published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Please read the abstract in the section, 00front, of this document / Thesis (PhD (Botany))--University of Pretoria, 2006. / Plant Science / unrestricted

The Central Asia Orogenic Belt is one of the largest accretionary orogenic belts in the world. In this belt, many sulfide‐bearing mafic‐ultramafic intrusions occur along faults, including the Kalatongke complex in southeast Chinese Altay and the Huangshandong intrusion in east Tianshan. The Kalatongke complex is a composite body including ~308Ma dioritic intrusion and 287Ma sulfide‐bearing mafic intrusion. The dioritic intrusion consists of biotite‐hornblende gabbro, diorite and quartz diorite. This intrusion was formed from a mixture of an evolved mantle‐derived magma and a crust‐derived adakitic magma combined with fractional crystallization of clinopyroxene, amphibole and plagioclase. The mafic intrusion is dominantly made up of norite in which sulfide ores, including disseminated, massive Ni‐Cu and massive Cu‐rich ores, are hosted. This intrusion was formed from two different pulses of basaltic magmas that had different magma evolution histories. The early magma pulse reached sulfide‐saturation due to minor crustal contamination and a small amount of sulfide (<0.03%) was removed before the emplacement. The evolved magmas then entered a shallow magma chamber and assimilated crustal materials to attain sulfide‐saturation again. Sulfide liquids segregated from the magma to form massive Ni‐Cu and massive Cu‐rich ores through further fractionation and residual silicate melts formed norites. A second pulse of magma underwent removal of <0.02% sulfides with stronger crustal contamination, and re‐attained S‐saturation during the emplacement and became a phenocryst‐laden magma. This magma then intruded the earlier formed massive sulfide ores and norites, forming the disseminated sulfide ores. The Permian Huangshandong mafic‐ultramafic intrusion hosts the largest magmatic sulfide deposit in east Tianshan. It consists of a layered unit of lherzolite, gabbro and diorite and a massive unit of olivine gabbronorite and gabbronorite. Both units formed from siliceous high magnesium basaltic (SHMB) magmas derived from a hydrous, depleted mantle source. The two units of the Huangshandong intrusion formed from magmas that have undergone different processes through the evolution of the magma plumbing system. The early magma pulse gained sulfur‐saturation before the emplacement and small amounts of sulfide (<0.03%) were removed to result in a PGE‐depleted, high‐Mg magma. This magma achieved sulfide‐saturation again in a staging magma chamber through crustal contamination and fractional crystallization of olivine and Cr‐spinel (an AFC process) to form the layered unit. A second magma pulse underwent fractionation of more olivine +/‐ Cr‐spinel but less sulfide (<0.003%) removal before the emplacement and became evolved, PEG‐undepleted and low‐Mg before the injection into the magma chamber. Mixing of the two magmas triggered sulfide‐saturation to form sulfide ores with variable PGE, Ni and Cu compositions. The study suggests that SHMB‐like magmatism, produced by melting of depleted and hydrous mantle source, may be an important feature of orogenic belts. Mafic‐ultramafic intrusions formed from SHMB‐like magmas may host economic sulfide deposits, particularly sulfide Ni‐Cu sulfide deposits. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

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