Porphyry-type Mineralization Research Articles

The formation of shoshonitic magma and its relationship to porphyry-type mineralisation: the Maronia pluton in NE Greece

The Oligocene shoshonitic Maronia pluton in NE Greece is part of an age-progressive belt of calc-alkaline intrusions and associated with a porphyry Cu-Mo±Re±Au mineralisation. We present new data on mineral and whole rock compositions as well as Sr, Nd and Pb isotopes of the monzodioritic to granitic rocks from Maronia, including the mineralised microgranite, which crosscuts the main intrusion. The age progression of the plutons in NE Greece follows the southward-directed trench retreat implying that the magmas formed during subduction of continental lithosphere after the closure of the Pindos ocean. The shoshonitic magmas of Maronia were generated by hydrous melting of a phlogopite-bearing mantle that was enriched by 3-5% of slab-derived sediment melts. A lower degree of melting controls the higher K, LILE and incompatible element contents of the shoshonitic magmas in comparison to the neighbouring calc-alkaline magmas. The mafic shoshonitic rocks in NE Greece contain much higher P2O5 contents than the associated calc-alkaline magmas, which probably reflects subducted phosphate-rich sediments in their source. Constant Sr- and Nd-isotopes with increasing SiO2 contents imply minimal crustal assimilation and that felsic magmas including the mineralised porphyritic granite were generated by fractional crystallisation of mafic magmas. Amphibole and apatite analyses provide evidence for the intrusion of S-poor, Cl-rich magmas at 5 to 6 km depths, followed by rapid uplift and exsolution of magmatic fluids. Late granitic dikes at Maronia indicate that volatiles, sulphur and metals became enriched during the late stages of the magma evolution.

Fluid Evolution of the Čukaru Peki Cu-Au Porphyry System (East Serbia) inferred from a fluid inclusion study

Čukaru Peki is a recently discovered copper-gold deposit in the Bor metallogenic zone in east Serbia. Three types of mineralization can be distinguished in this ore deposit: porphyry, high-sulphidation, and transitional epithermal type. This research was focused on fluid inclusion analysis of genetically different veins from the porphyry and the transitional zones of Čukaru Peki with an aim of better understanding the fluid evolution and mineralization processes in this system. Seven types of veins were identified in the porphyry zone of Čukaru Peki and four of these veins contained transparent minerals which were suitable for fluid inclusion analysis. Eight types of inclusion assemblages were distinguished in these veins: type 1 – primary inclusions with homogenization temperatures above 550°C and high salinity, type 2a- scattered polyphase inclusions two salt crystals, type 2b-polyphase inclusions with two salt crystals in crystal growth zones, type 3- brine inclusions with one salt crystal in crystal growth zones, type 4- vapour-rich inclusions, type 5- primary inclusions in anhydrite, and types 6 and 7- secondary low-temperature inclusions This research suggests that saline fluids (30-40% wt.% NaCl eq.) were the most important ones for the formation of porphyry-type mineralization and that the mineralization was formed at temperatures between 350 and 450°C and pressures between 100 and 500 bars. The epithermal stage was characterized by cooler low-salinity fluids with temperatures between 150-350°C, and salinity between 0 and 7 wt.% NaCl eq.

Multiple rejuvenation episodes of a silicic magma reservoir at the origin of the large diatreme-dome complex and porphyry-type mineralization events at Cerro de Pasco (Peru)

The Cerro de Pasco district in central Peru hosts one of the world largest porphyry-related epithermal polymetallic deposits. The district is centered onto a large diatreme-dome complex crosscut by numerous dacite to rhyodacite bodies showing domal structures and quartz-monzonite dykes. Three temporally distinct high-temperature porphyry-type mineralization events have been recognized (PM1, PM2, and PM3). Dating of the latter by molybdenite Re-Os and by zircon U-Pb (LA-ICP-MS and CA-ID-TIMS) geochronology complements the already available dataset of zircon U-Pb ages of the subvolcanic and volcanic rocks mostly dacitic in composition occurring in the district and shows the existence of successive short-lived episodes (<100 kyr) of shallow magmatic activity and porphyry-type mineralization. The new geochronology data indicate that the magmatic system was active during more than 400 kyr, spanning from 15.59 ± 0.12 Ma to 15.16 ± 0.04 Ma, punctuated by three porphyry-type mineralization events that are precursors (maximum gap of 0.9 Myr) of the last stage of epithermal polymetallic mineralization at Cerro de Pasco. Detailed petrographic and geochemical (whole rock and minerals) studies have been performed and silicate melt inclusions hosted in quartz phenocrysts from the subvolcanic and volcanic rocks emplaced between and after the different porphyry-type mineralization events have been analyzed by LA-ICP-MS. Our results suggest that prior to their emplacement at shallow level, magmas were stored at depth with a high degree of crystallinity (>50%) at pressures between 0.9 and 3.4 kbar and at temperatures between ~680 °C and ~725 °C. At such conditions, magma is beyond the point of rheological lock-up and is not eruptible. The emplacement of the mostly dacitic subvolcanic and volcanic rocks has required a series of rejuvenation events of the upper crustal high-crystallinity silicic magma reservoir. Field relationships and geochronology indicate that emplacement of the subvolcanic and volcanic rocks is preceded each time by high-temperature (>600 °C) quartz-pyrite-magnetite ± chalcopyrite and quartz-molybdenite veining forming the three recognized porphyry-type mineralization events. Hydrothermal quartz of these veins host silicate melt inclusions, a rare feature in hydrothermal veins. Their composition determined by LA-ICP-MS analysis indicates that the mineralizing fluids, potentially sourced from intermediate magma recharges, have circulated in a magma reservoir in which the residual interstitial melt was more evolved than the melt trapped as inclusions in the magmatic quartz. The combined geochemical and geochronological data obtained show that several episodes of rejuvenation of a highly crystallized upper-crustal silicic magma reservoir, probably triggered by intermediate magma recharges and by circulation of CO2- and S-rich fluids exsolved from them, are at the origin of the large diatreme-dome complex and porphyry-type mineralization events at Cerro de Pasco.

Lithogeochemistry of hydrothermally-altered host rocks by multiple mineralizations in the Mankayan Mineral District, Philippines

The overprinting episodes of porphyry-type and epithermal-type mineralization in the Mankayan District, northern Luzon, Philippines allow an investigation on variation of geochemical signatures with different alteration assemblages. Due to the multiple hydrothermal activities in Mankayan, some older porphyry-type deposits have been overprinted by acid-sulfate alteration that is commonly associated with high-sulfidation epithermal mineralization. In this study, we analyzed metavolcanic basement rocks and dioritic rocks that host porphyry-type mineralization in the Far Southeast deposit, Honeycomb prospect and Christine prospect, which all have near-neutral pH alteration assemblage of illite/muscovite + chlorite ± quartz. We compared their geochemical data with those of the Fatima porphyry deposit, which was overprinted by quartz + alunite ± kaolinite/dickite alteration. Furthermore, we also compared the geochemical data of the metavolcanic and dioritic rocks in the Carmen and Florence prospects hosting quartz-pyrite-gold and enargite veins which overprinted earlier porphyry-type mineralization. N-MORB-normalized multi-element diagrams show that the host rocks preserve negative anomalies of high field strength elements (HFSEs) that are typical of magmas generated in a supra-subduction zone setting. The non-mineralized metavolcanic and dioritic rocks show variable signature of the large ion lithophiles (LILEs), while the altered metavolcanic and dioritic rocks show a more consistent signature. Negative anomaly of Rb is associated with acid-sulfate alteration, while positive anomaly of Rb was observed in the dioritic rocks that have been altered by near-neutral pH fluids. Furthermore, acid-sulfate alteration significantly added LREEs and depleted HREEs compared to the near-neutral pH alteration.Mass changes in altered rocks were determined using the isocon technique. Mass changes are generally more pronounced in the acid-sulfate altered rocks compared to the near-neutral pH altered rocks. The metavolcanic rocks altered to quartz + alunite in Carmen and Florence significantly gained SiO2, Al2O3 and S, and lost Na2O, CaO, MgO and Fe2O3. The dioritic and metavolcanic rocks altered to chlorite + illite in the Far Southeast, Honeycomb, Christine and Fatima porphyry deposits lost SiO2 and Al2O3, while the concentrations of other elements remain relatively unchanged.The pH-dependence of the geochemical behavior of Rb in hydrothermal conditions was utilized to construct new molar element ratios that could differentiate the rocks that underwent K-metasomatism either under near-neutral pH or acidic conditions. The recognition of this behavior could be useful in a routine lithogeochemical analysis that is being used in exploration.

Mineralized Granitic Porphyry of the Yangla Copper Deposit, Western Yunnan, China: Geochemistry of Fluid Inclusions and H-O, S, and Pb Isotopes

The Yangla copper deposit (YCD) is located in the central part of the Jinshajiang tectonic belt (Jinshajiang metallogenic belt) and is one of the most important copper deposits which has the large-scale copper reserves of the northwestern Yunnan, China. The ore bodies are strictly controlled by the stratum, pluton, and structure, which are layered, lens, and vein-like within the contact or fracture zone of the pluton and surrounding rock. At Yangla, two styles of mineralization occur at the brecciated contact zone between the pluton (granodiorite and granitic porphyry) and carbonaceous wall rock and include strata bound/lens-shaped replacement of carbonate rocks (skarn style) and porphyry-style sulfide-quart-calcite veins. But, the granitic porphyry mineralization have received less attention; the isotope and fluid inclusion studies are relatively scarce for limited porphyry ore bodies that have been discovered at the YCD. Quartz-hosted fluid inclusions from the recently discovered granitic porphyry have homogenization temperature averaging around 180±20°C and 300±20°C with salinities ranging from 4 to 22 wt.% NaCleq, pointing toward the contribution of medium temperature-medium salinity and low temperature-low salinity fluids during the metallogenesis. These fluid inclusions have δ18OH2O values ranging between -1.91‰ and -1.02‰ and δD values ranging between -143.10‰ and -110‰, suggesting that the ore-forming fluid was a mix of magmatic and meteoric water. Ore-related pyrite/chalcopyrite have δ34SV-CDT values ranging from -1.0‰ to 1.0‰ and whole rocks have δ34SΣS = 0.34, suggesting that sulfur mainly derived from magmatic rocks of the Yangla mining area. The sulfides 208Pb/204Pb ranged from 38.8208-38.9969, 207Pb/204Pb from 15.7079-15.7357, and 206Pb/204Pb from 18.5363-18.7045, indicating that the lead mainly originated from the upper crust. It is demonstrated that the evolution of ore-forming fluid is continuous from the skarn ore body (SOB) stage to the porphyritic ore body stage and belong to the products of the same ore-forming fluid system, and the unisothermal mixing and cooling actions were maybe the main mechanism at the metallic minerals precipitation in mineralized granitic porphyry (MGP). A model is proposed according to the early stage, a magmatic fluid reacted and replaced with the surrounding carbonate rocks and then formed skarn-type ore bodies. The magmatic-hydrothermal fluid subsequently deposited porphyry-type quartz-calcite veins, veinlets, and stockwork mineralization.

The Quebrada del Diablo Lower West Au deposit (Gualcamayo mining district, Argentina): A Carlin-type mineralization?

The Gualcamayo Mining District (GMD), located in the eastern margin of the Argentini an Precordillera includes three Au deposits: Amelia-Ines, Magdalena, Quebrada del Diablo Main, and QDD Lower West. The district has reserves of 491,000 oz. and resources of 2.3 million oz of Au.The metallogenetic analysis of these Au deposits based on previous work and new micro-geochemistry (LA- ICP- MS), isotopic (C-O-S-Pb) and fluid inclusions studies revealed that they are genetically linked and share many characteristics with Carlin-type deposits, including the lithology of host rocks, structural control, geochemical signatures, ore paragenesis, and dissolution and decarbonization processes. However, they also display some noticeable differences. The sulfur isotopic composition supports a genetic link between these gold deposits and the precursor magmatism of the porphyry-type mineralization of the area. Besides, the fluids responsible for the Au mineralization proved to be neutral to slightly alkaline and Au-saturated. The link with the magmatism along with the character of the mineralizing fluids and the presence of significant base metal sulfides allowed classifying the GMD deposits as “distal disseminated gold deposits” that occur on the distal edges of magmatic-hydrothermal systems.

Mineral Mapping and Vein Detection in Hyperspectral Drill-Core Scans: Application to Porphyry-Type Mineralization

The rapid mapping and characterization of specific porphyry vein types in geological samples represent a challenge for the mineral exploration and mining industry. In this paper, a methodology to integrate mineralogical and structural data extracted from hyperspectral drill-core scans is proposed. The workflow allows for the identification of vein types based on minerals having significant absorption features in the short-wave infrared. The method not only targets alteration halos of known compositions but also allows for the identification of any vein-like structure. The results consist of vein distribution maps, quantified vein abundances, and their azimuths. Three drill-cores from the Bolcana porphyry system hosting veins of variable density, composition, orientation, and thickness are analysed for this purpose. The results are validated using high-resolution scanning electron microscopy-based mineral mapping techniques. We demonstrate that the use of hyperspectral scanning allows for faster, non-invasive and more efficient drill-core mapping, providing a useful tool for complementing core-logging performed by on-site geologists.

Sulfur isotope geochemistry of the Chodarchay Cu-Au deposit, Tarom, NW Iran

The Chodarchay porphyry–high-sulfidation epithermal Cu-Au deposit in the Tarom subzone of the western Alborz structural zone of NW Iran is related to quartz-monzonite and alkali-granite intrusions that were emplaced within the volcanic-volcaniclastic rocks of Karaj Formation during Tertiary. The Chodarchay deposit formed as a high-sulfidation epithermal overprint on porphyry type mineralization. The mineralization occurred as stockwork, dissemination, veinlet, open space filling and breccias. Chalcopyrite, pyrite, sphalerite, and galena are the main sulfide minerals in the area. The sulfur isotope composition of sulfide minerals from the Chodarchay deposit is positive, ranging from 0.2 to 6.8 ‰. The sphalerite-galena isotope geothermometer shows 360 °C for the crystallization temperature. Sulfur was sourced from a homogeneous magma, and its isotopic composition decreases with depth and temperature decreasing due to fluid oxidation changes. Therefore, sulfur isotope assemblages show a systematic spatial distribution within the Chodarchay system.

Mineralized breccia clasts: a window into hidden porphyry-type mineralization underlying the epithermal polymetallic deposit of Cerro de Pasco (Peru)

Cerro de Pasco (Peru) is known for its large epithermal polymetallic (Zn-Pb-Ag-Cu-Bi) mineralization emplaced at shallow level, a few hundred meters below the paleo-surface, at the border of a large diatreme–dome complex. Porphyry-style veins crosscutting hornfels and magmatic rock clasts are found in the diatreme breccia and in quartz–monzonite porphyry dikes. Such mineralized veins in clasts allow investigation of high-temperature porphyry-style mineralization developed in the deep portions of magmatic–hydrothermal systems. Quartz in porphyry-style veins contains silicate melt inclusions as well as fluid and solid mineral inclusions. Two types of high-temperature (> 600 °C) quartz–molybdenite–(chalcopyrite)–(pyrite) veins are found in the clasts. Early, thin (1–2 mm), and sinuous HT1 veins are crosscut by slightly thicker (up to 2 cm) and more regular HT2 veins. The HT1 vein quartz hosts CO2- and sulfur-rich high-density vapor inclusions. Two subtypes of the HT1 veins have been defined, based on the nature of mineral inclusions hosted in quartz: (i) HT1bt veins with inclusions of K-feldspar, biotite, rutile, and minor titanite and (ii) HT1px veins with inclusions of actinolite, augite, titanite, apatite, and minor rutile. Using an emplacement depth of the veins of between 2 and 3 km (500 to 800 bar), derived from the diatreme breccia architecture and the supposed erosion preceding the diatreme formation, multiple mineral thermobarometers are applied. The data indicate that HT1 veins were formed at temperatures > 700 °C. HT2 veins host assemblages of polyphase brine inclusions, generally coexisting with low-density vapor-rich inclusions, trapped at temperatures around 600 °C. Rhyolitic silicate melt inclusions found in both HT1 and HT2 veins represent melt droplets transported by the ascending hydrothermal fluids. LA-ICP-MS analyses reveal a chemical evolution coherent with the crystallization of an evolved rhyolitic melt. Quartz from both HT1 and HT2 veins also contains secondary, low-temperature (~ 300 °C) brine and aqueous fluid inclusions that record the cooling of the system. Both vein types are locally crosscut and/or reopened by a pre-diatreme polymetallic event consisting of pyrite, sphalerite with “chalcopyrite disease,” galena, chalcopyrite, tetrahedrite–tennantite, and minor quartz. LA-ICP-MS analyses of mineral and high-temperature fluid inclusions hosted in HT1 and HT2 veins and in situ secondary-ion mass spectrometry oxygen isotope analyses of vein quartz indicate a magmatic signature for the mineralizing fluids with no major meteoric water input and allow reconstruction of the source and chemical evolution of fluids that formed these porphyry-style veins as snapshots of the early and deep mineralizations at Cerro de Pasco. This detailed study of the porphyry-type mineralization hosted in clasts offers a unique opportunity to reconstruct the late magmatic and early hydrothermal evolutions of porphyry mineralization underlying the world-class Cerro de Pasco epithermal polymetallic (Zn-Pb-Ag-Cu-Bi) deposit.

Large-scale porphyry-type mineralization in the Central Asian metallogenic domain: A review

A series of porphyry-type Cu-(Mo)-(Au) deposits including some giant world-class deposits such as Kounrad, Aktogai, Kal’makyr, Oyu Tolgoi and Chalukou occur in the Central Asian metallogenic domain (CAMD). The outline of the CAMD almost overlaps with that of the Central Asian orogenic belt (CAOB), which is located between the East Europe, Siberia, Tarim and North China cratons. The CAMD comprises sparsely exposed tectonic slices of Precambrian high-grade metamorphic basement rocks that are sandwiched between Phanerozoic accretionary complexes and arc rocks. According to geological, metallogenic, geochronological and tectonic setting characteristics, the CAMD comprises three metallogenic provinces: (1) the Kazakhstan Cu-Au-Mo, (2) the Mongolia Cu-Au and (3) the Northeast China Mo-Cu metallogenic provinces. Early Paleozoic (∼490 to 440 Ma) and Late Paleozoic (∼330 to 295 Ma) large scale porphyry-type mineralization in the Kazakhstan metallogenic province is intimately associated with the evolution of the Central Tianshan–Yili–Northern Tianshan–Kokchetav–Chingiz Paleozoic arc system which was terminated by the late Permian closure of the western segment of the Paleo-Asian Ocean. In contrast, the ∼370 Ma and ∼240 Ma porphyry-type mineralization of the Mongolia metallogenic province is related to the Tuva–Mongolia arc collage system that was formed during the evolution of the Paleo-Asian Ocean in the Paleozoic and the Mongol–Okhotsk Ocean in the early Mesozoic. Furthermore, the Northeast China metallogenic province was affected by three distinct geodynamic processes that were associated with the Paleo-Asian, Mongol–Okhotsk and Paleo-Pacific Oceans during the Paleozoic (>250 Ma), the early Mesozoic (>200 Ma) and the late Mesozoic (200–90 Ma), respectively. Except for the Early Paleozoic Cu mineralization at Duobaoshan (∼480 Ma) and Bainaimiao (440 Ma), the porphyry-type mineralization of this metallogenic province is predominantly characterized by widespread Mesozoic Mo mineralization.In general, porphyry-type deposits of the CAMD have geological, structural, metallogenic, alteration and fluid characteristics, which are consistent either with those related to the oceanic subductional arc settings of the Circum-Pacific metallogenic domain or with those of the continental collisional environment in the Tethyan metallogenic domain. The involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits. Even though the prevalent MASH and slab melting models can be employed to interpret the genesis of some porphyry Cu deposits in the CAMD, a here newly suggested model, which is based on ‘pre-enriched mafic lower crust and the subduction of a relictic mid-oceanic ridge’, is thought to explain the large scale copper mineralization in the Balkhash–West Junggar metallogenic belt of the Kazakhstan metallogenic province. Nevertheless, most of the porphyritic suites associated with the Mo deposits in the Northeast China metallogenic province have relatively depleted mantle-like neodymium and hafnium isotopic compositions, suggesting that the ore-forming granitic magma may have predominantly been derived from juvenile lower crust. Upwelling of asthenosphere may have triggered the melting of the lower crust during post-collisional extension subsequent to the closure of the Paleo-Asian Ocean in the Triassic, the subduction of the Paleo-Pacific ocean in the Jurassic and the thinning of the lithosphere caused by rollback of the Paleo-Pacific plate in the Cretaceous. Ancient crustal components were only locally found to have been involved in the magma source of several medium-large Mo deposits.

Geology and fluid inclusion geochemistry of the Zijinshan high-sulfidation epithermal Cu-Au deposit, Fujian Province, SE China: Implication for deep exploration targeting

The giant Zijinshan Cu-Au deposit in the Zijinshan orefield, Fujian Province, southeastern China, is the first high-sulfidation epithermal deposit identified in mainland China. The Cu and Au orebodies occur as veins and pods in the NW-trending faults and breccias zones. Intensive and pervasive alteration is characterized by downward and outward zoning from intensively leached silicic alteration (or vuggy quartz, Q), through alunite-quartz-pyrite alteration (advanced aragillic alteration, Q-Alu) and the quartz-alunite alteration overprinting the sericite alteration (Q-Alu-Di-Srt), to sericite (or phyllic) alteration zone. Gold mineralization mainly occurs in the silicic alteration zone, while the copper mineralization is confined in the alunite-quartz alteration zone. On the basis of detailed petrographic study, an early porphyry type mineralization stage, characterized by chalcopyrite-bornite-molybdenite-pyrite-sericite assemblage is recognized at Zijinshan, which is subsequently and strongly overprinted by the sulfate alteration and high-sulfidation Cu-Au mineralization stages. A supergene stage is also identified at shallow depth of the deposit, with gold largely enriched but copper commonly leached. The ore-forming fluids related to the early sericite alteration and possibly porphyry type mineralization are high-temperature, high-salinity magmatic water, characterized by the presence of the halite-bearing inclusions. The CO2-H2O (C-type) inclusions are mostly vapor-rich and abundantly identified in the samples with advance argillic alteration (alunite alteration). They are regarded to be the buoyant vapor phase by fluid boiling of a single-phase, low- to moderate-salinity magmatic fluid at depth, where a separated saline phase and related porphyry mineralization might be expected. A group of secondary inclusions coexisting with enargite grains are recognized in the samples with alunite alteration and suggested to be trapped from the ore-forming fluids of the Cu-Au mineralization stage. The total homogenization temperatures and salinities of the secondary inclusions are below 300°C (peaking at 260–280°C) and under 10wt% NaCl eqv., respectively. Intensive fluid boiling is the major mechanism for the formation of the giant high-sulfidation Cu (covellite-, digenite-dominated) orebodies in the Zijinshan deposit. It is a deep-seated high-sulfidation epithermal deposit according to the estimated depth of 1.4–2.1km from the C-type inclusions in quartz grains from the alunite alteration zone. By fluid inclusion mapping of a nearly NW-trending cross section profile, the isotherms are extrapolated using the average total homogenization temperatures and the possible heat source is suggested. It is indicated that the heat source and possible concealed porphyry mineralization nearly coeval to the high-sulfidation Cu-Au mineralization at Zijinshan might be located at the southeastern Zijinshan deposit or the northern area between the Zijinshan and Wuziqilong deposits, where deep drilling is encouraged.

Singularity mapping of fracture fills and its relationship to deep concealed orebodies – a case study of the Shaxi porphyry Cu-Au deposit, China

Porphyry Cu-Au type mineralization forms as a result of magmato-hydrothermal activity and involves the migration of hydrothermal fluids through rock fractures, a process that causes the precipitation of fracture-filling minerals with a volume that is much larger than the orebodies themselves. This means that the mineralization-related geochemical anomalies within the minerals that fill these fractures (i.e. fracture fills) can be used to identify areas prospective for deep-seated or otherwise concealed porphyry-type mineralization. This study focuses on the Shaxi deposit, a concealed porphyry Cu-Au deposit located in the Anhui Province, China, and uses singularity techniques to identify and extract geochemical anomalies associated with porphyry Cu-Au-related fracture fills. These data were used to examine the relationships between geochemical anomalies and known deep and concealed mineralization distinguished from unaltered and unmineralized wall-rock material using a concentration–volume (C–V) model in the study area. This analysis indicates that the geochemical anomalies identified in this study are associated with known areas of mineralization in the Shaxi deposit. Areas defined by fracture fills containing anomalous concentrations of Cu only effectively delineate known areas of shallower Cu mineralization, whereas areas with fracture fills containing anomalous concentrations of Au effectively delineate areas containing either Au mineralization and/or deep-seated Cu mineralization. Our study also identified several other targets that have not been explored in the peripheral areas of the Shaxi deposit, some of which should be considered high priority targets for future exploration for concealed orebodies. This indicates that combining singularity mapping with fracture fill geochemical analysis can effectively delineate geochemical anomalies associated with deep-seated or concealed porphyry-type mineralization, an approach that also may well be applicable to exploration for other types of magmato-hydrothermal or hydrothermal mineral deposits.

Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa Terrane

Understanding the geological history of the Lhasa Terrane prior to the India–Asia collision (~55±10Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene (~18–10Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183–174Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr–Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I–S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

西藏玉龙铜矿带包买矿床含矿斑岩锆石U-Pb年代学

Baomai porphyry copper-molybdenite deposit is an important part of the northern Yulong copper belt, Tibet, with typical porphyry-type mineralization and alteration. The latest exploration shows that both Cu and Mo resources have reached the medium-sized deposit, but the research work is still very poor. Based on the basic geological characteristics, intrusion ages of biotite granite porphyry and biotit-monzogranite are 41.3 ± 0.2 Ma and 40.8 ± 0.2 Ma, respectively, according to the LA-ICP-MS zircon U-Pb geochronology method. These results are consistent with those of Yulong and Zhanaga deposits. All of them are the products of continent collision orogeny of India with Eurasia in Eocene. Geochronology evidences show that porphyries related to mineralization in the Yulong copper belt are mainly intruded at 37-42 Ma, and no obviously early (51 Ma), medium (41 Ma) and late (33 Ma) stages magmatic activities. From northwest to southeast, the ages of diagenesis and mineralization in Yulong copper belt do not change to be younger significantly.

Epithermal deposits in South China: Geology, geochemistry, geochronology and tectonic setting

South China Block (SCB) is the broad area including the Yangtze Craton in the northwest and Huanan Orogen in the southeast. It is an important epithermal metallogenic province in China, containing at least 1 high-sulfidation (HS) and 42 low-sulfidation (LS) Au-Ag±Cu±Pb-Zn±Sb epithermal deposits. Porphyry-type mineralization was recognized in four of the LS deposits, and thus they were regarded as LS–P type. These 43 deposits are mainly located in: (1) the Lower Yangtze River Belt and (2) the Northeastern Jiangnan Orogenic Belt in the Yangtze Craton, (3) the Wuyi-Yunkai Orogenic Belt and (4) the Southeast Coastal Volcanic Belt in the Huanan Orogen. They are mostly located in Mesozoic volcanic basins, especially where the regional faults and their subsidiaries occurred. The host rocks include Jurassic–Cretaceous volcanic-sedimentary rocks, coeval or slightly older subvolcanic, granitoids and breccias, and metamorphic basement rocks. The alteration of the HS epithermal deposit (Zijinshan Cu-Au) zoned from silicic (vuggy quartz), through alunite, to dickite and phyllic alteration zones, from the ore veins outwards. The alteration of the LS deposits is zoned from adularia-chalcedony-bladed calcite (or quartz pseudomorphs after bladed calcite) in ore veins to distal illite-sericite-chlorite-kaolinite assemblages. For those LS–P systems, besides the dominated LS alteration assemblages, phyllic and potassium silicate alteration related to porphyry mineralization were identified. Acid leaching textures and vein, stockwork and breccia structures are common in HS deposit, while the LS epithermal deposits are characterized by open-space filling, crustifications, colloform banding and comb structures. The ore-forming fluids are low-temperature, low-salinity meteoric water-dominated in most epithermal deposits in SCB, with variable input of magmatic water. The ore components were derived from both the deep magma and host rocks, and transported upwards or laterally and precipitated in the fracture systems by fluid boiling, mixing and cooling. Most of the epithermal deposits are formed at depth of <1.5km and <300°C, with few exceptions containing porphyry-type mineralization, such as the Zhilingtou, Yinshan and Longtoushan deposits. Deep drilling is suggested in these deposits as more epithermal and/or porphyry mineralization could be expected. The mineral systems were formed in Early Yanshanian (180–130Ma) and Late Yanshanian (120–90Ma) periods. The Early Yanshanian epithermal ore systems are mainly located in a series of E–W-trending metallogenic belts to the west of the Lishui–Haifeng Fault, which were formed in a syn- or post-collision tectonic setting by the collision between the SCB and its surrounding plates. The Late Yanshanian epithermal deposits are mainly located in Southeast Coastal Volcanic Belt, genetically related to the westward subduction of the paleo-Pacific plate.

Rb-Sr geochronology of single gold-bearing pyrite grains from the Katbasu gold deposit in the South Tianshan, China and its geological significance

The newly discovered Katbasu gold deposit in the South Tianshan region has a gold reserve of 76t at an average grade of 3.84g/t. It is the first large gold deposit in the central segment of the South Tianshan. Gold mineralization is hosted within granite, and is associated with potassic, phyllic and chloritic alteration. Gold-bearing pyrite occurs as disseminations in the host rock and as quartz-sulfide veins cross-cutting the potassic and phyllic alteration assemblage. Rubidium (Rb) - strontium (Sr) analyses on sericite within five individual pyrite grains from a phyllic alteration sample yield an isochron age of 322.5±6.8Ma (MSWD=3.2). The host granite has a SIMS U-Pb zircon age of 351.4±1.1Ma (MSWD=0.13). The Rb-Sr isochron age represents the mineralizing age of the Katbasu gold deposit, which significantly postdates the ore-hosting granite but is consistent with the age of regional porphyry type mineralization at ~320Ma in the South Tianshan. Discovery of the Katbasu gold deposits indicates huge potential for gold exploration in the central segment of the South Tianshan as it is geologically similar to the western and eastern segments of the South Tianshan, which both host many world-class gold deposits.

Heterogeneous melt and hypersaline liquid inclusions in shallow porphyry type mineralization as markers of the magmatic-hydrothermal transition (Cerro de Pasco district, Peru)

Recently identified occurrences of porphyry-style mineralization evidence the link of the world's second largest known epithermal base metal Cerro de Pasco deposit (Peru) to a porphyry system emplaced at depth. They consist of (i) quartz-monzonite dykes and (ii) the south-western part of the large diatreme-dome complex adjacent to the main ore bodies of Cerro de Pasco, and (iii) stockwork of banded quartz-magnetite-chalcopyrite-(pyrite) porphyry-type veinlets crosscutting trachyte porphyritic intrusion cropping out at surface in the central part of the diatreme-dome complex. The latter porphyry-type mineralization observed at the same erosion level as the main epithermal base metal carbonate-replacement ore bodies is the subject of this work. Geological constraints indicate a shallow emplacement level (depth<1km, P<270bar), implying rather unusual low-pressure and high-temperature environment for the formation of porphyry-style mineralization.The banded porphyry-type veinlets record a multiphase history of formation with two successive high-temperature (>600°C) stages, followed by a lower-temperature (<350°C) stage. More than 90% of the quartz in veinlets precipitates during the first two high-temperature stages. Stage 1 is characterized by the entrapment in hydrothermal quartz of inclusions containing variable proportions of both silicate melt and metal-rich hypersaline (>90wt% NaCl eq.) liquid, hereafter referred to as heterogeneous silicate melt inclusions (HSMIs). The latter are rarely described in porphyry-type mineralization. We suggest that during stage 1, the inclusions result from heterogeneous entrapment of an evolved hydrous rhyolitic melt mixed with a hypersaline fluid phase at low pressure (270bar) and high temperature (>600°C). The stage 2 is marked by the entrapment of metal- and sulfur-rich hypersaline liquid inclusions, with salinity around 70wt% NaCl eq., originated from the adiabatic ascent of magmatic hypersaline fluids transferred from deeper parts of the system. The lower-temperature stage 3 is characterized by an important temperature drop from >600°C to <350°C as revealed by microthermometry of aqueous two-phase liquid-vapor (L-V) inclusions. Quartz textures revealed by SEM-CL imaging allow ascribing the sulfide precipitation to the low-temperature mineralization stage 3. In-situ SIMS 18O/16O isotope analyses of quartz across the veinlets are indicative of a magmatic signature of the fluids during the first two stages; while quartz from stage 3 has oxygen isotopic compositions suggestive of minor contribution of meteoric waters to a predominantly magmatic aqueous fluid (~10vol.% of meteoric input), which probably triggered Cu-Fe sulfide precipitation in the stockwork. High metal and sulfur contents of HSMIs and hypersaline liquid inclusions determined by LA-ICP-MS are interpreted to represent the fluid composition prior to the main sulfide precipitation event. The similar Pb-Zn ratio of the bulk ore extracted from the epithermal ore bodies at Cerro de Pasco and the HSMIs and hypersaline liquid inclusions suggest a common source of the fluids associated with the different mineralization styles at Cerro de Pasco.

Trace and rare earth element characteristics in Fe-Mn carbonates associated with stratiform Ag-Pb-Zn mineralization from the Lengshuikeng ore district, Jiangxi Province: Implications for their genesis and depositional environment

We performed a systematic trace and rare earth element analysis for the bedded Fe-Mn carbonate rocks related to the stratiform Ag-Pb-Zn mineralization in the Lengshuikeng ore district, Jiangxi Province, South China. Three types of Fe-Mn carbonates are distinguished, namely, the massive, breccia, and vein types. Both carbonate and silicate fractions in the samples are analyzed for their trace and rare earth element concentrations using a step acid-leaching technique. Our results show that the carbonate fractions in the massive type samples have the lowest REE concentrations but pronounced positive Eu and Y anomalies with Eu/Eu* value from 1.3 to 6.2 and Y/Ho value from 40.1 to 59.5, and similar characteristics are also shown for the silicate fractions in the massive type samples (Eu/Eu*=1.0–6.7, Y/Ho=20.7–55.1). These REE characteristics are similar to those of Sedex type massive sulfide deposits worldwide, and we suggest that the massive type Fe-Mn carbonate rocks were likely formed from an exhalative volcanic-hydrothermal fluid feeding the depression basin of a volcanic lake. The high concentrations of redox-sensitive elements and ratios such as U/Th, V/Cr and V/(V+Ni) indicate a dysoxic environment for the Fe-Mn carbonate deposition. In contrast, the breccia type and vein type Fe-Mn carbonate samples show different trace and rare earth element features from those of massive type samples, and they are more similar to the volcanic rocks and magmatic-hydrothermal fluids in the Lengshuikeng ore district and may reflect strong overprinting from volcanic and sub-volcanic magmatism related to the porphyry type mineralization in the district.

Cretaceous subduction-related magmatism and associated porphyry-type Cu–Mo prospects in the Eastern Pontides, Turkey: New constraints from geochronology and geochemistry

This study focuses on the Elbeyli–Ordu, Emeksen–Giresun, Güzelyayla–Trabzon and Ulutaş–Ispir porphyry-type prospects located in the Eastern Pontides, Turkey. Our new LA-ICP-MS U–Pb zircon age data reveal that the Elbeyli–Ordu Mo–Cu mineralization is hosted by a 77.0±1.3Ma-old monzonite/monzodiorite with a shoshonitic character. The Emeksen Mo mineralization, located ~40km southeast of the Elbeyli–Ordu prospect, consists of NW- and NE-striking quartz veins crosscutting a high-K calc-alkaline to shoshonitic granite dated at 78.5±0.8Ma, a granodiorite dated at 78.7±0.5Ma and porphyry granite dated at 77.7±0.5Ma. The Güzelyayla porphyry Cu–Mo prospect consists of a stockwork-type Cu–Mo mineralization crosscutting a calc-alkaline 81.4±1.1Ma-old dacite porphyry and Late Cretaceous calc-alkaline andesite. The Ispir–Ulutaş mineralization is hosted within a highly sericitized 131.1±0.9Ma-old quartz-porphyry that intruded into a 132.9±0.6Ma-old calc-alkaline granite porphyry. Our new U–Pb zircon ages, lithogeochemical and radiogenic isotopic data of the host rocks associated with the porphyry-type prospects in the Eastern Pontides indicate that they formed in an arc-related environment during Cretaceous subduction of the Neotethys Ocean, and the Ispir–Ulutaş prospect is attributed to the main stage of the northward subduction of the Neotethys during the Early Cretaceous. We conclude that the Güzelyayla and Emeksen hydrothermal systems were formed during a transitional compressional to extensional tectonic evolution, whereas the Late Cretaceous Elbeyli hydrothermal system was emplaced during an extensional arc magmatic event. Highly-oxidized, high-K calc-alkaline to shoshonitic magmas at Emeksen and Elbeyli were derived from a metasomatized, heterogeneous and enriched lithospheric mantle, with variable degrees of partial melting of the mantle wedge and variable crustal contamination. Mixing/mingling processes between mafic magmas derived from the lower crust and acidic magmas at upper crustal levels played an important role in the formation of Cu–Mo porphyry-type mineralization in the Eastern Pontides.

Geological, Alteration and Mineralization Characteristics of Ali Javad Porphyry Cu-Au Deposit, Arasbaran Zone, NW Iran

Ali Javad porphyry Cu-Au deposit is located 20 Km north of Ahar city in Arasbaran metallogenic zone which is considered as a part of Alp-Himalayan mineralization belt. Magmatism in this area began in Late Cretaceous, followed by extensive magmatism in Cenozoic and Quaternary periods. Porphyry type mineralization developed in Ali Javad quartz monzonitic porphyry stock and Eocene pyroclastic and volcanic country rocks. Ali Javad porphyry intrusion has shoshonitic nature and shows characteristics of volcanic arc granitoids that it is have been emplaced in a post-collision tectonic setting. Alteration zones at the deposit demonstrated zoning which is comparable with Lowel-Guilbert model proposed for quartz-monzonite type porphyry copper deposits. Phyllic, argillic, silicic and propylitic alteration zones were observed at the surface while potassic alteration zone could be observed at depth in drill core samples. Mineralization was recognized both as supergene and hypogene, the latter was as veins, veinlets and disseminations. Dominant hypogene minerals were chalcopyrite, bornite, molybdenite, pyrite and magnetite while chalcocite, covellite and limonite were dominant supergene minerals. Four mineralization zones were observed in the deposit as leached, transitional, supergene and hypogene zones. Average grades were 0.75% for copper and 1.86 ppm for gold with 81.5 Mt proved reserve for copper and 37.8 Mt for gold.