Redskin Granite: a rare-metal-rich Precambrian pluton, Colorado, USA

Abstract

SummaryThe Precambrian Redskin stock is a high-silica alkalic granite that forms a late pluton related to the 1000 Ma-old Pikes Peak batholith. Zircon, fluorite, fluocerite, ilmenorutile, columbite, biotite, magnetite, and hematite are the most abundant accessory minerals. Thorite, monazite, and xenotime are sparse, and cassiterite and topaz very rare. The principal residences of Sn, Nb, and Ta are ilmenorutile and columbite. The occurrence of cassiterite intergrown with biotite and columbite and the high contents of Nb and Ta in cassiterite are evidence that cassiterite is also a primary mineral. The high concentrations of certain trace elements indicate a high degree of fractionation of magma prior to emplacement of the Redskin Granite. An extremely low crystallization temperature for the granite is indicated by the compositions of albite and K-feldspars, the presence of Fe-rich dioctahedral mica, the absence of Ti in magnetite, and the low content of Ti in biotite. This low crystallization temperature seems due largely to the high concentrations of F, Rb, and other volatile elements in the magma.