Alkaline Rocks and Carbonatites of the World

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

Sapukai (Sapucai; Sapucay)

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Occurrence number: 
130-00-017
Country: 
Paraguay
Region: 
Paraguari
Location: 
Longitude: -56.97, Latitude: -25.68
Carbonatite: 
Yes

Sapukai is an essexite plug cutting through olivine basalts and alkaline lavas, and is itself cut by dykes, mainly of phonolite. The alkaline lavas comprise principally leucitites and leucite and nepheline basanites, the chemistry of which is strongly potassic in character. The plug consists of outer and inner rings, the outer one comprising leucite tephrites and teschenites, and passing down into olivine basalts; biotite is plentiful and pseudoleucite also occurs. The inner plug, some 4 km in diameter, consists mainly of essexites containing phenocrysts of clinopyroxene, labradorite, a little olivine, nepheline, biotite and accessory apatite. In higher levels of the inner plug aegirine-nepheline microsyenite is found. Dykes of phonolite, trachyte with aegirine-augite and biotite, lamprophyres, described as akin to minettes but containing nepheline and some pseudoleucite, as well as kersantites, are abundant and extend to the northwest as far as Escobar. Some fenitization has been noted and attributed to phonolite dykes.

Age: 
K-Ar determinations on whole rocks gave a range of 98-178 Ma with basaltic lavas 178±10 Ma, and essexite, tephrite, basanite and phonolite 98-133 Ma (Comte and Hasui, 1971; Palmieri and Arribas, 1975).
References: 

COMTE, D. and HASUI, Y. 1971. Geochronology of eastern Paraguay by the potassium-argon method. Revista Brasileira de Geociencias, 1: 33-43.
PALMIERI, J.H. and ARRIBAS, A. 1975. El complejo alcalino potasico de Sapukai (Paraguay Oriental). Congreso Ibero-Americano de Geologia Economica, Buenos Aires, 2: 267-300

Map: 
Fig. 1_234 Sapukai (after Palmieri and Arribas, 1975, Fig. 4).
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith