Manto orebodies are stratabound

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

 irregular to rod shaped 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....

 occurrences usually horizontal or near horizontal in attitude.

Manto deposits are an important source of 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...

, forming one of the world major copper resources in Chile

Chile

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

 and southern North America.

The term manto is from the Spanish word for mantle although the geologic manto is more like a mantle roll than a sheetlike structure.

Classification

Manto ore deposits are defined by a strict stratigraphic control on their distribution, generally within a porous formation within a structural trap site. They are distinct from other copper ore bodies in that they are not associated with shear zone

Shear zone

A shear zone is a very important structural discontinuity surface in the Earth's crust and upper mantle. It forms as a response to inhomogeneous deformation partitioning strain into planar or curviplanar high-strain zones. Intervening blocks stay relatively unaffected by the deformation...

s, and an intrusive link to manto deposit formation is not conclusively proven.

Genetic model

The genetic model of manto formation is debated, but consists of the following broad principles;

• The source of ore within manto deposits is considered to be interformational, from a sedimentary source within an adjacent sedimentary basin, or from ore fluids driven off from a granite intrusive
• The transport of copper into the manto deposit position was likely hydrothermal, either a metamorphic solution or copper-bearing hydrothermal solutions generated by intrusive granites
• The trap where the ore materials concentrated is typically a coarse-grained member of a formation, and the manto is usually sited in a stratigraphic or structural pinch-out of this formation although it is now thought that hydrocarbon
  Hydrocarbon
  In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
  
  s may have assisted in the migration of metals into favorable trap sites

Morphology

Manto deposits were first described in great detail in Chile, where they sit within sedimentary strata overlying large granitic intrusions, in regions adjacent to porphyry copper deposits.

In Chile, the arid climate and deep regolith development, tended to favor preservation of chalcocite

Chalcocite

Chalcocite, copper sulfide , is an important copper ore mineral. It is opaque, being colored dark-gray to black with a metallic luster. It has a hardness of 2½ - 3. It is a sulfide with an orthorhombic crystal system....

-malachite

Malachite

Malachite is a copper carbonate mineral, with the formula Cu2CO32. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms...

-azurite

Azurite

Azurite is a soft, deep blue copper mineral produced by weathering of copper ore deposits. It is also known as Chessylite after the type locality at Chessy-les-Mines near Lyon, France...

 assemblages in the manto deposits, leading workers to believe that they were weathered equivalents of primary chalcopyrite

Chalcopyrite

Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black.On exposure to air, chalcopyrite...

 deposits of porphyry-copper derivation.

However, some recent work (Wilson & Zentilli, 2006) shows that there may be primary chalcocite

Chalcocite

Chalcocite, copper sulfide , is an important copper ore mineral. It is opaque, being colored dark-gray to black with a metallic luster. It has a hardness of 2½ - 3. It is a sulfide with an orthorhombic crystal system....

 and bornite

Bornite

Bornite is a sulfide mineral with chemical composition Cu5FeS4 that crystallizes in the orthorhombic system .-Appearance:Bornite has a brown to copper-red color on fresh surfaces that tarnishes to various iridescent shades of blue to purple in places...

 formed within degraded petroleum within trap sites, with copper precipitating from solution by reduction in contact with the reduced carbon. Thus, manto deposits need not be the weathered equivalents of primary chalcopyrite

Chalcopyrite

Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black.On exposure to air, chalcopyrite...

.

Manto deposits may be formed in proximity to intrusives, for instance in the La Providencia mine, Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

, a porphyry stock is the feeder for some twenty mantos as the pipe intersects favorable layers in the sedimentary sequence. However, these manto deposits are analogous to skarn

Skarn

Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Archean age limestones in Sweden's Persberg mining district. In modern usage the term "skarn" has been expanded to refer...

deposits, and in some cases terminology may be misused.

Examples of manto orebodies include: Magma Mine, Superior, Arizona; Tintic and Park City, Utah; Leadville and Gilman, Colorado and Pioche, Nevada in the United States.