Mafic-ultramafic igneous rocks and associated carbonatites of the Gem Park Complex, Custer and Fremont Counties, Colorado

Abstract

The Gem Park Complex (a new name in this report), which lies about 11 miles northwest of Westcliffe, Colo., is a small funnel-shaped composite body related to the McClure Mountain Complex a few miles to the northeast. The Gem Park Complex consists mostly of pyroxenite and gabbro with minor dikes and bodies of lamprophyre, syenite porphyry, and nepheline syenite pegmatite, and abundant dikes and irregular bodies of carbonatite, all of Cambrian age. A mass of fenite lies near the center of the complex. The whole complex lies discordantly in Precambrian gneissic terrane and is overlain by Tertiary volcanic rocks. Large areas in the complex are covered by Quaternary alluvium and colluvium. Some carbonatite dikes and fenite contain concentrations of niobium, rare-earth elements, thorium, phosphorus, some other elements, and vermiculite. The arrangement of carbonatite dikes, the position of the fenite, and other features suggest that a large carbonatite body lies beneath the surface near the center of the complex.

An integrated analysis of controlled and passive source seismic data across an Archean‐Proterozoic suture zone in the Rocky Mountains

“…The blue color is indicative of higher than average Poisson's ratios, and correlate well with where mafic intrusive bodies are exposed or interpreted to be present. The area at $150 km profile distance indicates the presence of mafic intrusive body underneath the Sierra Grande uplift as suggested by Suleiman and Keller [1985], and the blue area at $400 km profile distance correlates with the Wet Mountains where extensive Cambrian mafic intrusions are present [Parker and Sharp, 1970]. These mafic intrusions are also considered in the gravity model of Snelson et al [2005].…”

Th-rich loparite from the Khibina alkaline complex, Kola Peninsula: isomorphism and paragenesis

“…Recent studies of loparite m ineral i za ti on at t he Khi bina compl ex (Kozyreva et al, 1991;Tikhonenkova et al, 1982) also report the occurrence of Th-rich loparite in foyaite or related pegmatites. Parker and Sharp (1970) have described 'irinite' as an accessory constituent of vermiculite rock at the Gem Park Complex, Colorado. However, identification of this mineral as 'irinite' was based merely on its metamict state and resemblance of the X-ray diffraction pattern of the heated sample to that of Borodin and Kazakova's (1954) material (Parker and Sharp, 1970).…”

“…Parker and Sharp (1970) have described 'irinite' as an accessory constituent of vermiculite rock at the Gem Park Complex, Colorado. However, identification of this mineral as 'irinite' was based merely on its metamict state and resemblance of the X-ray diffraction pattern of the heated sample to that of Borodin and Kazakova's (1954) material (Parker and Sharp, 1970). Perovskite with ThO 2 content of up to 1.7 wt.% occurs in the Polino carbonatite diatreme, Italy (Lupini et al, 1992), and up to 4.9 wt.% in the carbonatite complexes of Kola Peninsula (Chakhmouradian and Mitchell, 1997).…”

Principal thorium resources in the United States

“…The thorium deposits are spacially and genetically related to three alkalic complexes of Cambrian age (Olson and others, 1977), the McClure Mountain Complex that includes the mafic-ultramafic rocks at Iron Mountain (Shawe and Parker, 1967), the Gem Park Complex (Parker and Sharp. 1970), and the complex at Democrat Creek (Heinrich, 1966, p. 339).…”