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• Four magmatic and associated metallogenic episodes can be defined. The metallogenic episodes are defined in four geographically distinct regions, the Pontides in the north, the western Anatolia province in the west, central Anatolian Crystalline Complex, and the Southeastern Anatolian Orogenic Belt in the east central part of Turkey are; late Cretaceous (∼88–76 Ma), latest Paleocene to early-middle Eocene (58–39.5 Ma); Oligocene-Miocene (30–18 Ma); Middle-late Miocene (16–8 Ma). • Late Cretaceous rocks have typical arc magma compositions except the Central Anatolian Crystalline complex, whereas Eocene to Miocene collisional to post-collisional rocks have compositions characteristic of arc magmas that over time interacted and assimilated by ancient crust and evolved toward slightly higher Sr/Y and La/Yb trace element characteristics reflecting the hydrous and oxidized nature of the magmas. • The late Cretaceous porphyry systems are common in the Pontides and the Central Anatolian Complex. The porphyry systems at the Pontides form a portion of a belt of porphyry Cu deposits that included world-class deposits in Serbia and Bulgaria, and extend eastward into the Caucasus of Georgia, Armenia and Iran. • Eocene porphyry systems in Turkey are the most common in Pontides, western Anatolia and southeastern Anatolian orogenic belt. Oligocene and Miocene porphyry systems are common in the adjoining countries in the Balkans and Iran, but are only known in the western Anatolia region of Turkey. • Overall, the distribution of porphyry Cu systems reflects complex plate interactions involving subduction, collision of continental blocks, closure of small oceanic basins, and rapidly shifting axes of magmatic activity. Continental collision between Eurasia and Afro-Arabia in Turkey along the Pontide subduction zone, İzmir-Erzincan-Ankara suture zone, Bitlis-Zagros suture zone, and Aegean subduction zone generated a fertile metallogenic environment with calc-alkalic and alkalic porphyry Cu (-Mo-Au) and magmatic hydrothermal systems emplaced in narrow arc segments over limited time durations within major magmatic events in the late Cretaceous to late Miocene. The major magmatic events represent multiple subduction zones that gradually stepped from north to south as small oceans closed during collisional events and the trench retreated or shifted southward as a result. Based on geological, new geochemical, and 40Ar/39Ar, U-Pb LA-ICP-MS geochronological data presented herein along with published data for igneous and hydrothermally altered rocks, four metallogenic episodes are defined; late Cretacecous, early-late Eocene, late Oligocene- early Miocene, and middle-late Miocene, in four geographically distinct regions, the Pontides in the north, the western Anatolian province in the west, central Anatolian Crystalline Complex, and the Southeastern Anatolian Orogenic Belt in the east central part of Turkey. Within those regions, porphyry Cu and intrusion-related hydrothermal systems begin in the late Cretaceous to the north, and generally young southward. They begin as porphyry Cu-Mo type, and tend to be more Au-rich from late Cretaceous to late Miocene. Published and new ages indicate early-late Cretaceous magmatic rocks in the Pontides were emplaced between ca. 131 and 65 Ma, peaking between ca. 88–76 Ma. Apart from the Re-Os molybdenite ages, published and new ages for porphyry Cu-related rocks and hydrothermal minerals from the Ayder, Konak, Esendal, Börekli, and Dereköy prospects indicate porphyry Cu formation near the end of that magmatic event (ca. 83–76 Ma). Published data indicate a somewhat shorter late Cretaceous magmatic event (86.5 to 70.3 Ma) peaking at ca. 86 to 80 Ma at the southeastern Anatolian orogenic belt with porphyry Cu systems reported to have formed contemporaneously. The latest Paleocene to early-late Eocene magmatism and porphyry-style hydrothermal systems are common across Turkey, with porphyry Cu systems formed in the eastern Pontides (58–37.9 Ma) based on the ages of their host rocks and syn -mineral stocks; in the western Anatolian province in the Tavşanlı porphyry belt (ca. 49.1–46.7 Ma) and the Biga porphyry belt (40.1–39.5 Ma), and in the Southeastern Anatolian orogenic belt (ca. 47 to 43 Ma). Oligocene-Miocene magmatism (30–18 Ma) and associated hydrothermal systems dominate during ca. 27.4 to 24.8 Ma the western Anatolian province in the Biga porphyry belt, but appear less common in other parts of Turkey except for the Cevizlidere porphyry deposit in the Southeastern Anatolian orogenic belt. Middle-late Miocene magmatism (ca. 16–8 Ma) and associated porphyry Cu systems predominate within the Afyon-Konya porphyry belt in western Anatolia, and contains the youngest porphyry related magmatic and hydrothermal systems (14.4–8.9 Ma). Calc-alkalic porphyry Cu ± Mo-Au systems dominate all belts except the Afyon-Konya porphyry belt where alkalic porphyry Au-Cu systems are present. The porphyry systems are dominantly metaluminous and medium to high-K rocks with a range in composition from diorite to granite, with monzonite and syenite associated with the alkalic porphyry systems. Late Cretaceous rocks have typical arc magma compositions except the Central Anatolian Crystalline complex, whereas Eocene to Miocene collisional to post-collisional rocks have compositional characteristic of arc magmas that over time interacted and assimilated by ancient crust and evolved toward slightly higher Sr/Y and La/Yb trace element characteristics. The trace element compositions along with rare earth element patterns share characterristics, typical of rocks associated with porphyry Cu-related magmas reflecting the hydrous and oxidized nature of the magmas. The late Cretaceous porphyry systems common in the Pontides form a portion of a belt of porphyry Cu deposits that included world-class deposits in Serbia and Bulgaria, and extend eastward into the Caucasus of Georgia, Armenia and Iran. Early-late Eocene porphyry systems in Pontides, western Anatolian province and southeastern Anatolian orogenic belt form clusters not extending the in the Balkans. Oligocene and Miocene porphyry systems are common in the adjoining countries in the Balkans and Iran, but are only known in the western Anatolia region of Turkey. Overall, the distribution of porphyry Cu systems reflects complex plate interactions involving subduction, collision of continental blocks, closure of small oceanic basins, and rapidly shifting axes of magmatic activity. [ABSTRACT FROM AUTHOR]

Field relationships and U-Pb data (zircon) are used to constrain the timing of tectonomaginatic events that occurred shortly after the formation of Late Devonian (~372 Ma) porphyry Cu-Au deposits at Oyu Tolgoi (Mongolia). In tire two northernmost of the several discrete porphyry centers (Hugo Dummett deposits), Upper Devonian rocks positioned stratigraphically above copper-gold mineralization preserve a record of uplift, exhumation, and subsequent burial shortly after mineralization. Strongly altered and mineralized quartz mon-zodiorite and volcanic rocks at Hugo Dummett are overlain by an unmineralized dacite sequence (369 ± 2 Ma). The basal breccia and conglomerate of the dacite sequence contain mineralized porphyry clasts derived from erosion of the porphyry deposits. Two zircon grains recovered from one of these mineralized porphyry clasts yielded chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) 206Pb/238U dates of 374.0 ± 1.9 and 371.4 ± 1.6 Ma, which are consistent with previously published ages for mineralized intrusions. This implies that Oyu Tolgoi or other nearby porphyry deposits were exhumed shortly after the main mineralization event. Weakly mineralized granodiorite dikes intruded the postmineralization dacite sequence, as well as Devonian sedimentary and voleaniclastic rocks that structurally overlie the dacite. A weighted mean 206Pb/238U age of 370.6 ± 0.5 Ma for this rock is based on the three youngest grains analyzed by the CA-TIMS technique (MSWD = 1.14). Burial of the Cu-Au deposits at Oyu Tolgoi soon after their exhumation was critical to their preservation. Exhumation and subsequent burial occurred at ~371 Ma, during a short time frame within the overlapping U-Pb zircon ages for the quartz monzodiorite, mineralized porphyry clast, unmineralized dacite sequence, and granodiorite unit. [ABSTRACT FROM AUTHOR]

Porphyry Cu (±Mo ±Au) and epithermal Au-Ag deposits are major sources of mined metals and are commonly formed by magmatic-hydrothermal fluids derived from hydrous magmas in Phanerozoic convergent margin settings. The igneous rock assemblages associated with porphyry mineral deposits are common in modem convergent margin settings, but while many have produced acidic magmatic fluids, very few, past or present, have produced sufficient metal, chlorine, and sulfur enrichments necessary to engender an ore deposit. The reasons for this remain uncertain. We report SHRIMP-RG ion microprobe analyses of hafnium, titanium and rare earth element (REE) abundances in zircon, a nearly ubiquitous and robust trace mineral in crustal magmas. Comparison of the compositions of zircons in ore-forming and barren granitic plutons indicate that ore-forming granites crystallized at relatively low temperature and have relatively small negative europium anomalies (mostly EUN/EUN* ≥0.4). We interpret these small zircon europium anomalies to indicate oxidizing magmatic conditions and hypothesize that in many cases this reflects oxidation due to SO2 degassing from magmas with a relatively low Fe/S ratio. Oxidation of europium and iron in the melt is produced by reduction of magmatic sulfate (S6+) to SO2 (S4+) upon degassing. This interpretation reinforces the important role of oxidized sulfur-rich fluids in porphyry and epithermal mineral deposit formation. Zircon compositions thus may be used to identify ancient magmas that released significant amounts of SO2-rich gases, and regional surveys of zircon composition are potentially a valuable tool for mineral exploration. [ABSTRACT FROM AUTHOR]

SHRIMP-RG U-Pb zircon geochronologic data together with published U-Pb ages from the succession of quartz diorite porphyry intrusions in the western porphyry Cu-Au centers at Reko Diq, western Balochistan, Pakistan, indicate the emplacement of four spatially distinct porphyry Cu centers over ~1 m.y. in the Miocene between ~12.9 and 11.9 Ma. Intrusive activity in the western porphyry cluster began with emplacement of hornblende-rich quartz diorite porphyry associated with the northern and uneconomic H79 porphyry Cu center with U-Pb ages of 12.87 ± 0.27 and 12.72 ± 0.3 Ma. To the south of the H79 porphyry Cu center, successively younger porphyry intrusive centers formed along a south-southwest trend. The economic H15 center has U-Pb zircon ages for four quartz diorite porphyry intrusions between 12.58 ± 0.29 and 12.18 ± 0.19 Ma with three of the porphyry intrusions that span the intrusive sequence in the H15 center having essentially identical ages between 12.58 ± 0.29 and 12.49 ± 0.20 Ma. The adjacent economic H14 center to the south has U-Pb ages on zircons for five quartz diorite porphyry intrusions between 12.22 ± 0.15 and 12.00 ± 0.16 Ma with four of the porphyry intrusions spanning the intrusive sequence having ages between 12.14 ± 0.14 and 12.00 ± 0.16 Ma. The southern end of the trend is the subeconomic H13 complex where mineralized quartz diorite porphyry has a U-Pb age on zircon of 11.93 ± 0.14 Ma. Two new Re-Os ages on molybdenite reported herein agree with the magmatic ages for the H15 (12.43 ± 0.05 Ma) and H14 complexes (11.95 ± 0.05 Ma), whereas previously published Re-Os ages on molybdenite are younger (H15: 11.73 ± 0.04 Ma; H14: 11.82 ± 0.04 Ma) than the youngest dated intrusion in those centers. Published K-Ar ages on hydrothermal biotite from the H79 center (13.0 ± 0.2 Ma), H14 (12.0 ± 0.2 Ma), and H13 (12.0 ± 0.2 Ma) indicate the individual system cooled rapidly. Overall the combined U-Pb geochronology dataset for the four porphyry intrusive centers suggests short-lived magmatic systems characterized each center. However, the available Re-Os ages on molybdenite suggest the potential for complexity in associated hydrothermal systems at the H15 and H14 porphyry Cu-Au centers. [ABSTRACT FROM AUTHOR]

The Lower Main zone of the Lorraine alkalic porphyry Cu-Au district, BC, Canada, is hosted in an intrusive complex that comprises pre- and late mineral biotite pyroxenites, monzonites, and syenites. Some of the biotite pyroxenites have interstitial sulfides, which appear similar to net-textured sulfides in magmatie ore deposits; however, the pyroxenites have undergone several stages of hydrothermal alteration. Main-stage mineralization produced sulfide zonation patterns consisting of a bornite-chalcocite or bornite-chalcopyrite core grading outward to domains of chalcopyrite, chalcopyrite > pyrite, and a peripheral domain of pyrite with minor chalcopyrite. Syenite in the inner bornite-chalcopyrite zone typically contains abundant turbid K-feldspar (>70%), whereas syenite marginal to the bornite-chalcopyrite core contains less K-feldspar (50-70%), indicating an increase in K metasomatism of syenites toward the core of the deposit. Main-stage mineralization predominantly occurs as fine-grained disseminated sulfides in syenite, biotite pyroxenite, and fine-grained K-feldspar biotite rock. Textural analyses have shown that (1) primary magmatie diopside in contact with sulfides has corroded and actinolite-altered margins, suggesting alteration of primary minerals, (2) scalloped relicts of biotite and diopside occur as inclusions in sulfides, implying that sulfides have replaced primary minerals, and (3) the deposit-scale sulfide zonation patterns overprinted numerous rock types, including the biotite pyroxenites that contain interstitial sulfides. These results provide evidence for replacement-style mineralization at Lorraine, where primary magmatie biotite and diopside were totally or partially replaced by sulfide minerals during main-stage alteration. U-Pb zircon dates from pre- and late mineral syenite dikes show that the timing of main-stage mineralization occurred between 178.8 and 176.0 Ma. Lorraine is hosted within the Quesnel island arc terrane, and mineralization and magmatism at Lorraine postdate accretion of the Quesnel terrane to ancestral North America by approximately 7 to 10 m.y. The Lorraine deposit represents the youngest known alkalic Cu-Au porphyry deposit within the Quesnel terrane, and appears to coincide with the last gasp of alkalic magmatism within the Quesnel terrane during the Mesozoic. [ABSTRACT FROM AUTHOR]

The Late Triassic Galore Creek porphyry district is the largest accumulation of Cu-Au prospects in British Columbia, Canada, in terms of contained metal. The principal economic resource is the Central zone deposit. It comprises three high-grade centers: the Au-rich North and South gold lenses and the Cu-dominated Central replacement zone. Alteration footprints, ore shells, and porphyry intrusions in these centers dip 45° to 60° to the west in the North gold lens and southwest in the South gold lens and Central replacement zone, indicative of significant postmineral tilting. This inclination created an oblique vertical expression of the Central zone at surface and at depth, providing a +700m depth profile through the deposit. Galore Creek is considered to be the end-member of the silica-undersaturated class of alkalic porphyry Cu-Au deposits. It displays a unique hydrothermal alteration footprint, generally devoid of quartz veining. Despite the lack of crosscutting veins, a paragenetic sequence of several discrete potassic and calcic alteration events has been established. During main-stage alteration, two mineralization events occurred that formed the economic resource in the Central zone. Highly oxidizing fluids derived from porpbyritic syenite to monzonite intrusions produced initial potassic alteration and sulfide mineralization in the North gold lens and South gold lens. Cu-Au ore shells are characterized by a gold-rich core dominated by bornite associated with hematite-dusted orthoclase, specular hematite, and anhydrite. The second period of hydrothermal activity caused brecciation and calcic alteration in the Central replacement zone. The calcic fluids formed hydrothermal cement grading from Ti-rich andraditic to grossularitic garnet in the core of the breccia to a diopside and magnetite-dominated assemblage at the margins. Calcic alteration also formed in the surrounding host rock. This alteration event was followed by potassic alteration and mineralization, characterized by biotite, anhydrite, and chal-copyrite in the Cu-rich ore shell of the Central replacement zone. Most of the Au is hosted in bornite that is spatially associated with oxidized (reddened) rock units dominated by an alteration assemblage of orthoclase ± hematite + specular hematite ± garnet ± anhydrite. High-grade Cu in the Central zone is related to abundant chalcopyrite that has commonly replaced an assemblage of biotite ± magnetite ± diopside. This distinct spatial separation strongly suggests that the local redox environment within the wall rocks governed sulfide and gold distributions. The switch from early Au-rich mineralization to late-stage Cu-dominated mineralization appears to have been controlled by varying redox conditions within the magma. The change from more oxidized alteration assemblages (Fe3+ > Fe2+) to more reduced assemblages (Fe3+ < Fe2+) is indicative of a change in oxidation potential that may have propelled sulfide saturation in the magma and, thus, the subsequent depletion of most of the Au. [ABSTRACT FROM AUTHOR]

Rapidly changing ore deposit types in the Late Cretaceous and early Tertiary in the Southeastern Anatolian orogenic belt in east-central Turkey, from Baskil on the south to Divrigi on the north, broadly reflect shifting tectonic environments in an evolving collisional orogen, a part of the extensive Tethyan orogen. Late Cretaceous (~83-79 Ma) subduction-related arc magmatism in the Baskil arc was followed by extension that exhumed the metamorphic basement, unroofed the obducted ophiolites, and filled basins with Maastrichtian to Paleocene subaerial and submarine sedimentary rocks. Calc-alkaline (Divrigi pluton, ~76-73 Ma) and alkaline igneous rocks (Hasançelebi and Keban districts, ~76-74 Ma) accompanied post-Baskil arc extension. In the early to middle Eocene, shallow and locally voluminous intrusions of intermediate composition (Çöpier, Kabatas, Bizmisen-Calti, Dedeyazi-Polat, Karamadazi, and Horoz), localized mainly along major strike-slip faults, formed during closure of the Neotethyan Ocean. These intrusions are dated between ~50 and 44 Ma, peaking at 48 Ma. Geochemical data from a suite of igneous rock samples across the transect reflect temporally based changes from arc-type to late orogenic environments, as demonstrated by Late Cretaceous rocks in the Baskil area on the south and the more deeply eroded Late Cretaceous plutons in the Divrigi area on the north (Divrigi). These magmatic products were followed in the Eocene by calc-alkaline magmatism related to either incipient slab-rupture or crustal-scale faults that cut from northeast (Çöpler, Kabatas, Bizmisen-Calti, and Polat-Cavuslu) to southwest (Karamadazi and Horoz) obliquely across the transect. The multielement patterns for the Late Cretaceous magmatic rocks resemble the patterns for magmas generated in enriched source regions compared to primitive mantle and mid-oceanic-ridge basalt. Locally, at Divrigi-Hasançelebi and Keban, the geochemical characteristics are suggestive of the influx of low field strength elements into the mantle source regions from a subducted slab, and an arc to postcollisional to late-orogenic setting for their generation. Eocene magmatic rocks display similar geochemical characteristics regardless of the geographic setting and associated hydrothermal system. Their characteristics favor a subduction zone enrichment that was inherited either from an older event, or from an older slab, or from a mantle wedge contaminated by a contemporaneous subduction component. 40Ar/39Ar and U/Pb geochronology on biotite, zircon, K-feldspar, hornblende, and sericite from a suite of magmatic rocks and alteration zones defines three magmatic-related metallogenic events in the Southeastern Anatolian orogenic belt between 78 and 44 Ma. The oldest metallogenic event between ~78 to 74 Ma is related to arc-type calc-alkaline magmatic rocks (83-79 Ma) intruded into the Bitlis-Poturge and Malatya-Keban meta-morphics and overlying Komurhan-Ispendere ophiolites of Tauride platform. Uneconomic porphyry-type Cu-Au systems formed at Topalkem-Baskil (Elazig) and Ispendere-Sisman (Malatya). A second metallogenic event, between ~74 and 69 Ma, is contemporaneous with postcollisional exhumation and extension-related magmatism. During this event, calc-alkaline followed by alkaline magmatism (76-73 Ma) was accompanied by formation of iron oxide copper-gold (IOCG) systems at ~74 to 73 Ma at Divrigi (Sivas). Alkaline magmatism at ~76 to 74 Ma is associated with IOCG systems at Hasançelebi (Malatya) and porphyry Cu-Mo and Pb-Zn veins at Keban (Elazig). The youngest metallogenic event between ~50 and 40 Ma is represented by porphyry Cu-Au deposits associated with calc-alkaline intrusive complexes at Çöpler and Kabatas and Fe skams at Karamadazi, Horoz, Dedeyazi, and Bizmisen-Calti. [ABSTRACT FROM AUTHOR]

The Paleocene to Eocene southern Peru porphyry belt contains three significant porphyry Cu-Mo deposits at Cuajone, Quellaveco, and Toquepala. Ten new zircon U-Pb Sensitive High Resolution Ion Microprobe-Reverse Geometry (SHRIMP-RG) ages for Cuajone and Toquepala, together with published ages for Quellaveco, establish a magmatic history characterized by episodic events. Punctuated magmatism at Cuajone is distributed over approximately 13 m.y., at Toquepala over 8 m.y., and at Quellaveco over 6 m.y. The ages of the porphyry intrusions hosting or associated with the introduction of Cu and Mo at the three deposits show remarkable similarity, with emplacement beginning and ending at approximately 56.5 to 53.0 Ma at Cuajone, 57.0 to 54.0 Ma at Toquepala, and at 58.4 to 54.3 Ma at Quellaveco. Field relations coupled with the U-Pb ages for synmineral intrusions suggest very similar timing of the cupriferous hydrothermal systems, with the youngest pyritiferous and Cu-poor hydrothermal systems being associated with porphyry intrusions as much as 2 m.y. younger than significant Cu introduction. Overall, the porphyry Cu-Mo intrusive complexes represent the youngest magmatic complexes formed during the Late Cretaceous and early Tertiary arc, having formed prior to eastward migration of the magmatic locus. [ABSTRACT FROM AUTHOR]

Abstract: Uranium–Pb (zircon) ages are linked with geochemical data for porphyry intrusions associated with giant porphyry Cu–Au systems at Oyu Tolgoi to place those rocks within the petrochemical framework of Devonian and Carboniferous rocks of southern Mongolia. In this part of the Gurvansayhan terrane within the Central Asian Orogenic Belt, the transition from Devonian tholeiitic marine rocks to unconformably overlying Carboniferous calc-alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation. Radiogenic Nd and Pb isotopic compositions (ε Nd(t) range from +3.1 to +7.5 and 206Pb/204Pb values for feldspars range from 17.97 to 18.72), as well as low high-field strength element (HFSE) contents of most rocks (mafic rocks typically have <1.5% TiO2) are consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc. The Late Devonian and Carboniferous felsic rocks are dominantly medium- to high-K calc-alkaline and characterized by a decrease in Sr/Y ratios through time, with the Carboniferous rocks being more felsic than those of Devonian age. Porphyry Cu–Au related intrusions were emplaced in the Late Devonian during the transition from tholeiitic to calc-alkaline arc magmatism. Uranium–Pb (zircon) geochronology indicates that the Late Devonian pre- to syn-mineral quartz monzodiorite intrusions associated with the porphyry Cu–Au deposits are ~372Ma, whereas granodiorite intrusions that post-date major shortening and are associated with less well-developed porphyry Cu–Au mineralization are ~366Ma. Trace element geochemistry of zircons in the Late Devonian intrusions associated with the porphyry Cu–Au systems contain distinct Th/U and Yb/Gd ratios, as well as Hf and Y concentrations that reflect mixing of magma of distinct compositions. These characteristics are missing in the unmineralized Carboniferous intrusions. High Sr/Y and evidence for magma mixing in syn- to late-mineral intrusions distinguish the Late Devonian rocks associated with giant Cu–Au deposits from younger magmatic suites in the district. [Copyright &y& Elsevier]

The geological relations and geochemical composition of extrusive and subvolcanic intrusive rocks of the Upper Miocene Farallón Negro Volcanic Complex (NW Argentina) were studied to reconstruct the evolution of a deeply eroded andesitic volcano over most its life history of some 3.5 my. This paper is part of an integrated study of the processes that generate magmatic-hydrothermal fluids responsible for the formation of porphyry-Cu-Au deposits. Here we present new data on bulk rock chemical and Nd, Sr and Pb isotopic compositions of unaltered volcanic and subvolcanic intrusive rocks, for which geological relations and ages are constrained by field-based stratigraphy and extensive Ar–Ar geochronology.The combined results indicate that voluminous volcanism started at ca. 9.7 Ma with the eruption of basaltic andesite to andesite lava flows and pyroclastic deposits. This basic to intermediate volcanism persisted until 7.5 Ma and was followed at 7.35 Ma by the eruption of dacites as the last recorded major extrusive event. The oldest andesitic intrusions, emplaced at 9.0 Ma, were followed by hypabyssal intrusions of basaltic andesite, andesite and dacite composition, which intruded the volcanic sequence between 8.3 and 6.1 Ma. Intrusions at 6.8±0.2 Ma led to the formation of over 800 Mt of porphyry-Cu-Au ore at Bajo de la Alumbrera. It was formed by a large flux of magmatic-hydrothermal fluids channeled through several phases of fractured dacitic porphyry, which together with immediately following barren andesitic intrusions make up a composite stock. After this magmatic-hydrothermal event, only minor rhyodacitic to rhyolitic intrusions were emplaced until magmatic activity ceased at 6.1 Ma.Geochemical data for the magmatic rocks indicate that the evolution of the system was dominated by mixing of a mafic magma with a felsic magma that contained a component of crustal material, as indicated by linear compositional correlations between compatible and incompatible elements. Initial strontium isotopic ratios vary between 0.7047 and 0.7118 while 143Nd/144Nd range from 0.5127 to 0.5124, and both isotopic variations correlate with each other and with SiO2 content of the rocks. After 8.5 Ma, a continuous increase in the silica content of intrusive rocks suggests the gradual formation of a magma chamber. A substantial magma reservoir (>7 km3) must have been established by the time of porphyry-Cu-Au mineralization, to allow rapid release of a large volume of ore-forming magmatic brine as a result of wholesale crystallization and de-volatilization of the magma chamber. [Copyright &y& Elsevier]