Research about Cripple Creek, Colorado

USGS2020

Chapter 17: Epithermal gold deposits related to alkaline igneous rocks in the Cripple Creek district, Colorado, United States

Cripple Creek is among the largest epithermal districts in the world, with more than 800 metric tons (t) Au (>26.4 Moz). The ores are associated spatially, temporally, and genetically with ~34 to 28 Ma alkaline igneous rocks that were emplaced into an 18-km 2 diatreme complex and surrounding Proterozoic rocks. Gold occurs in high-grade veins, as bulk tonnage relatively low-grade ores, and in hydrothermal breccias. Pervasive alteration in the form of potassic metasomatism is extensive and is intimately associated with gold mineralization. Based on dating of intrusions and molybdenite and gangue minerals (primarily using 40 Ar/ 39 Ar and Re-Os techniques), the region experienced a protracted but intermittent history of magmatism (over a period of at least 5 m.y.) and hydrothermal activity (intermittent over the final ~3 m.y. of magmatic activity). Key factors that likely played a role in the size and grade of the deposit were (1) the generation of alkaline magmas during a transition between subduction and extension that tapped a chemically enriched mantle source; (2) a long history of structural preparation, beginning in the Proterozoic, which created deep-seated structures to allow the magmas and ore fluids to reach shallow levels in the crust, and which produced a fracture network that increased permeability; and (3) an efficient hydrothermal system, including effective gold transport mechanisms, and multiple over-printed hydrothermal events.

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USGS2014

Further remarks on the Cripple Creek Volcano, Colorado

Structural evidence, particularly in the deeper mine‐workings, indicates that the volcano , which is of Tertiary age, was developed by explosive eruptions at a number of points along intersecting fissure‐systems that had been formed in pre‐Cambrian granite by east‐west compression, probably during the Laramide revolution. The volcanic breccia, which consists principally of phonolitic material, appears to fill several elongate or elliptical funnel‐shaped openings that coalesce upward and taper downward into roots. Local adjustments that followed the principal explosive eruptions developed fissure‐systems in the breccia parallel and transverse to the older fissure‐systems and permitted the intrusion of dikes and irregular masses of latite‐phonolite and syenite within the breccia mass. Mild regional readjustment, caused by compression in a nearly north‐south direction, ensued and reopened these fissure‐systems within and around the breccia mass. It was followed by the relatively widespread intrusion of dikes and irregular masses of phonolite. Local readjustment then recurred repeatedly, mainly along the master fissure‐systems, and was followed by three successive intrusions of alkaline basaltic dikes and finally by the formation of mineral veins.

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