REE investigation of the Plattkopf fluorite mineralization an extension of the Vergenoeg fluorite deposit (South Africa)

Günther T, Klemd R (2014)

Publication Language: English

Publication Type: Conference contribution, Abstract of lecture

Publication year: 2014

Event location: Hannover

Abstract

Plattekop hill with its concordant hematite-fluorite ore body represents an extension of the Vergenoeg pipe, one of South Africa's world-class fluorite deposits located in the Bushveld Complex. The pipe-shaped body of Vergenoeg strikes discordantly with a minimum depth of circa 650 meters through the rhyolitic bedrocks of the Palaeoproterozoic Rooiberg Group and accommodates different Fe-mineral dominated rock types, which are enriched in fluorite. Both deposits host an additional commodity in terms of Rare-Earth-Element (REE) minerals in their Fe-oxide (hematite or magnetite) and fluorite rich rocks. These are represented by the fluorocarbonate bastnaesite-(Ce) and the REE-phosphates monazite-(Ce) and xenotime-(Y).

Combined whole rock and single grain analyses via XRF and LA-ICP-MS and EMP, respectively show the high REE-potential of the sampled rocks from the uppermost gossan ores of Plattekop and Vergenoeg as well as from their deeper unweathered equivalent rock type with whole rock contents of REEs <4.5 wt. %. Thereby, C₁-chondrite normalized REE-patterns show on average (La/Lu)_CNratios of <5.3 with a relatively flat trend. The major rock forming minerals contain 100 ppm to 2500 ppm REEs/Fe-oxide and 3000 ppm to 7000 ppm REEs/fluorite on average. The minerals bastnaesite, monazite and xenotime are intercalated between Fe-minerals and fluorites with an abundance of <4 vol. % per sample. The light rare earth elements (LREE) are preferentially incorporated into bastnaesite and monazite with an order of abundance of Ce > La > Nd > Pr in contrast to xenotime, which exhibits enriched concentrations of heavy rare earth elements (HREE) and an order of abundance of Y > Er > Dy > Gd. Average concentrations are between 50 and 60 wt. % REEs/REE-mineral.

Petrological and geochemical evidences of sampled rocks suggest a hydrothermal origin for the REE-minerals after the primary mineralization of Vergenoeg and Plattekop precipitated. Secondary fluid inclusions within fluorite record temperatures between 150 °C and 500 °C for late stage hydrothermal events (Borroket al., 1998) from which bastnaesite may have crystallized at intermediate to basic pH conditions. Their alteration to monazite and xenotime marks a change of the hydrothermal conditions to a more acidic and phosphate rich environment. Thereby, balance calculations indicate a renewed REE-enrichment by the P-rich fluids. The remarkable enrichment of fluorite and REE-minerals within the upper 200 meters of Vergenoeg is probably a result of changes in temperature, pressure, and pH of the fluid system due to the channelized upward migration of the hydrothermal solutions towards the top of the pipe and the interaction to the adjacent bedrocks in contact.

Regarding the origin of the primary mineralization of Vergenoeg and Plattekop and the mineralizing fluids, negative Eu anomalies (Eu/Eu*) ranging from 0.08 to 0.57 for the Fe-oxides and 0.05 to 0.08 for the fluorites display the influence of reduced conditions in a possible felsic igneous-related source like the Lebowa Granite Suite of the Bushveld Complex. Furthermore, the chemical signature of the Vergenoeg magnetites correlates well with those of igneous Climax-Mo deposits (enriched in Al, Ga, Sn and depleted in Cr, Mg) and therefore, indicates a genetic relationship to the porphyry deposit type.

Authors with CRIS profile

Thomas Günther Lehrstuhl für Geologie (Exogene Dynamik) Reiner Klemd Professur für Geochemie von Lagerstätten

How to cite

APA:

Günther, T., & Klemd, R. (2014). REE investigation of the Plattkopf fluorite mineralization an extension of the Vergenoeg fluorite deposit (South Africa). Paper presentation at BGR-Jahrestagung2014, Hannover, DE.

MLA:

Günther, Thomas, and Reiner Klemd. "REE investigation of the Plattkopf fluorite mineralization an extension of the Vergenoeg fluorite deposit (South Africa)." Presented at BGR-Jahrestagung2014, Hannover 2014.

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