Thèse (D.R.Min.)-- Université du Québec à Chicoutimi. / Programme offert à l'Université du Québec à Montréal en vertu d'un protocole d'entente avec l'Université du Québec à Chicoutimi. CaQCU Document électronique également accessible en format PDF. CaQCU

D.Phil. / Lode-gold deposits usually occur in granite-greenstone terranes of low- to medium-grade of metamorphism. Such deposits are well studied in terms of their petrogenesis, ore mineralogenesis and structural control. Gold occurrences associated with high-grade terranes are, however, also known from the Yilgam Block in Australia (Griffin's Find) and Northern Marginal Zone of the Limpopo Belt in Zimbabwe (Renco), but the genesis of these deposits are not as well understood as that of their lower grade counterparts. The Doornhoek lode-gold deposit, situated in the granulite terrane of the Southern Marginal Zone of the Limpopo Belt in South Africa displays an important sequence of structural and metamorphic events that proved to be very useful in understanding the formation of metamorphic gold deposits formed under upper-amphibolite - granulite facies conditions. Structurally the Doornhoek gold deposit is situated in a large low-angle D, fold plunging towards the west at 10-15 °. The fold structure and the mineralised zone are affected by D2-strike-slip shear zones which occur both within and along the outer contacts of the ore zone. The gold deposit is also affected by southward verging D3 shear zones which thrusted Baviaanskloof Gneiss over and onto the Doomhoek Ore Body. The Doomhoek Gold Deposit is also situated in a highly altered zone of metasomatised rocks within the zone of rehydration of the Southern Marginal Zone. The actual Ore Body is represented by a remnant of BIF, mafic and ultramafic rocks surrounded by Baviaanskloof Gneiss. The alteration process, caused by high-temperature fluids channeled along the D2 shear zones was responsible for the formation of the different metasomatic lithologies. These altered rocks initially experienced a regional hydration event followed by the high-temperature metasomatic event. The very intense metasomatic activity was synchronous with the growth of prograde-zoned garnet and gold mineralisation associated with quartz veins. This scenario is suggested by the fact that gold associated with Zn, Ge, As, Y, Zr and Ni was trapped in the mineralised inner-ring of the zoned garnet, by the REE pattern and presence of Th232 and U238 in the biotite-garnetiferous formation, and by the mobility of major elements such as A1 203, K2O, SiO2 and TiO2 associated with the metasomatic activity. The alteration is probably related to externally derived magmatic fluids mixed with metamorphic aquitards that were active in both open and close system conditions along deep seated D2 shear zones. These fluids are characterised by the presence of high-density CO 2-rich and high salinity fluid inclusions. The gold mineralisation is closely associated with pyrrhotite, magnetite, lollingite, arsenopyrite, chalcopyrite, ilmenite, pentlandite, sphalerite and gold. The gold has a very low fineness (520), typical of gold precipitated from hydrothermal solutions at high-grade conditions. The textural relationships of the ore minerals hosted by the quartz veins, furthermore demonstrate a prograde pattern of mineralisation, similar as in the case of mineralisation trapped within different zones of the zoned garnet porphyroblast. The dark inner-ring of the garnet is characterised by high concentrations of sulphides, oxides and gold. The mineralising event initially deposited sphalerite and arsenopyrite at low temperatures of up to 569 °C with temperatures increasing to 673 °C, and even up to 750°C when lollingite was formed. Most of the gold is related to As-rich arsenopyrite, lollingite and graphite at temperatures ranging from upper-amphibolite facies to lower-granulite facies metamorphic conditions. The Doornhoek gold deposit is an example of a high-grade lode-gold deposit formed during a prograde hydrothermal event and demonstrates unequivocally the possibility of economic gold mineralisation during granulite facies conditions. This observation has important implications for gold exploration in high-grade geological terranes that to date have been mostly ignored by the gold mining industry.

The aim of this dissertation is an attempt to' provide a general guide for future gold exploration in tropical and sub-tropical terrains. The dissertation includes a brief discussion of the various exploration techniques used in regional and local exploration. This provide the necessary background knowledge to discriminate between the constraints and applications and to be able to select the techniques which are more suitable for gold exploration in tropical and sub-tropical terrains. Weathering, gold geochemistry and soil formation, fields often neglected, are emphasized to illustrate the importance of the mobility and dispersion of gold in the weathering of the lateritic soil profile. A sound knowledge and experience in regolith mapping is to the advantage of the explorationist. Case studies with special emphasis on Central- and Western Africa are included to illustrate the effectiveness of some of the gold exploration techniques in tropical and sub-tropical terrains. Gold exploration is a highly complex and demanding science and to be successfull involves the full intergration of all geological, geochemical and geophysical information available. An intergrated exploration method and strategy would enhance the possibility of making viable discoveries in this highly competative environment where our mineral resources become more depleted every day. Where applicable, the reader is refered to various recommended literature sources to provide the necessary background knowledge which form an integral part of gold exploration.

No description available.

A thesis submitted for the degree of Doctor of Philosophy in the Faculty of Science at the University of the Witwatersrand. / The present thesis is divided into three parts. The study described in Part I arose out of a request by the Chamber of Mines Mining Research Laboratory to the National Institute for Metallurgy to undertake a preliminary study of whether it would be feasible, in Witwatersrand conglomerates, to carry out rapid delimitation of areas rich in gold and/or uranium at the rock face, a procedure which would permit areas of rich ore to be removed selectively by means of the "rock-cutter". The approach adopted in this study was essentially geochemical, while conventional mineralogical techniques (macro-auto radiographs , thin section and polished section analyses) provided a control. The samples were drawn from the Vaal Reef at Hartebeestfontein and Zandpan and from the Ventersdorp Contact Reef at Venterspost, and were analysed quantitatively for gold, silver, uranium, pyrite, muscovite, pyrophyllite, chlorite, quartz, iron, potassium, nickel, titanium, zirconium and chromium. The intensity of the interrelationships between the elements and minerals analysed for was examined statistically by means of correlation covariance and factor analysis programmes written for an IBM 360/50 digital computer. A sympathetic relationship -- defined as significant positive correlation (with a correlation coefficient r> 0. 7) -- was found to exist between gold and uranium in both the Vaal Reef and Ventersdorp Contact Reef samples. These findings suggest that gold and uranium can be removed Simultaneously by means of the rock-cutter, and that radioactivity can be used as an indicator for on-site delimitation of areas rich in gold. In the course of the study described in Part I, it became evident that little detailed mineralogical work had ever been done on the phyllosilicates occurring in the Witwatersrand System. Accordingly, certain phyllosilicates from Witwatersrand conglomerate bands and other sources were examined in detail, this study being described in Part II of the present thesis. This study called for detailed chemical, optical, X-ray crystallographic, infra-red, differential thermal and thermogravimetric analyses, the results of which are presented. The findings were examined in the light of variolls classification schemes that have bep proposed for the phyllosilicates. This investigation revealed the need for a universally acceptable system of classification for the phyllosilicates, which should preferably be drawn up under the auspices of the International Mineralogical Association to avoid the confusion that exists at present. Part III of the present thesis is devoted to a discussion and description of various analytical techniques that had to be modified or developed to meet th8 requirements of the studies described in Parts I and II. The techniques described include: (1) An X-ray diffraction method which was developed for the quantitative analysis of pyrite, muscovite, pyrophyllite, chlorite and quartz in crushed ore from Witwatersrand conglomerates. This method makes use of novacul iie as an external standard and of binary mixtures as analytical standards, and had a mean absolute error of 1. 1 %. This method may be expanded to permit analysis of an n-component mixture. (2) A whole rock pressed powder technique of X-ray fluorescence analysis which was used for the quantitative determination of iron, potassium, nickel, titanium, zirconium and chromium. This method makes use of internstional rock standards as external standards. Six computer programmes used for the computation of the analytical results and in the statistical and crystallographic calculations are also presented in Part III. / AC2017

No description available.

Hydrothermal fluid flow is spatially and genetically associated with deformation in the earth�s crust. In the Otago Schist, New Zealand, the circulation of hydrothermal fluids in the Cretaceous formed numerous mesothermal gold-quartz vein deposits. Otago schist rocks are largely L-S tectonites in which the penetrative fabric is the product of more than one deformation phase/transposition cycle. Regional correlation of deformation events allowed mineralised deposits to be related to the structural evolution of the Otago Schist. Compilation of a detailed tectonostratigraphy of New Zealand basement rocks reveals that extensional mineralisation correlates with the onset of localised terrestrial fanglomerate deposition, thermal perturbation and granitic intrusion that mark the beginning of New Zealand rifting from the Antarctic portion of Gondwana. Laminated and breccia textures in mineralised veins suggest that host structures have experienced repeated episodes of incremental slip and hydrothermal fluid flow. However, analysis of vein orientation data in terms of fault reactivation theory (Amontons Law) shows that most deposits contain veins that are unfavourably oriented for frictional reactivation. Repeated movement on unfavourably oriented structures may involve dynamic processes of strain refraction due to competency contrasts, the effect of anisotropy in the schist, or localised stress field rotation. Deposits have been classified on the basis of host structure kinematics at the time of mineralisation into low angle thrust faults, and high angle extensional fault - fracture arrays. Low angle deposits have a mapped internal geometry that is very different from conventional imbricate thrust systems. This study applied ⁴⁰Ar/�⁹Ar geochronology to selected deposits and has identified at least three distinct mineralisation events have occurred within the central axial belt during the Cretaceous. Relationships between radiometric apparent age and inferred crustal depth reveal that after metamorphism, the onset of cooling and rapid exhumation of the schist belt coincides temporally and spatially with the age of mineralisation and structural position of a regional scale low angle shear zone in Otago.

Graduation date: 1994

Thesis (M.Sc.)--Memorial University of Newfoundland, 2006. / Bibliography: leaves 296-319. Also available online.

No description available.