Evaluation of capillary electrophoresis as an analytical technique using bulk ionic composition of fluid inclusions in quartz

Martin, Riana Theresa (2000-12)

Thesis (MSc)--Stellenbosch University, 2000.

Thesis

ENGLISH ABSTRACT: This study was initialized to introduce capillary electrophoresis (CE) as a useful technique in the analysis of fluid inclusions in quartz. lts advantages are low detection limits for the dissolved ionic content of the fluid, the small amount of sample (1 g or less) for a detailed qualitative and quantitative analysis, and the short time required to obtain results (one run for either cations or anions take approximately 10 minutes). The study area from which quartz veins were selected is situated within the Neoproterozoic Saldania belt. Syn- and post-tectonic S-, 1- and A-type granitoids from the Cape Granite Suite intruded the metamorphosed Malmesbury greywacke and pelites between 550 and 510 Ma. Additional periods of tectonism and metamorphism occurred during Cape Supergroup sedimentation (480 - 400 Ma) as well as Karoo sedimentation and the simultaneous Cape Orogeny (280 -215 Ma). The quartz-biotite±chlorite vems are hosted by Cape Granite as well as Malmesbury sediments. These barren quartz veins are part of two vein sets, one dipping at an angle between 15 and 500 to the S to SE and striking W, similar to Sn-mineralized quartz veins in the SW-cape, while the other is near-vertical and striking W to NW. Except for their orientation, no differences regarding associated minerals, inclusion characteristics or fluid chemistry indicated a difference in origin. Four fluid phases within a temperature range of 160 - 390 °C were identified as being largely late-magmatic and released from the underlying Cape Granite plutons, namely an early 370- 390 °C population, followed by the 310 - 360, 230 - 300 and lastly the 160 - 200 °C populations. Initiation of this fluid system occurred from at least SlOMa, after final granite intrusion, but the age of the final stage is unknown. Renewed fluid circulation occurred during a later period of metamorphism, possibly during the Cape Orogeny. These fluids had temperatures between 240 and 360°C and are of sedimentary origin, most likely released from the Malmesbury metamorphites. The technique of capillary electrophoresis has been evaluated for its application to bulk fluid inclusion analysis, and the crush-leach fluid extraction procedure of Bottrell, et al., (1988) optimized for CE analysis. Contamination factors were identified and minimized or eliminated, where possible. Bulk fluid inclusion chemistry obtained by CE was therefore proved to provide valuable information regarding the various fluid generations as long as inclusion populations are investigated individually to explain and correlate bulk data.

AFRIKAANSE OPSOMMING: Die doel van die studie was om te toon dat die tegniek van kapillêre elektroforese bruikbaar is in die analiese van vloeistofmsluitsels in kwarts. Die voordele van hierdie tegniek is lae deteksie limiete vir die opgeloste ioon inhoud van die vloeistof, die klein monstergrootte (< 1g) wat nodig is vir 'n omvattende kwalitatiewe en kwantitatiewe analise, en die kort tydsduur waarin resultate verkry word ('n katioon of anioon analise vir een monster duur lO minute). Die studie gebied waar kwarts are gemonster is, is binne die Neoproterosoïese Saldania Gordel geleë. Sin- en laat-tektoniese S-, I- en A-tipe graniete van die Kaapse Graniet Suite het die gemetamorfiseerde Malmesbury grouwakke en peliete tussen 550 en 510 Ma binnegedring. Latere periodes van tektonisme en metamorfose het tydens deponering van die Kaap Supergroep (480 - 400 Ma), en die gelyktydige episodes van Karoo sedimentasie en Kaapse Orogenese (280 - 215 Ma) plaasgevind. Die gasheer gesteentes vir die kwarts-biotiet±chloriet are is Kaapse Graniet sowel as Malmesbury sedimente. Hierdie ongemineraliseerde are is deel van twee aarstelsels, nl. een met 'n duik hoek tussen 15 en 50° S tot SO en 'n westelike strekking, soortgelyk aan die Sn- ,.gemineraliseerde are in die SW-Kaap, terwyl die ander stel are feitlik vertikaal is en W tot NW strek. Behalwe vir die verskil in oriëntasie was daar geen aanduiding, wat betref 'n verskil in geassosieerde minerale, vloeistofinsluitsel kenmerke of vloeistof chemie, dat hierdie twee aarstelsels van verskillende oorsprong is nie. Vier vloeistof fases binne 'n temperatuur gebied van 160 - 390 °C en 'n vloeistof saliniteit van 0 - 5.7 gewig % NaC1 ekw. is geïdentifiseer, met 'n laat-magmatiese assosiasie en vrygestel deur die onderliggende Kaapse Graniete. Dit behels 'n vroeë 370 - 390 °C populasie, gevolg deur die 310 - 360, 230 - 300 en laastens die 160 - 200 °C populasies. Inisiasie van hierdie sisteem kon moontlik rondom 510 Ma gelede plaasgevind het, maar die ouderdom van die finale fase is onbekend. Hernude vloeistof sirkulasie het tydens 'n later stadium van metamorfose onstaan, moontlik tydens die Kaapse Orogenese. Hierdie vloeistowwe het temperature tussen 240 en 360 °C en is van sedimentêre oorsprong waar dit moontlik deur metamorfose van die reeds gemetamorfiseerde Malmesbury gesteentes vrygestel is. Die tegniek van kapillêre elektroforese is vir die toepassing daarvan in die analise van vloeistof insluitsels in kwarts geëvalueer, terwyl die vloeistof vrystellingsmetode van Bottrell en Yardley (1988) vir hierdie tegniek geoptimaliseer is. Kontaminasie faktore is geïdentifiseer en verminder of uitgeskakel waar moontlik. Daar is getoon dat die vloeistof chemie, wat verteenwoordigend is van al die insluitsel populasies in 'n monster, wel bruikbaar is t.o.v. afsonderlike vloeistof generasies, solank elke populasie individueel bestudeer is om die omvattende chemiese data te verduidelik en met 'n enkele populasie te korrelleer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/51751
This item appears in the following collections: