversion
1017:tectonics
808:2156-2202
731:1476-4687
684:128945906
676:0016-7649
602:0191-8141
580:: 33–62.
510:Boudinage
399:sinistral
350:thickness
316:cap rocks
306:competent
294:diatremes
277:systems.
251:colloform
231:stockwork
183:fractures
155:within a
1558:Category
1530:Mylonite
1461:Vergence
1456:Syncline
1358:Cleavage
1283:Faulting
504:See also
495:, Alaska
377:stresses
292:sheets,
259:selvages
235:greisens
153:minerals
1431:Chevron
1418:Folding
1263:Fissure
1215:Terrane
1160:Orogeny
1140:Mélange
1075:Fenster
965:Tension
788:Bibcode
739:4333973
711:Bibcode
656:Bibcode
582:Bibcode
290:dipping
286:breccia
191:geology
167:. The
142:geology
94:scholar
1205:Suture
1190:Saddle
1130:Klippe
1095:Graben
955:Stress
945:Strain
806:
737:
729:
703:Nature
682:
674:
625:
600:
395:quartz
312:layers
298:mantos
271:geodes
219:quartz
187:normal
180:planar
96:
89:
82:
75:
67:
1540:Shear
1268:Joint
1150:Nappe
1110:Horst
1105:Horse
757:(PDF)
735:S2CID
680:S2CID
455:Japan
426:skarn
422:lodes
402:shear
314:, or
255:agate
239:skarn
233:, in
101:JSTOR
87:books
1441:Dome
1348:and
1273:Vein
1253:Dike
1185:Rift
996:Rake
860:2013
834:2013
804:ISSN
727:ISSN
672:ISSN
623:ISBN
598:ISSN
552:2013
419:gold
267:Vugs
201:and
157:rock
146:vein
144:, a
73:news
796:doi
719:doi
707:284
664:doi
652:128
590:doi
339:by
247:GPa
140:In
56:by
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