Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Franspoort

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Occurrence number: 
151-00-026
Country: 
South Africa
Region: 
Pienaars River Alkaline Complex (Franspoort Line)
Location: 
Longitude: 28.4, Latitude: -25.7
Carbonatite: 
No

This is the most southerly of the Franspoort line of intrusions and comprises an oval plug of foyaite having a maximum diameter of 1.6 km. The foyaite is composed of 5 mm-long prisms of microperthite, euhedral nepheline (1-3 mm), aegirine prisms with diopsidic cores, as well as rosettes of aegirine needles within analcime, sodalite and purple fluorite. An analysis is given by Shand (1922). Numerous inclusions of monchiquite and ijolite occur in the foyaite and it is traversed by dykes of monchiquite and foyaite. Around the northern margin are poorly exposed trachytic and phonolitic lavas which are intruded by the foyaite.

Age: 
A Rb-Sr isochron using six specimens of Franspoort foyaite combined with determinations on Buffelsdrift foyaite and Klipdrift and Haakdoornfontein syenites yielded an isochron age of 1306±1 Ma (Harmer, 1985); the Franspoort data alone give 1139±217 Ma.
References: 

HARMER, R.E. 1985. Rb-Sr isotopic study of units of the Pienaars River alkaline complex, north of Pretoria, South Africa. Transactions of the Geological Society of South Africa, 88: 215-23.SHAND, S.J. 1922. The alkaline rocks of the Franspoort line, Pretoria district. Transactions of the Geological Society of South Africa, 25: 81-100.

Location: 
All locations > Africa > South Africa > Pienaars River Alkaline Complex (Franspoort Line)
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith