16:15 〜 16:30
[SCG45-09] Zircon trace elements and physicochemical magma characteristics: insights in the formation of skarn deposit in Baguio Mineral District, Philippines.
キーワード：Thanksgiving Mine, Baguio Mineral District, Skarn, Zircon, Oxygen fugacity
Baguio Mineral District (BMD) in the Province of Province of Benguet, Northern Luzon, Philippine Islands has a series of mineral deposits containing porphyry copper, epithermal gold, and skarn deposits. The Thanksgiving Mine of Benguet Exploration, Inc. is located in BMD. Mining operations in Thanksgiving Mine began in 1957 with gold and silver as its primary commodity and lasted until 1987 citing financial difficulties.
The region is mostly composed of marine sedimentary rocks from the Late Oligocene to Early-Mid Miocene Zigzag Formation. The formation unconformably overlays Late Cretaceous to Paleogene metavolcanic and metasedimentary rocks from the Pugo Formation. These rocks were intruded by hornblende quartz diorite porphyry (22.33 ± 0.63 Ma; Jabagat et al., 2020) and andesite dikes (4.55 ± 0.15 to 3.45 ± 0.19 Ma; Waters et al., 2011). The ore occurs as veins and pods mainly along contacts between a 120m-thick limestone interpreted as the Early to Middle Miocene Kennon formation roof pendant within the diorite porphyry specifically known as the Black Mountain intrusive complex. The orebodies and the patches of skarn minerals are thought to have originated from the diorite-porphyry (Callow, 1967) based on geological observation. The sphalerite-rich skarn and massive sulfide ore formed due to the contact metamorphism of diorite porphyry.
There have been numerous researches on other areas of the Baguio Mineral District but less is focused specifically on Thanksgiving Mine. For this study, we collected samples of skarn, metamorphosed dacite, dacite, and hornblende quartz diorite. Metamorphosed dacite which includes epidote skarn seems to be thermally metamorphosed due to the diorite intrusion, however, the relationship among rocks is unclear. The petrological observation was done by a petrographic microscope and micro-XRF (M4 TORNADO Plus). Zirconium elemental map of dacite, metamorphosed dacite, and diorite shows an adequate amount of zircon.
The whole-rock compositions of dacite and diorite were determined utilizing ICP-MS after the acid and alkali fusion digestion of samples. Chondrite-normalized REE plots of dacite and diorite showed enriched light rare earth elements (LREE) compared to the slightly depleted heavy rare earth elements (HREE). Primitive mantle normalized spider diagrams exhibited relative enrichment in large ion lithophile elements (LILE) and depletion in high field strength elements (HFSE) such as Nb, Zr, and Ti. These show typical patterns of arc magma source.
The physicochemical conditions (e.g. pressure, temperature, oxygen fugacity, fluid composition) of magma significantly control the metallogenesis. In this study, we investigate the trace element concentrations in zircon to determine the oxidation state of dacite and diorite magmas and their temperature to understand the characteristics of magma that led to the skarn formation of Thanksgiving Mine. In the presentation, we present our method and results.
REFERENCES
K. J. Callow; The geology of the Thanksgiving Mine, Baguio District, Mountain Province, Philippines. Economic Geology 1967;; 62 (4): 472–481. doi: https://doi.org/10.2113/gsecongeo.62.4.472
Jabagat, K. D., Gabo-Ratio, J. A., Queaño, K. L., Yonezu, K., Dimalanta, C. B., Lee, Y. H., & Yumul, G. P. (2020). Petrogenetic constraints on magma fertility in the Baguio Mineral District, Philippines: Probing the mineralization potential of the igneous host rocks in the Sangilo epithermal deposit. Ore Geology Reviews, 125. https://doi.org/10.1016/j.oregeorev.2020.103703
Waters, Patrick & Cooke, David & Gonzales, Rene & Phillips, David. (2011). Porphyry and Epithermal Deposits and 40Ar/39Ar Geochronology of the Baguio District, Philippines. Economic Geology. 106. 1335-1363. 10.2113/econgeo.106.8.133
The region is mostly composed of marine sedimentary rocks from the Late Oligocene to Early-Mid Miocene Zigzag Formation. The formation unconformably overlays Late Cretaceous to Paleogene metavolcanic and metasedimentary rocks from the Pugo Formation. These rocks were intruded by hornblende quartz diorite porphyry (22.33 ± 0.63 Ma; Jabagat et al., 2020) and andesite dikes (4.55 ± 0.15 to 3.45 ± 0.19 Ma; Waters et al., 2011). The ore occurs as veins and pods mainly along contacts between a 120m-thick limestone interpreted as the Early to Middle Miocene Kennon formation roof pendant within the diorite porphyry specifically known as the Black Mountain intrusive complex. The orebodies and the patches of skarn minerals are thought to have originated from the diorite-porphyry (Callow, 1967) based on geological observation. The sphalerite-rich skarn and massive sulfide ore formed due to the contact metamorphism of diorite porphyry.
There have been numerous researches on other areas of the Baguio Mineral District but less is focused specifically on Thanksgiving Mine. For this study, we collected samples of skarn, metamorphosed dacite, dacite, and hornblende quartz diorite. Metamorphosed dacite which includes epidote skarn seems to be thermally metamorphosed due to the diorite intrusion, however, the relationship among rocks is unclear. The petrological observation was done by a petrographic microscope and micro-XRF (M4 TORNADO Plus). Zirconium elemental map of dacite, metamorphosed dacite, and diorite shows an adequate amount of zircon.
The whole-rock compositions of dacite and diorite were determined utilizing ICP-MS after the acid and alkali fusion digestion of samples. Chondrite-normalized REE plots of dacite and diorite showed enriched light rare earth elements (LREE) compared to the slightly depleted heavy rare earth elements (HREE). Primitive mantle normalized spider diagrams exhibited relative enrichment in large ion lithophile elements (LILE) and depletion in high field strength elements (HFSE) such as Nb, Zr, and Ti. These show typical patterns of arc magma source.
The physicochemical conditions (e.g. pressure, temperature, oxygen fugacity, fluid composition) of magma significantly control the metallogenesis. In this study, we investigate the trace element concentrations in zircon to determine the oxidation state of dacite and diorite magmas and their temperature to understand the characteristics of magma that led to the skarn formation of Thanksgiving Mine. In the presentation, we present our method and results.
REFERENCES
K. J. Callow; The geology of the Thanksgiving Mine, Baguio District, Mountain Province, Philippines. Economic Geology 1967;; 62 (4): 472–481. doi: https://doi.org/10.2113/gsecongeo.62.4.472
Jabagat, K. D., Gabo-Ratio, J. A., Queaño, K. L., Yonezu, K., Dimalanta, C. B., Lee, Y. H., & Yumul, G. P. (2020). Petrogenetic constraints on magma fertility in the Baguio Mineral District, Philippines: Probing the mineralization potential of the igneous host rocks in the Sangilo epithermal deposit. Ore Geology Reviews, 125. https://doi.org/10.1016/j.oregeorev.2020.103703
Waters, Patrick & Cooke, David & Gonzales, Rene & Phillips, David. (2011). Porphyry and Epithermal Deposits and 40Ar/39Ar Geochronology of the Baguio District, Philippines. Economic Geology. 106. 1335-1363. 10.2113/econgeo.106.8.133