Dissertations / Theses on the topic 'Cu-PGE'

The Garson Ni-Cu-PGE deposit is located on the South Range of the 1850 Ma Sudbury structure along the contact between the Sudbury Igneous Complex (SIC) and the underlying metasedimentary and metavolcanic rocks of the Paleoproterozoic Huronian Supergroup. It comprises four ore bodies that are hosted by E-W-trending shear zones that dip steeply to the south. The shear zones formed as south-directed D1 thrusts in response to flexural-slip during regional buckling of the SIC. They imbricated the ore zones, the SIC norite, the underlying Huronian rocks and they emplaced slivers of Huronian rocks and anatectic breccia into the overlying Main Mass norite. Coexisting garnet-amphibole pairs yielded syn-D1 amphibolite facies metamorphic temperatures ranging from ~550°C to 590°C. The shear zones were coeval with the moderately southdipping South Range and Thayer Lindsley shear zones, which formed to accommodate the strain in the hinge zone as the SIC tightened with progressive D1 shortening. The SE limb of the SIC was overturned together with the D1 thrusts, which were then reactivated as steeply south-dipping reverse shear zones during syn-D2 greenschist metamorphism. Syn-D2 metamorphic titanite yield a U-Pb age of ca. 1849 ± 6 Ma, suggesting that D1 and D2 are part of a single progressive deformation event that occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to the colinear L1 and L2 stretching mineral lineations. Ore types consist mainly of pyrrhotite-pentlandite-chalcopyrite breccia ores, but also include pyrrhotite-pentlandite-chalcopyrite disseminated sulfide mineralization in norite, and syn-D2 quartz-calcite-chalcopyrite-pyrrhotite-pentlandite iv veins. In the breccia ores, matrix sulfides surround silicate rock fragments that have a strong shape-preferred orientation defining a pervasive foliation. The fragments are highly stretched parallel to the mineral lineations in wall rocks, suggesting that the ore bodies are zones of high strain. Pyrrhotite and chalcopyrite occur in piercement structures, in boudin necks between fragments, in fractures in wall rocks and in fold hinges, suggesting that the sulfides were mobilized by ductile plastic flow. Despite evidence of high strain in the ore zones, the sulfide matrix in D1 and D2 breccia ores show little evidence of strain as they consist predominantly of polygonal pyrrhotite aggregates, suggesting that they recrystallized during, or immediately after D1 and D2. However, rare elongate pyrrhotite grains aligned parallel to S2 are locally preserved only in D2 breccia ores. Exsolution of pentlandite loops along grain boundaries of elongate pyrrhotite formed S2-parallel pentlandite-rich layers in D2 breccia ores, whereas the pentlandite loops are multi-oriented in D1 contact breccia as they were exsolved along grain boundaries polygonal pyrrhotite. Because exsolution of pentlandite post-date D1 and D2, and that individual pentlandite grains neither have a shape-preferred orientation nor show evidence for cataclastic flow, the sulfides reverted to, and were mobilized as a homogeneous metamorphic monosulfide solid solution (mss) during D1 and possibly D2. This is in agreement with predictions from phase equilibria as the average Garson composition plots within the mss field in Fe-Ni-S ternary diagram at temperatures above ~400°C. Disseminated and breccia ores at Garson have similar mantle-normalized multi-element chalcophile patterns as undeformed contact-type disseminated and massive ore, v respectively, at the well known Creighton mine in the South Range. This suggests that the Garson ores are magmatic in origin and that their compositions were not significantly altered by hydrothermal fluids and deformation. The lack of variations in Ni tenors between the disseminated and breccias ores suggest that the R-factor was not the process controlling metal tenors because the disseminated sulfides do not consistently have higher metal tenors than the breccia ore. The breccia ores are enriched in Rh-Ru-Ir and are depleted in Cu-Pd-Pt-Au, in contrast to footwall-type ore at the nearby Garson Ramp mine which is enriched in the same metals. When Ni100, Rh100, Ir100, Pt100 and Pd100 are plotted against Cu100, the breccia and footwall-type ore analyses plot along model mss fractionation and sulfide melt model curves, suggesting that these two ore types are related by mss fractionation. In summary, the Garson breccia ores are mss cumulates that settled quickly at the base of the SIC via a gravity filtration process, and were mobilized as a metamorphic mss by ductile plastic flow during D1 and D2. Despite minor local hydrothermal mobilization of some metals, the study confirms findings from other studies that highly deformed Ni-Cu- PGE deposits, such as the Garson deposit, can provide important information on the genesis of the deposits.

The Morrison deposit, located at the Levack mine in the City of Greater Sudbury, is a footwall-type Cu-Ni-platinum-group-element (PGE) deposit hosted within a zone of Sudbury Breccia in the Archean Levack Gneiss Complex beneath the North Range of the Sudbury Igneous Complex. It consists of sharp-walled, sulfide-rich veins that are enriched in Cu-Pt-Pd-Au relative to contact-type mineralization and can be subdivided based on vein geochemistry, mineralogy, texture, and morphology into a pyrrhotite-rich upper domain, a chalcopyrite-rich lower domain, and a pyrrhotite equal to chalcopyrite middle domain. All domains contain steeply to vertically dipping first-order sulfide veins, irregular and discontinuous second-order sulfide veins, and disseminated sulfides in country rocks. First- and second-order veins can be further subdivided into inclusion-free veins typically within Sudbury breccia matrix or along clast-matrix boundaries, and very irregular and inclusion-rich veins associated with leucosomes in mafic gneiss clasts and granophyric-textured dikes. First-order veins consist of pyrrhotite > chalcopyrite = pentlandite > magnetite in the upper domain, pyrrhotite = chalcopyrite > pentlandite > cubanite > magnetite in the middle domain, and chalcopyrite >> pentlandite > pyrrhotite = cubanite > magnetite in the lower domain. Second-order veins consist of pyrrhotite = chalcopyrite > pentlandite > magnetite and chalcopyrite = millerite = pentlandite in the middle domain, and chalcopyrite >> millerite, millerite > chalcopyrite, bornite >> chalcopyrite, and millerite > bornite > chalcopyrite in the lower domain. Second order veins are adjacent to and in contact with epidote, amphibole, chlorite, carbonate, quartz, and magnetite alteration minerals. Sulfide mineralization in the Morrison deposit is similar to other footwall mineralization associated with the SIC. The veins appear to have been emplaced preferentially into zones of Sudbury Breccia that were within ~400m of the basal contact of the SIC, because that lithology is more permeable and because those zones are within the thermal aureole of the cooling SIC permitting penetration of sulfide melts. The mineralogical, textural, and geochemical zoning in the chalcopyrite-pentlandite-pyrrhotite-rich parts of the Morrison deposit are best explained by partial fractional and/or equilibrium crystallization of MSS and ISS. Bornite ± millerite-rich mineralization are interpreted to have formed by reaction of residual sulfide melts with wall rocks, consuming Fe and S to form actinolitemagnetite- epidote-chlorite-sulfide reaction zones and driving the sulfide melt across the thermal divide in that part of the Fe-Cu-Ni-S system to crystallize borniteSS ± milleriteSS. Gold-Pt-Pd appear to have been more mobile than other metals, forming localized zones of enrichment, although it is not clear yet whether they were mobile as Au-Pt-Pd-Bi-Te-Sb-rich melts or aqueous fluids.

The Sakatti Cu-Ni-PGE (platinum group elements) deposit is a newly discovered mineral deposit in northern Finland. The deposit is a magmatic sulphide hosted in an ultramafic intrusion in the Central Lapland Greenstone Belt. The major lithologies and styles of mineralisation of the deposit are characterised and defined in this project and their origin investigated. The host rock is composed primarily of olivine with forsterite content between 0.85 and 0.91 and a Ni content between 3000-3700 ppm. This suggests that the olivine is undepleted with respect to Ni and has not been derived from a sulphide-saturated melt. The intrusion sits in a plagioclase-picrite and the locus of the deposit occurs at a change in gradient that occurs when the intrusion transgresses to a stratigraphically higher lithology. Sulphur isotope analysis shows that the Sakatti deposit has consistent δ34S values 2.6 ± 2.4 ‰. This is not consistent with the regional Matarakoski schists contributing S to the deposit. The deposit has unusually low Ni/Cu values, particularly the shallower portions. Magnetite trace element analysis, PPGE/IPGE values and Ni isotope analysis presented suggest that this is due to sulphide fractionation and loss of early fractionating Ni-rich sulphide cumulates. The PGE mineralogy in the Sakatti deposit is exclusively PGE tellurides, derived from sulphide melt. The dominance of tellurides leads to a wide array of moncheite-merenskyite-melonite compositions that is not seen elsewhere globally. A model is presented for the formation of the deposit where earlier Ni-rich cumulates are lost at an earlier stage in the conduit-like intrusion and remobilised by later silicate melt that does not re-equilibrate with the sulphides.

The Garson Ni-Cu-PGE deposit is located on the South Range of the 1850 Ma Sudbury structure along the contact between the Sudbury Igneous Complex (SIC) and the underlying metasedimentary and metavolcanic rocks of the Paleoproterozoic Huronian Supergroup. It comprises four ore bodies that are hosted by E-W-trending shear zones that dip steeply to the south. The shear zones formed as south-directed D1 thrusts in response to flexural-slip during regional buckling of the SIC. They imbricated the ore zones, the SIC norite, the underlying Huronian rocks and they emplaced slivers of Huronian rocks and anatectic breccia into the overlying Main Mass norite. Coexisting garnet-amphibole pairs yielded syn-D1 amphibolite facies metamorphic temperatures ranging from ~550°C to 590°C. The shear zones were coeval with the moderately southdipping South Range and Thayer Lindsley shear zones, which formed to accommodate the strain in the hinge zone as the SIC tightened with progressive D1 shortening. The SE limb of the SIC was overturned together with the D1 thrusts, which were then reactivated as steeply south-dipping reverse shear zones during syn-D2 greenschist metamorphism.Syn-D2 metamorphic titanite yield a U-Pb age of ca. 1849 ± 6 Ma, suggesting that D1 and D2 are part of a single progressive deformation event that occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to the colinear L1 and L2 stretching mineral lineations. Ore types consist mainly of pyrrhotite-pentlandite-chalcopyrite breccia ores, but also include pyrrhotite-pentlandite-chalcopyrite disseminated sulfide mineralization in norite, and syn-D2 quartz-calcite-chalcopyrite-pyrrhotite-pentlandite iv veins. In the breccia ores, matrix sulfides surround silicate rock fragments that have a strong shape-preferred orientation defining a pervasive foliation. The fragments are highly stretched parallel to the mineral lineations in wall rocks, suggesting that the ore bodies are zones of high strain. Pyrrhotite and chalcopyrite occur in piercement structures, in boudin necks between fragments, in fractures in wall rocks and in fold hinges, suggesting that the sulfides were mobilized by ductile plastic flow. Despite evidence of high strain in the ore zones, the sulfide matrix in D1 and D2 breccia ores show little evidence of strain as they consist predominantly of polygonal pyrrhotite aggregates, suggesting that they recrystallized during, or immediately after D1 and D2. However, rare elongate pyrrhotite grains aligned parallel to S2 are locally preserved only in D2 breccia ores. Exsolution of pentlandite loops along grain boundaries of elongate pyrrhotite formed S2-parallel pentlandite-rich layers in D2 breccia ores, whereas the pentlandite loops are multi-oriented in D1 contact breccia as they were exsolved along grain boundaries polygonal pyrrhotite. Because exsolution of pentlandite post-date D1 and D2, and that individual pentlandite grains neither have a shape-preferred orientation nor show evidence for cataclastic flow, the sulfides reverted to, and were mobilized as a homogeneous metamorphic monosulfide solid solution (mss) during D1 and possibly D2. This is in agreement with predictions from phase equilibria as the average Garson composition plots within the mss field in Fe-Ni-S ternary diagram at temperatures above ~400°C. Disseminated and breccia ores at Garson have similar mantle-normalized multi-element chalcophile patterns as undeformed contact-type disseminated and massive ore, v respectively, at the well known Creighton mine in the South Range. This suggests that the Garson ores are magmatic in origin and that their compositions were not significantly altered by hydrothermal fluids and deformation. The lack of variations in Ni tenors between the disseminated and breccias ores suggest that the R-factor was not the process controlling metal tenors because the disseminated sulfides do not consistently have higher metal tenors than the breccia ore. The breccia ores are enriched in Rh-Ru-Ir and are depleted in Cu-Pd-Pt-Au, in contrast to footwall-type ore at the nearby Garson Ramp mine which is enriched in the same metals. When Ni100, Rh100, Ir100, Pt100 and Pd100 are plotted against Cu100, the breccia and footwall-type ore analyses plot along model mss fractionation and sulfide melt model curves, suggesting that these two ore types are related by mss fractionation. In summary, the Garson breccia ores are mss cumulates that settled quickly at the base of the SIC via a gravity filtration process, and were mobilized as a metamorphic mss by ductile plastic flow during D1 and D2. Despite minor local hydrothermal mobilization of some metals, the study confirms findings from other studies that highly deformed Ni-Cu-PGE deposits, such as the Garson deposit, can provide important information on the genesis of the deposits.

Large Igneous Provinces (LIPs) form during short-lived pulses of extensive magmatic activity. LIPs are known for their ability to affect global climate as well as for their Ni-Cu-PGE ore potential. A key factor that controls the intensity of the climate impact of a LIP and its ore potential is the assimilation of volatile-rich sedimentary host rocks. Magmas of the High Arctic Large Igneous Province (HALIP), exposed in the Arctic, intruded volatile-rich black shales, carbonates and evaporites in the Canadian Arctic Islands, offering a great opportunity for studying magma-sediment interaction. The purpose of this study is to test whether assimilation of sedimentary sulphide can promote sulphide immiscibility in magma and thus aid formation of Ni-Cu-PGE ore bodies. This is done by analysing sulphur isotopes in pyrite grains hosted in a HALIP dolerite sill, which was emplaced into black shale, by using Secondary Ion Mass Spectrometry (SIMS). Four dolerite samples are analysed; two coming from the lower contact margin of the sill, one from 60 cm into the sill and one sample from a basaltic vein at the upper contact margin of the sill. A total of 14 pyrite grains (n = 246 individual SIMS spot analyses) were analysed for their sulphur isotope ratios. The results of the SIMS analyses show that all analysed sulphides have highly negative δ34S values ranging from -19.5 to -5.7‰ (average δ34S = -8.2 ± 0.83‰, 2SD), which therefore differ largely from that of the primitive mantle (0 ± 1.8‰). In order to put our four analysed dolerite samples into a broader context, δ34S data of our sulphides are compared with whole-rock δ34S and δ18O data from Hare Fiord shale and dolerite samples. The δ34S values of the sulphide samples from the sill typically trend toward the negative sulphur isotope composition of the sulphides in the surrounding shale, and the shale surrounding the sill experiences a loss of 32S near the contact of the sill. This indicates that sedimentary light sulphur (32S) has been locally incorporated into the sill by the surrounding shale, resulting in negative δ34S values in the magmatic sulphides. Since sulphide immiscibility in the Hare Fiord sill was triggered by assimilation of sulphur from host rock shale, the igneous rocks of the HALIP may be prospective for Ni-Cu-PGE mineralization, though more studies are needed. Furthermore, our results suggest that incorporation of crustal sulphur increased the volatile budget of HALIP magmas, which therefore could have contributed to a deterioration of the environmental conditions during the emplacement of the HALIP.
Stora magmatiska provinser (på engelska Large Igneous Provinces, LIPs) är vulkaniska event då enorma mängder magma avsätts över en väldigt stor yta under ett, i ett geologiskt perspektiv, kort tidsspann. Dessa stora vulkaniska utbrott har väckt stort intresse då de är samtida med flera av de största massutdöendena i jordens historia, men också för att en viss typ av sulfidmalm rik på nickel, koppar och platinametaller (Ni-Cu-PGE malmer) ofta förekommer i provinsernas magmagångar och magmakammare. En viktig faktor som till stor del avgör en magmatisk provins påverkan på klimatet och potentiella malmförekomster är inkorporering av sedimentära bergarter till magman som, när de hettas upp, kan frigöra gaser rika på svavel och kol. I Kanadas arktiska öar trängde magma tillhörande den högarktiska magmatiska provinsen (HALIP) in i svart skiffer, karbonater och evaporiter, som är sedimentära bergarter rika på flyktiga ämnen. Denna magmatiska provins erbjuder därför stora möjligheter till att studera interaktionen mellan magma och sedimentära bergarter. Syftet med denna studie är att testa om inkorporering av sedimentärt svavel kan främja bildandet av sulfidsmälta i magma och därigenom bidra till bildandet av sulfidmalmer. Detta görs genom att analysera svavelisotoper i sulfidmineral i prover från en magmagång, som trängde in i en skifferformation, tillhörande den högarktiska magmatiska provinsen i norra Kanada. Genom att analysera svavelisotopkvoten (δ34S) i sulfidmineral kan man få information om huruvida svavlet i mineralen är av sedimentärt ursprung (där skiffer generellt har negativa δ34S värden) eller om svavlet har δ34S värden liknande de från manteln (som har δ34S värden runt 0‰), vilket i så fall skulle innebära att magman inte har inkorporerat sedimentärt svavel. Genom att använda masspektrometri av typen SIMS analyseras totalt 14 sulfidmineralkorn (n = 246 individuella SIMS punkter) för deras svavelisotopkvoter. Resultatet av studien visar att alla analyserade sulfidmineral har mycket negativa δ34S värden mellan -19.5 och -5.7‰ (med ett δ34S medelvärde på -8.2 ± 0.83‰, två standardavvikelser). Genom att jämföra våra δ34S värden med δ34S och δ18O värden för andra prover från både magmagången och den omgivande skiffern kunde vi se att δ34S värdena för sulfidmineralen i de yttre delarna av magmagången har liknande negativa värden som den omgivande skiffern, och att δ34S värdena för skiffern närmast magmagången är mer positiva. Detta tyder på att sedimentärt svavel i kontakten mellan magmagången och skiffern har blivit inkorporerat i magman från den omgivande skiffern. Våra resultat tyder därför på att sulfidmineralen i våra prover från magmagången bildades genom assimilering av svavel från den omgivande skiffern. Detta innebär i sin tur att den kanadensiska högarktiska magma provinsen potentiellt kan vara en källa för sulfidmalm, även om ytterligare studier behövs. Dessutom visar våra resultat att inkorporering av sedimentärt svavel förmodligen ökade de vulkaniska gaserna i magman, vilket kan ha bidragit till klimatförändringar relaterade till den vulkaniska aktiviteten av den högarktiska magmatiska provinsen.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação em Geologia, 2018.
Submitted by Fabiana Santos (fabianacamargo@bce.unb.br) on 2018-08-21T18:49:57Z No. of bitstreams: 1 2018_CláudiaTharisAugustin.pdf: 5210708 bytes, checksum: 99f53f29a2d8ff706c6e29a34801ff12 (MD5)
Approved for entry into archive by Raquel Viana (raquelviana@bce.unb.br) on 2018-08-21T19:18:25Z (GMT) No. of bitstreams: 1 2018_CláudiaTharisAugustin.pdf: 5210708 bytes, checksum: 99f53f29a2d8ff706c6e29a34801ff12 (MD5)
Made available in DSpace on 2018-08-21T19:18:25Z (GMT). No. of bitstreams: 1 2018_CláudiaTharisAugustin.pdf: 5210708 bytes, checksum: 99f53f29a2d8ff706c6e29a34801ff12 (MD5) Previous issue date: 2018-08-21
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).
Inserido no contexto do Arco Magmático de Goiás, o Complexo máfico-ultramáfico Mangabal está associado a um conjunto de diversas intrusões neoproterozóicas formadas durante o a orogenia brasiliana, no centro do Brasil. Este trabalho tem como objetivo apresentar a evolução magmática e o metamorfismo do Complexo máfico-ultramáfico Mangabal. Para tanto foram realizados trabalhos de campo, descrição e amostragem de testemunhos de sondagem, descrições petrográficas em seções delgadas e polidas, química mineral, imageamento em microscópio eletrônico de varredura (MEV) e análises químicas isotópicas de isótopos de Sm e Nd. O Complexo Mangabal está inserido na Zona de Cisalhamento São Luís dos Montes Belos e é composto por dois corpos máfico-ultramáficos acamadados metamorfizados. O membro norte apresenta aproximadamente 6 km²; já o membro sul, distante aproximadamente 2 km do anterior, possui aproximadamente 29 km² de área em superfície. Ambos os corpos exibem a mesma mineralogia, sequência de cristalização ígnea e composição química mineral. A estratigrafia do Complexo de Mangabal pode ser dividida em três zonas principais: i. Zona Máfica Inferior, localizada na porção basal da intrusão, composta por norito adcumulático; ii. Zona Ultramáfica, caracterizada por dunito e harzburgito e iii. Zona Máfica Superior, predominantemente de composição norito, com porções isoladas de dunito feldspático. O complexo apresenta sequência de cristalização composta por: Olivina + Cromo-Espinélio > Olivina + Ortopiroxênio > Ortopiroxênio + Plagioclásio > Clinopiroxênio. A mineralogia primária das rochas é frequentemente substituída por mineralogia metamórfica, devido ao metamorfismo heterogêneo sobreposto ao Complexo. Apesar da recristalização mineralógica, tal transformação metamórfica muitas vezes preserva as texturas magmáticas. O metamorfismo sobreposto ao complexo atingiu fácies metamórfica anfibolito de alta pressão, marcada pela presença da paragênese cianita-ortoanfibólio-hornblenda-plagioclásio, atingindo pressões de aproximadamente 8.5 kbar e temperaturas de até aproximadamente 750 °C. A mineralização primária de Ni-Cu-EGP sulfetado ocorre em rochas máficas e ultramáficas do complexo, porém a deformação superimposta no complexo pode localmente remobiliza-la. A mineralização é predominantemente do tipo disseminada, tanto nas rochas máficas quanto ultramáficas, porem localmente ocorrem em textura maciça.
Inserted in the context of the Goiás Magmatic Arc, the mafic-ultramafic complex of Mangabal is associated with several neoproterozoic mafic-ultramafic intrusions formed during the Brasiliano Orogeny in the center of Brazil. This study included fieldwork data, systematic drill-core sampling, mineral chemistry and Sm-Nd isotopic geochemistry in order to better understand the petrology of the mafic-ultramafic complex of Mangabal and associated Ni-Cu-PGE mineralization. The Mangabal Complex is inserted in the São Luís dos Montes Belos Shear Zone and is composed of two metamorphosed mafic-ultramafic bodies. The northern limb is approximately 6 km² and is stretched towards E-W; already the south member, distant approximately 2 km of the previous one, is approximately 10km wide by 5.5km long. Both bodies exhibit the same mineralogy, igneous crystallization sequence and mineral chemistry. The stratigraphy of the Mangabal Complex can be divided into three main zones: i. Lower Mafic Zone, located in the basal portion of the intrusion, composed by addcumulatic norite; ii. Ultramafic Zone, characterized by dunite and harzburgite and iii. Upper Mafic Zone, consisting predominantly of norite composition, with isolated portions of feldspathic dunite. The complex has the following crystallization: Olivine + Chromium-Spinel> Olivine + Orthopyroxene> Orthopyroxene + Plagioclase > Clinopyroxene. The primary mineralogy is often replaced due to an overlapping heterogeneous metamorphic transformation. Despite the mineralogical recrystallization, metamorphic transformation often preserves the magmatic textures. The metamorphism superimposed on the complex reached high-pressure amphibolite facies, marked by the presence of kyanite-ortoamphibole-hornblende, reaching pressures of approximately 8.5 kbar and temperatures up to 780 ° C. The primary Ni-Cu-EGP sulfide mineralization occurs in mafic and ultramafic rocks of the complex, but the deformation in the complex can locally remobilize the sulfides and, particularly, nickel and palladium. The mineralization is predominantly disseminated, occurring in both mafic and ultramafic rocks, but massive sulfide levels occur locally, mainly in metamorphic portions.

The Caledonian mafic and ultramafic intrusions of the Grampian region of N.E. Scotland are a suite of synorogenic tholeiitic plutons of mid-Ordovician Age. They include layered cumulates, granular gabbronorites, quartz biotite norites and xenolithic contact facies lithologies. They postdate two regional deformation events in the enclosing Late Precambrian Dalradian metasediments, but are themselves locally deformed by a major regional ductile shear zone system. A detailed study of the Huntly-Knock area was undertaken combining geological mapping, petrological, geochemical and stable isotope techniques. In the study area, layered peridotitic to gabbroic cumulates, transitional cumulate types, granular gabbronorites quartz biotite norites and complex xenolithic contact facies rock types are present as a series of disrupted bodies formed by multiple intrusive events and subsequent deformation of a laccolithic and sheeted intrusive complex. Progressive cryptic fractionation trends are observed from basal peridotites to quartz biotite norites in the 'roof' of the intrusion. The chemistry and mineralogy of the rocks places them in the Lower and Middle Zone of the regional Younger Basic 'stratigraphy', although isolated pockets of Upper Zone may occur. Fine grained disseminated Fe-Ni-Cu sulphides are widespread throughout the mafic and ultramafic rock types. Richer sulphide concentrations locally occur as: gabbronorite hosted disseminated to massive bodies in the structurally complex, Littlemill-Auchencrieve contact zone; disseminated horizons within cumulates; disseminated to submassive graphite-rich pods in pyroxenitic pegmatites. The sulphide assemblage is dominated by pyrrhotite with minor pentlandite and chalcopyrite. Sulphide textures are attributed to magmatic processes with local modification by ductile deformation and hydrothermal reworking. Field, textural and Cu/Cu+Ni relations of certain submassive-massive sulphides is consistent with their derivation from an ultramafic parent. Maximum Ni and Cu levels are 3.02% and 6.46% respectively. The highest combined Pt+Pd+Au values occur in remobilised net sulphide (574ppb) and graphitic pyroxenite (700ppb). These metal values are generally low and comparable to other orogenic Caledonian intrusions. Sulphide immiscibility occurred many times during cooling of the tholeiitic parent magma(s), however early sulphide melts are generally of most economic importance. While there is abundant evidence for magma/country rock interaction, only locally is there evidence for involvement of metasediment sulphur, the system being dominated by a magmatic signature. In the Littlemill-Auchencrieve contact zone, crustal involvement may have been the principal factor controlling sulphide immiscibility. Subsequent hydrothermal reworking within ductile shear zones under amphibolite facies metamorphic conditions modified metal values. Depletion, especially of Au, Pt and Pd was mainly observed but local significant zones of enrichment may also be present.

Tese (doutorado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação em Geologia, 2014.
Submitted by Ana Cristina Barbosa da Silva (annabds@hotmail.com) on 2015-04-30T19:31:10Z No. of bitstreams: 1 2014_JonasMotaeSilva.pdf: 23053512 bytes, checksum: 47ee6942746173aecae50290d8979fb8 (MD5)
Approved for entry into archive by Ruthléa Nascimento(ruthleanascimento@bce.unb.br) on 2015-05-04T14:05:23Z (GMT) No. of bitstreams: 1 2014_JonasMotaeSilva.pdf: 23053512 bytes, checksum: 47ee6942746173aecae50290d8979fb8 (MD5)
Made available in DSpace on 2015-05-04T14:05:23Z (GMT). No. of bitstreams: 1 2014_JonasMotaeSilva.pdf: 23053512 bytes, checksum: 47ee6942746173aecae50290d8979fb8 (MD5)
Complexos máficos, máfico-ultramáficos e ultramáficos são os típicos hospedeiros de mineralizações magmáticas sulfetadas de níquel, cobre e elementos do grupo da platina (PGE). Em 2009 a Votorantim Metais descobriu o depósito Ni-Cu- (PGE) sulfetado de Limoeiro no leste do estado do Pernambuco. Motivado pela descoberta, esta tese objetivou entender a gênese e evolução geológica do Complexo Limoeiro e sua mineralização de Ni-Cu-(PGE) nas escalas local e regional. Para isso foram realizados trabalhos de campo, mapeamento geológico, descrição de testemunhos de sondagem, interpretação de seção de sondagem, amostragem seletiva de rochas frescas e de mineralizações, petrografia óptica, química de rocha total, química de minério, química mineral, imageamento em microscópio eletrônico de varredura (MEV), análises químicas pontuais por espectrômetro de massa acoplado a feixe laser (LA-ICP-MS), imagamento de zircões por cátodo luminescência (CL) e datação U-Pb. A mineralização do depósito Limoeiro é essencialmente disseminada [pirrotita (~70%), calcopirita (~15%) e pentlandita (~15%)] e hospeda-se no topo de uma intrusão tubular (Sequencia Superior), sub-horizontal, concentricamente zonada (harzburgito no centro e ortopiroxenito na borda) com centenas de metros na transversal e alguns quilômetros na longitudinal. Esta intrusão faz parte de um sistema de condutos que ocupa uma área de 70 x 15 km, orientado na direção ENE-WSW, totalizando cerca de 150 km lineares de rochas intrusivas. A estratigrafia da intrusão é formada por pelo menos quatro pulsos magmáticos principais (Baixo Cr, Superior, Zona de Transição e Inferior), sendo cada um deles distintos em termos de fracionamento e mineralização na região do depósito. Apesar disso, o magma parental formador de cada pulso magmático é similar entre eles. Trata-se de um magma toleítico picrítico de alto MgO com forte assinatura de contaminação crustal. O progressivo aumento da razão Cu/Pd (de 5200 para 5800) das rochas da Sequencia Superior em harmonia com a diminuição do tenor evidencia fluxo horizontal do magma para leste. Todo o complexo foi metamorfisado na fácies granulito baixo (750-800ºC em 634±6 Ma) o que promoveu a recristalização dos zircões, dos sulfetos de metal base e provavelmente a fusão dos bismutoteluretos portadores de PGE. O tipo de intrusão conolítica como de Limoeiro é típico de intrusões relativamente rasas em ambientes compressivos. Não foi alcançada uma idade precisa para cristalização da intrusão que hospeda o depósito Limoeiro, mas correlação entre razões Th/U e idades U/Pb em zircões metamorfisados sugerem uma idade de ca. 800 Ma. Nesta idade é possível que o sul da Província Borborema e sua continuidade na Africa experimentaram de modo concomitante extensão com abertura de assoalho oceânico e colisão continental. Ao mesmo tempo em que se desenvolvia crosta oceânica na parte oeste (Riacho do Pontal), na parte leste dominava ambiente colisional compressivo (Limoeiro). Em uma escala global a intrusão de Limoeiro é contemporânea à quebra do supercontinente de Rodínia e a existência de uma superpluma que tornou o manto extraordinariamente quente. _______________________________________________________________________________________ ABSTRACT
Magmatic sulfide nickel, copper and platinum-group elements (PGE) are typically hosted by mafic, mafic-ultramafic and ultramafic complexes. The Limoeiro Ni- Cu-(PGE) sulfide deposit was discovered in 2009 by Votorantim Metais in the eastern part of Pernambuco state, northeastern Brazil. Driven by this discovery, this thesis was undertaken to understand the geological evolution of the Limoeiro Complex and the genesis of its Ni-Cu-(PGE) deposit in local and regional scales. The methods involved field work, geological mapping, drill core descriptions, drilling section interpretation, fresh rock and ore sampling, optical petrography, whole rock and ore chemistry, mineral chemistry, electronic petrography using MEV, trace element mineral chemistry using LA-ICP-MS, zircon petrography using CL and U-Pb dating. The mineralization is essentially disseminated sulfide [pyrrhotite (~70%), chalcopyrite (~15%) and pentlandite (~15%)] and is hosted in the upper part (Upper Sequence) of a tubular, sub-horizontal, concentrically zoned (harzburgite core surrounded by orthopyroxenite shell) intrusion, of scale of hundreds meters in crosssection by a few kilometers long. This intrusion is part of a conduit system (150 linear km of intrusive rocks), which occurs in an area of 70 x 15 km elongated in the ENEWSW direction. The intrusion stratigraphy can be divided into at least four main magmatic pulses (Low-Cr, Upper, Transition Zone and Lower), which differ in terms of fractionation and mineralization-content. However, their parental magmas are similar, and can be classified as a high-MgO tholeiitic picrite with intense crustal contamination. The progressive increase of Upper Sequence Cu/Pd ratio (5200 to 5800) together with metal tenor decrease suggests horizontal magma flux to the east. The whole complex was metamorphosed in lower granulite facies (750-800ºC at 634±6 Ma), which resulted in the zircons and base metal sulfides recrystallization and probably in the melt of the PGE-bearing bismuthotelurides. Compressive geological settings are commonly associated with chonolithic intrusions, such as the Limoeiro Complex. The metamorphic zircons within the complex show a positive correlation between U/Pb age and Th/U ratio, which alow infer crystallization age of ca. 800 Ma for Limoeiro. During that time the Southern part of Borborema Province and its African continuity have experienced contrasting tectonic settings. The Western side was rifting and forming oceanic crust (Riacho do Pontal), whereas in the Eastern counterpart collisional and compressive settings (Limoeiro) prevail. In a global scale, the Limoeiro intrusion emplacement was coeval to the Rodinia supercontinent break-up and to a superplume activity, which overheated the mantle at ca. 800 Ma.

The Giant Mascot Ni-Cu-PGE deposit remains British Columbia’s only past-producing nickel mine (1958-1974) with ~4.2 Mt of ore grading 0.77% Ni, 0.34% Cu, minor Co, Ag, and Au, and unreported platinum group elements (PGE). The deposit is part of a new class of ‘convergent margin’ Ni-Cu-PGE sulphide deposits containing orthopyroxene and magmatic hornblende. The ultramafic-mafic intrusions that host these deposits have relatively small footprints, generally less than ~10 km2 (e.g., Portneuf-Mauricie Domain, Québec; Huangshandong, China; Aguablanca, Spain), and they are becoming increasingly important economic resources globally. Zircon was successfully separated from feldspathic ultramafic rocks and yield a weighted ²⁰⁶Pb/²³⁸U age of crystallization for the Giant Mascot ultramafic intrusion of ca. 93 Ma (CA-TIMS, n=8), thus constraining the age of mineralization and distinguishing it as one of the world’s youngest Ni deposits. The Giant Mascot intrusion is a crudely elliptical, 4×3 km plug composed of ultramafic arc cumulates (olivine-orthopyroxene, hornblende-clinopyroxene) that intruded the Late Cretaceous Spuzzum pluton. Sub-vertical pipe-like, lensoid and tabular bodies (n=28) host orthomagmatic Ni-Cu-PGE mineralization as disseminated, net-textured, semi-massive, and massive ores consisting of pyrrhotite, pentlandite, chalcopyrite, minor pyrite, troilite, and Pt-Pd-Ni bismuthotellurides. The sulphides have high tenors (3-14 wt% Ni, 0.1-17.1 wt% Cu, 84 ppb-5 ppm total PGE) and distinct iridium-group PGE concentrations that represent varying stages of monosulphide solid solution fractionation and subsequent metal enrichment of two magma types forming the Western and Eastern mineralized zones. Sulphur isotopes (n=34) for sulphides in ultramafic rocks reveal δ³⁴S values (-3.4 to -1.3‰) lighter than typical mantle values and overlap with analyses from locally pyritiferous Settler schist (-5.4 to -1.2‰). Sulphide saturation in the Giant Mascot parental magma(s) was triggered in response to 1) reduction of an oxidized, mantle-derived arc magma, 2) addition of external sulphur and silica by assimilation of Settler schist and Spuzzum diorites, and 4) fractional crystallization. The presence of high-tenor sulphides indicates that orogenic Ni-Cu-PGE deposits may be of greater significance to future exploration globally than previously assumed.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

The Early Jurassic (>188-185 Ma) Turnagain ultramafic-mafic body, a composite Alaskan-type intrusion in the Northern Cordillera of northern British Columbia, hosts a significant nickel-cobalt resource (Horsetrail zone, 1842 Mt @ 0.21 wt. % Ni and 0.013 wt. % Co), and minor copper-platinum group element (Cu-PGE) mineralization. The 24 km² Turnagain intrusion comprises four temporally, spatially, and chemically distinct ultramafic-mafic phases that include dunite, wehrlite, clinopyroxenite, hornblendite and diorite. The 1.5 x 2 km DJ/DB zone, an area of Cu-PGE enrichment that was discovered through soil geochemistry and drilling of a previously under-explored area of the intrusion, is located 2.5 km northwest of the nickel resource. Clinopyroxenites and hornblendites with minor wehrlite are the major rock types of the DJ/DB zone. Orthomagmatic sulphide mineralization ranges from predominantly disseminated sulphides (<5 vol. %) to rare massive ores, and contains chalcopyrite and pyrrhotite, with minor pyrite and pentlandite, and trace arsenides (nickeline), arsenic-antimony sulphides (cobaltite, gersdorffite), and platinum group minerals (PGM; sperrylite, sudburyite, Pd-melonite, testibiopalladite). Sulphide and PGM mineralization underwent minor remobilization related to post-magmatic hydrothermal alteration. The DJ/DB zone represents the products of a magmatic event that is younger than the magmatism that produced the Ni-Co-rich mineralization. Sulphide saturation of Mg-rich arc parent magmas through assimilation of sulphur and carbon from pyrite- and graphite-bearing metasedimentary rocks surrounding the intrusion lead to the formation of the DJ/DB zone following extensive olivine fractionation (i.e., Ni depletion). The distinct nature of Cu-PGE mineralization in the DJ/DB zone indicates that Ni-Cu-PGE sulphides in Alaskan-type intrusions may have more significant exploration potential in convergent margins than previously considered.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

A temporal and spatial relationship between plume magmatism, cratonic lithosphere and the occurrences of orthomagmatic Ni-Cu and platinum-group element (PGE) sulphide mineralisation has been documented in the literature. However the underlying causes for this correlation have yet to be resolved – is there an inherent feature of the cratonic lithosphere and its mantle ‘keel’ that controls mineralisation? Or is this correlation purely a preservational bias in the geological record? Scotland has experienced multiple tectono-magmatic events and provides an ideal testing ground, or ‘framework’, in which to assess the role of lithospheric mantle on chalcophile element (Ni and Cu) and precious metal (PGE and Au) abundances through time. Given the well-documented geological history of the region (including several suites of mantle xenoliths), coupled with exploration campaigns in Greenland (with which Scotland has comparable geology), this thesis aims to assess the contributions and influences of lithospheric mantle vs. asthenospheric mantle during melting and mineralisation. It also evaluates the Ni-Cu-PGE mineralisation potential for Scotland, particularly in a Noril’sk-type conduit-hosted setting within the British Palaeogene Igneous Province (BPIP). The earliest major tectono-magmatic event following cratonisation of the North Atlantic Craton (NAC) occurred c. 2.4 Ga during Palaeoproterozoic extension, forming the maficultramafic Scourie Dyke Swarm. Despite evidence for lithospheric mantle melting at this time, the subcontinental lithospheric mantle (SCLM) below the Scottish portion of the NAC did not become severely depleted in sulphides or PGE. Instead, spinel lherzolite mantle xenoliths from this region (e.g., Loch Roag) record an influx of carbonatite-associated sulphides at this time, enriched in PGE, and providing a deeper indication of continental extension that may be correlated to carbonatitic intrusions in Greenland. Subsequent collision and orogenesis of the NAC in the late Palaeoproterozoic (c. 1.9 to 1.7 Ga) represents a second significant tectonomagmatic event, recorded in the Scottish SCLM as sulphide (re-)melting and formation of discrete Pt-sulphide minerals (cooperite). Hence the lithospheric mantle here became appreciably enriched in precious metals during the Palaeoproterozoic, but crucially this preserved multiple co-existing populations of sulphides, distinct in their petrographic setting and geochemistry. Cratonic basement and associated mantle lithosphere are absent in the southern terranes of Scotland. This provides a direct comparison between lithospheric mantle geochemistry for Archaean-Palaeoproterozoic terranes north of the Great Glen Fault vs. Palaeozoic terranes south of the Great Glen Fault. Rifting of Rodinia and opening of the Iapetus Ocean in the late Neoproterozoic thus marks a significant change in geodynamic setting. This is especially apparent in the concentration of cobalt in lithospheric mantle sulphides, which appears to be inherently linked with the formation and/or later destruction (subduction) of oceanic crust during the Grampian event of the Caledonian orogeny. The impingement of the proto-Icelandic mantle plume initiated in the Palaeogene at the base of the NAC lithospheric mantle keel of Scotland and Greenland. The earliest Palaeogene magmas are enriched in Pt (i.e., have a high Pt/Pd ratio), whilst subsequent magmas associated with the opening of the Atlantic Ocean have successively lower Pt/Pd ratios. High Pt/Pd ratios are therefore coincident with magmas that have intruded through cratonic lithosphere. The SCLM at the margin of this region is known to be Pt-enriched (with cooperite) and therefore the changing Pt/Pd ratio of North Atlantic Igneous Province magmas suggests a fundamental interaction between the mantle plume and pre-enriched SCLM. Thus, whilst the concentration of metals, particularly Ni and Cu, is largely based on the high degree of asthenospheric mantle melting associated with the plume itself, the ratio of precious metals, such as Pt/Pd, can be strongly influenced by SCLM geochemistry. Overall, the intricate subtleties of metasomatic signatures recorded by mantle xenolith sulphides (or populations of sulphides) could allow for metallogenic ‘mapping’ of the upper mantle. This may identify areas of geochemical and mineralogical ‘preconditioning’, and together with geophysical constraints such as major lithospheric lineaments, it may be possible to establish the craton-specific fertility of a region. Finally, in order for orthomagmatic sulphide mineralisation to occur, magmas must achieve sulphur saturation in the upper crust, forming an immiscible sulphide liquid and thereby collecting PGE and chalcophile elements, possibly to economic grades. Thus a crucial part of assessing the mineralisation potential of a region must entail an investigation into the causes and locations of S-saturation. Given that crustal sulphur contamination is a common trigger for magmatic S-saturation, this thesis establishes the first S-isotopic (δ34S) framework for western Scotland in order to identify areas of sulphur contamination in the BPIP. In Scotland, the most readily available and S-rich rocks occur in the Mesozoic Hebrides Basin. Sulphur contamination of BPIP rocks is widespread and both S-saturation and S-undersaturation can be observed, suggesting that the region may be extremely fertile for orthomagmatic Ni-Cu-PGE mineralisation. By reconstructing the Hebrides Basin stratigraphy we can assess locations of contamination, even if these are above the current level of exposure (and since removed by erosion), and in some situations sulphide liquid sinking may be demonstrated, suggesting further possibilities for mineralisation present ‘up-stream’ in magmatic conduits. In conclusion, the Scottish BPIP represents a new exploration frontier not yet identified by industry for orthomagmatic Ni-Cu-PGE mineralisation. The conclusions are based on approximately 500 rock samples from across Scotland, which have been analysed for major elements and over thirty trace elements (including PGE) and S-isotopes. All data are available on an accompanying CD.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, Pós-Graduação em Geologia, 2017.
Submitted by Priscilla Sousa (priscillasousa@bce.unb.br) on 2017-11-07T13:40:28Z No. of bitstreams: 1 2017_AllanFrüchting.pdf: 3810773 bytes, checksum: 3203c84b2e476ab2127cea32ce9a5da2 (MD5)
Approved for entry into archive by Raquel Viana (raquelviana@bce.unb.br) on 2018-01-05T21:32:04Z (GMT) No. of bitstreams: 1 2017_AllanFrüchting.pdf: 3810773 bytes, checksum: 3203c84b2e476ab2127cea32ce9a5da2 (MD5)
Made available in DSpace on 2018-01-05T21:32:04Z (GMT). No. of bitstreams: 1 2017_AllanFrüchting.pdf: 3810773 bytes, checksum: 3203c84b2e476ab2127cea32ce9a5da2 (MD5) Previous issue date: 2018-01-05
A descoberta da intrusão ultramáfica de Limoeiro foi guiada por uma anomalia magnética, parcialmente associada a uma anomalia gamaespectrométrica circular com baixos valores de K-eTh-eU. Os primeiros dados de campo para validação das anomalias geofísicas mapearam rochas ultramáficas e exatamente no centro da depleção de K-eTheU, foi encontrada o primeiro indício de mineralização sulfetada, representada por um gossan rico em Ni-Cu-PGE. A porção aflorante e parcialmente erodida da intrusão ultramáfica apresenta 800m de diâmetro. Os produtos derivados do campo magnético anômalo mostram a continuidade da intrusão sob os paragnaisses dos Complexo Surubim. Mediante os indicativos desta continuidade e de indícios de mineralização em superfície, optou-se pela aplicação do método geofísico eletromagnético aéreo no domínio do tempo (VTEM). A modelagem e inversão de dados geofísicos multifonte somada a integração de dados geológicos de campo apontaram as primeiras interseções sulfetadas da mineralização de Ni-Cu-PGE. A mineralização associada aos corpos mineralizados intitulados de Piçarra, Retiro e Parnazo da intrusão ultramáfica de Limoeiro é constituída de vários níveis métricos e contínuos de sulfeto maciço (3% do volume do depósito), envelopados por sulfetação disseminada (97% do volume do depósito). Este resultado mostra que a exploração geofísica por métodos magnéticos, eletromagnéticos e elétricos é bastante eficaz para este tipo de mineralização. A assembleia de minerais de minério dos corpos de Limoeiro composta de pirrotita (Po), pentlandita (Pn), calcopirita (Cp) mostra que a mineralização possui uma assinatura magnética, condutiva, densa e polarizável. Os resultados do modelamento e inversão de dados geofísicos, incluindo algoritmo de filamentos Maxwell e inversão de resistividade em profundidade (RDI) para os dados eletromagnéticos, e inversão tipo MVI-Voxi dos dados magnetométricos aéreos e terrestres permitiram caracterizar a potencialidade dos corpos e a geometria do depósito. Após a descoberta dos corpos mineralizados e a validação com sondagem exploratória, o método elétrico da polarização induzida espectral (SIP) e a magnetometria terrestre foram aplicados e são considerados fundamentais na delineação dos corpos de minério e mapeamento dos condutos magmáticos. Os resultados petrofísicos serviram para validar os modelos e inversões de dados geofísicos, e também permitiram definir que alguns métodos não aplicados anteriormente podem ser empregados na busca de novos corpos de minério, como por exemplo a gravimetria gradiométrica. Os estudos detalhados de todos os dados disponíveis associado ao modelo geológico e tipo de mineralização, permitiu definir uma estratégia de exploração geofísica de sucesso para busca de novos depósitos magmáticos sulfetados como Limoeiro na Província Borborema.
The discovery of the Limoeiro ultramafic intrusion was guided by a magnetic anomaly that partly overlap a circular gamaspectrometric anomaly with low values of K-eTh-eU. The first field data for validation of the geophysical anomalies mapped the intrusion. In the center of the K-Th-U depletion, there was evidence of sulfide mineralization, represented by a gossan rich in Ni-Cu-PGE. The exposed and partially eroded portion of the ultramafic intrusion has 800 m in diameter. The derivate products of residual magnetic field mapped the extension of this the intrusion under the paragneisses of the Surubim Complex. Because of this continuity and evidence of surface mineralization, the Versatile Time Domain Electromagnetic (VTEM) airborne geophysical method was used, along with modeling and inversion of multi-source geophysical data combined with the integration of field geological data, leading to the first sulfide intersections of the mineralization of Ni-Cu-PGE. The mineralization associated with the Piçarra, Retiro and Parnazo orebodies of the Limoeiro ultramafic intrusion has multiple metric and continuous levels of massive sulfide (3% of the deposit volume), enveloped by disseminated sulfidation (97% of the deposit volume), thus rendering geophysical exploration by magnetic, electromagnetic and electrical methods quite effective. The assemblage of ore minerals of the Limoeiro orebodies, pyrrhotite (Po), pentlandite (Pn), and chalcopyrite (Cpy) makes the mineralization magnetic, conductive, dense and polarizable. Some steps of modeling and inverting geophysical data were applied, including Maxwell filament algorithm and resistivity-depth image (RDI) inversion for electromagnetic data and Magnetic Vector Inversion (MVI)-Voxi inversion of airborne and ground magnetometric data. After discovery of the mineralized orebodies, the electric method of spectral induced polarization (SIP) and ground magnetometry were important for delineating orebodies and mapping magmatic conduits. The petrophysical results validated the geophysical data models and inversions, making it possible to determine that some methodologies not previously applied can be used to search for new orebodies (e.g gradiometric gravimetric method). The detailed study of all available data associated with the geological model and type of mineralization allowed us to define a successful strategy of geophysical exploration in search of new magmatic sulfide deposits such as Limoeiro in Borborema Province.

The Nebo-Babel Ni-Cu-platinum-group element (PGE) magmatic sulphide deposit, a world-class ore body, is hosted in low-MgO, tube-like (chonolithic) gabbronorite intrusion in the West Musgrave Block, Western Australia. The Nebo-Babel deposit is the first significant discovery of a nickel sulphide deposit associated with the ca. 1078 Ma Giles Complex, which is part of the Warakurna large igneous province (LIP), now making the Musgrave Block a prime target for nickel sulphide exploration. The Musgrave Block is a Mesoproterozoic, east-west trending, orogenic belt in central Australia consisting of amphibolite and granulite facies basement gneisses with predominantly igneous protoliths. The basement lithologies have been intruded by mafic-ultramafic and felsic rocks; multiply deformed and metamorphosed between 1600 Ma and 500 Ma. The Giles Complex, which is part of the Warakurna LIP, was emplaced at ca. 1078 Ma and consists of a suite of layered mafic-ultramafic intrusions, mafic and felsic dykes and temporally associated volcanic rocks and granites. The Giles Complex intrusions are interpreted to have crystallised at crustal depths between 15km and 30km and are generally undeformed and unmetamorphosed.

Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: It is widely accepted that sulphide is the carrier and concentrator of PGEs during magmatic mineralization episodes in the Merensky Reef (MR). PGE concentration peaks and sulphide volume percent peaks are very closely correlated. Koegelenberg, (2011), showed in an experimental investigation that sulphide movement through a cumulate silicate and cumulate oxide pile behave in such a way that sulphide melt gets trapped in chromitite layers. When looking at the compositional distribution of sulphide within the MR it is noted that not only does the sulphide volume percent varies with MR stratigraphy but also the sulphide composition. Sulphide composition is more Cu-rich in the chromitite layers and more Fe and Ni dominated in the hanging wall to the chromitite layers. Until now the more Cu-rich assemblage of the chromitite layers are accepted to be of a sulphide melt composition compared to the Fe and Ni dominated Monosulphide Solid Solution or MSS composition in the hanging wall. In this study we used an experimental approach with a sulphide starting composition thought to exist as the parental sulphide composition of the MR to investigate the phase relations with changing temperature. It is found that the sulphide composition in the chromitite layers represent a sulphide melt composition at 1000 ± 50ºC. At 1000ºC, 50% of the sulphide system would exist as a melt. This Cu-rich melt would have segregated from the MSS and be trapped in the chromitite layer. Also at 1000ºC the partitioning of the Pt would have induced a secondary enrichment step of the Pt concentration in melt through the partitioning of Pt between a sulphide melt and a sulphide solid phase. The experimental evidence in this study points towards a possible source for the parental sulphide magma to the MR, which could have been a slightly Cu enriched mantle sulphide composition. Also, the secondary enrichment of Pt through sulphide melt fractionation at 1000ºC plays an important role in the shaping of the ore body.
AFRIKAANSE OPSOMMING: Dit word wydliks aanvaar dat die sulfied fraksie van die Merensky Rif (MR) die draer en die konsentrasie agent is vir Platinum Groep Elemente (PGE`s) gedurende mineralisasie episodes. PGE konsentrasie en sulfied volume persentasie is op `n hoogtepunt by gelyke stratigrafiese posisies in the MR. Koegelenberg, (2011), het deur middel van eksperimente bewys dat `n sulfied smelt deur `n voorafbestaande kumulaat laag kan beweeg en dat veranderende fisiese eienskappe tussen sulfied smelt en silikaat kristal en sulfied smelt en chromiet kristal, die sulfied smelt sal opsuig en verhoud om verder deur te suipel. Dit is egter oplettend dat nie net die sulfied volume persentasie varieer as `n funksie van die MR stratigrafie nie, maar ook die sulfied samestelling. Die meer Cu-ryke sulfied samestelling in die chromiet lae word aanvaar as `n sulfied smelt fraksie en die meer Fe en Ni dominerende sulfied samestelling in die oorhangende wandgesteentes verteenwoordig die Monosulfied Vaste Oplossing (MVO) soliede fase. In hierdie studie maak ons gebruik van eksperimentele petrologie tesame met `n begin samestelling verteenwoordigend van die oorsprong sulfied samestelling van die MR, om die fase verwantskappe van hierdie spesifieke samestelling te ondersoek. Dit word gevind dat die fraksionering tydens die vorming van die MR plaasgevind het by ongeveer 1000 ±50 C. By hierdie temperatuur is 50% van die sisteem teenwoordig as `n smelt fase. Hierdie Cu-verykte smelt was daartoe instaat om deur die silikaat laag te suipel, geskei te raak van die Fe en Ni dominerende MVO en vasgevang te word in die chromiet lae. Hierdie fraksionering van die sulfied smelt het ook `n sekondêre effek gehad op die verspreiding van Pt tussen sulfied smelt en sulfied soliede fases. Hierdie eksperimentele bewyse dui eerstens op die moontlikheid van `n sulfied smelt in die MR wat sy oorsprong vanuit `n effense Cu-verykte mantel bron kan hê, en tweedens op die belangrikheid van `n sekondêre proses vir Pt re-distribusie tydens die vorming van die MR.

The Marathon PGM-Cu deposit is hosted by the Coldwell alkaline complex, which consists predominantly of gabbro and syenite and was emplaced at 1108 Ma as part of the Mid-Continent Rift System. Mineralization at the Marathon PGM-Cu deposit is hosted by the Two Duck Lake Gabbro (TDLG), a fresh olivine-bearing gabbro. The Marathon deposit contains several zones of mineralization including the Basal Zone, the Main Zone and the W-Horizon. The W-Horizon is a high-grade PGE zone characterized by low S, low Cu/Pd and high Cu/Ni. The sulphide mineral assemblage is predominantly chalcopyrite and bornite. This contrasts with the Main Zone where the dominant sulphide mineral assemblage is chalcopyrite and pyrrhotite. The Main Zone contains higher S, higher Cu/Pd and shows a decrease in Cu/Pd and pyrrhotite/chalcopyrite from base to top. Four drill holes were selected for detailed analysis to characterize the W-Horizon style of mineralization. Detailed petrographic study of the pristine and largely unaltered TDLG shows that wide spread hydrothermal alteration is not responsible for the mineralization. Detailed outcrop mapping shows that the TDLG intruded as a series of multiple intrusions in a dynamic magmatic system. Geochemical studies through the W-Horizon show that the mineralization is not the result of crystallization in a layered intrusion. The results of geochemical assays and electron microprobe analysis of olivine grains show that the chemistry through the TDLG hosting the W-Horizon is erratic. This data supports the TDLG intruding as a series of sills in a dynamic conduit environment. The calculated sulphide metal tenors for the W-Horizon are higher than can be explained by closed system R Factor models. Multistage dissolution upgrading in an open system is examined as the process forming the W-Horizon. This model is able to produce the sulphide metal tenors observed in the W-Horizon. Sulphur loss also affects grades and tenors and was examined through geochemical and petrological data. The change in sulphide mineral assemblage from a pyrrhotite and chalcopyrite (S-rich) to chalcopyrite and bornite (S-poor) supports S-loss. Whole rock S and Se contents are also analyzed to investigate S loss, a lower S/Se indicates that sulphur has been removed from the system. Average S/Se values are ~800 for the W-Horizon, ~1980 for the Main Zone and ~1700 in unmineralized samples. The very low S/Se observed within the W-Horizon supports S-loss. Sulphur loss in a dynamic magmatic conduit system is proposed for the formation of the W-Horizon mineralization. In this model sulphur undersaturated basaltic magma interacted with an immiscible sulphide liquid in a magma conduit, resulting in the dissolution of sulphide into the basaltic melt and PGE enrichment.

The Bird River sill (BRS) is composed of layered mafic-ultramafic intrusive bodies which intruded the Bird River greenstone belt in southeastern Manitoba. Layered intrusions, such as those that collectively make-up the BRS, are important hosts to base and precious metal deposits. This study was initiated to examine and develop an emplacement model for the western half of the BRS and to establish the controls on Cr-Ni-Cu-PGE mineralization. The BRS intrusions were emplaced through multiple-magmatic injections into different stratigraphic levels in the Lamprey Falls Formation. It is interpreted that the central BRS intrusions are connected and represent a single conduit system. The BRS and the Lamprey Falls Formation are overlain by the metasedimentary rocks of the Peterson Creek Formation and are overturned. The stratigraphy of the BRS is divided into four series which are from the base upwards: 1) marginal mafic series, 2) ultramafic series, 3) transition series, and 4) mafic series. All significant concentrations of Cr-Ni-Cu-PGE are contained in the ultramafic series. Mineralization is magmatic in origin with significant Ni-Cu and PGE remobilization associated with late felsic magmatism. Ni-Cu remobilization is also associated with mineralized shear zones that cross-cut the BRS and Lamprey Falls Formation. The sulphur source could not be determined unambiguously based on sulphur isotopes alone but the δ34S values of the BRS intrusions suggests that the sulphur in the BRS is magmatic in origin and that two of the BRS bodies may have assimilated external sulphur. The findings of this investigation have considerable economic implications. The model that each BRS body is an individual intrusion implies each body may contain its own style of mineralization. Secondly, the Page body of the BRS is interpreted to represent a turbulent magmatic environment and to be the first intrusion to form at the lowest stratigraphic level. The magmas that formed the stratigraphically higher BRS intrusions are believed to have passed through the Page intrusion. Therefore, the Page body is an excellent exploration target as it represents a turbulent environment in which significant amounts of primitive magma have passed through which are two key factors in the formation of Ni-Cu-PGE deposits.

North Range low-sulfide mineralization is dominantly hosted by Sudbury breccia, with amphibole-plagioclase equilibrium metamorphic temperatures of 440 to 533 ± 75oC, produced by the SICs thermal aureole. Mineralization led to increases in the bulk halogen content of the host Sudbury breccia and the formation of Ni-enriched ferromagnesian silicates. South Range low-sulfide mineralization is typically hosted by metabasalts of the Huronian Supergroup. Garnet-biotite-plagioclase-quartz geothermobarometry produced equilibrium metamorphic conditions of 513 to 645 ± 50oC and 2.0 to 7.7 ± 1.0 kbar, probably corresponding to a late-Penokean overprint of peak Blezardian/Penokean metamorphism. Silicates associated with South Range mineralization are compositionally similar to the host rock equivalents and no alteration selvage is commonly observed due to subsequent recrystallization. Platinum-group minerals (PGM) from the North Range comprise platinum and palladium tellurides and bismuth-tellurides, with Sb-bearing palladium bismuth-tellurides and sperrylite from the South Range. Kotulskite-sobolevskite from the North Range shows a previously unreported Ag-Pd substitution, with michenerite from irregular veinlet style mineralization showing the substitution of Se and Sb for Bi. Two unknown PGMs were identified from the South Range, along with kotulskite-sobolevskite-sudburyite crystals displaying extensive Te-Bi-Sb solid-solution not noted before at Sudbury. A new Se-bearing variant of pilsenite was identified at McKim. Polyphase aggregates from both Ranges indicate that Bi-Te melts may have been widespread at some stage postdating the emplacement of the main magmatic sulfides. Normalized plots for low-sulfide mineralization show enrichments in the precious and semimetals relative to contact and sharp-walled vein mineralization. This enrichment has resulted in elevated concentrations of Ag and Se in chalcopyrite and Pd+Ag and Se in pentlandite from the North Range. The mass balance for North Range samples found that a significant fraction of Ag and Se occurs in sulfides with all other elements preferring discrete phases. A substantial fraction of Pd is hosted by pentlandite on the South Range, with gersdorffite also a major host despite its low abundance. The enrichments observed reflect the formation of low-sulfide mineralization from a fractionated sulfide liquid and hydrothermal fluids that have interacted with a fractionated sulfide source, and suggest that the precious and semimetals behave incompatibly with crystallizing sulfide.