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Evidence for magmatic-hydrothermal fluids and ore-forming processes in epithermal and porphyry deposits of the Baguio District, Philippines


Cooke, DR and Deyell, CL and Waters, PJ and Gonzales, RI and Zaw, K, Evidence for magmatic-hydrothermal fluids and ore-forming processes in epithermal and porphyry deposits of the Baguio District, Philippines, Economic Geology and The Bulletin of The Society of Economic Geologists, 106, (8) pp. 1399-1424. ISSN 0361-0128 (2011) [Refereed Article]

Copyright Statement

Statement: 2011 Society of Economic Geologists, Inc. Society of Economic Geologists, 7811 Shaffer Parkway, Littleton, CO 80127, USA

DOI: doi:10.2113/econgeo.106.8.1399


The Baguio district contains a diverse array of epithermal, porphyry and skarn deposits, together with a large, broadly strata bound, advanced argillic lithocap. Magmatism, mineralization, and alteration occurred in response to subduction of the South China Sea plate and the Scarborough Ridge beneath northern Luzon over the past 3 m.y. Rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry Cu-Au deposits. Most of the epithermal Au-Ag deposits of the Baguio district (including Antamok and Acupan, the two largest Au deposits) are intermediate sulfidation state quartz-carbonate-adularia-illite-base metal sulfide veins that contain electrum and minor Au-Ag tellurides. In contrast, high sulfidation mineralization at Kelly includes enargite, tennantite, electrum, and precious metal tellurides and is associated with advanced argillic alteration.

Although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities, stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type. The epithermal mineralizing fluids were dilute (generally, <2 wt % NaCl equiv) and had moderate temperatures (<300C). Porphyry-style mineralization was associated with high temperature (300 to >600C) hypersaline brines (30 to >70 wt % NaCl equiv) and low-density vapor. Sulfur isotope compositions of sulfides in the porphyry, skarn and intermediate sulfidation epithermal veins of the southern and central Baguio district are mostly between +1 and +6 per mil, consistent with a predominance of H2S in the mineralizing fluids (i.e., reducing conditions). In contrast, sulfides from the high sulfidation, porphyry, and intermediate sulfidation deposits located adjacent to the Baguio lithocap mostly have negative sulfur isotope values (6.9 to +0.8), consistent with oxidizing (SO42-predominant) mineralizing fluids.

Intermediate sulfidation epithermal veins at Acupan have crosscut a well-mineralized porphyry Cu-Au stockwork at Ampucao. The two deposits cannot be distinguished on the basis of radiometric age determinations (Ampucao: 0.51 0.26 Ma; Acupan: 0.65 0.07 Ma), and are interpreted to be cogenetic, with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction. Measured δ34Ssulfide (+1.1 to +6.6),δ34Ssulfate (+10.4 to +31.8) values and initial strontium ratios of anhydrite (0.703780.70385) are consistent with identical and predominantly magmatic sources of these components for the Ampucao porphyry and Acupan epithermal veins. Helium isotopes provide further evidence of mantlederived components in the epithermal veins (R/Ra values of 6.0 and 6.7). Oxygen, deuterium, and carbon isotopes provide evidence for predominantly magmatic water at Ampucao and for hybrid magmatic-meteoric waters at Acupan that precipitated precious metals due to boiling. The proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at Acupan. The common observation of cross-cutting relationships between porphyry and epithermal veins observed throughout the Baguio district imply that the evolution of porphyry-style to intermediate sulfidationstyle mineralization was a common phenomenon in this region, and contributed significantly to its rich metal endowment.

Item Details

Item Type:Refereed Article
Keywords:magmatism, mineralization, epithermal deposits, hydrothermal fluid, porphyry, Philippines
Research Division:Earth Sciences
Research Group:Geology
Research Field:Resource geoscience
Objective Division:Mineral Resources (Excl. Energy Resources)
Objective Group:Mineral exploration
Objective Field:Copper ore exploration
UTAS Author:Cooke, DR (Professor David Cooke)
UTAS Author:Deyell, CL (Dr Cari Deyell)
UTAS Author:Zaw, K (Professor Khin Zaw)
ID Code:74862
Year Published:2011
Web of Science® Times Cited:119
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2011-12-14
Last Modified:2014-04-30
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