Alkaline Rocks and Carbonatites of the World

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

Jebel Lado (Nirkenyi)

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Occurrence number: 
152-00-005
Country: 
South Sudan
Location: 
Longitude: 31.6, Latitude: 5.1
Carbonatite: 
No

This oval-shaped 4x3 km intrusion is enveloped in laterites overlying Precambrian basement rocks. The main rock type is a coarse nepheline syenite consisting of perthite, abundant nepheline (as much as 30%), in some varieties blue sodalite, a greenish clinopyroxene, which may be rimmed by amphibole, occasional biotite and accessories including zircon and titanite. Around the intrusion small rubbly outcrops of sanidine trachyte may derive from dykes. The rock contains a little quartz, amphibole, which may form phenocrysts, acicular aegirine and monazite.

Age: 
K-Ar determinations on three samples of nepheline syenite gave 113.0±3.1, 125.5±3.6 and 122.0±4.0 Ma (Civetta et al., 1980).
References: 

CIVETTA, L., DE VIVO, B., GIUNTA, G., IPPOLITO, F., LIMA, A., ORSI, G., PERRONE, V. and ZUPPETTA, A. 1980. Geological and structural outlines of the southern Sudan. Atti Convegni Lincei Academia Nazionale dei Lincei, 47: 175-83.HUNTING GEOLOGY AND GEOPHYSICS LIMITED, 1980. Mineral exploration of the Juba area. Unpublished Report, Democratic Republic of Sudan, Southern Regional Government, Regional Ministry of Finance, Industry and Economic Planning. 56 pp.

Map: 
Fig. 3_293 Distribution of occurrences 152-00-001 - 152-00-011 in South Sudan (based principally on various maps in Hunting Geology and Geophysics, 1980).
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith