Distribution, mineralogy and provenance of heavy minerals in cainozoic sediments of the Namaqua Mines area, West Coast of South Africa

Philander, Carlo (1999-12)

Thesis (M.Sc.) -- University of Stellenbosch, 1999.

Thesis

ENGLISH ABSTRACT: In view of the recent developments in heavy mineral exploration, a sampling programme was initiated to determine the economic potential of heavy mineral occurrences in the Kleinzee mining area. The primary objectives were to record the concentration and mineralogy of the heavy mineral population and also to determine their provenance. The heavy mineral occurrences are hosted by high maturity Miocene fluvial sediments and unconsolidated Plio-Pleistocene marine sediments overlying basement rocks of the Mjd-Proterozoic Namaqua Metamorphic Complex and Pan-African Gariep Supergroup. The development of the fluvial palaeochannels is linked to a major regression during the Late Oligocene whereas the marine deposits are genetically related to wave-cut, raised marine terraces between 0 and 90m amsl Quartz, followed by feldspar are the dominant light minerals. The total heavy fraction (>2.9 g/cm3 density) averages 6.4%, but concentrations are extremely variable and ranges from a few per cent in the fluvial sediments to as much as 60 per cent in particular marine successions. The mechanism anticipated for these anomalous accumulations is believed to be a powerful wave-regime with favourable burial conditions considered essential in preserving the mineralisation. Heavy mineral suites are diverse and consist of various proportions of ilmenite and its related alteration products, hematite, magnetite, rutile, zircon, garnet, amphibole, pyroxene, epidote, aluminosilicates, titanite, monazite, staurolite, collophane and glauconite. The economically valuable minerals, ilmenite, rutile and zircon constitute a very large portion of the total heavy mineral suite, often an order of magnitude greater than the gangue. Generally the total heavy mineral suite in the Kleinzee area is dominated by ilmenite (50-73 wt%), with zircon (6-12 wt%) and rutile (1 %) constituting the remainder of the economic fraction. The titanium-bearing minerals comprise in addition to pure ilmenite, a complex suite of Fe-Ti oxides often intimately intergrown. Single grain analyses indicate that ilmenites contain on average 51% Ti02 with only trace amounts of impurities. Only a small proportion (-8%) of the ilmenite fraction is altered and in most cases alteration was insufficient to enhance the titanium content of the ilmenite fraction. These results are remarkably consistent with previous studies conducted at other west coast localities, which indicates that climatic conditions during the Plio-Pleistocene were uniform along the entire west coast of South Africa. Zircon populations were found to be heterogeneous, displaying contrasting physical, geochemical, cathodoluminescent and radiometric properties. It is demonstrated that the heterogeneity of various zircon populations reflects the compositional maturity of their host sediments. As a result, zircon properties will allow conclusions about the evolutionary path of its host sediment. Similarly, zircon chemistry and radiometry can be useful to fingerprint and discriminate stratigraphic successions. Heavy mineral suites are qualitatively similar, _ indicating a uniform source area for the Kleinzee sediments. Heavy mineral assemblages indicate contributions from igneous and metamorphic as well as reworked sedimentary sources. Garnet, epidote, augite, hornblende, staurolite, titanite, rutile and aluminosilicates were demonstrated to be ultimately derived from metamorphic rocks. Other minerals such as the iron-titanium oxides, monazite and zircon were derived from igneous or metamorphic rocks. The striking similarity of mineral chemistry from Kleinzee sediments and lithologies from the NMC, unambiguously indicate the NMC as primary source terrain for the Kleinzee sediments. Mineralogical and textural evidence suggests that the majority of heavy minerals were eroded and transported from a nearby area, indicating a relative proximal source for the heavy minerals as -well as their host sediments. The present appraisal of the economic importance of heavy mineral occurrences in the study area indicates that it does not compare favourably with Quaternary megadeposits such as Richards Bay Minerals or Graauwduinen. The economic viability of the area is greatly impaired by the generally low heavy mineral content as well as the composition of the economic fraction which is dominated by less valuable ilmenite. Bulk chemistry as well as single grain analysis also indicate that the Ti02 content is low (<50%). However, a few target areas have been delineated which indicate limited economic potential and deserves a followup study in order to calculate their potential resources.

AFRIKAANSE OPSOMMING: In die lig van die huidige ontwikkeling in swaarmineraal eksplorasie is 'n monsteringsprogram geloods om die ekonomiese potensiaal van die swaarmineraal voorkomste in die Kleinzee mynbougebied te evalueer. Die primere doelwitte was om die konsentrasie, mineralogie en provenans van die swaarmineraal populasie te bepaal. Swaarmineraal konsentrasies in die studiegebied kom voor in volwasse Mioseen fluviale sedimente en ongekonsolideerde Plio-Pleistoseen mariene sedimente wat vloergesteentes oorle van die Mid-Proterosoiese Namakwa Metamorfe Kompleks en Pan-Afrikaanse Gariep Supergroep. Die ontwikkeling van prominente fluviale palaeokanale word verbind met 'n massiewe regressie tydens die Laat Oligoseen, terwyl die mariene sedimente geneties verwant is aan brandergekerfde, verhewe mariene terrasse wat gelee is tussen 0 en 90m bo gemiddelde seevlak. Kwarts, gevolg deur veldspaat is die dominante ligte minerale. Die totale swaarmineraalfraksie (digtheid >2.9 g/cm3 ) beloop gemiddeld 6.4%, maar konsentrasies is hoogs wisselend en is seide meer as 'n paar persent in die fluviale sedimente, maar kan so hoog as 60% wees in sekere mariene opeenvolgings. Anomale konsentrasies van swaarminerale was die gevolg van 'n kragtige golfregime en gunstige begrawings kondisies wat mineralisasie gepreserveer het. Swaarmineraal suites verskil in 'n hoe mate deurdat dit bestaan uit verskillende proporsies van ilmeniet en geassosieerde veranderingsprodukte, hematiet, magnetiet, rutiel, sirkoon, granaat, amfibool, pirokseen, epidoot, aluminiumsilikate, titaniet, monasiet, stauroliet, kollofaan en glaukoniet. Die ekonomies waardevolle minerale nl. ilmeniet, sirkoon en rutiel vorm In groot gedeelte van die totale swaarmineraal suite en in sommige gevalle in rangordes groter as die nie-ekonomiese fraksie. Die totale swaarmineraal suite van die Kleinzee area word oor die algemeen gedomineer deur ilmeniet (5-73%) met sirkoon (6-12%) en rutiel (1%) wat die res van die ekonomiese fraksie opmaak. Die titaan-bevattende minerale sluit in suiwer ilmeniet asook 'n komplekse suite van tussen vergroeide -en veranderde Fe-Ti oksiedes. Enkelkorrel analises dui aan dat die ilmeniete gemiddeld 51 % Ti02 en spoorhoeveelhede van onsuiwerhede bevat. Slegs 'n baie klein gedeelte (-8%) van die ilmeniet fraksie' is veranderd en in die meeste gevalle was verandering onvoldoende om die titaan-inhoud van die ilmeniet fraksie te verhoog. Hierdie resultate is merkwaardig in ooreenstemming met vorige studies wat uitgevoer was by ander weskus lokaliteite en dui daarop dat klimatiese toestande tydens die Cenoso·ikum konstant was langs die hele weskus van Suid-Afrika. Sirkoonpopulasies is heterogeen met betrekking tot fisiese, geochemiese, katodeluminisente en radiometriese eienskappe. Daar is gedemonstreer dat die heterogeniteit van die verskeie sirkoonpopulasies die samestellings rypheid van hulle gasheer sedimente reflekteer. Sirkoon eienskappe sal dit dus moontlik maak om afleidings te maak omtrent die evolusie van die gasheer sedimente. Soortgelyk kan sirkoon chemie -en radiometrie ook van waarde wees om stratigrafiese opeenvolgings te korreleer. Swaarmineraal suites is kwalitatief dieselfde en dui dus op 'n uniforme brongebied vir die Kleinzee sedimente. Swaarmineraal versamelings dui aan dat die swaarminerale afkomstig is van stollings -en metamorfe gesteentes sowel as herwerkte sedimente. Daar is getoon dat granaat, epidoot, ougiet, horingblende, stauroliet, titaniet, rutiel en aluminiumsilikate primer afkomstig is van metamorfe gesteentes. Die yster-titaanoksiedes, monasiet en sirkoon kon egter van stollings of metamorfe rotse kom. Mineraalchemie van Kleinzee sedimente en rotse van die Namakwa Metamorfe Kompleks (NMK) stem merkwaardig ooreenkom, wat onteenseglik daarop dui dat die NMK die primere brongebied vir die Kleinzee sedimente was. Mineralogiese en teksturele bewyse suggereer dat die oorgrote meerderheid van die swaarminerale ge-erodeer en vervoer was van 'n nabye gebied, wat moontlik aandui dat die swaarminerale sowel as hul gasheer sedimente afkomstig is van In relatiewe proksimale bron. Die huidige ekonomiese evaluering van swaamineraal konsentrasies in die studiegebied toon dat dit nie gunstelik vergelyk met Kwarternere mega-afsettings 5005 Richard Bay Minerals of Graauwduinen nie. Die ekonomiese vateaarheid- van Giiearea wordgrotendeels aan bande gele deur die baie lae swaarmineraal konsentrasie asook die samestelling van die ekonomiese fraksie wat gedomineer word deur minder waardevolle ilmeniet. Verder dui grootmaat-chemie sowel as enkelkorrel analises daarop dat die Ti02 inhoud (50%) van ilmeniet laag is. Nietemin is verskeie teiken-areas afgepen wat beperkte ekonomiese potentiaal aantoon.

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