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In situ elemental and Sr isotope characteristics of magmatic to hydrothermal minerals from the Black Mountain porphyry deposit, Baguio District, Philippines


Cao, M and Hollings, P and Evans, NJ and Cooke, DR and McInnes, BIA and Zhao, K and Qin, K and Li, D and Sweet, G, In situ elemental and Sr isotope characteristics of magmatic to hydrothermal minerals from the Black Mountain porphyry deposit, Baguio District, Philippines, Economic Geology, 115, (4) pp. 927-944. ISSN 0361-0128 (2020) [Refereed Article]

Copyright Statement

Copyright 2020 Society of Economic Geologists, Inc.

DOI: doi:10.5382/econgeo.4701


At the Black Mountain porphyry Cu-Au deposit in the Baguio district, Northern Luzon (Philippines), pre- and synmineralized rocks preserve magmatic and hydrothermal minerals (e.g., plagioclase, amphibole, titanite, and epidote) spanning the complete paragenesis of the deposit. Strontium isotope values in early crystallized plagioclase phenocrysts from all felsic porphyries can be divided into two types. The type-I plagioclase crystals show relatively homogeneous Sr isotope values (0.7035-0.7038, 1σ <0.0001), indicating crystallization from a relatively stable and long-lived felsic magma chamber. The type-II plagioclase grains have a wider range of Sr isotope compositions (0.7032-0.7039, 1σ <0.0001), indicating mafic and/or felsic magma recharge. In magmatic titanite, Nb/Ta values are higher than those in the whole rock, while Zr/Hf and Y/Ho values are lower. In hydrothermal titanite and epidote, the ratios are similar to those in the whole rock. These patterns reflect crystallization effects imposed during the magmatic stage but an absence of differentiation during the hydrothermal stage. The consistent gradual decrease in total rare earth element, Y, Zr, and U contents in both hydrothermal titanite and epidote from early to late stages indicates the effect of hydrothermal fluid evolution with decreasing temperature. The variation of 87Sr/86Sr values in magmatic amphibole, plagioclase, and hydrothermal epidote in felsic and mafic rocks indicates the addition of mafic magma-derived fluid into the felsic magma-derived fluid. One extra source of fluid (probably derived from wall-rock limestone) was required to generate the highly radiogenic 87Sr/86Sr values of some epidote (0.7038-0.7053). Thus, in situ elemental and Sr isotope variation in minerals from different paragenetic stages can be used to interpret formation process and source for both magmas and hydrothermal fluids.

Item Details

Item Type:Refereed Article
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)
ID Code:139370
Year Published:2020
Funding Support:Australian Research Council (IH130200004)
Web of Science® Times Cited:13
Deposited By:CODES ARC
Deposited On:2020-06-12
Last Modified:2022-08-08

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