The Haveri Au-Cu deposit is located in southern Finland about 175 km north of Helsinki. It occurs on the northern edge of the continental island arc-type, volcano-sedimentary Tampere Schist Belt (TSB) within the Palaeoproterozoic Svecofennian Domain (2.0 – 1.75 Ga) of the Fennoscandian Shield. The 1.99 Ga Haveri Formation forms the base of the supracrustal stratigraphy consisting of metavolcanic pillow lavas and breccias passing upwards into intercalated metatuffs and metatuffites. There is a continuous gradation upwards from the predominantly volcaniclastic Haveri Formation into the overlying epiclastic meta-greywackes of the Osara Formation. The Haveri deposit is hosted in this contact zone. This supracrustal sequence has been intruded concordantly by quartz-feldspar porphyries. Approximately 1.89 Ga ago, high crustal heat flow led to the generation and emplacement of voluminous synkinematic, I-type, magnetite-series granitoids of the Central Finland Granitoid Complex (CFGC), resulting in coeval high-T/low-P metamorphism (hornfelsic textures), and D₁ deformation. During the crystallisation and cooling of the granitoids, a magmatic-dominated hydrothermal system caused extensive hydrothermal alteration and Cu-Au mineralisation through the late-D₁ to early-D₂ deformation. Initially, a pre-ore Na-Ca alteration phase caused albitisation of the host rock. This was closely followed by strong Ca-Fe alteration, responsible for widespread amphibolitisation and quartz veining and associated with abundant pyrrhotite, magnetite, chalcopyrite and gold mineralisation. More localised calcic-skarn alteration is also present as zoned garnetpyroxene- epidote skarn assemblages with associated pyrrhotite and minor sphalerite, centred on quartzcalcite± scapolite veinlets. Post-ore alteration includes an evolution to more K-rich alteration (biotitisation). Late D₂-retrograde chlorite began to replace the earlier high-T assemblage. Late emanations (post-D₂ and pre-D₃) from the cooling granitoids, under lower temperatures and oxidising conditions, are represented by carbonate-barite veins and epidote veinlets. Later, narrow dolerite dykes were emplaced followed by a weak D₃ deformation, resulting in shearing and structural reactivation along the carbonate-barite bands. This phase was accompanied by pyrite deposition. Both sulphides and oxides are common at Haveri, with ore types varying from massive sulphide and/or magnetite, to networks of veinlets and disseminations of oxides and/or sulphides. Cataclastites, consisting of deformed, brecciated bands of sulphide, with rounded and angular clasts of quartz vein material and altered host-rock are an economically important ore type. Ore minerals are principally pyrrhotite, magnetite and chalcopyrite with lesser amounts of pyrite, molybdenite and sphalerite. There is a general progression from early magnetite, through pyrrhotite to pyrite indicating increasing sulphidation with time. Gold is typically found as free gold within quartz veins and within intense zones of amphibolitisation. Considerable gold is also found in the cataclastite ore type either as invisible gold within the sulphides and/or as free gold within the breccia fragments. The unaltered amphibolites of the Haveri Formation can be classified as medium-K basalts of the tholeiitic trend. Trace and REE support an interpretation of formation in a back-arc basin setting. The unaltered porphyritic rocks are calc-alkaline dacites, and are interpreted, along with the granitoids as having an arc-type origin. This is consistent with the evolution from an initial back-arc basin, through a period of passive margin and/or fore-arc deposition represented by the Osara Formation greywackes and the basal stratigraphy of the TSB, prior to the onset of arc-related volcanic activity characteristic of the TSB and the Svecofennian proper. Using a combination of petrogenetic grids, mineral compositions (garnet-biotite and hornblendeplagioclase thermometers) and oxygen isotope thermometry, peak metamorphism can be constrained to a maximum of approximately 600 °C and 1.5 kbars pressure. Furthermore, the petrogenetic grids indicate that the REDOX conditions can be constrained at 600°C to log f(O₂) values of approximately - 21.0 to -26.0 and -14.5 to -17.5 for the metasedimentary rocks and mafic metavolcanic rocks respectively, thus indicating the presence of a significant REDOX boundary. Amphibole compositions from the Ca-Fe alteration phase (amphibolitisation) indicate iron enrichment with increasing alteration corresponding to higher temperatures of formation. Oxygen isotope studies combined with limited fluid inclusion studies indicate that the Ca-Fe alteration and associated quartz veins formed at high temperatures (530 – 610°C) from low CO₂, low- to moderately saline (<10 eq. wt% NaCl), magmatic-dominated fluids. Fluid inclusion decrepitation textures in the quartz veins suggest isobaric decompression. This is compatible with formation in high-T/low-P environments such as contact aureoles and island arcs. The calcic-skarn assemblage, combined with phase equilibria and sphalerite geothermometry, are indicative of formation at high temperatures (500 – 600 °C) from fluids with higher CO₂ contents and more saline compositions than those responsible for the Fe-Ca alteration. Limited fluid inclusion studies have identified hypersaline inclusions in secondary inclusion trails within quartz. The presence of calcite and scapolite also support formation from CO₂-rich saline fluids. It is suggested that the calcic-skarn alteration and the amphibolitisation evolved from the same fluids, and that P-T changes led to fluid unmixing resulting in two fluid types responsible for the observed alteration variations. Chlorite geothermometry on retrograde chlorite indicates temperatures of 309 – 368 °C. As chlorite represents the latest hydrothermal event, this can be taken as a lower temperature limit for hydrothermal alteration and mineralisation at Haveri.The gold mineralisation at Haveri is related primarily to the Ca-Fe alteration. Under such P-T-X conditions gold was transported as chloride complexes. Ore was localised by a combination of structural controls (shears and folds) and REDOX reactions along the boundary between the oxidised metavolcanics and the reduced metasediments. In addition, fluid unmixing caused an increase in pH, and thus further augmented the precipitation of Cu and Au. During the late D₂-event, temperatures fell below 400 °C, and fluids may have remobilised Au and Cu as bisulphide complexes into the shearcontrolled cataclastites and massive sulphides. The Haveri deposit has many similarities with ore deposit models that include orogenic lode-gold deposits, certain Au-skarn deposits and Fe-oxide Cu-Au deposits. However, many characteristics of the Haveri deposit, including tectonic setting, host lithologies, alteration types, proximity to I-type granitoids and P-T-X conditions of formation, compare favourably with other Early Proterozoic deposits within the TSB and Fennoscandia, as well as many of the deposits in the Cloncurry district of Australia. Consequently, the Haveri deposit can be seen to represent a high-T, Ca-rich member of the recently recognised Fe-oxide Cu-Au group of deposits.

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.

The Silver Queen polymetallic vein system south of Houston, B.C., can be treated as a 2-dimensional problem for purposes of reserve/resource estimation. Complexities in obtaining reserve/resource estimates arise from (i) uncertainties in geological interpolation and extrapolation of the vein system, (ii) uncertainties in the distinction between vein and highly altered wallrock in some old drill logs, (iii) complex and multivariable geological character of the vein, (iv) a limited number of exploration drill holes and (v) a different support for drift and drill hole data. Each of these problems has been considered in detail. The study comprises geological analysis, data analysis, point kriging (analysis of thickness and metal distribution) block kriging and comparison of reserve/resource estimation by various procedures including ordinary kriging, inverse squared distance weighting, and polygonal methods. A novel component of the investigation is the use of correlograms (in reality, 1 minus the correlogram) as a substitute for the variogram in geostatistical estimates. This procedure was tested as a means of defining continuity of DDH and Drift assay data of differing support. Ordinary kriging of large polygonal blocks provides metal contents more or less comparable to but locally more conservative than polygonal results reported in a recent feasibility study. Differences are in part due to the use of somewhat different data for the two procedures. The effect of the volume of the selective mining unit on the recovered tonnage and grade is described and limitations of the indirect lognormal method are presented. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

The Dolly Varden camp, Alice Arm area, northwestern British Columbia, is characterized by stratiform and volcanogenic silver-lead-zinc-barite deposits in Early to Middle Jurassic calc-alkaline volcanic rocks of the Hazelton Group. These deposits, containing exceptional silver and significant base metal values, are in andesitic tuffaceous rocks, and occur typically as layers of quartz, carbonate, barite and jasper, with lesser amounts of pyrite, sphalerite and galena, and sparse chalcopyrite. Production from three deposits, the Dolly Varden, Northstar and Torbrit mines, totaled 1,284,902 tonnes of ore that averaged 484g silver per tonne, 0.38 percent lead and 0.02 percent zinc. The Hazelton Group is a thick, widespread assemblage of basaltic to rhyolitic volcanic flow rocks, their tuffaceous equivalents, and derived sedimentary rocks. Dolly Varden camp is underlain by more than 3,000m of Hazelton Group rocks comprised of one major volcanic and one major sedimentary formation. Volcanic rocks underlie sedimentary rocks and have been subdivided into footwall and hangingwall units based on stratigraphic position relative to the mineralized stratiform horizon. Footwall volcanic rocks consist of green ± maroon basaltic-andesite tuff, green ± maroon porphyritic andesite and green andesite shard tuff. Stratiform mineralization rests conformably upon the underlying green andesite shard tuff. Hangingwall volcanic rocks above the stratiform layer consist of pale grey basaltic-andesite ash tuff, maroon basaltic-andesite ash-lapilli tuff, grey-green porphyritic andesite, and pale green andesite ash tuff. Hangingwall volcanics are unconformably capped by sedimentary rocks consisting of maroon siltstone, calcareous and fossiliferous wacke, and black siltstone and shale; black siltstone and shale form the youngest rock unit of the Hazelton Group in the Dolly Varden area. Basalt and lamprophyre dykes intrude all rocks of the Hazelton Group. The rocks of the Hazelton group exposed in the Dolly Varden camp are folded into a series of anticlines and synclines with gentle, northwestern plunges. Two major sets of nearly vertical block faults cut all rock units; earlier faults trend northwest and younger faults trend north-northeast. Geological mapping, combined with petrologic, petrographic and isotopic data, indicate that the stratiform deposits probably formed as submarine exhalative deposits associated with andesitic volcanism of the Hazelton Group during the Early to Middle Jurassic. Evidence for a volcanogenic origin is the conformity of layered mineralization with stratigraphy, lateral and vertical mineral zonation patterns, consistent hangingwall versus footwall contact relationships, fragments of stratiform ore within tuffaceous volcanic rocks of the hangingwall, consistent differences in the stable isotopic compositions between the sulfides versus barite, quartz and carbonate gangue, and the Jurassic "fingerprint" for the lead-bearing deposits of the Dolly Varden camp. The Dolly Varden deposits display criteria for classification of a new, previously unrecognized, stratiform and volcanogenic, deposit type, named here, the "Dolly Varden type", and is characterized by silver-rich, low sulfide and high oxide stratiform mineralization within andesitic volcanic rocks. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Ph.D. (Geology) / Shear zone controlled hydrothermal alteration zones in the northern Kaapvaal craton (NKC) are developed in host rocks of vastly different chemical composition and metamorphic grade. Some carry appreciable Au and base metals and some are barren. Alteration zones in three different distinctive crustal zones were examined in detail to determine the controls of these two types of alteration. 1. The Matok Complex is situated in the southern marginal zone (SMZ) of the Limpopo Belt (LB), close to the zone of rehydration. Two major stages of hydrothermal alteration could be identified in local shear zones, a pervasive propylitization and a subsequent vein controlled quartzalbite alteration. The two-stage alteration occurred sometimes between the emplacement of the Matok Complex (2670 Ma) and the intrusion of unaltered mafic dykes (1900 Ma). Calculated isotopic compositions of the hydrothermal fluids indicate that magmatic ± meteoric waters as well as juvenile C02 were responsible for the establishment of the alteration zones. The fluids most probably were late magmatic fluids associated with the Matok magmatism. The propylitic alteration was accompanied by introduction of small amounts of CU + Au and represents an alteration type identical to that developed in porphyry copper deposits. The subsequent quartz-albite alteration was caused by extremely saline fluids which depleted the rocks of all the major and trace elements with exception of Si, Al, Na and Zr. 2. This chemical alteration pattern' contrasts with those developed in two alteration zones associated with economic gold mineralization in greenstone belts of the NKC (Sutherland and Pietersburg belts). At the Birthday and Eersteling gold mines, a biotite-calcite-quartz alteration is developed. The chemical pattern of the alteration is...

Fluids play a vital role in essentially all geologic environments and processes, and are the principal media of heat and mass transfer in the Earth. The properties of geologic fluids can be diverse, as fluids occur at conditions ranging from ambient temperatures and pressures at Earth's surface, to extreme temperatures and pressures in Earth's deep interior. Regardless the wide ranges of conditions at which geologic fluids occur, fluid properties are described and governed by the same fundamental thermodynamic relationships. Thus, application of thermodynamic principles and methods allows us to decipher the properties and roles of geologic fluids, to help understand geologic processes. Fluid inclusions in minerals provide one of the best available tools to study the compositions of geological fluids. Compositions of fluid inclusions can be determined from microthermometric measurements, based on the vapor-saturated liquidus conditions of model chemical systems, or by various microanalytical techniques. The vaporsaturated liquidus relations of the system H2O-NaCl-CaCl2 have been modeled to allow estimation of fluid inclusion compositions by either microthermometric or microanalytical methods. Carbon capture and storage (CCS) in deep saline formations represents one option for reducing anthropogenic CO2 emissions into Earth's atmosphere. Availability of storage volume in deep saline formations is a significant component of injection and storage planning. Investigation of the volumetric properties of CO2, brine and CO2-saturated brine reveals that storage volume requirements are minimized when CO2 dissolves into brine. These results suggest that a protocol involving brine extraction, CO2 dissolution and re-injection may optimize CCS in deep saline formations. Numerical modeling of quartz dissolution and precipitation in a sub-seafloor hydrothermal system was used to understand the role of fluid-phase immiscibility ("boiling") on quartz-fluid interactions, and to predict where in the system quartz could deposit and trap fluid inclusions. The spatial distribution of zones of quartz dissolution and precipitation is complex, owing to the many inter-related factors controlling quartz solubility. Immiscibility exerts a strong control over the occurrence of quartz precipitation in the deeper regions of fluid circulation. / Ph. D.

No description available.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography : leaves 48-50. / M.S.

Magmatic-hydrothermal ore deposits are formed in association with aqueous fluids that exsolve from hydrous silicate melts during ascent and crystallization. These fluids are invariably trapped as inclusions in vein-filling minerals associated with hydrothermal fluid flow, and their composition may be modeled based on the H₂O-NaCl system. Thus, if we know the pressure-volume-temperature-composition (PVTX) properties of H₂O-NaCl solutions, it is possible to interpret the PTX trapping conditions, which is important for understanding the processes leading to the generation of the hydrothermal system and ore mineralization. High salinity (> 26 wt. % NaCl) fluid inclusions contain liquid, vapor, and halite at room temperature, and are common in magmatic-hydrothermal ore deposits. These inclusions homogenize in one of three ways: A) halite disappearance (Tmhalite) followed by liquid-vapor homogenization (ThL-V), B) simultaneous ThL-V and Tmhalite, or C) ThL-V followed by Tmhalite. The PVTX properties of H₂O-NaCl solutions three phase (L+V+H) and liquid-vapor (L+V) phase boundaries are well constrained, allowing researchers to interpret the minimum trapping pressure of inclusion types A and B. However, data that describe the pressure at Tmhalite for inclusion type C are limited to a composition of 40 wt. % NaCl. To resolve this problem, the synthetic fluid inclusion technique was used to determine the relationship between homogenization temperature and minimum trapping pressure for inclusions that homogenize by mode C. These results allow researchers to interpret the minimum trapping pressure of these inclusions, and by extension the depth at which the inclusions formed. The temporal and spatial distribution of fluid inclusions formed in associated with porphyry copper mineralization has been predicted using a computer model. A simple geologic model of an epizonal intrusion was developed based on a Burnham-style model for porphyry systems and thermal models of the evolution of epizonal intrusions. The phase stability fields and fluid inclusion characteristics at any location and time were predicted based on PVTX properties of H₂O-NaCl solutions. These results provide vectors towards the center of a magmatic-hydrothermal system that allow explorationists to use fluid inclusion petrography to predict position with the overall porphyry environment when other indicators of position are absent. / Ph. D.

No description available.