A breccia pipe, also referred to as a chimney, is a mass of breccia

Breccia

Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....

, often in an irregular and cylindrical shape. When exposed at the surface, a breccia pipe may appear as an iron-stained knob, from several feet to several hundred feet in diameter. Breccia pipes may or may not be silicified. They usually consist of fragments of the host rock (the rock layer they are contained in) cemented together by silica. These formations are often hosts for ore

Ore

An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

 deposition especially in copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 and uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 mining districts. They are sensitive to oxidation, and due to their porous nature, may be oxidized to depths far below the ground surface. Breccia pipes that have never reached the Earth's surface are referred to as "blind".

Although the origin of breccia pipes is disputed, the most commonly accepted theory is that they formed at intersections of fractures. In these areas, hydrothermal solutions forced their way to the surface. However, there are some breccia pipes that are a result of limestone collapse by acidic water or other soluble rock types. Areas that contains many examples of breccia pipes include Copper Creek, Arizona

Copper Creek, Arizona

Copper Creek is a ghost town in Pinal County, Arizona, United States. Copper Creek is located in a canyon in the Galiuro Mountains.- History :...

, which contains approximately 500 mineralized breccia pipes, and the gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 mining area of Cripple Creek, Colorado

Cripple Creek, Colorado

The City of Cripple Creek is a Statutory City that is the county seat of Teller County, Colorado, United States. Cripple Creek is a former gold mining camp located southwest of Colorado Springs near the base of Pikes Peak. The Cripple Creek Historic District, which received National Historic...

 which contains breccia pipe ore deposits associated with a volcanic diatreme

Diatreme

A diatreme is a breccia-filled volcanic pipe that was formed by a gaseous explosion. Diatremes often breach the surface and produce a tuff cone, a filled relatively shallow crater known as a maar, or other volcanic pipes.- Word origin :...

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