 in - Porter, T.M. (Ed), 2002 - Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective, volume 2;
ABSTRACT
Strata-bound Cu- (Ag) deposits, long known as 'Chilean manto-type', occur along the
Coastal Cordillera of northern Chile hosted by Jurassic and Lower Cretaceous volcanic and
volcano-sedimentary rocks. These deposits are typical of the first stage of Andean evolution
characterized by an extensional setting of the arc magmatism along the active margin of South
America. Strata-bound Cu- (Ag) deposits were formed during two metallogenic epochs in the Late
Jurassic and uppermost Early Cretaceous. The mineralization took place at the time of structurally
controlled emplacement of batholiths within the Mesozoic volcanic and sedimentary strata. The
volcanic-hosted strata-bound Cu- (Ag) deposits invariably occur distal, but peripheral to coeval
batholiths emplaced within tilted Mesozoic strata. The prevalent view that these deposits have an
inherent genetic relationship with hydrothermal fluid derivation from subvolcanic stocks and dikes
is contended here, because these minor intrusions are largely barren and this hypothesis does not fit
well with Sr, Os and Pb isotopic data that call for crustal contribution of these elements. The
strata-bound Cu- (Ag) mineralization appears to be produced by fluids of mixed origin that were
mobilized within permeable levels and structural weakness zones of the Mesozoic arc-related
volcano-sedimentary sequence during the emplacement of shallow granodioritic batholiths under
transtensional regimes. These hydrothermal fluids deposited copper and subordinate silver when
reacted with organic matter, pyrite and/or cooled away from their heat sources. Although strata-bound
Cu- (Ag) mineralization took place during the same Cretaceous metallogenic event that
formed the magnetite-apatite bodies, and Fe-oxide-Cu-Au deposits along the present Coastal
Cordillera, the conceivable relationships with these other types of deposits are hampered by the
inconclusive debate about the origin of the Chilean Fe-oxide deposits. However, the available data
strongly suggest that the Fe oxide-rich deposits are metasomatic in origin and genetically related to
contact zones of Lower Cretaceous dioritic batholiths, whereas the iron-poor volcanic-hosted Cu-(
Ag) stratabound deposits constitute distal mineralization peripheral to Upper Jurassic of Lower
Cretaceous granodioritic batholiths.
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