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Alnoite lamprophyre (Oka Carbonatite Complex, Early Cretaceous, 124-125 Ma; Oka Niobium Mine, Quebec, Canada) | by James St. John
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Alnoite lamprophyre (Oka Carbonatite Complex, Early Cretaceous, 124-125 Ma; Oka Niobium Mine, Quebec, Canada)

Alnoite from the Cretaceous of Quebec, Canada. (~6.0 centimeters across at its widest)

 

This rare rock is an alnoite lamprophyre (= intrusive porphyritic mafic igneous rock) from a breccia pipe. The sample contains melilite, phlogopite mica, plus other minerals. It comes from Quebec's Oka Carbonatite Complex, a large body of alkaline igneous rocks intruded through Precambrian metamorphics. The Oka occurs in the western part of the Monteregian Hills Province in the Canadian Shield. Published research indicates that Oka rocks cooled from magma produced by partial melting of upper mantle rocks (inferred to be metasomatized garnet lherzolites). The rocks in the complex contain rare elements, including economic concentrations of niobium (Nb). Several mines exploit Oka rocks for their Nb content. Oka rocks include coarsely-crystalline calciocarbonatites (a.k.a. sövites; a.k.a. C1 calciocarbonatites), alnoites, ijolites, and okaites.

 

Age: mid-Barremian Stage, mid-Early Cretaceous, 124-125 Ma

 

Locality: Oka Niobium Mine, southeastern part of the Oka Hills, Oka Hills Inlier, Deux-Montagnes County, just west of Montreal & Laval, far-southern Quebec Province, southeastern Canada

 

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Taken on August 3, 2014