The Camarines Norte Ophiolite Complex (CNOC) is an ancient upper-mantle and crust sequence exposed along the northern shores of Camarines Norte and in the offshore Calaguas Island Group (CIG). Residual harzburgites comprising the upper mantle suite exhibit textural features that suggest recrystallization and dynamic and plastic deformation. The harzburgites contain olivine (Fo_89.1-92.1) and accessory spinel (XCr_0.33-0.44). Co-existing orthopyroxenes and clinopyroxenes have mean structural formulas of En_89.7-91Fs_8.4-.8Wo_0.6-2.2 and En_67.6-70.3 Fs_2.7-4Wo_27-28.2, respectively. High NiO contents in olivine implies the residual nature of the harzburgites, whereas the relatively low XCr of spinel suggests that the harzburgites experienced low to moderate degrees of partial melting. Mantle metasomatism effects seem absent in the upper mantle suite but this may be due to the limited number of analyzed samples.

Websterites that contain olivine with generally low NiO contents comprise the bulk of the deep-level cumulate rocks. The high Mg# (~0.96) of clinopyroxene suggests high-pressure crystallization. Post-cumulus amphibole in websterite and rare hornblendite dikes cutting into the ultramafic cumulate rocks may indicate the presence of elevated volatile activity during their generation. The crystallization order of the deep-level cumulate rocks is ol (+/-sp) / cpx y opx.

The mineral chemistry of the CNOC mantle supports a back-arc environment of generation. This has at least tw significant ramifications: (1) mineralization, if present, will not be as extensive as those of island-arc generation, and (2) Lagonoy and CNOC constitute an arc--back-arc ophiolite pair and, consequently, suggests a contiguous Bicol Peninsula basement.