Tesi sul tema "Geochemical prospecting"

This work takes a look at some of the literature on calcretes and especially the problem of geochemical exploration in calcrete terrains. The conclusion that will be reached is that exploration in calcrete terrains is not futile and that provided the explorationist is aware of the types of calcrete and their genetic implications calcrete can be used as a sampling medium and anomalies can be detected through calcrete (p.1.)
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The aim of this dissertation is an attempt to' provide a general guide for future gold exploration in tropical and sub-tropical terrains. The dissertation includes a brief discussion of the various exploration techniques used in regional and local exploration. This provide the necessary background knowledge to discriminate between the constraints and applications and to be able to select the techniques which are more suitable for gold exploration in tropical and sub-tropical terrains. Weathering, gold geochemistry and soil formation, fields often neglected, are emphasized to illustrate the importance of the mobility and dispersion of gold in the weathering of the lateritic soil profile. A sound knowledge and experience in regolith mapping is to the advantage of the explorationist. Case studies with special emphasis on Central- and Western Africa are included to illustrate the effectiveness of some of the gold exploration techniques in tropical and sub-tropical terrains. Gold exploration is a highly complex and demanding science and to be successfull involves the full intergration of all geological, geochemical and geophysical information available. An intergrated exploration method and strategy would enhance the possibility of making viable discoveries in this highly competative environment where our mineral resources become more depleted every day. Where applicable, the reader is refered to various recommended literature sources to provide the necessary background knowledge which form an integral part of gold exploration.

A low-density reconnaissance geochemical survey was made of the stream sediments and rocks in the Akaka/Ago-Iwoye, Egbe and Igbo-Ora districts of the southwestern basement complex, Nigeria. The areas are underlain by mainly Precambrian greenstone rocks in close association with granites, gneisses, metasediments (quartzites, quartz-mica schists) and pegmatites. Typical rain forest areas and streams are dissected by a closely and deeply developed dentritic-subdentritic drainage pattern. This study compares the three areas and includes recommendations for further prospecting. Field and mineralogical petrological evidence indicates sulphide mineralization, and geochemical trends in the amphibolites favour a tholeiitic affinity with ultrabasic igneous proliths overprinted by post-magmatic processes. The range of concentrations and geochemical characteristics of elements commonly found in rocks and sediments are reviewed. More than 350 samples were collected and analysed for 17 trace and 10 major elements by X-ray fluorescence, atomic absorption and inductively coupled plasma emission spectroscopy. Analytical precision was monitored using duplicates, standards and reference materials and the statistical basis of analytical quality control examined. Computer based univariate and multivariate statistical techniques are applied to the geochemical data. Initial univariate analyses clearly establish anomalous elemental abundances. Anomalously high Mo, significant Ni and Au values are characteristic of the areas investigated. Particular geochemical patterns of single-element distribution were found. In general, multi-element associations in the sediments were similar to those discerned in the associated bed-rocks. The application of multiple regression analysis to sediments from the Egbe area revealed enhanced Cu and Ni anomalous populations which were suppressed by iron-oxide coprecipitation. R-mode analysis identified models meaningful in terms of correlation either with underlying parent rock, secondary processes of the surifical environment and mineralization. However, there are no clearly defined indications of the ore potential of the Akaka area. The fourth-factor (Au-Sr) for rock samples in the Igbo-Ora complex confirms occurrence of gold mineralization. A clear-cut association of rare-earths are shown in all the areas. The most significant findings of the present work were the identification of exploration target areas worth further investigations. Other aspects highlighted were the possibility of reliable indicator elements for ore mineralization in these areas, significant anomalies being evident in the rocks and sediments.

Information from soil geochemical mapping programmes is useful within a number of different fields including for example mineral exploration and environmental research. The purpose of this thesis was to investigate the relationship between soil metal concentrations and geological factors such as bedrock lithology, structural geology, mineralizations etc. The study used data acquired in association with a nationwide soil geochemical mapping programme conducted by the Geological Survey of Sweden, SGU. These data contained both total element concentrations measured via X-ray fluorescence spectroscopy and acid leached concentrations measured with plasma technique. Basic statistical compilations were made, including classification of element concentrations into percentiles according to SGU standards, calculation of leachability and correlation analyses. Spatial analyses were also done, using GIS-software. The results showed that all investigated elements except zinc had elevated median values for total concentrations in the project area compared to the natural median values. The strongest correlation for total element concentrations was that between iron and cobalt with Spearman ρ=0.88. Furthermore, the results of this study indicated that sampling sites superimposing volcanic rocks contained the highest total concentrations of manganese. The results also suggested that manganese content increased with increasing age of the underlying bedrock. The highest median concentration of 0.80 g/kg was found in Archean rocks. Known mineralizations were often reflected in the form of positive element anomalies in the till geochemistry. The obtained results were also consistent with the average composition of the bedrock. No clear connections with any of the other investigated geological factors could be made.

Nos últimos anos, estudos de prospecção geoquímica aliados à análise estatística e a técnicas de geoprocessamento tornaram-se imprescindíveis na busca por novos depósitos minerais. O Serviço Geológico do Brasil (CPRM) executou o levantamento geoquímico na porção leste do Estado do Rio Grande do Sul, em uma área de aproximadamente 32.481 km², e disponibilizou dados de sedimentos de corrente e de concentrado de bateia. A área desse estudo está situada sobre o Escudo Sul-rio-grandense, mais especificamente no Cinturão Dom Feliciano Leste. Trata-se de uma área formada por um volumoso magmatismo granítico com características de retrabalhamento crustal, na qual predominam rochas de idades proterozóicas. Apesar de pesquisas pontuais haverem encontrado indícios para a descoberta de novas ocorrências minerais na porção leste do escudo, esta tem sido pouco estudada. Sendo assim, este trabalho objetivou investigar possibilidades de novos alvos a partir da identificação de valores anômalos nesta região, empregando técnicas estatísticas e de geoprocessamento. Foram analisadas 1528 amostras de sedimentos de corrente e 1477, de concentrados de bateia, disponibilizadas no banco de dados digital da CPRM (Geobank) Determinaram-se os limiares para elementos químicos de sedimentos de corrente que possibilitaram identificar áreas anômalas. Os dados de concentrados de bateia foram tratados de forma distinta, a partir da construção de mapas de densidade do tipo Kernel. As áreas anômalas foram apresentadas de duas formas distintas. As Anomalias Puramente Estatísticas correspondem às regiões que apresentaram elementos químicos com valores acima do limiar e consideram apenas a posição geográfica destes, independentemente da afinidade existente entre os mesmos. Já as Anomalias Prospectivas foram assim denominadas, pois a delimitação da área anômala foi baseada no agrupamento de elementos que possuem afinidade, utilizando conceitos de prospecção como assinatura geoquímica e elementos farejadores. Os resultados encontrados apontam para seis áreas anômalas na porção leste do escudo sul-riograndense, os quais apresentam assinaturas de depósitos IOCG, Pórfiro-epitermal e depósitos relacionados a granitos estaníferos. Este estudo geoquímico de escala regional revelou áreas anômalas inéditas no escudo sul-riograndense. Fica claro que existe um alto potencial na área da metalogenia a ser ainda estudado.
In the last few years, geochemical prospective studies allied to statistical analysis and geoprocessing techniques became indispensable in the search for new mineral deposits. The Brazilian Geological Survey (CPRM) performed a geochemical survey in the eastern portion of the Rio Grande do Sul State, in an area that covers 32.481 km², and provided stream sediment and pan concentrate data. The studied area is situated in the Rio Grande do Sul’s Shield, more specifically in the Dom Feliciano Eastern belt. The area is constituted by a massive granitic magmatism with crustal reworking characteristics, in which rocks of Proterozoic age prevail. Although some researches had found clues of new mineral occurrences in the eastern part of the Shield, it is still understudied. Thus, this study aimed to investigate the possibilities of new targets from the identification of anomalous values in the region, employing statistical and geoprocessing techniques. 1528 stream sediment and 1477 pan concentrate samples are available in the digital database of CPRM (Geobank) were analysed. The threshold values for stream sediment chemical elements were determined, which allowed identifying the anomalous areas The pan concentrate data was analysed differently, from the construction of Kernel density maps. The resulting anomalous areas of this study were presented in two different ways, as Purely Statistical Anomalies (PSA) and Prospective Anomalies (PA). The regions that presented chemical elements above the threshold value, considering just their geographical position, regardless of the chemical affinity between the elements, were denominated Purely Statistical Anomalies. In the Prospective Anomalies, the delimitation of the anomalous area was based on the grouping of the elements that had chemical affinity, using prospective concepts as geochemical signature and pathfinder elements. The results pointed to six anomalous areas in the Sul-Riograndense Shield, which presented signatures of Iron oxide copper-gold (IOCG), porphyry-epithermal and stanniferous granites deposits. This regional scale geochemical study revealed unprecedented anomalous areas in the Sul-Riograndense Shield. Besides that, it became clear that there is a great metallogenic potential that still need to be studied.

Diamonds have been discovered in a variety of potassic ultramafic rocks including group-I and group-II kimberlites, olivine lamproites and aillikites, all of which are macroscopically similar and can be difficult to differentiate when viewed under the microscope. However, group-I kimberlites, and to a much lesser extent group-II kimberlites and olivine lamproites, are known to contain economic concentrations of diamonds. This study addresses the problem of distinguishing among different types of kimberlitic and related rocks by developing a geochemically-based method for classifying them.
Geochemical methods have been largely ignored in the classification of kimberlites and related rock types due to high concentrations of xenoliths. However, this problem can be largely overcome by only selecting matrix material for analysis. An evolving kimberlitic magma will become enriched or improvished in Si due to the fractionation of olivine and phlogopite, depending on the initial Si concentration of the magma. As they have low Si concentrations, group-I kimberlites and aillikites can be separated from group-II kimberlites and meimechites, which have higher Si concentrations for any Mg content. Furthermore, since aillikites and meimechites are relatively rich in Fe compared to group-I and group-II kimberlites, these rock types form four separate fields on a Si vs. Fe discrimination diagram. Similar rock-type separation is observed when the ratio of La to Yb is plotted against the ratio of Sm to Yb. Kimberlite and other potassic ultramafic rocks were sampled from nine areas in Quebec: the Otish Mountains, Wemindji, Torngat Mountains, Desmaraisville, Temiscamingue, Ile Bizard, Lac Leclair, Baie James and Ayer's Cliff regions. Major and selected trace element concentrations were determined by XRF analysis for all samples, while a subset of representative samples was selected for trace element analysis by ICP-MS. Electron microprobe analyses of unaltered olivine and phlogopite were also conducted.
Of the 37 samples that were classified both mineralogically and chemically, 23 or 62% were correctly classified using Fe and Si. This number increases to 84%, if the REE are used in conjunction with Si and Fe. The Si vs. Fe discrimination diagram separates group-I kimberlite from most aillikite and meimechite rocks and group-II kimberlite/olivine lamproite rocks from most aillikite and meimechite rocks. Therefore, major and trace element geochemistry offers an important tool for the classification of kimberlitic rocks.
Vasilenko et al. (2002) and Francis (2003) both suggested that diamond grades can be correlated with the major element compositions of the kimberlites. The data collected in this study confirm the inverse relationship between TiO2 concentration and diamond grade. The lowest TiO 2 values were obtained on samples from the Otish Mountains and Renard samples in particular. Other areas of Quebec are characterized by higher TiO2 contents with most samples containing greater than 2 wt% TiO 2. Therefore, the kimberlitic rocks from the Renard locality have the greatest potential for an economic diamond deposit. The origin of this correlation needs to be explored, however, because it is unclear whether this is a feature of the mantle source, or reflects the survivability of diamonds within the kimberlites.

In tropical areas, the high rainfall induces severe-and pervasive weathering, producing a thick soil cover. The lithologies underneath may b~ recognised using geochemical mapping, which is based on certain elements that have the ability to differentiate between various lithologic units. Elements that are independent of the weathering process are normally selected for this purpose. The chemistry of mobility of base metals is an important factor to take into account when evaluating the mobility and distribution of these elements in a soil profile. Factors such as pH, Eh, organic material, clay minerals, Fe and Mn oxides are normally key aspects to be considered. When iron-rich rocks undergo deep weathering, lateritic profiles are developed. These are widespread in a belt bordering the equatorial zone, including the Brazilian shield, West and East Africa, parts of India and Northern Australia. In these profiles, the high rainfall promotes intense leaching of the different horizons. Where the pre-existing profiles are mostly preserved, the base metals are distributed throughout the profile: in the upper ferruginous horizon, goethite and hematite can adsorb large amounts of Mo, resulting in large dispersion halo. Other base metals such as Cu and Zn are less resistant in these freely-drained profiles and, therefore, they may be partly leached from the profile. In the lower horizons, Cu, ,zn, Ni and Co are retained, hosted in kaolinite and smectite, and thus, a high geochemical contrast will be identified in this horizon at the expense of a decline in the size of the dispersion haloes. The pre-existing profiles can be truncated, with a thin stone line developing at the contact between the lateritic profile and the recent soil. The conditions in these environments favour the retention of most of the pathfinder and target elements in all soil horizons, with the B horizon showing the highest contrast. If the primary rock is rich in AI, a bauxitic profile will be developed. The world distribution of bauxites closely resembles that of laterites. The behaviour of Co and Ni is very similar to that of iron during the bauxitization. Furthermore, the factors that induce residual enrichment of Al with removal of Fe in the soil profile will cause significant depletion of Co and Ni in these profiles. These metals are then concentrated at the base of the profile because of precipitation from downward percolating solutions. Many karst bauxite deposits in Southern Europe are enriched with Ni and Co in the basal horizon. Such horizon is mined as nickel ore in the bauxites of the Lokris region in Greece. Copper and molybdenum are strongly enriched.in bauxitic profiles. Concentration ratios are 8 and 3.2 for Cu and Mo respectively. Molybdenum is closely related to goethite and hematite, and therefore, the high concentration of Mo in a bauxitic profile will be consistent with the horizon where iron is concentrated. Copper concentrates at the base of the iron rich-horizon but also appears enriched in the saprolite together with Co. When sulphide bodies occur, in this environment, deep and penetrative weathering has resulted in considerable near-surface mobilization of iron and silica. The supergene alteration commonly obscures the identity of the primary sulphides at the surface. In this case, geochemical assessment of the resulting gossan has proved to be crucial in mineral exploration. A search in the secondary mineral assemblage, volatile and precious metals may lead to the information on the composition of the primary sulphide assemblage. The conclusion that will be reached is that if the geochemical properties (mobility, affinities with Fe or Mn oxides and/or clay minerals) of each of the base metals are understood, an appropriate sampling (optimum size-depth combination) will then be done. In such cases, a subdued, weak, but significant, geochemical response will be identified in the surface horizon.

Thesis (Ph.D.) -- University of Western Sydney, Nepean, 1998.
CD-ROM (appendix) contains complete lists of the species distribution for each water sample; the constant correction spreadsheet; and, the possible stability constants for aqueous ionic species as well as the data ranges for both the Girilambone study and the North Mungana study. A thesis presented in accordance with the regulations governing the award of the degree of Doctor of Philosophy in the University of Western Sydney, Nepean, School of Science. Includes bibliographical references at end of each chapter.

[Tuncated abstract] Soil is a relatively low cost and robust geochemical sampling medium and is an essential part of most mineral exploration programs. In areas of covered terrain, however, soils are less reliable as a sampling medium because they do not always develop the geochemical signature of the buried mineralisation; possibly a result of limited upward transport of ore related elements into the surficial overburden. As economic demands on the resources industry grow, mineral exploration continues to expand further into areas of covered terrain where the rewards of finding a new deposit relative to the risks of finding it may be comparatively low. Thus, improving the costeffectiveness of a geochemical exploration program requires a sound understanding of the mechanisms by which soil geochemical anomalies form in transported overburden. This thesis examines the deep biotic uplift of ore related elements by deep rooting vegetation as a mechanism for the development of soil geochemical anomalies within transported overburdens, in semi-arid and arid regions. '...' Vegetation and soils were analysed at two Au prospects in Western Australia: Berkley, Coolgardie and Torquata, 210 km south-east of Kambalda, in semi-arid Western Australia to complement both the mass balance and the differential modelling. At Berkley, both the vegetation and soils located directly over the mineralisation showed high concentrations of Au. There may be indirect evidence for the operation of the deep plant uptake flux taking effect from the field evidence at Berkley. Firstly, anomalous concentrations of Au were found in the surface soils, with no detectable Au in the transported overburden. Secondly, the trace element concentrations in vegetation showed correlation to the buried lithology, which to our knowledge has not been reported elsewhere. The results from the samples at Torquata, in contrast, were less conclusive because the Au is almost exclusively associated with a surficial calcrete horizon (at <5 m soil depth). Strong correlations of Ca and Au in leaf samples however, suggest that the vegetation may be involved in the formation of calcrete and the subsequent association of Au with the calcrete. Among the vegetation components, the litter and leaf samples gave the greatest anomaly contrast at both prospects. Finally, three main drivers for the deep biotic uplift of elements were identified based on the results from the mechanistic numerical modelling exercise: i) the deep uptake flux; ii) the maximum plant concentration and; iii) the erosional flux. The relative sizes of these three factors control the rates of formation and decay, and trace element concentrations, of the soil anomaly. The main implication for the use of soils as exploration media in covered terranes is that soil geochemical anomalies may only be transient geological features, forming and dispersing as a result of the relative sizes of the accumulative and loss fluxes. The thesis culminates in the development of the first quantitative, mechanistic model of trace element accumulation in soils by deep biotic uplift.

Thesis (MSc)--University of Stellenbosch, 2007.
ENGLISH ABSTRACT: The aim of the study is to ascertain whether geochemical exploration techniques can be used in the search for tanzanite deposits in the Merelani area, NE Tanzania. Previous studies have successfully demonstrated a partial extraction method (in situ soil leaching) in identifying prospective ultramafic bodies at the Rockland ruby mine in the Mangare area, Kenya, thereby demonstrating the usefulness of geochemical methods in gemstone exploration. In this study, a partial extraction as well as a whole-rock geochemical method was used to determine the applicability of these methods in prospecting for tanzanite mineralisation using different sampling media, such as soil, stream sediment and calcrete. It is possible that this geochemical approach may not be as effective as physical methods such as the separation and examination of heavy mineral suites. However, its viability needs to be evaluated due to the potential efficiency and relative logistic ease of the method. In essence the scientific method employed is to compare overburden (soils, stream sediments and calcrete) chemistry with known underlying geology, the latter having been established via diamond core drilling. A positive correlation would allow the prediction of overburden covered tanzanite mineralisation. Soil samples were collected from a trench dug perpendicular to regional lithological strike over both barren and tanzanite-bearing horizons. XRF trace element data for the soils was compared to the chemistry of the underlying lithologies. ICP-AE data derived from 1 molar HCL soil leachate (12 hour leach) and soil XRF data, from the same samples, was compared, using a mass balance index, to discern any hydromorphic dispersion of selected trace elements and to evaluate the leachate as a viable alternative to XRF analysis. In general, a good correlation exists between the soil and rock trace element data profiles over the length of the section. However, Ti- and Zr-normalised mass balance calculations show some down-hill drift, but this does not disrupt the overall pattern. The ICP-AE acid leach data show that hydromorphic dispersion is low, that the trace elements of interest (V, Cr, Ni and Cu) are hosted within non-soluble phases. Consequently, the leach technique is not a viable alternative to XRF analysis of the soils. XRF analysis of the soils was shown to be potentially useful in identifying new areas of mineralisation as the soils overlying a graphitic calc-silicate schist, that always occurs adjacent to the tanzanite mineralisation in the Merelani area, was found to be easily identifiable based on anomalous concentrations of V. An exploration concession was chosen for stream sediment sampling on the basis of the presence of large streams, of a few tsavorite mines indicating high prospectivity for tanzanite, and because of a variation in geology on the property. Tanzanite and tsavorite are cogenetic in the known tanzanite deposits. In this case the aim was to investigate the possible occurrence of tanzanite-like geochemical anomolies (i.e. the anomalous V observed in the soil chemistry investigation) could be detected in the vicinity of the tsavorite mines. Tsavorite, the gem variety of grossular garnet, also contains high concentrations of V. The samples were analysed by XRF whole-rock methods for trace element content. The data shows a number of clear positive V anomalies in the study area. The data also shows that each of the existing or abandoned mines in the area is marked by a positive V anomaly. This section of the study also demonstrated a relatively low degree of stream sediment dispersion of the trace elements of interest – most likely a function of the semi-arid climate. The fine fraction (<90μm), however was shown to be mobilised to a relatively larger degree than the coarse (180μm – 300μm) and medium (90μm - 180μm) fractions. As is predictable from the leachate analysis, factor analysis of the data shows that the trace elements are dominated by heavy mineral geochemistry and that a study in heavy mineral exploration might provide a cheaper and more viable option to those explored in this study. Calcrete samples were taken from an abandoned, 10m deep mine shaft, which was sunk through the calcrete to reach the tanzanite deposit. The shaft was sampled from the bottom, closest to the tanzanite mineralisation, to the surface to investigate the association between trace element geochemistry and proximity to the deposit. There was no vertical association between the trace element geochemistry of the calcrete and proximity to the tanzanite deposit. There was also no clear indication in the geochemistry of the calcrete of the existence of the tanzanite deposit beneath it. This further indicates the immobility of the elements of interest in this environment. This study has demonstrated that properly constrained soil and stream sediment geochemical studies may be of use in tanzanite exploration. However, it must be stressed that this is only the case if the geochemical signature of the lithological package associated with the mineralisation is unique and well known.
AFRIKAANSE OPSOMMING: Die doel van hierdie studie is om te bepaal of geochemiese eksplorasie tegnieke vir die soek na tanzaniet afsettings in die Merelani area, noord-oos Tanzanië, gebruik kan word. Voorige studies het gewys dat ‘n gedeeltelike ekstraksie metode (in situ grond looging) gebruik kon word om prospektiewe ultramafiese liggame by the Rockland rubyn myn in die Mangare area, Kenia te identifiseer. Hierby is gedemonstreer dat geochemiese eksplorasie metodes suksesvol in edelsteen eksplorasie toegepas kan word. In hierdie studie is ‘n gedeeltelike ekstrasksie en heel-rots geochemiese metodes gebruik om die toepaslikheid van hierdie metodes op tanzaniet eksplorasie te toets. Verskillende geologiese materiale is gemonster, naamlik grond, stroom sedimente en kalkreet. Dit is moontlik dat hierdie geochemiese benadering nie so effektief soos fisiese metodes soos swaar mineraal skeidings mag wees nie. Dit is nogtans belangrik om die toepaslikheid van hierdie metodes op tanzanite eksplorasie te toests, as gevolg van die potensiële effektiwiteit en relatiewe logistiese gemak van die metodes. Die essensie van die wetenskaplike metodiek wat in hierdie studie gebruik is, is om die geochemie van die grond, stroom sedimente en kalkreet te vergelyk met die geochemie van die onderliggende geologie wat deur middel van diamant boorwerk vasgestel is. ‘n Positiewe korrelasie sou dan dui op ‘n bedekte tanzaniet afsetting. Grond monsters is van ‘n sloot geneem wat loodreg op die strekking van die tanzaniet gemineraliseerde en ongemineraliseerde horisonne gegrawe is. XRF spoor element data van die gronde is vergelyk met die chemie van die onderliggende gesteentes. IGP-AE data wat bekom is deur die monsters met 1 molaar HCl te loog (12 uur loging) is vergelyk met XRF data van dieselfde monsters deur middel van ‘n massa balans indeks om te bepaal of daar enige hidromorfiese dispersie van sekere spoor elemente is en om die toepaslikheid van loging as ‘n alternatief tot die heel-rots metode te bepaal. In die algemeen is daar ‘n goeie korrelasie tussen die grond en rots spoor element data profiele oor die lengte van die seksie. Alhoewel, Ti- en Zr-genormaliseerde massa balans data profiele wys dat daar ‘n mate van afwaartse beweging van grond na die voet van die heuwel is, maar dat hierdie ‘n breuk in die algemene patroon vorm nie. Die IGP-AE data dui daarop dat die hidromorfiese verspreiding van spoor elemente laag is en dat die spoor elemente wat van belang is (V, Cr, Ni en Cu) in nie-oplosbare fases gesetel is. Gevolglik is die logings metode nie ‘n toepaslike alternatief tot die heel-rots XRF metode op gronde nie. XRF analises op die gronde het gewys dat die XRF metode moontlik nuttig kan wees om nuwe areas van tanzanite mineralisasie aan te dui, omdat die gronde wat ‘n grafietiese kalk-silikaat skis oorlê, wat altyd langs die tanzaniet draende horisonne voorkom, is op grond van anomale konsentrasies van V geïdentifiseer. ‘n Eksplorasie konsessie is op die basis van die teenwoordigheid van groot strome, ‘n paar tsavoriet myne wat aanduidend is van hoë prospektiwiteit vir tanzaniet is en as gevolg van ‘n variasie in geologie in die area vir stroom sediment monstering gekies. Tanzaniet en tsavoriet is kogeneties in bekende tanzaniet afsettings. In hierdie geval was die doel om te ondersoek of tanzanietagtige anomalieë (nl. die anomale konsentrasies van V wat in die ondersoek van die grond chemie opgemerk is) in die omgewing van die tsavoriet myne geïdentifiseer kan word. Tsavoriet, die edelsteen variëteit van grossulaar granaat, bevat hoë konsentrasies V. Die monsters is deur middel van die XRF heel-rots metode vir spoor elemente geanaliseer. Die data dui op ‘n paar monsters met hoë V konsentrasies in die ondersoek area. Hierdie studie het ook gedui op ‘n lae stroom sediment verspreiding van die spoor elemente van belang, heel waarskynlik is dit ‘n funksie van die semi-ariede klimaat. Die fyn fraksie (< 90μm) blyk tot ‘n groter mate as die growwer (90μm tot 180μm en 180μm - 300μm) fraksies gemobiliseer te word. Soos voorspel kan word deur die loogings analise het faktor analise gewys dat die spoor elemente deur swaar mineraal geochemie gedomineer word en dat ‘n studie op swaar minerale moontlik ‘n goedkoper en meer toepaslike eksploraise metode is as die wat in hierdie studie ondersoek is. Kalkreet monsters is van ‘n ongebruikte, 10m diep myn skag wat deur die kalkreet gesink is om by die tanzaniet gemineraliseerde horison uit te kom geneem. Monsters is van die bodem van die skag, naaste aan die tanzaniet mineralisasie, tot die oppervlak geneem om die assosiasie tussen die spoor element geochemie en afstand van die tanzaniet mineralisasie te ondersoek. Geen vertikale assosiasie tussen spoor element geochemie en die nabyheid tot die tanzaniet afsetting kon vasgestel word nie. Daar was geen duidelike aanduiding in die geochemie van die kalkreet op die onderliggende tanzanite afsetting nie. Hierdie is ‘n verdere annduiding op die nie-mobiele toestand van spoor elemente in hierdie omgewing. Hierdie studie het suksesvol gedemonstreer dat goed gedefinieerde grond en stroom sediment geochemiese studies moontlik in geochemiese eksplorasie vir tanzaniet bruikbaar kan wees. Dit is belangrik om in gedagte te hou dat dit slegs die geval is as die geochemie van die litologiese paket wat met die mineralisasie geassosieer is uniek en goed bekend is.

The Morokweng impact structure which is located in the North West province of South Africa, has attracted attention as a potential host for Ni-PGE mineralization. Geochemical exploration techniques using hydroxylamine partial extraction were used to determine the nature and source of surface geochemical anomalies known to occur in the overlying aeolian sang regolith. About 40 aeolian samples were taken from an area of about 35 square kilometer, located in the north eastern sector of the Morokweng impact structure. The samples were sieved to various grain size fractions and partially extracted using varying concentration of hydroxylamine hydrochloride at 50°
C.

This study involves the application, interpretation and utilization of regional geochemical data for target generation in the North West Province, South Africa. A regional soil geochemical survey programme has been carried out by the Council of Geoscience South Africa since 1973. A number of 1:250 000 sheet areas have been completed, but there are no interpretative maps which could aid in mineral exploration and other purposes. In order to utilize the valuable and expensive data, the project was motivated through data acquisition and interpretation to generate exploration targets. The study area is confined to Mafikeng, Vryburg, Kuruman and Christiana in the Northwest Province, where potential exploration and mining opportunities exist in areas of great geological interest. These include geological events such as the Bushveld Complex, the Kalahari manganese field and the Kraaipan greenstone belts. The aim of this project was to utilize geochemical data together with geophysical and geological information to verify and identification of possible obscured ore bodies or zones of mineralization, and to generate targets. Another objective was the author to be trained in the techniques of geochemical data processing, interpretation and integration of techniques such as geophysics, in the understanding of the geology and economic geology of the areas. Approximately 5 kg of surface soil was collected per 1 km2 by CGS from foot traversing. Pellets of the samples were prepared and analyzed for TiO2, MnO and Fe2O3, Sc, V, Cr, Ni, Co, Cu, Zn, As, Y, Ba, Nb, Rb, Th, W, Zr, Pb, Sr and U using the simultaneous wavelengthdispersive X-ray fluorescence spectrometer technique at the Council for Geoscience, South Africa. For each element the mean +2 standard deviations were used as a threshold value to separate the negative from the positive anomalies. The integration of geological, geophysical and geochemical information was used to analyze and understand the areas of interest. A number of computer programmes were extensively used for data processing, manipulation, and presentation. These include Golden Software Surfer 8®, Arc-View 3.2a®, TNT-Mips®, JMP 8 ®, and Microsoft Excel®. Through geochemical data processing and interpretation, together with the low resolution aeromagnetic data, gravity data and geological data, seven (7) exploration target areas have been generated: These have been numbered A to G. It is concluded that there is good potential for Cr, PGMs, vanadium, nickel, iron, copper, manganese, uranium and niobium in the targets generated. The results provide some indication and guide for exploration in the target areas. In Target A, Cu, Cr, Fe, Ni and V anomalies from the lower chromitite zone of far western zone of the Bushveld Complex, which has be overlain buy the thick surface sand of the Gordonia Formation. Target B occurs over the diabase, norite, andesitic lava and andalusite muscovite hornfels of the Magaliesberg Formation. This target has the potential for Cu, Fe and Ni mineralization. The felsic rocks of the Kanye Formation and the Gaborone Granite in target C have shown some positive anomalies of niobium, uranium, yttrium and rubidium which give the area potential for Nb, REE and U exploration. Target D is located on the Allanridge Formation, and has significant potential for Ni-Cu mineralization, and is associated with the komatiitic lava at the base of the Allanridge Formation in the Christiana Area. The light green tholeiitic, calc-alkali basalt and andesitic rocks of the Rietgat Formation are characterized by a north-south trending yttrium anomaly with supporting Ba and Y anomalies (Target E). This makes the area a potential target for rare earth elements. Calcrete on the west of the Kuruman has a low b potential target for vanadium. It is believed that the area might be potential for potassium-uranium vanadate minerals, carnotite which is mostly found in calcrete deposits. This study has proved to be a useful and approach in utilizing the valuable geochemical data for exploration and future mining, generated by Council for Geoscience Science. It is recommended that further detailed soil, rock and geochemical surveys and ultimately diamond drilling be carried out in the exploration target areas generated by this study.

This research centres on the use of portable X-Ray fluorescence (XRF) as a tool for archaeological geochemistry. The instrument was used as part of varied contextual, vertical and horizontal sampling strategies on three Viking Age sites in southern Norway in order to investigate archaeological geochemistry as a method of better understanding spatial and temporal variation in occupation deposits. Archaeological deposits are often truncated, redeposited or otherwise disturbed, which limits the application of more established methods for geochemical sampling by means of a static, horizontal grid. Instead, flexible sampling strategies were developed that included coring as a prospection method combined with high-resolution GPR data. The combination of portable XRF and coring, both within excavation contexts and as prospection, allowed high resolution analysis directly onto the core. The minimal sample preparation allowed a greater data volume to be gathered, and the data provided a geochemical chronological sequence for the deposits. Thus, both spatial and temporal planes were accessible where the archaeological material was suitable. The validity of this method, as well as the use of portable XRF for geochemical analysis in archaeology, was assessed critically throughout this research. The results suggest that there is a loss of accuracy and resolution by using portable XRF on unprepared samples; here this is deemed offset by the benefits. The method of coring, and thus preserving the stratigraphy for sampling and analysis, allows not only the continuity and change within the archaeological deposits to be assessed, but also details soil processes to a greater extent than established, extraction based methods such as ICP-MS. XRF analyses the whole sample, and whilst this can mute certain trends in the anthropological inputs, it means that interpretation can include the impact soil processes have had on these inputs by stratigraphic phase. Moreover, on sites where preservation is limited, deposits that would previously be disregarded for geochemistry can be used to form some understanding of past occupation from the little that remains. This approach is developed though the course of the three case studies, and the data statistically treated using principal component analysis, and interpreted from a geoarchaeological perspective. The research also attempts to embrace theoretical perspectives that enhance insight into past social and cultural practices. As archaeological geochemistry aims to understand space, it is also fundamental to understand the social meaning of space within the contexts investigated.

This study is informed by the rising demand for power needs in South Africa and aims at understanding the geophysical and geochemical characteristics of the energy minerals in the Springbok Flats Basin and relating them to the prevailing geological and structural setting for improved exploration targeting. The Springbok Flats Basin is part of the Karoo sediments and host to uranium, coal and coal bed methane (CBM) resources. The lithology sections in the basin indicate presence of basaltic lavas at the top, underlain by mudrocks, siltstones, sandstones, conglomerates and diamictite, with interbedded coal beds occasionally. The coals are uraniferous and shale bounded and of lower Beaufort age at 250 Ma. The regional radiometric data identifies the regional extent of the Springbok Flats Basin as a basin with low total count values. This information is useful in exploration as it gives an idea of the limits of the area where to focus application for prospecting licenses. The reduced to pole of the total magnetic field, residuals and first vertical derivative maps clearly show the high magnetic susceptibility nature of the surrounding Bushveld rocks as compared to the low Karoo sediment susceptibility within the basin. There are distinct ring shaped picks within the basin possibly due to known Karoo dolerite sills in particular to the central south western part of the grid. The regional geochemical mapping program is a cost-effective way of providing an overview of the relative abundance levels, regional trends and anomalous patterns in the underlying lithological units. Background values of elements in soils over different lithological units and the identification of anomalous values relative to these elements can easily be identified. The geochemical results show an excellent correlation between soil chemistry and underlying geological formations. A few distinct gravity highs are clearly shown within the basin. Assuming the effect of the Letaba basalt to the gravity readings is uniform across the basin; these distinct anomalies could be due to Karoo dolerite sills as they coincide with areas of distinct high magnetic signature. A conceptual model was generated assuming that the Karoo sediments’ layering is uniform across the gravity profile but changes in the residual are due to an increased thickness of the sill supported by the gentle changes on the surface topography. Satellite imagery has got its challenges especially in areas of vegetation but it does provide a very useful tool in exploration. A number of spectral analysis techniques and band rations can be used to differentiate the areas underlain by the Letaba basalts, the Karoo sandstones/shale and Bushveld granites for mapping purposes. The priority focus will be on the shallower Karoo sediments because of the potential for cheaper mining. Exploration targeting needs to be guided by observed geochemical and geophysical characteristics in order to prioritize areas taking into account the presence of Karoo intrusives such as the dolerite sills that tend to devolatize the coal hence affecting the quality/rank. Structures and gravity signatures are very important in delineating areas with thick sediments that have a potential for CBM. The same understanding in targeting goes a long way in planning drill holes, resource modelling and pre-feasibility stages for mine planning. A high resolution airborne geophysical survey is recommended over the basin to better resolve structures. Geophysical borehole logging is recommended to be part of the exploration drilling programs in the Springbok Flats Basin in order to define the in-situ geophysical characteristics. Geophysical logging is useful in particular for the uranium reserves that cannot be delineated from the surface due to deep intersection.

L'alteration supergene de trois indices de cuivre du bresil, localises entre 5**(o) et 24**(o) de latitude sud est etudiee. On determine les differentes phases d'alteration (smectitique et lateritique) correspondant a une grande mobilite geochimique. La plus grande partie du cuivre est lisciviee et le cuivre restant est associe a la goethite. Une application de cette etude a la prospection geochimique et a la mineralurgie est proposee

SP, resistivity/IP and seismic refraction responses of the Woodlawn Orebody and Mt.Bulga Deposit are examined and compared. Both exhibit similar responses produced mainly by uneconomic and disseminated sulphide mineralization and host rock features, demonstrating that the magnitude and character of electrical and seismic responses are not reliable indicators of size and economic sulphide content of volcanogenic sulphide ores. SP, soil geochemistry and electrogeochemistry are found to be the most effective exploration methods followed by resistivity/IP and seismic refraction. The large SP responses over both ore zones are simulated using new methods which allowed the width and depth of oxidation to be computed. Conventional and compensation array resistivity responses best define the deposits. Computer simulation shows that dipole- dipole and Unipole arrays are most useful. First order IP responses are large and similar, but the ore zones are not easily distinguished from polarizable host rocks. Second order responses, at Woodlawn, better define these lithologies and cross-plots of EM coupling removed first order parameters prove useful. The supergene and gossan zones are defined as sources of electrical anomalies and correlate with interpreted SP sources. Seismic velocities of fresh Woodlawn ore samples indicate only small contrasts with host rocks. Refraction travel-time data are highly complex but host rocks are clearly distinguished by their seismic velocities. Both deposits appear as low velocity zones at the general bedrock level which are shallower and narrower than the electrical sources associated with the ore zones. Extensive model simulation shows that the Reciprocal interpretation method is most useful when compared to other time- term methods for refraction interpretation but has some limitations. Computer simulation shows the significance of non- critical refractions, diffractions and laterally hidden zones which define the lateral resolution of the refraction method. The results of this study and the interpretative techniques developed will assist the exploration for similar and deeper massive volcanogenic orebodies in comparable geological environments.

Orientadores: Jacinta Enzweiler, Otávio Augusto Boni Licht
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências
Made available in DSpace on 2018-08-22T23:05:18Z (GMT). No. of bitstreams: 1 Barros_FernandaCeciliaDias_M.pdf: 7061274 bytes, checksum: fb0d51f8e86e9f4450483280c29b5fc9 (MD5) Previous issue date: 2012
Resumo: O uso da geoquímica de gases ou emanometria é um método com grande potencial em prospecção mineral de depósitos não aflorantes e/ou encobertos por rochas não-mineralizadas, porém ainda é pouco utilizado. A temperatura de formação da mineralização é um fator determinante à presença de alguns elementos- traço, dentre eles o Hg. Existe uma predileção do Hg por depósitos de zinco de baixa temperatura do tipo epitermal e stratabound. O depósito de Zn-Pb-Cu de Santa Maria, localizado na Bacia do Camaquã, município de Caçapava do Sul (RS) contém Hg associado à mineralização e, por isso, foi escolhido como área piloto para testes de emanometria. O objetivo desta pesquisa foi medir a concentração de Hg gasoso in situ e avaliar a sua potencialidade na prospecção de depósitos sulfetados de zinco. A concentração de Hg gasoso no ar foi medida ao longo de um percurso de 11 km com um espectrômetro portátil de absorção atômica a fim de definir a concentração de Hg atmosférico local, que variou de 2 a 10 ng/m3. O Hg gasoso no solo foi medido em buracos escavados em profundidades de 30 e 50 cm e a sucção do ar para o interior do espectrômetro, atingindo valor máximo de 19 ng/m3 acima da mineralização. Amostras de solo e de duas espécies de vegetação também foram analisadas. O tratamento estatístico dos resultados mostrou que o background de Hg medido nas amostras de solo variou entre 3,9 e 28 ng/g Hg, enquanto o background obtido para as amostras de carqueja (Baccharis trimera) variou entre 10,5 e 38 ng/g Hg. Os valores de background local e o padrão de anomalia gerado demonstraram que o Hg atmosférico, o Hg gasoso (especialmente em 30 cm) e a carqueja foram os meios amostrais mais eficientes para detectar a mineralização pela medição do mercúrio. As amostras de solo e vassourinha (Dodonea viscous) geraram uma fraca resposta geoquímica da mineralização. A localização e a dimensão das anomalias de Hg puderam ser associadas à mineralização sulfetada de Santa Maria, ao sistema de Falha Três Figueiras e atividades antrópicas na área
Abstract: The use of gas geochemistry or emanometry is a method with great potential in mineral exploration of deep ore deposits covered by non-mineralized rocks, although rarely used. The temperature of the mineralization is a determinant factor for the presence of certain trace elements, including Hg. There is an affinity of Hg for low temperature zinc deposits, especially epithermal and stratabounds type deposits. The Zn-Pb-Cu deposit of Santa Maria, located in Camaquã Basin, Caçapava do Sul (RS) contains Hg associated to the mineralization and was chosen as pilot area to test emanometry. The objective of this research was to measure gaseous Hg in situ and to evaluate the potentiality of its use in prospection of zinc sulfide deposits. The air Hg gas concentration was measured along a trajectory of 11 km with a portable atomic absorption spectrometer, resulting in atmospheric Hg concentrations that varied between 2 to 10 ng/m3. The Hg gas in soil was measured in holes excavated at depths of 30 and 50 cm by air suction into the spectrometer, attaining 19 ng/m3 over de mineralization. Soils and two species of vegetation were also sampled and analyzed. The statistical treatment of data showed that background Hg in soils samples varied between 3.9 and 28 ng/g, while the Hg in gorse (Baccharis trimera) varied between 10.5 and 38 ng/g. The local background values and the pattern of the anomaly showed that atmospheric Hg, gas Hg in soil (especially at 30 cm depth) and gorse were the most efficient sample media to detect the mineralization by using Hg. The soil and florida hopbush (Dodonea viscous) produced a weak geochemical response of the mineralization. The location and the dimension of Hg anomalies could be associated to the Santa Maria deposit, to the Três Figueiras fault system and to anthropogenic activities in the area
Mestrado
Geologia e Recursos Naturais
Mestra em Geociências

The use of geochemical analysis for characterization studies of archaeological material has been increasing for decades. In recent years, advancements in X-ray fluorescence (XRF) instrumentation have led to hand-held portable XRF (pXRF) instruments capable of on-site, rapid, non-destructive analysis. The addition of pXRF to the archaeologist's toolkit has the potential to revolutionize geochemical characterization studies as research design can be informed by field analysis, once off-limits museum collections may now be analyzable, and data can be gathered on in-situ objects without disturbing their context. This new instrumentation has shown promise in characterization studies on a variety of archaeological materials, including ceramics. Particularly, it has been shown to generate data useful in distinguishing the geochemical provenance of artifacts. While most existing provenance studies that employ pXRF involve obsidian, it is possible that pXRF is a suitable analytical tool for ceramics as well, since instrumental neutron activation analysis (INAA) and laboratory XRF have both been used in provenance studies of obsidian and ceramics. This thesis reports research that utilized a Bruker hand held pXRF analyzer to study ceramics and plaster floors from Classic Period (ca. AD 250-1000) archaeological sites in southeast Mesoamerica. The data gathered from this analysis are used to examine the ability of pXRF to address archaeological questions of archaeological provenance on ceramic material and human activity patterns on archaeological plaster. The data gathered on ceramic material is analyzed to determine if "valley profiles" (or "chemical fingerprints") can be created for samples excavated in the same valley and to investigate inter-valley trade. Data from the plaster samples is examined to determine if pXRF can detect human activity patterns on plaster floors and, if so, if the activity is identifiable. The results suggest that, while pXRF results can be used to create "valley profiles" for provenance research, it is difficult to ascertain if it can be used to identify items of trade. This investigation also shows that, while pXRF data can identify human activity on plaster, it is difficult to determine what those activities were. This leads to the conclusion that pXRF has potential for both provenance and prospection studies on earthen materials. However, methodological development is necessary to fine tune research design. This thesis contributes to a greater understanding of the potentials and limitations of pXRF instrumentation in characterization studies of archaeological materials as well as understanding cultural-historical details in Classic southeast Mesoamerica.

This thesis illustrates how geophysical and geochemical methods can be combined to study archaeological sites and obtain enhanced interpretations of the results using the complementary information they provide. Whilst these two disciplines tend to be used independently, this thesis brings them together, with a view to exploring their relationships and developing strategies that lead to non-destructive and cost-effective surveys. The investigation focuses on the correlation of geophysical and geochemical results over common archaeological features and their analysis using soil geochemistry in order to understand the factors of contrast involved in their detection. Five case study sites in Scotland were selected, each one presenting a specific challenge to be assessed by the integrated methodology developed in this thesis. The research employed a range of geophysical (earth resistance, magnetometry, magnetic susceptibility, FDEM and GPR) and geochemical (total phosphate and multi-element analysis) techniques routinely used in archaeological prospection. The different geophysical responses obtained over targeted archaeological features were considered with respect to soil texture, organic matter content, pH, conductivity and chemical composition from archaeological deposits, topsoil and subsoil samples. The results not only provide a nuanced understanding of the character of the archaeological features surveyed, but begin to develop a better insight of how the setting of a site may affect geophysical and geochemical datasets at Scottish archaeological sites. This thesis concludes that the detection of archaeological anomalies depends upon inter-related and site-specific contrast factors including: general site settings (e.g. the effect of highly variable glacial drift deposits), the type of features to be detected (e.g. cut or impervious), and the effect of soil post-depositional processes inside archaeological features and surrounding matrix. For example, at the prehistoric site at Forteviot site (Perthshire) redox processes inside archaeological ditches contribute to their negative magnetic response. Also, chemical composition related to anthropogenic organic materials may enhance the conductivity of theoretical impervious features as illustrated at the Bay of Skaill site (Orkney).

L'exploration minière axée sur des cibles cachées en profondeur nécessite (i) des techniques efficaces qui sont applicables sur le terrain pour identifier les systèmes de formation de minerai à grande échelle et (ii) des éclaireurs pour pouvoir localiser le minerai à plus petite échelle. Avec le développement rapide des équipements portables ces dernières années, l'importance de l'analyse en temps quasi réel sur le terrain a augmenté en aidant à la prise de décision rapide avant les demandes de laboratoire. Des équipements individuels ont été largement utilisés dans l'exploration des ressources minérales pour réaliser des analyses spectroscopiques. Cependant, les données obtenues par plusieurs techniques sont rarement appliquées pour caractériser les "vecteurs" qui peuvent fournir des informations intéressantes sur les variations dans la lithologie, la géochimie, la minéralogie et la chimie des minéraux. La combinaison des données spectrales obtenues à partir de divers instruments portables est encore plus rare. L’objectif principal de ce travail de thèse est de concilier les données géochimiques acquises à partir de différents appareils spectroscopiques portables afin de déterminer la meilleure information géochimique de chaque technique appliquée en combinant les informations minéralogiques et élémentaires. Dans cette étude, les données élémentaires et minéralogiques sont fournies par six techniques portables: (i) des analyses élémentaires telles que XRF et LIBS pour les éléments majeurs, les traces et les éléments légers, et (ii) des analyses minéralogiques telles que Raman, VNIR-SWIR, MIR et XRD pour contraindre les minéraux de formation de roche, de minerai et d'altération. L'objectif final de cette étude est d'identifier les vecteurs vers le minerai en appliquant les données multispectrales réconciliées, ceux qui sont obtenues à partir de l'échantillon "réel" dans le gisement de sulfure massif volcanogène (SMV) d'Elvira. Pour cela, des procédures étape par étape ont été réalisées : (i) comprendre la méthodologie de chaque technique, (ii) établir une base de données spectrales composée de minéraux naturellement monominéraux, (iii) concevoir d'un arbre de décision pour classer par minéral ou classes de minéraux en fonction des bandes diagnostiques, et identifier et quantifier des minéraux (iv) carbonate et (v) phyllosilicate (i.e., chlorites trioctaédriques et micas dioctaédriques), qui sont des indicateurs du gisement cible. Plusieurs limites de la spectroscopie portable ont été confirmées en fonction de l'appareil lui-même et de l'environnement géologique du gisement d'Elvira. Néanmoins, la spectroscopie portable est efficace pour identifier la présence et les changements de composition de divers minéraux dans des échantillons de roches hétérogènes. Par conséquent, l'analyse spectroscopique sur place peut être l'un des outils de vectorisation pour déterminer l'implication de la minéralisation dans les explorations de minerais cachés
Mineral exploration focused on deeply concealed targets at depth requires effective techniques applicable in the field in order to identify ore-forming systems on a large scale and pathfinders to locate ore on a smaller scale. According to the rapid development of portable equipment in recent years, the importance of near real-time analysis in the field has been increasing by helping fast decision-making support before laboratory requests.Spectroscopic analysis using individual equipment has been widely used in the exploration of mineral resources, but it is rare to apply integrated data from several techniques to characterize “vectors”, which provide variations in lithology, geochemistry, mineralogy, and mineral chemistry. In addition, it is even rarer if the combination of spectral data is obtained from various portable instruments. Therefore, this study aims at reconciling geochemical data acquired from portable spectroscopic devices in order to determine the best geochemical information from each technique applied by combining the mineralogical and elemental information. Elemental and mineralogical data are provided in this study by six portable techniques: (i) elemental analyses such as XRF and LIBS for major, trace, and light elements, and (ii) mineralogical analyses such as Raman, VNIR-SWIR, MIR, and XRD to constrain rock-forming, ore, and alteration minerals.The final objective of this study is to identify vectors to the ore by applying the reconciled multi-spectral data obtained from the “real” sample in the Elvira volcanogenic massive sulfide (VMS) deposit. To achieve this, step-by-step procedures were carried out: (i) methodological understanding of each technique, (ii) establishment of a spectral database consisting of naturally monomineralic minerals, (iii) design of a decision tree to classify by mineral or mineral classes based on diagnostic bands, and mineral identification and quantification of (iv) carbonate and (v) phyllosilicate minerals (i.e., trioctahedral chlorites and dioctahedral micas), which are indicators of the target deposit.Several limitations of portable spectroscopy were confirmed based on the device itself and the geological environment in the Elvira deposit. Nevertheless, portable spectroscopy is effective in identifying the presence and compositional changes of various minerals from heterogeneous rock samples. Therefore, spectroscopic analysis on-site can be one of the vectoring tools to determine the implication for ore mineralization in hidden ore explorations

Les grands réaménagements urbains génèrent d’importants volumes de terres excavées, dont la valorisation est désormais possible si elles sont compatibles avec le fond pédo-géochimique du site receveur. Afin de faciliter cette valorisation, cette thèse s’intéresse à des méthodologies de traitement de données acquises à d'autres fins que la détermination du fond pédo-géochimique, afin de fournir un référentiel de qualité géochimique des sols urbains à l'échelle d'un quartier ou d'une ville. Les premiers tests montrent les limites des calculs statistiques, usuellement utilisés avec des données dédiées au fond pédo-géochimique du fait de leur sensibilité à la limite de quantification, à la loi de distribution ou encore au pourcentage d'anomalie. Le découpage du territoire en entités géographiques cohérentes à partir de la nature des sols et sous-sols et des pressions anthropiques (actuelles ou passées) permet la constitution de différents niveaux de fond suivant la qualité géochimique des sols, mais une des difficultés concerne le renseignement de l'ensemble des entités. La classification statistique des échantillons, même spatialisée, n'apporte, actuellement pas de résultats exploitables pour la gestion des terres excavées. Enfin, le filtrage géostatistique via un modèle linéaire de corégionalisation présente une alternative solide pour le filtrage des anomalies et l'estimation du fond à l'échelle d'un quartier
Large urban redevelopments generate large volumes of excavated soils whose reusability is now possible if they are compatible with the pedo-geochemical background of the receiving site. In order to facilitate this valorization, this thesis focuses on processing methodologies on data acquired for other purposes than the determination of the pedo-geochemical background, in order to provide a geochemical quality reference system for urban soils at the scale of one neighborhood or city. The first tests show the limits of the statistical stresholds, usually used with data dedicated to the pedo-geochemical background because of their sensitivity to the limit of quantification, to the distribution law or to the percentage of anomaly. The segmentation of the territory into coherent geographical entities based on the nature of the soil and subsoil and the anthropogenic pressures (current or past) allows the constitution of different geochemical background levels according to the geochemical quality of the soils, but one of the difficulties concerns the information of all entities. The statistical classification of the samples, even if spatialized, does not currently provide usable results for the management of the excavated earth. Lastly, geostatistical filtering via a linear model of coregionalisation provides a solid alternative for anomaly filtering and background estimation at a neighborhood scale

La croute océanique formée aux dorsales lentes a une composition hétérogène. Pour expliquer sa formation, il est nécessaire d’invoquer des processus d’interactions magma-roche. Afin de contraindre la contribution des processus de cristallisation et d’interaction magma-roche sur le budget géochimique et l’architecture de la croute océanique hétérogène, j’ai étudié deux séquences gabbroiques échantillonnées in situ à l’Atlantis Massif (AM, 30°N, Dorsale Médio-Atlantique, MAR) et l’Atlantis Bank (AB, 57°E, Dorsale Sud-Ouest Indienne, SWIR). J’ai effectué (i) une étude multi-échelle pétro-structurale et géochimique, combinée à une modélisation numérique, de gabbros primitifs forés à l’AM, et (ii) une étude pétrographique et géochimique de gabbros à olivines forés à l’AB. La croute océanique inférieure hétérogène échantillonnée au Site U1309 (AM) présente des troctolites riches en olivines (Ol-T). Elles se distinguent par des olivines partiellement dissoutes, relativement riches en Fo et en Ni, ainsi que par la co-précipitation de clinopyroxènes riches en Mg et de plagioclases. Ces caractéristiques suggèrent que les Ol-T sont le résultat de l’imprégnation d’un protolithe riche en olivines par un magma sous-saturé en olivine. Les profils géochimiques plats entre les minéraux adjacents suggèrent que la composition du protolithe a été modifiée par le magma entrant. Pourtant, le Ni, Li et Co montrent des compositions extrêmement variables à Mg# de l’olivine constant, ce qui suggère qu’ils préservent la signature géochimique du protolithe. La modélisation géochimique indique que ces variations sont héritées d’une hétérogénéité dans les harzburgites U1309. Les expériences en laboratoire ont démontré que la distribution de magma en milieux poreux est contrôlée par la composition modale de la roche percolée. La distribution hétérogène d’orthopyroxène dans le protolithe mantellique contrôle la quantité de magma entrant, et ainsi la quantité d’olivine dissoute, comme indiqué par les variations modales et compositionnelles observées dans les Ol-T à l’AM. La modélisation géochimique indique que la formation des Ol-T peut être expliquée par la percolation de magma et l’assimilation de 5% de protolithe mantellique. Une conséquence de ce processus de réaction est le décalage des compositions du magma à l’AM vers de cristallisation fractionnée apparentes à haute pression. Pourtant, aucune signature géochimique de haute pression n’est observée dans les MORBs à l’AM, alors qu’elles sont observées dans les MORBs d’une portion amagmatique de la SWIR (61°-67°E). La croute océanique à l’AB est faite de gabbros à olivines (75%) et de gabbros à oxides (20%), et par endroits intensément déformée. Les études préliminaires ont mis en évidence des textures indiquant l’assimilation de plagioclase par un magma d’imprégnation, ainsi que la cristallisation de clinopyroxène. Les gabbros à olivines montrent des compositions relativement évoluées. Des études précédentes des gabbros à olivines de l’AB ont montré que leur formation peut être attribuée à l’assimilation de la croute océanique par un magma saturé en clinopyroxène. Les études de l’AM et de l’AB révèlent des processus d’interactions magma-roche associés au transport de magma dans la croute océanique inférieure. Des caractéristiques texturales et géochimiques similaires ont été documentées à Kane (24°N, MAR) et dans les ophiolites Alpines-Apennines. Elles indiquent que les interactions magma-roche sont omniprésentes et contribuent à façonner la croute océanique inférieure aux dorsales lentes. L’étude de roches gabbroiques forées à Hess Deep suggèrent que les interactions magma-roche interviennent également aux dorsales rapides. Le transport réactif de magma dans la croute océanique joue un rôle majeur dans le processus de formation de la croute océanique dans son ensemble. Leur contribution dans la composition des MORBs est probablement contrôlée par la production de magma durant la remontée mantellique
At slow-spreading mid-ocean ridges the lower oceanic crust is extremely heterogeneous, and its formation must be related to some extents of melt-rock interactions. To constrain the relative contribution of crystallization processes and melt-rock interactions on the geochemical budget and architecture of the slow-spread oceanic crust, I investigated two gabbroic sequences sampled in situ at the Atlantis Massif (AM, 30°N, Mid-Atlantic Ridge, MAR) and the Atlantis Bank (AB, 32°S, 57°E, Southwest Indian Ridge, SWIR), where gabbros are exposed by long-lived detachment faults. I performed (i) a multi-scale petro-structural, geochemical and numerical modeling study of primitive gabbroic rocks drilled at the AM, and (ii) a petrographic and geochemical study of olivine gabbros recovered at the AB. AM was drilled during IODP Expeditions 304/305. The heterogeneous lower oceanic crust recovered at Site U1309 presents discrete intervals of olivine-rich troctolites (Ol-T). They are distinguished by partially dissolved olivines with relatively high Fo (86) and Ni contents (>2000 ppm), and they are characterized by the co-precipitation of high Mg# (86-88) clinopyroxene and plagioclase. These characteristics suggest that Ol-T result from impregnation of an olivine-rich protolith by a melt undersaturated in olivine. The flat geochemical profiles across olivine and adjacent minerals suggest that the composition of the protolith was modified by this impregnating melt. Yet, Ni, Li and Co display extremely variable compositions at constant olivine Mg#, suggesting that they retain the signature of the precursor material. Modeling indicates that these chemical variations are likely inherited from the U1309D harzburgites. Experiments show that the melt distribution and paths in a porous media is controlled by the mineral modes of the host rock. The heterogeneous distribution of orthopyroxene in the precursor harzburgitic mantle locally drives the abundance of impregnating melt, leading to different extents of olivine dissolution, as evidenced by variations in mineral modes and chemistry of the AM Ol-T. Geochemical modeling indicates that the melt percolation and assimilation of about 5% of a mantle protolith can explain the formation of the Ol-T. One consequence of this reactive process in Hole U1309D is the shift of melt compositions toward apparent high pressure fractionation. However, no high pressure chemical signature is observed in MORBs from the AM, while it is recorded in MORBs from the nearly amagmatic region along the SWIR (61°-67°E). AB was drilled during IODP Expedition 360. The recovered lower oceanic crust is dominated by olivine gabbros (75%) and oxide gabbros (20%). The section is in places intensively deformed. Shipboard studies have documented textures of plagioclase assimilation by an invading melt crystallizing clinopyroxene. Compositions of olivine gabbros reach relatively evolved signature (Yb = 3-10 x C1-chondrite; MORB Yb = 19). Previous studies on olivine gabbros from AB showed that their formation can be ascribed to assimilation of an oceanic crust by clinopyroxene-saturated trace element enriched melts. The study of AM and AB reveals melt-rock interactions and mineral assimilation associated to melt transport through the accreting lower oceanic crust. Similar textural and chemical features are observed at Kane (24°N, MAR) and in ophiolite complexes (e.g., Alpine and Appennine ophiolites). These evidences indicate that melt-rock interactions are probably ubiquitous, and contribute to shaping the slow-spread lower oceanic crust. The characterization of gabbroic rocks drilled at Hess Deep suggests that melt-rock interactions may take place also at fast-spreading ridge. Melt transport and associated mineral assimilation processes likely play a major role in the building of the oceanic crust overall. Their contribution to the formation of MORB is likely controlled by melt productivity in the upwelling mantle

Les grands réaménagements urbains génèrent d’importants volumes de terres excavées, dont la valorisation est désormais possible si elles sont compatibles avec le fond pédo-géochimique du site receveur. Afin de faciliter cette valorisation, cette thèse s’intéresse à des méthodologies de traitement de données acquises à d'autres fins que la détermination du fond pédo-géochimique, afin de fournir un référentiel de qualité géochimique des sols urbains à l'échelle d'un quartier ou d'une ville. Les premiers tests montrent les limites des calculs statistiques, usuellement utilisés avec des données dédiées au fond pédo-géochimique du fait de leur sensibilité à la limite de quantification, à la loi de distribution ou encore au pourcentage d'anomalie. Le découpage du territoire en entités géographiques cohérentes à partir de la nature des sols et sous-sols et des pressions anthropiques (actuelles ou passées) permet la constitution de différents niveaux de fond suivant la qualité géochimique des sols, mais une des difficultés concerne le renseignement de l'ensemble des entités. La classification statistique des échantillons, même spatialisée, n'apporte, actuellement pas de résultats exploitables pour la gestion des terres excavées. Enfin, le filtrage géostatistique via un modèle linéaire de corégionalisation présente une alternative solide pour le filtrage des anomalies et l'estimation du fond à l'échelle d'un quartier
Large urban redevelopments generate large volumes of excavated soils whose reusability is now possible if they are compatible with the pedo-geochemical background of the receiving site. In order to facilitate this valorization, this thesis focuses on processing methodologies on data acquired for other purposes than the determination of the pedo-geochemical background, in order to provide a geochemical quality reference system for urban soils at the scale of one neighborhood or city. The first tests show the limits of the statistical stresholds, usually used with data dedicated to the pedo-geochemical background because of their sensitivity to the limit of quantification, to the distribution law or to the percentage of anomaly. The segmentation of the territory into coherent geographical entities based on the nature of the soil and subsoil and the anthropogenic pressures (current or past) allows the constitution of different geochemical background levels according to the geochemical quality of the soils, but one of the difficulties concerns the information of all entities. The statistical classification of the samples, even if spatialized, does not currently provide usable results for the management of the excavated earth. Lastly, geostatistical filtering via a linear model of coregionalisation provides a solid alternative for anomaly filtering and background estimation at a neighborhood scale

The Sunset Well study area, 10 kilometres east of Leonora in the Archaean Eastern Goldfields Province of Western Australia, forms part of a group of gold exploration tenements held by RGC Exploration Pty Ltd. Geological mapping and a variety of geochemical techniques have outlined alteration within a shear zone and mineralisation at the Prospero prospect. Geological mapping has delineated three lithostratigraphic sequences separated by NNW trending faults. The western succession is comprised of andesite-derived volcaniclastic sediments (sandstone, breccia) with minor fine grained clastic sediment (shale) which are interpreted to represent a stack of subaqueous debris flows derived from a subaqueous andesite-dominated volcanic complex. The central succession is dominated by massive tholeiitic and high-Mg basalts with minor sediments. Fine grained clastic sediments make up the majority of the eastern succession. All sequences have been intruded by dolerite/gabbro sills and the western and central successions are intruded by several granodioritic porphyry stocks. Deep lateritic weathering and subsequent partial erosion has exposed saprolitic subcrops over much of the area with remnants of lateritic duricrust. Surface geochemical anomalism related to the mineralisation within the Prospero shear is outlined in residual lateritic material with a Au-W association (380 ppb Au and 12 ppm W). Sampling of saprolite from surface soil and drilling samples displays a spatial but non-coincident Au-As-W-Pb-Sb-Cu-Zn association. Analysis of K and Na in saprolite and saprock material outlines the sericitic and albitic alteration zones with maximum values centred on the mineralised Prospero shear zone. Mineralisation at Prospero is located within a broad east-dipping shear zone between andesitic volcaniclastics and high-Mg basalt. Supergene saprolitic mineralisation is well developed in broad subhorizontal sheets in the middle saprolite with a smaller accumulation near the saprolite-saprock boundary. Bedrock mineralisation is associated with intense zonal metasomatic alteration comprising an outer chlorite-sericite-quartz-calcite, middle sericite-quartz and inner quartz-albite-sericite-dolomite/ankerite-fuchsite alteration zone. Sulphide mineralogy is dominated by pyrite with minor galena, chalcopyrite, arsenopyrite, sphalerite, chalcocite and covellite. Gold grades are generally 0.2-0.6 ppm in the sericite zone and 0.5-3.0 ppm in the inner silicified zone. Thin quartz veins contain higher grade (5.0-30.0 ppm) mineralisation, with gold occuring as fine (-5 micron) free grains. The primary mineralised zone has a Au-As-W-Cu-Sb-Sr-V-Si-K-Na association. Mineralisation is interpreted to have formed during D1 shear zone formation and synchronous with zonal alteration.

Thick, commonly lateritic regoliths are widespread in inter-tropical regions of the world, and present a challenges to current exploration techniques. The particular problem in Australian is the widespread deep and varied regolith, frequently with a complex geological history dating back to mid-Permian time. Within this long period, several episodes of deep weathering and selective chemical solution, transport and precipitation, differential erosion, and deposition of sediment, so that the primary features of primary ore deposits are considerably modified and deeply concealed. The lateritic and saprolitic Au associated with subsurface depletion is one of the most common results of the deep weathering. With these problems in mind, an integrated paramagnetic/lithogeochemical technique has been developed in the exploration for gold in heavily weathered terrain. This technique is based on the degree of impurity in quartz associated with ore deposits and measured by electron paramagnetic resonance (EPR) powder spectroscopy and chemical analysis of the quartz rich acid insoluble residue of the regolith. Electron paramagnetic resonance spectroscopy, which measures microwave absorption by unpaired electrons in a magnetic field, is a new concept in mineral exploration as quartz samples from mineralized zones often have strong EPR signals due to lattice imperfections. Quartz associated with mineralization has stronger electron paramagnetism than the barren quartz, whilst the EPR signals of residual quartz, including secondary chalcedony with inclusion of primary quartz, are not strongly affected by weathering. The acid treatment consists of sequential treatment of regolith samples with hot aqua regia, nitric acid and sulphuric acid, dissolving residual sulphides, iron, manganese and aluminium oxides and hydroxides, carbonates, phosphates, sulphates and clay minerals. The remaining acid insoluble residue consists of quartz with some residue sericite, rutile and traces of other resistate minerals. Three areas with a well described regolith profile and known bulk geochemistry were selected: the Mystery Zone, Mt Percy, at Kalgoorlie, the Rand Pit, Reedy Mine near Meekatharra in Western Australia, and Jim's Find in the Tanami Desert of Northern Territory. The depth of weathering in these areas varies between rock types, but generally below surface 60-90 m. As strong acid digestion, most of the weathering products have been removed from the reglith samples and this acid insoluble residue reflects the primary signature. In the acid insoluble residue, quartz associated with mineralization has an EPR spectra typical of lattice imperfections. Case studies of the Mystery Zone, Mt. Percy, the Rand Pit, Reedy Mine and the Jim's Find, Tanami have pronounced EPR signals at the surface above the mineralized zones as well as in Au depletion zones and in the wall rock alteration halos. The distribution of EPR 326.5±5 m T is in accordance with the distribution of certain trace elements, such as Al, K, Rb, W, V, Ga and Ge in all three working areas. In addition, wall rock alteration patterns are commonly expressed by strong [Al04] 0 centers in the EPR spectra, accompanied by increased K and Rb concentrations, and high Rb/Kand Rb/Al ratios. In contrast, the intensity of EPR 326.5± 100 m T resembles the element distribution of Fe, Mn, Zn and Ni indicating that EPR 326.5±5 mT weakly reflects the distribution of alteration. In the acid insoluble residue, the chemical expression of sericitic wall rock is Al, K Rb, V, Ga and W enrichment, high Rb/K ratios in surface material above mineralization, and high Rb/Al ratios in wall rocks. Aluminium, K, Rb, Ga, V, and W related to sericitic alteration in the acid insoluble residue, are commonly good indicators of Au mineralization through the regolith. In the Mystery Zone, Rand Pit and Jim's Find, Al, Cr, Ga, K, Rb, V, W, Rb/K and Rb/ Al consistently define the location of Au mineralization. The composite halos Al x K x Rb, Ga+Ge and As+ W +Mo also enhance the mineralization halo, with these cumulative indices more useful than the single low-level elements of Ge, As and Mo. Sodium, Ca and Sr depletion is caused by plagioclase destruction. Titanium, Zr, Nb, and possibly V, have a strong correlation to lithological variation and are surface enriched in resistate minerals. However, the acid insoluble residue of near surface material likely reflects secondary dispersion patterns of Ca, Sr, Cr, Cl and S presumably due to extrapment of submicroscopic inclusions. Similar results may be obtained for these and other potential pathfinder elements, like As, Sb, Bi and Cu, by total geochemical analysis of whole rock pulps. However, not all Au deposits have an associated suite of pathfinder elements, whilst research presented in this thesis suggests that there is always an EPR signal and high Al, K, Rb, V, Ga and W chemical expression in the acid insoluble residue.

Dissertação de Mestrado em Geociências apresentada à Faculdade de Ciências e Tecnologia
A prospecção através da realização de levantamentos geoquímicos e amostras de concentrados de minerais pesados de bateia, baseia-se no conceito de que, numa dada bacia de drenagem, processos químicos e fluviais transportam minerais e metais, comuns ou preciosos, podendo levar à sua deposição e acumulação. Essa técnica tem sido comumente aplicada a metais preciosos, gemas e outros minerais densos com importância económica. Mais recentemente, a análise química multi-elementar de minerais pesados tornou-se amplamente utilizada.Este estudo visa avaliar e identificar sub-bacias que possam conter concentrações anómalas de alguns minerais com potencial interesse económico. Sua relação com as formações geológicas presentes na área de estudo.O método de prospecção foi conduzido com observações de campo da bacia hidrográfica da área de captação do material, coleta de 32 amostras de sedimentos em linhas de água, com posterior concentração em bateia no campo, sendo depois em laboratório submetidas a separação magnética e análise química.Os dados resultantes de análises químicas e seu tratamento estatístico, permitiu identificar as zonas com concentrações de alguns dos elementos químicos. Houve duas bacias hidrográficas com concentrações anómalas de mineralização. Recomenda-se que um estudo geológico e geoquímico detalhado possa ser realizado em áreas a montante, principalmente a partir de locais com valores anómalos de metais. Isso é necessário para confirmar a presença ou não das diferentes mineralizações metálicas suspeitas na área.
The prospecting by conducting geochemical surveys and panned heavy mineral concentrates sample (Stream sediment or drainage surveys), are based on the concept that fluvial and chemical processes carry metals and minerals from within a drainage catchment (watershed) to a site of mineral either base metals or precious metals accumulation. This technique has been commonly applied for precious metals, gems and other dense minerals with economic importance which can be identified in the field. More recently, multi-elemental chemical analysis of heavy minerals has become widely used. This study is to evaluate and identify sub-basins that may be anomalous for some minerals with economic interest through chemical analysis of the stream sediments or panned concentrates, to locate the primary mineral deposits that may be present on the study area, to predict the geochemical environment of the geological formations present in the study area and their relationships and to establish the regional mineralogical and metallogenic characteristics by studying the heavy minerals present in panned concentrates and also with geochemical analysis of the fine fraction of stream sediments.The prospecting method was conducted with field observations for watershed as catchment area of materials, sample collection referred to watershed determination. Then, chemical analysis of X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) were applied for those collected sample that represented each of watersheds.Furthermore, the data were resulted from chemical analyses then applied with statistical data to classify thresholds values that separate the defined value ranges from the background and the anomalous valuesThere have been two basins are considered to have mineralization anomaly with the watersheds. Therefore, it is recommended that a detailed geological and geochemical study could be carried out in areas upstream, principally from sites of anomalous values of metals. This is necessary to confirm the presence or otherwise of the different suspected metallic mineralizations in the area.

Tese de doutoramento em Geologia, no ramo de Recursos Geológicos e Ambiente, apresentada ao Departamento de Ciências da Terra da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
The price and reliability of energy supplies, electricity in particular, are key elements in a country’s energy supply strategy. Electricity prices are of particular importance for international competitiveness, as electricity usually represents a significant proportion of total energy costs for industrial and service-providing businesses. In Portugal, the price of electricity and natural gas are among the highest in Europe Union. According to International Energy Agency, in 2016 20% of the electricity was generated by natural gas (52% of total electricity generation was made by fossil fuels) in this country. This project aims to identify onshore hydrocarbon emanations by surface geochemical prospecting, rock-eval pyrolysis analysis and thorium normalization/hydrocarbon anomalies, in order to characterized an unconventional petroleum system in South Portuguese Zone (Portugal). This thesis also aims demonstrate a correlation between airborne gamma radiation data and high-resolution satellite images WorldView-2, in order to be an alternative way and facilitate the acquisition of radiometric data, in view of the high costs associated to an airborne gamma ray survey. A total of 31 samples were collected for rock-eval pyrolysis performed by Weatherford Laboratories and Polish Geological Institute, financed by Repsol E&P (Spain), Partex Oil&Gas (Portugal) and Polish Geological Institute (Poland). The collection of all samples for surface geochemical prospecting was performed using Isojars, with distilled water and a bactericide added to inhibit any bacterial activities. Twenty-seven soil samples were collected for this study, using a drilling machine, a metal tube and a hammer. Thirty-one water samples were collected from artesian wells, boreholes and springs. The remote sensing methodologies, used to define the sampling areas, proved to be very efficient to show possible hydrocarbon emanations. From the geological prospecting point of view the presence of hydrocarbon gases in South Portuguese Zone formation is clear and evident. They are present in soil and water, with significantly high levels.
O preço e a confiabilidade dos estoques de energia, eletricidade em particular, são elementos essenciais na estratégia de fornecimento de energia de um país. Os preços da eletricidade são de particular importância para a competitividade internacional, já que a eletricidade geralmente representa uma proporção significativa dos custos totais de energia para a industria e prestação de serviços. Em Portugal o preço da eletricidade e do gás natural estão estre os mais caros da União Europa. De acordo com a Agência Internacional de Energia, em 2016 20% da eletricidade foi gerada por gás natural (52% do total da geração elétrica foi feita por combustíveis fósseis) neste país. Este projeto tem como objetivo identificar emanações onshore de hidrocarbonetos através da prospecção geoquímica de superfície, análise de pirólise rock-eval e normalização de tório/anomalia de hidrocarbonetos, a fim de caracterizar um sistema petrolífero não-convencional da Zona Sul Portuguesa (Portugal). Esta tese também pretende demonstrar uma correlação entre dados de radiação gama e imagens de satélite de alta resolução WorldView-2, a fim de ser uma alternativa e facilitar a aquisição de dados radiométricos, tendo em vista os altos custos associados ao levantamento aéreo de radiação gama. Um total de 31 amostras foram utlizadas para análises de pirólise rock-eval, tendo sido realizadas pelos laboratórios da Weatherford e do Insituto Polaco de Geologia, e sendo financiadas pela Repsol E&P (Espanha), Partex Oil&Gas (Portugal) e Instituto Polaco de Geologia (Polônia). Toda a amostragem para a prospeção geoquímica de superfície foi feita utilizando frascos Isojars, com água destilada e adicionando bactericida, para inibir qualquer atividade bacteriana. Vinte e sete amostras foram colhidas para este estudo, utilizando uma caroteadora, um tubo metálico e uma marreta. Trinta e uma amostras de água foram colhidas em poços artesianos, furos e nascentes. As metodologias de detecção remota, utilizadas para definir as zonas de amostragem, mostraram-se bastante eficientes na indicação de zonas com possíveis ocorrências de emanações de hidrocarbonetos. Do ponto de vista da prospecção geológica a presença de hidrocarbonetos gasosos nas formações da Zona Sul Portuguesa é clara e evidente. Eles estão presentes no solo e na água, em quantidades significativas
Sciences Without Borders program (CNPq Brazil) – 201943/2014-0; Statoil ASA (CNPq); DigitalGlobe Foundation; Centro de Geociências (FCT); Centro de Interpretação da Terra e do Espaço (FCT); Instituto Dom Luiz (FCT)

Bibliography: leaves 233-260.
xxi, 260, [30] leaves : ill. (chiefly col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Uses the late-orogenic, structurally-controlled Junction gold deposit near Kambalda, Western Australia, to examine the potential of soil-gas geochemistry as an exploration vector in an environment where mineralisation is present, but no ore-related trace elements are detectable in the near-surface regolith.
Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics 1999

M.Sc. (Geology)
The purpose of this study was to assess the MLA’s ability to characterise (e.g. modal mineralogy, elemental assay, particle size distribution, particle density distribution and mineral associations) a coal product from New Vaal Colliery, with the aim to determine any liberation and beneficiation characteristics. In general the MLA assessment on coal is comparatively new and novel, especially at Spectrum (University of Johannesburg), hence research in this regard is required. For the first time New Vaal coal product was characterised with the MLA 600 FEG SEM. The coal product supplied to Lethabo Power Station for the study’s samples, consisted of Top Seam and Middle Seam coal from New Vaal Colliery which is located in the Cornelia subbasin of the Vereeniging-Sasolburg coalfield, South Africa. The proximate analysis characterised the coal as a high-ash (42.25% air-dried) and low calorific value (13.92 MJ/kg air-dried) product. Chemically SiO2 was the most abundant oxide followed by Al2O3 for the XRF analysis, which was mostly derived from the abundant kaolinite clay mineral (determined by petrography, XRD and MLA analysis). Mineralogically inertinite was the most abundant coal maceral encountered during the petrographic analysis. With geochemical characterisation, chalcophile, siderophile, lithophile and radioactive trace elements were found to be mostly comparable to the global average.

The Mount Ayliff Complex (MAC) is situated on the border between Kwa-Zulu Natal and the Eastern Cape provinces in the Republic of South Africa, approximately 90 km due west of Port Shepstone. The Complex forms part of the Karoo Igneous Province and includes five lobes (Ingeli, Insizwa, Tonti, Tabankulu, and Horseshoe) that are the remnants of a single continuous intrusive sheet that had an original extent of 18,000km2• The current outcrop is estimated at 800km2• The lobes all show extensive internal differentiation, from basal ultramafic cumulates to diorites and monzonites at the top, while most other intrusions in the Karoo Igneous Province cooled rapidly enough to produce relatively homogenous dolerites. Most work conducted on the Complex thus far has centered on the Insizwa lobe due to the presence of a Ni-sulphide occurrence near the base of the lobe at Waterfall Gorge. The setting of the ores has analogies to the Noril'sk-Talnakh deposits, which has raised considerable exploration interest on the Mount Ayliff Complex over the last century. The current study investigates the Ni-Cu sulphide potential of the Ingeli and Horseshoe lobes, which have been poorly studied in the past. To this effect, a stream sediment survey was conducted around the Ingeli lobe to try and detect potentially hidden magmatic sulphide ores. Further, the five lobes of the Complex have been compared in terms of lithology and lithogeochemistry. Analytical techniques used for the current study include: XRF, ICP-MS and electron microprobe. Stream sediment samples were analysed using XRF and ICP-OES. Olivines from the ultramafic cumulates of the Ingeli and Insizwa lobes are undepleted in Ni, whereas olivines from the Horseshoe and Tabankulu lobes are strongly depleted in Ni. This suggests that the rocks of the latter two lobes crystallized from parental magmas that interacted with a sulphide liquid and that the magmatic flow direction was from the north to the south. The data indicate that the ultramafic rocks of the Complex plot on or near control lines between olivine and Karoo dolerite indicating that the rocks are mixtures of cumulus olivine and trapped melt of Karoo dolerite composition. There appears to be a copper enrichment towards the top of the ultramafic package in the Ingeli lobe. This pattern corresponds to other studies conducted in the InsiZWa lobe and suggests that the two lobes had originally been connected. The lowermost cumulates of the Ingeli lobe contain an enhanced crustal component suggesting some in situ contamination. No significant sulphide enrichments were encountered in the Basal Zone rocks of the Ingeli lobe. However, the stream sediment data indicate localized PGE enrichment indicating the possible presence of a localized hidden sulphide occurrence of the type found at Waterfall Gorge. Small amounts of sulphides were found associated with the Basal Zone rocks in the Horseshoe lobe consistent with the trends of Ni-depletion of olivines. However, a lack of Co depletion in the ultramafic rocks of this lobe suggests that any sulphide segregation event that did take place was of a relatively small scale.
Dissertation (MSc)--University of Pretoria, 2006.
Geology
MSc
Unrestricted

SUMMARY: The diploma thesis is focused on application of natural science methods - geophysics and above all geochemistry - in archaeology. Geophysical and geochemical techniques have become an integral part of non-destructive archaeology over time. While geophysical methods have been practiced in a wide array of archaeological surveys for many decades, geochemical methods have been used to a greater extent up to in recent years. In addition, the application of geochemistry in archaeology is, in most cases, limited only to the analysis of phosphates in soil applied to small spatial units. The potential of geochemistry in dealing with archaeological issues remains still unused due to the limited understanding of the context. This is also reflected in the absence of publications that would allow a good-quality interpretation of geochemical data in connection with archaeology. Geophysical and geochemical procedures were applied during the survey of the selected area in the locality of Hillfort Vinoř, located on the northeastern outskirts of Prague. The aim of this survey was to contribute to the widening of the existing knowledge of the locality with an emphasis on the wider context. Two methods were chosen for the geophysical survey - dipole electromagnetic profiling (DEMP) and electrical resistivity...

MESMEG
Department of Mining and Environmental Geology
This study entails geochemical and mineralogical characterization of gold tailings of Nestor Mine and Glynn’s Lydenberg Mine of the Sabie-Pilgrim’s Rest goldfields. A total of 35 samples were collected and were analysed for chemical composition (XRF and ICP-MS), mineralogical composition (XRD). In addition, acid-base accounting (ABA) techniques had been conducted to predict the potential for acid mine drainage. Seepage from Nestor tailings dump and water samples from the adjacent Sabie River were also collected and analysed by means of inductively coupled plasma mass spectrometry (ICP-MS) and immediate constituent (IC) -analytical techniques. The study revealed that Sabie-pilgrim’s rest goldfield is characterized by both acid generating and non-acid producing tailings, and this is attributed to variations in the mineralogy of source rocks. Gold occurred within the Black Reef Quartzite Formation in the Nestor Mine and within the Malmani Dolomite in the case of Glynn’s Lydenburg Mine. Mineralogy and bulk geochemical analyses performed in this study showed a clear variation in the chemistry of Nestor Mine and Glynn’s Lydenburg Mine tailings. Predominant oxides in Nestor mine tailings samples are SiO2 (ranging from 66.7-91.25 wt. %; followed by Fe2O3 and Al2O3 (in range of 0.82-15.63 wt. %; 3.21-12.50 wt. % respectively); TiO2 (0.18-10.18 wt. %) and CaO (0.005-3.2 wt. %). Also occurring in small amounts is CaO (0.005-3.2 wt. %), K2O (0.51-2.27 wt. %), MgO (0.005-1.46 wt. %), P2O5 (0.029-0.248), Cr2O3 (0.013-0.042 wt. %) and Na2O (0.005-0.05 wt. %). The samples also contain significant concentrations of As (137-1599 ppm), Cu (34-571 ppm), Cr (43-273 ppm), Pb (12-276 ppm), Ni (16-157 ppm), V (29-255 ppm), and Zn 7-485 ppm). In the Glynn’s Lydenburg Mine tailings SiO2 is also the most dominant oxide ranging between 47.95 and 65.89 w%; followed by Al2O3 (4.31 to 16.19 wt. %), Fe2O3 (8.48 to 11.70 wt %), CaO (2.18 to 7.10 wt. %), MgO (2.74 to 4.7 wt. %). Occurring in small amounts is K2O (1.12-1.70 wt. %), MnO (0.089-0.175 wt. %), P2O5 (0.058-0.144 wt. %) and Cr2O3 (0.015-0.027 wt. %). Arsenic (As), is also occurring in significant amounts (807-2502 ppm), followed by Cr (117-238 ppm), Cu (10-104 ppm), V (56-235 ppm), Ni (45-132 ppm), Pb (13-63 ppm) and Zn (90-240 ppm). Nestor Mine tailings associated with Black Reef Formation mineralization have net neutralizing potential (NPR) <2, hence more likely to generate acid; and their acid potential (AP) ranges 1.56 to 140.31 CaCO3/ton and neutralizing potential (NP) range from -57.75 to -0.3 CaCO3/ton. Glynn’s Lydenburg Mine tailings dump which is vi associated with dolomite mineralization, however, was not leaching acid. Based on acid-base accounting results, these tailings have more neutralizing potential (ranging between 57.6 and 207.88 CaCO3/ton) than acid potential (ranging between 7.5 and 72.1 CaCO3/ton); and their NPR>2, hence unlikely to produce acid. This is confirmed by paste pH which was in the ranges between 7.35 and 8.17. Tailings eroded from Nestor Mine tailings dump were also found to be characterized by high content of metals and oxides, namely, As, Cu, Ni, Pb, V, and Zn with SiO2, Fe2O3 and TiO2. The tailings were observed eroded into the Sabie River where AMD related precipitate (yellow boy) was also observed, indicating further oxidation downstream. Field observations, onsite analyses of water samples and laboratory results revealed that Nestor Mine tailings storage facility discharges acid mine drainage with considerable amounts of Al, As, Cu, Fe, Mn, Zn and SO4 and very low pH exceeding the limit as per South African water quality standards. High concentrations of these metals have toxicity potential on plants, animals and humans. Upon exposure to oxygen and water, tailings from Nestor Mine are more likely to generate acid mine drainage that can cause detrimental effect to the environment and the surrounding communities. Potential pollutants are Fe, Mn, Al, As, Cr, Cu, Ni and Pb. Tailings from Glynn’s Lydenberg showed no potential for acid mine drainage formation.
NRF