ABSTRACT Superimposed porphyry systems are a subset of telescoped porphyry deposits, whereby significantly younger ore zones overprint older, nongenetically related systems. Recognition of superimposed features in porphyry systems is important for determining and assessing their prospectivity. The Mount Nansen gold corridor in the southern Dawson Range gold belt of Yukon, Canada, contains porphyry prospects and epithermal deposits with enigmatic genetic models. Geologic, petrologic, temporal (U-Pb zircon, Re-Os molybdenite), and geochemical (whole-rock) studies are used to demonstrate the presence of superimposed porphyry systems in this district. The arc-related episodic magmatism of the Mount Nansen gold corridor has been classified into four intrusive suites: (1) Late Triassic Minto, (2) mid-Cretaceous Whitehorse, (3) Late Cretaceous Casino (eLKc; 80–72 Ma), and (4) Late Cretaceous Prospector Mountain (lLKp; 72–65 Ma). Geochemical fingerprinting of these suites indicates intermediate to evolved, calc-alkaline compositions with a common lower crust melt source. The eLKc and lLKp suites lack an Eu anomaly and show increasing amounts of light rare earth element (LREE) enrichment and heavy rare earth element (HREE) depletion over time. These features suggest that garnet was stable in the melt source and oxidized magmas were generated in these Late Cretaceous suites. The mildly alkaline lLKp and associated Carmacks Group shoshonitic basalts reflect localized extension in an overall compressive arc setting in the Mount Nansen gold corridor, hence a setting conducive for Au-rich porphyry and epithermal systems. The ca. 79 to 72 Ma Casino suite is commonly interpreted as the causative magmatic event for most well-endowed porphyry deposits (76 to 74 Ma in age) in the Dawson Range gold belt. However, our detailed study of the Klaza setting shows that at this locality, intermediate-sulfidation epithermal veins are a distal expression of a Prospector Mountain-age (ca. 71 Ma) porphyry system, which overprints two Casino-age porphyry systems (ca. 77 and 80 Ma). The Mount Nansen gold corridor thus hosts at least two spatially and temporally overprinting Late Cretaceous magmatic-hydrothermal systems in the Dawson Range gold belt. Importantly, recognition of this feature at other porphyry deposit settings in the Dawson Range gold belt (e.g., Freegold Mountain district) is critical as it provides the potential for metal (Cu-Au-Mo)-enriched hypogene ore shells.

Abstract Some arc magmas lead to the formation of porphyry deposits in the relatively shallow upper crust (<5 km). Porphyry deposits are major sources of Cu and an important Au source but lack significant amounts of platinum group elements (PGE). Sulfide phases control the behavior of chalcophile elements and affect the potential to form ore deposits either by remaining in the mantle residue or by fractionating from arc magmas at lower crustal levels, although in detail the role of sulfide saturation in the lower crust remains poorly understood. Lower crustal cumulate rocks from the 85 Ma Chilas Complex of the Kohistan arc, Pakistan, provide insight into processes that occur at depth in arcs. Here we provide Cu, Ni, Au, and PGE concentrations and Os isotope ratios of the Chilas Complex in order to constrain the extent of sulfide saturation in the lower crust and the effect of sulfide saturation on the metal budget of evolved melts that ascend to the upper crust. The Chilas rock suite contains less than 0.17 wt % sulfides and low PGE concentrations. In situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) measurements of the sulfide inclusions in silicate minerals show enrichment in several chalcophile elements (up to 34 wt % Cu, 23 ppm Au, 245 ppm Pd, and 20 ppm Pt), whereas iridium group PGE (IPGE- Os, Ir, Ru) are mainly below detection limits. The metal content of the parental melt was modeled based on the elemental concentrations of the sulfides. The modeled parental arc magmas contain 70 to 140 ppm Cu, 0.2 to 1.5 ppb Au, and 1.2 to 8 ppb Pd, but low concentrations of IPGE, suggesting that IPGE were likely retained in the mantle source. Mass balance calculations show that segregation of a sulfide melt in the lower crust could further deplete the melt by more than 95% in Pd and Pt, 33 to 85% in Au, and 13 to 60% in Cu. Thus, magmas that ascend to the upper crust would contain very low concentrations of Au (< 0.2 ppb) and Pd (< 0.04 ppb), but they would retain sufficient concentration of Cu (~45–57 ppm) to form porphyry Cu deposits upon emplacement in the upper crust, as is commonly observed in arc settings.

Abstract The Cerro Vetas porphyry deposit is part of the Titiribi district of the Middle Cauca porphyry-epithermal belt of western Colombia. The Cerro Vetas porphyry stock consists of a premineral diorite intruded by a late-mineral quartz monzonite, with intrusion and contact breccias. These units intrude pre-Cenozoic basement metabasalts and schists, Oligocene-Miocene Amagá Formation sedimentary rocks with intercalated andesite flows. Two phases of potassic alteration are recognized, a biotite-dominant phase in the diorite, and secondary K-feldspar in the quartz-monzonite intrusion. An overprinting and grade destructive, calcic-sodic alteration (actinolite + albite ± magnetite) affects both porphyries. Biotite alteration is overprinted by weak-moderate phyllic alteration in the upper 100 m in the deposit. Below 100 m, phyllic alteration assemblages are constrained to structural zones. Mineralization is dominated by a chalcopyrite-gold-pyrite assemblage associated with biotite that is hosted in a truncated stockwork in the apical portion of the deposit with metal ratios typical of a gold-rich copper-gold porphyry. The intrusions were dated, using U-Pb in zircon laser ablation inductively coupled plasma-mass spectroscopy, to between 7.65 to 7.24 Ma, consistent with other deposits in the Middle Cauca belt. Lithologic, alteration, and stratigraphic relationships at the deposit suggest that the Cerro Vetas porphyry was emplaced at shallow depths and that the upper portion of the deposit has been eroded.

Abstract A northerly trending zone of porphyry Cu-Au, porphyry Au, polymetallic replacement Pb-Zn-Au-Ag, and sedimentary rock-hosted Au deposits along the northwest margin of the Late Cretaceous Timok Magmatic Complex forms a part of the Bor metallogenic zone in eastern Serbia. The porphyry Cu-Au, epithermal quartz-alunite, and polymetallic replacement deposits in the northwest margin of the Complex represent parts of zoned magmatic-hydrothermal systems that are linked to Late Cretaceous oxidized, hornblende-biotite diorite porphyry intruded over a ~5- to 6-m.y. period between 83.6 ± 0.5 and 78.5 ± 1.3 Ma (U-Pb SHRIMP-RG ages on zircon), making them slightly younger than the larger Late Cretaceous (89-83 Ma) porphyry Cu-Au and high-sulfidation Cu-Au deposits in the eastern part of the Complex. The low-temperature sedimentary rock-hosted Au deposits in the northwest lie spatially near to, but are always separated by faults from, the polymetallic replacement and porphyry Cu-Au deposits. However, the common but not ubiquitous spatial association between the sedimentary rock-hosted Au deposits and the zoned porphyry Cu polymetallic replacement deposits, coupled with available exploration geochemical vectors evident in soil geochemistry, does suggest a genetic linkage between all the hydrothermal deposits. An important component required to fit the deposit types into a zoned magmatic hydrothermal model is a revised geologic and tectonic understanding that can also be extended to the entire Timok Magmatic Complex. A component of the revised model emphasizes the role of the Cenozoic faults formed during oroclinal bending of the region. Two fault generations are significant. Postmineral easterly trending normal faults bounding basins filled largely by early Miocene sedimentary rocks preserved the low-temperature sedimentary rock-hosted Au deposits and helped preserve deposits in the eastern area of the Complex. These faults accommodated elongation of the Complex and are kinematically linked to dextral strike-slip faults, such as the Timok-Cerna fault system, with as much as 100 km of displacement. Major, postmineral, NW-trending faults dismembered deposits in the northwest and accommodated sinistral displacement, which on a larger scale facilitated rotation between large crustal blocks, as well as Timok Magmatic Complex-scale shortening normal to the Complex during oroclinal bending of the region. The end result of the postmineral deformation during oroclinal bending and extensional and strike-slip deformation is preservation of different crustal levels, not just in the northwest but also throughout the region. The deformation furthermore enhanced the preservation of Cretaceous ore deposits beneath younger rocks. Because the Complex was constructed over a highly faulted Variscan and older basement terrane, it is possible that reactivation of the pre-Cretaceous basement faults in the basement beneath the Complex, such as the Variscan Blagojev-Kamen-Rudaria fault systems, played a role in the Late Cretaceous history of the Bor metallogenic zone, as well as controlling post-Cretaceous deformation in the Complex.

Abstract The Kassandra mining district in the eastern Chalkidiki Peninsula of northern Greece contains ~12 Moz Au in porphyry and polymetallic carbonate-hosted replacement sulfide orebodies. Zircon U-Pb geochronology defines two distinct magmatic episodes in the late Oligocene (27-25 Ma) and early Miocene (20-19 Ma). Both suites are characterized by high K calc-alkaline magmas with the younger early Miocene porphyritic stocks and dikes having indications of shoshonitic geochemistry. Normalized rare earth element patterns support plagio-clase fractionation among the late Oligocene suite, whereas amphibole or garnet fractionation is more likely for early Miocene porphyries. Carbonate replacement mineralization is hosted in marble contained within the semibrittle Stratoni fault zone. Mineralization varies along the 12-km strike length of the fault zone from Cu-bearing skarn adjacent to the late Oligocene Stratoni granodiorite stock westward into Au-Ag-Pb-Zn-Cu carbonate replacement deposits at Madem Lakkos and Mavres Petres. Piavitsa, at the western end of the exposed fault zone, hosts siliceous Mn-rich replacement bodies associated with crustiform Au-rich quartz-rhodochrosite veins. Structural and alteration relationships suggest that carbonate replacement mineralization is syn- to postemplacement of the late Oligocene Stratoni granodiorite stock at 25.4 ± 0.2 Ma. The Olympias Au-Ag-Pb-Zn carbonate replacement deposit, located north of the Stratoni fault zone, is hosted in marble and associated semibrittle structures. Olympias is broadly similar to the Madem Lakkos and Mavres Petres deposits. Early Miocene Au-Cu mineralization at Skouries is associated with a narrow pipe-shaped multiphase porphyry stock emplaced into the hinge zone of a regional antiform. Late Oligocene and early Miocene magmatism overlaps spatially within the district but defines distinct petrogenetic events separated by about 5 m.y. Carbonate replacement massive sulfide deposition was largely controlled by an extensional structure and receptive host rocks within the fault zone, whereas a major regional fold axis localized the Skouries porphyry system. The change in character of mineralization with time may reflect a combination of factors including preexisting structural control, magmatic-hydrothermal processes, and the availability of reactive host rocks.

Abstract The Kişladağ porphyry gold deposit (16.8 Moz) is located in western Anatolia, Turkey, and is hosted in a nested complex of monzonite porphyries that intruded coeval volcanic rocks of the Beydagi stratovolcano and the Menderes metamorphic basement. The intrusions and volcanic rocks have a high K calc-alkaline to shoshonitic affinity similar to the regional volcanic rocks of western Anatolia. Three main intrusive phases are recognized with average gold grades highest in the early intrusions, Intrusion 1 (~0.8 g/t Au) and Intrusion 2 (~0.7 g/t Au), followed by the weakly mineralized Intrusion 3 (typically <0.2 g/t Au). The highest gold (~0.84 g/t) is also associated with the higher temperature potassic (biotite-K feldspar ± actinolite) core of the deposit in Intrusion 1. Molybdenum is most closely associated with Au, whereas the Cu concentration on average is unusually low (~200 ppm) but increases with depth (500-1,000 ppm). Surrounding and partly overlapping the potassic zone is a distinct tourmaline-white mica (± pyrite ± albite ± quartz) alteration with tourmaline abundant up to 500 m from the center of the deposit. White mica is more widely distributed with compositions varying from proximal muscovite-paragonite to distal phengite. Stockwork veinlets are common within the potassic and tourmaline-white mica zones and evolve from volumetrically minor quartz-rich, to quartz-pyrite, to quartz-pyrite with tourmaline envelopes, to the most abundant pyrite-tourmaline veins and breccias, and finally pyrite-only veins. A poorly mineralized advanced argillic alteration assemblage (quartz-alunite ± dickite ± pyrophyllite ± pyrite) postdates the tourmaline-white mica alteration and is particularly abundant in the eastern flank of the deposit and as a lithocap. The most widespread alteration is argillic comprising kaolinite ± smectite ± pyrite ± quartz, and overprinting all alteration phases, and is particularly widespread in the surrounding volcanic package. New geochronological results from the Kisladag deposit constrain the timing and duration of the main gold mineralization stage to <0.4 m.y. (14.76 ± 0.01-14.36 ± 0.02 Ma). The system evolved in the following sequence: (1) Intrusion 1 (>14.76 ± 0.01 Ma), (2) Intrusion 2 (14.76 ± 0.01 Ma), (3) potassic alteration coeval with mineralization (14.4 ± 0.1 Ma), and (4) Intrusion 3 (14.36 ± 0.02 Ma). The deposition of gold is constrained by the emplacement of the sulfide mineralization dated at 14.49 ± 0.06 Ma by Re-Os on molybdenite. The Kişladağ deposit is classified as a gold-only porphyry deposit due to its exceptionally low Cu/Au ratio («0.03). There are few economically significant global analogues—examples include the Maricunga porphyry deposits (9.8 Moz Au) in Chile and La Colosa (33.2 Moz Au) in Columbia. The low Cu/Au ratio may in part be related to the shallow level of emplacement (<1 km?) but also reflects the postcollisional setting. The deposit formed at least 50 m.y. after closure of the northern Neotethys ocean that was related to Cretaceous collision and compression, and 15 m.y. after the commencement slab roll-back of the southern Neotethys ocean and the onset of upper plate extension in the late Eocene to early Oligocene. The Miocene volcanic rocks that host Kisladag are in part related to a slab tear that resulted in upwelling of asthenospheric mantle, which melted previously metasomatized subcontinental lithospheric mantle. Postcollision extension, fertile upper mantle, shallow subduction, and slab tear-induced magmatism, and shallow level of emplacement may have been important factors in the gold-rich nature of Kisladag.

Abstract The Biga Peninsula in northwestern Turkey hosts a large number of high- and low-sulfidation epithermal gold-silver-(copper) and associated copper-gold porphyry deposits and prospects, associated with voluminous, Eocene-Miocene calc-alkaline volcanism and plutonism. In this area, 50 to 20 Ma intermediate to felsic volcanic and volcaniclastic strata overlie metamorphosed basement rocks of the Camlica Group. The volcanic sequence is variably altered over an area covering several hundreds of square kilometers, including argillic, advanced argillic, and massive to vuggy residual quartz alteration, the latter present at the tops of many of the higher elevation peaks in the area. Moderate- and high-angle normal and oblique faults are common in the area and influenced the distribution of mineralization. While gold mineralization associated with these high-sulfidation epithermal systems and flanking low-sulfidation epithermal systems has long been recognized, the existence of porphyry roots to these systems was not fully appreciated until the discovery of the Halilaga porphyry in 2008. In the southern part of the TV Tower property, low relief areas consist of schist and serpentinite intruded by the Kuşçayir pluton, a composite, ~40 Ma intrusion that averages granodiorite in composition. Intermediate volcanic and volcaniclastic rocks are exposed in the highest elevation areas. The northern edge of the pluton, at low to intermediate elevations, consists of at least six intrusions of similar age and composition that differ primarily in degree of porphyritic texture and phenocryst quartz content. The intrusions are parsed into pre- syn- and late mineralization phases with respect to hydrothermal alteration and mineralization related to at least two Au-Cu porphyry centers, Valley and Hilltop. The porphyry systems occur below and are to some degree overprinted by high-sulfidation alteration and mineralization. The porphyry/high-sulfidation system was subjected to weathering and oxidation, giving rise to a supergene copper enrichment blanket that lies near the transition from the high sulfidation into the porphyry environment. Alteration associated with the porphyry systems includes chlorite-magnetite-actinolite, K-feldspar-biotite-quartz-magnetite-hematite (“potassic”), and, at higher elevations, overprinting quartz-muscovite (“phyllic”) alteration. Quartz stockwork veining is ubiquitous in the phyllic and potassic assemblages, and includes quartz-K-feldspar “A” veins, quartz sulfide “B” veins, pyrite-quartz “D” veins, and quartz-magnetite “M” veins. Copper mineral assemblages range from bornite-chalcopyrite to chalcopyrite-pyrite, and chalcopyrite-chalcocite or chalcocite-covellite-digenite in the supergene zones. High-sulfidation epithermal mineralization is dominantly oxidized, and consists of residual vuggy and massive quartz, alunite, pyrophyllite, and iron oxides. New U-Pb dates for the Kuşçayir pluton and Hilltop and Valley intrusions range from 38 to 40 Ma, consistent with other Cu-Au porphyry systems in the region, whereas most dated high-sulfidation epithermal deposits in the region formed at roughly 29 Ma, coeval with an Oligocene suite of intrusions. It is possible that the epithermal-porphyry relationship at Karaayi is one of overprinting of two unrelated hydrothermal systems.

Abstract Epithermal Au-(Ag) and porphyry Cu-Au-(Mo) mineralization of the Biga Peninsula in northwestern Turkey occurs in a district comprised of NE- to ENE-trending metamorphic horst blocks separated by half-graben volcano-sedimentary basins. These developed as a result of rollback of the northward-subducting African slab during the Eocene, Oligocene, and Miocene. We propose that epithermal and porphyry systems occupy distinct, favorable positions within the overall extensional architecture and fault/fracture array. High- and low-sulfidation epithermal alteration systems, along with related quartz veins, preferentially occupy half-graben basins and border faults. These epithermal systems are found above a core complex detachment fault system, forming major strata-bound silicified zones fed by steeply dipping extensional faults and associated fractures above inferred intrusions. At greater depths and higher pressure and temperature conditions, porphyry-style alteration systems are spatially associated with porphyritic stocks that occur in close association with plutonic bodies. These plutons have intruded the footwall of ductile to brittle extensional faults and spatially and temporally link to metamorphic core complex exhumation. Episodic changes in the tectonic stress resulted in pulses of crustal extension that favored porphyry-type and high-sulfidation-style mineralization during mid to late stages of Eocene and Oligocene extensional tectonic phases. On the other hand, the early stages of each extensional phase promoted higher structural permeability, enabling the development of vein systems and low-sulfidation epithermal-style mineralization. Postemplacement crustal extension resulted in “domino-style” block rotations and half-graben formation throughout the Miocene and Pliocene. Since the early Pliocene, the westward propagation of the North Anatolian fault has resulted in dextral transtension in the Biga Peninsula and, as a result, postmineralization structural dismemberment of deposits and alteration systems is common.

Abstract This contribution reviews the metallogenic setting of the Lesser Caucasus within the framework of the complex geodynamic evolution of the Central Tethys belt during convergence and collision of the Arabia-, Eurasia-, and Gondwana-derived microplates. New rhenium-osmium molybdenite ages are also presented for several major deposits and prospects, allowing us to constrain the metallogenic evolution of the Lesser Caucasus. The hostrock lithologies, magmatic associations, deposit styles, ore controls, and metal endowment vary greatly along the Lesser Caucasus as a function of the age and tectono-magmatic distribution of the ore districts and deposits. The ore deposits and ore districts can essentially be assigned to two different evolution stages: (1) Mesozoic arc construction and evolution along the Eurasian margin, and (2) Cenozoic magmatism and tectonic evolution following Late Cretaceous accretion of Gondwana-derived microplates with the Eurasian margin. The available data suggest that during Jurassic arc construction along the Eurasian margin, i.e., the Som-kheto-Karabagh belt and the Kapan zone, the metallogenic evolution was dominated by subaqueous magmatic-hydrothermal systems, VMS-style mineralization in a fore-arc environment or along the margins of a back-arc ocean located between the Eurasian margin and Gondwana-derived terranes. This metallogenic event coincided broadly with a rearrangement of tectonic plates, resulting in steepening of the subducting plate during the Middle to Late Jurassic transition. Typical porphyry Cu and high-sulfidation epithermal systems were emplaced in the Somkheto-Karabagh belt during the Late Jurassic and the Early Cretaceous, once the arc reached a more mature stage with a thicker crust, and fertile magmas were generated by magma storage and MASH processes. During the Late Cretaceous, low-sulfidation-type epithermal deposits and transitional VMS-porphyry-epithermal systems were formed in the northern Lesser Caucasus during compression, uplift, and hinterland migration of the magmatic arc, coinciding with flattening of the subduction geometry. Late Cretaceous collision of Gondwana-derived terranes with Eurasia resulted in a rearrangement of subduction zones. Cenozoic magmatism and ore deposits stitched the collision and accretion zones. Eocene porphyry Cu-Mo deposits and associated precious metal epithermal systems were formed during subduction-related magmatism in the southernmost Lesser Caucasus. Subsequently, late Eocene-Oligocene accretion of Arabia with Eurasia and final closure of the southern branch of the Neotethys resulted in the emplacement of Neogene collision to postcollision porphyry Cu-Mo deposits along major translithospheric faults in the southernmost Lesser Caucasus. The Cretaceous and Cenozoic magmatic and metallogenic evolutions of the northern Lesser Caucasus and the Turkish Eastern Pontides are intimately linked to each other. The Cenozoic magmatism and metal-logenic setting of the southernmost Lesser Caucasus can also be traced southward into the Cenozoic Iranian Urumieh-Dokhtar and Alborz belts. However, contrasting tectonic, magmatic, and sedimentary records during the Mesozoic are consistent with the absence of any metallogenic connection between the Alborz in Iran and the southernmost Lesser Caucasus.