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Oxygen and Carbon Isotope Study of Calcite and Dolomite in the Disseminated Au‐Ag Telluride Bulawan Deposit, Negros Island, Philippines
Author(s) -
MAGLAMBAYAN Victor B.,
ISHIYAMA Daizo,
MIZUTA Toshio,
MATSUBAYA Osamu,
ISHIKAWA Yohei
Publication year - 2001
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/j.1751-3928.2001.tb00085.x
Subject(s) - geology , dacite , breccia , geochemistry , dolomite , calcite , sericite , sphalerite , fluid inclusions , carbonate , mineralogy , galena , pyrite , andesite , hydrothermal circulation , volcanic rock , chemistry , seismology , organic chemistry , volcano
The disseminated Au‐Ag telluride Bulawan deposit, Negros island, Philippines, is hosted by dacite porphyry breccia pipes which formed in a Middle Miocene dacite porphyry stock. Electrum and Au‐Ag tellurides occur mostly as grains intergrown with or filling voids between sphalerite, pyrite, chalcopyrite, galena and tennantite. Calcite, quartz and rare dolomite are the principal gangue minerals. Four types of alteration were recognized in the deposit, namely; propylitic, K‐feldspar‐sericitic, sericitic and carbonate alteration. Carbonate alteration is correlatable to the gold deposition stage and occurs mostly along fault zones. The δ 18 O and δ 13 C compositions of calcite and dolomite in propylite zone and ore‐stage dacite porphyry breccia were determined. The δ 18 O values of calcite in propylitized andesite range from +12.2 to +14.7%, and their δ 13 C values range from ‐6.1 to ‐1.0%. The δ 18 O values of calcite and dolomite in sericite‐ and carbonate‐altered, mineralized dacite porphyry breccia and dacite porphyry rocks range from +15.1 to +23.1%, and the δ 13 C values of calcite and dolomite range from ‐3.9 to +0.9%. The δ 18 O and δ 13 C values of the hydrothermal fluids were estimated from inferred temperatures of formation on the basis of fluid inclusion microthermometry. The δ 18 O values of hydrothermal fluid for the propylitic alteration were calculated to be +8.5 ‐ +9.5%, assuming 375°C. On the other hand, the δ 18 O values of ore solutions for base metal and Au mineralization were computed to be +13.6 ‐ +14.6%, assuming 270°C. The hydrothermal fluids that formed the Bulawan deposit are dilute and 18 O‐enriched fluids which reacted with 18 O‐ and 13 C‐rich wallrocks such as limestone.