Ni Mineralization Research Articles

Prediction of hidden Au and Cu–Ni ores from depleted mines in Northwestern China: four case studies of integrated geological and geophysical investigations

Integrated geological and geophysical investigations were carried out in 26 active mines in Northwestern China during the period 2001–2006 to explore for hidden extensions of known ore bodies and to search for new mineralization. This paper presents four case studies from northwest China: the Kuoerzhenkuoa volcanogenic hydrothermal gold deposit, the Nanjinshan breccia-associated gold deposit, the Duolanasayi deposit, associated with a ductile–shear zone, and the Hulu magmatic Cu–Ni sulfide deposit. In these studies, detailed mine-scale geological studies were carried out to determine the location and controls on ore formation. Based on these investigations and a review of previous exploration data, genetic models for the deposits were evaluated, and specific new targets were generated. These target areas were tested with surface geophysical surveys using the Stratagem EH4 system, a hybrid-source magnetotellurics (MT) method. Analysis of the data obtained in the surveys identified geophysical target anomalies that were subsequently drilled. Many of these test holes demonstrate the presence of Au and Cu–Ni mineralization. Evaluation of the geological models was crucial in developing conceptual targets as a basis for surface geophysical surveys. These models established the most likely target areas where Au and Cu–Ni mineralization could occur, but they did not define the limits or the geometries of the mineralized zones. Hybrid MT surveys played an important role in defining the location of buried mineralized systems and in testing the validity of the conceptual targets. The resistivity cross-sections obtained by imaging the MT data established the boundaries and geometries of the host rocks, including the distribution of lithology, structures, alteration, and mineralization. The four case studies in this paper show how this integrated geological and geophysical approach was used successfully to discover hidden mineral deposits.

Chemical and mineralogical heterogeneity in the basal zone of the Partridge River Intrusion: implications for the origin of Cu–Ni sulfide mineralization in the Duluth Complex, midcontinent rift system

Copper–nickel sulfide mineralization in the Partridge River Intrusion of the 1.1 Ga Duluth Complex is restricted primarily to a 100 m thick zone near the base of the intrusion, which is heterogeneous at meter scales in terms of both sulfide contents and rock types, which include dunite, melatroctolite, troctolite, leucotroctolite, gabbro, olivine gabbro, gabbronorite, and rare norite. Olivine-rich troctolites and melatroctolites appear to have required mineral accumulation on a substrate, whereas augite troctolite and gabbros are thought to have formed via in situ crystallization of magmas ranging in composition from high-Al olivine tholeiite to high-Ti tholeiite. δ18O values of orthopyroxene-poor rocks in the Partridge River Intrusion range from 5.2 to 6.7‰. δ18O values of 6.7‰ are consistent with less than 20% contamination by high-18O metasedimentary country rock, either via devolatilization or local partial melting. Rocks with greater than ∼15% orthopyroxene, gabbronorites, and norites, are characterized by δ18O values in excess of 6.9‰, and required the assimilation of larger amounts of siliceous country rocks. Sulfur isotopic values in leucotroctolitic rocks that contain less than ∼400 ppm S and that overlie the basal zone range between −1.5 and 2‰, values that are consistent with those of mantle-derived sulfur. In contrast, δ34S values in the basal zone range from −1.4 to 10.5‰, where the 34S-enriched samples require an input of sulfur from metasedimentary country rocks. δ34S values of the rocks in the basal zone correlate with variations in olivine Fo content but not with S abundance. The wide range in δ34S values of rocks in the basal zone strongly suggests that magmas interacted with layers in the sedimentary country rocks that were themselves characterized by variable sulfide contents and δ34S values. The S isotopic data suggest that the heterogeneity observed in the basal zone results from the emplacement of relatively thin sheets of compositionally distinct magma. All rock types present in the basal zone can be produced as a result of variable degrees of fractionation of a parental high-Al olivine tholeiite, followed by varying degrees of contamination of derivative liquids by country rocks. The S-contamination process was essential for the development of Cu–Ni mineralization, and was restricted to the earliest stages in the development of the Duluth Complex at a time when volatile species such as S and H2O, and low-T partial melts of country rocks, were available to magmas.

Geochronology and petrogenesis of the post-orogenic Cu–Ni sulfide-bearing mafic–ultramafic complexes in Jilin Province, NE China

Northeastern (NE) China is a well-documented example of a collisional zone characterized by widespread post-orogenic granites and mafic–ultramafic complexes. Based on a study of the Hongqiling and Piaohechuan Cu–Ni sulfide-bearing mafic–ultramafic complexes in central Jilin province, we present geological, petrological, geochemical and geochronological data which indicates their post-orogenic origin. The Hongqiling complex comprises pyroxenite, olivine websterite, lherzolite, gabbro and leucogabbro. Zircon U–Pb SHRIMP analyses on a leucogabbro of the Hongqiling complex yield a weighted mean 206Pb– 238U age of 216±5 Ma. The Piaohechuan complex is composed of gabbro, pyroxenite and dolerite, exposed as dikes. A plagioclase-bearing pyroxenite has a U–Pb zircon weighted mean 206Pb– 238U age of 217±3 Ma, identical to that of the Hongqiling complex. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than the regional metamorphism (∼240 Ma) and syn-orogenic granitic magmatism (246±4 Ma). This suggests that these mafic–ultramafic complexes are post-orogenic in origin. The age data also indicated a short period of lithospheric stabilization of about 30 Ma after cessation of orogenic activity. Geochemical investigation indicates that the primary mafic magma was a lithospheric mantle-derived basalt resulting from the upwelling of asthenosphere due to lithospheric delamination during post-orogenic processes. The magmatic source was contaminated by a small amount of crustal material, and subsequent crystal fractionation resulted in the Cu–Ni mineralization. The widespread occurrence of mafic–ultramafic complexes in the Xing'an–Mongolian Orogenic Belt of NE China and in the Altay–Tianshan–Junggar Orogenic Belt of Northern Xinjiang indicates that mafic intrusions are an important magmatic suite that evolved during post-orogenic processes. Portions of this mafic magma could have underplated the lower crust, and served as the heat source for associated late-stage granitic magmas.

Comments on the paper “Ochreous laterite: a nickel ore from Punta Gorda, Cuba” by Oliveira et al.

The paper, “Ochreous laterite: a nickel ore from PuntaGorda, Cuba,” by Oliveira et al. (2001) presents acharacterization of oxidized nickel ore from the PuntaGorda deposit in the Moa district (eastern Cuba). Theauthors assume that the nickel ore derives from an ophioliticassociation (serpentinized ultramafic rocks, olivine gabbros,and plagiogranites) strongly affected by lateritization. Theynote that ‘no extensive study has so far been published aboutthe Ni mineralization in regard to the mineralogical andchemical nature of the ore’ and reach the conclusion thatnickel is associated with goethite and cobalt with manga-nese minerals. The authors find two ore types, Ni-rich(1.56–2.06%) and Ni-poor (0.24–0.96%), and infer that thetwo types are related to differences in the parent rocks.Oliveira et al. contend that the Ni-rich ore derives fromperidotites containing Ni-bearing orthopyroxenes and thatthe Ni-poor ore forms from peridotites containing Al-clinopyroxene depleted in Ni. Despite their interestingattempt, we believe these points require some criticalcomments that point to possible alternative interpretations.First, the Moa-Baracoa ophiolitic massif consists of alower unit of mantle tectonites made up of serpentinizedharzburgite with minor dunite, ‘impregnated peridotite’(plagioclase- and clinopyroxene-bearing peridotite), wehr-lite, and pyroxenite and a crustal sequence composed oflayered gabbro (olivine gabbro and gabbronorite) anddiscordant pillowed basalts and sediments of the Quivija´nFormation (Guild, 1947; Wadge et al., 1984; Ri´os andCobiella, 1984; Fonseca et al., 1985; Iturralde-Vinent, 1989,1996, 1998; Keer et al., 1999; Proenza et al., 1999a,b).Towards the top of the mantle tectonites, the harzburgitecontains increasing amounts of dunite, gabbro sills, andchromitite, which form elongated pseudotabular bodiesparallel to the foliation of the host harzburgite, as well asdiscordant dikes of gabbro and pegmatitic gabbro (Fig. 1).This upper zone has been considered as forming part of theMoho Transition Zone (MTZ) (Proenza et al., 1999a,b).Second, Oliveira et al. (2001) ignore many publishedstudies on the geological, mineralogical, and chemicalcharacteristics of the Cuban lateritic nickel deposits(Kudelasek et al., 1967; Vera, 1979; Formell and Oro,1980; Vershinin et al., 1984; Quintana-Puchol, 1985;Ostroumov et al., 1985, 1987; Cordeiro et al., 1987;Rojas-Puro´n et al., 1993; Rojas-Puro´n and Carballo, 1993;Capote et al., 1993; Almaguer and Zamarzry, 1993;Rojas-Puro ´n and Beyris, 1994; Rojas-Puron and Orozco,1995; Almaguer, 1995, 1996; Lavaut, 1998). These studiescontain extensive results about the Ni mineralization in theMoa district and conclude that Ni in ochreous laterite isassociated with goethite and Co with manganese minerals(asbolanes).Third, the differences in the mineralogical and chemicalcomposition of the Ni-rich and Ni-poor ores cannot beexplained by the presence of Ni-bearing orthopyroxene orNi-depleted, Al-rich clinopyroxene in the parent rock, asOliveira et al. (2001) conclude, because the Moa peridotitesare made up of only harzburgites and dunites (Proenza et al.,1999a,b), neither of which contains significant clinopyrox-ene. The average forsterite and NiO content of olivine in theharzburgites is 91.0 and 0.39 wt%, respectively, whereas indunites, these values are 91.5 and 0.38 wt% (Table 1). TheNi content of orthopyroxene is very low (NiO , 0.1 wt%),usually below the detection limit of the electron microprobe(Table 1). However, clinopyroxene-bearing harzburgites arevery scarce in the whole Moa-Baracoa massif. Therefore,the Ni-rich ore can only derive from harzburgite and dunite

Low cost catalytic sorbents for NO x reduction. 1. Preparation and characterization of coal char impregnated with model vanadium components and petroleum coke ash

Spanish coal, char and activated char doped with model vanadium components (V 2O 5 and NH 4VO 3) and petroleum coke ash (enriched in V, Fe, and Ni) were prepared and characterized as potential catalytic sorbents for NO x reduction. The phase-mineral and chemical composition, content and behavior (capture, retention, distribution, and redistribution) of transition metals, as well as morphogenesis, surface area, acid–base properties, surface active sites and oxidation–reduction transformations of the catalytic sorbents were characterized. It was found that minerals and phases such as anhydrite, calcite, clay minerals, pyrite, pyrrhotite, magnetite and fusinoid-type ingredients have a leading role for the behavior of loaded transition metals. Some original (pyrite, jarosite, shcherbinaite, coulsonite, trevorite, Ni oxide) and newly formed (pyrrhotite, magnetite, wuestite, hematite, paramontroseite, karelianite) Fe, V and Ni minerals in the catalytic sorbents are perspective redox indicators for the physicochemical conditions in such complex system. The data indicate that the V–Fe–Ni containing minerals dispersed onto and into the carbon support may be the most active catalytic sites. The preparation procedure that could provide the most favorable conditions for the production of effective and low cost catalytic sorbents for NO x reduction is also described.

Environmental impact of heavy metals (Fe, Ni, Cr, Co) in soils waters and plants of triada in euboea from ultrabasic rocks and nickeliferous mineralisation

Soil, water and vegetation samples were collected from the Triada area of Central Euboea and analysed for heavy metals in order to evaluate their environmental impact. The geology of the area studied includes ultrabasic rocks that are overlaid by Upper Cretaceous limestones whereas Fe–Ni mineralisation is intercalated between either the ultrabasic parent rocks or the karstified Jurassic/Triassic carbonates and the transgessive Upper Cretaceous limestones. All the samples were analysed for heavy metals by using atomic absorption spectroscopy. The heavy metal ranges (in μg g−1) for soils samples are: Ni 480–4000, Cr 240–2720, Co 40–208, Fe 24,000–380,000, Mn 46–1680, Pb 16–56, Zn 40–144, Cu 2–82. The values of soil samples of the Triada area are much higher than the values found for Ni, Cr, Co and Fe, in normal soils of the world. The heavy metal ranges (in μg L−1) for water samples are: Ni 19–24, Cr 19–476, Co <5, Fe <100, Mn <100, Mg 5.7–220.5, As 30–69, Cd <2, Pd <10, Zn 5–11, Cu 2–7. The water samples of the Triada area have Cr and Mg concentrations higher than the permittable values. The heavy metal ranges (in μg g−1) for vegetation samples are: Ni 1–135, Cr 0–24, Co 1–21.5, Fe 20–680, Mn 10–206, Cd 0–10, Pb 0–14, Zn 14–70, Cu 0–10.5. The vegetation samples of the Triada area have so high values of Ni, Cr and Co that are considered toxic. The intercorrelated elements Fe, Ni, Cr, Co of the Triada soils, waters and vegetation reflect their association with the ultrabasic rocks and with the Fe–Ni mineralisation.

Experimental proof of the distinct electronic structure of a new meteoritic Fe–Ni alloy phase

We provide an experimental proof that the so-called `paramagnetic phase’ seen in Fe–Ni-bearing meteorites has a very different electronic structure from that of all other known Fe–Ni minerals, in support of the recent proposal that it is a low moment phase and a new meteoritic mineral. 57 Fe Mössbauer isomer shift measurements, corrected for second-order Doppler shifts, give local electronic densities at the probe nuclei corresponding to a surplus local density of 0.42 electrons per Bohr radius cubed compared to the densities of all other Fe–Ni minerals and all known high-moment synthetic Fe–Ni alloys. This implies that the paramagnetic phase cannot simply be either Fe-rich high-moment face centered cubic phase (taenite) or atomically ordered Fe 3Ni, as previously proposed, and it represents an unprecedented situation where two minerals (the new low moment phase, antitaenite, and taenite) have the same crystal structure and can have the same composition but differ only in electronic structure and associated properties. We also report the bulk production by mechanical alloying of synthetic low-moment Fe–Ni material. These are the first observations of low moment Fe–Ni phases, giving insight into the conditions for metastability and the mechanisms of formation of these unusual alloys.

The Late Archaean bonanza: metallogenic and environmental consequences of the interaction between mantle plumes, lithospheric tectonics and global cyclicity

The Late Archaean records periods of intense magmatism and the development of prodigious metallogenic provinces of Ni, Fe, CuZn and Au deposits. In particular, the period 2.74-2.66 Ga represents one of the most widespread episodes of ultrabasic and basic volcanism preserved in the geological record, as well as anomalously widespread granitoid magmatism. Extensive assemblages of this age, which comprise komatiites and komatiitic basalts derived from mantle plumes, together with tholeiites and calc-alkalic volcanic rocks, are preserved on most Late Archaean cratons. Intense submarine volcanism in plume-like environments resulted in rich komatiite-hosted Ni mineralization in continental-margin basins, and CuZn sulphide mineralization in extensional volcanic arcs. Peak submarine magmatism was accompanied by marine transgression and thereby flooding of previously exposed continental crust. Elevated hydrothermal activity and widespread su☐ic conditions in submarine basins are reflected by sulphide-rich carbonaceous sedimentary rocks, that contain the organic remains of bacterial communities, and banded iron formations (BIF). A major episode of mesothermal gold mineralization accompanied accretionary tectonics, as metal-and carbon-rich submarine volcanic and sedimentary successions were subducted or incorporated into nascent continental crust by 2.59 Ga.Comparison with Neoproterozoic and Phanerozoic tectonic and metallogenic patterns indicates that the period 2.78-2.59 Ga represents the first half of an ∼ 360 m.y. global tectonic cycle. This period records the breakup of a supercontinent and the opening and closing of marginal basins along long-lived convergent margins of the external ocean to that supercontinent. Enhanced magmatic events between 2.74 and 2.66 Ga were most likely the result of intrabasinal mantle plumes and a subsequent global plume-breakout event. Together, the plume events were responsible for the extreme environmental conditions during the Late Archaean relative to both the preceding and succeeding periods of Earth history. Interactions between mantle plumes and long-lived convergent margins of a Pacific-type ocean were responsible for the prodigious metal inventory of Late Archaean granitoid-greenstone terranes. Extensive convergent-margin and plume magmatism during that period, coupled with episodic periods of low-angle subduction underplating by oceanic lithosphere, may also have been the cause of development of the buoyant, continental mantle lithosphere that is responsible for the preservation of these highly mineralized cratons. It is also likely that the bonanza metallogenic provinces in the Witwatersrand basin and Paleoproterozoic orogens of West Africa and Laurentia-Baltica reflect interactions of mantle plumes with long-lived convergent margins of the external ocean.

A late Archaean-Palaeoproterozoic (2.6 Ga) palaeosol on ultramafics in the Eastern Transvaal, South Africa

This article describes a palaeosol developed on Archaean (3.4 Ga) ultramafics and overlain by sedimentary rocks of the Chuniespoort Group (2.55 Ga). The palaeosol is thick, mature and complex, forming carapaces on palaeohills. From base to top it comprises four lithological units: (1) carbonated serpentinite; (2) black talc rock; (3) silcrete-dolocrete; (4) silcrete breccia in mudstone matrix. Petrographic and geochemical studies (major elements, plus V, Cr, Ni, Zn, Ga, Y, Zr, Nb, PGE and Th) indicate that units 1 to 3 represent former saprolites and silicified-carbonated saprolites with bedrock textures still preserved. Unit 4 has been more intensely leached, with some admixture of allochthonous sialic material, collapse of the original texture and concentration of the immobile elements. An irregular Ni mineralization in the bottom part of the profiles is described and compared with equivalent modern lateritic deposits. A high carbon content suggests the presence of a surficial mat of primitive micro-organisms which could have contributed to the stability of the palaeosol on the hilly topography and greatly enhanced the weathering rate. The presence of silcrete is indicative of a semi-arid climate, possibly with alternating wet and dry seasons, or of a dry period having succeeded a wet one. The absence of Fe oxides and the general deficiency of this element in the upper part of the profiles, taking into account that the soil was well drained and aerated, support the model of an atmospheric O 2 level much lower than at present by an order of two magnitudes.

Tourmalinite-associated Pb-Zn-Ag mineralization at Bottino, Apuane Alps, Italy; geologic setting, mineral textures, and sulfide chemistry

The Pb-Zn-Ag deposits of Bottino, Italy, are among the most significant in the Apuane Alps (NW Tuscany) mining district and were actively exploited in the past. The orebodies constitute a system of veins hosted within Paleozoic sedimentary and volcano-sedimentary sequences. These rocks were metamorphosed in the greenschist facies (350 degrees -450 degrees C, 3-4 kbars) during Tertiary Apenninic metamorphism (27-12 Ma). The orebodies are closely associated with tourmalinites and appear to be mostly conformable to the main wall-rock foliation (S 1 ) that developed during the first regional deformation (D 1 ). Locally, a relic pre-Apenninic foliation is recognizable both in the host rocks and in tourmalinites.The mineralogy of tourmalinites includes variable amounts of tourmaline, quartz, white mica, carbonates, chlorite, apatite, zircon, rutile, pyrrhotite, pyrite, arsenopyrite, and galena. Tourmalinites show a variable bulk-rock chemistry and are consistently enriched in Au, Ag, Sn, and W with respect to the host rocks. Tourmaline crystals show variable size and distribution, strong pleochroism, and irregular optical zoning. Their compositions belong to the schorldravite series and are similar to tourmalines from exhalative tourmalinites, whereas they differ significantly from granite-related tourmalines.The mineralogy of the ore veins is especially complex. Galena, sphalerite, pyrrhotite, arsenopyrite, pyrite, chalcopyrite, meneghinite, and Ag-rich tetrahedrite are the most widespread ore minerals. The occurrence of Ni minerals such as ullmannite and gersdorffite establishes a nickeliferous character for the Apuane Alps mining district, in contrast to other districts of the Tuscan metallogenic province.Textural features of the orebodies and ore minerals, and their inferred correlation with regional-scale deformational events, indicate that the mineralization at Bottino resulted from a complex, multistage process spanning at least the entire time of Apenninic metamorphism. Arsenopyrite geothermometry indicates an evolution of the ore-forming environment from temperatures close to peak metamorphic conditions ( approximately 450 degrees C), decreasing in a later stage to about 350 degrees C. The late appearance of monoclinic pyrrhotite replacing earlier hexagonal pyrrhotite indicates that temperatures eventually dropped to

Multigeneration pitchblende from the Midwest uranium – nickel deposit, northern Saskatchewan

Four generations of pitchblende and pitchblende alteration products have been identified in the ore-mineral assemblage of the Midwest deposit. Each generation is texturally and compositionally distinctive. The formation of each generation appears to have been preceded by an episode of fracturing and brecciation, indicating extensive reworking of the deposit with time. Microprobe analysis of each generation shows decreasing Pb and increasing Si, Ca, Al, and As with successive reworking events.The earliest pitchblende noted is botryoidal and contains more Pb than subsequent generations. The botryoids were fractured and altered in an episode of brecciation that was accompanied or followed by the introduction of fluids. Second-generation massive pitchblende and pitchblende alteration products (including coffinite and uranium arsenate) enclose altered fragments of first-generation pitchblende. Of the second-generation materials, this massive pitchblende contains slightly lower amounts of Pb than first-generation botryoidal pitchblende, and the alteration products of pitchblende contain substantially less Pb. Coffinite and some As-rich pitchblende contain water. A second episode of fracturing and partial dissolution of the earlier assemblages preceded precipitation of third-generation colloform pitchblende, which contains significantly less Pb than do previous generations. The fourth and youngest episode of uranium deposition is represented by disseminated pitchblende and coffinite and by pitchblende crust and veinlets. These last phases contain the least Pb and are enriched in many minor elements. All generations are accompanied by a variety of Co-bearing Ni minerals and by illite or sericite. Other important gangue minerals are quartz, hematite, siderite, calcite, and goethite.

Sulfide paragenesis in the Eastern Metals deposit, Montmagny County, Quebec

The Eastern Metals deposit, Montmagny County, Quebec, is characterized by two sub-parallel zones of mineralization approximately 400 ft. apart on the surface. The Ni minerals millerite, gersdorffite, and violarite have been identified in the North zone, and chalcopyrite is the ore mineral of the South zone. Sphalerite is present in each zone. The ores are localized in zones of silicification and carbonatization along the contact between a serpentinized peridotite and slate fingers penetrating into the SW. end of the peridotite. The mineralization is postulated to have come about by the dissolving of separate pods of copper and nickel sulfides that originated during the crystallization of the peridotite. The agent responsible for the solution and deposition of the sulfides was oxidizing solutions that accompanied the intrusion of granodiorite dikes. The minerals were deposited in the alkaline environment of the silica-carbonate zone. The sphalerite was derived from the surrounding sediments by solution by the same solutions that carried the Cu and Ni.