Dissertations / Theses on the topic 'Orogenic gold deposits'

Here we report new and previously published Re-Os and trace elemental data on gold as well as coeval sulfides and oxides from various Archean to Alphanumeric gold deposits. When possible, measured concentrations and isotopic ratios were used to determine geochronology as well as the likely source reservoir of the gold mineralization. Rhenium-osmium ages of some gold and related minerals are consistent with existing geochronology and in some cases better constrain genetic models of mineralization. The initial Os isotopic composition is also preserved within some ore minerals and reflects the importance of both crustal and mantle material in the generation of specific deposits. However, many of the gold deposits show evidence of post-crystallization Re-Os disturbance, and so age and source information are not preserved. In these cases, it is likely that hydrothermal fluids added or removed Re or Os subsequent to primary mineralization. Preservation of age favors minerals with high Re and Os concentrations and/or minerals from monocyclic gold deposits without multiple influxes of fluids. More specifically, gold and pyrite from the 2890--2710 Ma Witwatersrand basin, typically form ca. 3000 Ma isochrons with chondritic initial 187Os/188Os values. The Os concentrations of the gold range from approximately 2 to over 4000 ppb and are significantly elevated compared to other gold deposits. The older age, mantle source and high concentration of the gold support modified paleo-placer models with minor hydrothermal modification but not significant deposition of gold via hydrothermal fluids of any age. Other gold deposits have low average Os concentrations ranging from approximately 20 ppt to 1 ppb and Re/Os ratios generally similar to average continental crust. The initial 187Os/188Os of these deposits vary but seem to have more crustal signatures than the Witwatersrand deposits. Data support gold deposition from leaching of gold and Os via hydrothermal fluids from crustal lithologies. Os concentration and Re/Os data of gold show systematic variation with the age of the deposit. These trends may result from a decrease in the efficiency of partial melts to extract juvenile gold and Os from the cooling mantle and the increasing importance of recycling gold from pre-existing continental crust.

La scheelite, la tourmaline et le rutile des gisements d'or orogénique, encaissés dans des roches de composition et de faciès métamorphique variés ont été étudiés pour établir des paramètres discriminants pour contraindre les campagnes utilisant les minéraux indicateurs pour l'exploration aurifère. La texture et les associations minérales ont été investiguées par microscopie optique et microscopie électronique à balayage (MEB). La scheelite, la tourmaline et le rutile présentent une grande variabilité de taille, de texture et d'association minérale, qui ne sont pas informatives pour les campagnes de minéraux indicateurs. La composition minérale a été déterminée par microsonde électronique (EPMA) et ablation laser et spectroscopie de masse avec plasma couplée par induction (LA-ICP-MS). Les résultats ont été investigués par des diagrammes élémentaires et des analyses multivariées incluant des analyses en composantes principales (PCA) et des analyses de réduction des moindres carrées (PLS-DA). La composition et le faciès métamorphique des roches encaissantes régionales exercent un fort contrôle sur la composition en éléments traces de la scheelite, de la tourmaline et du rutile. Dans la scheelite, Sr, Pb, U, Th, Na, Éléments des Terres Rares (ETR) et Y; dans la tourmaline Ga et Sn; et dans le rutile Nb, Ta, V et Cr varient avec la composition de la roche encaissante. Dans la scheelite, ETR, Y, Sr, Mn, Nb, Ta et V; dans la tourmaline, Ga, Sn, Ti, ETR, Zr, Hf, Nb, Ta, Th et U; et dans le rutile Nb, Ta, V et Cr varient avec le faciès métamorphique des roches encaissantes. La composition en éléments traces de la scheelite varie avec l'âge de la roche encaissante alors que la tourmaline et le rutile ne montrent pas de variation compositionnelle avec l'âge de l'encaissant. La variation compositionnelle résulte des échanges fluide-roche lors de la circulation du fluide hydrothermal jusqu'au site de dépôt de l'or. Les résultats pour les minéraux des gisements d'or orogénique sont comparés avec ceux d'autres types de gîtes et de paramètres géologiques variées de la littérature. La scheelite et la tourmaline des gisements d'or orogénique présentent clairement une variation compositionnelle distincte comparée à celle d'autres types de gîtes et paramètres géologiques. La scheelite des gisements d'or orogénique a une signature distincte en Sr, Mo, Eu, As et Sr/Mo mais similaire en ETR par rapport à la scheelite provenant d'autres types de gîtes. Les diagrammes binaires tels que Sr/Li vs V/Sn, Sr/Sn vs V/Nb, Sr/Sn vs Ni/Nb et Sr/Sn vs V/Be discriminent la tourmaline des gisements d'or orogénique de celle provenant d'autres sources. Les diagrammes élémentaires mettent en avant une variation transitionnelle de la composition en éléments traces de la tourmaline provenant d'environnement métamorphique, à hydrothermal-magmatique, à magmatique. Le rutile des gisements d'or orogénique a une composition distincte en Mn, V, Sn, Sb et W comparée aux rutiles provenant d'autres types de gîtes et paramètres géologiques. Les diagrammes binaires incluant V vs Sb et Nb/V vs. Sn/V discriminent le rutile des gisements d'or orogénique et celui provenant des environnements magmatique-hydrothermaux et magmatiques. D'autres diagrammes binaires tel que Nb/V vs W permettent de distinguer partiellement le rutile des gisements d'or orogénique et celui provenant d'environnement hydrothermaux et métamorphique-hydrothermaux.
Scheelite, tourmaline and rutile from orogenic gold deposits and districts, hosted in varied country rocks and metamorphic facies of various ages were investigated to establish discriminant features to constrain indicator mineral surveys for gold exploration. Texture and mineral associations were investigated by optical microscopy and Scanning Electron Microscopy (SEM). Scheelite, tourmaline and rutile present a wide range of size, texture, and mineral association that are not informative for indicator mineral surveys. Mineral composition was determined using Electron Probe Micro-Analyzer (EPMA) and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Results were investigated with elemental plots and multivariate statistics including Principal Component Analysis (PCA) and Partial Least Square-Discriminant Analysis (PLS-DA). The composition of the metamorphic facies of the local country rocks as well as the regional country rocks exert a strong control on scheelite, tourmaline and rutile trace element composition. In scheelite Sr, Pb, U, Th, Na, REE and Y; in tourmaline Ga and Sn; and in rutile Nb, Ta, V and Cr vary with the country rock composition. In scheelite, REE, Y, Sr, Mn, Nb, Ta and V; in tourmaline, Ga, Sn, Ti, REE, Zr, Hf, Nb, Ta, Th and U; and in rutile Nb, Ta, V and Cr vary with the metamorphic facies of the country rocks. Scheelite trace element composition vary with the country rock age whereas tourmaline and rutile do not show any compositional variation with the country rock age. Compositional variation results of fluid-rock exchange during fluid flow to gold deposition site. Results for minerals from orogenic gold deposits are compared with those from various deposit types and geological settings from literature. Scheelite and tourmaline from orogenic gold deposits present clearly a distinct compositional variation, compared to scheelite and tourmaline from other deposit types and geological settings. Scheelite from orogenic gold deposits have distinct Sr, Mo, Eu, As and Sr/Mo, but indistinguishable REE signatures, compared to scheelite from other deposit types. Binary plots such as Sr/Li vs V/Sn, Sr/Sn vs V/Nb, Sr/Sn vs Ni/Nb and Sr/Sn vs V/Be discriminate orogenic gold deposit tourmaline from that from other sources. Elemental plots highlight a transitional variation in the trace element composition of tourmaline from metamorphic, to hydrothermal-magmatic to, magmatic environments. Rutile from orogenic gold deposits has a distinctive Mn, V, Sn, Sb and W composition compared to those from various deposits types and geological settings. Binary diagrams, including V vs Sb and Nb/V vs Sn/V, discriminate rutile from orogenic gold deposits from those from hydrothermal-magmatic and magmatic deposit types. Other binary diagrams, such as Nb/V vs W, discriminate partially orogenic gold deposit rutile from hydrothermal and metamorphic-hydrothermal environments.

Orogenic gold deposits occur within metamorphic belts throughout the world and have through time represented the source for over 25% of the world’s gold production. Although orogenic gold deposits are of great economic importance, controversies exist on the subject of fluid and metal sources and there have been few studies of gold´s distribution and mobility outside of large economic deposits. Research made by Pitcairn et al. (2006), on the Mesozoic Otago and Alpine schists of New Zealand, observed systematic depletion of Au and a suite of 6 associated elements with increasing metamorphic grade. This depletion was identical to the suite of elements enriched in the Otago gold deposits and provided strong evidence that orogenic gold deposits form due to metamorphic processes. The mobilization of metals was attributed to the recrystallization of sulfide minerals during prograde metamorphism causing dehydration and release of metal-rich metamorphic fluids.  This thesis is part of a larger project aimed at testing the “Otago model” in a classic metamorphic terrain: The Dalradian metamorphic belt of Scotland. Rocks in the study are from the southern higlands group and the Appin and Argyll group which range in metamorphic grade from chlorite zone greenschist facies to sillimanite zone amphibolite facies. Three main aspects, which supplement earlier research, are addressed in this study: 1) Investigation of the sulfide paragenesis at Loch Lomond and Stonehaven was carried out to map the evolution of sulfides with metamorphic grade and the possible relations to the distribution of gold. Using SEM scanning to quantify the abundance of different sulfide minerals together with previous data on the Glen Esk region, a complex sulfide evolution pattern for the Dalradian Supergroup is identified. The sulfide evolution describes the same changes in texture and chemistry as observed in the Otago Schists but is made complex by the difference in geological evolution for the different regions. 2) Reinvestigation of the higher grade zones of Glen Esk (staurolite to sillimanite) was carried out as samples from the previous study were very weathered. Results from ultralow detection limit methods (HG-AFS and a gold detection method developed by Pitcairn et al. 2006) showed significant systematic depletion of Au and As with metamorphic grade. From chlorite to sillimanite zone average values of Au and As were showed to decrease by 65% and 88% respectively. Furthermore, a suite of 10 major and 12 trace elements were analyzed using ICP methods showing no trends of systematic depletion with increased metamorphic grade.  3) Investigation of Pb-Ag Veining and vein samples from each of the metamorphic index mineral zones in the Glen Esk area was carried out to identify fluid composition and ore mineralogy. Using microthermometry and Raman laser spectroscopy two distinct fluids were identified. The first type is a H2O-CO2-N2-salt fluid of low salinity (0-15 weight percent NaCl equivalent) and medium temperature (150 to 250 °C) locally containing minor amounts of CH4. It is found in the veins from the mineral index zones of Glen Esk and was formed in the ductile regime most likely related to late stage metamorphic devolatilization released during Caledonian uplift of the Dalradian. Pb-Ag veins from the locality of Hardhill host the second fluid type which was formed in the brittle regime  accompanied by brecciation as a high salinity (15 to 20 weight percent NaCl equivalent) low temperature (70-140°C) H2O-salt fluid with calcic composition was precipitated. This fluid bears much resemblance to Carboniferous calcic brines responsible for economic base-metal precipitation with widespread occurrence in southwest Scotland and Northern Ireland. Results of this thesis show many similarities with the Otago study, with a connection between metal mobility and metamorphic grade, providing support for the dehydration model as a viable mechanism for the generation of orogenic gold deposits.

Les tourmalines, les scheelites et les magnétites provenant des gisements aurifères de type orogénique (n=22) et des sédiments glaciaires (n=5) du district minier de Val-d’Or (Québec, Canada) ont été investiguées à la microsonde électronique (EPMA) et par ablation laser et spectrométrie de masse à plasma à couplage inductif (LA-ICP-MS) afin de déterminer leur signature chimique et d’évaluer leur potentiel en tant que minéraux indicateurs pour l’exploration aurifère. Les tourmalines de Type I provenant de dépôts aurifères de type orogénique encaissés dans des roches felsiques et intermédiaires calco-alcalines montrent de faibles teneurs en V, Cr, Mn, Fe, Co, Ni, Zn et Sn et une teneur élevée en Mg par rapport aux tourmalines de Type II provenant de dépôts aurifères de type orogénique encaissés dans des roches mafiques tholéiitiques. Les tourmalines de Type III provenant de dépôts aurifères de type orogénique situés au contact entre des roches mafiques volcaniques et métasédimentaires montrent une chimie similaire aux tourmalines de Type I avec des teneurs en Li, Mn et Pb légèrement plus élevées. Les tourmalines des gisements aurifères de type orogénique sont caractérisées par des teneurs en Zn, Cu, Sn et Pb plus faibles que les tourmalines associées aux miniéralisations de type Cu-Zn, Pb-Zn-Cu et Sn. Les tourmalines récupérées dans le till portent la signature chimique des tourmalines provenant des gisements aurifères de type orogénique avec une majorité portant la signature des tourmalines de Type I. Les scheelites provenant de dépôts aurifères de type orogénique encaissés dans des intrusions calco-alcalines de composition intermédiaire sont caractérisées par des teneurs en Na, ÉTR et Y plus élevées que les scheelites provenant de dépôts aurifères encaissés dans des roches sédimentaires ou mafiques. Les scheelites récupérées dans le till portent la signature chimique des scheelites provenant des gisements aurifères de type orogénique. Les magnétites sont rare dans les dépôts aurifères de type orogénique du district de Val-d’Or. Les magnétites d’origine hydrothermale provenant des veines aurifères sont caractérisées par des teneurs plus élevées en Cr, Zn, Mn, K, Ca, Ti et Al que les magnétites d’origine magmatique retrouvées dans les roches encaissantes de composition dioritique ou gabbroique. Les magnétites associées à la minéralisation aurifère forment des grains fins disséminés (< 0,05 mm), ce qui suggère que les magnétites grossières récupérées dans le till ne proviennent probablement pas des veines de quartz aurifères.
Tourmalines, scheelites and magnetites from orogenic gold deposits (n=22) and glacial sediments (n=5) of the Val-d’Or mining district (Québec, Canada) were investigated by Electron Probe Micro-Analyzer (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) in order to determine their chemical signature and to assess their potential as indicator minerals for gold exploration. Type I tourmalines from orogenic gold deposits hosted in felsic and intermediate calc-alkaline rocks have low contents of V, Cr, Mn, Fe, Co, Ni, Zn, and Sn and a high content of Mg compared to Type II tourmalines from orogenic gold deposits hosted in mafic tholeiitic rocks. Type III tourmalines from orogenic gold deposits located at the contact between mafic volcanic and metasedimentary rocks show a chemistry similar to Type I tourmalines with slightly higher Li, Mn, and Pb contents. Tourmalines from orogenic gold deposits are characterized by lower contents of Zn, Cu, Sn, and Pb than tourmalines associated to Cu-Zn, Pb-Zn-Cu, and Sn mineralizations. Till tourmalines carry the chemical signature of tourmalines from orogenic gold deposits with a majority carrying the signature of Type I tourmalines. Scheelites from orogenic gold deposits of the Val-d’Or district hosted in calc-alkaline intrusions of intermediate composition are characterized by high Na, REE, and Y contents compared to scheelites from sediment- or mafic-hosted gold deposits. Till scheelites carry the chemical signature of scheelites from orogenic gold deposits. Magnetites are rare in orogenic gold deposits of the Val-d’Or district. Magnetites of hydrothermal origin occuring in gold veins are characterized by higher contents of Cr, Zn, Mn, K, Ca, Ti, and Al than magnetites of magmatic origin found in the dioritic or gabbroic host rocks. Magnetites associated to the gold mineralization form fine disseminated grains (< 0.05 mm), which suggests that the coarse magnetites recovered in the till probably do not originate from the gold-bearing quartz veins.

A review of Archean granite-greenstone terranes, orogenic gold deposits, the Slave Province and modern exploration tools, techniques and methods was conducted to identify prospective areas in the Yellowknife domain for hosting orogenic gold deposits and illustrate the best exploration methods for delineating this deposit type. This study identifies Archean granite-greenstone terranes as economically important hosts to quartz-carbonate vein-hosted orogenic gold deposits. These deposits occur at convergent plate margins, but can also be related to local extensional tectonics within a convergent setting. Heat generated from tectonic processes can trigger hydrothermal fluid movement along first-order faults and shear zones. Precipitation of gold-bearing quartz-carbonate veins from the hydrothermal fluids occurs in second- and third-order faults and shear zones related to the first-order structures. This study also identifies the Archean Slave Province in northern Canada as a well-endowed craton with numerous orogenic gold deposits, diamondiferous kimberlites, VMS deposits and several other mineralization styles. In particular, three greenstone belts (Yellowknife, Cameron River and Beaulieu River) associated with likely first-order structures are comprised of prospective rocks for hosting orogenic gold and VMS mineralization. The Yellowknife greenstone belt hosts the past-producing and former world-class Con and Giant orogenic gold deposits, but has been little explored with modern exploration techniques. The Cameron River and Beaulieu River greenstone belts host numerous base and precious metal VMS and BIF-hosted orogenic gold prospects and deposits, indicating mineralization is present. There is considerable potential for significant discoveries to be made using modern exploration techniques in the greenstone belts; however, exploration in the region has been hindered over the past decade by ongoing political negotiations. Once the political negotiations are finalized, application of modern exploration methods and techniques in the prospective greenstone belts should be carried out. Regional scale methodologies should be applied to generate targets using predictive modelling, implicit 3D modelling, 3D geochemistry and exploration targeting so decisions defining a businesses strategy for ground acquisition of high priority targets are made using quantitative analysis. Once ground is acquired, field-based exploration for orogenic gold and VMS deposits should include geological mapping with a focus on structural geology, geochemical sampling and airborne magnetic, radiometric and EM geophysical surveys. Prior to reconnaissance drilling, integration of all data layers and interpretation within a common 3D earth model should be conducted. Following successful reconnaissance drilling, definition drilling along strike and down dip of intersected mineralization, combined with borehole geophysics, should be carried out to delineate the extent of mineralization.

[Formulae and special characters can only be approximated here. Please see the pdf version of the abstract for an accurate reproduction.] The formation of world-class Archean orogenic gold deposits in the Eastern Goldfields Province of Western Australia was the result of a critical combination of physical and chemical processes that modified a single and widespread ore-fluid along fluid pathways and at the sites of gold deposition. Increased gold endowment in these deposits is associated with efficient regional-scale fluid focusing mechanisms and the influence of multiple ore-depositional processes at the deposit-scale. Measurement of the complexity of geologic features, as displayed in high-quality geologic maps of uniform data density, can be used to highlight areas that influence regional-scale hydrothermal fluid flow. Useful measurements of geological complexity include fractal dimensions of map patterns, density and orientation of faults and lithologic contacts, and proportions of rock types. Fractal dimensions of map patterns of lithologic contacts and faults highlight complexity gradients. Steep complexity gradients, between domains of high and low fractal dimensions within a greenstone belt, correspond to district-scale regions that have the potential to focus the flow of large volumes of hydrothermal fluid, which is critical for the formation of significant orogenic gold mineralization. Steep complexity gradients commonly occur in greenstone belts where thick sedimentary units overly more complex patterns of lithologic contacts, associated with mafic intrusive and mafic volcanic units. The sedimentary units in these areas potentially acted as seals to the hydrothermal Mineral Systems, which resulted in fluid-pressure gradients and increased fluid flow. The largest gold deposits in the Kalgoorlie Terrane and the Laverton Tectonic Zone occur at steep complexity gradients adjacent to thick sedimentary units, indicating the significance of these structural settings to gold endowment. Complexity gradients, as displayed in surface map patterns, are an indication of three-dimensional connectivity along fluid pathways, between fluid source areas and deposit locations. Systematic changes in the orientation of crustal-scale shear zones are also significant and measurable map features. The largest gold deposits along the Bardoc Tectonic Zone and Boulder-Lefroy Shear Zone, in the Eastern Goldfields Province, occur where there are counter-clockwise changes in shear zone orientation, compared to the average orientation of the shear zone along its entire length. Sinistral movement along these shear zones resulted in the formation of district-scale dilational jogs and focused hydrothermal fluid-flow at the Golden Mile, New Celebration and Victory-Defiance deposits. Faults and lithologic contacts are the dominant fluid pathways in orogenic gold Mineral Systems, and measurements of the density of faults and contacts are also a method of quantifying the complexity of geologic map patterns on high-quality maps. Significantly higher densities of pathways in areas surrounding larger gold deposits are measurable within 20- and 5-kilometer search radii around them. Large variations in the sulfur isotopic composition of ore-related pyrites in orogenic gold deposits in the Eastern Goldfields Province are the result of different golddepositional mechanisms and the in-situ oxidation of a primary ore fluid in specific structural settings. Phase separation and wall-rock carbonation are potentially the most common mechanisms of ore-fluid oxidation and gold precipitation. The influence of multiple gold-depositional mechanisms increases the potential for significant ore-fluid oxidation, and more importantly, provides an effective means of increasing gold endowment. This explains the occurrence of negative δ34S values in ore-related pyrites in some world-class orogenic gold deposits. Sulfur isotopic compositions alone cannot uniquely define potential gold endowment. However, in combination with structural, hydrothermal alteration and fluid inclusion studies that also seek to identify multiple ore-forming processes, they can be a useful indicator. The structural setting of a deposit is also a potentially important factor controlling ore-fluid oxidation and the distribution of δ34S values in ore-related pyrites. At Victory-Defiance, the occurrence of negative δ34S(py) values in gently-dipping dilational structures, compared to more positive δ34S(py) values in steeply-dipping compressional structures, is potentially associated with different gold-depositional mechanisms that developed as a result of fluid-pressure fluctuations during different stages of the fault-valve cycle. During the pre-failure stage, when fluids are discharging from faults, fluid-rock interaction is the dominant gold-depositional mechanism. Phase separation and back-mixing of modified ore-fluid components are dominant during and immediately after faulting. Under appropriate conditions, any, or all, of these three mechanisms can oxidize orogenic gold fluids and cause gold deposition. The influence of multiple gold-depositional mechanisms during fault-valve cycles at dilational jogs, where fluid pressure fluctuations are interpreted to be most severe, can potentially explain both the large gold endowment of the giant to world-class Golden Mile, New Celebration and Victory-Defiance deposits along the Boulder-Lefroy Shear Zone, and the presence of gold-related pyrites with negative δ34S values in these deposits. This study highlights the interplay that exists between physical and chemical processes in orogenic gold Mineral Systems, during the transport of ore fluids in pathways from original fluid reservoirs to deposit sites. Potentially, a single and widespread orogenic ore-fluid could become oxidized, and lead to the formation of ore-related sulfides with variable sulfur isotopic compositions, depending on the nature and orientation of major fluid pathways, the nature of wall-rocks through which it circulates, and the precise ore-depositional processes that develop during fault-valve cycles.

Ädelfors is situated ca 17 km east of Vetlanda, Jönköping County, in the N-S striking Trans-scandinavian igneous belt and is a part of the NE-SW striking 1.83-1.82 Ga Oskarshamn-Jönköping belt emplaced during a continental subduction towards the Svecofennian continental margin. The continental arc hosts the 1.83 Ga metasedimentary Vetlanda supergroup composed of foliated metagreywacke, metasandstone and metaconglomerate. The sequence is intercalated by mafic and felsic volcanites and hosts the Cu-Au-Fe-mines at Ädelfors. Ädelfors mining field consists of ca 330 mineralized quartz veins hosting both copper, gold and iron. The iron mines Nilsson’s iron mine (NFE) and Fe-mine (FE), the copper mine Kamelen (KM) and the gold mines Brånad’s mine (BR), Adolf Fredrik’s mine (AF), Old Kron mine (GKR), Old Kolhag’s mine (GKO), Thörn mine (TH), New Galon mine (NG), Stenborg’s mine (ST), Tysk mine (TG), Hällaskallen (HS) and Fridhem (FR) have been investigated to deduce a possible genetic relation between the veins and their origin. Sulfur isotope ratios have also been conducted on pyrite from KM, AF and FE. The veins can stucturally be divided into several groups. AF, GKR, ST, NG, TH and possibly NFE are striking 10-70° with a dip of 55-70°. BR, GKO and KM are striking 110-140° with a dip of 80-90° whereas TG and HS strike 90-110° dipping 85°. Fridhem, being distal to the other mines, strikes 70° and dips 80°. A chlorite-quartz-biotite-sericite-rich metapelite hosts the veins in all localities except; FR where a layered, beresitizised felsic volcanite rich in plagioclase, sericite, biotite and quartz hosts disseminated pyrite; and NFE, HS and NG which are hosted by a mafic tuffite. Quartz veins are mainly milky and equigranular, exceptions are FE with black pyrite-bearing quartz veins, cutting through the banded magnetite-metapelite and KM with its dynamically recrystallized quartz. Chlorite-, zeolite-, carbonate-, hematite-, amphibole-, kalifeldspar-, sericite-, biotite- and epidote alteration has been observed among the localities. The ore minerals are dominated by: fractured sub- to euhedral pyrite in cataclastic aggregates or selvage bands, interstitial chalcopyrite in pyrite, marcasite, pyrrhotite, gold and sporadic chalcopyrite diseased sphalerite and arsenopyrite. Previously not reported tetradymite, staurolite, galena and Ce-monazite have also been observed. Bismuthinite and tetradymite as inclusions in pyrite were observed in AF, GKR, FR and TG. Gold was observed in AF, BR, GKR and TG as inclusions in pyrite or quartz with a Au/Ag median of 78.41. HS distinguishes itself with Au/Ag ratios of 4.66-5.25. The trace element ratios in pyrite reveal two major types of pyrite. 1) found in FE and KM (pyrite type 1) with Co/Ni ratio of 10.94, Bi/Au of 1.79, Bi/S of 0.037, Au/Ag of 11.13, S/Se of 235.96 and As/S of 0.006. 2) found in NG, GKO, ST, TH, AF, NFE, HS, GKR, BR, FR, TG and as stringers in KM4 py1 pyrite type 2) with an average Co/Ni ratio of 5.26, Bi/Au of 1.95, Bi/S of 0.031, Au/Ag of 4.19, S/Se of 0 and As/S of 0. δ34S values strengthens this grouping as KM and FE has 1,3-2,6 ‰ and AF 3,6-3,8 ‰. The following geological interpretation has been concluded: The banded iron formation in FE is the earliest mineralization and was later fractured, emplacing quartz veins with pyrite of type 1. During this event, the Cu-vein in KM was also formed. A second generation of fractures, emplaced after the Småland granitoids formed, were filled with quartz and pyrite of type 2 at mesozonal depth. This is the main stage of gold mineralization and includes NG, GKO, ST, TH, AF, NFE, GKR, BR, FR and TG. During this event, pyrite of type 2 was added to KM, causing recrystallizing of the quartz. HS is possibly emplaced last or altered as it is more enriched in silver. Morphology, mineralogy, alterations, mineral chemistry and sulfur isotope signatures indicates an orogenic origin of the gold-rich quartz veins at Ädelfors as well as the copper-rich vein in KM.
Ädelfors ligger ca 17 km öster om Vetlanda, Jönköpings län, i det N-S strykande Transskandinaviska granit och porfyrbältet och är en del av det NÖ-SV strykande 1,83-1,82 Ga Oskarshamn-Jönköpingsbältet (OJB) bildad i en kontinental subduktionszon i kanten av den Svecofenniska kontinentalplattan. I denna kontinentalbåge ligger Vetlanda supergruppen som är en metasedimentär del av OJB bestående av starkt folierad 1,83 Ga metagråvacka, metasandsten och metakonglomerat med inlagringar av mafiska och felsiska vulkaniter. Ädelfors gruvfält består utav ca. 330 kvartsgångar förande mestadels guld men också koppar. Järnmineraliseringar i form av bandad järnmalm finns också i området. Geologin, mineralogin och pyritens kemiska sammansättning från järngruvorna Nilssons järngruva (NFE) och Fe-gruvan (FE), koppargruvan Kamelen (KM) och guldgruvorna Brånadsgruvan (BR), Adolf Fredriks gruva (AF), Gamla Krongruvan (GKR), Gamla Kolhagsgruvan (GKO), Thörngruvan (TH), Nya Galongruvan (NG), Stenborgs gruva (ST), Tyskgruvan (TG), Hällaskallen (HS) och Fridhem (FR) har undersökts för att finna eventuella genetiska likheter. Svavelisotopförhållande har fastställts för pyrit från AF, FE och KM. Strukturellt kan gångarna delas in i ett antal grupper. AF, GKR, ST, NG, TH och möjligtvis NFE stryker 10-70° och stupar 55-70°. BR, GKO och KM stryker 110-140° och stupar 80-90° medan TG och HS stryker 90-110° och stupar 85°. Fridhem stryker 70° och stupar 80°. En klorit-kvarts-sericit-biotitrik metapelit utgör värdbergarten i alla gruvor förutom; FR där den utgörs av en beresitiserad felsisk vulkanit rik på plagioklas, sericit, biotit och kvarts med disseminerad pyrit; och NFE, HS, NG vilka har en mafisk tuffitisk moderbergart. Kvartsgångarna är mjölkvita med undantag för FE:s svarta, pyritförande kvarts vilket uppträder som sprickfyllnad i den bandade järnmalmen och är senare bildad. Kvartsen i KM är starkt dynamiskt omkristalliserad. Svag till måttlig foliation är vanlig i sidoberget med undantag av stark foliation i TG och NFE, vilka är lokaliserade i förkastningssprickor med stark kloritförskiffring av värdbergarten. Klorit-, zeolit-, karbonat-, hematit-, amfibol-, kalifältspat-, sericit-, biotit- och epidotomvandling förekommer i majoriteten av lokalerna. Malmmineralen är dominerande sprött deformerad subhedral till euhedral pyrit som kataklastiska aggregat eller band, interstitiell kopparkis i pyrit, markasit, magnetkis, guld och sporadiskt kopparkissjuk zinkblände och arsenikkis. I det här arbetet har även tetradymit, staurolit, blyglans och Ce-monazit observerats. Bismutinit och tetradymit i form av inneslutningar i pyrit observerades i AF, GKR, FR och TG. Guld observerades i AF, BR, GKR och TG som inneslutningar i pyrit eller fritt i kvarts med Au/Ag medianvärde på 78,41, avvikande är HS med värden mellan 4,66-5,25.    Förhållanden mellan spårelement i pyrit indikerar två typer av pyrit. Typ 1 funnen i FE och KM har följande värden: Co/Ni = 10,94, Bi/Au = 1,79, Bi/S = 0,037, Au/Ag = 11,13, S/Se = 235,96 och As/S = 0,006. Typ 2 funnen i NG, GKO, ST, TH, AF, NFE, HS, GKR, BR, FR, TG och som sliror i KM4 py1 har följande värden Co/Ni = 5,26, Bi/Au = 1,95, Bi/S = 0,031, Au/Ag = 4,19, S/Se = 0 and As/S = 0. δ34S värden styrker denna uppdelning där KM och FE har värdena 1,3-2,6 ‰ och AF 3,6-3,8 ‰. Den geologiska utvecklingen av fältet har tolkats som följande: FE-gruvans bandade järnmalm är den tidigaste mineraliseringen vilket följs utav uppsprickning och läkning av kvarts med pyrit typ 1 som också bildar kopparmineraliseringen KM. Senare sprickzoner efter Smålandsgraniternas intrusion läks av kvarts med pyrit typ 2 på mesozonalt djup vilket bildar NG, GKO, ST, TH, AF, NFE, GKR, BR, FR, TG och omkristalliserar och introducerar nya pyritsliror i kvartsen i KM. HS bildas möjligtvis sist eller har blivit omvandlad eftersom den är anrikad på silver. Morfologi, omvandlingar och svavelisotop-signaturer tyder på ett orogent ursprung för Ädelfors guldrika kvartsådror samt den kopparrika kvartsådern i KM.

The Kumasi Basin in South-west Ghana lies at the centre of the best-endowed Paleoproterozoic gold province in the world. The Kumasi Basin and margins of the adjacent volcanic belts are host to six world class gold camps: (1) 62 Moz Obuasi camp, (2) 22 Moz Prestea-Bogoso camp, (3) 11 Moz Asanko Gold Mine camp, (4) 9 Moz Edikan camp, (5) 7 Moz Bibiani camp, (6) 5 Moz Chirano camp, as well as several additional minor gold camps and many more prospects. Cumulatively these camps account for>116 Moz of endowment and contribute to making south-west Ghana the greatest Paleoproterozoic gold province in the world. Gold deposits in the Kumasi Basin are shear zone hosted and mineralisation ranges from disseminated to massive sulphide refractory deposits, to free milling quartz vein style deposits. Structural relationships and age dating indicate that most deposits are genetically related and were formed during a single episode of gold mineralisation during the D4 NNW-SSE crustal shortening deformation event of the Eburnean Orogeny (2125 – 1980 Ma). The understanding of structural controls on mineralisation is critical for exploration success as it allows exploration to focus on areas where these structural controls exist. This study uses a mineral systems approach to understand the relationship between the geodynamic history and structural controls on gold mineralisation in the Kumasi Basin at various scales, and define targeting criteria which can be applied for the purpose of developing predictive exploration models for making new discoveries in the Asanko Gold Mine camp located in the Asankrangwa Belt. The study used a quantitative analysis to establish residual endowment potential in the Asankrangwa Belt, providing the basis for a business model and resulting exploration strategy. Once established, a Fry autocorrelation analysis was applied to identify trends in deposit and camp spatial distribution to which critical geological processes were ascribed. Observed trends were mapped from multi-scale geophysical data sets and through interpretation of existing geophysical structure models, and structural criteria for targeting orogenic gold deposits at the regional and camp scales were developed. Results show that different structural controls on mineralisation act at the regional and camp scale. At the regional scale the distribution of gold camps was found to be controlled by fundamental N-S and NW-SE basement structures with gold camps forming where they intersect NE-SW first and second order structural corridors. At the Asanko Gold Mine camp scale, deposit distribution was found to be related to the intersection between major second order D3 NE-SW shear zones, minor third order D4 NNE-SSW brittle faults, and cryptic NW-SE upward propagating basement structures. In addition to these structural criteria, deposits in the Asanko Gold Mine camp were found to be aligned along a NNE-SSW lineament caused by the interaction between the N-S basement structure and the NE-SW trending Asankrangwa Belt shear corridor.

Yafei Wu’s PhD project has explored different ore-forming aspects of a world-class Chinese orogenic gold deposit. The results show that orogenic gold could be sourced from either metamorphism or magmatism. Silica has an important role in gold transport. Gold zoning in pyrite records both fluid conditions and local kinetics. Gold significantly redistributes during pyrite replacement. The knowledge gained increases our understanding of the genesis of orogenic gold widely distributed in Australia, New Zealand and worldwide.

The well-known Skellefte Ore District, northern Sweden, hosts a large number of massive sulphide deposits, a few porphyry-type-deposits and a number of gold deposits in different geological settings. Southwest of this district a new ore province, the so called Gold Line, is presently being uncovered. During the past decade a number of gold occurrences have been discovered in this area. Only one deposit is in production, the Svartliden gold deposit (2 Mton at 4.3 ppm Au). However, with regards to tonnage the Fäboliden gold deposit stands out with a known mineral resource of c. 16 Mton with 1.33 ppm Au. Additional 24.5 Mton with 1.5 ppm Au is indicated down to a depth of 350 m. The late- to post-orogenic, c. 1.81-1.77 Ga, Revsund granite constitutes the main rock type in the Fäboliden area and surrounds a narrow belt of metavolcanic rocks and metagreywackes. The metasedimentary rocks are strongly deformed, within a roughly N-S trending subvertical shear zone, with boudinaged competent horizons that indicate E-W shortening and a suggested dextral sense of shear within the shear zone. The mineralization at Fäboliden constitutes a 30-50 m wide, N-S striking, steeply dipping ore zone. The mineralization is commonly hosted in arsenopyrite-bearing quartz-veins, which parallel the main foliation, within the metagreywackes in the shear zone. The fine-grained (2-40 µm) gold is closely associated with arsenopyrite-löllingite and stibnite and found in fissures and as intergrowths in the arsenopyrite-löllingite. Gold is also seen as free grains in the silicate matrix of the metagreywacke host rock. Microprobe analysis shows that the gold occurs as electrum (Au:Ag 2:1). The proximal ore zone display enrichment in Ca, total S, As, Ag, Au, Sb, Sn, W, Pb, Bi, Cd, Se, and Hg, whereas K and Na are slightly depleted. The hydrothermal alteration assemblage in the proximal ore zone is diopside, calcic amphibole, biotite, and minor andalusite and tourmaline. This type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide. The c. 1.3 km long ore body (lode) is steeply dipping and known to a depth of 150 m, with a few deeper boreholes indicating a continuation of the mineralization towards depth. The mineralization is also open towards north and south. The fabric that hosts the mineralization is also found in the outer margin of the surrounding Revsund granite. It is therefore suggested that at least the final stages of the gold mineralization are late- or post-orogenic in age, and the maximum age for the mineralization is constrained at c. 1.80 Ga (Revsund age). The mineralizing fluids were composed of CO2-CH4-H2S. Gold, arsenopyrite- löllingite, and graphite were precipitated from this fluid. The crystal structure of the graphite, enclosed in the gold related quartz veins, indicates a maximum temperature of 520-560ºC for the mineralizing event, temperature conditions equal to mid-amphibolite facies. These temperatures indicate pressure conditions of c. 4 kbar for the mineralizing event. During deformation mineralizing fluids are often concentrated into deformation zones. Therefore, the potential for economic mineralization in the Lycksele-Storuman region is regarded as very high since the initial results from this project have indicated the existence of several larger ductile to semi-ductile shear zones and accompanied silica alteration in the studied area. During 2004 the project strongly assisted in locating a new gold target in the Gold Line area. For more effective future exploration in this area a better understanding of the structural conditions and evolution is a key factor.
Godkänd; 2005; 20061214 (haneit)

The PhD project investigated the role of carbonaceous material in the formation of Macraes orogenic gold deposits. It provided the first evidence that in-situ carbonaceous material directly contributes to Au incorporation into polyframboids which may provide the source of Au for the Macraes gold deposit; that carbonaceous material in mineralized rocks of gold deposit is most likely hydrothermally deposited and contributes to Au precipitation indirectly; and that dodecanethiol may transport Au in hydrothermal systems.

The Fäboliden gold deposit is an ore body in northern Sweden’s Bothnian Basin and has been the subject of studies and test mining since the early 2000s when the Gold Line, an area of anomalously high-Au glacial till in Northern Sweden, became a center of economic interest. The deposit is a hypozonal orogenic gold deposit that displays many characteristic features of ore bodies of this type, including the presence of compound sulfide grains composed of a core of löllingite surrounded by a rim of arsenopyrite, and an abundance of pyrrhotite throughout the deposit and surrounding alteration zone. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to first map the distribution of trace elements in several of the arsenpyrite-löllingite grains, then to perform spot analyses of pyrrhotite grains in samples from across the distal and proximal alteration zones of the deposit. The maps of the trace elements in the compound löllingite-arsenopyrite grains show that: As and Au are found in greater abundance in the löllingite than in the arsenopyrite; Cu, Fe, S, and Ti are found in greater abundance in the arsenopyrite than in the löllingite; and Ag, Au, Bi, La, Mn, Pb, Sr, Ti and Tl are found in zones of secondary enrichment along fractures within the grains. Uranium and V may also be enriched along fractures, although this isn’t clear on all of the maps. Gold is an element of particular interest, because its distribution throughout the sulfide phases can be used to constrain the mechanism and relative timing of mineralization within the deposit. The presence of invisible gold within the löllingite, but not within the arsenopyrite, shows that gold is not incorporated into arsenopyrite at high temperatures and will instead be concentrated in the löllingite core of the composite grain and at the margin between the two sulfide phases as the löllingite is altered to arsenopyrite. Previous research on the Fäboliden gold deposit, including geothermometric analysis of vein-hosted graphite within fluid inclusions and garnet-biotite geothermometry as well as structural evidence provided by regional deformation, indicate that mineralization occurred post-peak metamorphism. The textures seen are therefore not conclusive of mineralization occurring syn- or pre-peak metamorphism, as has previously been proposed based on research of orogenic gold deposits in Western Australia. The spot analysis of pyrrhotite samples from across the deposit shows a distinct decrease in Ni and Co content in the proximal alteration zone, suggesting uptake of these elements by other minerals such as the löllingite and arsenopyrite. Multiple analyses performed on single grains show local variation, but are insufficient to establish the presence or determine the character of growth zonation within pyrrhotite.

Cette thèse correspond à une étude comparative détaillée de trois gisements aurifères birimiens (~ 2 Ga) du craton ouest africain (Syama, Tabakoroni et Tellem), situés sur la ceinture de Bagoé au Mali. La minéralisation se concentre dans les roches où les structures de déformation fragile sont les plus développées (basaltes et métasédiments bréchifiés, microgranite à Tellem) et se développe préférentiellement en bordure des veines. Les sulfures majeurs (pyrite à Syama et pyrite + arsénopyrite à Tabakoroni et Tellem) sont zonés avec : i) un cœur arsénifère riche en inclusions d'albite, d'ankérite et de rutile (accessoirement pyrrhotite); ii) une bordure limpide, globalement moins arsénifère que le coeur mais présentant une fine zonation avec des alternances de zones riches en As et de zones pauvres en As. L'or se présente sous forme d'or invisible inclus dans le réseau cristallin des sulfures, de petits grains individualisés en inclusion dans les sulfures, souvent accompagnés de sulfoantimoniures, notamment la tétraédrite et la chalcostibite, et d'or libre associé au quartz. Les pyrites arsénifères et les arsénopyrites des gisements de la ceinture de Bagoé sont parmi les plus riches en or invisible de tous les gisements d'or de l'Afrique de l'Ouest et tout à fait comparables à ceux de la ceinture d'Ashanti au Ghana
This thesis presents a comparative study of the Syama, Tabakoroni and Tellem gold deposits, located in the N-S trending Bagoé greenstone belt of Mali. Mineralization is found preferentially along the edges of millimetre- to centimetre-sized quartz, quartz-albite, quartz-ankerite, dolomite-quartz veins developed in tension gaps that formed during brittle deformation. Gold mineralization is mostly associated with pyrite in the three deposits, and also with arsenopyrite at Tabakoroni and Tellem. These sulphides are zoned with (i) an arsenic-rich core containing several albite, ankerite and rutile inclusions (less commonly, pyrrhotite) and (ii) a clear border of finely alternating As-rich and As-poor bands. Gold occurs in the form of i) invisible gold included in their crystal lattices, ii) small individual grains bound to these sulphides, frequently accompanied by sulphoantimonides, mainly tetrahedrite and chalcostibite and iii) free gold associated with quartz. The arseniferous pyrites and arsenopyrites of the Bagoé belt deposits are among the richest in invisible gold in all gold deposits in West Africa and are quite comparable to those of the Ashanti Belt in Ghana

Le craton ouest-africain héberge de nombreux gisements et occurrences aurifères encaissés dans des terrains paléoprotérozoïques. Ces terrains birimiens se sont formés et accrétés lors du cycle orogénique éburnéen qui s’est déroulé entre 2,25 et 1,98 Ga. Six gisements d’or situés au Burkina Faso et au Ghana ont été étudiés dans le but d’établir une corrélation entre les différentes phases de l’orogenèse et le (ou les) événement(s) minéralisateur(s). L’étude détaillée de la minéralisation de ces six gisements a confirmé leur nature orogénique, mais a également révélé la présence d’un porphyre à Cu (±Au) dans le district minier de Gaoua, Burkina Faso. Par ailleurs, nos observations ont mis en évidence le caractère polyphasé de la minéralisation au sein d’un même gisement. Les datations Re-Os menées sur des sulfures directement liés à la minéralisation en or permettent de distinguer deux grandes périodes métallogéniques au sein de l’orogenèse éburnéenne. La première période se déroule lors de la phase d’accrétion magmatique D1 et de la phase de transition D2, soit entre 2200 et 2120 Ma. Cette période est caractérisée par une minéralisation à faibles teneurs disséminée dans les roches encaissantes. La deuxième période métallogénique prend place lors des stades cassants tardifs de l’orogenèse, aux alentours de 2050-2040 Ma. Elle est représentée par une minéralisation à or visible à plus fortes teneurs, concentrée dans des veines, des brèches et des zones de cisaillement. La mise en évidence de l’existence de minéralisations aurifères précoces pourrait avoir des conséquences sur la compréhension des gisements de type paléoplacer observés notamment au Ghana. Ces minéralisations primaires pourraient en effet constituer la source de l’or des paléoplacers tarkwaïens, mis en place à partir de 2130 Ma, qui demeure inconnue
The West African craton is a region enriched in gold deposits and occurrences which are hosted in Paleoproterozoic terrains. These Birimian terrains formed during the Eburnean orogeny which took place between 2.25 and 1.98 Ga. Six gold deposits situated in Burkina Faso and Ghana were studied in order to define a correlation between the different orogenic phases and the mineralizing event(s). The detailed study of the mineralization of the six deposits confirmed the importance of the orogenic gold deposits in the West African craton. Moreover, the existence of a Cu (±Au) porphyry deposit was revealed in the mining district of Gaoua, southwestern Burkina Faso. Our observations highlighted the polyphased character of gold mineralization within nearly all of the studied deposits. Re-Os dating performed on sulfides directly linked to the gold mineralization permitted two main metallogenic periods to be distinguished. The first period was coincident with the D1 and D2 orogenic phases, occurring between 2200 and 2120 Ma, and representing respectively magmatic accretion and transition towards a collisional regime. This period was characterized by low grade disseminated gold mineralization. The second metallogenic period took place during the later brittle deformational phases of the orogeny, ca. 2050-2040 Ma. This secondary mineralization contains visible gold concentrated in veins, breccias and shear zones, and displays higher gold grades. Geochronological evidence for the existence of early gold mineralization could have consequences for the understanding of paleoplacer-type deposits, observed primarily in Ghana. Indeed, this primary mineralization could represent a potential source for gold found in Tarkwaian paleoplacers, which formed after 2130 Ma, and for which the provenance of the gold remains unidentified

Within the mining industry, all phases of the operation are dependent on the resource model. The focus of the mining operation is a model, which is often based on incomplete or flawed data. An orebody is commonly a poorly understood geological entity, and the resource model is generated from samples taken from this orebody. The inherent variation caused by geological complexity within the orebody can cause errors in the resource model. In order to reduce errors, the grade distribution of the deposit needs to be quantified, the sampling and resource evaluation protocols need to be optimised, and the level of inherent risk within the model needs to be identified and managed. Two gold deposits (Golden Pig and Marvel Loch) in the Southern Cross Greenstone Belt of the Yilgarn Craton were studied to determine the effect that these factors have on the resource model. Fractal analysis was applied to the Taurus orebody of the Golden Pig deposit. The grade distribution within the Taurus shear zone could be split into two different domains using the concentration-area method of fractal analysis. As the majority of fractal methods are two-dimensional, the technique was modified to determine the fractal dimensions of the deposit in three dimensions. This is the first study known to have applied fractal techniques to a mining based dataset in three dimensions. The grade distribution of the Taurus shear zone features two fractal dimensions, separated by a "threshold" value of 7 g/t. Geological interpretation of the Taurus shear zone indicates that two mineralising events are present, one overprinting the other. The geological evolution of the shear zone is thought to have produced the two differing fractal dimensions, with the "low" grade distribution due to low grade, more pervasive mineralisation, and the "high" grade distribution relating to cross cutting high grade tension veins. Sampling protocols were optimised for four different mineralisation styles: Haddons and Taurus orebodies from Golden Pig, and Boulder and East orebodies from Marvel Loch. The application of Gy sampling theory was shown to reduce errors within the processing of samples of broken rock. Heterogeneity tests were used to determine the sampling constant (K) of Gy theory value for each of the orebodies, and thereby to propose an optimised sampling regime. Gy nomograms were used to determine whether each of the protocols would breach "Gy's Safety Line". A constant sample size of 1 t for each of the mineralisation styles was found to minimise the fundamental sampling error to acceptable levels, with the total error never exceeding ±10%. Comparing the orebodies showed that the K value of the deposit correlated with the percentage coarse gold within the deposit. Resource evaluation techniques were also optimised for four different mineralisation styles: the Haddons and Taurus orebodies from Golden Pig, and the Undaunted and Sherwood orebodies from Marvel Loch. Resource evaluation techniques used both estimation and simulation, and all case studies included an optimised estimation method. In three of the case studies, conditional simulation models are also presented. Quantitative Kriging Neighbourhood Analysis (QKNA) was used to determine a suitable search area for the individual orebodies. Each of the orebodies was modelled using a variety of techniques and search areas, and comparisons were made between the global mean grade of the model with the declustered mean grade of the input data, individual blocks from the model, and trend plots and grade tonnage curves of the individual models. The Haddons case study was also reconciled with a known bulk sample grade to illustrate the suitability of the modelling technique. The optimised evaluation technique is different for every orebody, illustrating how a blanket approach to resource evaluation is unsuitable. The financial risk from incorrectly modelling variograms for the Haddons orebody was quantified. Variograms were modelled using an experimental variogram and there is an inherent risk that variograms maybe modelled incorrectly. The case study presented here aims to quantify the financial risk involved in modelling the variogram parameters (the nugget effect and range) incorrectly. The Haddons case study illustrates how modelling the nugget effect incorrectly by 20% can result in a Moderate financial loss, but is Very Likely to occur, which is deemed to be a high risk situation. Modelling the range at slightly longer lengths than the "true" range also results in a financial loss, but the loss is smaller, being classified as Minor. This scenario is also Very Likely to occur. The level of risk involved in a single decision made at the beginning of the resource evaluation procedure can be seen to have significant impacts throughout the project. Financial modelling using the incorrect block models illustrates how a discrepancy in the variogram modelling could affect whether the deposit is developed into a mine or not. As all of the deposits studied in this thesis are classified as Archaean Orogenic Gold Deposits, the specific conclusions may only be pertinent to this style of mineralisation. Even within this single style of mineralisation, different resource evaluation approaches are needed for each orebody. Gaining a more thorough understanding of the grade distribution, optimising sampling and resource evaluation protocols, and identifying inherent risks are important in each case and for all mineralisation styles. Good management of all factors involved in the production of a resource model is vital if unnecessary errors, which can have major financial consequences, are to be avoided.

PALEOFLUID CHEMISTRY OF OROGENIC GOLD DEPOSITS: NOVEL ANALYTICAL METHODS AND CASE STUDIES FROM THE BOHEMIAN MASSIF Tomáš Hrstka1 1 Charles University in Prague, Faculty of Science, Institute of Geochemistry, Mineralogy and Mineral Resources, Albertov 6, Praha 2, CZ-128 43 Abstract of the Ph.D. Thesis Fluid inclusions represent a unique tool for understanding the processes leading to the formation of mineral deposits and fluid-rock interactions in general. Orogenic gold deposits in the central part of the Bohemian Massif (Libčice and Kasejovice deposits) were studied in order to provide a better understanding of their genesis. A multifaceted approach was adopted including a broad spectrum of micro-analytical methods. While traditional methods were used as the basis of this study (e.g., microthermometry, SEM and optical microscopy), the application and improvement/development of modern analytical methods (e.g., LA-ICP- MS and Raman spectroscopy) or introduction of alternative innovative techniques (CLSM, Nano- tomography, QEMSCAN) constituted a significant part of this study. This study reveals the importance of the HCO3 - species in hydrothermal fluids (i.e., >100 řC to ~350 řC). Previously, the prevalence of Cl- and other anions was reported for hydrothermal paleofluids and the majority of studies suggested...

Research Doctorate - Doctor of Philosophy (PhD)
Sulfur- and lead-isotope signatures for 64 deposits/systems located in the Central and Easternn Subprovinces of the Lachlan Orogen in eastern New South Wales were characterised in the present study. Here are presented four new ⁴⁰Ar/³⁹Ar dates, 644 new sulfur- and 105 new leadisotope analyses, plus a collation of 386 unpublished and 277 published sulfur isotope and over 560 unpublished and published lead isotope analyses for middle Silurian to Early Carboniferous mineralisation. Measured δ³⁴S values for 22 VHMS deposits range between -7.4‰ to 38.3‰. S-isotope values for Currawang East, Lewis Ponds, Mount Bulga, Belara and Accost (Group 1) range from - 1.7‰ to 5.9‰ with the ore-forming fluids for this group of deposits likely to have been reducing and sulfur derived largely from magmatic sources. By contrast, S-isotope signatures for sulfides from Black Springs, Calula, Captains Flat, Commonwealth, Cordillera, Gurrundah, Kempfield, Peelwood mine, Sunny Corner, The Glen, Wet Lagoon and Woodlawn (Group 2) have average δ³⁴S values between 5.4‰ and 8.1‰. These deposits appear to have formed from ore fluids that were more oxidising than those for Group 1 deposits, representing a mixed contribution of sulfur derived from partial reduction of seawater sulfate, in addition to sulfur from other sources. Four deposits, Elsinora, John Fardy, Mount Costigan and Stringers, have heavier average δ³⁴S signatures (10.1‰ to 13.2‰) than Group 2 deposits, suggesting that these deposits included a greater component of sulfur of seawater origin. The S-isotope data for barite from Black Springs, Commonwealth, Stringers, Gurrundah, Kempfield and Woodlawn range from 12.6‰ to 38.3‰. Over 80% of the δ³⁴S values are between 23.4‰ and 30.9‰, close to the previously published estimates for the composition of seawater sulfate during Late Silurian to earliest Devonian times, providing supporting evidence that these deposits formed concurrently with a Late Silurian volcanic event. New Pb isotope data for eleven VHMS deposits included in the present study support earlier Pb-isotope studies which indicate that lead was largely sourced from the host sequence. However, the data for Black Springs, Elsinora and Commonwealth indicate that some lead, included in these deposits, was sourced from units forming basement to the Silurian troughs. Sulfur isotope values for thirteen orogenic gold systems range between -7.5‰ and 16.1‰ (excluding outliers). The Wyoming One–Myall United system has an average δ³⁴S value of -5.5‰ and a primitive mantle-derived lead isotope signature implying that sulfur and gold were sourced from a fractionated mantle-derived intrusion. The δ-isotope data for Adelong, Bodangora, Calarie, Hargraves, Hill End, London–Victoria, Sebastopol, Sofala–Wattle Flat and Stuart Town are all very similar with average δ³⁴S values close to 0‰ (range -2.8 to 3.4‰). Sulfur in these deposits was derived from reduced fluids, sources from magmatic reservoirs either as a direct input or through dissolution and recycling of rock sulfide. For deposits hosted by the northern HET it is suggested that sulfur and gold were sourced from mantle-derived units located beneath the HET rather than the siliclastic fill of the trough itself. Windeyer and Napoleon Reefs have heavier S-isotope signatures suggesting a greater contribution of sulfur derived from reduced seawater sulfate reservoirs. Springfield, located adjacent to the northern HET, has the heaviest S-isotope signature (15.4 δ³⁴S‰) for orogenic gold deposits included in the present study. For this deposit it is suggested that HET-derived basinal fluids containing reduced seawater sulfate migrated along faults and leached gold from Ordovician mantle-derived units forming basement to that area. Seven sulfide-rich orogenic base metal deposits were included in the present study. Average δ³⁴S values for Currawang South, Frogmore, Montrose, Ruby Creek, Wallah Wallah vary between 3.5‰ and 6.0‰ (Group 1), with Kangiara, and Lucky Hit–Merrilla, having heavier average δ³⁴S values (10.0‰ and 8.2‰ respectively — Group 2). Group 1 deposits are small, and S-isotope signatures suggest significant sulfur was sourced from magmatic reservoirs; whereas, Group 2 deposits are larger and δ³⁴S signatures indicate a larger component of sulfur was derived from reduced seawater sulfate reservoirs. The Pb-isotope data for these deposits suggest that the majority of the lead was derived from older Ordovician and Silurian crustal reservoirs. The data for Mount Werong and Merrilla support a Middle Devonian Pb-model age; whereas, those for Wallah Wallah point to an Early Carboniferous Pb-model age. Browns Reef, in the Central Subprovince, is now interpreted to be a syn-deformational orogenic base metal deposit, for which the S-isotope data are similar to Group 2 orogenic base metal deposits and Pb-isotope data suggest lead was sourced from the fill of the Rast Trough. Five epithermal systems were included in the present study. Bauloora, Bowdens and those in the Yerranderie district are intermediate-sulfidation epithermal systems; whereas, Yalwal and Pambula are low sulfidation epithermal systems. Yerranderie, Yalwal, Pambula and Bauloora have δ³⁴S values close to 0‰. Sulfur in these deposits was derived largely from a magmatic reservoir. The Yerranderie system is zoned with respect to S-isotope distribution and shows mineralogical zonation along the Yerranderie Fault. Yalwal is zoned with 0‰ S-isotope values correlating with sericitic alteration assemblages and heavier S-isotope values (up to 17.9 δ³⁴S‰) correlating with assemblages that include minerals characteristic of argillic alteration. Sixteen middle Silurian to Early Devonian intrusion-related deposits were included in the present study. Collector, Dargues Reef, Mayfield, Ryans, Tallawang, Whipstick and Yambulla are located east of the I–S granite line, with Dargues Reef, Majors Creek, Mayfield, Whipstick and Yambulla hosted by or adjacent to their causative intrusion. These deposits have S-isotope signatures close to 0‰ (range -3.6‰ to 3.0‰) similar to that for granites east of the I–S line (range -1.5‰ to 4.9‰). The Pb-isotope data for these deposits includes both crustal- and mantle-derived lead. Deposits distal to their causative intrusions (Collector and Ryans) have heavier S-isotope signatures (7.7‰ and 4.3‰ respectively) indicating that some sulfur was probably sourced from the host sequence. The majority of lead, for these deposits, was sourced from the host sequence and/or older reservoirs. The S-isotope data for Tallawang suggest that the sulfur was largely sourced from the host sequence. Eight deposits are located to the west of the I–S line. Nasdaq, Phoenix, Tara, Rye Park and Mineral Hill have heavier S-isotope signatures (range: 2.6‰ to 7.3‰) which overlap with the range of values typical of granites located to the west of the I–S line (1.9 to 9.6‰) supporting the interpretation that the majority of sulfur was derived from the causative intrusion. The Pb-isotope data for Nasdaq, Mineral Hill and Tara suggest that lead originated from the host sequence or from older lead reservoirs; whereas, at Rye Park and Phoenix lead was probably sourced from the causative intrusion. Ardlethan and Browns Creek deposits have near 0‰ S-isotope signatures, lower than the range of δ³⁴S values for granites west of the I–S line which is accounted for by mantle-derived volatiles and a possible biogenic sulfur component. The Pb-isotope data for these two deposits are consistent with a lead sourced largely from the causative intrusion; although, some mantlederived lead is probably present. Red Hill has the highest S-isotope signature (13.7‰) indicating that the majority of sulfur was sourced from a seawater sulfate reservoir. ⁴⁰Ar/³⁹Ar dating showed that intrusion-related mineralisation at Tara formed at 420 ± 2 Ma; VHMS-related mineralisation at The Glen (Glen E deposit) formed at 418.2 ± 2.2 Ma; and that the Yerranderie and Bauloora intermediate sulfidation epithermal systems formed at 372.1 ± 1.9 Ma and 371 ± 13 Ma (respectively). New dating plus a review of timing constraints to Tabberabberan and Kanimblan cycle-related mineralisation highlighted metallogenic events at ~430 Ma (intrusion-related), ~420 Ma (intrusion- and VHMS-related) and a mid Devonian epithermal event. The timing of orogenic-related mineralisation is diachronous across the study area with the majority of orogenic gold systems in the west forming during the Middle Devonian Tabberabberan Orogeny; whereas, similar mineralisation in the northern HET formed during the Early Carboniferous Kanimblan Orogeny.

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The Kanmantoo Cu-Au deposit is located 55km east of Adelaide, on the eastern edge of the Mt Lofty Ranges, South Australia. It is of Delamerian age and is hosted in the Tapanappa series of the Kanmantoo Group, a pelitic turbidite sequence metamorphosed to amphibolites facies. Models for mineralisation vary from sedimentary exhalative system to epigenetic mineralisation. Despite recent work, the structural evolution of the deposit is largely unknown and this allows for the absence of a definitive model for mineralisation. Detailed face mapping of the 1190RL bench in conjunction with handheld X-Ray Fluorescence Niton gun was adopted to further investigate the relationship between key structural features and element distribution. Micro analysis by petrographic studies, Edax element maps and δ34S isotope analysis was completed to gain understanding into fluid-rock relationships and origin of mineralising fluids. The findings of this study strongly suggest timing of copper mineralisation was associated with the first phase of orogenic extension at 490 ± 3 Ma. The extensional reactivation of compressional D3 shear zones, along with the injection of partially oxidised igneous derived fluids interacting with Fe-rich sediments, allows for the formation of the Kanmantoo magmatic hydrothermal deposit. Sulphur isotope results, and the mapping of magnetite-pyrite-chalcopyrite bearing K-feldspar veins are a very strong evidence of an igneous influence. Cu precipitation is as a result of a cooling oxidised magmatic hydrothermal fluids reacting with Fe in metasediments, and partially interacting with a reducing environment, rather than being directly associated with Fe rich metasomatism. Broad unmineralised zones of chlorite alteration suggest circulation of magmatic hydrothermal fluid with copper mineralisation preferentially precipitating in veins within and adjacent to reactivated D3 shears and D3 antiformal zones.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2012

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South Australia’s Kanmantoo Cu-Au deposit is currently operated by Hillgrove Resources and has an extended history of exploration and production dating back to 1846. However, there is little consensus on the paragenesis and structural controls of the deposit. Empirical work specifically on Au mineralogy and paragenesis has been completed. To investigate the mineralogical and geochemical associations between Au and host mineralogy, drill core samples, grab samples and ore concentrates and tailings have been collected from the East Kavanagh, Central Kavanagh, West Kavanagh, Spitfire and Nugent ore lodes. Petrographic analysis, Mineral Insights Goldsniffer analysis, secondary electron microscopy, mineral liberation analysis (SEM-MLA) and Laser Ablation (LA-ICP-MS) analysis observed and recorded evidence for four textural settings of Au. Two stages of Au development are proposed: early Au (associated with the main economic Cu-bearing hydrothermal fluids) and late Au (associated with retrograde Bi-rich hydrothermal fluids). Variations observed in major and trace element composition reflect changing input from a thermally-anomalous hydrothermal fluid source. The stability field for Au nanoparticles and the rarity of precipitated visible Au supports a late-peak to post-peak metamorphic origin. This study has implications about how Au can be recovered within the Kanmantoo Cu-Au deposit. The mineralogy and geochemical characteristics of Au at the Kanmantoo Cu-Au deposit can also be utilised as an exploration pathfinder within the greater Adelaide fold belt and the Delamarian-affected terrains at other exploration provinces within the Adelaide fold belt.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2018

The Telfer Au (+Cu) deposit is one of Australia's premier gold-producers, currently accounting for approximately 400,000oz. per year. It's discovery in 1972 heralded the recognition of the Proterozoic Paterson Province, in which it is located, as a polymetallic terrane with the potential for significant gold and base-metal mineralisation. The Paterson Province represents a small exposure (= 36 000km²) of the large NW -SE trending Paterson Orogen, a continental-scale orogenic belt that passes across northern Western Australia and into central Australia. Rocks in the Paterson Province have recorded a protracted Proterozoic history for this orogenic belt, which includes continent-continent collision at ~1250Ma (Watrara Orogeny) and late-Proterozoic collisional tectonism (the Paterson Orogeny) between 700 and 600Ma. The latter generated considerable mineralisation in middle- to late-Proterozoic metasedimentary rocks of the Paterson Province. Late-Proterozoic mineralisation in the Paterson Province is well developed in the NE region where numerous syn- and post-tectonic granitoids, gabbros and dolerites intruded the metasedimentary sequence. However, mineral exploration in this region is commonly hindered by extensive Phanerozoic and Tertiary cover that precludes observation of much of the Proterozoic sequence. Additionally, the province lies within the Great Sandy Desert, and is thus covered by extensive aeolian sand deposits. The large amount of younger cover has resulted in relatively small scattered "windows" that expose the mineralised Proterozoic rock sequence. The NE region of the Paterson Province provides one of the best exposures of this sequence and hosts the Telfer deposit. Sampling of gossanous and stratabound quartz veining in the Telfer Dome (a regional antiformal fold) in 1972 by geologists from both Day Dawn Minerals and Newmont Pty Ltd identified gold enriched horizons within the pelitic sedimentary sequence (Telfer Formation) exposed in the dome. Subsequent drilling of these horizons confirmed an initial resource of 1 Million ounces of gold and mining activity commenced in 1975. During the early 1980's mining concentrated on one particular reef that outcropped in Main Dome, a sub-dome of the Telfer Dome. This reef, the Middle Vale Reef (MVR) exhibited strong secondary enrichment of gold and has historically comprised a significant resource in the Telfer deposit (Dimo, 1990). During the middle to late 1980's a shift to high-volume low-grade mining was facilitated by the ongoing success of dump leach extraction of gold from rocks previously too low-grade to be milled. This incresased throughput caused production to expand to the second subdome (West Dome) as the E-Reefs were mined, and helped to make Telfer one of the top four gold producers in Australia during the late 1980's. More recently, deep diamond drilling in Main Dome (commenced in 1992) has led to the discovery of approximately ten to twelve new reefs at depth in the dome. Underground mining, which had commenced in 1990, has been extended through an exploration decline 10 the upper of these newly discovered reefs (MIO and M30). This decline is currently being extended to reach the deepest reef, the 130, at approximately 1 100m below the present ground surface. This should occur by the end of 1997. Another consequence of the deep drilling has been the further confirmation of an epigenetic genesis for the Telfer deposit. and particularly the identification of mineralisation in units other than the Telfer Formation. Initial research on the stratabound reefs in the Telfer deposit suggested that they had formed through syngenetic exhalative processes (Tyrwhitt, 1979; Turner, 1982). A variation on this, whereby the MVR was considered to have formed as an evaporite horizon that was subsequently replaced by quartzsulphide assemblages, was proposed by Royle (1985). However, the expansion of mining and deep drilling within the deposit provided increasing evidence for an epigenetic origin. This came both through structural observations and geochemical fluid-inclusion studies that indicated the reefs were locally discordant, had associated stockwork veining in both the foot- and hanging-walls, contained magmatic elements in the ore-assemblage and that the ore-fluids were of variable salinity and temperature (Goellnicht, 1987). These observations led to an epigenetic model whereby magmatic fluids from the regional granitoids had mixed with cooler connate/formational waters, and had precipitated in structurally controlled, and compositionally favourable, sites within the Telfer Dome (Goellnicht, 1987; Goellnicht et al., 1989). Subsequent research downgraded the role of the granites, suggesting that they acted more as heat sources to convectively circulate connate/contact-metamorphic fluids that scavenge elements from the sedimentary sequence (Hall & Berry, 1989; Rowins. 1994). The changing ideas on the genesis of the Telfer mineralisation are reflected in the changing focus of mineral exploration in the Telfer region and the Paterson Province. Initial exploration, utilising the syngenetic exhalative model, concentrated on locating further outcropping Telfer Formation. The inferred variable thickness of exhalative lenses was considered to have assisted the formation of the regional domal antiforms (Turner, 1982), and consequently those domes that exposed the Telfer Formation were targeted. However, recognition of an epigenetic genesis has focussed exploration activity towards targeting favourable host structures, such as regional folds and other ore-fluid traps. The change in exploration strategy means that a greater reliance is now placed on the structural geological setting of mineralisation in the Paterson Province. This study represents the first formal examination whereby the structural geological setting of mineralisation in the Telfer Mine is integrated with the regional- and orogenic-scale tectonic development of the Paterson Province.

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The Kanmantoo Cu-Au deposit, situated 55 km south-east of Adelaide, is hosted in the Tapanappa Formation of the Kanmantoo Trough. Recent evidence supports an epigenetic mineralising model for the deposit with respect to the Delamerian Orogeny of ~514 to 490 ±3 Ma. The Delamerian deformation event is the oldest portion of the Tasmanides, a 20 000 km orogenic belt along the eastern palaeo-pacific margin of Gondwana. Mineralisation of the Kanmantoo deposit has been linked with post-Delamerian multi-phase extension in east dipping normal faults. The final stages of extension resulted in non-mineralised north dipping normal faults and proximal discrete fracturing. Structural analysis of geology centred on the Kanmantoo deposit has classified a systematic set of extensional fracturing, developed in- the Kanmantoo deposit and in the region surrounding the deposit for >5 km radius. The fracture set trends east-west and dips steeply to the north with a recorded mean orientation of 75/359°. Fractures are characteristically not offset by shearing, strike for tens of metres, have variable frequency, and alterations influenced by fluid migration. Petrographic and geochemical analysis (SEM)in this study has defined a regionally distributed fracture-hosted albitic alteration, which is relatively enriched in Na, Ca, Al and depleted in Fe, Mg and K. A late stage extensional setting is supported for the development of the discrete sub-vertical fracturing.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2009

Dissertação de Mestrado em Geociências, Recursos Geológicos, apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
Na Zona Centro Ibérica (ZCI) são predominantes as ocorrências minerais, especialmente as mineralizações de estanho-tungsténio e ouro-prata, sobretudo de tipo filoniano. A riqueza desta região desde cedo despertou o interesse do Homem, remontando a prospeção e exploração nesta zona, pelo menos, ao tempo da ocupação romana da Península Ibérica. A área sobre a qual este trabalho incide designa-se por Escádia Grande, pertence à ZCI e localiza-se no sector NW da região Centro, a cerca de 30 km de Coimbra, no Concelho de Góis e é reconhecida desde há muito pela sua mineralização de Au-Ag e pela exploração da mesma. O presente estudo tem como objetivo geral conhecer as caraterísticas e a origem dos fluidos mineralizantes do depósito de ouro de Escádia Grande. Pretende-se ainda que possa dar indicações sobre o tipo de depósito de ouro. Assim, procedeu-se à petrografia da mineralogia do filão, análises químicas minerais e à caraterização e definição da tipologia das inclusões fluidas do quartzo. O filão é constituído na sua quase totalidade por quartzo, sendo a mineralização dominantemente constituída por arsenopirite, pirite, esfalerite e galena. O ouro encontra-se sob a forma de electrum e ocorre preferencialmente associado à arsenopirite, pirite, quartzo e galena. Os fluidos presentes nos cristais de quartzo são dominantemente aquosos de baixa salinidade, encontram-se mais raramente inclusões fluidas de natureza aquocarbónica, também de baixa salinidade. O aprisionamento destes fluidos ocorreu a uma temperatura e pressão mínimas de 294 °C e 24 MPa, às quais corresponde uma profundidade de aprisionamento de cerca de 2,4 km, em regime hidrostático.
In the Central-Iberian Zone (CIZ) mineral occurences are prevalente, especially tin-tungsten and gold-silver mineralization, mainly in vein type. The richness of this region since early aroused the interest of the man, raising the exploration and exploitation of the área, at least, at the time of Roman occupation of the Iberian Peninsula. The area on which this study focuses is called Escádia Grande, belongs to CIZ and is located in the NW sector of the Central region, about 30 km from Coimbra, in Góis Municipality, and is recognized for long by its Au-Ag mineralization and exploitation. The presente study has as general objective to know the characteristics and origin of the mineralizing fluids of Escádia Grande gold deposit. It is also intentend that it can give an indication of the type of gold deposit. So we proceeded to the petrography of lode mineralogy, mineral chemical analysis and characterization and definition of the type of fluid inclusions of the quartz. Escádia Grande vein is almost constituted by quartz, being the mineralization domantly constituted by arsenpyrite, pyrite, sphalerite and galena. The gold occur in the form of electrum and preferentialy occur associated with arsenopyrite, pyrite, quartz and galena. The fluids presente in quartz cristals are dominantly aquous with low salinity, finding more rarely aqucarbonic fluid inclusions, also with low salinity. The entrapment of this fluids occured at a minimum pressure and temperature of 24 MPa and 294 °C, which corresponds to an entrapment depth of 2.4 km in hydrostatic regimen.