Thesis (M.S.)--Brigham Young University. Dept. of Geology, 2004. / Includes bibliographical references (leaves 32-35).

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Four folded plates in pocket. Includes bibliographical references (leaves 285-303). Available also in a digital version from Dissertation Abstracts.

Thesis (Professional Degree)--University of Missouri, School of Mines and Metallurgy, 1929. / Figures 2-5 and Tables 1-5 are missing from text document. The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed October 1, 2009)

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. Includes bibliographical references.

Most of the economic gold and uranium placers are developed on low angle disconformities in the Central Rand Group and concentrations of gold and uranium are usually at their optimum on unconformity surfaces. Examples include the Kimberley Reef and South Reef of the East Rand, the Main Reef Leader of the Central Rand, the Carbon Leader of the Carletonville goldfield, the Vaal Reef of the Klerksdorp goldfield and the Basal/Steyn placers of the Welkom goldfield. The individual goldfields represent fluvial fans which are composed of a large number of tectonogenetic sedimentary packages separated by unconformities. The tectonic responses between cycles of sedimentation produced unconformities and tectonically controlled cyclic sedimentation is one of the key factors culminating in the preparation and deposition of auriferous placers within the Witwatersrand succession. Unconformities, which represent breaks in sedimentation, result in the preconditioning of palaeosurfaces and redistribution of sediments and heavy minerals on them. Winnowing of sands produced heavy mineral residual accumulations on erosion surfaces which were generally preserved by small-pebble lags or algal mats. Reworking of units truncated by the unconformities provided additional gold, uranium and heavy minerals to unconformity surfaces.

This investigation is concerned with primary variations in the silver content of gold which occurs in hydrothermal deposits, particularly those of hypothermal character which are found in Basement rocks in Southern Rhodesia. The nature of the gold produced by a number of different mines has been studied by reference to production data, and microscope techniques as well as gold and silver assays have been used to determine and to explain the variations in gold fineness. The literature does not contain a great deal of information which is relevant to this topic, but an attempt has been made here to summarize the more important contributions by different writers. From this it emerges that the interpretations given by different investigators are in conflict and that paradoxes may arise when efforts are made to explain observed variations in fineness in terms of certain generalizations which have become entrenched in the literaure. In particular, it is shown that falling temperature alone cannot account for the occurrence of silver-rich gold in certain deposits. The Gwanda district of Southern Rhodesia has been selected as a typical gold belt, and the variation in fineness in 150 producers is described. The deposits are hypothermal in character, and the average fineness of the gold is high but variable, but in a small proportion the fineness is low. It is shown that the nature of the host rock and the distance of a deposit from the granite contact appear to have no influence on the fineness of the gold and that there is no zonal arrangement of fineness values. There is a suggestion that diversity of mineral species in any particular area may be accompanied by rather wide fluctuations in the gold fineness. The variations of fineness in eight typical Southern Rhodesian deposits are studied in detail, by analysis of production data, by assaying specimens of the ore and by the examination of polished specimens of gold-bearing ore. Briefer reference is made to two other deposits in the territory, and to deposits in other countries which appear to bear out the conclusions reached in this section. It emerges that there are two factors which can commonly be correlated with variations in fineness. The first of these is the grade of the ore: high-grade ore generally contains purer gold than low-grade ore. Secondly, the textural evidence indicates that gold which separates relatively early in the paragenesis contains more silver than that which is deposited in the final stages of metallization. A general survey which draws on the literature as well as on the writer's examinations of deposits in the territory indicates that, in general, gold which is associated with late-stage minerals such as tellurides, antimony, bismuth and bismuthinite is silver-poor. Gold associated with galena may be either silver-rich or silver-poor, whereas gold which is of the same age as chalcopyrite or sphalerite is very frequently rich in silver. The difficulty which is encountered in establishing the age of gold which is intimately associated with pyrite and arsenopyrite renders uncertain the correlation between fineness and age of gold in these latter cases. There are, however, indications that gold which is truly contemporaneous with either pyrite or arsenopyrite is silver-rich. In the discussion, the objections to the common practice of singling out temperature as the most potent factor controlling gold fineness are listed. Chief amongst these objections is the fact that gold does not in all deposits increase in fineness with increasing depth: examples are quoted where fineness was found to decrease as deeper levels of the ore body were exploited. It is shown that there is no consistent relationship between the size of gold grains and their silver content. It is the writer's conclusion that in hydrothermal deposits in this territory the high fineness of the gold is due to increasing solubility of silver in the ore fluids in the late states, and that where hydrothermal deposits are characterized by gold with low average fineness, an unusually large proportion of the gold has been deposited early in the paragenotic sequence. In the majority of hypothermal deposits, however, the bulk of tho gold separates late in the sequence and the fineness is accordingly high. It is believed that the relationship which exists between fineness and tenor in many deposits is due to protracted crystallization of gold in those portions of the ore body which remained permeable to the latest stages. These portions of the ore body, which represent either valuable ore shoots or ore shoots in miniature, are likely to contain gold of variable character, but the average silver content will be low because a large proportion of the gold is "late" gold. The factors which might cause epithermal gold to have a lower fineness than mesothermal or hypothermal gold are briefly discussed. Some possible applications of this study are indicated in the final chapter. It is claimed that records of gold fineness might constitute a valuable addition to mill records. Tentative suggestions are made regarding a method whereby the approaching exhaustion of a deposit might in some cases be predicted. With regard to the origin of the gold in the Witwatersrand sediments, it is pointed out that the modified placer hypothesis is not fully equipped to explain certain of the variations in the composition of the gold.

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.

A remarkable correlation between hydrothermal gold mineralisation and geological structure is discussed. The mineralisation occurs in vein quartz which occupies a fissure in Archaean greenstones of the Basement Complex in Rhodesia, It has been determined that gold which is silver-rich is typical of low-grade ore, and is associated in space with sulphides that crystallised early in paragenesis. Silver-poor gold is characteristic of highgrade ore which is concentrated along the crestal zone of anticlinal warps in the fissure. It is suggested that the local pattern of fracturing and folding is related to fundamental wrench faulting.

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.

In recent years our understanding of the genesis of porphyry copper systems has advanced to a sufficient level to be able to construct predictive models that enhance exploration for these deposits. Our understanding of primary and secondary geochemical dispersion around these deposits is not so advanced as variables such as climate and topography cause geochemical patterns to be distorted or masked at surface with the result of different deposits having quite different geochemical characteristics. In this study the geology and geochemistry of a porphyry copper-molybdenum from the Canadian Cordillera is examined with the aim of demonstrating how primary geochemical patterns are affected by the development of a supergene enrichment blanket and leached capping. Topographic controls on the extent of leaching and supergene enrichment are also explored. The Berg porphyry copper-molybdenum deposit is in the Tahtsa Mountain Ranges, approximately 84 km southwest of Houston, central British Columbia. Mineralized zones are centered on a circa 50 Ma composite quartz monzonite stock. Hydrothermal alteration zones are similar to those of the classic model by Lowell and Guilbert. Central zones are potassic (orthoclase and biotite) while peripheral zones are propylitic (chlorite, epidote, carbonate). Intense phyllic alteration (quartz, sericite, pyrite) occurs at the north and south margins of the stock. Hypogene mineralization (characterized by pyrite, chalcopyrite and molybdenite) is concentrated in an annular zone straddling the quartz monzonite contact. Best grades are localized in altered quartz diorite and altered and hornfelsed Telkwa Formation (Hazelton Group) volcanic rocks at the east side of the deposit. The nature of these altered hornfelsed rocks has been a subject for much debate in previous studies. One school of thought suggests that they are part of a hornfels aureole associated with the quartz diorite. Others suggest that it is an alteration zone associated with the quartz monzonite stock. Thirteen diamond drill holes on a north south cross section of the deposit were logged (GEOLOG) and sampled. Outcrop samples were collected where possible close to each drill hole. Major elements were determined by XRF, trace metals by flame AAS and fluorine by specific ion electrode. A sequential extraction was used to study the distribution of copper between different host minerals. The origin of the hornfelsed rocks is solved by field mapping and geochemistry. In the field cross cutting relationships show that the quartz diorite predates the stock and that the hornfels zone is spacially related to it. Major element binary and ternary plots demonstrate that significant amounts of potassium have been added to these rocks in the mineralized zone. This implies that biotite alteration was superimposed onto an earlier hornfels. Trace metal data was partitioned into anomalous and background populations with probability graphs. In the hypogene zone Cu, Mo and Ag occur in an annular zone corresponding with the mineralogically defined potential ore zones. Fluorine is anomalous over the area of the potassic alteration zone. Lead and zinc are anomalous in peripheral haloes around the potential orebodies. These zones can be traced to surface through an extensive supergene enrichment blanket and leached capping. Three zones of supergene mineralization are recognized: supergene sulphide (covellite, digenite, chalcocite), supergene oxide (malachite/azurite, cuprite, tenorite, native Cu) and leached capping. Sulphides are the dominant host for Cu throughout most of the deposit but locally on steep slopes where supergene oxide is developed Cu is hosted in carbonate and oxide minerals. Enrichment or depletion of elements in the supergene is demonstrated with interelement ratios. Enrichment factors can be derived in two ways: a) by ratioing supergene values to hypogene values, or, b) by ratioing to a constant (e.g. TiO₂ ) for each zone and then ratioing this value between zones. Enrichment factors of <1 therefore imply depletion and >1, enrichment (1=hypogene grade). Results show that all elements (studied) are enriched in the supergene sulphide and oxide zones. In the leached cap Cu, Mn and Zn are depleted while Mo, Pb and Ag are significantly enriched. These elements are incorporated into immobile limonite mineral's (ferrimolybdite, jarosite, goethite etc.). / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate