Massive Ore Research Articles

Редкие и редкоземельные элементы в Cu-Ni рудах Норильского района

The deposits of the Norilsk region are confined to the marginal northwestern part of the Siberian platform and are associated with the manifestation of the Early Mesozoic trap volcanism. Sulfide mineralization is concentrated in the intrusive facies of the volcano-intrusive complex. Four main types of Cu-Ni ores are distinguished according to textural features: massive, vein-disseminated, brecciated, and disseminated. The main types of Cu-Ni ores differ significantly from each other in the chemical composition and content of rock- and ore-forming components. The enrichment ratios of ore trace elements in the Oktyabrskaya and Talnakhskaya vein-disseminated ore mainly reach hundreds (S, Pt, Au, Se,Te, Pb, As, Sn, Mo) and thousands (Ni, Cu, Ag, Pd) times. A rather high enrichment of all types of Bi, Re and Cd ores has been revealed, which are potentially industrially significant as high-tech metals, and can be promising for associated mining. The amount of rare-earth elements (REE) in ores is several times less than in the upper crust and more than in the primitive mantle. The concentration of rare earths in the main types of ores, with the exception of massive ones, exceeds the level of the chondrite standard, and REE fractionation is weak. The distribution spectra of chondrite-normalized REEs have a slight negative slope: the total content of light REEs is higher than that of heavy ones. The similarity of the geometry of the REE spectra of massive, vein-disseminated, brecciated and disseminated types of ores containing a significant admixture of host rocks indicates the inheritance of the REE composition in ores from the host rocks. In the disseminated ores of common taxite gabbro-dolerites, the Eu anomaly is present in the Kharaelakhsky (Oktyabrskoye Deposit) and Talnakhsky (Talnakhskoye Deposit) intrusions, it is positive, and in the Norilsk I Intrusive (in the same rocks), it is negative. Higher concentrations of REEs and significant fractionation of light and heavy rare elements are typical for host contact-metamorphic and metasomatic rocks with vein-disseminated (exocontact) ores. For olivine-free hornfels and skarns in brecciated ores, as well as for vein-disseminated ores, significant fractionation of light REEs with relatively heavy ones and a pronounced Eu minimum are characteristic. In massive ores, the distribution of REEs is determined by the composition of xenoliths.

GEOLOGY, MINERAL COMPOSITION OF ORE AND ALTERED HOST ROCKS OF MASSIVE SULPHIDE MINERALIZATION OF THE AKZHARSKY ORE FIELD (SOUTH URALS)

The article describes the geological structure of the Akzharsky ore field, of five individual massive sulphide mineralization: Yuzhnoye, Yuzhno-Akzharskoye, Novoye, Bezymyannoye and Burozheleznyakovoye. The results of a microscopic study of the mineral composition of ores and altered host rocks are discussed. It is shown that all ore mineralizations are concentrated at a single lithological-stratigraphic level, but differ from each other in details of the structure, scale and mineral composition of mineralization. Massive ores prevail, and embedded and densely embedded ores are subordinate. The composition of the ore is mainly chalcopyrite-pyrite, to a lesser extent sphalerite-chalcopyritepyrite and pyrite. In the direction from south to north of the ore field, there is a change in the direction of increasing «polymetallicity» in ore mineralogy. Texture and structure of the ores of the Akzharsky ore field are rather uniform. Linear structures predominate (from banded to schistosely banded). Massive structures have a sharply subordinate distribution; brecciated ones are noted in isolated cases. Hydrothermal alterations formed mainly in rhyodacite-basalt strata from foot wall of ore bodies and, according to mineral composition, belong to propylites. They are characterized by an unstable set of mineral facies, weak contrast of metasomatic zones, and extremely uneven of rocks alteration. It has been established that the volcanic complexes of the ore field contain deposits not typical for the Ural massive sulphide ore province, differing in the mineral composition of ores, the conditions of their geological setting and the nature of the rocky alterations. This made it possible to concretize the concept of the relationship between the considered mineralization and volcanism and significantly supplement the already known typical models of pyrite-bearing ore-magmatic systems.

Re-Os Age and Stable Isotope (O-H-S-Cu) Geochemistry of North Eastern Turkey’s Kuroko-Type Volcanogenic Massive Sulfide Deposits: An Example from Cerattepe-Artvin

The eastern Pontide tectonic belt (EPTB) contains greater than 350 identified Kuroko type volcanogenic massive sulfide deposits/mineralization/occurrences (VMSD). The deposits are associated with Late Cretaceous felsic volcanics consisting mainly of dacitic and rhyolitic lavas and pyroclastics that outcrop within a narrow zone running parallel to the eastern Black Sea coast and represent the axial zone of a paleo-magmatic arc. The Cerattepe deposit is the second-largest and is a hybrid VMS system with some epithermal features. To date, no geochemical research constrains the origin and timing of mineralization in the Cerattepe VMS deposit. Here, we provide Cu, O, H and S, isotope analysis of ores and alteration minerals to understand the hydrothermal history of the deposit and date the massive ore with Re-Os geochronology. Secondary weathering mobilized and redistributed metals in the deposit. The copper isotope signatures of shallow ores in the gossan follow patterns resulting from oxidative weathering of copper minerals with gossan Fe oxides of δ65Cu = −2.59‰, enrichment zone copper sulfide of d65Cu = +2.23 and +1.73‰, and primary ores of δ65Cu = +0.71 and +0.41‰. At the boundary of the enrichment zone, further cycling and migration of enrichment zone copper are evidenced by two samples having larger ranges of the δ65Cu = +3.59‰, and −2.93‰. Evidence for a magmatic source for fluids and S are evidenced by the O and H isotope values from quartz veins (δ18O = +7.93‰ to +10.82‰, and δD = −78‰ and −68‰) and sulfides that possess δ34S ratios of –5 and 0‰ from drill core samples. 187Os/188Os–187Re/188Os ratios from drill core sulfide samples of Cerattepe VMS deposit yields a 62±3 Ma isochron age and a highly radiogenic Os initial ratio. This age is compatible with silicate alteration ages from a proximal deposit and clearly shows mineralization occurs at a much younger time than previously proposed for VMS mineralization in the eastern Pontides. The new Re-Os age and source of Os imply that mineralization in the area occurs at a distinctly younger interval in the back-arc basin and metals could be sourced from the surrounding host rocks.

Chromitites of the Kraka ophiolite (South Urals, Russia): geological, mineralogical and structural features

The paper describes disseminated tabular, podiform massive, and transitional chromitite deposits from a mantle section of the Kraka ophiolite massif, South Urals, Russia. The chromitite is hosted by dunite with no correlation between their size and quality and the size of the dunite bodies. Thick dunite bodies mostly host disseminated fine-grained banded chromitite; massive ores are composed of coarse-grained chromitite typically with a thin dunite envelope. The chromitite and host ultramafic rocks exhibit plastic deformation of silicates and chromite, which is expressed in microstructural features, preferred orientation of rock-forming olivine, and folding of the chromitite bodies. The ultramafic rocks are also characterized by deformation-induced textures leading to the formation of the small-size chromite grains on structural defects of plastically deformed rock-forming olivine and orthopyroxene. The formation of dunite bodies and associated chromitite is related to the localization of deformation of rising mantle flows under decompression conditions. Dunite was the most rheologically weak zone exhibiting a focused solid state flow and effective separation of mineral phases (olivine and chromite). The higher amount of the latter in dunite is a result of deformation-induced breakdown of enstatite and removal of trace elements from olivine. The structural features of massive chromitite aggregates indicate that they are a product of concentration and aggregation of grains under the influence of tectonic stresses at high temperatures and pressures, similar to pressure sintering.

The forward modeling for surface-borehole observation responses of polarized sphere in uniform electric field

Surface-borehole induced polarization method is a common geophysical method in metal exploration. The forward calculation results of the borehole observation responses can provide reference and support for practical work. In particular, the forward results of spherical polarized target can be equivalent to massive ore body or karst caves and other low-resistivity anomalies. In this paper, the forward simulation of borehole induced polarization responses is carried out by using the electric dipole model equivalent spherical polarized body. The results show that the polarization degree of the excitation source at different positions is different, and the closer the proximity is, the stronger the secondary field anomaly is. Borehole observation has advantages for the identification of deep ore bodies. Under the same offset condition, the closer the distance from the borehole is, the stronger the responses will be. The results of this paper can provide reference and basis for relevant research work.

Isotope geochemistry, age, and origin of the magnetite-vonsenite mineralization of the Monchi Mine, SW Iberia

The Monchi Mine (Ossa Morena Zone, SW Iberia) is a rather unique ore deposit characterized by unusually high Fe grades and an ore assemblage that includes dominant magnetite but with abundant B (vonsenite), U (uraninite), Co (cobaltite), As (lollingite, safflorite) and rare earth elements (allanite). The mineralization occurs at the western edge of a Variscan concentrically zoned gabbro to granodiorite pluton, the Burguillos del Cerro Plutonic Complex. Moreover the western side of the complex is within a large N–S trending dextral strike-slip shear zone in which Ediacaran to early Cambrian metapelitic and calc-silicate hornfels and marble constitute a vertical screen between an outer syn-tectonic sheet of foliated biotite monzogranite and an inner post-tectonic amphibole-biotite diorite unit. The magnetite-vonsenite mineralization is adjacent to the screen and forms large lens-shaped bodies with sharp contacts with the intrusive rocks and is directly related with a granoblastic U-REE-bearing Fe-pyroxene-rich hornfels which is locally brecciated and cemented by pegmatite dominated by albite, K feldspar, quartz, clinoamphibole/biotite and axinite. Within the enclave there is a large post-tectonic exoskarn, including calcic and magnesian types which predates the diorite that mainly replaced the calc-silicate hornfels and the marble. The calcic exoskarn is dominated by grandite and hedenbergite and was retrogressed to actinolite, epidote, calcite and magnetite with variable amounts of pyrite and chalcopyrite. U–Pb TIMS dating of allanite from the U-REE-rich hornfels yielded 337.13 ± 0.99 Ma, i.e., within the range of ages of the Burguillos Plutonic Complex (335–340 Ma). Sr–Nd isotope geochemistry shows that the mineralization (including skarn and massive ore) has isotope signatures (eNd338 between -0.8 and -4.1; 87Sr/86Sr338 = 0.7071–0.7112) mostly intermediate between those of the igneous (− 6.8 to − 2.3; 0.7047–0.7097, respectively) and the sedimentary (− 11.7 to − 8.3; 0.7090–0.7164, respectively) rocks. The massive high grade mineralization could be the result of a syn-magmatic interaction of an unknown protolith with deep sourced fluids that were focused along early thrusts and shear zones probably rooted at a magma chamber in the middle crust. Alternatively it could also be the product of crystallization of a boron-bearing iron melt. This melt would be somewhat similar to the magnetite-(apatite) deposits elsewhere but in which the fluxing agent is boron. Fluids exsolved from these rocks produced a high-temperature magmatic-hydrothermal system that formed the post-tectonic exoskarn. The ultimate origin of these immiscible Fe-B melts could hypothetically be the assimilation at depth of former shallow marine metasediments.

Ore genesis and tectonic setting of the Bieluwutu Cu-Pb-Zn volcanogenic massive sulfide deposit in Xing’an-Mongolia orogenic belt, China

The Bieluwutu Cu-Pb-Zn deposit is located in the Ondor Sum region of the western Xing’an-Mongolia orogenic belt, North China. The host rocks of the deposit consist of metasandstone, tuffaceous slate, andesitic tuff and fragmented felsic volcanic rocks, which have previously been regarded as the Early Carboniferous Amushan Group. Zircon U-Pb ages for two tuffaceous units are 435 ± 2 Ma and 430 ± 2 Ma, showing that volcanism occurred in the Early Silurian. The tuffaceous rocks are enriched in large ion lithophile elements (LILE; e.g., Rb, Ba, K) and light REE, and depleted in high field strength elements (HFSE; e.g., Nb, Ta and Ti) with depleted isotopic components (εNd(t) = 0.14–0.84), indicating that they were derived from partial melting of lower continental crust with the involvement of mafic magma.Bieluwutu is intended to be a Kuroko-type VHMS deposit formed in an interarc rift basin in the Early Silurian. Three types of ores have been identified at Bieluwutu, including massive Pb-Zn, brecciated Cu-Zn and disseminated Cu ores. Results of sulfide laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses indicate that Se and Sn are enriched in chalcopyrite from the disseminated and brecciated ores with high Se/Te ratios. Tellurium, Co, Pb and Bi are enriched in chalcopyrite, sphalerite and pyrite from the brecciated ores, whereas Mn, Ni and Tl concentrations are higher in pyrite from the massive ores. These differences suggest a decreasing temperature and increasing f(O2) trend from the disseminated to brecciated and massive ores. High contents of Mn, Tl, Ni in massive ores are typical for metals derived from surrounding felsic volcanic rocks. Strong enrichment of trace elements, such as Bi, Te, Se and Sn, is consistent with a magmatic contribution to the ore-forming fluids. The underlying subvolcanic intrusion not only served as a heat engine but also supplied volatiles and metals.

New Geochemical and Mineralogical Data on Rocks and Ores of the NE Flank of the Oktyabr’skoe Deposit (Norilsk Area) and a View on Their Origin

The Oktyabr’skoe deposit in the Norilsk ore district is the largest platinum-copper-nickel deposit in the world. It contains a huge main orebody (2.4 km3) of massive sulfide ores and some smaller sulfide bodies. Almost all publications on this deposit are devoted to the main orebody. However, to solve the problems of the deposit genesis, it is necessary to take into account the geological structure of the entire area and the composition of all orebodies. For the first time we present data on the inner structure, geochemical and mineralogical characteristics of the intrusive body, and related the disseminated and massive sulfide ores (orebody number C-5) in the northeastern flank of the deposit. The intrusion studied in the core of the borehole RG-2 consists of several horizons including the following rock varieties (from bottom to top): olivine gabbro-dolerites, taxitic gabbro-dolerites, picritic gabbro-dolerites, troctolites, olivine-free gabbro-dolerites, ferrogabbro, and leucogabbro. The intrusion shows a strong differentiated inner structure where high-Mg rocks (up to 25 wt.% MgO troctolites and picritic gabbro-dolerites) in the bottom are associated with low-Mg rocks (6–7 wt.%, gabbro-dolerites, leucogabbro, ferrogabbro) without intermediate differentiated members (8–12 wt.% MgO olivine gabbro-dolerites). Rocks are characterized by low TiO2 content (≤1 wt.%). Taxitic gabbro-dolerites, picritic gabbro-dolerites, and troctolites contain disseminated sulfide chalcopyrite-pyrrhotite mineralization (32 m thick). Cu and Ni concentrations reach up 0.74 and 0.77 wt.%, respectively. Massive ores (27 m) occur in the bottom part of the intrusion. The ores consist of pentlandite, chalcopyrite and pyrrhotite, the latter mineral dominates. Their chemical composition is stable: Cu/Ni ~1, Pd/Pt varies from 5 to 6. The C-5 orebody is similar to the C-3 orebody in terms of mineral and chemical compositions, and differ from the nearby the C-4 orebody which is characterized by a Cu/Ni ratio changing from 5 to 8. On the basis of geochemical and mineralogical data, it is assumed that orebodies C-3 and C-5 are associated with one intrusion, while the orebody number C-4 is related to another intrusive body. Thus, the deposit has a more complex structure and includes several more intrusions than is usually considered.

Formation of serpentinite-hosted, Fe-rich arsenide ores at the latest stage of mineralization of the Bou-Azzer mining district (Morocco)

The Bou Azzer district in the central Anti-Atlas of Morocco is the world’s unique mining district where Co is exploited from serpentinite-hosted hydrothermal Co-Ni-Fe arsenide ores. This paper provides the first-ever mineralogical and geochemical characterization of a suite of Fe-rich arsenide orebodies found during recent mining in the Ait Ahmane area, in central Bou Azzer district. These are lens-like orebodies of massive and disseminated Fe-rich ores fully hosted in serpentinites (hereafter named as serpentinite-hosted ores) that are typically enveloped by arsenide-poor, carbonated serpentinite, evolving irregularly outwards to talc-rich serpentinite. The central part of these orebodies mainly consists of massive ore made up of aggregates of zoned spindle-like crystals of löllingite whereas the outer zone of disseminated ore consists of rosette-like löllingite. These ores often contain accessory grains of chromite that display strong fracturation, zoning and alteration.We propose a general model for the formation of the Bou-Azzer Co-Ni-Fe arsenide ores associated to the infiltration of high-temperature (>400 °C) slightly alkaline, oxidized and CaCl2-rich fluids through opening fault and fractures. When channeled through faults separating serpentinite and quartz diorite (or other rocks) the fluids deposited Ni- and Ni-Co-rich ores in these fault-related open spaces (here re-defined contact-type ores). Over the course of mineral deposition, the generated Ni-poor fluids tended to migrate into serpentinite, first through networks of thin entwined veins and progressively by intergranular percolation, promoting dissolution of the infiltrated serpentinite and precipitation of Co-Fe ores (the presence of remnants of chromite included in coexisting arsenides and calcite sustains the role played by dissolution/precipitation, ore-forming process). Further circulation of the evolving fluids through weak zones of massive serpentinite away from the serpentinite-quartz diorite (or other rocks) contact (intra serpentinite faults), formed the serpentinite-hosted, Fe-rich ore type represented by the F55 lens. These fluids most probably evolved at low temperature (~200 °C) towards slightly higher pH values and oxidizing conditions increasing the proportions of CO2 and CO32−, promoting the dissolution of serpentine, the increase in the magnetite component of chromite, the formation of Cr and Fe hydroxides, the mobilization of silica out of the reactive zone and the precipitation of calcite + Fe-rich arsenides.

Mineralogy, geochemistry, and genesis of the Chahgaz (XIVA Anomaly) Kiruna-type iron oxide-apatite (IOA) deposit, Bafq district, Central Iran

The Chahgaz iron oxide-apatite (IOA) deposit is one of the main IOA deposits in the Bafq metallogenic province, Central Iran. The Chahgaz mineral deposit is hosted by Early Cambrian felsic to intermediate, altered subvolcanic to effusive rocks that range compositionally from granite to diorite. Geochemical, geochronologic and tectonomagmatic investigations of various host rock types in the Bafq province indicate that mineralization was the product of Early Cambrian active continental margin processes that evolved calc-alkaline felsic igneous rocks followed by formation of diabase dykes in a back-arc basin environment. Magnetite is present in massive magnetite-rich ore bodies and veinlets that cut the massive ore bodies. Detailed macro- and micro-scopic characterization of mineralized samples and host rocks reveals a paragenetic sequence containing three generations of magnetite that are distinguished from one another compositionally and texturally. The massive ores contain apatite in trace amounts, consistent with IOA deposits globally, and locally exhibit textures that are visually similar to lava flow structures, as described for the El Laco IOA deposit, Chile. The ore bodies contain miarolitic cavities that are filled by calcite, hematite and quartz. The host rocks for the Chahgaz deposit have undergone widespread hydrothermal metasomatism including Na-Ca, K-, Mg-, Si-, sericitic, argillic and carbonatization alteration. The compositions of two generations of magnetite, referred to as Mag1 and Mag2, in massive ore overlap compositions reported for igneous and high-temperature magmatic-hydrothermal magnetite. The third generation of magnetite, which is referred to as Mag3 and is present in veinlets cross-cutting the massive magnetite ore bodies, overlaps compositions reported for low to moderate temperature magmatic-hydrothermal magnetite. Pyrite is present as disseminated grains coeval with Mag1 and micro-fracture filling in the massive magnetite-rich ore bodies.The δ18O values obtained for magnetite from representative samples of massive magnetite Mag1 ore range between 2.18 and 6.32‰ and are consistent with δ18O values reported for igneous and magmatic-hydrothermal magnetite from other deposits in the Bafq district and globally. The δ34S values for pyrite range from 22.54 to 24.94‰ and are consistent with an evaporitic sulfur source; plausibly by magma contamination with evaporitic rocks of the Early Cambrian Volcano-Sedimentary Sequence (ECVSS). The data presented here are consistent with formation of the massive magnetite-rich ore bodies in the Chahgaz IOA deposit by an iron-rich magmatic-hydrothermal fluid.

Fahlbands of the Keret archipelago, White Sea: the composition of rocks and minerals, ore mineralization

This paper presents a complex mineralogical and geochemical characteristic (based on SEM-EDS, ICP-MS analysis) of the fahlband rocks of the Kiv-Guba-Kartesh occurrence within the White Sea mobile belt (WSMB). The term “fahlband” first appeared in the silver mines of Kongsberg in the 17th century. Now fahlbands are interlayers or lenses with sulfide impregnation, located in the host, usually metamorphic rock. The level of sulfide content in the rock exceed the typical accessory values, but at the same time be insufficient for massive ores. Fahlbands are weathered in a different way than the host rocks, so they are easily distinguished in outcrops due to their rusty-brown color. The studied rocks are amphibolites, differing from each other in garnet content and silicification degree. Ore mineralization is represented mainly by pyrrhotite and pyrite, and pyrrhotite grains are often replaced along the periphery by iron oxides and hydroxides, followed by pyrite overgrowth. At the same time, the rock contains practically unaltered pyrrhotite grains of irregular shape with fine exsolution structures composed of pentlandite, and individual pyrite grains with an increased Ni content (up to 5.4 wt.%). A relatively common mineral is chalcopyrite, which forms small grains, often trapped by pyrrhotite. We have also found single submicron sobolevskite and hedleyite grains. The REE composition of the fahlband rocks suggests that they are related to Archean metabasalts of the Seryakskaya and Loukhsko-Pisemskaya structures of the WSMB, rather than with metagabbroids and metaultrabasites common in the study area.

The geology, magnetite geochemistry, and oxygen isotopic composition of the Akesayi skarn iron deposit, Western Kunlun Orogenic Belt, Xinjiang, northwest China: Implications for ore genesis

The Akesayi skarn iron (Fe) deposit is hosted by the Huangyangling Group within the Tianshuihai Terrane of the Western Kunlun orogenic belt, Xinjiang, China, and consists of several orebodies that formed along contacts between Miocene syenogranite, diorite porphyry dykes and late Paleozoic carbonate rocks. Manganese-bearing skarn minerals are common within the deposit. The ore-forming process can be divided into five stages: Prograde skarn stage (I), retrograde skarn stage (II), oxide stage (III), quartz-sulfide stage (IV), and carbonate stage (V), with this evolution being typical of Fe skarns. Magnetite, which formed mainly during the retrograde skarn and oxide stages, includes banded (BO), disseminated (DO), and massive (MO) magnetite. Backscattered-electron images indicate that magnetite within the massive ores can be further classified as primary (MO-1) and secondary (MO-2) magnetite.Magnetite within all ore types exhibits a strongly negative correlation between Si and Fe3+ contents, indicating that Si was incorporated into intra-crystalline sites of magnetite by substitution of Si4+ for Fe3+. Positive correlation among Al, Mn, Mg, and Si contents indicate that these elements behaved similarly during magnetite formation. The δ18OV-SMOW values of MO-1 magnetite range from 4.3‰ to 4.7‰, higher than magmatic magnetite (1‰–4‰), while the BO and DO magnetite have lower δ18OV-SMOW values of 1.7‰ to 2.4‰ and 1.8‰ to 2.5‰ respectively. Its anomalous oxygen isotopic composition indicates that most magnetite in the Akesayi Fe deposit precipitated from evolved ore-forming fluids formed by reaction between country rocks and primary magmatic fluids during the early stages of mineralization, with input from meteoric water during the later stages of mineralization. Trace-element patterns indicate that the different types of magnetite share a common source, with variations in the magnetite geochemistry amongst the different ore types of the Akesayi Fe deposit reflecting variations in the extent of fluid-rock interaction, dissolution-reprecipitation, mineral precipitation, temperature, and oxygen fugacity (ƒO2). The different types of magnetite of the Akesayi skarn Fe deposit form distinguishable populations in (Ca + Al + Mn)-(Ti + V) and (Ni/(Cr + Mn))-(Ti + V) discrimination diagrams, with the range of compositions possibly indicating more variable magnetite compositions in skarn deposits than previously thought.

Zircon and garnet U-Pb dating and in situ trace element of magnetite from the Hongyuntan Fe deposit, Eastern Tianshan, NW China

The relationship between the timing of volcanism and hydrothermal alteration and the geochemistry of magnetite are studied to better understand the metallogeny of the Hongyuntan deposit. The orebodies are hosted in the volcanic rocks with banded or lenticular forms, and main massive, disseminated, and veined ores and subordinate mineralized andesite and dacite host rocks are identified at Hongyuntan. SHRIMP zircon U-Pb dating of dacite and LA-ICP-MS garnet U-Pb dating of skarn yield nearly the same ages of 333.8 ± 5.3 Ma and 331.0 ± 6.4 Ma, respectively, indicating an isochronous relationship between volcanic rock and skarn. The age of the diabase dike that crosscuts the orebodies and volcanic strata indicates that the mineralization occurred earlier than 307.6 Ma. The dataset of trace element compositions shows that magnetite grains from stratiform mineralized andesite have high Ti, V, Cr, Ni, Mg, and Sn contents and formed under high-temperature and high-oxygen-fugacity conditions, whereas disseminated magnetite grains from mineralized dacite and chlorite skarn have medium above-element contents, suggesting they were hydrothermally altered under relatively high-oxygen-fugacity and fluid-rock interaction conditions. The fluid mixing and reduced temperature and oxygen fugacity might result in the deposition of massive ores. The increasing Cr, Ni, Mg, and Sn contents in magnetite grains from veined ores and their associated mineral assemblages indicate that overprint mineralization occurred in the Hongyuntan deposit, which was probably caused by multiple periods of volcanic activity or intrusion emplacement. Discrimination plots show that Hongyuntan different magnetite samples have compositions similar to different deposit types and likely formed in magmatic and hydrothermal processes.

A Trace Element Classification Tree for Chalcopyrite from Oktyabrsk Deposit, Norilsk–Talnakh Ore District, Russia: LA-ICPMS Study

The Oktyabrsk PGE-Cu-Ni deposit is one of the largest resources in the Norilsk–Talnakh ore district, Russia, and it is viewed as an ore giant on a global scale. It contains three types of ores: massive, disseminated and veinlet-disseminated. The two former ore types were formed by a liquation process, whereas the latter was associated with fluid-induced selective metasomatic replacement of metamorphosed wall rocks. One of the major ore minerals in all ore types is chalcopyrite. In this study, we determined concentrations of trace elements in this mineral using laser ablation inductively coupled plasma mass spectrometry. It appeared that standard geochemical tools, such as plotting the data in the form of diagrams of normalized concentrations, binary and ternary plots, do not allow one to distinguish chalcopyrite from visually and genetically different ore types. In contrast, more advanced statistical methods such as cluster analysis show different groupings of elements for each ore type. Based on the element clustering, a classification tree was suggested, which allowed for the differentiation of massive, disseminated and veinlet-disseminated ore types of the Oktyabrsk deposit by Se, Te, Cd and Pb concentrations in chalcopyrite with a success rate of 86%. The general feature is that chalcopyrite of veinlet-disseminated ore is poorer in these elements compared to chalcopyrite of the two other ore types. Chalcopyrite of massive ore is poorer in Se and Te when compared to chalcopyrite of disseminated ore.

Zircon U–Pb dating and sulfide Re–Os isotopes of the Xiarihamu Cu–Ni sulfide deposit in Qinghai Province, Northwestern China

The Xiarihamu Cu–Ni sulfide deposit is the second-largest Cu–Ni deposit in China, located in the Eastern Kunlun orogenic belt. However, despite previous study, the formation and evolution of this deposit remains a key unknown in the tectonic evolution of the Eastern Kunlun Orogenic Belt. Moreover, the petrogenesis of the ore-bearing rocks and the nature of ore genesis are the subjects of ongoing debate. Here, we present detailed field observations, petrology, zircon U–Pb geochronology, and Re–Os isotopic analyses to constrain the timing and genesis of the Xiarihamu Cu–Ni sulfide deposit. Sulfides from the massive ores yielded a Re–Os isotopic isochron age of 408 ± 11 Ma. Four samples from the ore-bearing Xiarihamu mafic–ultramafic intrusions yielded zircon U–Pb ages of 423.1 ± 2 Ma, 422.9 ± 3.1 Ma, 422.7 ± 2.3 Ma, and 422.6 ± 2.7 Ma, respectively, indicating that the ore formed during the Silurian. The calculated initial 187Os/188Os ratio and γOs values ranged from 0.5109 to 0.8499 and from 311 to 584, respectively, indicating that crustal contamination played an extremely important role in triggering sulfide saturation. In combination with previous research, drill core observations and Re–Os data provide robust evidence for multiple pulses of magma replenishment throughout the process of ore genesis. Based on this evidence, the large-scale magmatic Cu–Ni mineralization in Xiarihamu likely occurred in a post-collisional setting related to tectonic slab breakoff.

Re–Os dating of pyrite and mineral chemistry of magnetite from the Yamansu Fe deposit, Xinjiang, northwestern China

The Yamansu iron deposit, hosted in submarine volcanic rocks, is located in the Aqishan–Yamansu Fe–Cu metallogenic belt of eastern Tianshan, Xinjiang. New pyrite Re–Os and pyroxene diorite intrusion ages and the chemistry of magnetite constrain the origin of the deposit. The Yamansu orebodies display banded or lenticular forms and sharp contacts with marble and garnet skarn. Pyrite associated with magnetite from hydrothermal massive ores has a Re–Os isochron age of 320.3 ± 9.1 Ma, which is consistent with the Carboniferous age of volcanic rocks. However, the pyroxene diorite age (252.1 ± 3.7 Ma) is obviously younger than the mineralization age, implying no temporal relationship between mineralization and intrusion. Magnetite samples from different ores in the Yamansu deposit are suggested to have a magmatic–hydrothermal origin. The magmatic primary magnetite is rich in TiO2 and poor in SiO2, MgO, and CaO, similar to magnetite from Kiruna type deposits. The hydrothermal magnetite is rich in FeO, CaO, and SiO2 but poor in TiO2 and shows oscillatory zoning. Moreover, magmatic and hydrothermal magnetite samples show different characteristic normalized rare earth element and trace element patterns. A combination of ore fabrics, discrimination diagrams, and normalized patterns for magnetite samples can reflect the magmatic–hydrothermal process. The Yamansu iron deposit is spatially and temporally associated with Carboniferous volcanism, and we propose that the magmatic magnetite ores were derived from iron-rich melt through melt immiscibility. The residual iron-rich magma ascended and erupted along with hydrothermal activity; then moderate to large amounts of hydrothermal massive, banded, or disseminated magnetite formed with skarns.

U-Th-He Geochronology of Pyrite from the Uzelga VMS Deposit (South Urals)—New Perspectives for Direct Dating of the Ore-Forming Processes

We report on the application of the U-Th-He method for the direct dating of pyrite and provide an original methodological approach for measurement of U, Th and He in single grains without loss of parent nuclides during thermal extraction of He. The U-Th-He age of ten samples of high-crystalline stoichiometric pyrite from unoxidized massive ores of the Uzelga volcanogenic massive sulfide (VMS) deposit, South Urals, is 382 ± 12 Ma (2σ) (U concentrations ~1–5 ppm; 4He ~10−4 cm3 STP g−1). This age is consistent with independent (biostratigraphic) estimations of the age of ore formation (ca, 389–380 Ma) and is remarkably older than the probable age of the regional prehnite-pumpellyite facies metamorphism (~340–345 Ma). Our results indicate that the U-Th-He dating of ~1 mg weight pyrite sample is possible and open new perspectives for the dating of ore deposits. The relative simplicity of U-Th-He dating in comparison with other geochronological methods makes this approach interesting for further application.

The Varvarinskoye Complex Copper–Gold Deposit in Northern Kazakhstan: Mineral Types and Ore Composition

The Varvarinskoye copper–gold deposit, large in terms of Au and small in terms of Cu, was discovered in 1979 in the western part of the Torgai trough in Kazakhstan. It is composed of Devonian volcanosedimentary and intrusive rocks. Ore zones with a thickness from a few meters to a few tens of meters have been identified against a background of disseminated ore mineralization. They are composed of densely disseminated (porphyry) up to massive ores. The ore zones are localized in the thermal metamorphism band of volcanosedimentary and intrusive rocks, while disseminated mineralization is widespread beyond it. Ten ore mineralization types can be distinguished. The Au–Cu mineralization type is common in volcanosedimentary rocks and diorites, while the Au–Cu–Ni ores occur in serpentinites formed after thermally metamorphized intrusive rocks. Densely disseminated and massive magnetite ores are confined to skarns. Sulfide and sulfide–arsenide mineralization can also be observed. Each type of Au–Cu mineralization (pyrrhotite, chalcopyrite–marcasite–pyrite, pyrite, and gold–sulfide–arsenopyrite) can be correlated to an analog of Au–Cu–Ni mineralization (pentlandite–pyrrhotite, chalcopyrite–pentlandite–pyrite, pentlandite–pyrite, and gold–nickeline–gersdorffite). This indicates the uniform ore-forming process in serpentinites and volcanosedimentary rocks with diorites and borrowing of ore material from host rocks, at least, partially. The gold–chalcopyrite mineralization type, synchronous to the thermal metamorphism and analogous to mineralization of the alkali stage at porphyry copper deposits, has no analog in the Au–Cu–Ni mineralization. Gold is present in all mineralization types, but gold–chalcopyrite and sulfide–arsenide are the most enriched in Au. Eighty ore minerals have been found at the studied deposit. Pyrrhotite disulfidization and chalcopyrite pyritization are universal in occurrence. These processes likely led to the formation of chalcopyrite–marcasite–pyrite and chalcopyrite–pentlandite–pyrite mineralization after pyrrhotite and pentlandite–pyrrhotite types, respectively. Invisible gold present in chalcopyrite was enlarged during these processes.

Setting, sulfur isotope variations, and metamorphism of Jurassic massiveZn‐Pb‐Agsulfide mineralization associated with arc‐type volcanism (Skra, Vardar zone, Νorthern Greece)

AbstractMassive Zn‐Pb‐Ag sulfide mineralization appears conformable with felsic volcanism, developed in an Upper Jurassic volcanic arc to the Southwest (SW) of the Serbo‐Macedonian continent in Northern Greece. The host volcanic sequence of the mineralization comprises mylonitized rhyolitic to rhyodacitic lavas, pyroclastics, quartz‐feldspar porphyries, and cherty tuffs. A “white mica—quartz—pyrite” mineral assemblage characterizes the volcanic rocks in the footwall and hanging‐wall of massive sulfide ore layers, formed as a result of greenschist‐grade regional metamorphism on “clay‐quartz‐pyrite” hydrothermal alteration haloes. Massive ore lenses are usually underlain by deformed Cu‐pyrite and quartz‐pyrite stockworks. Most of the sulfide ore bodies have proximal‐type features. Ductile deformation and regional metamorphism have transformed many of the stockwork structures. The mineralization is characterized by high Zn, Pb, and Ag contents, while Cu and critical metals are low. Primary depositional textures, for example, layering, clastic pyrite, colloform, and atoll textures were identified. The overall textural features of the mineralization indicate it has undergone mechanical deformation. The most prominent features of the effects of metamorphism, folding and shearing, are modification of the ore body morphology toward flattened and boudinage structures and transformation of the ore textures toward the dominance of planar fabrics. Sulfur isotope analyses of sulfides along with textural observations are consistent with a dual source of sulfide sulfur. Sulfur isotope values for sphalerite, non‐colloform pyrite, galena, and chalcopyrite fall in a limited range from −1.6 to +4.8‰ (mean δ34S + 2‰), indicating a hydrothermal source derived from the reduction of coeval seawater sulfate in the convective system. Pyrites with colloform and atoll textures are characterized by a34S depletion, indicating a bacterial reduction of coeval seawater sulfate. The morphology of ore beds, the mineralogy, sulfide textures, and ore chemistry along with the petrology and tectonic setting of the host rocks can be attributed to typical of a bimodal‐felsic metallogenesis. Although similar in many respects to classic Kuroko‐type volcanogenic massive sulfide mineralization, it has some atypical features, like the absence of barite ore, which is possibly a result of significant temporal depletion in sulfate due to bacterial reduction, a conclusion supported by the widespread occurrence of colloidal and atoll textures of pyrite.

Geochemical characteristics of pyrite in the Dabaozhuang deposit in the Middle-Lower Yangtze River Metallogenic Belt, Eastern China

Dabaozhuang is a pyrite deposit in the Luzong Volcanic Basin, Eastern China, and has similar exhalation-sedimentary features to volcanic massive sulfide deposits (VMS), which commonly form in seawater. To better understand the ore-forming process of this special type of deposit, we employed SHRIMP-SI and LA-ICP MS to measure sulfur isotope and trace element compositions of anhydrite and four types of pyrite from the Dabaozhuang deposit. SHRIMP in situ sulfur isotope analysis indicates a narrow range in δ34S of anhydrite, 21.0–21.7‰, and variable ranges for pyrite, 9.9–10.7‰, for pyrite vein in the deep (Py I); −9.2 to 2.0‰, for cyclic annular and oval-shaped pyrite in massive ore (Py II); 3.1–5.3‰, for massive or disseminated pyrite in the footwall tuff and hematite (Py III); and −29.7 to 30.4‰, for euhedral and coarse pyrite in the carbonate cement (Py IV). δ33S and δ36S in four types of pyrite have no abnormal values, indicating that sulfur isotope fractionation is mainly controlled by thermochemical sulfate reduction (TSR). The higher δ34S values in type I pyrite and anhydrite indicate a mixing process of magmatic fluid and evaporates at depth. Py II and IV have negative δ34S data, indicating the formation temperature of pyrite decreases because of the mixing of lake water. δ34S values in Py III are close to magmatic sulfur, which shows the igneous sulfur (tuff) is an important sulfur source for the disseminated mineralization. Cobalt and Ni content also show that the formation temperature of Py I is highest, and Py IV is lowest. This research indicates that the “VMS-like” deposits could be formed in continental volcanic lakes and are genetically related to SO42−-rich IOA (iron oxide-apatite) deposits.