Several large Eocene volcanic centers in the Absaroka Mountains of northwestern Wyoming host significant porphyry copper-silver along with some associated gold. Mining districts in the Absarokas include Kirwin, Stinking Water, Sunlight, and New World (Cook City). Veins associated with the porphyries were first worked in the late 1800s. Large-tonnage, low-grade polymetallic porphyry deposits include disseminated, stockwork, and vein mineralization accompanied by hydrothermal alteration halos. The volcanic centers also exhibit some supergene enriched deposits, replacement deposits within Paleozoic carbonates (in the New World district), and related downstream gold placers. Historically, these placers had little economic importance, however, amateur prospectors continue to work some of them today.