IRON HILL COMPLEX
Southwestern Colorado's Iron Hill Carbonatite Complex has a mix of unusual intrusive igneous rocks and is known to have a relatively high concentration of scarce elements (e.g., Nb, Ti). It was intruded in the late Neoproterozoic, at about 570 million years. Some Early Paleozoic dikes have cut through a portion of the northern part of the complex.
Rocks reported in the Iron Hill Complex principally include magnesiocarbonatite, pyroxenitic peridotite, nepheline syenite, ijolite, and uncompahgrite. Below is a sample of microcline-bearing pyroxenite.
Microcline-bearing pyroxenite (a.k.a. aegirine-bearing syenite) (9.3 cm across) from the Iron Hill Complex of southwestern Colorado, USA.
Dark green = aegirine pyroxene.
~Whitish = microcline feldspar.