Dissertations / Theses on the topic 'Lithogeochemistry'

Porphyry copper deposits (PCDs) typically have large alteration haloes that extend several kilometers from economic mineralization providing a geochemical footprint potentially an order of magnitude larger than the deposit. The Paleocene (64±2 Ma) Los Morteros batholith comprises four granodiorite units and hosts four syn-mineralization porphyry units. These units are interpreted as the product of four magmatic differentiation cycles with three magmatic recharges. Alteration assemblages observed within the system include potassic, propylitic and phyllic, with intensities varying between weak to moderate for potassic and phyllic alteration, and weak to strong for propylitic. Lithogeochemical characterization and quantification of alteration is an important exploration tool that has the potential to lead to exploration success. Two hundred and ninety-six surface rock samples were collected in a grid covering 65 km² centered over the Relincho PCD in the Atacama region, Chile to assess the suitability of surface rock lithogeochemistry as a medium for lithological and alteration characterization. Aqua regia ICP-MS, pressed pellet XRF, and fusion-ICP results, combined with shortwave infrared (SWIR) spectra, alkali feldspar staining, petrography and field observations were used to classify lithological units and identify and quantify alteration. Data evaluation and modeling is completed through the use of exploratory data analysis, simple mass balances and molar element ratios (MER) complimented by hand and thin-section observations and SWIR analyses. Gain-loss variations are consistent with spatial element distributions indicating: the addition of SiO₂, K₂O, Ag, Cu and Mo and loss of CaO, Na₂O during potassic alteration; and the addition of Na₂O and loss of SiO₂ during propyltic alteration. Wavelengths of SWIR chlorite features indicate that chlorite is more Fe-rich proximal to mineralization and Mg-rich distally. Simple and molar element ratios are used as proxies for the potassic, propylitic and phyllic alteration assemblages. From these ratios, alteration indices are calculated. The potassic index (K₂O/Th) and propylitic-phyllic index ((18Ca + 14Na + 25K)/(2Si + 7Al + 4(Fe + Mg)) identify and quantify potassic, phyllic and propylitic alteration. Alteration thresholds derived from probability plots indicate that these indices would identify the Relincho deposit as a potential PCD exploration target at a sample spacing of up to 2000 m. Supplementary materials: http://hdl.handle.net/2429/50971<br>Science, Faculty of<br>Earth, Ocean and Atmospheric Sciences, Department of<br>Graduate

The San Antonio Gold Mine, at Bissett, Manitoba, was a major precious metals producer. Over the history of the mine more than 45 thousand kilograms (1.35 million ounces) of gold and 6 thousand kilograms (194 thousand ounces) of silver were produced. The mine is in the Archean Rice Lake Greenstone Belt of the Superior Province. Ore zones are structurally controlled within extensional stockwork veins and shear veins, which are primarily restricted to one basaltic unit. The purpose of this study is to describe the mine site lithologies, particularly the auriferous host rock, and to examine lithogeochemical patterns within the mine. Key objectives of the research were; i) to establish hydrothermal alteration patterns, ii) to detail the effects of igneous differentiation on the chemistry of the gold hosting SAM Unit, and iii) to define a suite of elements that can be useful as gold pathfinders in future exploration. The SAM Unit, host to most of the productive veins on the property, represents a sequence of basalt flows with thin interflow sediments. The lower part of the SAM Unit is a single flow member that has undergone differentiation by crystal settling of olivine, plagioclase and pyroxene from the melt. Around the large gold bearing extensional stockwork veins in the SAM Unit, both visible and cryptic alteration can be detected. An examination of XRF whole rock chemical analyses, using Gresens (1967) mass balance methods, indicate that a 5 percent volume increase and multi-element enrichment occurs in a halo (envelope) about gold rich zones, as compared to unaltered host rock. Visible (megascopic) alteration zones underwent a 10 percent volume increase. Albitization of wallrock is the dominant alteration type. Multi-element ICP analysis patterns were studied, revealing discrete populations and elemental groupings associated with ore zones, halos and host rocks. Silver, arsenic and tungsten are the most sensitive pathfinder elements for gold. The halo zones are marked by an enrichment of the base metals, copper, lead and zinc, whereas both halos and ore zones exhibit elevated values for sodium, potassium, and barium. The significance of the alteration element suites and presence of halos is in enhancing the ability to recognize mineralized structures where gold values are sporadic. In the orientation study case, the halos effectively doubled the width of the exploration target. Potential for gold exploration has also been identified for the North Basalt Unit, the Gabrielle Unit and Unit 'A' in the minesite area. These are competent volcanic units that reacted in a similar manner to the SAM Unit to regional tectonism. An ancillary objective of the research was to examine the variation of gold with depth in the San Antonio Gold Mine. It is the author's finding that gold values in the lowest levels of the mine (Domain III), where the bulk of the current reserves are situated, should yield grades as rich as the historical recovery from the upper levels (Domain I).<br>Science, Faculty of<br>Earth, Ocean and Atmospheric Sciences, Department of<br>Graduate

In exploration, a lithogeochemical approach can be used to aid the characterisation of rocks surrounding metamorphosed and hydrothermally altered deposits. Accurate description of the geological setting of deposits is crucial for understanding the ore forming processes and identifying targets for exploration. The Svärdsjö Zn-Pb-Cu deposit is located in the heavily mineralised and metamorphosed Bergslagen ore province of south-central Sweden. The deposit and surrounding minor occurrences were actively mined for over 500 years, producing more than 1 Mt of Zn-Pb-Cu-Ag massive sulphide ore. The combination of strongly metamorphosed and hydrothermally altered rocks in Svärdsjö makes geological interpretation challenging. Therefore, an approach combining lithogeochemical and petrographic methods is used in this study. The characterisation of the rocks and hydrothermal alteration surrounding the deposit allowed for an interpretation of ore formation and its implications for further exploration in the Svärdsjö area. The results verified that the Svärdsjö mineralisations are hosted by 2–15 m thick dolomitic marble units, commonly altered to skarn. Surrounding the deposit are subvolcanic intrusions and volcanoclastic rocks of mainly dacitic composition. The combined approach also helped identifying a strong to intense hydrothermal chlorite-sericite alteration enveloping the mineralised marble units and resulted in large mass gains of Fe and Mg whereas Na was depleted. Multiple episodes of alteration and metamorphism are evident from cross-cutting relationships with less altered dykes and overprint by metamorphic minerals such as cordierite and anthophyllite. An ore formation model involving sub-seafloor volcanic-associated replacement is suggested for the Svärdsjö deposit based on (i) the presence of a zoned hydrothermal alteration system within a volcanoclastic rock sequence and (ii) the irregular stratabound sulphide lenses hosted by thin marble units in the centre of the alteration system. Additionally, it is inferred that the stratabound nature of the deposit is caused by the neutralisation of a hot acidic fluid, resulting in precipitation of the sulphides within the marble. Finally, two geochemically distinct lithological units have been identified adjacent to the mineralised zones, providing new, larger exploration targets in the area. Mass change calculations reveal that Fe and Mg enrichment and Na depletion are useful vectors towards mineralisation, with detectable changes extending for up to 100 m from the mineralised lenses. These findings showcase the usefulness of the incorporation and careful interpretation of lithogeochemical data when exploring for metamorphosed hydrothermal ore deposits in mineralised provinces of the Fennoscandian Shield or elsewhere in the world.

The Cirque deposit is one of several Devono-Mississippian stratiform sediment-hosted Ba-Pb-Zn-Ag deposits in the Akie Zn-Pb district of northeastern British Columbia. It has drill indicated reserves of 32.2 million tonnes grading 7.9% Zn, 2.1% Pb, and 47.7 g/tonne Ag. The "ore" zone is a syngenetic exhalite deposit. Its deposition, however, was but one of many wide-ranging "ore"-related events that dominated sedimentation in the shale basin. These "ore"-related events include exhalative activity, influxes of turbidites and increased organic productivity. Many details of the "ore"-related events can be deduced from field observations and bulk lithogeochemical data. In this study 271 samples representing over 700 m of drillcore were analysed for up to 33 elements. These lithogeochemical data were investigated using a standardization procedure in which analyses were ratioed to the abundances of the relatively immobile detrital components, alumina and zirconium. After this transformation, anomalous abundances of "ore" constituents (Ba, Fe, Zn, Pb, Ag and S) and many other chemical components, were identified in the host rocks beyond the immediate vicinity of the "ore" zone. This procedure also facilitated an estimate of provenance for the host rocks and their relative rates of sedimentation. Geochemical trends are also evident within the "ore" zone. Ba:Sr ratio trends mimic Pb:Zn ratio trends and may be a useful tool in the study and exploration of other stratiform barite deposits. They delineate zoning patterns and may act as a guide to exhalative vent areas which may be of economic interest.<br>Science, Faculty of<br>Earth, Ocean and Atmospheric Sciences, Department of<br>Graduate

Geological and high-field-strength element (HFSE) relationships for Chester Group felsic volcanic rocks and corresponding sub-volcanic intrusives in the south-east Swayze greenstone belt (SESGB) indicate deposition in an dynamic volcanic-arc tectonic setting, from two separate magmas with calc-alkaline and HFSE-depleted trace element signatures respectively. Chester Group, Yeo Formation rocks have undergone a regionally extensive sericite-quartz (type 1) alteration, involving the loss of 3.25 wt.% Na2O, addition of 12 wt.% SiO2 and 2.2 wt.% K2O, and 13% net mass-gain, indicating water/rock ratios of at least 6. Chlorite-sericite +/- biotite +/- garnet (type 2) alteration at paleo-hydrothermal vent sites was localized along synvolcanic fault structures. Type 2 alteration was accompanied by a loss of 2.44 wt.% Na2O and 8.69 wt.% SiO2, and a gain of 5.90 wt.% Fe2O3, requiring water/rock ratios of at least 432.<br>Hydrothermal sediments or iron formation (IF) within the SGB are composed largely of Si and Fe. Base-metal mineralization in the SESGB and other localities in the SGB is hosted by brecciated hydrothermal sediments, overlain and flanked by, more broadly distributed pelitic IF, enriched in large ion lithophile elements (LILE), Al2O3, TiO2 and HFSE, with distinct Fe2O3/TiO2 versus Al2O 3/(Al2O3 + Fe2O3 + MnO) ratios indicative of mixing with locally derived volcanic material. Well-laminated BIF-type hydrothermal sediments are distributed widely throughout the SGB and are enriched in MnO, depleted in LILE, HFSE and transition elements, and have a wide range of Ce/Ce* values reflecting diverse redox conditions in paleodepositional environments distal to hydrothermal venting. Thermodynamic calculations suggest that hydrothermal fluids responsible for generation of hydrothermal sediments have lower temperatures (250--300°C) but similar pH (~4) to polymetallic volcanogenic massive-sulphide ore-forming fluids.

Cordierite-orthoamphibole rocks associated with contrasting polymetallic mineralization occur in a wide range of metamorphic conditions in the Atik Lake, Manitoba, and Nemiscau and Montauban, Quebec, metamorphic terranes.<br>Lithogeochemistry and geothermobarometry investigations using whole rock major, trace and rare earth elements and mineral chemistries have established the chemical and physical changes that occurred during hydrothermal alteration and subsequent regional metamorphism. The Log(Ratio) method, utilizing ratio profiles of the immobile elements $ rm Al sb2O sb3$, TiO$ sb2$, Zr, Nb, Y V and Cr, was designed to identify the protoliths of the metamorphosed altered rocks.<br>Detailed geothermobarometry and textural evidence indicate that cordierite-orthoamphibole rocks in the three terranes formed at peak P-T conditions of ${ sim}2.5$ kbar and ${ sim}55 sp circ$C at Atik Lake (andalusite zone), ${ sim}4.5$ kbar ${ sim}650 sp circ$C at Nemiscau (sillimanite zone), and ${ sim}6.5$ kbar and ${ sim}620 sp circ$C at Montauban (kyanite-sillimanite zone). Cordierite-orthoamphibole rocks in the terranes exhibit a range of bulk chemical compositions with the most Fe-rich occurring in the Atik Lake belt, and the most Mg-rich in the Montauban mine sequence. Mineral assemblages in these rocks were in equilibrium with contrasting sulfide-oxide $ pm$ arsenide fO$ sb2$-fS$ sb2$ buffers: pyrrhotite-ilmenite $ pm$ arsenopyrite $ pm$ lollingite at Atik Lake, pyrrhotite-pyrite-magnetite at Nemiscau, and pyrrhotite-rutile-sphalerite at Montauban.<br>The partitioning of Fe-Mg between cordierite and anthophyllite was studied for use as a geobarometer. The partitioning coefficient ($ rm K sbsp{D}{Fe-Mg}$) is slightly temperature dependant and strongly pressure dependent. This new geobarometer was empirically calibrated using mineral chemistry from the three terranes and from the literature.<br>High $ rm X sb{H sb2O}$ of the metamorphic fluid is required so that the X$ sb{ rm Fe}$ values of the anthophyllite will be in equilibrium under peak P-T conditions with the appropriate sulfide-oxide $ pm$ arsenide assemblage. Metamorphic dehydration of chlorite-rich hydrothermally altered rocks in the three terranes is compatible with the generation of such water-rich fluids during the crystallization of the cordierite-orthoamphibole rocks.

The Palaeoproterozoic Dannemora inlier is situated in the north-eastern Bergslagen region. The inlier consists of primary and reworked volcanic deposits, stromatolitic limestone and skarn that have been subjected to upper greenschist facies metamorphism. Thicknesses of the different volcanic deposits indicate deposition within a caldera, where syn-volcanic alkali alteration was strong. The deposition was submarine and below wave base in the eastern part of the inlier, but above wave base in the central part where erosion channels together with cross-bedding occurs frequently. The Dannemora Formation is the volcanosedimentary succession of the inlier. Two borehole profiles, a northern and a southern, cover the whole Formation and show different alteration patterns. A strong depletion of Na2O and enrichment of K2O dominate in the southern profile, whereas this pattern is not as evident in the northern profile. The uppermost section of the totally eight constituting the Formation, is intercalated with ore-bearing dolomitic limestone and skarn, and has experienced at least two episodes of alteration. An anticline has been established lithogeochemically from immobile element ratios and the reoccurrence of an accretionary lapilli bed. Numerous altered sub-alkaline, calc-alkaline and basaltic dykes have been recorded in the Dannemora inlier. They are the result of mixing and fractionation of at least three magmatic sources and carry a mixed signature of subduction zone and within-plate volcanic tectonic setting. A seismic profile across the Dannemora inlier images a strong reflector package that dips c. 50° E to the east of the inlier. This package coincides with the polyphase, E-up reverse, brittle-ductile Österbybruk deformation zone (ÖDZ). Yet another steep reflector in the Dannemora ore-field extends to a depth of more than two kilometres. This reflector might represent either a deep-seated iron deposit or a fluid-bearing fault zone.

This thesis covers two separate but complimentary themes. Firstly, work on the spinel composition of the ultramafic rocks of has provided evidence that they formed as Alaskan-type intrusions. This has implications both for prospectivity and for the understanding of neoproterozoic plate movements. Additionally, the study of the rock and soil geochemistry has been used to identify exploration targets and evaluate the prospectivity of the major complexes. It is proposed here that the ultramafic complexes Tulu Dimtu, Kingy, Daleti, Ankori and Yubdo, in the Western Ethiopian Shield are Alaskan type intrusions. Alaskan-type intrusions are concentrically zoned ultramafic intrusions thought to be the feeder pipes of volcanoes. They have dunite at the core and grade outwards to clinopyroxenite and sometimes hornblendite. These intrusions typically occur in continental arc settings such as Alaska, British Colombia and the Urals. This compares with ophiolite complexes which are thought to be obducted oceanic upper mantle and crust. The two types of complex may be difficult to distinguish because if ophiolites are dismembered and deformed fragments, they may resemble Alaskan-type intrusions. This thesis documents several features of these Ethiopian complexes that are typical of Alaskan type intrusions. Mapping of the Yubdo complex has shown a circular out crop pattern with concentric zones of clinopyroxenite at the edge to dunite at the centre. New mapping of the Tulu Dimtu area has shown a similar zoned circular body. Both the Yubdo and Tulu Dimtu complexes show concentric zones of Cr values, where the greatest values occur at the edge and the lowest in the centre. These mafic and ultramafic intrusions are very altered by surface weathering but contain chrome- spinels which have a geochemistry which is unlike ophiolites and similar to Alaskan-type intrusions. The analysis of these spinels demonstrates how the compositions of spinel Fe2+ and Cr values may be used to distinguish between an Alaskan type or ophiolite complexes. In Alaskan-type intrusions, spinels with Fe2+ values greater than 0.85 frequently have Cr values which are lower than 0.5. Such low Cr values in spinels with high Fe2+ values are rare in ophiolite complexes. The variations in Ni, Cu, Cr and Al contents of highly altered ultramafics and fresher ultramafics have been used to investigate the magmatic and post-magmatic ore forming processes that have influenced the Pt and Pd content of the complexes. It is expected that medium to low temperature hydrothermal activity may have had a significant impact on the geochemistry of even the fresher rocks. The discovery of high Pd values and low Pt in lithologies such as talc-schists and quartzite support the idea that Pd is more mobile than Pt in medium to low temperature conditions. Furthermore, in the Tulu Dimtu Main Intrusion, the altered rocks indicate that Pd has been removed from the magmatic sites of concentration. In a few places it is possible to see through the extensive alteration and potential magmatic processes can be considered. Within the Tulu Dimtu Main Intrusion and the Main Yubdo Intrusion, the most primitive rocks occur at the flanks. Furthermore, it is indicated that sulphide segregation may have occurred in the Tulu Dimtu Main Intrusion and Daleti Ultramafic. In the Daleti Ultramafic, regardless of the presence of sulphides, the Pt and Pd values remain low - it is therefore unlikely that the complex hosts economic grades. However, at Tulu Dimtu and Yubdo, it is recommended that any future exploration be targeted at the flanks of the complexes, where magmatic and post-magmatic processes may potentially co-incide to elevate the grade. Much work has been published to document the nature of platinum-group minerals (PGM) in the alluvial and eluvial placers around the Yubdo area and some PGM have been discovered in the serpentinsed dunites of the main Yubdo intrusion. In this thesis further discoveries of PGM have been made in the serpentinised dunites and chromites from the Yubdo area. In the course of this work new base maps covering the ultramafic complexes and the surrounding basement have been produced. These have revealed many smaller ultramafic bodies which are referred to here as the Lensoid Ultramafics. Both spinel and whole rock geochemistry supports the hypothesis that these are slivers of rock "sheared-off" the outside of larger complexes. The conclusion that these complexes have an Alaskan-type origin has consequences for the understanding of plate movements in this part of the Neoproterozoic Western Ethiopian Shield. Additionally, the identification of exploration targets will help focus efforts to uncover any potential economic mineralisation.

The Neoproterozoic Alexander terrane Niblack Cu-Au-Zn-Ag volcanic-hosted massive sulfide camp is on Prince of Wales Island, southeast Alaska. Multiple massive sulfide deposits occur at different stratigraphic levels in 565 ±1.25 Ma felsic volcanic strata. Host rocks are vent-proximal felsic pyroclastic volcanic breccia, lapilli tuff, coherent flows (Lookout deposit, Trio zone) and vent-distal felsic ash tuffs (Niblack Mine, Mammoth and Dama zones). New geochemical data and volcanic lithofacies indicate the host stratigraphy was deposited in a juvenile oceanic back-arc basin. Sub-seafloor mineralization (Lookout deposit, Trio zone) consists of 15-75% sulfide with disseminated to net-textured to semi-massive sulfide textures. These ores precipitated in unconsolidated water-laden vent-proximal felsic volcanic stratigraphy. Seafloor exhalative mineralization (Niblack Mine, Mammoth and Dama zones) is comprised of massive (>90%) poorly-banded sulfide. This type of sulfide precipitated on the paleo-seafloor in, or above, less-permeable vent-distal felsic ash tuff stratigraphy. Sub-seafloor sulfide, related hydrothermal alteration assemblages, and variations in metal ratios represent hydrothermal fluid flow and cooling through the host stratigraphy. Temperature estimates from chlorite microprobe data indicate sub-seafloor 1:1 Cu:Zn and 1:10 Au:Ag chlorite-rich alteration (Lookout deposit) formed at 321 ±19°C and seafloor exhalative 3:1 Cu:Zn and 1:10 Au:Ag magnesium-rich chlorite alteration (Niblack Mine) formed at 307 ±16°C. Sulfur, oxygen, deuterium and carbon stable isotope results are used to identify the origin of hydrothermal fluids. Sulfide mineral separates have δ³⁴S values of +6.6 to +10.5‰. Calculated fluid compositions of chlorite and sericite have values of +2.3 to +5.9‰ δ¹⁸O(water) and -24.9 to -77.1‰ δD(water). Calculated δ¹⁸O(water) values of magnetite are +8.1 to +15.5‰ and values of carbonate are -13.5 to +9.0‰ δ¹⁸O(water) and -4.4 to -0.5‰ δ¹³C(calcite). The sulfur isotope results indicate sulfur was derived from leached igneous sulfide and minor seawater sulfate reduction. The oxygen, deuterium and carbon isotopic signatures indicate evolved seawater and magmatic hydrothermal fluid sources. The Lookout deposit is the largest in the camp and has the largest magmatic fluid component. Seafloor exhalative sulfide mineralization (Niblack Mine) formed from an evolved seawater-dominant hydrothermal fluid. This suggests magmatic fluids contributed extra metals and sulfur to the hydrothermal system that enhanced the size of the Lookout deposit.

The Rävliden mine is located in the Skellefte district in northern Sweden. In close proximity lays the Kristineberg deposit containing zinc, copper and lead ore which has been mined since the 1940’s. The district is rich in massive sulphide deposits and the mining history can be dated back to the 1920’s. New deposits are still being discovered and understanding the origin of the ores and their formation processes are more and more important when looking for new orebodies. The area itself is ca 1.8 Ga and most rocks have undergone hydrothermal alteration and been metamorphosed. The main purpose of this study was to determine the host rock protolith and the method chosen was developed by MacLean and Barrett (2005) in which immobile element ratios are used for determining the chemostratigraphy.     Two main alteration types are recognized and two minor ones. The dominant ones being sericite and chlorite alteration. The boreholes also display some silicification and carbonate alteration. While the TAS-diagram shows that most samples are either dacitic or rhyolitic with a small group of andesitic rocks. Further usage of both the Alteration box plot and various immobile element plots show that the amount of dacitic samples are low. Instead rhyolite is the predominant rock type with four subgroups, there is also one dacite group and one probable andesitic intrusion. The mineralisation is low so it was not possible to correlate alteration type to ore occurrence, nor was it possible to see any correlation between protolith and mineralisation. The study did determine the protolith for the boreholes and the data and therefore the method can be used for exploration in other areas.<br>Rävlidengruvan ligger i Skelleftedistriktet i norra Sverige och i dess närhet ligger även  Kritinebergsgruvan där zink, koppar och bly har brutits ur malmkroppen sedan 1940-talet. Distriktet är rikt på massiva sulfid avlagringar och gruvdrift i området kan dateras tillbaka till 1920-talet. Nya fyndigheter upptäcks fortfarande och förståelse för deras uppkomst och malmernas bildningsprocesser blir är allt viktigare när man ska söka nya malmkroppar. Skelleftedistriktet är ca 1,8 Ga och de flesta bergarter har antingen genomgått metamorfos eller hydrotermal omvandling. Huvudsyftet med denna studie var att fastställa ursprungsbergarten för området, innan hydrotermal omvandling skedde, med hjälp av en metod som har utvecklats av MacLean och Barrett. Metoden grundar sig i att man jämför relationerna mellan immobila grundämnen för att på så sätt fastställa kemostratigrafin.     Fyra omvandlingstyper återfinns i borrhålen där två är mer prominenta, serecit och klorit omvandling. De mindre vanliga omvandlingstyperna är silicifiering eller kvartsomvandlig samt karbonatomvandling. De flesta prover är antingen daciter eller ryoliter med en liten grupp andesiter så visar de olika diagrammen med immobila elementet på att mängden daciter är få. Istället finns det fyra typer av ryoliter, en grupp daciter och en trolig andesitisk intrusion. Mängden mineralisering var låg så det var inte möjligt att korrelera omvandlingstyp till malm bildning, inte heller var det möjligt att se något samband mellan protoliten och mineralisering. Studien besvarade hypotesen om ursprungsbergarten för borrhålen och metoden kan användas för andra prospekteringsområden.

The ‘giant’ Tambogrande volcanogenic massive sulphide (VMS) deposits within the Cretaceous Lancones basin of northwestern Perú are some of the largest Cu-Zn-Au-Ag-bearing massive sulphide deposits known. Limited research has been done on these deposits, hence the ore forming setting in which they developed and the key criteria that permitted such anomalous accumulation of base-metal sulphides are not understood. Based on field relationships in the host volcanic rocks and U-Pb geochronology, the deposits formed during the early stages of arc development in the latest Early Cretaceous and were related to an extensional and arc-rift phase (~105-100 Ma, phase 1). During this time, bimodal, primitive basalt-dominant volcanic rocks were erupted in a relatively deep marginal basin. Phase 1 rhyolite is tholeiitic, M-type, and considered to have formed from relatively high temperature, small batch magmas. The high heat flow and extensional setting extant during the initial stages of arc development were essential components for forming a VMS hydrothermal system. The subsequent phase 2 (~99-91 Ma) volcanic sequence comprises more evolved mafic rocks and similar, but more depleted, felsic rocks erupted in a relatively shallow marine setting. Phase 2 is interpreted to represent late-stage arc volcanism during a waning extensional regime and marked the transition to contractional tectonism. The Tambogrande deposits are particularly unusual amongst the ‘giant’ class of VMS deposits in that deposition largely occurred as seafloor mound-type and not by replacement of existing strata. Paleomorphology of the local depositional setting was defined by seafloor depressions controlled by syn-volcanic faults and rhyolitic volcanism. The depressions were the main controls on distribution and geometry of the deposits and, due to inherently confined hydrothermal venting, enhanced the efficiency of sulphide deposition. Geochemical and radiogenic isotope data indicate that the rhyolites in the VMS deposits were high temperature partial melts of the juvenile arc crust that had inherited the isotopic signatures of continental crust. Moreover, Pb isotope data suggest the metal budget was sourced almost wholly from mafic volcanic strata. Therefore, unlike the implications of many conventional models, the felsic volcanic rocks at Tambogrande are interpreted to have only played a passive role in VMS formation.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>A Unidade Santo Aleixo, em sua localidade-tipo, é representada por gnaisses homogêneos, e, mais restritamente, por gnaisses bandados e gnaisses com inclusões máficas e félsicas. Todos os tipos litológicos mostram contatos gradacionais entre si. Na área de pesquisa, ocorrem ainda leucognaisses, migmatitos, granitos tardios e diques de diabásio. A área é marcada por foliação principal com trend NE e mergulho de baixo a médio ângulo, ora para SE ora para NW, relacionado a dobramento com traço do plano axial NE-SW. Foram descritas zonas de cisalhamento dúcteis a rúpteis de fases deformacionais tardias. A análise modal dos diversos tipos gnáissicos revelou uma composição tonalítica a granítica e menos comumente, quartzo-monzodiorítica e quartzo-monzonitica. A biotita está sempre presente podendo ou não vir acompanhada de hornblenda. Os acessórios mais comuns nessas rochas são apatita, zircão e opacos, enquanto titanita e allanita são mais variáveis, e às vezes podem estar ausentes. É rara a presença de granada que apenas foi observada em uma amostra do gnaisse homogêneo. Observou-se cloritização de biotita e sericitização e formação de muscovita a partir de plagioclásio. Os resultados geoquímicos apontam para a existência de apenas um grupo subalcalino disposto ao longo de um trend calci-alcalino. A maioria das amostras são metaluminosas a fracamente peraluminosas. Os gnaisses apresentam valores de terras raras pesadas inferiores a 10 ppm, o que resulta em elevadas razões (La/Lu)N. As comparações petrográficas e litogeoquímicas entre a Unidade Santo Aleixo e do Complexo Rio Negro mostram que: a) a Unidade Santo Aleixo compreende uma série petrográfica expandida enquanto que o Complexo Rio Negro é representado por séries mais restritas; b) o quimismo das duas unidades é semelhante, e representa um magmatismo calci-alcalino metaluminoso à biotita e hornblenda; c) as unidades são semelhantes em termos de ambientação tectônica, representando um ambiente do tipo arco vulcânico; d) os gnaisses da Unidade Santo Aleixo são empobrecidos em terras raras pesadas em comparação aos gnaisses do Complexo Rio Negro; comportamento causado pela presença de granada na fonte geradora. A inclusão da Unidade Santo Aleixo no Complexo Rio Negro, portanto, é sustentada pelas semelhanças petrográficas e geoquímicas, entendendo-se que o Complexo inclui tipos magmáticos com modos de evolução e fontes diferentes.<br>The Santo Aleixo Unit in its type-location is represented by homogenous gneiss and subordinated banded and inclused mafic-felsic-rich gneisses, all rocks separated by gradational contacts. Leucogranitic gneiss, migmatites, late-tectonic granite stocks and diabase dikes also occur in the studied area. The gneissic foliation dips to SE or NW with low to medium angles according to large vertical folds with a NE trending axial plane. The main foliation is deformed by late tectonic ductile to brittle shear zones. The gneisses are classified as tonalites to granites and, subordinated quartz-monzodiorites and quartz-monzonites. Biotite is always present with or without hornblende. Garnet was described only in the homogenous gneiss. Apatite, zircon, opaque minerals and minor titanite and allanite are the acessory minerals. Biotite chloritization and plagioclase sericitization are the observed metamorphic-hidrotermal processes. Lithogeochemical data classify the Santo Aleixo Unit gneisses as metaluminous metaigneous rocks from a calc-alkaline sequence. Heavy REE concentrations are lower than 10 ppm, resulting in elevated (La/Lu)N ratios. Comparing petrographic and lithogeochemical data from the Santo Aleixo Unit and the Rio Negro Complex points to the following statements: a) Santo Aleixo Units petrographic series are expanded while Rio Negro Complexs series are more restricted; b) the units presents same chemical signatures (calc-alkaline volcanic arc metaluminous magmas with biotite and hornblende); c) the Santo Aleixo Unit gneisses are depleted in heavy REE related to the presence of garnet at the magma source. Therefore, the incorporation of the Santo Aleixo Unit into the Rio Negro Complex is sustained by petrographic and lithogeochemical similarities, and also makes clear that the arc magmatism had different sources and evolutionary paths.

Orientador: Guillermo Rafael Beltran Navarro<br>Resumo: A Formação Corumbataí é uma unidade sedimentar pelítica a psamo-pelítica de idade permiana, pertencente à Supersequência Gondwana I da Bacia do Paraná, sobre a qual poucos estudos foram realizados quanto à proveniência e suas implicações paleoambientais. Este trabalho visa preencher estas lacunas, apresentando correlações de composição e de proveniência entre seções aflorantes da Formação Corumbataí nos município de Rio Claro (SP), Santa Rosa de Viterbo (SP) e Mineiros (GO), e uma seção aflorante da Formação Serra Alta (Permiano da Bacia do Paraná, correlacionável com a base da Formação Corumbataí) no município de Cesário Lange (SP), bem como suas implicações paleoclimáticas, paleogeográficas e possíveis implicações na compreensão dos mecanismos de abertura do Atlântico Sul. Os dados mostram que as rochas permianas sobrejacentes à Formação Irati que ocorrem nas áreas de estudo são classificadas quimicamente com mais frequência como “wackes” e litoarenitos, formados por sedimentos derivados predominantemente de rochas sedimentares e/ou metassedimentares e ígneas ácidas, com a região de Cesário Lange discordando das demais regiões por indicar contribuição exclusiva de rochas supracrustais. Em se tratando das amostras da Formação Corumbataí, a maturidade química e textural aumenta de norte em direção a sul, bem como o grau de submissão dos sedimentos originais ao processo de reciclagem sedimentar. As rochas sedimentares foram depositadas em ambientes tectonicamente quiescentes, ... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: The Corumbataí Formation is a pelitic to psammo-pelitic sedimentary unit of Permian age, belonging to the Gondwana I Supersequence of the Paraná Basin, about which few studies have been conducted regarding its provenance and its paleoenvironmental implications. This work aims to fill these gaps, presenting correlations of composition and provenance between outcropping sections of the Corumbataí Formation in the municipalities of Rio Claro (SP), Santa Rosa de Viterbo (SP) and Mineiros (GO), and an outcropping section of the Serra Alta Formation (Permian of the Paraná Basin, correlated with the base of the Corumbataí Formation) in the municipality of Cesário Lange (SP), as well as its paleoclimatic and paleogeographic implications and possible implications in the understanding of the opening mechanisms of the South Atlantic. The data show that the Permian rocks overlying the Irati Formation that occur in the study areas are most commonly chemically classified as “wackes” and lithoarenites, formed by sediments derived predominantly from sedimentary and/or metasedimentary and acidic igneous rocks, with Cesário Lange region disagreeing with the other regions as it indicates exclusive contribution of supracrustal rocks. Regarding the Corumbataí Formation samples, the chemical and textural maturity increases from north to south, as well as the degree of submission of the original sediments to the sedimentary recycling process. The sedimentary rocks have been deposited in tectonicall... (Complete abstract click electronic access below)<br>Doutor

Sixteen samples from 8 locations within and surrounding the Björkdal mine area in northern Sweden were chosen in order to reevaluate and characterize previous interpretations of the lithology and hydrothermal alteration. Geochemical analysis by ICP-MS was made in order to chemically classify the lithology of the area and petrological studies were made by study of thin sections and core logging. Three different sets of major alteration types with similar protolith were noted where two dominated: a) a silicified, sericitic, deformed unit; b) a felspathic altered unit with various intensity of epidote; c) amphibole and a so called green banded unit that has undergone Ca-Mg-metasomatism. The main host rock lithology could be identified as a coarse grained, equigranular, plagioclase and (Na-K)-feldspar dominated rock with slightly elongated, stubby grains that have an interlocked, igneous texture. Apatite is a reoccurring accessory mineral in all samples and remains relatively undamaged. Fragmental quartz occur in the samples and is primary to later forming alteration minerals.Amphiboleis also considered to be primary, but can also been formed during regional metamorphism. Two lithologies could be identified in addition to the main protolith. Two samples were located above the marble horizon and was classified as basaltic unit with Ca-plagioclase, biotite and amphibole. One sample mainly consisted of aligned amphibole and biotite and is considered to be an amphibolite xenolith or a dyke intruding the main protolith rock. An increase in the alteration minerals albite, amphibole, epidote and allanite, with peak intensity found north-east of the mine site. This is confirmed by the geochemistry of major elements Fe2O3, MgO, CaO and the ratio between Na2O and K2O. The zonation is explained by a suggested increase in temperaturecondition during metamorphosis. This could be explained by either an underlying intrusion or bystructurally controlled variation in metamorphism by e.g. major faults running through the area.Comparisons with previous work in Björkdal favors an intrusion-related origin for the gold deposit.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>O Complexo Juiz de Fora (CJF) na região de Três Rios (RJ) é constituído por uma ampla variedade composicional, tendo desde granitos, tonalitos a rochas de composição gabróica. Através da litogeoquímica pôde-se subdividir essa unidade em 4 conjuntos: (i) cálcioalcalino de alto-K, (ii) cálcioalcalino de médio-K, (iii) toleítico e (iv) alcalino. Pela análise geocronológica (LA-ICPMS, U-Pb) foi obtida a idade de 2,1Ga para o conjunto cácioalcalino de médio-K, duas idades neoproterozóicas (615.9 6.4 Ma e 589.1 5 Ma) foram datadas em um ortogranulito do conjunto toleítico, que foram interpretadas como sendo idades de metamorfismo. A idade modelo de Nd (&#8776; 2,37 Ga) e os dados de U-Pb e litogeoquímicos balizam a hipótese do conjunto cálcioalcalino de médio-K representar rochas de um arco magmático juvenil. A análise isotópica em conjunto com a litogeoquímica sugere que a série toleítica do CJF da região estudada foi gerada em ambiente de fundo oceânico, sendo diferenciada a partir de uma fonte depletada com alguma contribuição de uma fonte enriquecida.<br>The Juiz de Fora Complex (JFC) in the region of Três Rios (Rio de Janeiro) is appointed by an ample variety composicional, having from granites, tonalite to rocks of composition basic. Through the lithogeochemistry it was possible to subdivide this unity in 4 associations: (i) calc-alkaline of high-K, (ii) calc-alkaline of medium-K, (iii) tholeiitic and (iv) alkaline. By the geochronological analysis(LA-ICPMS, U-Pb) was obtained the age of 2,1Ga for the calc-alkaline group of medium-K, two ages neoproterozoic (615.9 6.4 Ma and 589.1 5 Ma) were dated in an orthogranulite of the toleítico group, what they were interpreted like ages of metamorphism. The model age of Nd (&#8776; 2,37 Ga) and the data of U-Pb and lithogeochemical mark the hypothesis of the calc-alkaline group of middle-K represents rocks of a youthful magmatic arc. The isotópica together with the lithogeochemistry analysis suggests that the toleítica group of the CJF of the studied region were produced in environment of ocean extensional, being differentiated from a fountain depletada with some contribution of a rich fountain.

Myra Falls is a series of polymetallic, volcanic-hosted massive sulfide (VHMS) deposits located in central Vancouver Island, 90 km southwest of Campbell River, British Columbia, Canada. As of April 2013, production has exceeded 30 Mt of ore at average grades of 5.5% Zn, 1.6% Cu, 0.6% Pb, 2.0 g/t Au and 54.0 g/t Ag. There are 10 VHMS deposits at Myra Falls, which are spatially and temporally related to episodic felsic volcanism, in the Devonian Sicker Group, which define two district-scale stratigraphic members. The near surface L-M-P member is host to the Lynx, Myra, and Price orebodies. Whereas the HW, Trumpeter Zone, Battle, Extension Zone, Ridge Zone West, Ridge Zone North, and Marshall Zone orebodies are in the lower H-W member. While previous studies have focused on the HW, Battle, and Ridge Zone West orebodies, questions regarding the lithostratigraphic architecture and the depositional age of the H-W member remain. The West Block Area provides a geological-link between the Battle and Ridge Zone West orebodies. This research presents: (1) a detailed description of the lithology and nature of VHMS mineralisation in the West Block Area; (2) a proposed geological framework linking the Battle and Ridge Zone West orebodies; (3) mineralogical and geochemical proximity indicators to ore; (4) immobile element discrimination of altered volcanic rocks from systematic pXRF analysis; (5) age constraints from U-Pb zircon geochronology of felsic volcanic rocks in the H-W and L-M-P members; and (6) develop useful criteria for exploration in the Myra Falls VHMS district and elsewhere on Vancouver Island. Detailed and simplified district-scale cross-section interpretations of the West Block Area were generated from underground drilling, in conjunction with company data, to assess the distribution of identified lithological units, alteration, and sulfide mineralisation. Stratigraphy in the West Block Area comprises coherent, volcaniclastic and marine sedimentary rocks of the Price and lower Myra Formations. The Price Formation, at least 80 metres-thick, is characterised by a submarine, extrusive sequence of coherent, andesitic lavas and related breccias. The 150 to 175 metres-thick H-W member (lower Myra Formation) consists of syn- and post-eruptive volcanic and marine-sedimentary rocks. Polylithic siltstone, sandstone and conglomerate of the Basal Volcaniclastic Unit extends west over 500 metres to the Ridge Zone West orebody, where it marks the base of the lower Myra Formation. The Basal Volcaniclastic Unit is overlain by intercalated argillite and chert of the Caprocks Unit. The overlying HW Rhyolite comprises felsic volcaniclastic rocks, which are overlain by coherent, quartz and feldspar-phyric rhyolite, 10 to 40 metres in thickness. Coherent rhyolite domes of the West Block Area extend east over 500 metres to the Battle orebody and north over 250 metres to the Ridge Zone North orebody. A 10 to 50 metre-thick, plagioclase and pyroxene-phyric coherent andesite lava is the youngest extrusive unit of the H-W member, and overlies the HW Rhyolite, extending >500 metres to the west, above the Ridge Zone West orebody. The Hanging Wall Andesite member unconformably overlies the H-W member, and consists of polylithic, volcaniclastic sandstone and conglomerate, locally with clasts of massive sulfide and chert. Polymetallic sulfide mineralisation in the West Block Area occurs in altered andesite of the Price Formation (footwall) and a rhyolite-dominant, volcano-sedimentary sequence of the lower Myra Formation. Styles of sulfide mineralisation are disseminated, stringer, semi-massive and massive. Disseminated sulfide is pyrite-rich, and occurs in altered, Price Formation andesite and all rock types of the H-W member. Sphalerite-rich and pyrite-dominant stringer-style mineralisation is present in altered coherent and volcaniclastic rhyolite of the HW Rhyolite. Less common in the West Block Area are semi-massive and massive zinc-rich, polymetallic, mineralisation styles, which are hosted in altered coherent rhyolite and autobreccias of the HW Rhyolite, and polylithic conglomerate of the Basal Volcaniclastic Unit. Volcanic-hosted massive sulfide mineralisation is located at two stratigraphic positions — upper zone and contact zone. The “upper zone” is stringer-style, semi-massive and massive sulfide mineralisation, 30 to 75 metres above the Price Formation contact. The “contact zone” comprises semi-massive and massive sulfide mineralisation at or near the Price Formation contact. Mineralisation consists of sphalerite, pyrite, chalcopyrite, and galena with accessory tennantite-tetrahedrite, stromeyerite and pearceite-polybasite. Precious metal minerals are electrum and hessite. Four paragenetic stages of mineralisation are proposed. Stage-1 includes early, inclusion-rich pyrite. Stage-2 consists of inclusion-free pyrite rimming Stage-1 pyrite accompanied by the precipitation of sphalerite, with minor galena-chalcopyrite-barite ± tennantite and tetrahedrite. Stage-3 is characterised by the modification of Stage-2 mineral phases in the form of grain coarsening, homogenisation of sphalerite(?), and local remobilisation of sulfide and sulfosalt phases. Stage-4 encompasses metamorphic remobilisation with pearceite-polybasite veinlets crosscutting Stage-2 and -3 mineral assemblages. The timing of electrum and hessite precipitation is unresolved, and could have occurred during Stage-3 and/or Stage-4. Determining the intensity, zonation and extent of hydrothermal alteration associated with VHMS deposits can provide important implications for mineral exploration. A laterally continuous footwall alteration zone extends beneath the West Block Area and the Battle, Ridge Zone North and Ridge Zone West orebodies. Alteration of the Price Formation is mineralogically and texturally diverse. Weak alteration, defined from the Thelwood Valley locality, consists of a pervasive, texturally non-destructive, chlorite-calcite ± epidote alteration. Moderate alteration, defined from the West Block Area, consists of pervasive, texturally nondestructive, chlorite-calcite-pyrite and chlorite-sericite alteration. Intense alteration occurs in the footwall below the Ridge Zone North and Battle orebodies, and consists of feldspardestructive, sericite-quartz-pyrite, chlorite-rich, and chlorite-sericite-pyrite alteration. Footwall alteration associated with the West Block Area, Ridge Zone North and Battle orebodies has several mineralogical and geochemical characteristics that show systematic changes with increasing proximity to ore. The Fe/Fe+Mg of chlorite decreases from 0.49-0.27 in least to moderately altered andesite to <0.20 in intensely altered andesite immediately below ore. In general, K-mica compositions shift from phengitic in least-altered andesite to muscovitic in intensely altered andesite, proximal to ore. Least-altered footwall alteration whole-rock lithogeochemical trends, include elevated Na\(_2\)O, Rb/Sr <0.1, and moderate alteration index (AI) and Chlorite-Carbonate-Pyrite Index (CCPI) values that plot in the diagenetic field of the alteration box plot. Proximal, within 100 metres to ore, lithogeochemical trends include depleted Na\(_2\)O (≤0.75 wt. %), variably elevated S (up to 16.0 wt. %), Rb/Sr >1.0, AI values >80, and CCPI values from 35-95. Distal, up to 500 metres away from ore, lithogeochemical signatures are characterised by variable Na\(_2\)O and S values, and Rb/Sr from 0.1-1.0. Alteration Index and CCPI values, that plot in the hydrothermal alteration field on the alteration box plot, form an array from the least-altered andesite field to the chlorite-pyrite and white mica fields. As these mineralogical and lithogeochemical alteration trends change systematically relative to the position of ore they can be used in the exploration for other deposits in the district. A new method for lithological discrimination of altered volcanic rocks based on systematic portable X-ray fluorescence (pXRF) analysis of drill core has been developed. A compilation of published conventional XRF lithogeochemical data from the Myra Falls VHMS district shows robust and discrete Ti/Zr trends for coherent volcanic rocks. Single-spot pXRF analysis of pressed powder dill core samples and three-spot pXRF analyses measured from the flat, cut and clean surface of drill core samples were compared with conventional XRF results from the same sample sets. Both pXRF sampling methods reproduce the laboratory XRF results for Ti and Zr, and there was no significant improvement in accuracy or precision between drill core powders and unprepared drill core samples. Calibration, estimation of total measurement uncertainty, and data reduction procedures for systematic three-spot pXRF analysis of drill core samples were developed to improve lithological logging of altered volcanic rocks. Portable- XRF analysis, combined with detailed logging of volcanic lithofacies can improve geologic and stratigraphic interpretations, which are vital for developing mineral exploration models for VHMS deposits and other economic mineral systems. Previous attempts to date the volcanic rocks at Myra Falls have resulted in relatively imprecise crystallisation ages that do not resolve the temporal relationship between the L-M-P and H-W members. New U-Pb zircon CA-ID-TIMS results from the HW Rhyolite and LA-ICPMS results from the LMP Rhyolite, combined with published age constraints and stratigraphic relationships, confirm at least two phases of felsic volcanism at Myra Falls that were episodic over a period of ~7 million years. High precision CA-ID-TIMS results indicate that VHMS mineralisation in the Ridge Zone North orebody is hosted in 362.4 ± 0.4 Ma coherent rhyolite. For the first time, the felsic volcaniclastic stratigraphy of the L-M-P member is constrained by U-Pb zircon geochronology, with LA-ICPMS results providing a maximum deposition age of 355.5 ± 2.8 Ma for the LMP Rhyolite of the Price orebody. These age constraints at Myra Falls correlate with previously dated VHMS deposit stratigraphy in the Cowichan Lake uplift on Vancouver Island. Future VHMS mineral exploration in the Sicker Group on Vancouver Island should consider ~362 Ma felsic stratigraphy located within 200 metres of the upper contact of the Price and Nitinat Formations, as well as ~355 Ma felsic stratigraphy located in the top 100 metres of the Myra and McLaughlin Ridge Formations. This research advances the overall understanding of the H-W member stratigraphy, the nature of hydrothermal alteration, and the temporal relationship of felsic host rocks at Myra Falls. These advancements have implications for the advancement of mineral exploration in the Myra Falls district and throughout Vancouver Island. In short, VHMS exploration targeting in the belt should focus on felsic volcanic stratigraphy (Ti/Zr ratios between 9-12) with U-Pb zircon crystallisation ages of approximately 362 Ma and 355 Ma. The siliceous Caprocks unit is a distinguishing lithological feature for the H-W member VHMS orebodies, therefore mineral exploration should also target Late Devonian marine basin depositional environments intercalated with felsic volcanic deposits and fine-grained marine sedimentation.

The Seneca Prospect is a volcanic-hosted Zn-Cu-Pb deposit 120 km east of Vancouver in southwestern British Columbia. Volcanic strata at Seneca form part of the Weaver Lake Member of the Lower to Middle Jurassic Harrison Lake Formation of the Harrison Terrane. The rocks at Seneca comprise four principal facies: 1) vent to vent-proximal facies consisting of basaltic to rhyolitic lavas and associated breccias; 2) vent-proximal to distal facies consisting of volcaniclastic debris flows and siltstones; 3) coeval intrusions consisting of basaltic andesitic to rhyolitic sills and dikes, and 4) distal marine facies consisting of a pumice-bearing argillaceous unit. The volcanic strata can be subdivided into three intervals from bottom to top as follows: 1) the Footwall Interval below the mineralized horizon which comprises subaqueously deposited basaltic lavas and felsic debris flows; 2) the Seneca Horizon which hosts the mineralized zones, and 3) the Hangingwall Interval which is consists largely of felsic flows, intrusions and volcaniclastic rocks. Volcaniclastic rocks in the Footwall Interval are dominated by coarse, poorly-sorted debris flows whereas the volcaniclastic rocks of the Hangingwall Interval are mostly massive to well-bedded ashes and volcanically-derived turbidites. The Seneca volcanic sequence is a bimodal suite of rocks of calc-alkaline to transitional calcalkaline- tholeiitic affinity (Zr/Y ratios >3.5, LaN / YbN ratios > 2.0). Pearce element ratio analysis of the mafic rocks shows that the chemical variation in a least-altered subset can be explained by the fractionation of plagioclase, olivine and clinopyroxene although variation within basaltic and basaltic andesitic subgroups can be explained by plagioclase fractionation alone. Major element variations in the least altered felsic rocks can be explained by fractionation involving the crystallization o f feldspar, quartz ± pyroxene and/or hornblende. Trace element trends can be accounted for by 30 to 40 % fractional crystallization o f the assemblage feldspar-hornblende-magnetite±apatite. Mass change calculations revealed both a vertical zonation and spatial differences in the hydrothermally altered stockwork zones. In general, the stockworks can be subdivided into upper and lower alteration zones. The upper quartz-sericite zone has experienced net mass gain with mass gains of Si02 and K20 and mass losses of Na2O and CaO resulting from silicification and the destruction of feldspar. The lower sericite-chlorite zone has had small net mass gains or losses as a result of mass gains of K20 and MgO and losses of Na2O, CaO and in places Si02 . The MgO gains throughout the Vent Zone are much smaller or absent in the Fleetwood Zone, perhaps indicating that the larger Vent Zone hydrothermal system was more capable of incorporating seawater magnesium than the Fleetwood Zone stockwork systems, which may have been sealed by overlying flows or volcaniclastic sediments. Mineralization in the Pit Area consists of zones of disseminated to conformable massive sphalerite, pyrite, chalcopyrite, galena and barire hosted by the strongly altered ore zone conglomerate (OZC). Stratigraphic relationships indicate that these zones may have formed contemporaneously with the stockwork sphalerite-pyrite-chalcopyrite mineralization in the Fleetwood and Vent Zones. The stockwork zones possibly were vertical conduits for hydrothermal fluids which then migrated laterally through the permeable OZC where they interacted with seawater and formed the Pit Area sulphide mineralization. The volcanic rocks which host the Seneca deposit have geological and geochemical similarities to younger rocks of the Lau Basin and Tofua Arc in the southwest Pacific and the Hokuroku Basin in Japan. These similarities suggest that the Seneca volcanic sequence and sulphide mineralization may be in rifted sub-basins within a calc-alkaline volcanic arc formed at a destructive plate margin involving two oceanic plates with little or no continental crustal influence.

Tulsequah Chief is a polymetallic, massive sulpliide deposit of Carboniferous age hosted in a bimodal felsic volcanic sequence in the western part of the Stikine terrane, in Northwest British Columbia. Present ore reserves are estimated at 8.7 Mt of 1.27% Cu, 1.18% Pb, 6.35% Zn, 2.43 g/tonne Au and 99.44 g/tonne Ag. Basaltic to basaltic andesite flows and breccias form the footwall of the deposit, and are strongly altered by sericite and quartz-pyrite stringers to >200 m below the sulphide lenses. A distinctive cordierite-biotite mineral assemblage tends to occur peripherally and within the sericitized zone in the footwall. The deposit consists of stacked sulphide-rich lenses hosted in sericitized and variably silicified felsic flows and felsic volcaniclastics. These rocks include variably pumiceous lapillistone, ash and other sandy to blocky felsic-rich volcaniclastics. Relatively unaltered massive rhyolite flows and breccias form the hanging wall of the deposit. A second package of basaltic rocks and volcanic sediments caps the felsic rocks in the mine area. A massive, semiconcordant gabbro sill, of similar mineralogy and chemistry as the overlying basalts, intrudes and splits the felsic sequence above the sulphide lenses. The stratigraphy and sulphide lenses are structurally deformed into a set of open, steeply northward plunging folds. Two post-ore faults, the 4400E and 5300E, with up to 40 m dextral displacement, divide the mine stratigraphy. These structures occur on each side of the sericite-altered zone in the footwall rocks, and on each side of the of the largest massive sulphide lenses, the AB2- and H-Zones, which follow the plunge of a synclinal axis. The upper ore zones are pipe-like to lenticular in shape and of composite architecture. They consist of varying proportions of banded to massive sulphides and gangue. Sulphides include pyrite, sphalerite, galena and chalcopyrite. The gangue is largely quartz and sericite with lesser barite and minor epidote, chlorite and carbonate. Layers of sulphide-bearing debris, constitute a semimassive ore-facies, and are interstratified or cap the sulphide lenses. The debris includes disseminated sulphides and fragments of sulphide and barite. Other mineralization includes crosscutting chalcopyrite, tetrahedrite, sphalerite and galena-bearing veinlets; some veinlets contain visible gold. A zone of anhydrite mineralization occurs stratigraphically below the western edge of the AB2 sulpliide lens east of the 4400E fault and is associated with massive to disseminated pyrite. Other less extensive and less complex pyrite and sphalerite-rich sulpliide lenses are hosted in the felsic stratigraphy below the H-Zone sulphide lens. The elongated morphology of the main ore body along the axis of a fault bounded syncline and the presence of mass flow debris covering a portion of the sulphide lenses imply that sulphide deposition took place in a graben. Preexisting faults, parallel to the 4400E and 5300E structures, may have focused hydrothermal fluids responsible for the sericite alteration and intense quartz-sulphide stringer mineralization in the footwall of the deposit. Lithogeochemical data indicates the presence of three groups of felsic rocks and at least two groups of mafic footwall rocks despite the severe alteration near the deposit. Mass changes calculated for the altered lower felsic rocks indicate large additions of K20 and loss of Na20 and CaO. Samples of least-altered felsic and mafic volcanic rocks at Tulsequah Chief display light rare-earth element enrichments and other chemical features that suggest that they are of tholeiitic to transitional affinity. The volcanic sequence is interpreted to have formed in a rifted arc setting, above a metasomatized mantle wedge. Several rifting events may have occurred in the area of the deposit, with sulphide deposition taking place just after the transition from mafic to felsic volcanism. [Scientific formulae used in this abstract could not be reproducted.]

The Hidden Creek deposit constitutes the largest accumulation of massive sulphides in the Anyox Pendant, a volcanic-sedimentary succession preserved as a roof pendant along the eastern margin of the Coast Plutonic Complex, about 160 kilometres north of Prince Rupert, B.C. The deposit produced 21 Mt of ore grading 1.57% Cu, 9.26 g/t Ag and 0.17 g/t Au. It consists of 8 ore zones that occur near the volcanic-sedimentary contact. Each ore zone includes a number of lenticular to sheet-like, massive sulphide bodies consisting of pyrite, pyrrhotite and lesser chalcopyrite, with minor sphalerite and magnetite. Stockwork veins in the upper volcanic and lower sedimentary sequence are interpreted as footwall feeders to the massive lenses. The Anyox volcanic rocks are tholeiitic basalts and basaltic andesites with Zr/Y[sub (avg)]=2.4 and Zr/Ti*1000[sub (avg)]=9.9. Although they are mainly normal mid-ocean ridge basalts (NMORB), it is possible to distinguish enriched (E-MORB) and transitional (T-MORB) groups. N-MORBs have P/Ti ratios <0.075 and are depleted in the LREEs, whereas EMORBs have P/Ti ratios >0.15 and are enriched in the LREE. T-MORBs are transitional between these two end-members. Hydrothermal alteration increases in proximity to mineralized zones. Chlorite-epidotequartz alteration is prevalent in the footwall volcanic rocks. Alteration in the sedimentary sequence is zoned outward from a quartz-chlorite core to a quartz-sericite-pyrite margin. In the sediment-hosted ores, quartz and calcite are the common gangue minerals, whereas in volcanic-hosted ores, Mg-Ca-Al silicates are common. There is a strong association between chalcopyrite and pyrrhotite in the sulphide lenses and in the underlying vein networks. Mass change calculations for the volcanic rocks indicates a progressive loss of CaO + Na₂0 and gain in MgO + FeO corresponding to breakdown of plagioclase and formation of chlorite during hydrothermal alteration. K has been added (now biotite) to upper volcanic rocks. Ti0₂/Zr ratios indicate that the detrital component in the sediments cannot be related to the volcanic rocks and must have been derived from a more evolved source. Chemical changes in the altered sediments are similar to those in the volcanic rocks, although they probably had higher initial K values. In the eastern Pacific Ocean, N-MORB is common but E-MORB and T-MORB are reported from Middle Valley on the Juan de Fuca Ridge, and along the East Pacific Rise from 11°-13°N. Alteration and mineralization in the sedimentary sequence at Hidden Creek are similar to sediment-hosted alteration and mineralization adjacent to sulfide deposits at Middle Valley and at Windy Craggy deposit (Triassic) in northern BC. Fluid inclusion data from the Hidden Creek deposit are similar to sediment-covered hydrothermal systems at Windy Craggy, and in the Guaymas Basin in the Gulf of California. The modern examples provide partial analogs for the seafloor setting and styles of mineralization at Anyox.

This item is only available electronically.<br>Geochemical data, including Nd isotope ratios, were used to help establish stratigraphic correlations between Kanmantoo Group sedimentary rocks on the mainland and Kangaroo Island, as well as constrain their provenance. Whole-rock geochemistry of the Kangaroo Island and mainland Kanmantoo Group varied, with little consistency, suggesting a mixed sediment source. The Talisker Formation however has a distinctly higher abundance of mafic detritus compared to other Kanmantoo Group formations. Initial Nd data from the Kangaroo Island Kanmantoo Group is between -12 to -15, compared to those from the mainland which range between -9 and -12 (Turner et al. 1993). The Nd data are similar to basement of the Gawler Craton and east Antarctica (Prydz Bay), which are two possible source terrains for the sediments. Palaeocurrent data on Kangaroo Island indicate a southern provenance. The Nd values of Prydz Bay charnockites and felsic gneisses at around 500 Ma are similar to that of the Kangaroo Island Kanmantoo Group. Results from the outcomes of this study suggest that the Kanmantoo Group was derived from a mixture of sources, including the Gawler Craton, west Antarctica (Ross Orogeny) and Adelaidean rocks. However, there appears to be a dominance of sediment from the east-Gondwana Orogenic belt in east Antarctica.<br>Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2008

The Hope Bay greenstone belt (HBGB) is one of several Late Archean greenstone belts recognised within the Slave Structural Province (SSP) in the Northwest Territories, Canada. Unlike most other major greenstone belts in the SSP relatively little is known about the age and evolution of the HBGB. The main goal of this study was to construct a detailed chronostratigraphic and chemostratigraphic framework for the belt that would constrain the temporal and tectonic evolution and thus permit the HBGB to be placed in the regional geological context of the Slave Structural Province. A regional geochronological and lithogeochemical program was carried out in conjunction with geological mapping by BHP Minerals Canada Ltd. personnel. A total of 21 UPb age determinations, 174 major and trace element analyses, and 19 rare earth element analyses resulted from the study. U-Pb geochronology was selected as the critical tool for constraining the stratigraphic and temporal evolution of the belt because of its high blocking temperature and the precise ages that can be obtained using this method. Major, trace, and rare earth element data were employed to characterise the geochemistry of various igneous units and investigate the possible paleotectonic settings in which individual units were generated. The HBGB is characterised by a basal series of mafic dominated tholeiitic volcanic flows (Young Group), overlain by a sequence of calc-alkaline volcanic rocks (Westerberg Group), that are in turn overlain by sedimentary rocks of the Tweedy and Farrar group. These sequences were deposited over a period of at least 116 m.y. from ca. 2716 to ca. 2600 Ma. Chemical compositions of volcanic rocks are typified by low abundance of HFSE and depletions in Nb, Ti, Eu, and P relative to REE. The striking similarity between the overall lithologic assemblage and the geochemical signature of volcanic rocks in the HBGB with modern arc and back-arc systems (e.g. Mariana and Tonga-Kermadec regions) suggest the HBGB evolved in an arc-backarc geodynamic setting.

The Cambra-Ordovician Seventy Mile Range Group occurs as an east-west trending volcano-sedimentary sequence which is host to several significant volcanichosted massive sulphide (VHMS) deposits. In the Mt Farrenden area the base of the Group is comprised of the fine sedimentary units of the Puddler Creek Formation. These continent-derived units were deposited into a back-arc environment. This Formation is- overlain conformably by the rhyoli te-dominated Mt Windsor Volcanics, and by the Trooper Creek Formatioh with mixed andesitic, volcaniclastic sedimentary and daci tic units. Whole rock geochemistry of a limited sample suite supports a subduction-related relatively low-K calc-alkaline volcanic arc environment for the latter two Formations. The recognised volcanic textures are not unequivocal in their support for a subaerial to subaqueous environment for the Mt Windsor Volcanics, although there is better evidence for a deeper water (submarine?) environment for the T,rooper Creek Formation. The uppermost part of the Group, the Rollston Range Formation, is not represented here. In the Mt Farrenden area the Sevent:y Mile Range Group is exposed in a prominent south plunging syncline which is a major deviation from the otherwise general east-west trend of the Group. The fold axis contains the thinnest development of the Mt Windsor Volcanics, and a part of the largest outcrop area of andesi te within the Group in the Trooper Creek Formation. Intrusion of the Black Jack Granodiorite in the northeast and Policeman Creek Granodiorite in the west occurred during the Late Silurian-Early Devonian. Massive, coarsely crystalline bari te occurs in a small ( 30m by 7m) outcrop at the contact between the Puddler Creek Formation and the overlying Mt Wirtdsor Volcanics. The barite may represent the remnants of a submarine hydrothermal vent of the type associated with volcanic-hosted massive sulphide deposits. However, hydrothermal alteration, in general, is very poorly developed within the study area.

This item is only available electronically.<br>Mineralisation overlain by extensive cover can be identified through the geochemical signature dispersed through the surrounding regolith. This project aimed to use portable XRF (pXRF) analysis to increase the understanding of the regolith geochemistry in the proximity of the Cygnet-Snelling Shear Zone (CS-SZ), Kangaroo Island. The shear zone is significant as it hosts several potentially economic deposits including the Bonaventura Copper (Cu) deposit as well as the Dewrang and Kohinoor Lead - Zinc (Pb-Zn) prospects. By using pXRF analysis at 2m intervals on drill hole transects taken from the vicinity of the CS-SZ it was hoped to be able to discern known pathfinder elements associated with Cu, Pb and Zn mineralisation. The data collected from these transects can be used to develop a model of the regolith sequence lithogeochemistry, and to determine which elements can be reliably analysed by pXRF within a regolith sequence such as that seen on Kangaroo Island. The study has also attempted to identify any geochemical signatures associated with Cu, Zn or Pb mineralisation, their spatial extent and potential as geochemical vectors towards mineralisation.<br>Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2014