Porphyry Belt Research Articles

The Ciclón - Exploradora epithermal polymetallic ore deposit: An Eocene Cordilleran-type of mineralization in the Domeyko Cordillera, Northern Chile

The Ciclón-Exploradora Project is located in the Exploradora Porphyry Copper District, which corresponds to an old artisanal mining and exploration area 65 km northeast from El Salvador Copper Mine, between 3200 and 4000 m.a.s.l. and inserted within the Eocene-Oligocene metallogenic porphyry belt and Domeyko Cordillera. Exploitation has been discontinuous since the late mid-19th century. It first started with production at the Copper Exploradora Mine, and later for Au–Ag at the Ciclón and San Carlos mines. Nevertheless, after decades of work and exploration the district has great potential for new discoveries.Epithermal polymetallic (Cu–Ag–Zn–Pb–Au) mineralization took place related to the evolution of the Exploradora Plutonic and Porphyry Complex. This Eocene Complex is a composite of dioritic to monzodioritic magmatic intrusions including several intermediate composition Cu–Au and Cu–Mo porphyry centers, mostly emplaced in NNE to NE-oriented corridors. The hosted rocks consists of folded Triassic and Jurassic calcareous sedimentary units partially altered by a kilometric metasomatic envelope that contains skarn mineralization.The complex was mainly emplaced syntectonically along the Sierra Castillo Fault System, which is part of the margin-parallel Domeyko Fault System. These faults together with NE and NW striking transversal faults were active during the Eocene, playing a key role in the emplacement of magmatism and mineralization at the district.The main magmatic phases of the Exploradora Complex record different levels of alteration exposure, mineralization and geochronological ages suggest at least three discrete and continuous episodes of magmatism during ∼4 m.y. (1) An early composite of dioritic to monzodioritic intrusions (38-36 Ma), generally associated with coarse Ca (K) alteration and spatially close to Zn or Fe exoskarn mineralization. (2) An early to inter mineral hypabyssal rocks (36-35 Ma) composed of dacitic to rhyolitic porphyries and aplitic rocks, mostly affected by k-feldspar, propylitic, quartz and argillic alteration, locally with secondary biotite and Cu anomalies. Include quartz monzodiorite porphyries exposing Cu–Au mineralization associated with potassic alteration (biotite-magnetite plus albite) and related quartz-veinlets. (3) CODELCO's Exploradora Cu–Mo mineralization (35-34 Ma) associated with late dacitic and dioritic porphyries, HS-Au mineralization veinlets and a post-mineral diatreme.Polymetallic mineralization occurs at the western part of the district, hosted mainly in sedimentary and intrusive rocks and partially at major intrusion contacts. The Ciclón-Exploradora polymetallic deposit is a 5 km-long NS- and NNW-striking vein-breccia-fault, with mainly sinistral movements, it includes carbonate replacement deposits and dissolution breccia bodies nearby.The tectonic stress field orientation related to the vein-breccia-fault mineralization records subhorizontal NW-trending σ1, SW-trending σ3, and subvertical σ2. Polymetallic hypogene mineralization shows a consistent evolution from low sulfidation conditions to intermediate sulfidation assemblages, spatially related to an early skarn stage characterized by the presence of magnetite, pyrrhotite, Fe-rich sphalerite, developed in calcareous sedimentary rocks. Skarn zonation includes garnet-pyroxene-wollastonite-scapolite minerals. Epithermal polymetallic mineralization shows four main stages. The first and second stages consist of pervasive chlorite followed by chlorite-pyrite veinlets that may or may not contain quartz, and massive pyrite mineralization bodies generally forming euhedral crystals. The second phase ends with a Cu-dominant stage given by chalcopyrite-quartz (±chlorite - sericite – pyrite) and lower contents of Ag-bearing sulfosalts. The third stage is recognized as a polymetallic event characterized by multiple veinlets emplaced both in intrusive and sedimentary rocks where it also forms replacement ore bodies along lithological contacts. It consists of Cd-rich sphalerite, galena, Fe–Mn–Zn carbonates, and minor amounts of chalcopyrite, tennantite-tetrahedrite, and other Ag sulfosalt minerals. Gold is present as native and spectrum minerals with quartz. Main alteration minerals are quartz-kaolinite and minor amounts of sericite. The last stage consists of calcite ± arsenopyrite veinlets crosscutting the previous mineralization. This paragenetic evolution is similar to the one observed in several epithermal porphyry-related polymetallic “Cordilleran” deposits (e.g., Cerro de Pasco, Perú).Crosscutting relationship and exposure of epithermal mineralization, porphyry alteration and magmatism suggests that, in a short period (38–34 Ma), the whole district was exhumed probably several kilometers (3–6 km), related to a compressional to transpressional deformation regime.

Random forest rock type classification with integration of geochemical and photographic data

Systematic manual and algorithmic classification workflows to characterize rock types are increasingly applied in the mineral exploration and mining industry, leveraging large systematically collected datasets. The aim of these are robust and repeatable classifications to aid more traditional visual logging practices. This study uses random forest algorithms to examine the impacts of integrating distinct datasets with complementary characteristics; chemistry to enable compositional distinctions, and photography to enable textural distinctions. We use a random forest classifier to examine the accuracy metrics of models producing rock type classifications using these two data types independently and integrated together. Prediction accuracy, measured using 10-fold cross validation, was 87% for geochemical-only inputs, 85% for photographic-only inputs, and 90% for mixed inputs from both datasets. A mining and exploration project in the Late Miocene to early Pliocene porphyry belt in Chile is the site of this case study, where datasets were systematically acquired using in-field methods on historical drill-cores. Results indicate that classification of lithology is improved by integration of photography-based and composition-based feature inputs. We infer that the benefits of integration would increase in proportion with increasing compositional similarity between rock types. This approach might also be applied to similar geological problems, such as alteration or metallurgical classifications; and with somewhat distinct datatypes, such as geochemical interval data and photographic metric extraction from coincident intervals in core photos.

Trace Element Composition and Cathodoluminescence of Quartz in the Hongniu–Hongshan Skarn Deposit in Yunnan Province, Southwest China

The Hongniu–Hongshan Cu skarn deposit is located in the central part of the Zhongdian porphyry and skarn Cu belt in southwestern China. Various elements, including Al, Ti, Li, K, Na, Ca, Fe, and Ge, have been completed by using scanning electron microscopy–cathodoluminescence (SEM-CL) and laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) on quartz phenocrysts from the Hongniu–Hongshan porphyry and skarn Cu deposit. Three quartz generations were identified in the porphyritic granite based on the CL textures and trace element signatures. Samples of the first-generation quartz (Qtz1) contain dark gray luminescent cores assaying 22–85 ppm Ti, 58–129 ppm Al, 4–18 ppm Li, and 0.43–40 ppm Fe. The Ti-in quartz geothermometer indicates crystallization temperatures of 593–664°C for Qtz1. Samples of the second-generation quartz (Qtz2) are characterized by clear bright gray oscillatory overgrowths with medium Ti concentrations of 51–70 ppm with elevated and variable amounts of Al, Li, and Fe, and low K. The Ti-in quartz geothermometer indicates crystallization temperatures of 672–706°C. Samples of the third-generation quartz (Qtz3) contain narrow light gray rims assaying 56–93 ppm Ti, 80–101 ppm Al, 11–19 ppm Li, 1.42–17 ppm K, and 2–25 ppm Fe. The Qtz3 crystallised crystallized at higher temperatures of 706–799°C. Our study indicates that the quartz phenocryst in the Hongniu–Hongshan porphyry may have undergone two mixing episodes involving a second hotter magma. Before the first resorption, average Ti concentration in the quartz phenocryst cores was 24 ppm, and Ti of the bright band halo at the edge of the crystal core is 56 ppm; the maximum temperature difference is 109°C higher than that of the pre-resorption. Furthermore, the Ti concentration is 75 ppm at the edge of the quartz phenocryst before resorption. After resorption, the average Ti increased to 81 ppm at maximum temperature difference of 54°C higher than that of pre-resorption. Moreover, on the basis of quartz composition collected from 14 different deposits and our new dataset, we propose that covariations of Ge/Al ratio can be used to effectively discriminate magmatic quartz and hydrothermal quartz. Magmatic quartz has a Ge/Al ratio of <0.013, and the hydrothermal quartz has a ratio of >0.013.

Geological constraints on magmatic evolution in subduction zones and cumulative factors effective on the fertility of Cenozoic host porphyritic rocks associated with major porphyry copper deposits in the Lut Block and Kerman porphyry copper belt, Iran

Iranian porphyry copper deposits (PCDs), resulted from the evolution of Neo–Tethys Ocean during the Mesozoic and Cenozoic, dominantly distributed in the five main tectono-magmatic belts that meanwhile the Kerman Porphyry Copper Belt (KPCB) is the most famous and important belt in the south of Iran while the Lut Block is the oldest and modern known porphyry belt in eastern Iran. PCDs of the KPCB (+Najmabad; group 1) hosting moderate to giant world-class deposits belong to the Oligocene–Miocene. On the other hand, PCDs of the Lut Block (except Najmabad; group 2) formed during the Eocene–Oligocene, are mostly subeconomic to barren. Despite the similarities in tectonic setting, host rock composition, hydrothermal alteration zones, and mineralization type, there are significant differences in geochemical characteristics (depression in MREE/HREE pattern (group 1) vs. horizontal trend (group 2), Sm/Yb greater than 2.4 (group 1) vs. < 3 (group 2)), melting conditions (Eu/Eu* = 0.8–1.2 (group 1) vs. 0.49–0.96 (group 2), La/Yb greater than 20.1 (group 1) vs. < 21 (group 2) and Sr/Y greater than 40.8 (group 1) vs. < 58.1 (group 2)), source composition (Sr/Y, Dy/Yb greater than 1.5 (group 1) vs. < 1.8 (group 2) and La/Yb ratios)), and magma generation depth (Dy/Yb and La/Yb ratios). The review of different geochemical processes shows that alongside the agents such as dehydration, magma generation depth, source composition, Eu anomaly, and oxygen fugacity, the metal source is the most prominent factor in the formation of porphyry type mineralization.

Geological, Mineralogical-Petrographical and Fluid-Inclusion Characteristics of the Çatalçam (Soma-Manisa) Au-Pb-Zn-Cu Mineralization

The study area is located in the southeastern Biga Peninsula. As result of field, drilling and laboratorystudies, diorite porphyry intruded to Lower Miocene and older units and contained Au, Pb, Zn and Cu anomalies, has been determined. Intersected potassic, propylitic, phyllic and argillic alteration zones were developed in the pluton and host rock. Veins-veinlets developed in the pluton and host rock, contain native gold, silver, pyrite, chalcopyrite, sphalerite and galena. They are composed of undulated quartz in the deeper levels, and massive quartz, calcite/dolomite and barite in the middle and upper levels. According to the fluid inclusion data from sphalerite, quartz and barite, temperature of ore-bearing fluids are in three groups (argillic:150-220°C, phyllic:250-350°C, potassic:>400°C). Fluid inclusions, including solid phases such as hematite, chalcopyrite and salt as well as liquid and gas phases, indicate that Çatalçam Au-Cu mineralization is intrusion-related system. Fluid inclusion data display temperature and salinity of the ore-bearing fluids in the early stage (porphyry) are high, whereas relatively lower in the late stage (epithermal). In conclusion, Çatalçam mineralization was developed in two different phases as porphyry Au-Cu and epithermal Zn-Pb-Cu-Au, which is the first porphyry gold deposit related to Miocene magmatic-hydrothermal system in the Biga porphyry belt.

Recognition of a Middle–Late Jurassic arc-related porphyry copper belt along the southeast China coast: Geological characteristics and metallogenic implications

AbstractRecent exploration has led to definition of a Middle–Late Jurassic copper belt with an extent of ∼2000 km along the southeast China coast. The 171–153 Ma magmatic-hydrothermal copper systems consist of porphyry, skarn, and vein-style deposits. These systems developed along several northeast-trending transpressive fault zones formed at the margins of Jurassic volcanic basins, although the world-class 171 Ma Dexing porphyry copper system was controlled by a major reactivated Neoproterozoic suture zone in the South China block. The southeast China coastal porphyry belt is parallel to the northeast-trending, temporally overlapping, 165–150 Ma tin-tungsten province, which developed in the Nanling region in a back-arc transtensional setting several hundred kilometers inboard. A new geodynamic-metallogenic model linking the two parallel belts is proposed, which is similar to that characterizing the Cenozoic metallogenic evolution of the Central Andes.

Geochemistry and Geochronology of the Cenozoic Zhalaga Granitoids of the Yulong Alkali‐rich Porphyry Belt in Eastern Tibet (Xizang), SW China: Petrogenesis and Tectonic Implications

AbstractLarge‐scale Cenozoic magmatic rocks from the interplay between the Indian and Eurasian plate are exposed in the Yulong porphyry copper belt in the northern Jinshajiang–Ailaoshan domain. Alkali‐rich magmas along the Yulong porphyry copper belt can reveal the tectono‐magmatic processes in the Sanjiang region. In this study, we present new zircon U–Pb–Hf isotopes and whole rock geochemistry of Cenozoic granitoids from the Zhalaga area in the northern Yulong porphyry copper belt. The Zircon U–Pb dating results show that the Zhalaga granitic porphyry crystallized at ca. 42–38 Ma. These porphyry deposits are depleted in Nb, Ta, Sr, and Ti enriched in alkaline and rare earth elements (REEs), and exhibit high zircon saturation temperatures, that strongly indicate A‐type affinity. These data and the generally positive ∊Hf(t) values (2.0–4.5) suggest the magmas originated from a hybrid of partial melting of subduction‐modified lithospheric mantle, possibly triggered by upwelling of the asthenospheric mantle. Geochronological and geochemical data of the current and previous studies distinguish three magmatic phases during the Cenozoic in the Jinshajiang–Ailaoshan region: (1) ca. 62–48 Ma; (2) ca. 44–30 Ma; and (3) ca. 28–16 Ma. The strong collision between the Indian and Eurasian plates produced relatively fast convergence rates during the first episode (ca. 62–48 Ma), whereas the subsequent right‐lateral strike‐slip faulting in the Jinshajiang fault zone initiated at ca. 43 Ma is associated with the relatively low India–Eurasia convergence rates during ca. 44–30 Ma. These significantly impacted the nature and spatial distribution of the magmatism and the large‐scale metallogeny during the Cenozoic in the Sanjiang region. We suggest that the Zhalaga alkali‐rich magmas occurred in a transition period from involving soft to hard collisional settings. This remarkable example demonstrates that alkali‐rich magmas with A‐type affinity are also generated in an orogenic tectonic setting.

Carmacks Copper Cu-Au-Ag Deposit: Mineralization and Postore Migmatization of a Stikine Arc Porphyry Copper System in Yukon, Canada

Abstract Late Triassic to Early Jurassic porphyry Cu mineralization is common in British Columbia, yet there are few age-equivalent porphyry occurrences in Yukon. This study presents new data for the enigmatic Carmacks Copper Cu-Au-Ag deposit in south-central Yukon, Canada, which is hosted in amphibolite facies metamorphic inliers within the Early Jurassic Granite Mountain batholith. Sulfide mineralization occurs mainly as net-textured bornite and chalcopyrite in leucosome, and as chalcopyrite ± pyrite blebs and disseminations in amphibolite and quartz-plagioclase-biotite schist. Several studies suggest that the Carmacks Copper deposit and the nearby Minto deposit are related to porphyry belts in British Columbia, but constraining the timing of alteration, mineralization, and metamorphism has been difficult. This study establishes a geologic and high-precision geochronologic framework for sulfide mineralization and its host rocks at the Carmacks Copper deposit, using Re-Os dating of molybdenite, and chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) analysis of both whole zircon grains and laser-cut fragments of complexly zoned zircon grains. Our data indicate that the igneous protolith of the metamorphic inliers formed at 217.53 ± 0.16 Ma, followed by peak metamorphism at amphibolite facies at 205.82 ± 0.23 Ma, which occurred prior to Granite Mountain batholith emplacement but subsequent to Cu-Au-Ag mineralization of the protolith. An early phase of the Granite Mountain batholith was emplaced at 199.84 ± 0.14 Ma, followed by the main phase at 195 to 194 Ma. A second generation of metamorphic zircon in migmatite at 196.01 ± 0.12 Ma represents a partial melting event associated with Granite Mountain batholith emplacement. Two petrographically distinct populations of molybdenite are present in unstrained, net-textured copper sulfides. A sample dominated by strained molybdenite yielded an 187Re/187Os age of 212.5 ± 1.0 Ma, which represents the minimum mineralization age of the protolith. A sample dominated by euhedral grains yielded an 187Re/187Os age of 198.5 ± 0.9 Ma, constraining the maximum age of sulfide remobilization. These results indicate that primary mineralization is &amp;gt;212.5 Ma and potentially coeval with the ~217.5 Ma generation of Late Triassic magmatism. The mineralized protolith, best interpreted as the potassic alteration zone of a Late Triassic (~217–213 Ma) porphyry Cu-Au system, was metamorphosed to amphibolite facies at ~206 Ma, and subsequently migmatized during 200 to 194 Ma intrusion of the Granite Mountain batholith. The chalcopyrite-bornite-dominant assemblage in neosome precipitated from an immiscible Cu-Fe-S melt phase that partly consumed xenocrystic molybdenite and reprecipitated new molybdenite grains. The Carmacks Copper deposit and the related Minto deposit are remnants of a Late Triassic porphyry belt, where a significant fraction of the original metal endowment was likely lost through digestion of mineralized rocks by midcrustal magma in the Early Jurassic. These Yukon deposits are rare examples of metamorphosed porphyry Cu systems in the global geologic record, where rapid tectonic burial following mineralization was the principal factor in their preservation.

High-sulfidation veins in the Jiama porphyry system, South Tibet

The giant Jiama polymetallic ore deposit is a porphyry–skarn system in the eastern Gangdese porphyry belt of the Tibetan Plateau. Steeply dipping high-grade massive sulfide veins are classified as lode-type high-sulfidation (HS) mineralization comprising mainly Cu-sulfosalts in Au-poor and Au-rich veins. Au-poor veins contain an As-rich pyrite–enargite–tennantite assemblage, whereas Au-rich veins contain an Sb-rich enargite–luzonite–tetrahedrite–chalcostibite–watanabeite assemblage. The coexistence of pyrite, dendritic muscovite, and euhedral quartz in the Cu-sulfosalts indicates slightly acidic or near-neutral formation conditions. Most Au- and Ag-bearing minerals are inclusions of tellurides (hessite, sylvanite, and petzite) in tennantite–tetrahedrite, and watanabeite. Au and Ag concentrations in tennantite–tetrahedrite, watanabeite, and chalcostibite are much higher than in enargite and luzonite, confirming that they were controlled by intermediate-sulfidation state Cu–As–Sb–S solid solutions, with Au tending to be enriched in Sb-rich minerals compared with As-rich solid solutions. The HS veins overlying the known porphyry intrusion and cutting skarn orebodies in the Jiama deposit constitute a porphyry–skarn–high sulfidation system. The occurrence of HS veins suggests that channels in paleo-fumaroles and the mineralization that resulted may be ascribed to expansion of magmatic vapor. HS veins close to the porphyry intrusion exposed at the surface indicate that shallow epithermal disseminated mineralization was likely removed by rapid regional uplift and erosion of the Gangdese porphyry belt.

Episodic porphyry Cu (-Mo-Au) formation and associated magmatic evolution in Turkish Tethyan collage

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.

Cargo Porphyry Cu-Au Deposit – Where is the High Grade Core?

The Cargo Copper-Gold Porphyry deposit lies within the world class porphyry belt of the Ordovician Macquarie volcanic arc. It is one of several porphyry complexes in the Lachlan Orogen including Cadia Valley (42.8 MOz Au), Northparkes, Cowal and Copper Hill.The Cargo Porphyry Intrusive Complex is a calc-alkaline suite of late Ordovician age (467 Ma) intrusives comprising quartz monzodiorite and diorite intruded by coeval andesitic and trachy-andesitic volcanics. The most prominent NW trending structural zone is characterised by areas of strong silicification, pyritisation and tectonic brecciation together with stockwork and sheeted quartz veining. It is up to 300 m wide bounded on the southern side by a major 60o SW dipping normal fault and on the Northern side by 75o SW dipping shear zones.Mineralization and alteration is zoned from a western core of fracture controlled, potassic altered porphyry (Cu-Mo-Au) to a peripheral zone of phyllic altered gold rich quartz-sulphide veining up to 200 m wide, surrounded by an outer propylitic zinc rich halo.The peripheral zone of Cargo contains gold rich sheeted quartz veins which hosted 14 small gold workings in the late 1800’s. Two lode systems, Dalcoath and Spur, have JORC inferred resource of 4 Mt @ 1.19g/t gold for 154,000 Oz Au.A classically zoned porphyry Cargo’s geochemical footprint is comparable in size to the famous Bingham Canyon and the Bougainville Panguna deposits despite the fact that Cargo’s porphyry deposits’ western half has been faulted away.

Petrogenesis of Eocene mineralized porphyry in Bijiashan, eastern margin of Tibet Plateau: Constraints from geochronology, geochemistry and Hf isotopes

The Ailaoshan-Jinshajiang porphyry belt located in the Sanjiang area of eastern Tibetan Plateau is one of the major polymetallic metallogenic belts in China. However, the nature and genesis of magmatic intrusions associated with the porphyry copper mineralization in this belt remain contentious. Here we focus on the Bijiashan Deposit, one of the large-scale porphyry copper deposits in this area, to gain insights on the host rock, petrogenetic mechanism, tectonic setting based on geochemistry, zircon UPb geochronology and LuHf isotopic compositions. Zircon UPb dating of the ore-hosting porphyry yielded an age of 35.6 ± 0.2 Ma. The major elements of the porphyry show wide range in SiO2 (58.33–70%), high K2O (2.83–8.85%) and Na2O + K2O (mostly>8%), and moderate range in A/CNK (0.56–1.17). Our data suggest that the porphyry belongs to high-Kcalc-alkaline-alkaline and metaluminous-peraluminous series. The trace elements are characterized by enrichment in K, Rb, Ba, La and Nd, but depletion in Ta, Nb, P and Ti, and enrichment in LREE but depletion in HREE with LREE/HREE of 9.78–20.10. The main intrusion associated with mineralization corresponds to alkali-richA-type granitoid, with high TFeO (0.49–3.4%), low Na2O/K2O (0.23–1.62), and high 1000*Ga/Al (2.17–2.64 except 1.57), and right-declinedREE patterns. However, some of the geochemical features also are consitent with the typical characteristics of C-adakite rocks, including high contents of Al2O3 (13.49–16.12%) and Sr (>400 ppm), lower MgO (mostly <3%), depleted Y (<18 ppm) and Yb (<1.9 ppm), and slightly negative Eu anomalies (δEu = 0.83). The zircon εHf (t) values show a wide range from negative to positive (−13.65 to 2.60) with TDMC varying from 947 Ma to 1982 Ma, suggesting that the Eocene porphyries were derived from the partial melting of the lower crustal materials, together with the addition of mantle source materials. Combined with the regional geological evolution, our study suggests that the ore-hosting porphyry formed under a setting of post-collisional crustal extension. Following the collision between the Indian and Eurasian plates, the stress relaxation resulted in extension and magma emplacement along major faults and the copper polymetallic mineralization formed along the Chenghai-Binchuan Fault.

Melt recharge, f O2-T conditions, and metal fertility of felsic magmas: zircon trace element chemistry of Cu-Au porphyries in the Sanjiang orogenic belt, southwest China

The magmatic hydrothermal Pulang Cu deposit (Triassic) and the Beiya Au-Cu deposits (Eocene) are located in the Sanjiang copper porphyry belt, southwest China. Zircon chemistry was used to constrain the magmatic evolution and oxidation state of the porphyries. The results show that porphyries of the Beiya district formed from an early oxidized melt and a later relatively reduced and more evolved magma, whereas Pulang experienced a normal Cu porphyry evolutionary trend. The Pulang porphyries crystallized from more oxidized magma (∆FMQ + 2.9–4.6, average = 4.0 ± 1.0, n = 3) with an average temperature of 709 ± 6 °C compared to the Beiya porphyries (∆FMQ + 0.6–3.5, average = 1.9 ± 1.3, n = 5) with a mean magmatic temperature of 780 ± 22 °C. These data, combined with data from other Cu- and Au-rich porphyries in the Sanjiang belt (i.e., Machangjing Cu, Yao’an Au), are consistent with previous experimental work showing that elevated Cu and Au solubilities in magma require oxidizing conditions. A compilation of existing geochemical data for magmatic zircons from fertile and barren porphyry systems worldwide establishes an optimal diagnostic interval on CeIV/CeIII-TTi-in-zircon and (Eu/Eu*)N plots for generating magmatic hydrothermal Cu-Au deposits.

Metallogeny, structural evolution, post-mineral cover distribution and exploration in concealed areas of the northern Chilean Andes

Mineral exploration of prospective areas concealed by extensive post-mineralization cover is growing, being very complex and expensive. The projection of rich and giant Paleocene to early Oligocene porphyry-Cu-Mo belts in northernmost Chilean Andes (17.5–19.5°S) has major exploration potential, but only a few minor deposits have been reported to date, due to the fact that the area is largely covered by post-mineral strata. We integrate the Cenozoic stratigraphic, structural and metallogenic evolution of this sector, in order to identify the most promising regions related to lesser post-mineral cover and the projection of different metallogenic belts. The Paleocene to early Eocene metallogenic belt extends along the Precordillera, with ca. 30km wide, and includes porphyry-Cu prospects and small Cu (±Mo-Au-Ag) vein and breccia-pipe deposits. Geochronological data indicate an age of 55.5Ma for an intrusion related to one deposit and ages from 69.5 to 54.5Ma for hydrothermal alteration in one porphyry-Cu prospect and largest known Cu deposits. The middle Eocene to early Oligocene porphyry belt, in the Western Cordillera farther east, is associated with 46–44Ma intrusions. It is estimated to be 40-km wide, but is largely concealed by thick post-mineral cover. The youngest Miocene to early Pliocene metallogenic belt, also in the Western Cordillera, is well-exposed and includes Au-Ag epithermal and polymetallic veins and manto-type deposits.The Oligocene-Holocene cover consists of a succession of continental sedimentary and volcanic rocks that overall increase in thickness from 0 to 5000m, from west to east. These strata are subhorizontal in the west and folded-faulted towards the east. Miocene gentle anticlines and monocline flexures extend along strike for 30–60km in the Precordillera and were generated by propagation of high-angle east-dipping blind reverse faults with at least 300–900m of Oligocene bedrock offset. The thickness of cover exceeds 2000m in the eastern Central Depression, whereas it is generally less than 1000m in the Precordillera along the Paleocene to early Eocene porphyry-Cu belt and it can reach locally up to 5000m in the Western Cordillera, above the middle Eocene to early Oligocene belt.In the studied Andean segment, the Miocene to early Pliocene metallogenic belt is superimposed on the Paleocene to Oligocene belts in a 40–50km wide zone. This overlap may be explained by an accentuated migration of the magmatic front, from east to west, since ca. 25Ma, as a consequence of subduction slab steepening after a period of magmatic lull and flat subduction from ca. 30–35 to 25Ma. The identified areas of lesser cover thickness are prone to exploration for concealed deposits, especially along the projection of major porphyry-Cu-Mo belts.

Review of Mesozoic multiple magmatism and porphyry Cu–Mo (W) mineralization in the Yidun Arc, eastern Tibet Plateau

The Yidun Arc was formed in response to the westward subduction of Garze–Litang Ocean (a branch of Paleotethys) in the Late Triassic, where abundant porphyry Cu–Mo deposits (221–213Ma) developed along the regional NW–SE sinistral faults and emplaced in the southern portion of the arc. The ore-related porphyries are mostly metaluminous or slightly peraluminous, belonging to shoshonitic high-potassium calc-alkaline I-type granites, with εHf(t) values of −6.64 to +4.12. The ore-bearing magmas were probably derived from the partial melting of subduction-metasomatic-enriched mantle, with the contamination of underplated mafic materials. The Late Cretaceous (88–80Ma) highly fractionated I-type granite belt and related porphyry Cu–Mo deposits and magmatic-hydrothermal Cu–Mo–W deposits occur along approximately N–S-trending faults in the Yidun Arc. This belt extended across the Yidun Arc and Garze–Litang suture zone to the north and across the Yangtze Craton to the south, intruding the Late Triassic porphyry belt. The ore-related porphyries are characterized by high silica and high total alkalis, with enrichment in large ion lithophile elements (LILEs; Rb, U and K) and depletion in high field strength elements (HFSE; Nb, Ta, P and Ti) and Ba. They have lower εHf(t) values varying from −9.55 to −2.75, and significant negative Eu anomalies, indicating that the ore-bearing porphyritic magmas originated from ancient middle-upper crust. Two-stage magmatism and mineralization were superimposed in the Xiangcheng-Shangri-La district. Some ore deposits comprise two episodes of magmatism and associated mineralization such as both 207±3.0Ma granodiorite and 82.1±1.2Ma monzogranite intruded in the Xiuwacu deposit, causing Cu–Mo–W polymetallic mineralization. To date, 11 Late Triassic porphyry Cu deposits (e.g. the Pulang giant deposit with 5.1 Mt Cu), and five Late Cretaceous porphyry Cu–Mo (W) deposits (e.g. Tongchanggou Mo deposit with 0.59 Mt Mo) have been evaluated in the Xiangcheng-Shangri-La district. The continuity and inheritance of multiphase magmatism and the new understanding of superimposed mineralization will help to guide future exploration.

High Sr/Y Magma Petrogenesis and the Link to Porphyry Mineralization as Revealed by Garnet-Bearing I-Type Granodiorite Porphyries of the Middle Cauca Au-Cu Belt, Colombia

Porphyry-style Cu (Au, Mo) mineralization is widely associated with igneous suites with Sr/Y > 40 and low heavy rare earth element (HREE) content. This geochemical signature is commonly attributed to garnet or amphibole fractionation in the lower crust where mantle derived melts evolve into intermediate composition arc suites. However, the presence of a residuum related to mineralized porphyry systems where amphibole and garnet are stable is generally inferred from geochemistry and has nowhere been documented directly. We here report on two occurrences of late Miocene garnet-bearing granodiorite porphyry at the Tesorito Au-Cu prospect in the Quinchia district and El Poma Au-Cu prospect in the Middle Cauca Au-Cu porphyry belt in Colombia. These rocks provide proof that garnet was stable in the lower crust at the time of porphyry mineralization. At both studied sites, garnet-bearing I-type granodiorite porphyries were intruded by intramineralization garnet-free plagioclase phyric granodiorite porphyries that were cut by quartz and K-feldspar veins and affected by biotite alteration. Garnet-bearing porphyries predate intramineralization porphyries by 0.4 to 2 m.y. Garnet occurs as unzoned grains, commonly included in large plagioclase phenocrysts, that in some cases also contain inclusions of igneous epidote; the latter indicating pressures of >1 GPa for early crystallized phases. Large plagioclase phenocrysts exhibit two growth stages separated by a resorption boundary. High-Al amphibole phenocrysts as well as titanite and magnetite formed after the first stage but prior to the second stage of plagioclase growth at pressures of ca. 0.9 GPa. Whole-rock geochemical compositions of garnet-bearing porphyries are consistent with only limited garnet fractionation whereas some of the intramineralization porphyries have Y 40, which is, together with other trace element indicators, taken as evidence for significant garnet fraction at depth during porphyry mineralization. HREE content of zircon in garnet-bearing porphyries are higher than that of intramineralization porphyries, which supports the interpretation that garnet fractionation in the lower crust was significant during the formation of the intramineralization porphyries. The phase relationships and geochemical data reflect a geodynamic change from an environment that permitted rapid ascent of oxidized garnet-bearing porphyries prior to Au-Cu mineralization to a regime that favored melt evolution in the lower crust where garnet was a residual phase and at the same time allowed the formation of large mid- to upper-crustal magma chambers. The latter are widely inferred to be essential for porphyry mineralization to occur.

Dismembered Porphyry Systems near Wickenburg, Arizona: District-Scale Reconstruction with an Arc-Scale Context

This study combines results from reconnaissance-scale mapping of hydrothermal alteration, rock types, and structures to provide a district-scale cross section and associated palinspastic reconstruction of an area with two previously undescribed Laramide (~70 Ma) porphyry systems at Sheep Mountain and Copper Basin (Crown King). Extension at the district scale is placed in an arc-scale context using an original compilation of strike and dip measurements on Tertiary rocks to reconstruct the Laramide porphyry belt prior to extension. The study area contains five sequential, partially superimposed sets of normal faults that are nearly planar where exposed. Dips of all normal faults initiated at 60° to 70° and rotated during slip to angles as gentle as 20°. A palinspastic reconstruction reveals that two, spatially distinct hydrothermal systems overlie different cupolas of a Late Cretaceous pluton. Hydrothermal alteration is zoned from greisen to potassic to transitional greisen-potassic assemblages from deep to shallow structural levels. The reconstruction is used to identify two covered exploration targets. The prospects may be porphyry molybdenum systems of the quartz monzonitic-granitic porphyry Mo-Cu subclass, joining others in an arc that is best known for porphyry copper deposits. The Laramide porphyry belt prior to extension displays a variably well-defined axis, ~100 km wide, with gaps and clusters of deposits along its 700-km strike length. The majority of deposits lie along the axis, but others lie in fore- or rear-arc positions. The interpreted preextensional geometry of the Laramide porphyry belt resembles other porphyry belts and the distribution of active volcanoes at convergent margins.

Evolution of the Hazelton arc near Terrace, British Columbia: stratigraphic, geochronological, and geochemical constraints on a Late Triassic – Early Jurassic arc and Cu–Au porphyry belt

Understanding the development of island arcs that accreted to the North American craton is critical to deciphering the complex geological history of the Canadian Cordillera. In the case of the Hazelton arc (part of the Stikine terrane, or Stikinia) in northwestern British Columbia, understanding arc evolution also bears on the formation of spatially associated porphyry Cu–Au, epithermal, and volcanogenic massive sulfide deposits. The Hazelton Group is a regionally extensive, long-lived, and exceptionally thick Upper Triassic to Middle Jurassic volcano-sedimentary succession considered to record a successor arc that was built upon the Paleozoic and Triassic Stikine and Stuhini arcs. In central Stikinia, near Terrace, British Columbia, the lower Hazelton Group (Telkwa Formation) comprises three volcanic-intrusive complexes (Mt. Henderson, Mt. O’Brien, and Kitselas) that, at their thickest, constitute almost 16 km of volcanic stratigraphy. Basal Telkwa Formation conglomerates and volcanic rocks were deposited unconformably on Triassic and Paleozoic arc-related basement. New U–Pb zircon ages indicate that volcanism initiated by ca. 204 Ma (latest Triassic). Detrital zircon populations from the basal conglomerate contain abundant 205–233 Ma zircons, derived from regional unroofing of older Triassic intrusions. Eleven kilometres higher in the section, ca. 194 Ma, rhyolites show that arc construction continued for &gt;10 million years. Strata of the Nilkitkwa Formation (upper Hazelton Group) with a U–Pb zircon age of 178.90 ± 0.28 Ma represent waning island-arc volcanism. Telkwa Formation volcanic rocks have bimodal silica concentrations ranging from 48.1 to 62.8 wt.% and 72.3 to 79.0 wt.% and display characteristics of subduction-related magmatism (i.e., calc-alkaline differentiation with low Nb and Ti and high Th concentrations). Mafic to intermediate rocks form a differentiated suite that ranges from high-Al basalt to medium- to high-K andesite. They were derived from hydrous melting of isotopically juvenile spinel lherzolite in the mantle wedge and from subsequent fractional crystallization. Compared to basalts and andesites (εNd = +5 to +5.5), rhyolites have higher positive εNd values (+5.9 to +6.0) and overlapping incompatible element concentrations, indicating that they are not part of the same differentiation suite. Rather, the rhyolites formed from anatexis of arc crust, probably caused by magmatic underplating of the crust. This study documents a temporal and spatial co-occurrence of Hazelton Group volcanic rocks with a belt of economic Cu–Au porphyry deposits (ca. 205–195 Ma) throughout northwestern Stikinia. The coeval relationship is attributed to crustal underplating and intra-arc extension associated with slab rollback during renewed or reconfigured subduction beneath Stikinia, following the demise of the Stuhini arc in the Late Norian.

Timing and duration of hydrothermal activity at the Los Bronces porphyry cluster: an update

New geochronological data from the Los Bronces cluster of the Rio Blanco-Los Bronces mega-porphyry Cu-Mo district establish a wide range of magmatism, hydrothermal alteration, and mineralization ages, both in terms of areal extent and time. The northern El Plomo and southernmost Los Piches exploration areas contain the oldest barren porphyritic intrusions with U-Pb ages of 10.8 ± 0.1 Ma and 13.4 ± 0.1 Ma, respectively. A hypabyssal barren intrusion adjacent northwesterly to the main pit area yields a slightly younger age of 10.2 ± 0.3 Ma (San Manuel sector, U-Pb), whereas in the Los Bronces (LB) open-pit area, the present day mineral extraction zone, porphyries range from 8.49 to 6.02 Ma (U-Pb). Hydrothermal biotite and sericite ages are up to 0.5 Ma younger but consistent with the cooling of the corresponding intrusion events of each area. Two quartz-molybdenite B-type veins from the LB open pit have Re-Os molybdenite ages of 5.65 ± 0.03 Ma and 5.35 ± 0.03 Ma consistent with published data for the contiguous Rio Blanco cluster. The San Manuel exploration area within the Los Bronces cluster, located about 1.5–2 km southeast of the open-pit extraction zone, shows both the oldest hydrothermal biotite (7.70 ± 0.07 Ma; 40Ar/39Ar) and breccia cement molybdenite ages (8.36 ± 0.06 Ma; Re-Os) registered in the entire Rio Blanco-Los Bronces district. These are also older than those reported from the El Teniente porphyry Cu(-Mo) deposit, suggesting that mineralization in the late Miocene to early Pliocene porphyry belt of Central Chile commenced 2 Ma before the previously accepted age of 6.3 Ma.

Punctuated Magmatism Associated with Porphyry Cu-Mo Formation in the Paleocene to Eocene of Southern Peru

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.