Mineralogy and provenance of the Namakwa Sands heavy mineral satellite deposits

Carelse, Candice (2012-12)

Thesis (MSc)--Stellenbosch University, 2012.


ENGLISH ABSTRACT: Five areas proximal to the world class Namakwa Sands heavy mineral deposit have been studied and include the farms Houtkraal Remainder Portion 2, Houtkraal Remainder, Geelwal Karoo, Graauwduinen and Rietfontein. These are locally referred to as the satellite deposits and are sub-economic occurrences. The primary objective of the study was to quantify the mineralogy and mineral chemistry, determine the provenance of the heavy mineral suite and draw a comparison between the satellite deposits and the Namakwa Sands deposit from an exploratory point of view. Methodology used to achieve the above objectives included optical microscopy, Scanning Electron Microscope (SEM), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN), X- Ray Fluorescence (XRF) and Zr-geothermometry of rutile. The five satellite areas contain the same heavy mineral suite but mineral proportions differ. The total heavy mineral population (THM) are diverse and consist of ilmenite and its alteration products (hydrated ilmenite, pseudorutile and leucoxene), magnetite, hematite, spinel, rutile, tourmaline, pyroxene, amphibole, garnet, aluminosilicates, staurolite, corundum, epidote, zircon, monazite and sphene. Ilmenite and garnet are the two most dominant heavy minerals present. The valuable heavy minerals (VHM) suite consists of ilmenite, zircon, rutile and leucoxene. The mineralogy of the satellite areas and chemistry of the ore minerals (rutile, zircon, ilmenite and leucoxene) are similar to the Namakwa Sands deposit. The whole spectrum of ilmenite alteration products (hydrated ilmenite, pseudorutile, and leucoxene) is present and allowed the quantitative use of the alteration index. The indices is low (22-24%) and indicates that the surficial deposits have formed under arid to semi-arid climatological conditions which preserved the pristine character of most of the minerals. This allowed reliable provenance studies using the characteristics of most of the heavy mineral suite, which showed that the minerals were derived from a diversity of source rocks. These included mainly medium to high-grade metamorphites and felsic intrusives of the underlying Mesoproterozoic Namaqualand Metamorphic Complex and a minor contribution from the Neoproterozoic Gariep Supergroup. This relationship indicates a limited transport distance from source to depositional basin. Mineral ratios in particular the THM-VHM relationship showed that the deposits located close to the shoreline such as Geelwal Karoo, Graauwduinen and Rietfontein have a relatively low proportion of valuable heavy minerals whereas those more inland such as Houtkraal Remainder Portion 2 and Houtkraal Remainder are close to unity. Heavy mineral concentration as such is low in the satellite areas and the mechanism to increase the concentration is clearly not only a function of distance from the present shoreline but is also topographically controlled. Steep sided linear depressions channelled the unconsolidated sediments and heavy minerals were upgraded into economic concentrations by aeolian processes. The quality of the valuable heavy minerals in the satellite areas however is similar to those of the adjacent Namakwa Sands deposit. This study has demonstrated that Houtkraal Remainder is the northeasterly continuation of the red aeolian sand (RAS) associated East Mine orebody and offers the best exploration potential.

AFRIKAANSE OPSOMMING: Vyf areas proksimaal aan die Namakwa Sands swaar mineral afsetting is bestudeer en sluit in Houtkraal Remainder, Houtkraal Remainder Portion 2, Geelwal Karoo, Graauwduinen en Rietfontein. Hierdie areas word plaaslik na verwys as satelliet afsettings en is subekonomies. Die hoofdoel van hierdie studie was om die mineralogie en mineral chemie te kwantifiseer, die oorsprong van die swaar mineraal suite te bepaal asook n vergelyking te tref tussen die satelliet areas en die Namakwa Sands afsetting vanuit n verkennende eksplorasie oogpunt. Optiese mikroskopie, SEM, LA-ICP-MS, QEMSCAN, XRF en die Zr-geotermometer van rutiel is gebruik om bostaande doele te bereik. Die vyf satellite areas bestaan uit dieselfde swaar minerale maar mineral proporsies verskil. Die totale swaar mineraal populasie is divers en bestaan uit ilmeniet en ilmeniet se veranderingsprodukte (gehidreerde ilmeniet, pseudorutiel en leukokseen), magnetiet, hematiet, spinel, rutiel, toermalyn, pirokseen, amfibool, granaat, aluminiumsilikate, stauroliet, korund, epidoot, sirkoon, monasiet and sfeen. Ilmenite en granaat is die twee mees dominante swaar minerale teenwoordig. Die waardevolle swaar mineraal populasie bestaan uit ilmeniet, rutiel, sirkoon en leukokseen. Die mineralogie van die satelliet areas en die chemie van die erts minerale (rutiel, sirkoon, ilmeniet en leukokseen) is dieselfde as die van die Namakwa Sands afsetting. Die hele spektrum ilmeniet veranderingsprodukte is teenwoordig en het die kwantitatiewe gebruik van die alterasie indeks toegelaat. Die alterasie indekse is laag (22-24%) en dui aan dat die oppervak afsettings gevorm het tydens droë tot semi droë toestande wat die eertydse karakter van meeste minerale bewaar het. Deurdat die karakter van meeste minerale behoue gebly het, kon provenans studies toegepas word op die swaar mineraal suite. Provenans studies het aangedui dat die swaar minerale afkomstig is van n verskeidenheid van bron gesteentes. Dit sluit in medium tot hoë graad metamorfe gesteentes en felsiese intrusies van die Mesoproterosoïese Namakwaland Metamorfiese Kompleks met n geringe bydrae van die Neo Proterosoïese Gariep Supergroep. Hierdie verhouding dui n beperkte vervoer afstand aan vanaf die bron tot by die afsettings omgewing. Mineraal vehoudings spesifiek die totale swaar mineraal-waardevolle swaar mineraal verhoudings dui aan dat afsettings na aan die kus soos Geelwal Karoo, Graauwduinen en Rietfontien n lae inhoud van waardevolle swaar minerale het teenoor afsettings soos Houtkraal Remainder Portion 2 en Houtkraal Remainder wat meer land in is met verhoudings na aan eenheid. Swaar mineral konsentrasie is laag in die satellite areas en die meganisme verantwoordelik vir die toename in konsentrasie is nie net n funksie van die afstand van die bestaande kuslyn nie maar word ook deur topografie beheer. Steil sydige lineêre depressies kanaliseer die ongekonsolideerde sediment en swaar minerale en word opgradeer tot ekonomiese konsentrasies deur wind prossese. Die kwaliteit van die waardevolle swaar minerale in die satelliet areas is egter dieselfde as die van die aangrensende Namakwa Sands afsetting. Hierdie studie het gewys dat Houtkraal Remainder is die noordelike voortsetting van die Rooi Aeoliese Sand geassosieerde Oos Myn ertsliggam en bied die beste eksplorasie potensiaal.

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