Apolymetallic replacement deposit, also known ascarbonate replacement deposit orhigh-temperature carbonate-hosted Ag-Pb-Zn deposit,[2] is an orebody of metallic minerals formed by the replacement of sedimentary, usually carbonate rock, by metal-bearing solutions in the vicinity of igneous intrusions.[3] When the ore forms a blanketlike body along the bedding plane of the rock, it is commonly called amanto ore deposit. Other ore geometries are chimneys and veins.[4] Polymetallic replacements/mantos are often stratiform wall-rock replacement orebodies distal toporphyry copper deposits,[5] or porphyry molybdenum deposits.[6] The term manto is derived from the Spanish wordmanto, meaning "mantle" or "cloak".
Although similar in orebody geometry, host-rock lithology, and the presence of lead and zinc,carbonate hosted lead zinc ore deposits, also known as Mississippi Valley type, are considered a different type of ore deposits. Mississippi valley type ore deposits lack silver and gold mineralization, are lower temperature, and are not associated with nearby igneous intrusions.
Polymetallic replacement deposits are significant sources ofcopper,[7]gold,silver,lead, manganese, andzinc.
The metallic ore minerals are mostly in sulfides, such asgalena,sphalerite,enargite, andargentite. Gangue minerals includequartz,pyrite,rhodochrosite andbarite.
The mineralogy changes with distance from the intrusive rock. Closest to the intrusion is the copper-gold zone; next is the lead-silver zone, then the zinc-manganese zone.[8]
Manto ore deposits are defined by a strict stratigraphic control on their distribution, generally within a porous formation within a structural trap site.[citation needed] They are distinct from other copper ore bodies in that they are not associated withshear zones, and an intrusive link to manto deposit formation is not conclusively proven,[citation needed] but is often inferred.
The genetic model of manto formation is debated, but consists of the following broad principles;
Manto deposits were first described in great detail in Chile, where they sit within sedimentary strata overlying large granitic intrusions, in regions adjacent toporphyry copper deposits.[citation needed]
In Chile, the arid climate and deep regolith development, tended to favor preservation ofchalcocite-malachite-azurite assemblages in the manto deposits, leading workers to believe that they were weathered equivalents of primarychalcopyrite deposits of porphyry-copper derivation.[citation needed]
However, recent work suggests that there may be primarychalcocite andbornite formed within degraded petroleum within trap sites, with copper precipitating from solution by reduction in contact with the reduced carbon.[9] Thus, manto deposits need not be the weathered equivalents of primarychalcopyrite.
Manto deposits may be formed in proximity to intrusives, for instance in the La Providencia mine,Mexico, a porphyrystock is the feeder for some twenty mantos as the pipe intersects favorable layers in the sedimentary sequence. However, these manto deposits are analogous toskarn deposits, and in some cases terminology may be misused.[citation needed]
In many instances, manto/ polymetallic replacement/ carbonate replacement deposits can be considered as the distal part of a continuum with skarn deposits.[2][6]