Editing Breccia (section)

===Hydrothermal===
[[File:Hydrothermal Breccia.jpg|thumb|left|Hydrothermal breccia in the Cloghleagh Iron Mine, near Blessington in Ireland, composed mainly of [[quartz]] and [[psilomelane|manganese oxides]], the result of [[seismic]] activity about 12 million years ago]]
{{Main|Ore genesis#Hydrothermal processes}}
Hydrothermal breccias usually form at shallow [[Crust (geology)|crustal]] levels (<1&nbsp;km) between 150 and 350&nbsp;°C, when seismic or volcanic activity causes a void to open along a fault deep underground. The void draws in hot water, and as pressure in the cavity drops, the water violently boils. In addition, the sudden opening of a cavity causes rock at the sides of the fault to destabilise and implode inwards, and the broken rock gets caught up in a churning mixture of rock, steam and boiling water. Rock fragments collide with each other and the sides of the void, and the angular fragments become more rounded. Volatile gases are lost to the steam [[Phase (matter)|phase]] as boiling continues, in particular [[carbon dioxide]]. As a result, the chemistry of the [[fluid]]s changes and [[ore]] minerals rapidly [[Precipitation (chemistry)|precipitate]]. Breccia-hosted [[ore]] deposits are quite common.<ref>{{cite journal|doi=10.1016/S0169-1368(97)00009-7 |author=Michel Jébrak |title=Hydrothermal breccias in vein-type ore deposits: A review of mechanisms, morphology and size distribution |journal=Ore Geology Reviews |volume=12 |pages = 111–134 |year=1997|issue=3|bibcode=1997OGRv...12..111J }}</ref>
[[File:PO-breccia.jpg|thumb|right|Silicified and mineralized breccia. Light gray is mostly [[Dolomite (rock)|dolomite]] with a little translucent quartz. Dark gray is [[jasperoid]] and [[ore mineral]]s. Veinlet along lower edge of specimen contains [[sphalerite]] in carbonates. Pend Oreille mine, [[Pend Oreille County, Washington]]]]

The morphology of breccias associated with ore deposits varies from tabular sheeted veins<ref name="SherlockEtal1995">{{cite journal |last1=Sherlock |first1=Ross L. |last2=Tosdal |first2=Richard M. |last3=Lehrman |first3=Norman J. |last4=Graney |first4=Joseph R. |last5=Losh |first5=Steven |last6=Jowett |first6=E. Craig |last7=Kesler |first7=Stephen E. |title=Origin of the McLaughlin Mine sheeted vein complex; metal zoning, fluid inclusion, and isotopic evidence |journal=Economic Geology |date=1 December 1995 |volume=90 |issue=8 |pages=2156–2181 |doi=10.2113/gsecongeo.90.8.2156|bibcode=1995EcGeo..90.2156S }}</ref> and [[clastic dike]]s associated with overpressured sedimentary strata,<ref>{{cite journal |last1=Yahata |first1=M. |last2=Kurosawa |first2=K. |last3=Ohtsu |first3=S. |last4=Takahashi |first4=T. |last5=Tomagae |first5=S. |last6=Kawamori |first6=H. |last7=Mori |first7=M. |title=Hydrothermal alteration and sedimentation at the formative period of a hot spring gold deposit |date=1994 |journal=Shigen-Chishitsu|volume=44 |doi=10.11456/shigenchishitsu1992.44.1}}</ref> to large-scale intrusive [[diatreme]] breccias ([[breccia pipe]]s),<ref name="NortonCathles1973">{{cite journal |last1=Norton |first1=Denis L. |last2=Cathles |first2=Lawrence M. |title=Breccia Pipes, Products of Exsolved Vapor from Magmas |journal=Economic Geology |date=1 July 1973 |volume=68 |issue=4 |pages=540–546 |doi=10.2113/gsecongeo.68.4.540|bibcode=1973EcGeo..68..540N }}</ref> or even some synsedimentary diatremes formed solely by the overpressure of pore fluid within [[sedimentary basin]]s.<ref name="CartwrightSantamarina2015">{{cite journal |last1=Cartwright |first1=Joe |last2=Santamarina |first2=Carlos |title=Seismic characteristics of fluid escape pipes in sedimentary basins: Implications for pipe genesis |journal=Marine and Petroleum Geology |date=August 2015 |volume=65 |pages=126–140 |doi=10.1016/j.marpetgeo.2015.03.023|bibcode=2015MarPG..65..126C }}</ref> Hydrothermal breccias are usually formed by [[hydrofracture|hydrofracturing]] of rocks by highly pressured [[hydrothermal]] fluids. They are typical of the [[epithermal]] ore environment and are intimately associated with intrusive-related ore deposits such as [[skarn]]s, [[greisen]]s and [[porphyry (geology)|porphyry]]-related mineralisation. Epithermal deposits are [[Mining|mined]] for copper, silver and gold.<ref name="Jebrak1997">{{cite journal |last1=Jébrak |first1=Michel |title=Hydrothermal breccias in vein-type ore deposits: A review of mechanisms, morphology and size distribution |journal=Ore Geology Reviews |date=December 1997 |volume=12 |issue=3 |pages=111–134 |doi=10.1016/S0169-1368(97)00009-7|bibcode=1997OGRv...12..111J }}</ref>

In the mesothermal regime, at much greater depths, fluids under [[lithostatic pressure]] can be released during seismic activity associated with mountain building. The pressurised fluids ascend towards shallower crustal levels that are under lower [[hydrostatic]] pressure. On their journey, high-pressure fluids crack rock by [[hydrofracture|hydrofracturing]], forming an angular ''in situ'' breccia. Rounding of rock fragments is less common in the mesothermal regime, as the formational event is brief. If boiling occurs, [[methane]] and [[hydrogen sulfide]] may be lost to the steam phase, and ore may precipitate. Mesothermal deposits are often mined for gold.<ref name="Jebrak1997"/>