Philippine porphyry and epithermal deposits: an introduction

[Extract] The Philippines is one of the most richly endowed parts of the Southwest Pacific, with many porphyry copper-gold and epithermal gold-silver deposits scattered along the archipelago (e.g., Sillitoe and Gappe, 1984; Mitchell and Leach, 1991; Fig. 1). Chinese mining artifacts discovered in the Baguio and Masbate districts suggest that gold and silver mining dates back to at least the 14th century. Several placer gold mining regions were active during the Spanish regime (1521 to 1898; Bureau of Mines and Geosciences, 1986). Since World War II, gold and silver production has risen fairly steadily, from 2.0 t Au and 1.4 t Ag in 1946 to 37 t Au and 34 t Ag in 2009 (Bureau of Mines and Geosciences, 1986; Fig. 2). Between 2005 and 2009, the Philippines accounted for approximately 1.5 and 0.1 percent of global gold and silver production, respectively, when approximately 37 t Au and between 14 and 34 t Ag were produced each year (George, 2011; Brooks, 2011; Fig. 2)

Tectonic transition in the Aqishan-Yamansu belt, Eastern Tianshan: Constraints from the geochronology and geochemistry of Carboniferous and Triassic igneous rocks

A combination of zircon U-Pb ages, whole-rock geochemistry, Sr-Nd isotopes, and in situ zircon Hf isotope, for newly found felsic igneous rocks from the Hongshanliang copper deposit district in the Aqishan-Yamansu belt, NW China, are presented to investigate the petrogenesis and tectonic or even crustal evolution of the Eastern Tianshan during the Late Paleozoic to the Early Mesozoic. Zircon U-Pb ages show two phases of igneous activity in the Early Carboniferous (348.8 +/- 2.1 Ma and 343.3 +/- 2.3 Ma for rhyolite and granite porphyry) and the Triassic (250.2 +/- 3.5 Ma and 235.7 +/- 2.4 Ma for (monzonitic) granodiorite and monzogranite) in the Hongshanliang copper deposit district. The Carboniferous granitic rocks are enriched in Rb, Ba, and Pb, and depleted in Nb and Ta, with low WY ratios, showing arc-related affinities. Dominantly positive epsilon(Hf)(t) values ( +2.55 to +7.15 and +1.54 to +5.03 for the rhyolite and granite porphyry, respectively), crustally-derived geochemical elements ratios (e.g., Nb/Ta, Th/U, Ta/U, and Th/La) and Mg-# values (< 37), combined with epsilon(Nd)(t) values (-0.1 to +0.6 and 03 for the rhyolite and granite porphyry), suggest the Carboniferous granitic rocks were derived from partial melting of the Mesoproterozoic lower crust with mantle-derived magmas involvement. The Triassic (monzonitic) granodiorite and monzogranite are medium-K calc-alkaline, enriched in LILE, and depleted in HFSE, with high SiO2, Al2O3, Sr, and Sr/Y, and low Y and HREE values, characteristic of adakite-like rocks. The Triassic granitoids have low MgO, TiO2, Cr, Co, and Ni contents and high Fe2O3T/MgO ratios (3.07-3.23), with geochemical features of juvenile crust (e.g., low Nb/U and Ta/U ratios and depleted epsilon(Hf)(t) values) and mantle-derived magmas (e.g., high Th/U and Th/La ratios and Mg-# values), which suggests that the Triassic granitoids were derived from partial melting of thickened juvenile lower crust with minor mantle-derived components. Integrating published cognition and our work, we propose that the Aqishan-Yamansu belt underwent a tectonic transition from an Early Carboniferous fore-arc basin extensional setting to a Triassic within-plate one. Early Carboniferous granitic magmas were emplaced during the southward subduction of the Kangguer oceanic slab and Triassic granitoids were formed after later collision between the Dananhu-Tousuquan island arc and the Yili-Central Tianshan block. Moreover, we also conclude that the major crustal growth in the Eastern Tianshan occurred at ca. 444-270 Ma and was accompanied by abundant Fe-Cu-Ni-Au mineralization, with crustal reworking at ca. 250-200 Ma. (C) 2019 Elsevier B.V. All rights reserved

Late Paleozoic magmatism and metallogenesis in the Agishan-Yamansu belt, Eastern Tianshan: Constraints from the Bailingshan intrusive complex

The Aqishan-Yamansu belt in the Eastern Tianshan (NW China) contains many intermediate to felsic intrusive rocks and spatially and temporally associated Fe (-Cu) deposits. Zircon U-Pb dating of the Bailingshan granitoids, including diorite enclaves (in granodiorite). diorite, monzogranite and granodiorite, and andesitic tuff from the Shuanglong F-Cu deposit area yielded ages of 329.3 +/- 2.1 Ma, 323.4 +/- 2.6 Ma, 313.0 +/- 2.0 Ma. 307.5 +/- 1.7 Ma and 318.0 +/- 2.0 Ma, respectively. These new ages, in combination with published data can be used to sub-divide magmatism of the Bailingshan intrusive complex into three phases at ca. 329-323 Ma, ca. 318-313 Ma and ca. 308-297 Ma. Of the analyzed rocks of this study, the Shuanglong diorite enclave, diorite and andesitic tuff show calc-alkaline affinities, exhibiting LILE enrichment and HFSE depletion, with negative Nb and Ta anomalies. They have high MgO contents and Mg-# values, with depleted epsilon(Hf)(t) and positive epsilon(Nd)(t) values, similar crustal-derived Nb/Ta and Y/Nb ratios, low Th/Yb and Th/Nb, and high Ba/La ratios. which are consistent with them being sourced from a depleted mantle wedge metasomatized by slab-derived fluids and crustal contamination. However, the monzogranite and granodiorite are metaluminous with characteristics of low- to high-K calc-alkaline I-type granites. The granitic rocks are enriched in LILE, depleted in HFSE and have significant Eu anomalies, with high Y contents and low Sr/Y ratios, resembling typical of normal arc magmas. Depleted epsilon(Hf)(t) and positive epsilon(Nd)(t) values with corresponding young T-DM(C) ages of zircons, as well as Nb/Ta, Y/Nb, Th/U and La/Yb ratios suggest that the granitic rocks were probably formed by re-melting of juvenile lower crust or pre-existing mantle-derived mafic-intermediate igneous rocks. Integrating published data, we conclude that the Bailingshan granitoids (excluding the Shuanglong diorite and diorite enclave) were derived from re-melting of juvenile lower crust and mantle-derived mafic-intermediate igneous rocks, with mantle components playing a more prominent role in the formation of the younger and more felsic rocks. A comprehensive review, including our new data, suggests that the Aqishan-Yamansu belt formed as a fore-arc basin during the Carboniferous (ca. 350-300 Ma) when the Kangguer oceanic slab subducted beneath the Yili-Central Tianshan block. The ongoing southward subduction of the slab resulted in the closure of the Aqishan-Yamansu fore-arc basin (ca. 320-300 Ma), due to slab steepening and rollback followed by slab breakoff and rebound. During the Aqishan-Yamansu fore-arc basin inversion, the main phase of the Bailingshan granitoids emplaced in the Aqishan-Yamansu belt, accompanied by contemporary Fe and Fe -Cu mineralization. (C) 2018 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved

Element transport and enrichment during propylitic alteration in Paleozoic porphyry Cu mineralization systems: Insights from chlorite chemistry

Chlorite is one of the most widely developed minerals in propylitic alteration around porphyry deposits and can be used to investigate element transport and enrichment processes during hydrothermal alteration. The Paleozoic Tuwu porphyry Cu deposit (metal reserve: 0.7 Mt Cu @ 0.67%), located in the southern margin of the Central Asian Orogenic Belt, is one of the most economical and largest porphyry Cu deposits in NW China. The Tuwu porphyry Cu deposit comprises an early porphyry Cu mineralization (including potassic, propylitic and phyllic alteration stages) and later overprinting Cu mineralization periods with chlorite found in both. Chlorite from the propylitic zone at Tuwu is geochemically similar to propylitic chlorite in younger Cenozoic porphyry systems, but enriched in Mg and K and depleted in Fe and Al relative to the overprinting chlorite. Scandium, V, Ti and Ga are enriched, and Li, Sr, Mn and Zn are depleted in the Tuwu propylitic chlorite proximal to the orebody, consistent with Cenozoic deposits. Compared with metamorphic chlorite from Proterozoic metamorphic terranes in Australia, Tuwu propylitic chlorite has higher Mg and K, lower Fe, Al and As. Our results suggest propylitic alteration in the Tuwu district is probably the product of cooling of fluids derived from the magmatic-hydrothermal system, but not from peripheral waters, and trace element variations in chlorite are mainly controlled by temperature although other factors such as fault development could affect variation trends. The common elemental features of chlorite in both Paleozoic and Cenozoic porphyry Cu deposits indicate it could act as a potential tool for mineral exploration

Hydrothermal alteration and short wavelength infrared (SWIR) characteristics of the Tongshankou porphyry-skarn Cu-Mo deposit, Yangtze craton, Eastern China

The Early Cretaceous Tongshankou Cu-Mo deposit is located in the eastern Yangtze craton and comprises both porphyry and skarn mineralization. The porphyry ore is hosted in a granodiorite porphyry with the skarn mineralization found along the contacts with the carbonate host rocks. Alteration in the porphyry mineralization can be divided into three stages: potassic alteration, phyllic alteration and a carbonate stage, with phyllic alteration associated with the main porphyry mineralization. No propylitic alteration is present at Tongshankou. The skarn-type alteration comprises five stages: early skarn stage, late skarn stage, oxide stage, quartz-sulfide stage and late vein stage. Short wave-length infrared (SWIR) analysis identified 15 hydrothermal minerals in the Tongshankou deposit, including illite, dickite, halloysite, phengite, talc, muscovite, saponite, gypsum, chlorite, prehnite, montmorillonite, serpentine, phlogopite, actinolite, kaolinite, with montmorillonite, illite and chlorite being the most common. SWIR parameters and the electron microprobe results of chlorites show that chlorites close to the mineralization center tend to be iron-rich and have high FeOH absorption position (Pos 2250 > 2251 nm). Consequently, chlorite may be a useful indicator mineral for mineralization in the Tongshankou deposit. Pos 2250 is not correlated to temperature as calculated using a chlorite geothermometer but does correlate with the iron contents of the chlorites. Our results show that the ore-forming fluids are Fe-rich in the proximity to the mineralization but Mg-rich towards the distal area. Unlike in other porphyry deposits the white mica show no consistent variation in the Tongshankou deposit and cannot be used as vectors towards mineralization. The Fe-Mg-Al poor carbonate host rocks of the Tongshankou deposit restrict the development of a propylitic alteration zone. The Fe-Mg-Al host rocks also prevent Tschermak exchange in white mica ((Si-iv(Mg,Fe)(vi) (AlAlvi)-Al-iv)), making white mica Pos 2200 and Illite crystallinity (IC) randomly distributed. Our results show that SWIR spectroscopy of chlorite may be an applicable exploration tool in skarn-related hydro thermal systems