The Ray Gulch tungsten skarn and the Eagle Zone intrusion-related gold deposit are associated with the Dublin Gulch intrusion, which forms part of the mid-Cretaceous Tombstone Plutonic Suite. Tungsten mineralization occurs in a roof pendant of hornfelsed Neoproterozoic to Early Cambrian Hyland Group metasedimentary rocks. Five main paragenetic stages include Stage I wollastonite-quartz skarn and later Stage II pyroxene-garnet-scheelite skarn that forms the main tungsten mineralization. Stages III (quartz-scheelite-clinopyroxene), IV (quartz-amphibole-calcite) and V (quartz-K-feldspar-pyrrhotite-molybdenite-arsenopyrite-pyrite-chalcopyrite) are vein related and are volumetrically insignificant (<10 vol. %). Geochemical analysis of the skarn and veins indicates that the deposit lacks gold and bismuth. The earliest veins in the Eagle Zone are similar to Stage V veins at Ray Gulch. Gold at the Eagle Zone occurs in a later sericite-carbonate-bismuth-sulphide vein stage; this stage is critically absent from the skarn. Thus, although tungsten is commonly associated with intrusion-related gold mineralization, it predates gold-bismuth and may occur spatially separate from it.
