Location
The Wenatchee mining district embraces approximately 320 square miles in southeastern Chelan County. It is drained in its northern and western parts by Wenatchee River and Mission Creek. In the southern and central portions small, intermittent streams drain into Columbia River which lies along the district's eastern boundary. Kittitas County is on the southern boundary, Entiat Mountains the northern boundary, and the line between Ranges 18 and 19 East separates the Wenatchee district from the Leavenworth and Blewett districts on the west. Although this is one of the least rugged of the county's mining districts, there is a difference in elevation of more than 6,000 feet between Columbia River and some of the highest peaks. Roads have been built in nearly all the stream valleys, rendering the district easily accessible.
Geologic Section
North of Wenatchee River is pre-Ordovician Swakane gneiss in which is a large northwestward-trending band of Swauk sandstone, shale, and conglomerate. The Swauk formation covers approximately three-quarters of the whole district, but south of Wenatchee River it is covered in part by nearly flat-lying Columbia River basalt. The Swauk is moderately folded, and in the heights just south of Wenatchee on a domal structure located by Lupton an oil and gas test well is being drilled. Glaciofluval gravel, in many places in large terraces, floors the valleys of Wenatchee and Columbia Rivers. The terraces are best known for their famous fruit orchards but are also valuable as sources of practically unlimited supplies of sand and gravel for commercial uses.
Ores and Ore Minerals
The only ores which have been mined are those of gold and silver and of antimony. Cinnabar, the ore mineral of mercury, was reported many years ago, but complete absence of any mention of that ore in the district since that time indicates that the early report was erroneous.
Ore Deposits
Excepting the probably non-existent mercury deposit, and an antimony deposit reported to have produced in 1916 but about which nothing else has been recorded, all of the mineral locations reported are on a "dike," which is prominently exposed on the ridges south of Wenatchee from Squillchuck Creek northwestward across Dry Gulch to Squaw Saddle. The dike-like body is a nearly vertical mass 200 to 800 feet wide io Swauk sandstone cut by a network of small quartz stringers. This part of the Swauk appears to have been thoroughly impregnated with silica-bearing solutions, so that in places original textures have been almost completely destroyed, thus giving rise to the names "rhyolite dike" and "aplite dike" often applied to the body. The silicifying solutions circulating along a wide and much-fractured fault zone may have risen as thermal solutions from a magma which also furnished the small amount of gold and silver deposited probably during the time of the silica deposition.
Timber and Water
Neither timber nor water is abundant in the district, but sufficient quantities of both have been available for mining and milling operations.
