Unique Mineral Assemblage of Fossil and Active Hydrothermal Systems in Northern Palawan : Signatures of a Mantle Magma Source?

Rogel A. Santos¹, Alvin Matos¹, Resty C. Gomez¹, Larry Panerio¹, Francia Olaguera², Brian Zoilo A.M. Esber¹

¹Mines and Geosciences Bureau, Central Office
²Mines and Geosciences Bureau, Region IV- MIMAROPA

Abstract

As a consequence of exploration for REE’s gold, nickel and cobalt in the El Nido-Taytay area. Northern Palawan, extensive outcrops of hydrothermal alteration and an active hot spring were identified.

The fossil hydrothermal system is characterized by narrow zones of argillitic alteration (including clay-hematite), widespread silicification and pockets of silica-pyrrhotite-Co pentlandite mineralization. The active Makinit hot spring in Baratuan, El Nido is depositing substantial silica sinters and numerous Mn nodules. These newly identified hydrothermal alteration products are developed over quartzo-feldspathic sandstones of the Bacuit Formation sedimentary unit.

Initial assay results include one (1) sample out of thirty-two (32) samples analyzed containing 10.4gm/ton gold in veined massive silica (jasperoid?). Remaining forty-seven samples is still being analyzed at this writing. Ni-Co assays by AAS total decomposition procedures are still ongoing although qualitative colorimetric analyses of two sulphide-bearing samples (one silicified sandstone and one epidote-chlorite altered gabbro) confirmed the presence of Ni.

The extent of alteration which affects areas within 600 km² is significant necessitating a considerably large subterranean heat and element source. Element associations of Fe-Ni-Co and actively depositing terrestrial Mn nodules point to a mantle magma source. However, mechanism of including this mantle magma source in the known continental fragment scenario (i.e. North Palawan Continental Terrain) is debatable although the possibility is being considered. Furthermore, subduction of the oceanic ridge may have induced closure of the Trough in the north Palawan segment by accretion of various sialic materials (Liminangcong Chert, Minilog Limestone, Bacuit Formation and Kapoas Intrusives) onlapped over the trough and extending eastwards to mainland Palawan.