Igneous Geochemistry of Mineralized Rocks of the Baguio District, Philippines: Implications for Tectonic Evolution and the Genesis of Porphyry-Style Mineralization
2011
The Baguio district of the Philippines is one of the world’s premier mineral provinces, containing >35 million
ounces (Moz) of gold and 2.7 million metric tons (Mt) of copper in epithermal, porphyry, and skarn deposits
that formed in the last 3.5 m.y. Pliocene and Pleistocene magmatic rocks of the Baguio district that are
spatially and temporally associated with mineralization can be broadly subdivided into an intermediate to felsic
suite of mineralized low to medium K intrusions, some of which have adakitic affinities and a suite of mafic
to intermediate, medium K to shoshonitic hornblende-phyric dikes. The geochemical and isotopic characteristics
of the dikes are consistent with primitive mantle-derived melts that underwent minimal crustal contamination
as they ascended through the arc crust. In contrast, the intermediate to felsic suite has been contaminated
by young arc crust, suggesting ponding and fractionation within shallow-crustal magma chambers.
The Philippine arc has formed in a complex tectonic environment and is currently sandwiched between two
active subduction zones. Eastward-directed subduction of the Scarborough Ridge along the Manila trench is
currently associated with flattening of the downgoing slab. The formation of the Mafic dike complex is broadly
coeval with the onset of subduction of the Scarborough Ridge and slab flattening. The extinct Scarborough
Ridge would have been younger than the downgoing plate and consequently more susceptible to melting.
These melts can account for the isotopic recharge of the Pliocene subarc mantle as well as the generation of
the primitive melts and adakitic rocks found within the Baguio district. The interaction between primitive
mafic melts and the more felsic calc-alkaline rocks has
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