Location
The Chiwawa mining district, including about 450 square miles, lies in the west central part of Chelan County. It includes the drainage of Little Wenatchee, White, and Chiwawa rivers. That portion which embraces the upper Chiwawa River drainage was once designated the Leavenworth mining district (1897). The present enlarged and renamed district is bounded on the west by Snohomish County, on the east by the Entiat district, and on the north by the Railroad Creek district. The Cascade Range marks the west boundary, and the Entiat Mountains the east and north boundaries. The whole district lies in the Wenatchee National Forest. State, county, and Forest Service roads extend up the main river valleys, and areas of sharp high ridges and steep stream gradients are made accessible by a network of Forest Service trails.
Geologic Section
As shown on the preliminary geologic map of the state (1936) the oldest rocks in the district are Carboniferous and other Paleozoic sedimentaries regionally metamorphosed to marbles, quartzites, and argillites. They outcrop in a narrow strip along the Entiat Mountains on the southeastern border of the district and in narrow anastomosing fingers along Little Wenatchee and White rivers. In most of the northern and much of the southern part of the district is exposed the Mesozoic [Waters, 1932) intrusive granodiorite of the Chelan batholith. In the southeastern corner of the district are the sandstones, shales, and conglomerates of the Swauk formation, this being the most northerly occurrence of those rocks in the state. Mapped with the Mesozoic intrusives on the state map (1936) are an older gneiss and a younger diorite as well as the Chelan granodiorite. At least part of the gneiss probably is part or a correlative of the pre-Ordovician Swakane gneiss of Waters (1932). Division of Geology field studies indicate the younger diorite to be part of a group of similar rocks which outcrop extensively in the northern Cascades.
Ores and Ore Minerals
The ore minerals pyrrhotite, chalcopyrite, native copper, arsenopyrite, and sphalerite yield copper, gold, silver, and zinc. Of these, copper has had the largest production, closely followed by gold.
Ore Deposits
Little is known about ore deposits in the district as a whole, but at the Royal Development mine the ore minerals occur with chlorite, quartz, and calcite as matrix in a wide breccia zone at the contact of granodiorite and an older gneiss. Pyrrhotite and chalcopyrite, the most abundant ore minerals, are found as disseminations and in sheets and veinlets. The zone of sulphide mineralization is not sharply defined; ore bodies therefore have assay walls. A ccompanying the sulphides in the breccia matr ix are astonishingly large quantities of chlorite. Probably the mineralizing solutions ascending over a long period deposited first pyrrhotite, and then chalcopyrite, quartz, arsenopyrite, chlor1te, calcite, and marcasite in that order, with considerable overlapping deposition of all the minerals [ Richarz, 1933).
Timber and Water
Ao adequate supply of timber and water for mining and milling purposes is to be had on or in the near vicinity of most of the properties. Considerable electric power for smaJJ operations could be generated from several of the streams.
