An evolving subduction-related magmatic system in the Masara Gold District, Eastern Mindanao, Philippines. Issue 1 (15th June 2019) - Buena, Alfred Elmer
Graphical abstract: Highlights: New geochronological data document three different intrusive units in the Miocene. A new lithologic unit, the Lamingag Intrusive Complex (LIC), is proposed. A shift from tholeiitic to calc-alkaline magmatism during the Tertiary is recorded. Epithermal gold mineralization is associated with calc-alkaline magmatism of the LIC. Abstract: The Masara Gold District in Eastern Mindanao, Philippines, is one of the most prolific gold provinces in the Philippines. Recent district-scale mineral exploration makes it possible to undertake geologic and geochemical studies and thus to yield better insights about the mineralization environment of the Masara Gold District. In the Masara Gold District, mineralization is hosted in andesitic rocks and multiple stocks of diorite intrusions. New U-Pb and whole rock K-Ar age dating of these host rocks reveal Eocene to Plio-Pleistocene ages for the magmatic suites. A new lithologic unit is proposed to accommodate the composite diorite phases associated with mineralization. Major and trace element geochemistry of these host rocks show that the Eocene magmatic suite exhibits a tholeiitic character while the diorite and subvolcanic andesite pulses of the Miocene are calc-alkaline in composition. Adakitic rocks were emplaced during the Late Miocene and Plio-Pleistocene. Mineralization in eastern Mindanao is associated with several intrusive events formed during the Oligocene to the Pliocene. The majority of these mineralization events is associated with calc-alkaline magmatic suites. Based on this study, epithermal gold mineralization in the Masara Gold District is closely related to the Late Miocene magmatic rocks which exhibit calc-alkaline and adakitic signatures.