Found out that the pluton in AK that I think might be showing signs of early volcanism is associated with hot springs elsewhere in the state. So we might be getting a few new hot springs up there! Still means magma down below. Some sampling of this pluton yielded a copper outcrop, and 2 cores that had 4-9000 ppm titanium, 1000 ppm potassium, 50 ppm zircon, 20 ppm uranium and thorium, but only 4-5 ppm of gold. These cores are from 8 miles downstream. We'll be working material from the next pluton over.
Here's the pluton info.
Fine- to coarse-grained or porphyritic, light- to dark-gray, rarely pink, granitic rocks. Unit ranges in composition from granite to quartz diorite, and includes syenite, granodiorite, and quartz monzonite. Biotite and hornblende are locally common; muscovite is uncommon. K/Ar and 40Ar/39Ar ages range from about 76 Ma to about 57 Ma; the vast majority of samples yielded ages in the range 70 to 59 Ma. Available U/Pb zircon ages fall within the same ranges. Unit includes many of the plutons shown on various source maps for this map that are commonly labeled TKg. These plutons tend to be small and are exposed in a broad belt from southwest Alaska through interior Alaska and into the Yukon. They tend to be potassium-rich, even at lower SiO2 contents, having as much as 6 percent K2O at 60 percent SiO2 in the Dillingham quadrangle (F.H. Wilson, unpub.data). Plutons of this unit are common in the western Dillingham quadrangle (Wilson, 1977) and are unusual in that they tend to have biotite and pyroxene, often orthopyroxene, as their mafic minerals, regardless of the overall pluton composition. Unit consists of hundreds of individual plutons. Many of the hot springs of interior Alaska are spatially associated with these plutons (Motyka and others, 1983). Associated mineralization includes gold, tin, and mercury (see
http://ardf.wr.usgs.gov for more information about mineral resources in Alaska)
