Colorado Gulch Gold

The regional mineral belt is well known for two separate and distinct types of mineral deposits. Lead-zinc-silver strataform sulfide deposits occur within black graphitic shales  of the Paleozoic Wood River and Milligan Formations and constitute one type, whereas, gold-bearing fissure veins cutting granitic intrusive bodies are the second type. 

The gold-bearing veins are predominate throughout Colorado Gulch claims. Northwest-striking quartz veins carrying pyrite, arsenopyrite, chalcopyrite, native gold and electrum cut medium grained diorite and the veins are themselves cut but are not displaced by younger basalt dikes. Best exposures of the southwest-dipping auriferous quartz veins are in and near the lower Magdalena adit where recent underground work has exposed one or more veins ranging from six inches to ten feet in width.

As many as three and likely more veins occur on the claims. Veins are exposed in underground workings at the Barbara adit and the upper and lower Magdalena adits as well as in numerous prospect pits and bulldozer trenches throughout the property. Vein widths at surface are a few inches to six feet and are strongly oxidized. However, a number of exposures contain sulfides at surface.

At this point in time, the extent of underground openings is limited and surface exposures are widespread so that it is not possible to comment accurately on the actual strike length of any one vein system. But, whether one or more vein systems are observed, it is probable that the strike length or lengths are persistent and can be as long as 3,800 feet. In addition, judging from the persistence of the vein in the lower Magdalena adit with regard to sulfide content and width, it is reasonable to assume that ore shoots within the vein will persist to depths at least equal to their near surface strike lengths.